Uncharted Territory

December 4, 2011

Fixing FITs some more

Filed under: Electricity, Energy, Energy policy, Feed-in tariffs, Global warming, Solar PV — Tim Joslin @ 1:40 pm

I noted yesterday that the UK’s expensive feed-in tariff (FIT) is not structured to support the development of the highly efficient technologies (turning 30%+ of the energy in incident sunlight to useful electricity) that the country will need in the future.

Here’s a more concrete example of what is happening. If we look at the web-site of one reputable supplier, Spirit Solar, we see that they offer several types of panel. The stand-outs are Sanyo’s “Hybrid Mono” products, with the HIT-N240SE10 achieving 19% efficiency. These are still just silicon based (I understand that best results will eventually be obtained with layered panels, each layer using a different technology to capture light of particular wavelengths), but optimised for efficiency. The Sanyos are just a tad more expensive than the bog-standard panels at 14-15% efficiency. But here’s what Spirit Solar say:

“The Sanyo are the most expensive per Watt of power generated. Their one big advantage is that by using a different ‘hybrid’ technology they give approximately 25% more power per square metre than any other panel. …the Sanyo gives 190 Watts per square metre, compared to between 134 [actually none are this low – the figure is presumably out of date and the text should read “141”] and 149 Watts per square metre for the other panels. The downside is that they currently cost around 50p more per Watt – so for a 2 kWp system you will pay around £1000 more if you choose Sanyo. So if you are wondering whether to buy Sanyo or not, ask yourself what are you trying to maximise – the total power you can squeeze out of your roof or your financial return? If your objective is simply to maximise the power output from your available roof space without regard to budget, then you should choose the Sanyo hybrids. Don’t choose the hybrids if you want to maximise your financial return.” [my stress]

You have to email for a quote, and PV prices are currently all over the place, but that extra £1000 is on a system costing at least £5000, probably somewhat more. That is, for 20% more, tops, you get 25% more power for a given area. No-brainer.

But, as discussed yesterday, the FIT scheme does not provide an incentive to maximise output per unit area.

In fact, the FIT scheme seems to have been devised with no thought as to the behaviour it will encourage. The sole goal seems to have been to “bung up a few solar PV panels”.

Another page on Spirit Solar’s rather informative site illustrates another problem. Scroll through some of the pictures of the company’s installations. There are a number of examples of roofs where far more area could have been covered with panels.

Why wouldn’t customers want to cover their whole roof? Because there’s no incentive to do so, of course. Many installations will be of 4kW capacity (4kWp, where p stands for “peak”) or slightly under. Why? Because larger schemes receive a lower tariff. In fact, as I understand it, and using the tariffs to be put in place from now on, there’s no point at all in putting up a scheme of 4-4.8kWp. That’s right – you get less for a 4.8kWp system than for one of 4kWp. (The generating tariff for a scheme up to 4kWp is 21p/kWh, whereas for 4-10kWp it’s only 16.8p/kWh, so schemes of 4-4.88kWp will earn less revenue than those of 4kWp or just less!).

Of course, this problem could be simply fixed by qualifying the first 4kWp for the higher tariff and only additional capacity for the lower rate. This would at least mean that solar PV generators have an incentive to cover the whole available roof area.

Another solution would be simply to have more bands. The worst thing about the whole scheme is that you need a large unshaded roof area to reach the optimal 4kWp (about 25m^2 for standard panels, 20m^2 for the Sanyos), so there should be bands for smaller roofs (say 1kWp and 2kWp, but this should be done on installation area as discussed yesterday) and to ensure larger roofs were fully utilized (say 6kWp, 8kWp as well as 10kWp, and more subdivisions up to 50kWp).

There is another problem, though, which is that the export tariff is only 3p/kWh. That is, if you use the electricity, you displace electricity (or gas) you would otherwise have had to buy for around 10p/kWh (or 5p/kWh for gas). Since most households would be hard pushed to make use of more than 4kW for any length of time (though I don’t see why solar PV generators don’t invest in a 20kW battery to store energy for the hours of darkness), this means the drop-off in revenue above 4kWp is even worse.

Surely the policy is eventually to generate electricity for sale to the grid. If this is the case, then shouldn’t the export tariff be somewhat higher? I gather the 3p/kWh is based on the wholesale price for electricity. But solar PV electricity is more useful than bog-standard electricity. It’s renewable for a start, so should qualify for ROCs (renewable obligation certificates) which otherwise cost money. And it’s at a peak time (except perhaps at weekends). One problem is that you don’t want the export tariff to exceed the retail gas price, because then solar PV generators have an incentive to use gas rather than electricity (since they can sell the electricity to pay for the gas and still be quids in), but there’s still scope for an increase to, say, 4.5p/kWh. This would make it a little more worthwhile for people to cover their whole roof with panels.

It may be worth DECC thinking through the FIT scheme a little more thoroughly, since these panels are going to last for decades – they’re typically guaranteed to provide at least 80% of their original output in 25 years. Once they’re up, it’s not going to be worth taking panels down – especially those qualifying for FITs – to replace them with more efficient technology.

Why don’t we try to get something right first time for once?

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1 Comment »

  1. Couldn;t agree more

    Comment by Mike Joslin — March 1, 2012 @ 11:52 pm


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