4 Things to Consider Before Going Solar Thermal

Kipnis.jpgSolar thermal technology (ie, solar hot water) provides space heating and/or hot water and is a frequently forgotten member of the solar power family. These highly effective systems are popular in many parts of the globe, from China to Canada to Zimbabwe. The panels are typically 70%-90% efficient, compared to around 20% efficiency for solar photovoltaic (pv) systems. Solar thermal energy displaces the use of the existing hot water heater and heating equipment, typically displacing either natural gas or electricity.

Solar thermal is a more mature technology than solar pv systems that produce electricity. It has been used for centuries for water heating. Even Leonardo Da Vinci had one on his home for heating water.

When considering the installation of such a system, it is important to consider the following items.

Southern Exposure

In the northern hemisphere, it is best to point the panels facing south. If the mounting surface is not angled to face due south, the efficiency of the system may decrease. If the panels are at a southeast angle for example, performance will improve in the morning, but suffer significantly in the afternoon.

Solar thermal panels are usually mounted in a fixed position and do not have tracking equipment to follow the sun. This is because the panels have copper pipe connected to them and a fluid running through the panel. They also can be heavy and a bit clunky to follow the sun’s angle.

It is important to consider your solar window and how much shade may interfere with the system. Solar thermal panels generate heat, instead of an electric current, so they are not as sensitive to a little shade as pv panels. It is however recommended to have clear solar exposure from 10 am-2 pm as a minimum.
Remember that the sun is lower in the sky in the winter months. If your solar system will provide heat, a good winter solar window is very important. If the roof of your home is not ideal, it is sometimes possible to mount panels as an awning, on the ground, or on a garage.

Space for Solar Equipment

Solar thermal systems in cooler climates require room for a solar storage tank near the existing hot water heater. This heater becomes the back-up when there is not enough sunshine to heat the water. Therefore, you will need space for a tank up to 30 inches in diameter for most applications. It needs to be in a space that will not freeze and will have a pipe connecting it to the existing hot water heater.

Heating Equipment

If you live in a cooler climate and you have enough room for panels, the solar system can assist with heating your home. Solar works best with forced air furnaces and radiant floor heating systems. Radiators that use boilers operate at a higher temperature and are not usually good for interfacing with solar.


Before forking out a bunch of money on a solar system, it is a good idea to consider energy efficiency first. Weatherization and conservation are often a low hanging fruit for energy and money savings. Water-saving shower heads, front loading washers, and washing clothes with cold water can help to maximize your solar energy.
The sun can heat between 50%-100% of the water used in a home, depending on climate, use, and system size. Efficiency helps increase that percentage, especially on cloudy days.


Sarah Lozanova is the director of marketing for Bubble Train Toys and is passionate about the new green economy. She is a regular contributor to environmental and energy publications and websites, including Natural Home & Garden, Energy International Quarterly, Triple Pundit, Green Business Quarterly, Renewable Energy World, and Green Business Quarterly. Her experience includes work with small-scale solar energy installations and utility-scale wind farms. She earned an MBA in sustainable management from the Presidio Graduate School and is a co-founder of Trees Across the Miles, an urban reforestation initiative.


Photo Credit: Nathan Kipnis Archictects

Sarah Lozanova is a green copywriter and communications professional specializing in renewable energy and clean technology. She is a consultant for Sustainable Solutions Group and a regular contributor to environmental and energy publications and websites, including Mother Earth Living, Home Power, Earth911, and Green Builder. Her experience includes work with small-scale solar energy installations and utility-scale wind farms. She earned an MBA in sustainable management from the Presidio Graduate School and she resides in Belfast Cohousing & Ecovillage in Midcoast Maine.

10 responses

  1. Hey thanks for the great blog, I love this stuff. I don’t usually do much for Earth Day but with everyone going green these days, I thought I’d try to do my part.
    I am trying to find easy, simple things I can do to help stop global warming (I don’t plan on buying a hybrid). Has anyone seen that http://www.EarthLab.com is promoting their Earth Day (month) challenge, with the goal to get 1 million people to take their carbon footprint test in April? I took the test, it was easy and only took me about 2 minutes and I am planning on lowering my score with some of their tips.
    I am looking for more easy fun stuff to do. If you know of any other sites worth my time let me know.

  2. Adrian, you might actually be interested in this site I’ve been working on. It’s called the Green Home Huddle. It’s all about green product research and reviews. Although you’re not interested in hybrids, we’ve got those, electric cars, green cleaning products (which are better for you AND the environment), and lots more.

    We’ve also got some pretty fun wikis about how to give green gifts to greening your drinking.

    And Sarah, thanks for this great blog. If you’re interested, we’d love to have you turn it into a wiki in the Huddle!

  3. Worldoffset.org is a great site for simple lifestyle choices. It breaks it down into pounds of carbon to help quantify the impact of various actions.

  4. Recent developments in reflector/capture technology renders systems like the one in the link more efficient than the classic black collectors, and tracking technology is cheaper than it used to be.
    Shown is a commercial concept, but it could be scaled for distributed generation use…
    This can supply hot water and electricity.

  5. The problem with these transpired solar collectors is that they don’t allow for energy storage. Other systems allow heat to be stored in water, so the energy can be used long after the sun has set.

  6. it was mentioned above that the efficiency of thermal solar energy is 80-90%, while this of solar cell is 20%.
    these numbers are striking.
    how the high percentages were calculated?
    why the thermal solar system are not widely used?

  7. Ofer-
    The Solar Rating and Certification Corporation (http://www.solar-rating.org/)runs tests on solar thermal panel efficiency. The solar photovoltaic companies publish data on their solar panel efficiency.
    The difference in efficiency makes sense if you consider the science behind it. Solar thermal panels take sunlight and capture the heat. Solar photovoltaic panels convert sunlight to electricity, which is much more complicated.
    Solar thermal is much more popular in overseas than in the US, particularly in China, Greece and Israel.

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