I am often asked whether a solar thermal system can be used for space heating as well as for hot water.

Technically, it can.  However in most cases it is neither cost effective nor energy efficient to do so.  The cost of upgrading the system to work with space heating as well as hot water can be expensive.

The first thing to point out is that during the winter, when space heating is required, solar energy is at its weakest.  Solar thermal systems that are designed to contribute to space heating are generally designed to contribute on the cross over days from winter to summer when we have clear but cold days. 

For solar thermal to be effective for space heating you need a much larger surface area of collector – approximately 0.5m² - 1m² of collector area per 10m² of floor area to be heated.  This large collector area means that a larger storage capacity is needed to allow the system to cope when the space heating is not being used during the summer months. 

This is one of the major stumbling blocks as most houses in the UK do not have enough space for the 1000ltr, or bigger, thermal store required.  It is important that the store is correctly sized so that it can manage the heat produced by the panels during the summer months ,when the heating is not required.  If it is not the solar panels will overheat and reduce the life of the system.

Using a solar thermal system to contribute to space heating in new builds is much more attractive.  The system can be integrated into the build at the design stage and if the building has a low level heating system, like underfloor heating, and good insulation levels solar can make a contribution of up to half of the space heating.

On the continent about a third of new solar thermal systems installed are designed to contribute towards space heating.  This is largely due to their forward thinking approach to designing houses and heating systems which, unfortunately, is not as prevalent here in the UK.

When SunGift Solar is looking at fitting solar thermal to assist with space heating on an existing building, we make it clear that the solar contribution will depend on the space available for solar collectors, space for storage and, of course, your budget. It is important to get the balance right.  
In the right situation, solar thermal can be an effective way of contributing to space heating.  If not, a combination of alternative renewable technologies can be used to create an energy efficient heating system.

About the author: Gabriel Wondrausch is founder and director of SunGift Solar, which installs solar thermal and other renewable energy systems in the South West of England.

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