November Generation Statistics

Here's the results of our solar panels electricity generation results for November:

The graph below shows kWh on the vertical axis, days of the month on the horizontal axis for our 1.98kW (8 panel) HIT solar panel array on a south-facing roof with a pitch angle of approx 35-40°.

I've added a linear trendline to show the average.  With the sun getting so low in the sky now, on the 30th Novermber, even at midday with a cloudless sky the array was only just topping 1kW of power. 

At 8.30am this morning (2nd December 2013) the sky is very gloomy and overcast, and the inverter showed a 0W input from the panels.

Predicted vs Actual:

On installation, we received an SAP forecast for the year of 1645kWh.  Dividing by monthly average sunlight, for December we should have achieved an average of 2.17kWh per day to keep on track to hit this total.  The panels actually achieved a daily average for the month of 1.93kWh, slightly below target.

Total kWh forecast for November = 65.01kWh

Total kWh achieved for November = 57.9kWh

For the year so far, the panels have achieved 93.49% of their forecast amount.  Not a bad prediction, but I'd hoped they would have outperformed the prediction. Here's hoping that the spring/summer months turn things round for the year!

I've also put together a graph showing how the average amount of kWh generated per hour has fallen from month to month as we approach winter solstice.  December's value is only based on 1 day's measurement, so it is not accurate.  Note the number of daylight hours is not measured from sun-up to sun-down, it is from met office stats for average hours of actual cloudless sunshine over previous years.

I've also had the first request for the Feed-In Tariff (FIT) meter read from npower - a total of 315.89kWh generated since installation.  When you fill in the FIT application forms, npower give you the option of supplying meter reads online or by post. I opted for online.  They ask for a quarterly read, and you have 25 days to file the reading, otherwise it rolls over to the next quarter.

October solar generation results

Welcome to the blog page for October's generation results.  

Recap:  We have a 1.92kW array (8 x 240W Panasonic HIT solar panels) installed on our south-facing roof, at an angle of approx 35-40°.  We received a SAP prediction on installation of 1645kWh for the year.

The forecast for October (broken down by average sunlight per month) is 103.76kWh.  However, the panels actually achieved only 90.3kWh over the month, which is 87% of the prediction. Here is a graph of the daily totals for the month:

(plus a little bit of November on there too).   This underperformance is due to the higher than average number of heavily overcast days. 

Here is the graph of the monthly totals to date, shown against predictions:

September overshoot and October's undershoot pretty much balance each other out, so we're still on target for achieving the predicted yearly amount of 1645kWh.  Here's to an unseasonably sunny November!

Theoretical maximums?

One photograph to explain this post:

I took this pic of the inverter at about 1pm today. Outside, the bright autumnal sunshine is slowly warming the cold air. The sun is only about halfway up in the sky, but that's the highest it's going to get today.

Check out the input power (Pin) reading on the inverter - 2140W.  I had to look at it a few times myself to let it sink in.  

The theoretical maximum of our array is 240W per panel x 8 panels. That's 1920W (1.92kW).

This puzzled me on two counts:

1. It's approaching the middle of October - I thought that as the sun got lower in the sky, the radiant energy falling on the panels decreased, meaning that the output power of the panels dropped as you approach the winter solstice.
2. Irrespective of the time of year, how can the array be kicking out more kW than its theoretical maximum?

 I've decided not to call it a theoretical maximum anymore, since it obviously isn't. I shall call it the nominal maximum. After a moderate bit of googling, I have two ideas that I think explain this anomaly. 

1. All solar panel nominal maximum ratings are calculated from their measured W per square meter rating (W/m2), multiplied by their surface area in meters.  My solar panels have a measured rating of 190W/m2, and are 1.6m x 0.8m in size. Multiply them together, and you get 240W output. But... for the sake of standardised comparison, all panels have their W/m2 rating measured with a level of 1000W/m2 of radiant energy shining on the panel.  Apparently, the maximum energy from the sun measured at the surface of the earth is 1367W/m2. http://www.powerfromthesun.net/Book/chapter02/chapter02.html 
   So it is entirely plausible, depending on atmospheric conditions, that more than 1000W/m2 could be landing on the panel, in which case it would be generating more than its nominal maximum.
2. The thermal coefficient.  http://www.solar-facts-and-advice.com/solar-panel-temperature.html
   All solar panels have a thermal coefficient, which means that as the panel itself get hotter, they get less good at turning sunlight into electricity. All panels have their output measured at a temperature of 25 degrees celsius, and as the temperature of the panel goes below or above that, the panel's conversion efficiency goes up and down. The cold air and windy weather will have the effect of cooling down the panel, making it more efficient.

I think a combination of these two factors explain why I'm getting 220W more out of my array than it says it can generate.

A surprise. A very pleasant one, to be sure, but a surprise nonetheless.

Are all solar panels created equal?

Short answer, No. 

It depends on the technology used in the crystalline silicon plates.  I'm talking about the black-blue square plates that make up the panels. These do the magic of turning sunlight into electricity.  Each of these plates has an efficiency which is affected by the technology of the silicon plate used.  

The amount of sunlight energy that falls onto the plate can be measured in Watts (W) and the amount of electrical energy the plate gives out can also be measured in W.  The efficiency value is a comparison of how much of the sunlight W get turned into electrical W, given as a %.  

With today's technology, it is impossible for a solar panel to convert all of the sunlight energy into electrical energy.  In fact, we can't even get half of it (50%) turned into electrical energy.  It may surprise you to learn that solar panels convert only 14-19% of sunlight energy into electrical energy.

I'm only talking about the solar panels that you or I can buy, to stick on our roof (or wherever) -  commercial, mass market, domestic solar panels.  So not research/prototype technologies (of which there are many still in development), and not concentrator solar panels (CSP).  CSP is a maturing technology used currently for industrial generation, and use specialised plates with very high conversion efficiency (currently around 40%-44%). 

See http://en.wikipedia.org/wiki/Concentrated_solar_power

I'm also ignoring the panel *size* - a panel that is twice the size of another panel will generate twice the amount of electricity.  I'm looking at how different panels compare, assuming they're both the same size, and both have the same amount of sunlight shining on them.

How panels convert light to electricity is incredibly complicated, and requires degree level electronics (n- and p- doping, electron/hole tunnelling, atomic energy levels and that kind of thing).  I studied electrical and electronic engineering at Liverpool University for 3 years, but I didn't pass my Part I exams and so didn't finish my degree (BEng ButFailed).  Even so, I struggle to get my head round exactly what's going on at an atomic level, but if you're interested in warping your brain, have a read of this:

http://www.ife.no/en/ife/departments/solar_energy/projects/Nordic-coe-pv-details/presentations_narvik/lode_carnel.pdf

Seriously, my brain was melting by page 4 and I thought I had a modest grip on stuff like this.

I thought I'd do a simple guide for people who don't have degree level electronics understanding (pretty much most people).

