Thermal solar panels generate hot water, not for your central heating, but for use in your taps or your shower. Thermal systems are cheapest to install on properties without combi-boilers because then you will probably already have a storage tank in place to store the hot water they generate. If you install them on your house or business, then you will be eligible for the Renewable Heat Incentive.
This sort of system was developed in the 1950s. A dark flat plate lies in the solar module, which absorbs the solar energy. A transparent cover allows solar energy to pass through, but reduces heat losses. A heat-transport fluid (water), removes heat from the absorber (it is hard to heat up something that is already hot!), and at the back of the panel there is a heat insulating backing, to ensure that as much heat as possible is taken away by the heat-transport fluid.
These consist of a row of glass tubes, each containing a vacuum. Heat cannot escape a vacuum, hence why it's there! In the centre of each tube, a heat pipe is in place, to transfer away all the heat to a heat-transferring liquid. These are much more commonly seem, since they are much more efficient than flat plate collectors, and they work particularly well in colder climates.