Solar Thermal FAQ


For questions on renewable energy, see our renewable energy FAQ.

Is there a difference between solar thermal and solar water heating?

Yes. The Solar Guide uses solar thermal as a catch-all term, but it is important to note that solar thermal and solar water heating fall into three or more very different types of systems:

Why would I choose solar thermal or solar water heating?

Solar thermal and other solar water heating systems (solar pool heating) are easy to install and can work year round to heat water for your home. These systems pre-heat your water before it enters your hot water tank or pool. Free heat of the sun (year round) gives you significant savings on your energy bill.

Solar water heating systems cost between $3,500 and $5,000 installed, depending on the type of system you choose. These can reduce your hot water heating bill by up to $100 per month, depending on how much you use and where you live. The payback period for an investment in a solar thermal water heating system is three to five years. After that, the savings are all yours and systems have been known to last longer than twenty years.

What is the best solar thermal system?

"Best" is a relative term. We'll answer your question in terms of most practical, most reliable or most energy efficient, but these all depend on where you live.

For any climate where it freezes, the use of a closed loop thermal glycol based solar system might be the only practical choice. Drainback systems are also used under these conditions, but these are not as popular because they are not quite as reliable.

For warmer climates, another collector that are the most energy-efficient is thermosiphon. It requires no electric pumps to operate (in technical terms, this makes it a passive solar thermal system). The sun heats the fluid until it rises to the top of the panels, where it flows into a tank or heat exchanger. From the heat exchanger, only the hottest water is skimmed off from the top of the tank as you draw down the hot water.

How many solar thermal panels would I need to heat water for my home?

You can get the best answer to this by contacting a solar thermal dealer. This will depend on how many people in your household, on how much hot water you use and how much sunlight you receive.

However: a typical family of four might require four square meters, and we can roughly guess that a square meter per person is a fairly accurate estimate. But don't hold us to that!

How do I find a solar thermal dealer?

You can look in your local phone book, in the Yellow pages, under solar.

What is the difference between solar thermal and photovoltaics?

Solar thermal systems generate heat (for water or air) with the radiation of the sun.

A solar photovoltaic system uses solar radiation to generate electricity.

How does the conversion of solar energy to heat in a glycol-based system work?

Solar radiation hits the absorber (solar thermal panel) and is then transmitted to the heat transfer medium (glycol, usually) and converted to heat. The vacuum plus the insulation provided by layers of the absorber assure that heat remains in the solar thermal system.

Solar thermal systems with glycol use a composite tube that is made up of a jacket tube and absorber tube. Since these are made completely of glass, they are well-protected against degradation.

Do you really think solar and renewable energies are a good investment?

Solar energy, solar thermal and other forms of renewable energy will become cheaper, as people continue to invest in them. As people invest in them, this will drive down the cost-- as it already has (significantly) over the last few decades.

This has a snowball effect: the technology becomes more usable, cheaper and convenient.

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