Monocrystalline or Polycrystalline?

If you read the specification of different solar panels, some of them are described as monocrystalline, and some as polycrystalline. 

Monocrystalline plates are made from a slice of one single silicon crystal. Polycrystalline plates are made from a number of smaller silicon crystals, "glued" together.

There aren't any other kind, they have to be one or the other. Technically, it's true to say mono is better than poly.  I couldn't find any actual hard measurements, but the difference is slight.  But it turns out it's pretty much an irrelevant distinction. Poly generates fractionally less electricity than mono, but the manufacturers build their poly panels slightly bigger to make up the difference.  The baseline cost of the panels is the same, so there's nothing to choose between them..A roof-full of mono panels will take up slightly less space than the equivalent amount of poly panels but they'll cost you the same.

HIT / c-Si ?

Both HIT and c-Si solar panels are based on the same technology, but the difference in the detail as to how it is exploited is significant.  I've discussed in previous posts about HIT panels (our panels are HIT panels) and how they're better than c-Si panels, but I'm going into more depth about it here.

'Conventional' solar panels use what's called c-Si technology.  The Si stands for Silicon (same stuff computer chips are made of). I haven't bothered finding out what the c stands for.  I'd like to think it's 'conventional' but I'm sure it's not.

'HIT' panels use what's called Heterojunction Intrinsic Thin layer technology (HIT is a whole lot easier to say). These also use silicon, but (glossing over the brain-melting stuff) it's 'wired' in a different way (on an atomic level).

Boffins at Sanyo developed HIT technology in the 1990s, which has now filtered through to mass-market solar panels, manufactured exclusively by Panasonic.  The technology has not been licensed to any other panel manufacturers, so if you want HIT panels, you have to buy them from Panasonic.  I am not going to go into the reasons and consequences here, this post is just a geek out about the technology ;-)

If you read the technical specifications of a HIT panel, it will quote the panel efficiency as 19%.   Standard c-Si panels come in around 14% efficiency.   A 5% improvement, which doesn't sound like much.  But a 5% improvement on a 14% efficiency is a third as much again.  That is significant.

I posted the graph below before on a previous post, but I've included it again here to explain in greater detail.  

The graph above is calculated from measurements taken throughout one day from two physical panels side-by-side, both receiving the same amount of sunlight.  The hours of the day going along the bottom, and the % output of the panels going up the y-axis. (OK, technically, it's not %, it goes from 0 - 1 rather than 0 - 100, but it's the same thing really).

You can see on the graph that on the day these measurements were taken, the HIT panels were peaking at about 88% of their maximum power output, whereas the c-Si panels manage about 80% of their maximum.  The panels were not receiving enough sunlight to achieve their maximum output, which means the measurements were taken under non-optimal conditions. Still, the comparison is valuable.  It tells me that under non-optimal sunlight, the output from the c-Si panel falls more rapidly than it does from the HIT.

This may seem a bit puzzling, because according to the manufacturer's quoted figures (as above), the HIT's 19% efficiency should be outperforming the c-Si 14% by about a third. Why doesn't the graph show this?

This is because the graph is showing the sensitivity of the panels under less than optimal sunlight levels, not the efficiency with which they convert sunlight to electricity. The y axis of the graph is showing normalized output power, which means that each panel's output has been converted into a % of its own maximum output.  Even if a solar panel had 100% efficiency, you could still plot a curve on this graph showing how its output changes as the sunlight level changes.

Let's say you have two panels, one c-Si and one HIT, both exactly one square metre in size, both with optimum sunlight falling on them.  Optimum sunlight level is 1000W per square meter. At 14% efficiency, the c-Si panel will be generating 140W, and the HIT panel (19%) will be generating 190W.  The HIT panel is outperforming the c-Si by about a third.

Here in the UK, cloud cover is our ever-present friend. The number of days of optimal sunlight are, let's say, limited.  Looking at the graph above, we can see that as sunlight falls below the optimal level, the output from the c-Si panel falls more rapidly than from the HIT panel.  If the sunlight has faded such that the HIT panel's output has fallen to 167W (88% of 190W), then the c-Si output will have fallen to 112W (80% of 140W).  At this level, the HIT panel is now outperforming c-Si by nearly 50%.

The Financial Aspect
The only reason you'd want to choose c-Si is that they're cheaper.  For an 8-panel array, it costs about £600 more to go for HIT instead of c-Si. But, over the 20-year projected lifespan of the panels, you will get *at least* a third more electricity out of the HITs compared to the c-Si.

So how long before I get back the £600 extra I've paid going for HIT?  From the measurements I've made so far on our 8-panel HIT array, I'm expecting to get about 1800kWh in total for the first year. If I'd bought a c-Si 8-panel array, I'd expect this to be at most 1350kWh for the year (1/3 less than HIT). That's a difference of a minimum 450kWh per year.

Choosing HIT is a long term investment. But then choosing solar panels is a long term investment too. From the savings I make on electricity I've not bought from the grid, plus the feed-in tariff, it'll be about 5 1/2 years *extra* to cover the extra cost of the HIT panels compared to the c-Si.   But then over the 20 year life of the feed in tariff, buying HIT over c-Si will benefit me by approx £1600 (at today's electricity prices - it will be more than this if electricity prises rise).

So, if you're in it for the long-haul, it follows that I would recommend to anyone considering panels, if you can afford it, pay the extra for HIT.

What price solar? (caution - includes satire)

What happens when a country invests too heavily and too quickly in solar power?

Take a look at the debacle that's going on in Spain at the moment. Due to the global financial crisis, the whole country is in dire straits in general, but they've also been pouring money virtually unchecked into solar generation for over 10 years.

Spain gets a lot of sun. Brits love it as a holiday destination for exactly that reason.  Using solar panels to make use of all that sun seems on the surface a very sound and sensible plan.

The Spanish Government have been paying solar generators $556 per 1000kWh (mWh) for their electricity. This is way higher than the UK  - I'm getting £149 per mWh under the feed-in tariff.  At the same time, electricity generated from coal or gas plants was only being paid at $52 per mWh.

Whilst I agree wholeheartedly with the principle that it is good to encourage a move from coal/gas generation to solar/renewables, it seems the Spanish Government have rather mismanaged the finances of this transition.

Spain's electricity generation capacity is now 60% more than their peak national consumption. For a number of years, Spain have been paying for electricity they don't use and don't need.  That's quite a big problem.

In Spain, there is a huge amount of small-scale household generation (people like me who have bought solar panels and stuck them on their roof to make their own electricity).  The Spanish government have actively encouraged this with incentives like the feed-in tariff we have in the UK.  But the Government there are now faced with such massive financial deficits,  they have taken some unprecedented and frankly, rather bonkers steps with new legislation due to come in later this year.

1. Anyone who generates all their own electricity from solar panels, but is too far away from the grid to be connected, will have to have a meter installed. They will then have to pay a tax on the total amount of electricity they generate and use.

