Replies

1. GBA Editor
   Martin Holladay | May 26, 2010 04:11pm | #1

   Dear Zone 4 Marine,
   Solar hot air collectors work. However, they are not cost-effective compared to many other energy-conservation measures -- or even many other renewable-energy measures.

   When a solar hot air collector is producing heat, you don't need any thermal energy. That's because a well-designed house doesn't need any space heat on a sunny day; plenty of heat comes through ordinary windows to heat a well-designed house. So a solar thermal system needs storage; in practice, that means a rock bin.

   The two weak links in most solar hot air systems are duct leakage and inefficient blowers. If you are able to build an airtight bin to hold your rocks, and an airtight duct system, and if you use a very efficient blower (or a PV-powered DC blower), your solar hot air system can work. But it won't be cheap; there are far better ways to spend your money.

2. 
   D8Es96G26a | Apr 20, 2011 12:17pm | #2

   Maybe it's because I am living in a cold climate (Montreal, Canada) but I do not totally agree with the answer. When the thermometer is showing 15F or below outside, your home is loosing heat even if your home is well insulated.

   I think that the best usage for that kind of system is to heat a basement since the sun can't heat it.

   In 2008, I installed a MC2 Energy hot air solar heating system (actually the best system in the North America market - confirmed by the SRCC ) to heat my basement and I am very pleased with it but I must agree that this kind of system is not paying himself rapidly ( but it depends of your electricity rates). In Montreal, they are low ( 0,08$/kWh ) so the delay will be long ( maybe 15-20 years )

   If you want more information about my system, you can find more here: http://eco-energie-montreal.com/index.php?pages/Hot-air-solar-heating-experience-mc2-energy

   I am even broadcasting results in real time on my site here : http://www.eco-energie-montreal.com/meteo/chauffage-solaire-solar-heating.htm

   Jean-Claude

3. 
   jklingel | Apr 20, 2011 09:18pm | #3

   Jean-Claude: "When the thermometer is showing 15F or below outside, your home is loosing heat even if your home is well insulated." Maybe you'll have a net loss, maybe not. It depends on how much solar you have available, and how you define "well insulated" and "well designed". Search here for the Sunrise House, for example. I don't think +15 is that big of a deal to warm w/ passive solar, but that is just from what I read; I have not built the new house yet.

4. 
   kevin_in_denver | Apr 21, 2011 01:49pm | #4

   Martin sums it up pretty well. I can add a few points:

   1. Extremely few rock bins have been built since the 80's
   2. Solaron, the biggest air-based solar company in the 70's was installing 98% water systems by 1983. (I worked there)
   3. Why would you spend $2000 on a Solar Sheat that sits idle all summer when you could apply that money to a solar DHW system that runs all year?
   4. Operational results from air-based whole house solar systems were so bad that most of the systems were torn out.

5. 
   D8Es96G26a | Apr 22, 2011 06:43am | #5

   Hi everybody. First, excuse me for the poor quality of my english but my primary language is french.

   As I was suggesting, the hot air solar heating is well suited for heating a basement because normally you only have little windows and the sun rays can warm it. And, if you are not there during the day, you can use it to accumulate heat. And since the heat is going up, during the night it will heat your first and second floor.

   Personnaly it is how I would like to use it but with only one pannel it is not enough to accumulate heat. My pannel can provide 1700 watts ( 5800 BTU ) max when the sun is perfectly aligned. Since it is cold in Montreal ( the thermometer can show less than 0F ) and that my house was built in 1975 ( the insulation is probably not as good as new house ) I would need more power.

   At this time of the year , as you can see on my real time solar heating page (http://www.eco-energie-montreal.com/meteo/chauffage-solaire-solar-heating.htm) , when I stop to heat during the day, the room temperature is falling from 69F to 63F in 4 hours. On a sunny day, the solar system will be able to warm it to 66F approximatively. So there is not risk to overheat the room with only one pannel. And for that reason I will probably add a new one. The advantage of the system is that it can stop when a certain temperature is reached (it is not the case with windows). On my first floor I got a lot of heat from the sun entering by the patio-door and by my other windows, maybe a little bit too much at spring since the sun is low in the sky. But for my basement it is an another story.

   I also owned a water solar heating system (for pictures since it is written in french: http://eco-energie-montreal.com/index.php?post/chauffe-eau-solaire-resultats-a-montreal) but for me it's a less interesting system since it cost a lot more. For example, my hot air solar system cost me about 2000$ and is producing 750 kWh by year and my water solar heating system cost me 6500$ (3500$ for the system and 3000$ for hardware and installation) and is producing 1200 kWh by year. And I will need to replace the glycol after some years. With the hot air solar heating system you don't have any maintenance

   Jean-Claude