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The Solar Combi System / Thermal Store Tank

The Solar Combi System / Thermal Store Tank

This type of solar thermal is becoming fairly common in the uk and we at Gondawana Green Heat have been designing / fitting this solar system layout since day one.  The main adaptation from option 1 is that the cylinder / tank is a used to heat dhw and space heating, meaning solar is also heating your radiators/ underfloor heating as well as your dhw.  The tanks are generally larger and have many adaptations to include different heat sources eg oil, gas, biomass.  These tanks are generally made to order, however we do a range of off the shelf options imported from Germany.  Small solar combi systems can range from  180 liters to 500 litres and can be vented or sealed systems or a combination of the 2 when needed.  For small  tanks / thermal stores which are not available off the shelf we use MacDonald engineering in fife, who make vented and sealed thermal stores for the uk market.

Solar combi systems can also be taken to the next stage, where large quantities of hot water are stored for when you need it.  This is called seasonal solar hot water storage systems, they do as the name suggests store large volumes of  hot water  in a large tank .  In northern Europe we typically need heating during the winter, however the sun generally shines in the summer that’s where this solar concept comes in to play, you heat the tank during the summer and use the solar energy trapped in the tank during the winter, as you can imagine you need a much larger tank to store enough energy to heat your home through the winter.  These tanks generally come with a set of ports / trappings to incorporate other heat sources gas / oil / biomass / heat pump etc.

However it is possible to heat a property from solar completely using these tanks, to do this there are many factors affecting the suitability of such a project.

To view Macdonald engineering brochure pls click the link



  • Do you have a large enough area for a large scale solar thermal aray ? eg 20 sqm +.
  • What is the heat loading of the building ? the smaller the better eg passivhaus  / low energy / 1-2 kw per 100sqm.
  • Can you fit a seasonal storage tank into the property.

If you can answer is yes to all the above then your property could be  heated solely by solar/ the sun.  This type of property is called a Sonnenhaus and is becoming increasing popular in Germany and Switzerland.  For those of us who cant reduce the heating load down to Pasivhaus  or Sonnenhaus standards then a large seasonal storage  tank is still a very viable option, allowing you to run prominently from solar while having the back up of a conventional heat source like gas / oil /biomass or our favorite a wood burning boiler stove.  These tanks can be made from 700 litres to 200 000 for very large property’s and are not necessarily to heat a single home, they can be used in flats and district heating system.



Swiss Solartank