2. Everyone else who generates their own electricity from solar panels must be grid connected and will also pay a tax on the total amount of electricity they generate and use.

Anyone who doesn't comply will be liable to pay a fine up to $30 million. Yes, I did say million.

Taxing the sun? I think they've been sitting in it for too long.

The background to this situation can be read on a number of news websites:
http://www.businessweek.com/news/2013-08-01/spain-solar-producers-burned-by-plan-to-penalize-homegrown-power
http://www.forbes.com/sites/kellyphillipserb/2013/08/19/out-of-ideas-and-in-debt-spain-sets-sights-on-taxing-the-sun/
http://my.telegraph.co.uk/expat/annanicholas/10151634/why-spain-has-sold-out-the-sun/
http://www.bloomberg.com/news/2013-08-01/spain-hurts-solar-with-plan-to-penalize-power-producers.html

Perhaps the Spanish government would appreciate some of my suggestions to help them out of this financial predicament:

What about people who collect rainwater in water butts?  They should have flow meters installed and be made to pay water tax on all they collect and use.  That'll stop them defrauding the water companies out of their rightful income.

And as for those deviants who grow their own food, I mean, really, that's quite weird.  Everyone knows food comes from shops.  Besides, they're cheating Tescos* out of honest turnover, threatening employment. Where is the sense of community spirit?  They're practically terrorists!  Although I must confess I've not quite worked out the details of soil tax yet.

Finally, people have been taking breathing for granted for far too long now - I think it's high time air should be taxed.  I mean, it costs a lot of money keeping all that air nice and clean, what with all the poisons and toxins that industry has to pump out - no one wants to breathe that.  It's only fair that the people breathing it should pay to have it cleaned.



*other supermarkets are also available, see local press for details

First complete month

... practically.

As regular readers will be aware, our solar panels were out of action for 5 days this month. (See "Hiccups").

But apart from that, I now have a complete month's worth of readings.

For the sake of calculating an average, I've accounted for the 5 days of missing readings by allocating the predicted average value for each missing day (4.97kWh).

I've spreadsheeted the results, which are as follows:

The purple line at the right hand side is the readings from the last few days of August, and the red line is the readings for the whole of September.

The predicted daily average is 4.97kWh per day.  I've not added this line to the graph, but you can see where it would lie from the flat section between 19th-23rd, where the panels were out of action.

I've put a dotted linear trend line in to show the underlying change in the actual kWh generated for September. Oddly, it climbs towards the end of the month. I was expecting it to go down as the amount of daylight diminishes towards winter. I suspect this is because the weekend at the end of the month was unusually sunny, thus skewing the trend line upwards.

I have put together another graph, which shows the predicted generation for the whole year, broken down into months.  I have divided up the predicted annual generation figure into 12 months based on the average number of hours of sunlight per month from the met office figures at

http://www.metoffice.gov.uk/climate/uk/averages/19812010/sites/blackpool.html

The predicted total for September was 149kWh, and the actual generated (including assumed average for 5 days as discussed above) was 157kWh.

Other stats I've pulled out of the readings: 

• The actual readings are 105.4% higher than the predicted
• the array is generating 0.37kWh per each hour of daylight (sun up to sun down, irrespective of clouds)

It is satisfying to see that the actuals are slightly higher than the predicted.  It will be interesting to see how October pans out.

Dreaming the Big Dream Part 3 - Wind Turbines

Following on from Part 2 (Energy Storage)

Using *only* solar panels to generate our electricity, it is apparent that for our household to become electrical energy independent, the long-term energy storage required is unfeasibly expensive (although not impossible).

How then to generate more energy during the autumn/winter months while there is not so much sun around?

Which brings me onto wind turbines.  We all know about wind turbines - there are plenty of them dotted up and down the country already. Wind turbines are windmills that generate electricity when the wind blows them round. We live on the North West coast of England, and by 'eck it's blowy. A wind turbine would seem a very appropriate source of renewable energy.

This is the offshore wind farm at Morecame Bay, just up the coast from where we are.

This is commercial wind generation. Commercial turbines are HUGE (blade lengths up to 50m). There are a number of different models, and they generate between 1500kW and 3000kW.  They are fed into the grid, and are part of the country's national energy generation.

See this link for some tech. spec. on commercial turbines:

http://www.aweo.org/windmodels.html

Obviously not appropriate for domestic generation. You'd have great difficulty sticking one of these puppies in your back garden.

But there are many different sizes and designs of wind turbines.  A lot of product development has gone into domestic turbines over the last few years. You can get teeny-tiny ones that you fix onto the side of your house (or motorhome or boat etc.) that generate enough electricity to charge a battery or light a few lights (50W).

Like this vertical-axis turbine. Without traditional horizontal blades they take up a lot less room. But at about £600 a go, they are a lot of money for the small amount of power you get from them.

I have identified 6 factors to consider in a domestic wind turbine:

1) How much electricity does it generate?

2) What is its operating range?

• the operating range of a wind turbine is the slowest to the fastest wind speed in which they can generate electricity (There is a minimum wind speed below which they will not generate anything at all, and there is a maximum wind speed above which they switch off to prevent damage to the generator.)

3) What is its survival speed?

• the fastest wind speed the turbine will tolerate before it is physically damaged (eg. in a storm)

4) How much does it cost / cost effectiveness? (what is its £ per kW)

5) What are the on-going maintenance/repair costs? (Turbines, unlike solar panels, are mechanical devices with moving parts that wear out, and need to be serviced/maintained to keep them operating)

6) How big is it? (Will it physically fit on your property? Will you get planning permission to install it?)

A little bit about wind speeds - there is a thing called the Beaufort scale which classifies wind speeds (primarily for nautical use, but a handy guide) http://en.wikipedia.org/wiki/Beaufort_scale  This describes wind levels in easy-to-understand terms such as 'light breeze - wind felt on bare skin, leaves rustle' etc.

In the UK, you're allowed to put a wind turbine on your property without having to apply for planning permission as long as you adhere to these conditions:

http://www.planningportal.gov.uk/permission/commonprojects/windturbines#Windturbine:standalone

I've discounted house-mounted turbines, they're too small to be of any decent use. The most pertinent restrictions for pole mounted turbines are:

• the maximum allowed rotor diameter is 2.2m.
• the lowest point of the rotor sweep must be at least 5m off the ground. So for a 2.2m diameter turbine, it must be mounted on a pole at least 6.1m off the ground.
• the pole it is mounted on must be positioned at a minimum distance away from all your property boundaries, so that if the pole snaps at the base and falls over, it must land completely within your own property, whichever direction it falls in. 

Of course, you can install wind turbines that exceed these specifications, but you'd have to go through formal planning application. And if one of your neighbours objects to the idea, it would become difficult to secure permission to do it.

