Solar collectors reduce the cost of hot water heating at home

By Martha Shaw (Martha’s Vineyard, MA)

The luxurious practice of bathing and showering in hot water for health and wellbeing can be traced back thousands of years across cultures from the Far East to ancient Rome. Only within the last century, however, have Americans come to rely on hot water available in every bathroom with the twist of knob or push of a button. Not only do we expect it on demand for bathing, but also for washing our clothes and getting our dishes squeaky clean. Barring the presence of geothermal springs in the earth below, this means raising the temperature of water. Throughout time, man has been heating hot water by burning wood, oil, gas, coal, or compost; and in many parts of the world, natural sunlight is used to heat water on rooftops. Now, solar hot water systems are taking their rightful place in history. In fact, heating hot water is among solar energy’s most efficient usages.

It’s easy to guesstimate the amount of energy coming from the sun. Ten square feet of surface on the planet exposed to direct sunlight receives about 1.4 kilowatts of sun power. The power level of one kilowatt for one second is an energy measurement called a BTU (British Thermal Unit). Think of a BTU as about the same amount of energy that comes from lighting one kitchen match. A BTU is also defined as the amount of energy needed to raise one pound of water one degree Fahrenheit. In general, it’s fair to assume that a fixed solar collector on an unobstructed roof on a sunny day receives 1 BTU per 10 square feet. A typical solar collector panel is 32 square feet so it can receive about three BTU’s per second. That’s roughly 10,000 BTU’s per hour for a collector about the size of a sheet of plywood. Five hours of bright sunshine in a day can make about 50,000 BTU of solar heat from one collector panel.

In the solar hot water system, this heat energy is then used to raise the water temperature of the well or town water. For instance, if well water is 50 degrees, and you want to raise its temperature 70 more degrees to reach 120 degrees, you can calculate how many gallons can be heated. If you divide the 50,000 BTU from the collector panel, by the 70 degree temperature rise needed, you can conclude that 714 pounds of hot water, or about 79 gallons, could be obtained per day from a single solar collector, minus the losses in transferring heat and storing the hot water. Back in the 1970s, during the energy crisis, solar collectors rose in popularity, but the movement lost its momentum as soon as the tax benefits and rebates disappeared. Now, state and federal incentives have returned as energy issues take the spotlight, and solar is back in full swing. The cost of a simple solar hot water installation can be as little as $2,500 including parts and labor, using sitebuilt or refurbished equipment. New systems with warranted equipment cost a bit more.

In December, Sarah Kuh and Chas deGeofroy of Chilmark decided to go ahead with solar hot water when they heard about a good deal offered by contractor Chris Fried of Vineyard Haven, who not only installs systems but also likes to invent them. “If you have a good roof angle and plenty of exposure, why not?” says Sarah. “There’s a sense of responsibility to use renewable resources as time goes on, and there are so many problems around energy, not the least of which is war. It’s readily available for free as long as the sun is shining.” Their system cost a total of $2,500, including labor. Though the solar collectors won’t reach their full potential until summer, on a sunny winter day, water temperatures in their 50-gallon solar tank can easily get to 100 degrees and up. This preheated water feeds into their gas water heater, reducing its load and reducing their dependence of fossil fuel.

“Everyone’s going to have to deal with the end of cheap oil,” says husband Chas. “We may not run out for a hundred years or more, but it’s going to get more expensive. Besides, it’s stupid to invade countries for cheap oil and then squander it. I think this is a good thing to get into… the wave of the future.”

Jim and Debbie Athearn of Morning Glory Farm worked with contractor Erik Lowe to design and install a solar hot water system for their home to replace their electric hot water heater. “We also intend to heat our dining room with looped hot water coils installed in the flooring,” says Jim. “But we’re still waiting to see how much hot water the collectors can produce.” Because the Athearns pre-plumbed the house to someday use solar hot water to heat their floors, their total cost was approximately $10,000. Most of their water heating is now provided for free, which they feel good about, both economically and politically. “But for right now,” Jim adds, “the Arabs are still heating my dining room. Either them or the Texans.”

South Mountain Company Inc. chose Laurel Wilkinson’s house in Island Co-Housing to demonstrate and monitor a new Enerworks solar hot water system that cost about $7,500 total. Laurel, who works at the eco-friendly firm, prefers the soft hum of the system’s pump to the sound of the oil furnace firing up. She says, “As a child, I was raised not to use what I don’t need, and that includes both water and energy. In my family, we turned down the thermostat at night and wore an extra layer to stay warm. College years are the age when people look at their own values and what’s important to them. For me this was during an energy crisis. I began to study various environmentally conscious topics around architecture. Being here at South Mountain I am fortunate to have the opportunity to integrate my values with my work.”

The house has a large south-facing roof with two solar collectors that have been producing most of the home’s water heat for two years now and their performance is monitored with great enthusiasm. “For me, one of the big things is seeing where the energy is coming from,” says Laurel. “It’s like seeing where your food is grown.”
Contractors on the Island are revving up their capacity to install systems, now that incentives for solar hot water heating have been issued again. Both state and federal tax credits are currently available for new, warranted equipment that has been approved by the Solar Rating and Certification Corporation. Forty plumbers, heating contractors, architects and builders on the Island will attend a solar hot water training workshop on March 16.

To find out more about solar hot water and opportunities for funding, visit

This article is sponsored by the Vineyard Energy Project through a grant from the U.S. DOE’s Million Solar Roofs program. The Vineyard Energy Project promotes sustainable energy choices through education, outreach, and renewable energy projects. The author, Martha Shaw, is a member of the Vineyard Energy Project’s advisory board. The Times publishes these columns as a service to its readers.

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