First read our introduction to solar hot water. Maybe talk to other system owners, read books, attend courses, ask questions – get as much basic information as you can. Make sure your home is well-insulated, in good repair and dry before thinking about renewable energy systems. We would recommend these measures first anyway, even though for solar hot water, it doesn’t really matter if your home isn’t insulated at all, because the hot water tank itself will be insulated. However, there will be more environmental (and comfort, and cost) benefits from sorting out these things first.
A solar hot water system is for delivering hot water. It can be used for supporting space heating, but those types of systems are significantly more expensive and make specific requirements of your house – for example, it needs to be super-insulated and you need more panels. Ideally, for space heating support, the angle of your roof will be between 55-70°. Most roofs are 30-45°, which is ideal for solar hot water.
Does it suit your lifestyle?
How do you use hot water? Some people don’t use very much hot water at all – maybe just for a shower once a day. Also, do you have a hot water tank/cylinder? If you do, then you’re heating water and storing it for use later. Solar hot water is very compatible with this kind of system. If, on the other hand, you’re heating water as you require it (on-demand), via an electric shower or a combi boiler (instant hot water), then there’s no hot water storage. It’s very difficult to fit solar thermal to this type of system. The key (and this is the difference between solar thermal and solar pv) is that solar hot water systems generate energy that can’t be exported (to the national grid, for example). It has to be used on-site.
This is why it matters a lot how you use hot water, and how much you use. If you use a reasonable amount of hot water, regularly, and you have storage, it really makes sense. This also applies if you’re thinking of moving from instant hot water to a stored hot water system. It is possible to use solar with a combi boiler, but it’s more expensive and often doesn’t deliver the best results.
Does it suit your building?
So, if solar hot water suits your lifestyle, does it suit your building? More than three quarters of buildings in the UK are suitable. Here’s what to look out for.
Do you have a roof or other location for panels that is facing in the right direction? South is best; south-east to south-west is still good; and even east-west is possible, but with some performance reduction.
The best angle for solar hot water panels in the UK is 30-40° if your roof faces any direction from south-east to south-west, and a slightly smaller angle if east or west. Check how much your roof is shaded. If you live in the middle of the woods, it’s quite unlikely that the panels will have a clear enough view of sky for them to perform well. The same is true if you are next to tall buildings, in a valley or next to mountains – or if you have a large chimney or dormer next to where you intend to install panels. The biggest energy contribution in a day is going to be between 10am-2pm, so that’s the time you really don’t want your panels shaded; but the longer the time period without shade, the more energy you’ll get.
NB: you want to avoid bird droppings from overhanging TV aerials, as this is another type of shading.
Work out why you want it
Are you thinking about solar hot water purely from the money-saving angle? Yes, you can save money, but it depends on how much hot water you use, how much you pay for your system and what fuel you’re displacing. Oil is more expensive than gas, so if you have an oil boiler, you’ll save more. See the costs, savings and incentives section below for more information.
Alternatively, you may be interested in solar hot water (and other renewables) for environmental reasons, because you want to be more self-sufficient or for energy security – to protect yourself from energy shortages and/or to reduce the percentage of energy you have to purchase from corporations. Solar hot water will be beneficial in all these cases.
Solar thermal can be a good first experiment with renewables. Some people use it to ‘dip their toe into the (hot?) water’. The thing that makes solar thermal easier, and different from other renewable heat technologies is that others aim to replace your boiler completely, whereas solar thermal aims to supplement it. You don’t have to get rid of what you’re comfortable with and you still have it as a back-up.