On a purely geek-interest level,  I've found a French company that have designed a new type of turbine blade. They use a 3D scooped design that has been engineered using fluid dynamics to produce zero wind-shear. This means they are silent in operation (well, not quite, but to all intents and purposes).  Because of this engineering, they have a wider operating range than traditionally-bladed turbines.   They are rudderless, and will automatically point in the correct direction to collect the incoming wind.  But my goodness they do look weird.  Here's one:

This is the Nheowind 3D-50. You'd need planning permission for one of these - the rotor blades have a 3.2m diameter. It has a maximum power output of 2kW. It starts generating electricity at a minimum wind speed of 6mph, reaches its maximum output at 29mph, and has a cut off speed of 68mph. It can physically survive wind speeds up to 112mph. 

It's 6mph turn-on speed is equivalent to 2 on the Beaufort scale ('light breeze' - wind felt on exposed skin, leaves rustle.)  Its maximum output is achieved at 29mph, or 6 on the Beaufort scale ('strong breeze' - large branches in motion, umbrella use becomes difficult, empty plastic bins tip over.) It continues to pump out 2kW all the way up to 68mph, ('fresh gale' - some twigs broken from trees, cars veer on road, progress on foot is seriously impeded).   It's survival speed, 112mph, is classified as level 2 hurricane on the safir-simpson wind scale. Thankfully we have never experienced one of these on the Fylde coast.

I've found some wind speed data for our area on the met office website:

http://www.metoffice.gov.uk/climate/uk/nw/

According to the data in the link above, the average annual wind speed (AAWS) for the North West varies between 7-10 knots (8mph - 11.5mph). This is measured at a height of 69m amsl (above mean sea level) which is rather high to be sticking a small turbine. More investigation needed to see how the wind speed drops at lower heights. 

This data is from measurements taken between 1971-2000 at Ringway (Manchester airport).  I fancy the Fylde Coast may be higher than this.

According to the datasheet for the Nheowind 3D50, using the met office figures above it will turn in about 1000 kWh over the year.  Considering the additional time and effort required to get through planning, that's pretty poor compared to the solar panels, which are looking like giving me around 1800kWh for the year. 

The viability of wind energy is highly dependent on what your local average wind speed is.  For comparison, an AAWS of 20mph (5 on the Beaufort scale -'fresh breeze' - branches of a moderate size move, small trees in leaf begin to sway)  would produce about 6000kWh over the year.  I doubt the Fylde Coast average is that high, but you can see we're getting into the realms of viable investment.

Cost-wise, I've found a UK distributor charging £4400 for the 3D50 bundled with a Power One inverter

http://www.orionairsales.co.uk/nheowind-wind-turbine-3d-50-2kw-with-power-one-inverter-3455-p.asp?gclid=CIz42L-j0LkCFZShtAodT2cAyA

Then there is the 3D50's big brother, the Nheowind 3D100.  This turbine has a rotor diameter of 4m compared to the 3D50's 3.2m, yet it turns in more than double the power: 3000kWh per year at 9mph AAWS, rising to 15,000kWh per year at 20mph AAWS.

But in the meantime I reckon it's worthwhile spending a few quid putting up a wind speed monitor for a few months to see just what we're getting. It's impossible to make a sensible judgement before knowing that.

Addendum: just found a couple of handy little resources:

http://www.greenspec.co.uk/small-wind-turbines.php

http://www.renewableuk.com/en/publications/guides.cfm/Smallwindplanningguidance

- I've not read them through properly yet, but the first one has some info on how wind speed varies depending on how high off the ground the turbine is.

...........................
Second addendum:  Just found out about the qr5 - a mid-scale vertical axis turbine that has some impressive figures... http://www.quietrevolution.com/qr5/faqs-technical.htm
It is a 6kW turbine, already MCS approved and the company is working on a smaller 2.5kW version.
...........................

Third addendum: I've found a more localised wind speed database for the Fylde Coast on the Department of Engery and Climate Change website.  It is indeed higher than at Ringway.
http://tools.decc.gov.uk/en/windspeed/default.aspx

You have to enter the OS square code for the area you want to know the windspeed, and then click on 'find wind data' to search the database. AAWS results come back in m/s at various heights above sea level. Our little chunk of Fylde Coast is SD324300.

At 10m above sea level, our AAWS is 5.8m/s (12.9mph) ; at 25m above sea level, our AAWS is 6.6m/s (14.7mph).  

A qr5 vertical axis turbine being installed on a roof

From what I've read since last night, I'm beginning to get the impression that the vertical axis wind turbines (VAWT) like the qr5 are going to be the future of small-scale wind generation. Their design is simpler - they have no 'yaw' considerations (they don't have to turn to point in the direction of the oncoming wind - they spin on their vertical axis no matter which direction the wind comes from. This means they also capture more energy from turbulent gusts that rapidly change direction. They are visually appealing (I think so at least!)  They have a much larger 'wind capture' area than an equivalently sized horizontal axis turbine (HAWT) so you get more kWh in the same space. I must confess the 3D50 scooped blade design has a charm of its own, but I think for the above reasons, VAWT is the way to go.

I've found an independent review of it, and it seems to come out very well.  
http://www.bettergeneration.co.uk/wind-turbine-reviews/qr5-wind-turbine.html
However, it also includes the price, which is way out of anything we could realistically afford (£25,000 installed). Shame. I think it's a beautiful bit of tech.  I look forward to investigating their smaller 2.5kW version when it comes out at.

Hiccups...

Solar panels are a very simple technology. No moving parts, no batteries, nothing like that. You simply shine sun on them and they generate electricity.

Not so with inverters however.  Inverters are jam packed with very clever electronics to convert the DC power from the panels into a stable AC signal that can be fed directly into the mains grid.

The inverter is smart - when the panels aren't generating enough electricity to be able to provide a stable feed into the grid, it shuts itself down, with a helpful little message on the screen "waiting for sun".

Yesterday afternoon, in bright sunshine, the inverter switched itself off.  It decided there was no electricity coming from the panels, and shut itself down.  Because I like to go and peek at it at regular intervals, I became aware of this quite promptly.  I've rung the installation company and they've asked me to check a few things (have you turned it off and on again?), all to no avail.

So now, 24 hours later, it is still switched off. Waiting for the sun. And the sun is beating down from a clear blue sky this afternoon and ALL THAT BEAUTIFUL SUNLIGHT IS BEING WASTED. *sob*

They can't get out to me before the weekend, so now I'm powerless (groan) over the weekend.

That's going to knacker my averages :/

Here's the last week's generation results:

Weds 11th Sept 0.8kWh
Thurs 12th Sept 4.2kWh
Frid    13th Sept 2.5kWh
Sat     14th Sept 10.8kWh
Sun     15th Sept 1.3kWh
Mon   16th Sept 4.3kWh
Tues   17th Sept 1.3kWh

Total for the week of 25.2 kWh
average 3.6 kWh per day

Energy distribution during the day

As I've outlined in previous posts, solar panels don't generate energy at full whack all day long.

