The winter months have brought lots of snowfalls, or as they are known in the world of solar energy, ‘shading events.’ You might be forgiven for wondering what exactly happens to the performance of solar panels when they are covered in snow, or anything else for that matter.

Shading is a big issue for solar arrays. A small amount of shading on one solar panel can result in a big power loss for the entire system. This is because of how they are connected together; a solar panel is made of a number of solar cells connected in series. Each solar cell has a current of around 8 Amps and a small voltage of 0.6V or so when under full sunlight. For those who remember their physics classes from school, this means that when they are connected in series the voltages add up but the current stays equal. Solar panels are then connected together in series to make a string, so the current still stays the same (on large arrays multiple strings are connected in parallel).

What this means is that if one solar panel, or even one cell of one solar panel is affected, it will affect all the others. When a cell is shaded its output current decreases, which means the current for all the other cells and modules is also limited. So one small patch of shade can disproportionately reduce the power output of the whole system.
This effect can be limited by a number of means.

The best way is to make sure your solar panels are not going to be shaded in the first place. This should be checked as part of the site survey, conducted by your MCS accredited installer. You should ensure that nothing will shade the modules during the middle of the day, when your system should be producing the most energy. Shading can be checked using a special design tools that show the path of the sun behind various shading objects. This can be either a lens that shows the horizon and path of the sun in front of you, or a full design software package that uses photographs of the surroundings.

With snow it does help to clear it off. But there isn’t usually much sun when its snowing, and if the sun does come out, the snow melts pretty quickly.

If you cannot eliminate shading as is often the case in built up areas, there are several technologies that can limit the effect of it. Many solar panels now include bypass diodes that disconnect groups of solar cells if they are shaded. It is fairly crude but often works well. When you buy solar panels make sure to ask about bypass diodes.

A second technology that is not available yet in Europe but soon will be is distributed conversion. Here, rather than have power electronics (like the inverter) positioned all in one place, you have some electronics placed on each module. This allows each module to operate independently. One company in the US called Enphase claims this technology increases power output by upto 25 percent.

These are all things to bear in mind when buying a photovoltaic system.

Solar thermal heating systems could be something of a common sight on south-facing roofs in the UK with the introduction of a feed-in tariff. Previously, the high cost of solar thermal kits has put off householders wishing to invest in renewable energy generation but with the announcement of the introduction of feed-in tariffs for solar thermal in the UK in April 2011, solar thermal installation is set to become much more attractive.

The government’s feed-in tariff scheme to be called the Renewable Heat Incentive, will work by offering small-scale producers of renewable energy premium rates over a period of around 25 years for units of energy fed back into the national grid. Feed-in tariffs have been successful in countries such as Germany where they have proved to be an extremely effective way of off-setting the high costs of investing in solar power equipment.

Germany saw a massive uptake in all types of solar energy generation with tariff schemes rendering investments viable in the face of competition from traditional fossil fuel sources. For more information on how the tariff legislation is broken down year by year all of the information is available on solarfeedintariff.co.uk

In the UK, the essential figures are that homeowners wishing to invest in a typical £5000 solar thermal kit for their properties can hope to expect healthy returns on investment of around £500 p/a over a period of around 25 years not including the average £100 saving on utility bills per year. Such returns and savings are the basis of the tariff scheme and solarfeedintariff.co.uk is hopeful that these incentives will be sufficient to help the UK solar industry take off.

Through the installation of roof mounted solar panels, the sun’s energy is absorbed by the panel’s in-built technology which in turn is used to heat the water. The hot water is pumped through storage cylinders where it is heated further, providing households with south-facing roofs a good supply of hot water through the summer months and a contribution to water heating energy through the gloomier seasons.

Households aside, the government is also hopeful that the tariff legislation will bring about a grassroot change in attitude towards green energy as a whole and see technologies such as solar thermal become commonplace rather than an exceptional sight in the UK.

Solarfeedintariff.co.uk is already hopeful that with the obvious environmental benefits of utilising renewable energy sources along with the financial incentives built in to green energy schemes, the UK is set to follow in the footsteps of what are generally regarded to be the ‘greener’ nations such as Germany and Sweden. Households and community projects will all be set to capitalise on the feed-in tariff in the coming years with cash savings, investment yields and carbon emission reduction providing ample rewards for investors and communities.

