Active solar energy is where solar technologies are used to take solar energy and convert it into a usable form of energy such as heat, stored heat, air movement for ventilation purposes or usable light. Active solar energy is normally achieved through the use of mechanical or electrical equipment, such as fans or pumps, in order to significantly increase the usable heat within a system. Any solar energy system that collects and uses solar energy without using external energy is considered to be a passive solar energy system.
A great deal of active solar energy technology is based around heat collectors in which the usual storage method is using water and which is then transported around the system using low voltage electrical pumps (often aided by gravity) to a central storage tanks which then supplies the hot water or is circulated around in order to fill radiators and heat space. In the United Kingdom this is not sufficient for all of the energy needs but it will supply quite a significant percentage of the total energy needed and can be incorporated into a system that utilises multiple sources. It is also a good add on to improve the energy efficiency of existing buildings.
In addition to electrical pumps, these solar water systems can use fans to circulate the water (as well as an anti-freeze liquid) and / or air through the solar collectors and this is what gives them the classification of active technologies. The collectors that are used will normally be flat-plate collectors or non-concentrating, or other types of concentrating designs. On the whole solar-thermal collectors use fixed mounting, but they will record better performances if they are able to track the sun as it passes across the sky. These solar trackers that are used for day-lighting or to correctly orient photovoltaic arrays, are capable of being driven by both active and passive solar technology.
The advantage of active solar thermal systems using small fans or pumps over passive systems is that they are able to have much increased solar savings fractions than passive solar energy technology, thanks to their significantly improved heat transport and heat transfer. The most common solar technologies to actively utilize solar energy are made up of solar photovoltaics or solar pv cells. These are often paid for with the help of feed in tariffs which are proving to be a popular way to encourage the spread of solar energy.