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:
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.
Maybe look at this a different way - Maybe you could look at it simply by producing enough profit in the good months to absorb the cost of the bad months?
ReplyDeleteI'd not thought of that approach... We pay 15p/kWh to buy electricity from npower, and we would be selling the solar energy at 14.9p/kWh on the feed-in tariff, so it should almost exactly balance itself out. Although I don't know if npower would entertain our continued use of their service if their net income from us for the year was £0! We'd basically be using the grid as a giant battery!
ReplyDeleteThe Government still pays you for the energy you create, even if you use it yourself, yes?
ReplyDeleteBased on the numbers you've seen so far, can you produce enough energy during a peak hour to cover what you use during the same period? I presume the energy over a day is very much like the graph in your main post, but wanted to check!
Can you take the difference between the generated and consumed amount and plot a graph to see if there's an average above or below break even?
I'm hoping that at the peak point of the day (which hopefully will be a more than one hour) you generate all the energy you use, and coupled with the feed in kick back you can offset costs during the darker hours.
Then it all comes down to minimising energy usage when there's low energy generation!
Q1 - yes.
ReplyDeleteI've done some observations during the day, and you're right, there is a peak during the central hours. The peak is wider and higher during the longer days over spring/summer, but we're now on the downward trend towards winter.
At the moment, the peak is about 3 hours wide, with a 4 hour curve on either side. I've got a good pic showing this on the inverter taken on 14th sept (clear sky all day) which I'll bung up on another post.
I have two meters - the 'normal' electricity meter (which now shows only how much energy I have bought in from the grid); and the solar meter, which shows how much electricity I have generated. Unfortunately, this means I now can't measure how much electricity I'm actually consuming in total, since some of the solar generated electricity will be fed back to the grid when I'm not using it.
Since installation, there have been times when I've been generating more electricity than I'm using (I can tell this when the meter showing electricity coming in from the grid stops going up), but it's impossible to know how much. It's more the case that in general I'm using all the solar generated electricity and still having to buy in from the grid. I'm imagining during the spring/summer months, there will be more occasions when I'm generating more than I'm using.
Is that any clearer?!