Radiant heat is a type of hydronic (hot water) heat that circulates warm water through particular piping installed in or base floors, in walls, or in the ceiling. Warm floors mean warm feet. Radiant heat warms you, not the air, reducing the dry sensation caused by forced air systems.
Tides are driven by gravitational energy and plate tectonics by the heat generated by the radioactive decay of elements in the Earth’s mantle, but the energy driving the atmosphere, oceans, and living organisms is supplied by the Sun. To a limited extent this energy can also be harnessed directly to perform useful work for humans. Solar heat can be used directly to warm buildings and water, desalinate water, and cook food. Sunlight can be converted into electricity. Electrical power can also be generated from wind and sea waves and, because the atmospheric circulation responsible for wind and wind-driven waves is driven by solar heat, these are also forms of solar energy.
The outer layer of the Sun, which is what we see and the region from which the Sun radiates, is at a temperature of about 6000 K and it radiates energy at 73.5×106 W from every square meter of its visible surface (the photosphere; being entirely gaseous, the Sun has no solid surface). The figure can be calculated because the Sun behaves as a ‘black body’. This is a body that absorbs all the energy falling on it and radiates energy at the maximum rate possible; the rate is calculated by using Stefan’s law and is proportional to the absolute temperature raised to the fourth power.
The Sun radiates in all directions and the Earth, being a very small target at a distance of 150 million km, intercepts 0.0005 per cent of the total. At the top of the Earth’s atmosphere this amounts to about 1360 W m−2, a value known as the ‘solar constant’......
