Guide To Passive Solar Power

Mankind has always understood the power of the Sun, probably after getting sunburned once too often. To this extent, it has been put to work in many of the earliest civilizations through to modern times. In most of these cases, it could be said that the Sun's power has been used passively until around the 1950's when photovoltaic cells were first developed. This article is a short guide to passive solar power and some of it's uses.

So, the basic principle behind utilizing passive solar power is to collect the Sun's thermal energy and then transfer the heat generated to other uses.

As mankind has become more adept at using passive solar power, various innovations have occurred. The innovations have mainly dealt with making the solar collector more efficient at collecting and holding heat energy. Or, at understanding were is the best place to locate the collector to maximize contact with the Sun's energy. This has involved understanding how solar heat energy is transmitted and absorbed by materials and what materials are best for this purpose.

Thermal Energy is transmitted by three methods : conduction, convection and radiation.

Conduction deals with how heat moves within a material or how it is passed from one molecule to another. Heat will travel from the warmer part of the material to the cooler part. Conduction generally applied to solid structures like metal and wood.

Convection deals with how heat moves through liquid and gases. This includes air or the atmosphere. The idea of hot air rises illustrates this point. Hot air is lighter than colder air and will move above the colder air. In this way heat moves from one point to the other. The same idea is applied to heating water. The hot water will rise and the colder water will sink.

Radiation deals with how heat is transferred through air or the atmosphere. Warmer objects radiate more heat than colder ones. Heat is transmitted by electromagnetic radiation from the hotter to colder object. This is the basis behind how the Sun's heat reaches the Earth. In terms of passive solar power, the more an object heat via radiation an object can absorb the better. In this respect, objects that are painted a matt black color absorb more radiation than one that may be painted glossy white in color.

By understanding the three methods by which heat energy moves through different materials, passive solar power collectors can be made more efficient. So a solar water collector would typically be made of metal because metal is a good conductor of thermal energy. It may be painted black to absorb more heat energy transmitted through the air from the Sun. Water passed through the collector would heat up. By convection the heated water would rise allowing water to circulate through the collector until all the water was of at the same temperature.

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