When thinking about renewable electricity for your home, two options spring to mind; photovoltaic panels and small wind turbines. But which one should you choose? The government has introduced a feed-in-tariff that pays a subsidized amount for the electricity they produce and the amount paid for small wind turbines is similar to that paid for small PV systems (34p/kWh compared to 41p/kWh).

The key criteria to deciding which technology will be the most profitable is the cost of producing a unit of energy from each one. For this you need to factor in the up front costs such as equipment and installation, and then look at how much energy they will produce once out there over an average year. Without going too heavily into numbers my argument is that in some instances, micro-wind turbines will have a lower cost of energy than solar panels, but for the majority of cases solar panels will be better and this can be explained by some basic science.

Without a doubt, on a large scale, wind energy is cheaper than solar. The cost of energy from large-scale wind farms is somewhere around 10p/kWh whereas the cost of energy from large-scale solar is three to four times greater at present. Big wind turbines are now very well designed products and many years of industry development means that the costs have fallen dramatically and continue to do so. Big solar farms are also rapidly reducing in cost and make a lot of sense in some locations, particularly in the many regions where wind farms are not suitable, but for now they do not compete.

On the small scale however, the economics are drastically different. As the size of a solar installation decreases, the performance falls linearly with the amount of area used, and therefore the cost of energy does not change so dramatically. In contrast, as wind turbines get smaller their performance gets disproportionately worse. This is for two mains reasons:

The first reason is that as the turbine blade length gets shorter, the ‘swept-area’ decreases quadratically. This means that if you decrease the length of a blade from 80 meters to 40 meters, the area covered by the blade decreases from 20 thousand square meters to just 5 thousand. The ‘swept-area’ determines how much wind energy the turbine can use. So when you decrease the blade length you still need all the expensive moving parts like the generator, but you get disproportionally less energy – for one big wind turbine you would need thousands of smaller ones to cover the same area. The second reason is that where you use micro-wind turbines the wind speed is generally slower. This is because most of us live in built up areas where there are other buildings nearby. These buildings disrupt the wind, making it irregular and slow. Wind speed is crucial to the effectiveness of a wind turbine, again because the energy contained in the wind is disproportional to its speed. If the wind speed drops by a factor of 2, the energy produced by a wind turbine decreases by a factor of 4. Comparing most built up areas, the average wind speed is much lower than half the wind speed found high-up in open spaces where you find most wind farms.

These two factors combine to mean that for most homeowners solar panels are the most sensible and safest option. Of course, if you live near an open space and get a lot of wind then a micro-wind turbine could be a great investment. However, if you do live near a windy open space, I would suggest trying to build as big a wind turbine as possible, as their cost effectiveness increases dramatically with size.

With the UK government announcing the imminent introduction of a feed-in tariff for renewable energy generation, the UK solar industry is already seeing the development of a grass roots approach to solar energy.

Feed-in tariffs which have been established in other developed countries with the basic motive of attracting investment in fledgling renewable industries will be replicated in Britain with solar installers being offered premium rates (typically 25p/kWh over a project’s lifetime) for the units of energy fed back in to the national grid.

Such incentives are of course absolutely necessary in order to make investment in expensive technologies viable by offering attractive returns on investment to investors.

One of the first projects to take advantage of the feed-in tariff or ‘Clean Energy Cash Back’ scheme is a social housing scheme in Manchester which plans to generate around £900 per household a year by selling renewable energy back in to the national grid.

The Manchester based co-operative called Horizon Energy Corporative is working with landlords in the Manchester area to maximise the potential of solar energy in the Manchester region.

The scheme, put together by EIC has received the full support of the department of Energy and Climate Change (DECC) which hopes that such schemes will help the UK to catch up with other countries where feed-in tariffs have been established now for some time while at the same time offering financial rewards for social housing projects.

Managing Director of EIC, Andrew Melchior stated that,

“Our energy will be used to drive down the costs of electricity and hot water for those in need of relief from fuel poverty, while supplying community-generated energy to householders in North West England.

With sufficient support there is no reason we shouldn’t end up producing energy output equivalent to one quarter of a conventional coal-fired power station.”