Harnessing the Sun's Energy for Water and Space Heating

Installation of rooftop solar water heaters is increasing worldwide, according to the Earth Policy Institute.
From Lester R. Brown, Earth Policy Institute
January 5, 2012
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Solar rooftop thermal collectors are gaining popularity around the world as a convenient and inexpensive way to heat both water and space.

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The pace of solar energy development is accelerating as the installation of rooftop solar water heaters takes off. Unlike solar photovoltaic (PV) panels that convert solar radiation into electricity, these "solar thermal collectors" use the sun's energy to heat water, space, or both.

China had an estimated 168 million square meters (1.8 billion square feet) of rooftop solar thermal collectors installed by the end of 2010 -- nearly two thirds of the world total. This is equivalent to 118,000 thermal megawatts of capacity, enough to supply 112 million Chinese households with hot water. With some 5,000 Chinese companies manufacturing these devices, this relatively simple low-cost technology has leapfrogged into villages that do not yet have electricity. For as little as $200, villagers can install a rooftop solar collector and take their first hot shower. This technology is sweeping China like wildfire, already approaching market saturation in some communities. Beijing’s goal is to reach 300 million square meters of rooftop solar water heating capacity across the country by 2020, a goal it is likely to exceed.  

Other developing countries such as India and Brazil may also soon see millions of households turning to this inexpensive water heating technology. Once the initial installment cost of rooftop solar water heaters is paid back, the hot water is essentially free.

In Europe, where energy costs are relatively high, rooftop solar water heaters are also spreading fast. In Austria, 15 percent of all households now rely on them for hot water. Germany is also forging ahead. Some 2 million Germans are now living in homes with rooftop solar systems. Roughly 30 percent of the installed solar thermal capacity in these two countries consists of “solar-combi-systems” that are engineered to heat both water and space.

The U.S. rooftop solar water heating industry has historically concentrated on a niche market -- selling and marketing more than 9 million square meters of solar water heaters for swimming pools between 1995 and 2005. Given this base, the industry was poised to mass-market residential solar water and space heating systems when federal tax credits were introduced in 2006. Led by Hawaii, California, and Florida, annual U.S. installations of these systems have more than tripled since 2005.  

Despite the recent growth in U.S. installations, the country ranks 36th in installed capacity relative to its population, with just 0.01 square meters installed per person. Cyprus, on the other hand, currently leads the world in solar water heater area on a per capita basis, with 0.79 square meters per person. Israel ranks second with 0.56 square meters per person.  

Inspired by the rapid adoption of rooftop water and space heaters in Europe in recent years, the European Solar Thermal Industry Federation (ESTIF) has established an ambitious goal of one square meter of rooftop collector for every European by 2020. Over the long term, ESTIF estimates that solar thermal has the potential to meet most of the region’s low-temperature heating needs.

Numerous policies promoting renewable energy use for water and space heating exist around the world. Some governments have gone a step further, passing laws requiring solar water heaters in new construction. For a quarter-century, Israel was the only country to have a national mandate for solar hot water in buildings. Then in 2006, Spain began requiring that solar collectors be installed on all new or renovated buildings. Portugal followed quickly with its own mandate. In the United States, Hawaii now requires that all new single-family homes have them.

Solar water and space heaters in Europe and China have a strong economic appeal, often paying for themselves from electricity savings in less than 10 years. With the cost of rooftop heating systems declining and more countries implementing favorable policies, the shift from fossil fuels to solar energy for heating water and space will likely accelerate.

Lester R. Brown is President of Earth Policy Institute and author of Full Planet, Empty Plates. He is recognized worldwide for his global perspective on environmental issues and for his development of Plan B, a plan to save civilization through stabilizing population, cutting carbon emissions, and restoring the earth’s natural support systems. Find him on .

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Post a comment below.


12/5/2014 5:36:55 PM
How do we get the USA government involved in our local utility company to support us citizens in gaining support in getting solar power???? thanks. I have wanted it for years but here the cost is nearly the cost of the home.

11/25/2013 1:51:28 AM
Excellent statistics.

Where I am from, solar is popular because we have a lot of government workers who know about the incentives available for various types of solar... therefore increasing the return on investment.

If more people knew about these incentives and savings, more and more people would begin to invest in solar.

- Eddie

1/26/2012 9:44:59 PM
I use small solar/LED units in out-sheds where I only need an occasional dim light so I don't trip over something. It's cheaper than running a line to the shed. I also tried a motion sensor unit once, but there was enough activity at nite to prevent it from holding a charge very long, so it proved useless... The author of the article is being disingenuous when he lauds the Europeans for using solar installations. With gasoline $9/gal and electricity $0.40/kW-hr (4x our US rate) solar is a viable alternative there now. With 300 yrs' worth of coal and another 300 yrs' worth of natural gas availabe here, there's no sense in avoiding grid power unless you're way off in the boonies, too far to run lines. Maybe we'll figure out cold fusion sometime in the next 6 centuries. and then even the irrational greenies will be happy.

Shawn Henry
1/26/2012 5:10:45 PM
I don't have an issue with solar power it has its uses, but pushing it as a main source right now is crazy. I installed solar powered motion lights around my chicken coop and have had no light for 7 days. You need sun to charge the batteries and i have had none for 7 days here in Ohio. Kinda beats the reason i bought them so i can see in the winter. Gonna wire up some new ones to the good oldfashon 110Volt.

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