As a follow up to the recent article on inverters, I thought it would be a good idea to warn you that if you wanted to buy an inverter in time for Christmas I’m afraid you’re out of luck. As result of the huge demand for residential PV systems Germany described on this site below, it is virtually impossible to find an inverter of any size or manufacturer in the whole of Europe at the moment.

The big manufacturers; SMA, Fronius, Mastervolt and the like are all completely sold out and are unclear when their next shipments can be made. Wholesellers are operating on a first come first serve basis and taking orders three months in advance. This means that if you were thinking of installing a PV system in the next few months but haven’t ordered your equipment yet you’d better get a move on. We’ve even heard reports of SMA shipping inverters to German customers without LCD displays in efforts to meet demand. (apparently the displays will be delivered in a few months time when they can be clipped on).

I guess the shortage is a good sign that the solar industry is alive and kicking. However if the feed-in-tariff is announced in the UK soon and it turns out to be a good one, there’s going to be a lot of frustrated people out there unable get involved for the lack of an inverter.

Following on from the various criticisms of the government’s recently announced Clean Energy Cash Back System, comes the announcement of the closure of phase two of the Low Carbon Building Program for solar installations in the UK.

The news is a blow to the industry as it will leave a crucial funding gap until the feed-in tariff comes into operation in April 2010. The move which has been made because of what the government calls ‘unprecedented demand’ seems to have become a victim of its own success.

Initially the government had earmarked £18 million of grants for solar PV installations for public sector buildings such as schools, hospitals and housing installations however it is feared that this cessation of the grant system will kill the solar PV industry in its tracks with the Clean Energy Cash back system still months away.

It is generally believed by industry insiders that the gap left by the closure of the low carbon program comes at an extremely bad time especially with regards to the general economic climate and Britain’s desire to become a real global player in solar PV. Speaking as general manager of UK solar firm, Sharp Solar, Andrew Lee commented that,

“The government’s decision to close the Low Carbon Building Programme Phase 2 is one that threatens to kill the UKs PV industry. At a time when the UK should be building-up interest and support ahead of the introduction of a UK Feed in Tariff next year, the decision to end the LCBP grant procedure because of too much demand is just another unnecessary hiatus in support.

adding,

“PV continues to be overlooked as the government conducts a stop start approach to adopting renewable energy. While we understand that PV technology is part of a wider renewable mix – if every building in the UK had a solar panel on its roof, there would be no need for any other energy source.”

The Department of Energy and Climate Change (DECC) has come under the fiercest criticism since the dual release of the Clean Energy tariff details and now the low carbon program closure news. Some industry observers have commented that the DECC’s hand is being forced by a strong anti-solar lobby currently operating within Westminster and that this news is a hiatus possibly designed to appease the lobby headed by the utility companies.

Defending criticism of the government, a spokesman for the DECC stated,

“It’s very encouraging that there’s been an unprecedented demand for this technology but we have to be fair to all renewable technologies. We’ve put £18 million into the solar PV ‘pot’ since April which is more than the industry asked us for, so it’s really an unprecedented demand. FITs that come in next April will provide future incentive for solar PV projects.”

Many people have been asking us when the government will finally announce the size of the UK feed-in-tariff which is a fair question since it’s supposed to come into force next April after all. Unfortunately we’re not able to give a definitive answer, and nor are any of the people we’ve spoken to about it.

The ‘We Support Solar’ campaign has done well to generate publicity around the feed-in-tariff. Now the government has mentioned 36.5 pence per kilowatt hour as a provisional figure, asking for an increase on that of just 10p is a strong argument. Whether the government sees it that way is yet to be known however. Alan Simpson, one of the most active and vocal MPs on the subject believes that the delay in feed-in-tariff decision may be a tactical decision by Labour. For example, an announcement on the feed-in-tariff could be used to boost popularity at a key moment – perhaps even during next week’s summit in Copenhagen.

Alternatively, if both the Tories and Labour believe the feed-in-tariff to be a votes winner, there could well be a bidding war taking place behind closed doors between the two parties right now. Neither party would want to be seen as stingier than the other when it comes to creating green electricity and green jobs. This is pure speculation of course, but if it were true it would be great thing for the UK renewables industry.

The opposite could also be true however. With many households already stretched by their energy bills, the government could be looking to reduce the cost of implementing a feed-in-tariff. It is hard to see them going below the already announced 36.5 pence (it would be better to scrap the whole feed-in-tariff together), but they could be waiting for a moment when the newspapers are distracted by another issue to announce the feed-in-tariff plans.

