Main article: Solar Especially popular are compact home computers, typically composed of a tank of 150 liters and a collector of about 2 square meters. These kits, available in both open and closed circuit can deliver 90 of annual hot water needs for a family of 4 persons, depending on the radiation and use. These systems prevent emission of 4.5 tons of harmful gases into the atmosphere. The approximate time of return energy (time required to save the energy used to manufacture the device) is one year and a half. The life of some equipment may exceed 25 years with minimal maintenance, depending on factors such as water quality.It is normal to find facilities in which the accumulator contains a backup electric resistance, which acts in case the system is not capable of use temperature (usually 40 C), in Spain this option has been prohibited after the approval of the CTE (or technical Building Code) and the heat resistance may, if the panel is colder than the integrated accumulator, heat the panel and lose heat, and therefore energy through it. In some countries are marketed equipment using gas as a support. The construction characteristics of the collectors respond to the minimization of energy losses upon heating the fluid that passes through the tubes, so they are driving isolates (empty or otherwise) and low temperature reradiation.Besides their use as hot water, heating and cooling (via absorption chiller), the use of solar thermal (generally cheap materials such as polypropylene) has proliferated to the heating of outdoor residential pools in countries where legislation prevents energy use for other purpose.