1.1. Definitions

Eurostat and IEA see solar thermal heat as renewable energy. Their definition of renewable energy is: “Renewable energy is energy that is derived from natural processes that are replenished constantly.” There are various forms of renewable energy, deriving directly or indirectly from the sun, or from heat generated deep within the earth. They include energy generated from solar, wind, biomass, geothermal, ambient heat, hydropower and ocean resources, solid biomass, biogas and liquid biofuels. Waste is a fuel consisting of many materials coming from combustible industrial, institutional, hospital and household wastes such as rubber, plastics, waste fossil oils and other similar commodities. It is either solid or liquid in form, renewable or non-renewable, biodegradable or non-biodegradable. Waste is in general partly renewable and partly non­renewable.

Heat is in general the result of a conversion of an energy source into heat. If the source is renewable, the heat output is renewable heat. This is shown in the figure [6,7]

Useful renewable heat output

Electricity or other energy carrier

Renewable heat can be defined on the input site or on the output site. The input definition is in line with the Eurostat energy balances. The output will be called “Useful heat output”. Eurostat counts all renewable on the input site. Solar thermal heat is according to the input method from Eurostat:

“The Solar thermal production is the heat available to the heat transfer medium minus the optical and collector heat losses”. In general solar thermal experts give figures on the output of the solar thermal systems or energy saved by the solar thermal systems. Some countries use nationally the substitution method (specifically the Netherlands, Germany and France). This method calculates the fossil energy that is saved by the use of a renewable source. The Therra proposal for a

calculation method does not include the use of such a substitution method since this method would be too complicated for energy statistics on a European scale.