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Electricity or heat? It is noteworthy that energy from solar electricity (PV’s), which is otherwise not covered here, costs, per unit, about 3-5 times more than solar hot water. However, the maintenance of PV’s costs less than the maintenance which is required for antifreeze based solar water heating systems.

Since over 70% of energy in the home is used in the form of heat, rather than electricity, it makes sense, from the engineering perspective, to collect energy in the same form in which it will be used and not in some other form. This is one of several reasons why solar water heating tends to be considerably more cost effective than solar electricity.

Some people also look at value for money from a carbon saving perspective, rather than just a money saving viewpoint. This brings in the interesting but very detailed subject of “environmental valuation” with respect to energy, a subject which is not covered here. The EU’s Externe Project is an interesting introduction. The common (financial) denominator for many solar customers starts with the initial cost of their solar heating installation, minus any grant. It is worth noting here, that zero carbon solar is likely to cost slightly more to buy, since zero carbon solar includes its own miniature solar electric power station, rather than just a length of cable. Additional costs over 20 years or so, of maintenance and electricity (if any), to run the system also need to be estimated.

On the plus side, annual savings come from fossil fuel saved, plus the fact that boilers last longer and may need less maintenance because less fuel will be put through them when solar is used to displace fuel. Where water softeners are fitted, they have running costs which may be offset by increased efficiency in hot water cylinders and savings on cleaning materials such as detergents, scourers and soap. Capital cost or whole life costing? So rather than looking only at initial capital costs, the above “whole of life” approach towards solar, examines total capital cost, less running costs, maintenance costs plus fuel and other savings. In general, this big picture approach can favour zero carbon solar and solar which requires low maintenance over older technologies.