By Editor • 1 year ago

You know how things get heated by sunlight even in temperate climates.

If not, just go outside and search for a boulder or stone and touch. You would feel how hot it is.

You would be thinking… How on the Earth that distant star heats the things on the Earth whilst it is far away from us.

Yes, it is really an amazing topic to think of.

As we know it, water in oceans, rivers, lakes, etc. heats up and injects a vast amount of water vapor into the atmosphere at every point in time.

So… Why do we still use electricity for water heating while the Sun is capable of heating anything exposed to its power?


Let’s discuss.

We have already discussed the amount of solar power hitting the Earth’s surface. It is nearly 1000 W/m2. Any object absorbs energy from sunlight and gets heated upon exposure to sunlight.

The idea of solar thermal energy technology is neither abstruse nor new. As we discussed in the previous article, even ancient people utilized solar energy to dehydrate some foodstuffs. Anyway, the first successful solar energy device was developed in 1767 by a Swiss inventor Horace de Saussure who is credited with developing the world’s first solar collector to harness energy from sunlight [1]. It could be used for cooking or to heat water. It took more than a century to develop a vendible solar water heating system. Thereby Clarence M. Kemp patented the world’s first commercial water heater in 1891 [2]. Since then solar thermal energy has been used in various applications (water pumping, domestic water heating, swimming pool heating, etc.).

In the beginning, the solar thermal technology could not enter the market as nearby environment provided natural energy sources and sufficient amount of energy for cooking and heating. The rapid increase in global population and urbanization, however, led to shrink the potential and availability of natural energy sources hence limiting access to them. Then people started thinking of the abandoned solar water heating technology. Commercial solar water heaters were then available on the market even in European countries where average solar flux is far lower than Asian and African countries. Its popularity had been gradually growing and the demand then noticeably increased after 1960.

Israel was a trailblazer in manufacturing and installing solar hot water systems and had widely been using solar water heating systems even in the 1960s. Then the global oil crisis occurred in 1973 surprisingly, triggered a sharp increase in the number of solar hot water systems being installed. Currently, rooftop solar hot water systems provide hot water to over 50 million houses in the world [3], saving an overwhelming amount of electricity and fossil fuels thereby cutting tonnes of greenhouse emissions and alleviating the anthropogenic climate change.


Solar hot water systems are being used in all the continents except Antarctica. China, USA, Spain, Australia, Italy, Greece, and Israel enjoy the highest per capita solar energy utilization for water heating. Several solar hot water technologies have been developed and are being used. Their manufacturing cost, energy harvesting efficiency, and technical features vary with the technology. We can decide which technology fits us depending on our purchasing power, location, climate pattern and average weather conditions

In next article, let us discuss different configurations/ technologies used in solar water heating systems and the advantages of using solar hot water systems as well.

[1] Katsioloudis, P. J., Bondi, S., and Deal, W. F. (2009). Energy from the skies: empowering future generations: from the beginning of civilization, humans have been experimenting with the power of the sun. The Technology Teacher68 (6), 11-19.
[2] Shukla, A., Buddhi, D., & Sawhney, R. L. (2009). Solar water heaters with phase change material thermal energy storage medium: a review. Renewable and Sustainable Energy Reviews13(8), 2119-2125.
[3] Martinot, E. (2005). Renewables 2005: Global status report. Washington, DC: Worldwatch Institute.