Solar panels are becoming increasingly common in domestic properties. Is it really possible to heat and light your house from the power of the sun alone?
There are a variety of methods of collecting the sun’s heat. At its simplest, passive solar collects heat through your windows, walls and floors. At the other end of the scale you can use either solar photovoltaic (PV) panels to convert daylight into electricity or solar thermal panels to heat water.
Panels are at their most effective when they face true south (in the northern hemisphere). An angle of 30 – 40 degrees is optimum (which is why roofs are ideal), and of course, the bigger the area the better – 7m2 is the recommended minimum. You might live in a sunny climate, but consider things that could block sunlight and hamper their efficiency, like a lot of cloud cover, overhanging trees or chimneys.
Solar PV panels are made from a semi-conducting material like silicon. When sunlight hits it, the silicon generates an electric current. The sun doesn’t need to be hot to generate electricity, just bright, so electricity can be generated even in winter, as long as there is sunshine. The electricity passes through an inverter, which turns the current into AC, which is the type of current used in domestic electrical appliances.
So that’s your electricity sorted; what about hot water? This is where you do need heat from the sun. Solar collectors contain a fluid similar to antifreeze (called a transfer fluid). This is first heated by the sun. A heat sensor then switches on a pump when the fluid in the collector is hotter than the water in the home’s hot water cylinder. The fluid is pumped around your hot water cylinder and the heat in the transfer fluid is transferred to the water in the cylinder.
Estimates for cost and CO2 savings of course depend on the size of your system, how much sunlight or heat your collectors receive, and how much electricity you use. However, it’s estimated that a solar hot water system can save around half a tonne of CO2 emissions per year[1].
But solar does have its drawbacks. The cost of installing a system is high, requiring scaffolding, possible strengthening of your roof, and some wiring and plumbing work. A domestic PV or thermal system will take around one to two days to install. Both systems will only work on a south facing (or as near as possible to south facing) roof, and any obstructions like trees or clouds will severely affect performance. On the plus side, sunlight is free, and neither system pumps carbon dioxide or other harmful gases into the atmosphere. Your electricity bills and water heating costs will fall, but remember to factor the cost of installing the system in your calculations.