Solar Thermal Systems throughout History

You are here

You may be surprised to learn that humans have used solar thermal systems in one form or another not just for decades, but for thousands of years. They may not have installed complicated electrical control systems, clever pumps and man-made materials for improved efficiency but they certainly knew a great deal about harnessing the sun's energy and using it to provide hot water. As far back as early cave dwellers, there are signs that humans understood the most basic form of the sun's power. Tribes and social groups preferred to live in caves that faced southeast, where the rising sun would warm them without getting too hot in summer. This trend is also visible in the south-western regions of the US, where Native Americans built pueblo dwellings so they'd capture the low sun's warmth in winter but overhanging rocks and cliffs would block the higher summer sun's pounding heat.

Moving forward a little from cave dwellers, the Greek and Roman Empires both used solar thermal systems extensively. This is probably in part because they both completely deforested their countries and needed to find an alternative power source! Excavations show that Greek houses were built to capture the sun's energy efficiently, even to the point where entire cities were carefully planned to ensure that everyone got an equal amount of warmth. The Romans took things further than the Greeks: they built many different styles of house (which is normal, given the huge variety of climates over which their empire extended) and used advanced techniques to capture the sun's power more efficiently. They used glass in their windows to enhance the sun's warmth and extended their architectural efforts to much larger buildings such as greenhouses and bath houses. They reached such a relatively advanced technological level that Roman laws included "sun rights".

Unfortunately, most of this learning was lost – as was a lot of other technology - with the fall of the Roman Empire. Most of the world lived without any effective solar power until glassmaking was revived in the Renaissance period from the 14th to the 17th Centuries. With the return of glass windows, a naturalist called Horace de Saussure began experimenting with "hot boxes" in the 1700s. He painted simple boxes black and used glass to cover one side, discovering many principles that are used in today's technology and birthing the solar cooker. Unfortunately, his efforts didn't lead to many advancements and it wasn't until almost two hundred years later that solar power made its comeback.

By the end of the 1800s, the world had changed a great deal. Direct water supply to individual homes was becoming more common and, just like today, home owners wanted to heat the cold supply. Most heaters ran on fossil fuels - coal or wood – but in 1891 a man named Clarence Kemp patented the world's first commercial solar thermal heater. He called it the "Climax" and it was much like de Saussure's hot boxes: a black box with glass on one side. The main difference was that the Climax came in an insulated