EcoRenovator - View Single Post - Solar heat for your entire house extremely cheap

ThePrudentNinja · 07-11-15, 12:49 AM

Heating your home with solar. Something I experimented with a little last winter.

My results: open curtains in the day and closed at night seems to work, but I found a better method. Similar to what "Solar" has said, I put black cloth over the windows. I left a 2-3in gap at the top and bottom. I covered the entire window when the sun stopped shining on it. The effect I noticed was the sun would heat the black fabric and the heat would rise into the room. Using a ceiling fan helped distribute the warmth. On the majority of winter days, I was able to keep my whole house warm (60+ degrees F) when the sun was shining (in other words, I didn't use any other form of heat during most winter days despite temperatures outside being between 20-35 degrees F). I didn't manage to figure out any worthwhile solution to STORING any heat and had to use supplemental heat at night. My home is setup in a rather useful way. Half the windows are on the south facing side and half on the north facing side. In the summer I can block the south windows and leave the north windows bare and it helps keep the inside temps a little cooler. The best effect I've seen this summer is 10 degrees cooler inside than outside without the use of any air conditioning (using ventilation through the north side windows with the help of nearby trees). This winter I may attempt a little more "radical" solar heating setup just to see how well it works. Basically a large exterior box to collect solar heat and pump it into the house. Still not sure a good way to store any collected heat. It helps though that I have low ceilings and a large south facing exposure compared to the square footage of the house (think rectangular).

Now, the "average" BTUs in sunlight on an "average" day is around 300 useful BTUs per hour per square foot. If you halve it, that's still 150 BTUs per hour per square foot. A watt can be turned into 3.412 BTUs. So a square foot of area could realistically see about 44 watts worth of heat on a winter day. The exact amount can vary WILDLY depending on so many factors. Just roughly estimating here and trying to be conservative.

So, let's assume you have a room that is 100 square feet and of "average" insulation with 7ft ceiling. You will "typically" need about 7,600 btus an hour to heat it in a typical cold area of the USA (sorry Canada, this example is not for you). This figure too can vary WILDLY. So you would need about 50 square feet of solar collection to heat that room entirely with solar and be pretty dang sure. Of course this will only be during sunny days when the sun is actually shining on the collector. So, you would need a collection area of roughly seven feet by seven feet. Using a typical window, the collection box could be about 3ft by 16 foot. So in theory for a 100 square foot room with a south facing window, you could heat it entirely with solar by having a roughly 3ft by 16ft solar collector. You could also just install a bunch of windows lol.

Can a home be entirely heated by solar? Of course. Can a typical home be heated entirely by passive solar? Probably not without a lot of work. Can you save money by using solar to help heat your home? Of course. Just realize one typical south facing window in a room will not do all that much if your house is not heated by other means. It's still worth it. For a typical window, you could gain about 2200 BTU/hr of heat that doesn't cost you a penny. Almost like a 650 watt heater running. About 75-80 kWh a month of free heat if you get four hours of good sunlight every day. Of course you will probably get closer to 50. For me, that is $5 a month I could save for one room by spending roughly a few minutes a month opening and closing the window curtain. Multiply that by however many windows you have that can get good solar. Not bad and worth it to me.

The issue with solar is it isn't a steady constant source of heat. If you get a string of cloudy days, you will be using some other form of heat. A rocket stove mass heater may be a better solution for small homes. Not sure about large homes. Of course the best solution would be to build a house to be heated passively by solar, store the heat for the night time, and be passively cooled in the summer. Earthships come to mind (and boy can they be pricey).

If I made errors in my stats/calculations, forgive me. It's late, I'm tired.

07-11-15, 12:49 AM	#29
ThePrudentNinja Lurking Renovator Join Date: Jul 2015 Location: North Carolina Posts: 3 Thanks: 0 Thanked 1 Time in 1 Post	Heating your home with solar. Something I experimented with a little last winter. My results: open curtains in the day and closed at night seems to work, but I found a better method. Similar to what "Solar" has said, I put black cloth over the windows. I left a 2-3in gap at the top and bottom. I covered the entire window when the sun stopped shining on it. The effect I noticed was the sun would heat the black fabric and the heat would rise into the room. Using a ceiling fan helped distribute the warmth. On the majority of winter days, I was able to keep my whole house warm (60+ degrees F) when the sun was shining (in other words, I didn't use any other form of heat during most winter days despite temperatures outside being between 20-35 degrees F). I didn't manage to figure out any worthwhile solution to STORING any heat and had to use supplemental heat at night. My home is setup in a rather useful way. Half the windows are on the south facing side and half on the north facing side. In the summer I can block the south windows and leave the north windows bare and it helps keep the inside temps a little cooler. The best effect I've seen this summer is 10 degrees cooler inside than outside without the use of any air conditioning (using ventilation through the north side windows with the help of nearby trees). This winter I may attempt a little more "radical" solar heating setup just to see how well it works. Basically a large exterior box to collect solar heat and pump it into the house. Still not sure a good way to store any collected heat. It helps though that I have low ceilings and a large south facing exposure compared to the square footage of the house (think rectangular). Now, the "average" BTUs in sunlight on an "average" day is around 300 useful BTUs per hour per square foot. If you halve it, that's still 150 BTUs per hour per square foot. A watt can be turned into 3.412 BTUs. So a square foot of area could realistically see about 44 watts worth of heat on a winter day. The exact amount can vary WILDLY depending on so many factors. Just roughly estimating here and trying to be conservative. So, let's assume you have a room that is 100 square feet and of "average" insulation with 7ft ceiling. You will "typically" need about 7,600 btus an hour to heat it in a typical cold area of the USA (sorry Canada, this example is not for you). This figure too can vary WILDLY. So you would need about 50 square feet of solar collection to heat that room entirely with solar and be pretty dang sure. Of course this will only be during sunny days when the sun is actually shining on the collector. So, you would need a collection area of roughly seven feet by seven feet. Using a typical window, the collection box could be about 3ft by 16 foot. So in theory for a 100 square foot room with a south facing window, you could heat it entirely with solar by having a roughly 3ft by 16ft solar collector. You could also just install a bunch of windows lol. Can a home be entirely heated by solar? Of course. Can a typical home be heated entirely by passive solar? Probably not without a lot of work. Can you save money by using solar to help heat your home? Of course. Just realize one typical south facing window in a room will not do all that much if your house is not heated by other means. It's still worth it. For a typical window, you could gain about 2200 BTU/hr of heat that doesn't cost you a penny. Almost like a 650 watt heater running. About 75-80 kWh a month of free heat if you get four hours of good sunlight every day. Of course you will probably get closer to 50. For me, that is $5 a month I could save for one room by spending roughly a few minutes a month opening and closing the window curtain. Multiply that by however many windows you have that can get good solar. Not bad and worth it to me. The issue with solar is it isn't a steady constant source of heat. If you get a string of cloudy days, you will be using some other form of heat. A rocket stove mass heater may be a better solution for small homes. Not sure about large homes. Of course the best solution would be to build a house to be heated passively by solar, store the heat for the night time, and be passively cooled in the summer. Earthships come to mind (and boy can they be pricey). If I made errors in my stats/calculations, forgive me. It's late, I'm tired.