When the sun rises, the amount of sunlight reaching the panels starts increasing.  When there is a measurable amount (a few Watts), the inverter switches on and starts supplying power to the grid.

Then, as the sun gets higher in the sky, the power coming from the panels rises and rises until it reaches the peak.  The peak is higher during the summer months as the sun is higher in the sky and more watts of light energy are falling on the panel than compared to the low winter sun.

This is a photo of the graph on the inverter taken at the end of 14th September 2013.

Each column on the graph is an hour's generation. Each horizontal line is 25% of maximum output power. This was a good day to demonstrate how the energy generated changes during the day, since there was no clouds in the sky all day, and the change in output energy is purely due to the changing position of the sun in the sky.

The peak plateaus out at just under 75% power over lunchtime for about 3 hours. In mid-September, the sun is now too low in the sky even at midday to get 100% out of the panels. The array was generating for a total of 11 hours.

A total of 10.8kWh generated for the day is certainly very respectable for a 1.92kW array. It will be interesting to see how this graph compares to midwinter, and then again at midsummer.

Dreaming the Big Dream Part 2 - Energy Storage

I can see this is going to be the killer issue for becoming electrically self-sufficient. There is one significant stumbling block to overcome, which I shall explain:

As described on the previous blog entry, I've worked out I would need approximately 40 solar panels to generate all our household's electricity requirements for an entire year.

Assuming that theoretically, I could install 40 panels, I've made a graph showing how the average amount of electricity generated per day changes over the year due to the change in sunlight / daylight hours (red bars).  (These figures are for 40 panels, but they're derived from the estimate/predictions for our 8-panel array.)

Also, on the same graph, I've shown the average amount of electricity we use per day (blue bars). I've taken these numbers directly from our npower 2012 consumption figures.  The monthly distribution is a bit squiffy, presumably due to when they take meter readings, but the total for the year is correct.

You can see straight away that the two graphs are almost perfect opposites of each other. Whilst the total kWh generated over the year matches the total kWh used during the year, we use more than we generate during October - March. And then we generate more than we use during April - September.

For us to survive just on solar panels, we would need to store all this energy generated during the spring/summer months so we could use it during the winter months.  The total surplus generated from April-Sept would be 2198.17kWh.

And herein lies the killer problem.  That is a thumping huge amount of electrical energy to store, and it needs to be stored for 6 months.  We would need to start using the stored energy during October, and would continue using it all the way through til March.

I have done some very trivial research into electrical energy storage - apart from the obvious (sealed lead-acid batteries) there are a number of other energy storage technologies that are being developed. Here's two:

FLYWHEELS
Flywheel energy storage is a maturing technology. Here's an example:

http://temporalpower.com/technology/

From what I've read, this looks like a fantastic technology for energy storage- it's very simple and there's little to go wrong. They're about the size of R2-D2, so you'd need a bit of space to install it (they can go underground). But.... and it's a big but, they don't have the long-term requirements we'd need.

Flywheels 'leak' energy due to them gradually slowing down, even with vacuum chambers and magnetically suspended flywheels, the second law of thermodynamics means they can't store energy indefinitely.  Graph showing storage time for flywheel  Click that to see the graph - it quotes 95% of stored energy still available after 10 hours, which means it would leak all of its stored energy after 8 days (200 hours).  One of these flywheels can store 50kWh, which is enough for about 1½ - 2 days worth of electricity.  This technology would be ideal for storing solar generated energy for use overnight, or for covering shortfall in generation due to a particularly rainy day, so they are definitely worth keeping on the radar.

CRYOGENIC COOLING

Cryogenic cooling energy storage is another technology being developed. This is a lot more complex though. The process uses excess energy to liquify gases by cooling them to very low temperatures, and then when the energy is needed back, the liquid gases are pumped into room temperature chambers, and the resultant expansion of the gases used to drive a turbine to generate electricity.   http://en.wikipedia.org/wiki/Cryogenic_energy_storage

Whilst being quite a cool (groan) technology, it goes without saying that this is *way* outside anything realistic for domestic use.

BATTERIES

Which leaves us with batteries. Normal, sealed lead-acid batteries (car batteries).  A very mature technology, mass produced and cheap. After a quick google, there are loads of different kinds, and you're talking about £30 for a 12V-12Ah battery. If my A-level physics is still up to scratch, that translates into 0.144kWh, fully charged, for one battery. Remember, the excess energy from the summer is 2198.17kWh, which would all need to be stored in batteries. Now you see the problem. I'll do the maths for you - that's over 15,000 car batteries. Not going to happen. This is a dead end, we need to back up and look at this another way. But that's for another day.

EDIT:  I have just found a lead acid battery rated at 200Ah. http://www.rapidonline.com/Electrical-Power/Leoch-LP12-200-Sealed-Lead-Acid-Battery-SLA-12V-200Ah-18-0869/?source=googleps&utm_source=googleps&gclid=CLrKyaid0LkCFebJtAodO3wA9g

This gives a total storage capability of 2.4kWh - a much more respectable figure, but we'd still need 916 of them to get us through the winter.  And that would set us back over £11,000, and they'd fill an entire shed.  So I think realistically, we can still discount batteries as a solution.

What do you think? Please comment.

Dreaming the Big Dream

This week I started daring to dream the unthinkable dream:

Would it ever be possible to become completely self-sufficient for our electricity needs?  Is it possible that I would never have to buy another kWh from the national grid, ever again?  How much would it cost? Is this something socially responsible and worthwhile to pursue?

If we were to disconnect every single electrical appliance in our home, and never turn a light on again, then obviously the answer would be yes. But this is not an acceptable solution for me and my household.  You could quite accurately accuse me of being an energy non-conformist activist, but I'm not about to become a hemp-wearing yurt-dwelling beardy wonder.

So let me rephrase the question:  Assuming my household continues to use the amount of electricity we're using at the moment, would we ever be able to generate that amount indefinitely? Then we would be truly electrically self sufficient.

Being an electrical/electronically minded geek type, I find this kind of thing interesting so I'd like to investigate what it would take to actually make this happen.

As for being a socially responsible and worthwhile project to pursue, I'd say unequivocally, a resounding yes. Given that our country is muddling its way through an emerging energy crisis, and will continue to do so over the next 5 or 10 years, reducing my demands on 'the system' is a wholly responsible thing to do. 

The cost? This is also key. Making a responsible judgement on the use of our finances (in conjunction with my loving and long-suffering wife of course) must be weighed into the equation. Is becoming electrically independent something only the filthy rich could aspire to?

I've broken the question down into three solvable parts:

1) How much electricity *do* we use at the moment?

2) How many solar panels/wind turbines/insert other renewable energy source here* would be needed to generate that amount?

3) What kind of energy storage requirements would be required to make sure the energy was available to use even when the sun isn't shining and the wind isn't blowing?

