Solar energy potential
About the half of the world energy consumption is dedicated to heating and cooling
As an example, the figure shows the final energy usage in the EU.
In a scenario with a large penetration of renewable in the energy mix, most of that thermal energy demand should be supplied by solar thermal collectors
Solar thermal collectors can transform solar radiation directly into usable heat at efficiencies as high as 70% (for normal incidence).
Through the absorption cycle it is also possible to transform heat into cooling. The higher is the temperature at which the heat is supplied, the higher is the cooling efficiency of the absorption machine!
T=80ºC => COP=70%
T=130ºC=> COP=130%
Flat Plate Collectors in the Market
Depending on the temperature level required, different collectors should be used.
For low temperature applications such as domestic hot water preparation flat plate collectors can be efficiently used.
Flat plate collectors are simple and robust. But they are not suited for higher temperature applications.
Nowadays flat plate collectors can produce heat at a competitive price in the range of 45 to 80 ºC.
For high potential uses a collector able to reach temperatures between 80 and 250ºC.
For solar cooling and freezing starts working at 80ºC but efficiency is doubled at 160ºC.
Industrial processes like laundries, Food and beverage industries, chemical plants etc. need to work in this range of temperatures.
Radiation Concentration
To reach temperatures above 100ºC with a good efficiency it is necessary to concentrate radiation either with a lens or with a mirror.
Most concentrating collectors available nowadays are designed for large scale electricity generation. These concentrating collectors offer more cost efficient alternative to Photo Voltaic cells for solar electricity production through the use of conventional steam turbines.
Large collectors for electricity production can reach temperatures up to 500ºC (and higher). But they are not suited for applications with “in situ” heat use such as solar cooling or industrial process heat. It is not possible to integrate them into hotel, residential or industrial buildings due to its size and geometry.
Some companies are developing new concentrating collectors with smaller sizes.All of them have moving reflectors that greatly hinder its integration in building roofs.