Posts tagged with: panels

Friends of the Earth is urging the Government to re-think its plans to slash payments for solar electricity schemes today (Monday 12 December 2011), as the rush to install solar payments ahead of a crucial payment deadline comes to an end.

The Government has halved the payments for any solar electricity scheme completed from today, which will almost double the payback period for homes, businesses and communities.

Later this week (Thursday 15 December 2011) Friends of the Earth and two solar companies – Solarcentury and HomeSun – will ask the High Court for permission to challenge Government plans to cut the payments.

The premature cuts could cost up to 29,000 jobs and lose the Treasury up to £230 million a year in tax income, a report commissioned by Friends of the Earth and Cut Don’t Kill – an alliance of solar firms and consumer and environmental organisations – revealed last month. Earlier this month construction firm Carillion warned 4,500 workers their jobs are at risk because of the Government’s proposals.

Countless schemes have already been abandoned, denying cash-strapped homes and businesses the chance to free themselves from soaring fossil fuel prices.

Friends of the Earth’s Executive Director Andy Atkins said:

“These Government cuts will cast a huge shadow over our thriving solar industry and pull the plug on thousands of jobs.

“We don’t oppose modest payment cuts in line with falling installation costs – but the size and speed of these proposals will decimate an industry that could play a key role in weaning the nation off of expensive fossil fuels.

“Ministers must think again and give their support to an industry that could and should be at the cutting edge of a clean energy revolution.”

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….

If you’ve ever carried a solar panel you’ll know that they’re pretty heavy (about 25kg for a 1.5sqm panel), and if you add on the racking that’s required it makes things even heavier. This is a bit of a problem for roofs that can’t support large weights, and for the installers who have to get the stuff up there.

As with many things in life however, technology has a solution on the way. In this case the solution comes in the form of flexible solar panels. This new type of solar panel doesn’t use glass as the supporting material; it uses transparent, flexible plastic sheets. They can be rolled up like carpets and unfurled across a low-sloping roof. This process is much quicker and easier than normal solar panel installation. The solar panels just need to be tacked down at the edges, rather than have heavy metal racking bolted into the frame of the roof. The material is also light enough so that any roof can support its weight.

This technology is spreading quickly but has yet to win dominance in the market. This is for several reasons. Firstly – only one company in the world is making flexible solar panels in large volumes. That company is UniSolar, based in Michigan, USA. UniSolar have developed their own proprietary process for depositing thin-film solar cells (see discussion “REF TO previous article”) on flexible plastic sheets.

In order to increase efficiency of the panels, their design in fact uses three solar cells stacked one on top of the other. Each solar cell responds to a different part of the sun’s spectrum so it maximizes the amount of energy converted to electricity. Despite this compmexity, these solar panels are significantly less efficient than traditional, crystalline silicon solar panels. They are made from ‘amorphous’ silicon and are currently around 6-8 percent efficient, compared to 16 percent for crystalline silicon panels. This means you have to cover a larger area of the roof.

A number of companies claim to have more efficient versions of the technology on the way. Companies such as US based Advent Solar, claim to have flexible solar panels that will soon reach over 10 percent efficiency while other companies, such as G24 Innovations in Wales claim to have lower manufacturing costs for this technology.

Given the success of UniSolar with their low efficiency and complex design, any company that can make an improvement is likely to have success with flexible solar panels. Let’s wait and see…