Solar hot air, solar hot water and solar electric are all options. Which is best?
All three options are great projects, I've built all three and they each have their advantages. One of the goals of the SimplySolar e-mail group is to keep solutions as simple as possible, so air and water based systems get the most focus here. They are very safe, much less expensive and offer a much quicker payback.
Air and water based panels of the same size each capture about the same amount of heat. These are the main points to consider in choosing:
Factors to consider for Air:
- Very easy to build
- Freeze protection is unnecessary
- Least expensive with quickest payback
- No need for thermal storage as heat is used immediately
- Almost instant heat when the sun is shining
- Panels usually are situated nearer the house, though good success has been obtained with outdoor buried ductwork
- Thermal storage is more difficult
- Larger ductwork required
- Larger holes in house
- Difficult to use for solar domestic hot water
Factors to consider for Water (hydronic):
- Lots of flexibility in panel placement
- Build as big as you like
- Easy to bring small pipes into house
- Easily transport heat where you want
- Ability to store heat in an easy to construct thermal storage tank (which can be used simultaneously for domestic hot water and space heating)
- Still have heat on cloudy days (as long as there aren't too many in a row)
- Heat can be distributed in a more controlled and comfortable manner by installing an under floor radiant heat system
- Easier to insulate pipe
- By using the panels for both space heating and hot water, they are useful year round
- Slightly more difficult to build than air, but not much more.
- Freeze protection is required - accomplished by either installing a drain back system so that the water is in a warm environment when the sun isn't shining or adding antifreeze and leaving the water continually in the loop.
- If you want to store heat (optional), you'll need a thermal storage tank. They are easy and inexpensive to build, but they will require some space in your basement, crawl space, garage or outdoors.
- For space heating, you'll need to install a distribution system such as under floor radiant heat or baseboard heat (but that can be done easily and inexpensively).
In summary, for an inexpensive infusion of quick heat as long as the sun is shining, air is a great option. For a more controlled distribution of heat with storage and the ability to heat your solar domestic hot water, a water system is the way to go. They both have their place and I'm happily using both here.