Solar Thermal Energy

What is it?

Solar thermal energy is a general term for utilizing solar energy to produce heat. It includes many technical applications from swimming pool heating to large scale solar thermal electricity generation.

This information page is mostly about solar thermal technologies applicable for domestic use such as domestic hot water and space heating systems.

How can I benefit from
solar thermal energy?

By a smart solar thermal installation you can cut a significant part of your heating and hot water expenses. Depending on the size of the system, your house's thermal properties, location and the weather conditions in your area you can save from 10% up to 70% annually, or even more!

Utilizing solar thermal energy is one of the most significant individual contributions one can make to lower the stress we humans cause on our own environment. By favoring renewable energy technologies you will set an example to everyone around you.

How does it work?

All solar thermal applications require solar thermal collectors for collecting the radiant energy of the sun and to convert it into useful heat. Today there are several different collector technologies of which the flat-plate collector is the most commonly used for domestic solar heating systems. Evacuated-tube collectors have also gained publicity in recent years and have established their position as a plausible option for domestic solar heating systems. Mutual to both of these technologies is that they consist of an absorber surface and a piping through which the working fluid (air, water or water and anti-freeze mixture) flows. The energy absorbed by the absorber surface is transferred to the collector's working fluid which is then stored or used depending on the system.


The performance of a solar thermal collector is dependent on its optical efficiency and on the heat losses that occur in the collector. The optical efficiency is a product of the transmittance of the collector cover glass (if any) and the absorptance of the absorber surface. It indicates the fraction of the incoming radiant energy the collector is able to capture. The amount of heat losses occurring in the collector are dependent on the collector's insulating properties which can be expressed in terms of two factors: the collector losses when the temperature of the working fluid is equal to the temperature of the surroundings and the temperature dependency of the collector's heat losses. These are called loss coefficients a1 and a2. The higher the value of a2, the greater the influence of ambient temperature is on the collector. The properties of a collector can be found from a datasheet provided by the manufacturer.


In addition to solar thermal collectors a solar thermal domestic hot water and/or space heating system requires also the necessary plumbing, a storage tank for hot water, heat exchangers and pumps (unless the system is desigend to operate passively, in which case there are no pumps or other electrical components). Alternatively a system that utilizes air as the working fluid requires a thermal storage such as an under-floor pebble bed. This is why introducing a solar thermal system to your house requires professional design and installation services. However by running simulations in Solar Arena you can easily get a realistic idea of how a solar thermal system could perform installed into your house!


Like with all electrical applications introducing a PV-system to your house requires professional installation services. You may also want to consult professionals about optimizing the system to your needs, but you can also easily get a realistic idea of the potential to produce solar energy at your location by running simulations in Solar Arena!

Global effects

Buildings use about 40% of the annual energy produced globally, causing a significant fraction of the world’s greenhouse gas emissions. Along with energy efficient building, favoring renewable technologies such as solar thermal energy is a way to preserve the earth. The technology to integrate solar thermal energy to domestic heating systems has been commercially available for over 30 years. The required individual effort, energy legislation and above all general unawareness have limited the growth thus far. At the moment solar thermal heating's contribution to meet the global energy demand with renewable energies is second to wind power. Our goal is to bring the products, services and up-to-date knowledge about solar energy to everyone in a clear and simple way and to boost the solar markets to a new era.