Hopefully in the near future I’ll be able to write a reaction to a government announcement. Until then though, if you haven’t already written to your local MP asking what they personally have done to support the UK feed-in-tariff then go do it, now!

The whole idea of this feed-in-tariff business is that you earn money by selling units of energy produced by your solar panels. So much so that after 25 years of operation you’ve made your money back and have even turned a tidy profit. This means that in order to know whether putting up some solar panels makes any sense, you need to know exactly how much energy they’re going to produce over the 25-year guarantee period.

Easy, you might say – the calculation is pretty straightforward. You find out the average annual irradiation (sunnyness level) from your local weather station, and multiply by the efficiency of your solar panels and the number of square metres you have. This will give you a nice number and away we go. The only problem is you might be more than 50% wrong because we’ve missed out a couple of variables. Variables such as temperature coefficient, tilt angle, diffuse-light fraction, solar cell type, shading losses, inverter losses, cable losses, degradation, module de-rate factor, mismatch losses, anti-reflective coatings, snow and lightning strikes, to name a few.

Of course there are an infinite number of effects that can influence the output of your photovoltaic system (solar eclipse, anyone?). The question is whether you have considered the important ones or not.

Knowledgeable installers use one of a number computer programs designed specifically to take these factors into account. You type in what type of solar panel you’re using, how many, where they are, what angle they’re tilted at, what direction they’re facing and then press ‘go’. It then calculates the amount of energy you’ll produce each month and even the return on investment if you want it to. Behind these models is actually some physics that describes the behaviour of solar cells under different light intensities and correctly.

The most commonly used model in Europe is called PVSyst, developed at the University of Geneva. This software package contains information on a large number of different solar panel types and is capable of taking into account many of the above listed factors. Installers across Europe use this software package to predict the energy yield of residential solar systems, as do many banks pondering whether to provide multi-million euro loans to super-large PV power projects. Even with this advanced software package however, some of these factors are very complex, and improving these models is an active area of research.

Here, I’ll deal with a couple of these complications as examples. When you buy a solar panel, it invariably comes with a power rating. Full size modules are generally around 200W. What does this mean though? In principle, the power rating indicates what you get when the panel is illuminated by full-sunlight. ‘Full sunlight’ is not very specific, so the international community has defined what is known as Standard Test Conditions (STC), which corresponds to an irradiation of 1000 W/m2 and a cell temperature of 25oC, when the light has a specific spectrum (or colour) known as Air Mass Index 1.5. So the power of your solar panel comes from its performance under exactly these conditions. In general this is measured using special type of lamp called a ‘solar simulator’ that tries to reproduce the AM1.5 spectrum as closely as possible. Calibrating these lamps precisely is notoriously difficult and there are very few testing centers around the world that are truly trusted. The National Renewable Energy Laboratory (NREL) in Colorado, USA uses at least two different lamps and one outdoor measurement to record STC performance, after a long period of calibration.

Because measuring the STC performance is so tricky, the power rating you get has a plus or minus 5 percent error margin. This is hard to include in your simulation. In addition, manufacturers will often deliberately under-rate the power of their solar panels to be sure they don’t fall below the warranty. This means you may well get considerably more power than you expect.

Another factor that adds to uncertainty is the degradation factor. When you buy solar panels they are normally guaranteed for 20 years, but only to 80% of the initial power output. This means the manufacturer expects them to degrade 1% per year on average. When calculating performance in the models, people also tend to use a 1% degradation rate per year. This is only a rough estimate however. During the certification process, solar panels are given all sports of nasty treatment to test their reliability to breaking point. This doesn’t tell you much about the rate of degradation when the solar panels are outside under normal operation though. The only reliable way to test degradation over 20 years is to wait 20 years, but this is complicated by the fact that technology improves reliability much faster than that. So the degradation of solar panels made in 2008 has only been tested since, well, 2008.

What these issues highlight is that understanding the energy yield output of your solar panels is not as straightforward as it may at first seem. When having your system designed, make sure who-ever you’re dealing with has some experience, and if possible, get a second opinion.

The other critical piece of information for understanding the financial viability of a solar installation is how much you will get paid per kWh under the feed-in-tariff. Unfortunately, the UK government has not released the final figures yet, which means no-one in the UK can make a reliable financial plan for getting solar panels, even when the launch date for the feed-in-tariff is just 4 months away.

Hopefully I will be able to update you on this in the near future. For now though, it’s better to be more conservative with your numbers than too ambitious….