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%).
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:
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.
