We often think that modern societies were the first to use solar energy. Not true! Early cave dwellers preferred caves that had openings facing southeasterly that allowed the morning sun to warm them up without overheating in the warm months.  Native Americans in the Southwest oriented their pueblo dwellings.  So the low winter sun would keep the buildings by direct solar radiation, cliffs and overhangs blocked the sun during the summer months, helping to keep the dwellings cooler when the sun was high in the sky.

The ancient Greeks, with a climate that was sunny almost year-round, built their houses to take advantage of the sun’s rays during the moderately cool winters and to avoid the sun’s heat during the summer.  Modern excavations of many classic Greek cities show that individual homes were oriented towards the South and entire cities were planned to allow equal access to the winter sun.  It is interesting to note that by 500 B.C., when the Greeks had almost completely deforested their whole country and needed to find a reliable alternative fuel source, they chose solar energy.

The Roman Empire advanced solar technology by adapting home building design to different climates, using clear window coverings such as glass to enhance the effectiveness of solar heating, and expanding solar architecture to include greenhouses and huge public bath houses.  Solar architecture became so much a part of Roman life that sun-rights guarantees were eventually enacted into Roman law.  This society depleted its forest resource as well after the fall of the Roman Empire. For example, solar energy was used to heat roman baths, i.e. to increase the temperature in caldarium (room with hot water) without warming the frigidarium (room with cold water).

The use of glass to enhance solar gain in buildings was mostly forgotten over much of history.  Interest in passive solar architecture and greenhouses was rekindled during the Renaissance.  As technologies advanced glass manufacturing was revived, resulting in an increased use of glass windows.  This also made large greenhouses possible for agricultural purposes, as well as for recreation.

In the 1700s, a leading naturalist named Horace de Saussure began to experiment with solar hot boxes.  These precursors to today’s active solar collectors were no more than insulated boxes painted black on the inside and with one side covered with glass.  They were very similar to today’s solar cookers, and in fact, many early experimenters used their hot boxes to cook with.  In 1891, Clarence M. Kemp patented the world’s first commercial solar water heater, called “The Climax”.  It was a black painted water tank mounted in an insulated box with glass on one side, not unlike many contemporary solar water heaters. Many of the solar principles we use today were identified during those early experiments. It was a success, though it was able to prepare hot water only for evening baths, as most of accumulated heat was lost during the night, and in colder regions was exposed to freezing.

Solar water heating became popular in Florida and California during the 1920s. Due to an abundance of sunlight in Israel, solar water heaters were used by 20% of the population by 1967. Following the energy crisis in the 1970s, the Israeli Knesset passed a law requiring the installation of solar water heaters in all new homes (except high towers with insufficient roof area). As a result, Israel is now the world leader in the use of solar energy per capita (3% of the primary national energy consumption).

During this time, there was a renewed interest in solar heating in North America. Technical innovation had improved the performance, life expectancy, and ease of use of these systems. Installation of solar hot water heating is the norm in countries with an abundance of solar radiation, like Israel, Cyprus and Greece, as well as in Australia and Japan.

Solar hot water systems have gained popularity in China, where basic models start at around 1,500 yuan (Eu 150), about 80% cheaper than in Western countries. Over 30 million households in China now enjoy solar hot water.

In 2005, Spain became the first country in the world to pass legislation requiring the installation of photovoltaic electricity in new buildings, and the second (after Israel) to require the installation of solar hot water systems.

In fact, nearly all the energy we use is actually solar energy.  Solar energy stored in plants millions of years ago has slowly been converted to such fossil fuels as coal, petroleum, and natural gas. Hydroelectric power plants harness the energy of moving water–and there would be no moving water without the sun.  The sun’s heat evaporates moisture, so that it falls back to earth as rain and other forms of precipitation.  The sun also powers the air currents that cause the wind to blow. Only nuclear energy has nothing to do with our closest star.