4) What kind of costs are we talking about?

Question 1:

This is dead easy to solve - I'm with npower, and they have a very helpful website showing me how much energy I've used over the past years, broken down by month.  For the whole of 2012, we used 8969kWh. I gather this is quite high for domestic consumption, but then I work from home and have a number of computers/air con etc. in the office that's in use 9-5 throughout the working week. Broken down by month, December was the highest with 982kWh. July was the least at 393kWh.  From the 2013 readings so far, our consumption has dropped slightly this year, probably due to me fitting LED lighting in the office and throughout the house.

Question 2:

I'm not yet in a position to answer this accurately. Our solar panels have been up for just over 2 weeks, so the predications/estimates for the amount generated this year are just that. According the latest figures I've compiled, we could be generating between 1700-2000kWh per year with our 8 panels.  Using a simple division of the 2012 yearly amount, this shows we would need between 36 and 42 panels. We could fit another 2 onto our south-facing roof, taking us up to 10 panels. Still only about a quarter of the power we would need for the year.  But even now, this doesn't sound absolutely out of the question - even using only solar power. For the sake of three more bits of roof that are the same area as ours is currently, it is looking quite achievable from a generation perspective...

More later on this methinks... off out to walk the dog with the wife...

Please feel free to leave comments/ideas about this topic.

Sept 4th - Sept 10th

Generation results for the week:

Wed 6.5

Thur  6.8

Fri    1.3

Sat   4.3

Sun   5.6

Mon 6.7

Tue   11.0

Total 42.2 kWh for the week

Avg 6.03 kWh per day.

With 11kWh, Tuesday was the highest generation day yet, with only very thin patchy cloud from sunrise to sunset.  

As an aside, I managed to dig out this graph showing the measured performance difference between conventional (c-Si) solar panels and the HIT panels:

(taken from the Panasonic datasheet for the panel)

For those of you with a mathematical bent, you may have noticed that there is a maximum difference of only about 10% between the two panel technologies at optimum sun conditions. Away from the centre of the peaks, the two panels' performance are very similar.  Although it is the area under the curve that matters when comparing the two.

First full week

Right, first full week of solar generation completed - here's the total kWh generated for each day over the last week since installation:

Wed 8.3
Thur 5.2
Fri    3.9
Sat 10.4
Sun  2.5
Mon 5.5
Tue   5.8
Total 41.6 kWh for the week
Avg 5.9 kWh per day.

As you can see, the values vary considerably despite being over 7 consecutive days, with virtually identical amounts of daylight (sun up to sun down).  The differences are due to cloud cover.  Even for the HIT panels, when the sun goes behind moderate cloud, the drop off is noticeable.

I've detailed in a previous blog post ("First full day") about how I have worked out the predicted average daily kWh for each month.  The seven days above span across the end of August and beginning of September, so I've crunched those two months averages and the prediction shows an average of 5.46kWh/day for this period.

Therefore at the moment, I'm getting about 8% more than predicted, which, if consistent over the year, translates into a final year prediction of 1776 kWh for the year.

As the winter nights draw in, and the cloud cover is more frequent, the predicted daily averages drop off as follows:
October:     3.18 kWh / day
November: 1.79 kWh / day
December:  1.13kWh / day

The panels were working absolutely flat out for a good chunk of Satuday (August 31st). I checked the inverter a couple of times over lunch when the sun was at its highest, and they were kicking out 1920W, which is their theoretical maximum. It was sunny all day on Saturday, with only intermittent hazy cloud cover from time to time - hence the 10.4kWh total for that day. It's worth noting that the predicted daily kWh average for *June* is 7.59kWh.

Generation updates

You'll probably be pleased to hear that I'm well aware of the fact it could get very dull very quickly if I post updates for every single day's result. Seeing as I'm posting anyway, I'll post yesterday's total - wall to wall solid white cloud all day long meant it was the poorest result yet at 3.9kWh for the day.

For future updates, I'll go to a week-at-a-time, eventually dropping to month-at-a-time (as the novelty wears off).  I'm keeping the totals on a spreadsheet with some actual vs predicted comparisons, which I'll post as and when.

Feed in Fusspots

I've been having fun and games applying for the Feed-in Tariff:

I was warned by the installation company that the energy companies are notoriously tricky when it comes to applying for the FiT.  They recommended I post off my application recorded delivery - they have a habit of 'losing' the paperwork.

So I pored painstakingly through the application forms, and the boss bloke from the solar panels company confirmed it was all filled in correctly.

We're with npower for our elec/gas, so it is with npower's application form that I have experience (they vary from energy company to energy company).

At the end of the form, it asks for you to supply 'supporting documents'.

I am already an npower customer, so I didn't need to supply a photocopy of my driving licence and two utility bills addressed to me at my address.

But I did have to supply:

• the EPC certificate for our house, showing at least band D (to qualify for maximum FiT rate)
• the MCS certificate from the installer showing the installation is complete and has been carried out to regs
• the invoice from the installer showing my home address to confirm my relationship with them having installed it

I sent all these off on Tuesday, recorded delivery, with the forms, thinking I've dotted every i and crossed every t.

But I thought I'd better ring npower's FiT team this morning to check they've received the application and that everything is ok.

The 'helpful' lady at the other end of the line confirmed that they had indeed received my application, but they had had to reject it because the invoice does not state that it has been paid in full, and have returned it to me second class post.  She said that if I can get another invoice from my installer showing that it has been paid in full, I can re-apply and all will be fine.

*steam*

I rang the Low Carbon Energy Company this morning and explained the situation. The chap had a steam also, ranting a bit about how picky the energy companies are becoming about these FiT applications. He's posting me out a fresh invoice, showing that it has been paid in full, so I can re-apply.

I'm now thinking, 'have npower really posted my application back to me? She did say "second class"... perhaps that's code for 'You've not received it? Oh it must have been lost in the post'.....

Ah well, have to wait and see... I'm half expecting to have to fill out a brand new form again.  Good job I only sent scans of the original documents, and not the original documents themselves...

Clouds

Cloud cover has meant today has not been as good as yesterday for solar generation.  The day started reasonably bright, with horizon-to-horizon white cloud, slightly drizzly.  By 10am the solar array was only just managing 0.5kW.  The clouds hung around all over lunchtime, which meant it was only pulling about 0.6-0.7k during peak time. But the clouds started breaking up about 3.30pm, and between 4-5pm, the rig was pulling a more healthy 0.9-1kW during breaks in the cloud.

It's now (practically) 6pm, and it's down to about 300W in bright sunshine. I may get a bit more today, but not much.

Total for 29th August 2013:  5.1kWh

First full day

Well, the panels have had their first (practically) full day.  It's twenty to eight and the sun is just disappearing behind the houses at the end of the road.  The inverter is showing the princely sum of 6W currently being generated by the array. That's about as much as I'm going to get today.  I've found the aurora has a cool little graph to show the energy generated throughout the day.

