Solar thermal panels use sunshine to heat the water in your hot water tank. It is a simple idea and cost effective. A grant of up to £400 is available.
Photovoltaic Panels (PV) do not depend on sunny weather. They generate electricity from sunlight whatever the weather. You can use the electricity immediately in your home eg for providing hot water or heating. Alternatively you can export it to the grid (at about 18p a unit) and set the money against the cost of the electricity supplied to you through the grid system. PV panels are expensive but the price is coming down all the time and grants of up to £2,500 are available. It may be many years before the savings in electricity cover the cost of the investment but it should increase the value of your home.
http://www.lowcarbonbuildings.org.uk/home/
One reason solar panels are expensive to install is that you need scaffolding which will be about 25% of the total cost. If you need other work on your roof, or your windows need re-painting or chimneys re-pointing, you will already be paying for scaffolding, so it would be cheaper to install solar panels at the same time.
By 2050, to meet the Government target of a 60-80% cut in carbon dioxide emissions most homes will have to use one or more technologies such as solar thermal or PV panels.
How can we do that cost-effectively? One way is to have groups of householders sign up so a batch of installations can be done at the same time. That way we get the benefits of bulk-buying.