It is amazing how effective solar heating the greenhouse is. Out Pit Garden awoke this morning under the tarp at a heat maintained 50 degrees. The temps were well below zero, but by 10AM, with our insulated tarp off, they started rising. By noon it was 70 degrees and at the peak of the day you can see in the image above we hit 82 degrees!
This not only is great for the plants during the day, but we’re able to store this energy in our trash can heat sync and cement walls, requiring much less energy to keep the temp above 50 degrees tonight. With the sun so low on the horizon our good solar heat exposure is from about 11AM till 3PM each day. It is usable about one extra hour on each side so we get about 6 hours of solar heating.
That heat seems to take about 6-8 hours to bring the temp of the greenhouse back down to 50 degrees. If we didn’t have starts currently going, something that we’ll almost never do this time of year, I’d let the earthen walls and heat sync do their job. This year though, due to our late start, that remaining 8-10 hours we’re using propane and electric heat to keep it warm.