We just experienced a major outage here, about 3-4 days, and our heater preformed quite well. Since we had no power for fans, we had to use a little more heat to maintain an acceptable temp. throughout the GH. These record temps. are costing an arm and leg, but...
I've applied bubble wrap to most (2/3s) of the exposed vertical surface, and it seems to have little negative effect on the light available. Next year I hope to attach a solar blanket to the roof as well. If these temps continue to be a trend, we may have to opt out to a more protected area for winter use and let this house go dormant. We have an area behind the house facing SW and have considered a solarium there. With a Trombe wall and other solar features such as black drums behind the glass and under the (SW) bench it should be more cost effective. Our living room has 132sq' of glass facing SW with a 6-8" insulated concrete floor which helps quite a lot with heating and gives a lot of guest houseplant envy.