"Brave Helios wake up your steeds/bring the warmth the countryside needs"

While volunteering at the Minnesota State Fair's solar energy exhibit this summer I fell hard for solar thermal energy. I mean, we always hung out and stuff, but during those two weeks I realized it could be so much more.

With solar thermal technologies, the energy in the sun's rays is harnessed as heat, which can be used to heat a swimming pool,heat water for home and industrial uses, heat interior spaces, and even create electricity for the grid. I was not really aware before my volunteer stint how practical and easy-to-implement solar thermal technologies are.

I had not really given much thought to using the sun for space heating a home, but it the "solar furnace" idea is actually very old, going back to the Roman times. It has been experimented with in various "hot box" forms since the 1800s that would be recognizable today. The Victorian greenhouse and solarium are passive solar collectors themselves, albeit room-sized.

Today's solar thermal furnace is, most simply, an insulated metal frame with a glass surface on one side and another plate of metal inside the box, to concentrate the heat. The box (or boxes) are installed on the south-facing wall of the house, and the air in the box is heated by the sun. Fans circulate air from the home's interior into the box to be heated, then push the air back into the home when warm. A thermostat/controller keep the air flowing when needed, and a system of ducts and fans bring heat to the entire home

One installer I spoke to this summer said under the most optimal conditions, a solar furnace could provide up to 30% percent of a home's space heating before the "backup" furnace would have to kick in, be it a furnace burning conventional fuels like natural gas or oil, or a non-traditional system. Of course, the 30% number depends on a lot of things, including how large your home is and particularly how weatherized and well-insulated it is. Also, the solar furnace will not heat the air when it is dark or gloomy out, hence the backup furnace.

To me, the solar furnace is an attractive solution to cold-weather heating needs:

1. Very simple technology and few moving parts mean less maintenance.
2. The fuel source is free; the fans and controller can be run using the sun's power as well, with a small photovoltaic panel.
3. Thoughtful weatherization/insulation can reduce the baseline heating need, and boost the contribution from the solar furnace.
4. A high conversion efficiency coupled with a first-year installed per-kWh cost lower than solar hot water and solar photovoltaics make it one of the most cost-effective entries into renewable energy for individual homeowners.
5. Solar thermal installations qualify for federal and state incentives, speeding up the return on investment.

Adding solar thermal space heat isn't a simple decision, and a lot of homeowners may find the barriers to doing it are more than they want to deal with. One significant concern I heard from fair goers was that the utilitarian boxes don't really blend in with the architecture of their homes or neighborhoods. And dependent on each home's location, there may not even enough solar exposure to make the systems cost-effective.

Still, if I could do one thing involving renewable technologies, adding solar space heating would be the first on my list. For now, solar thermal energy and I are holding hands and making plans for a sustainable future together that I hope comes soon.