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Domestic solar energy falls into two categorise: thermal and photovoltaic. Thermal is where the sun heats water in the solar panel, which feeds into the standard hot water system. Photovoltaic solar panels convert sunlight into electricity, which is then fed into an inverter to make it AC and then into the general household electricity main. The two different categories themselves are divided into various types, each with lots of different models to choose from. It can be a bit confusing, with little in the way of cost-to-output data to compare them. I have put a few suggestions below for options that appear good to me, so hopefully this will help. Check out the shop for purchase options.
Most solar panels can be fitted without planning permission, but listed buildings or those in conservation areas will need prior consent. It is always a good idea to check with your local council anyway, as rules vary from council to council. Your house is probably suitable for a solar panel if you have a flat roof with a southerly aspect (panels can be put on a frame) or a sloping roof facing between southwest and southeast. An east or west facing roof will probably give 85% output compared to south facing, with a totally north facing roof 60%. The best angle of dangle for the roof pitch is 30o to 40o.
Please note that solar panels do not need direct sunlight to work, but can heat water and produce electricity on cloudy and even rainy days. Snow is a bit of a problem, mind.
Solar Thermal
It is worth noting that solar thermal systems do not generally power household central heating, but usually heat only water for showers, baths, washing machines etc. Some systems do a bit of central heating as well, especially underfloor heating, but it is tricky and not particularly good.
Solar panels for producing hot water are generally pretty low maintenance and come in two flavours: flat plate (simple and cheap) or evacuated tube (fancy but pricey). The way they work is fairly similar, absorbing heat from the sun and transferring it to an internal liquid – usually antifreeze. This antifreeze gets hot, is pumped to the hot water tank, where it runs through a copper coil to transfer its heat to the water in the tank. The cold antifreeze is then pumped back to the panel to heat up again.
The size of panel is often set to provide all your hot water in summer and a fair bit in the winter. Although this makes sure there is no waste, I can’t help thinking that it might be better to design for autumn and spring, as the panels themselves are not that expensive. If you’re going to the expense of fitting one anyway, why not pay a little bit more and get better payback? Anyway, the standard fitting design averages out to about 60% of total hot water requirement over a whole year, with likely savings between £50 and £200 per year. The evacuated tube types are more efficient that flat plate in bad weather, so will give a better output in winter when needed most. Remember that savings will only be made from the water you use from your hot water tank: cold fill appliances, electric showers etc will not be included. If your central boiler currently heats little water (not including central heating, remember), a solar panel will save you almost no money.
Solar thermal systems cost around £2,500 to £5,000 to have them fully installed, or from £800 DIY; you may need tools, expertise and extra bits to install a panel yourself. For most houses a panel of around 3 square meters should suffice.
The panels almost always feed into a hot water tank and tend to need a traditional boiler/water-tank/header-tank arrangement. There are some that can work with combi boilers and mains water pressure, but they are not the norm and many combi boilers can’t hack it anyway. Most of the systems use a single hot water tank, but others need two. The single hot water tanks have the coil containing the solar antifreeze at the bottom of the tank, so it acts as the main heat source for heating the water. There is then a second coil in the centre of the tank to take the heat from the traditional boiler (or other heating system, such as biomass), which ensures the water always reaches an adequate temperature no matter what the weather (usually 55o to 65o). This means that your existing hot water tank will have to be replaced.
Installers come in all shapes and sizes, with many resembling double-glazing sales companies, but the decent ones should be able to advise on whether your home is suitable for a panel and what the best options are for your situation. The bad ones probably will too, but may not be quite as truthful. I have had a look around and the companies below caught my eye - if you don't want to take my word for it, you can find a certified installer for your region on the BRE website Greenbook.
Navitron are my personal favourites, as they are down-to-earth and offer exceptional value. Their website has good information, but is a little techy. They only sell the products themselves, including complete DIY kits, but they can organise a local installer to put the systems in for you if you want. They also offer to help out on specific bits of the installation, so you can do the work you’re happy with and keep the cost down. Their evacuated tube solar panels for heating an average house cost only £400, which is excellent value, but they are not the prettiest things on earth. They also have solar powered pumps to power the system, which is easy to deal with and efficient.
Solar Twin have an unusual system that heats mains water directly in the solar panel rather than using antifreeze and a coil to exchange heat in the hot water tank. The hot water from the panel is fed into the top of the hot water tank rather than the bottom. They claim that this is very efficient, but I am not sure whether the efficiency of direct heating is outweighed by the efficiency with which antifreeze absorbs heat from the sunlight. They also provide a good DIY kit with just about everything need to fit the panel. The installation is very easy as there is no need to change the hot water tank and there is only a minor plumbing requirement; the main difficulty is fixing the panel to the roof. They also have solar powered pumps to power the system, which is easy to deal with and efficient.
Solar Utilities appear to provide a good system, with an excellent hot water tank that integrates well with mains pressure water feeds and which also powers underfloor central heating. They have a reasonable self-assessment form, but it does need to be returned to them by post/fax with a sketch or photo of the roof. I’m not sure how long it takes to get a reply.
Imagination Solar provides panels that work with combi boilers, although they still need to install a hot water tank. They have DIY packages or can install the system for you. They have a self-assessment Wizard which asks all the normal questions, but it does give an instant result with recommended solar panel, control unit and cylinder, plus costs.
