role in reducing solar radiation may increase applications. Researchers who support passive mirror cooling applications on a mass scale, such as Ye Tao of MEER, argue that carbon dioxide removal alone will not work fast enough to prevent global temperature increases from surpassing life-threatening levels. Space-based applications Solar thermal applications The intensity of solar thermal energy from solar radiation at the surface of the earth is about , of area normal to the direction of the sun, under clear-sky conditions. When solar energy is unconcentrated, the maximum collector temperature is about . This is useful for space heating and heating water. For higher temperature applications, such as cooking, or supplying a heat engine or turbine-electrical generator, this energy must be concentrated. Terrestrial applications Solar thermal systems have been constructed to produce concentrated solar power (CSP), for generating electricity. The large Sandia Lab solar power tower uses a Stirling engine heated by a solar mirror concentrator. Another configuration is the trough system. Space power application "Solar dynamic" energy systems have been proposed for various spacecraft applications, including solar power satellites, where a reflector focuses sunlight on to a heat engine such as the Brayton cycle type. Photovoltaic augmentation Photovoltaic cells (PV) which can convert solar radiation directly into electricity are quite expensive per unit area. Some types of PV cell, e.g. gallium arsenide, if cooled, are capable of converting efficiently up to 1,000 times as much radiation as is normally provided by simple exposure to direct sunlight. In tests done by Sewang Yoon and Vahan Garboushian, for Amonix Corp. silicon solar cell conversion efficiency is shown to increase at higher levels of concentration, proportional to the logarithm of the concentration, provided external cooling is available to the photocells. Similarly, higher efficiency multijunction cells also improve in performance with high concentration. Terrestrial application To date no large scale testing has been performed on this concept. Presumably this is because the increased cost of the reflectors and cooling generally is not economically justified. Solar power satellite application Theoretically, for space-based solar power satellite designs, solar mirrors could reduce PV cell costs and launch costs since they are expected to be both lighter and cheaper than equivalent large areas of PV cells. Several options were studied by Boeing corporation. In their Fig. 4. captioned "Architecture 4. GEO Harris Wheel", the authors describe a system of solar mirrors used to augment the power of some