Getting into hot water with the SUN

Energy from the sun can be used in buildings by various methods writes Chris Laughton of The Very Efficient Heating Company. These include generating electricity using photovoltaic modules through to simply heating alls behind glass, as in a greenhouse. However Penny Pincher solar water heating, using roof mounted collectors, is established as the most reliable and accessible way to actively use this free energy supply in our homes.

Contrary to popular belief, the UK has a plentiful supply of solar energy amounting to over 1000 kWh per square metre, although often this is diffused through clouds which does not feel as hot as direct sunshine. By collecting both direct and diffused sunshine it is possible to heat over half the annual hot water demand of a normal domestic house, most of this occurring in the summer. In its simplest form it is possible to enjoy a solar heated shower by hanging a black plastic bag outside for a few hours to collect the sunshine. However to reap the full benefits it is necessary to integrate solar heating with a conventional boiler.

During sunny summer days it is possible to switch off the conventional boiler and rely on solar heating alone, whereas during the rest of the year the conventional boiler tops up any shortfall. Although possible to use solar energy for space heating of rooms i.e. central heating, this can only be done with difficulty and requires special low temperature heat emitters such as under-floor tubing set in insulated concrete.

For a competent, skilful person it is possible to DIY a solar heating system, however specialist professional installers are worth considering especially if the solar collectors are to be mounted on a roof. At the very least, it is worth finding a supplier of parts who will encourage and support your DIY project perhaps designing the plumbing and electrical layout for you. There are books to assist you as well.

Typically solar water heating is principally comprised of collectors, usually mounted on the roof, facing as near south as permits and (fortuitously!) at the same angle as a typical pitched roof. These collectors can take various forms, the most advanced, efficient and expensive being the evacuated glass tube heat-pipe type which are grouped, 20 to 30, into manifolds, looking very like roof windows from a distance. The tubes are highly insulated, due to a vacuum inside the glass, and use alcohol as a transfer fluid instead of water hence they are quick to respond to changing weather and are automatically temperature regulated.

Commercially manufactured flat plate types consist of specially coated black metal surfaces, boxed behind glass or plastic, in which water flows in pipes soldered onto the plates. Despite their lower performance, the payback is often as good as the advanced type due to reduced material costs. These can be assembled from reclaimed materials however the resulting low performance and longevity makes this a questionable exercise for the extra work involved especially considering the harsh environment they receive on a normal roof.

The solar hot water from all these collectors is normally pumped down to a well insulated copper storage cylinder, controlled by an electronic temperature sensing switch to avoid unnecessary pumping, where the heat is indirectly exchanged to the domestic hot-water via a coil allowing use of special anti-freeze in the collector.

There are a number of options for the exact plumbing arrangements depending on budget, space and appearance perhaps most important being the ability of the existing boiler to accurately respond to preheated water. The opportunity to update existing heating controls should never be missed along with increasing pipe insulation.

A solar water heating system could pay for itself after eight years, for a DIY installation, although this would depend heavily on the hot water usage and upon the fuel which is being displaced by the sun. Fifteen years is more likely for a professional installation supplying water for two or three people. Many people use solar heating as their contribution to reducing pollution, as well as it being a fascinating subject which ultimately can pay for itself many times over.

Further information and advice is available from of the The Very Efficient Heating Company.

Introduction | Getting into Hot Water with the Sun | Optimizing Solar Water Systems |