Solar Energy Utilisation
The relevant properties of, as well as subsequent factors influencing, the net solar irradiance incident at the Earth's surface are examined. The methods currently employed (and those under near term development) able to convert solar energy into other usable energy forms, such as thermal, electrical and chemical energy, are surveyed. The efficiencies and likely cost structures of these conversion processes are compared. The direct conversion of solar energy to heat is identified to be the most efficient process (>70%) and employs well-established technologies which are generally cost competitive with other heat sources when sited in favourable locations (at latitudes below 45°). Additionally, the solar powered generation of electricity is shown to be of comparable cost and overall efficiency (∼20–30% of incident flux on the area utilised), whether based on the latest implementations of ‘conventional’ silicon Generation I photovoltaic technologies or high temperature concentrating solar heat capture systems when coupled to thermal engines driving electric generators. Exotic, but more efficient (>30%), non silicon multi-junction (Generation II) photovoltaic technologies are further from practical application and are not cost effective unless combined with solar concentration systems. Generation III (for example organic photovoltaic) technologies hold promise for low cost/unit area but are currently less efficient (<5%) than semi-conductor photovoltaics. Bio-solar approaches, employing natural photosynthetic organisms, allowing the conversion of solar energy to fuels, particularly hydrogen, have the lowest overall efficiencies of those technologies examined (∼1–2% maximum). The use of biomimetic catalysts to enhance hydrogen production using solar generated electricity is considered.