Heating is not included in the Feed In Tariff system, so you will have to wait for the Renewable Heat Incentive to start before you can get any financil help.
Solar Photovoltaic
Photovoltaic systems (PV) use lots of small ‘cells’ to convert sunlight into electricity. Each cell contains layers of a semi-conducting material (usually silicon) which generate an electrical field when illuminated. This electrical field then causes a tiny electrical current, which is collected along with all the other tiny electrical currents from all the other cells to give enough power to run the house (hopefully). The harder the sun shines, the greater the flow of electricity. This is exactly the same thing as happens in a solar powered calculator, only on a grander scale: between 10m2 and 20m2 of solar panels will be needed to power a house.
There are three types of PV solar panels:
1. Thin film - these perform better in low light conditions, but need a large surface area to produce a sensible amount of electricity.
2. Crystalline cells – these are more efficient in intense light, require a smaller surface area and make up 85% of the market.
3. Dual – uses both crystalline and thin film elements to give a high performance panel in all light conditions.
PV panels have generally been fairly inefficient things, converting only 5% to 10% of the sunlight that strikes them into electricity. This is improving, with efficiencies of 20% now achievable. Sanyo and Kyocera seem to make panels that are about as efficient as they get.
PV panels come in all sorts of shapes and sizes, ranging from grey 'solar tiles' that can replace standard roof tiles, through standard panels to transparent cells that you can use on conservatories to provide shading as well as generating electricity. The panels can be fixed over the top of an existing roof or can be incorporated within the roof itself, as can the solar tiles. Using solar panels or tiles to form an integral part of the roof is slightly more expensive, but does give a good saving on the cost of standard materials that would have been used instead.
Solar panels are not light and the roof must be strong enough to take their weight, especially if the panel is placed on top of existing tiles.
PV panels are defined by the amount of energy they generate in full sunlight, known as kilowatt peak or kWp. Both main types of solar panel cost about the same relative to the amount of electricity they produce (as opposed to surface area), which for a standard household is likely to be between 1.5 and 3 KWp. The dual system panels will cost more.
The likely cost for installing a PV system is likely to be between £5,000 and £8,000 per KWp. The Feed In Tariff (FIT) for an average 3kW installation will give you about 36p/kWh generation. Assuming you generate only the 5,000 kWh that you as an average household use each year, and that you heat with natural gas or something similar, then you will save youself £400 in bills & get given £1,800 in FIT. This means you will net £2,200 for something that cost you £24,000 in the first place, giving you a return of about 9%.
This gives a payback of between 10 and 20 years, depending on whether you are paying interest on money borrowed or investing the FIT cash. The panels often last around 30 years or more and need little maintenance. Remember, however, that sunlight varies quite a lot across the kingdom: those bronzed beach bums near Land’s End will get a lot more sunlight than those hardy souls near John O’Groats. Consider your position carefully before opting for solar PV.
Some further disparity in prices is down to whether a PV system is connected to the electricity grid or not. If the system is connected, there is no need to buy any batteries to store spare electricity generated in times of high sunlight and low use. Any spare electricity can be sold back to the grid as it is generated, with any later shortfall met by buying in more as it’s needed. This saves the purchase and maintenance costs of the battery module, although fairly smart electricity meters will be needed to measure purchase/sale quantities, sort out billing etc.
The company that installs and/or connects your PV system to the grid should be able to help negotiate your electricity purchase and sale price. The grid company may try to buy cheap and sell expensive, but don’t have any of it: there are renewable obligations to be met and green electricity commands a higher price than the normal stuff, so demand price parity.
Scottish & Southern is now offering an excellent price for electricity exported to the grid from domestic or small scale commercial solar panels. In June 2009 they were apparently offering 28p per kWh (or possibly still 18p as in 2008 - we did ask them, but they weren't 100% sure), which is excellent but included the Renewable Obligation Certificate element of the energy production. This is actually good news, as they will go through the process of registering your production for you, which is tortuous for individuals and usually not done. This is likely to reduce the payback time for solar PV to something that is more sensible.
It is worth noting that The Energy Saving Trust Solar PV Certification Scheme closed down on the 31st March 2007. Certification for products and installers within the Low Carbon Buildings Programme is now provided through the Microgeneration Certification Scheme managed by BRE Certification.
Some providers of PV systems that I liked the look of are:
Solar Century is a down-to-earth company with no fuss or frills. They are squarely aimed at selling PV panels to commercial organisations and large projects, so for domestic customers all they ask you to do is fill in a form. An accredited installer will then get back to you, assess your house, specify the right kit and put it in for you. They will help with grants too.
The Energy Development Co-Operative Ltd is aimed mainly at commercial situations or remote applications where connecting to the national grid is not an option. However, it is a good site that has easily accessible price lists, good information on individual products and offers a full solar PV and wind turbine design service.
Sunpowered Energy Systems provide and install solar PV systems for domestic properties. The site is a bit clunky, but there is quite good information about the panels on offer, sans prices. You need to fill in their questionnaire on the ‘contact us’ page to get to the next stage (presumably an assessment of your house, but that’s not terribly clear). Not too 'salesy', which is nice.
Other Sites
PV certification scheme www.ukmicrogeneration.org
Search for certified microgeneration installers by region at greenbook.
Search for certified microgeneration products by type at greenbook.
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