More to the point, the inverter is showing the very princely value of 8.3kWh for the total generated today. This, I am very happy with indeed.

I have done a bit of rummaging around the t'interweb, and have found a great web page on the met office showing the average sunlight (amongst other things) for Blackpool over the years 1981 - 2010, broken down into months.

http://www.metoffice.gov.uk/climate/uk/averages/19812010/sites/blackpool.html

Note this is not all daylight hours - this is hours of actual direct sunlight, excluding hours when the sun is behind cloud. Very useful for solar panel calculations... I have crunched this with the predicted yearly total kWh to give the predicted monthly average kWh for each month.  I've then broken each month down into days simply by dividing by the number of days in the month. For August, I should be generating an average of 5.98kWh per day to achieve the predicted monthly average of 185.39kWh. At 8.3kWh, this is 139% of the predicted average.  I know this is only one day, but we are at the end of August, and I would expect this to be the worst end of the month for sunlight. The beginning of the month would have yielded higher values. 

If I were to (probably quite foolishly) extrapolate this increase across the whole year, my revised predicted total kWh generated would be 1645 x 139% = 2286kWh.  I think it is probably a bit rash to be expecting this much, but I am cautiously looking sidelong at 2000kWh... Today's actual v predicted kWh does seem to correlate very nicely with the "about a third more" quotes I was getting regarding these 3rd gen HIT panels. Only time will tell....

The boss bloke from the solar panel installation company has been today to sign off on the rig so I can apply for the feed in tariff (and so he could collect his cheque...!)   I have posted off the FIT forms, and he tells me it takes about 2 months for them to process them.  They backdate the payments to the commissioning date, so I don't lose any payments, they just make you wait for it.  

The official documented maximum supply of my 8 panel array is 1.92kW (each panel is actually only 240W, not 250W), although it's referred to as a 2kW array.

So how much of that maximum did I see today? Today has been a bit overcast, with some broken cloud and hazy sun.  You can see on the little graph on the photo there's only a narrow peak in the middle couple of hours around lunchtime when I'm getting the maximum out of the system.  Although the peak in the middle could have been wider, it's just that the broken cloud cover today meant it wasn't maintaining it's maximum as long as it could have.  I looked at the screen around 1pm.  Whilst the sun was behind hazy cloud, it was hovering around 1.6-1.7kW. When the sun popped out of the broken cloud and the array received direct sunlight, the meter peaked temporarily at 1.90kW.  I'm guessing that this is as high as it's going to get in August - I assume it could only hit its theoretical maximum at midsummer (end of June) when the sun is at the optimum angle in the sky.

Update on the drop in voltage on being connected to the grid:   Rubbish. This was just me being a plantpot (not the first time).  What actually happened is that whilst the bloke was tinkering with initialising the inverter, a good 10-15 minutes passed between him connecting the array and the inverter finally getting connected. It was during this 15 minutes that the voltage dropped off, simply due to the sun dropping in the sky.  As described in the paragraph above, it has hit very close to its theoretical maximum at times.

One final note that is worth making - this aurora inverter runs practically silent.  I had to put my ear onto it to make out a faint hum. 

So that's that... Feel free to ask q's - the future updates will be less wordy, I'll post actual vs predicted values at regular intervals.

The first drops of juice

The panels going in.

All 8 in their final resting place. Long may they generate.

And the inverter showing the juice coming in.  The boss bloke has emailed and he's coming round tomorrow to go through the feed-in tariff paperwork and approve the system for MCS.

The large numbers show the input power being delivered at 517W (just over 1/2 kW).  It is a sunny day today, so I assume the system is running at maximum power. This puzzles me as it is a 2kW array. What is happening to the other 1 1/2 kW?  Will get back to you on that one... Question for boss bloke tomorrow methinks.

The input voltage of the solar array is steady at 338V (42.25 Volts per panel). I noticed that when it was first powered up and began initialising, the inverter showed the array input voltage at 399V (50V per panel) which is the absolute maximum, as I would expect on a sunny day. Once the inverter had finished initialising, it clicked into 'ready' mode and connected the solar energy to the grid. The input voltage of the array immediately dropped to about 338-340V, and steadied there.  It appears that putting the array under load decreases its output voltage.  

Not sure what the little graph on the left of the screen is for.  I guess it will show the increase and decrease in energy generated over the day.The first row of small numbers below the large numbers is how many kWh generated today (currently 0.2kWh). This will reset every 24 hours (at midnight I assume). The second row of small numbers below is how many kWh generated in total, since installation (currently showing 0kWh - I assume this will update once a day at the end of every day).

Finally the panels go up

The installers are hard at work. The retiling of the roof is complete (you can tell the difference in colour between next door's roof and ours). The panels are currently leaning against the conservatory awaiting their final journey. All tested, all producing about 50 volts each. I had a brief chat with the gaffer about the HIT panels and about how I could expect them to perform compared to standard panels. He said that in full, direct sunshine, they generate about 10% more than a standard panel, but that I'll notice the difference most in 'diffuse' sunlight. For example, on an overcast day, they'll produce pretty much full whack, whereas the output of a standard panel will drop more noticeably.  Also, in the morning, as the sun rises, these panels will rise to maximum output earlier, and also as the sun sets in the evening, they'll remain at maximum output longer. So they're operating at maximum output for more hours each day. He says that in England's weather/sunlight patterns, this translates to approximately 1/3 more kWh over the year compared to a standard panel.

The panels attach onto pairs of rails, which are fixed to the roof on brackets. You can see two of the rails on the photo - all the brackets are installed, and the top rail has yet to go in. For each bracket they lift out a tile and fix the bracket to a roof joist, and seal up the gap in the tiles with a lead flap to prevent rain getting in.

Each panel has two watertight connectors, to allow them to be daisy chained together, and the first and last one then connect to the two DC cables that run through the roof, into the loftspace and down into the under stairs cupboard.  You can just about see on the photo where the two cables disappear under a tile.

Where it all began

This is my blog about our solar panels.  I first looked into solar panels about 3 years ago when the UK feed-in tariff was launched. Back then, the householders who generated their own electricity were earning 41.3p per kWh (solar or wind).  Sticking a thumping great turbine up at the bottom of the garden would not have helped our good relationship with our neighbours, and besides would certainly not have received planning permission, so that left us with solar.  I asked for a quote from a local specialist, and it came back at 'about £15,000'. We didn't have that kind of cash, so I reluctantly had to let it go.

A few months ago, I decided to look into it again. The government are now offering a feed-in tariff of 14.9p/kWh for installations that are commissioned before October 2013 (http://www.energysavingtrust.org.uk/Generating-energy/Getting-money-back/Feed-In-Tariffs-scheme-FITs#rates)

• A little aside about the feed-in tariff system:  You have an electricity meter installed with your system that measures just the electricity you generate from the panels. You get paid (by whichever energy company supplies your electricity) for every kWh your system generates. The early adopters are still getting 41.3p for their electricity - and will continue to get that until their tariff expires. Each feed in tariff runs for 20 years from date of commission. The price you earn is 'locked in' from day 1 of your tariff. So we'll fall into the pre-October 2013 tariff, which means we'll get 14.9p for every kWh we generate from now until 2033.  Another important note is that since 2012, the government have introduced a restriction to feed in tariffs - to be eligible for the full rate (14.9p currently) your house must have an Energy Performance Certificate (EPC) of at least band D.

But what's a kWh and a kW?
Every panel generates a certain amount of kW (kilowatts). Usually 1/4kW each. If you have 4 panels, then your system will generate 4 x 1/4 = 1kW. If you have 8 panels, then your system will generate 8 x 1/4kW = 2kW.  These values are the absolute maximum power they can generate, in full, direct sunshine. Overcast days or panels in shade will generate less than this. Obviously, at night time, they generate nothing at all (duh).

But you don't get paid for kW, you get paid for kWh (kilowatt-hours). The longer you leave them 'turned on', the more kWh they generate. If you leave a 2kW system running for an hour, it will generate 2kWh. If you leave a 2kW system running for two hours, it will generate 4kWh. Leave it running for 3 hours, 6kWh, and so on and so forth.  Remember, these are maximum values - you will not get the maximum out of your panels from sun-up to sun-down (more on that below - see prediction calculators).

14.9p per kWh? But you're getting so little compared to the early adopters?
Yes we are. But, 3 years down the line, solar panel technology has rapidly developed, with 3rd generation ("HIT") panels now available for a lot less than the 1st generation panels. For the same amount of sunlight, each of my panels (http://www.evoenergy.co.uk/wp-content/uploads/2012/05/Datasheet-HIT-240W.pdf) will generate about 1/3 more electricity than the panels I could have bought 3 years ago. And they're smaller, so I can fit 8 of them where I could only fit 6 of the 1st gen panels. Another point to note is that all solar panels degrade over time. Even the 3rd gen panels are quoted as generating only 80% of their original power after 20 years (90% after 10 years).

Prediction calculators.
There are a number of online forecast calculators (eg http://www.energysavingtrust.org.uk/Generating-energy/Getting-money-back/Solar-Energy-Calculator) that will predict how much energy (kWh) per year you are likely to generate. They take into account things like: how many kW of panels you're putting up;  the direction your roof points; how long the sun is in the sky each day; where abouts you are in the UK (southern homes will get more sunlight than northern homes and so therefore generate more electricity); the angle your roof is at (about 30-40 degrees is the optimum angle so I believe - panels laid flat or vertically generate less, something to do with reflectivity).  Our rig has been predicted at 1645kWh per year using the above calculator.  I've chatted with two solar panel installers, and both told me that every single installation they have put in has generated more than the predicted amount. But they are not allowed to give a more accurate estimation, they have to use the gov't figures. They added that it's better to get a pleasant surprise than be disappointed!

I found a company online called the Low Carbon Energy Company.  They've been installing solar panels for about 15 years, they're MCS registered (Micro Generation Certification Scheme) which means they're approved for commissioning the installation for the feed-in tariff (essential).  I was quoted £5270, all in, to install the system (8 panels - 2kW) and commission it.  Where do I sign, I said (after checking with the wife and the savings account, naturally.)

Financial aspect
From an investment point of view, using the official generation prediction, we'll be generating 1645 kWh x 14.9p per year. This is £245 per year, which equates to a 4 1/2 % return on the investment, worse case scenario. You'll struggle to find 2% on even a locked-in deposit account so it makes great sense from a purely financial point of view. But it doesn't end there. I am perfectly entitled to use the electricity I am generating. I still get paid for every kWh I generate, even if I use it all myself. The only proviso being that it has to be used as it is being generated, ie, during daylight. But it doesn't end there. The government assumes I am going to use half of the solar generated energy myself, and I get paid again at 4.64p per kWh for the remaining half I'm sending back to the grid. Which is another £38 per year. A pittance, but still.

I work from home, and my office has 3 computers, 21 downlighters and an air con. The dishwasher and washing machine are in regular use during the day. I don't know how much of the solar generated energy I will use, but it'll be a large portion of it.  All my home-grown energy I'm using is energy I'm not having to buy from the grid. So I'm making a saving on my electricity in addition to the money I'm being paid from the feed-in tariff. If I estimate that I am using half the energy I'm generating, that equates to 822.5 kWh per year. I'm paying 15.1p per kWh for my electricity at the moment, so that is a yearly saving of £124. So we'll be better off to the tune of £245 (f.i.t.) + £38 + £124 = £407 a year.  This gives a total time to repay the £5270 investment of just under 13 years, so it's a long term investment. However, I'm cautiously optimistic that the actual figures will be a lot better than these, but only time and the sunshine will tell. In addition, as electricity prices go up (and you can bet your bottom dollar they will), the savings we're making will increase.

We're in the fortunate situation that the back of our house faces due south, which is ideal for solar panels, because they're collecting direct sunlight all day long.  From the conversations I've had with installers and proponents of the industry, you can put solar panels on west- or east- facing roofs, but they will only generate significant amounts of power in the morning or evening.  That doesn't mean you can't put solar panels on east or west facing roofs, but they won't provide as high a return. North facing roofs are not worth the bother.

Rear of our house with the scaff up ready to install. Half a day's work for three scaff men. Would have been quicker but they had to do a bridge over the conservatory.

The complicating factor
Our house has an original roof - this means that when the tiles were laid back in the 1930s, they were laid directly onto the wooden roof battens, without a layer of felt between the two (as they do nowadays).  The previous owners of the house, in their infinite wisdom, decided to insulate the loft on the underside of the roof with that spray on insulation foam stuff that sets hard (looks a bit like cinder toffee).  Because it was sprayed directly onto the underside of the tiles, it welded them all together, absolutely welded them. When the roofers came to examine the roof, every time they tried to remove a tile to fit the brackets for the panels, it would crack all the tiles around it. And when they tried to removed the cracked tiles to replace them with good tiles, they would crack all the tiles around it.

Anyway, after a discussion with the company, they said the best thing to do was to remove all the old tiles (and insulation foam underneath) and re-tile the south face of the roof prior to installing the panels, which I agreed to since they gave me a very competitive price to do it.

The electrics are all in. You need space for an inverter (the heffing big box) which converts the DC energy from the panels into AC energy that it compatible to be fed into the national grid. You also get a little digital meter to show how much energy you've generated, and the whole thing is topped off with two isolator switches to shut it off.  You also need a spare slot on your main electricity consumer unit which is how the power gets fed back into the grid.

These are the 8 panels themselves. They're Panasonic HIT-N240SE10 and represent the cutting edge in solar power generation.  They're going up later this week (all being well) after which I'll update the blog.