We are fully into the “Persephone Period,” that time of year when the days are short enough that there is very little growth in any of the salad greens.  But by adding just a little bit of heat in some of the greenhouses, we can get some of the greens to grow back slowly.  The chard that you see above are in our wood-pellet heated greenhouse.  Maybe it shows my status as a child of the 1970s, but I am fascinated by the creative ways that people find to push the envelope on renewable heating. I spent my teenage years in a passive solar house that my parents built in 1981. We have applied for a grant to study the feasibility of using heat pumps and a hot-water storage tank to store the heat produced by the daytime sun, and pump that heat back into the greenhouse at night.  It worked at a greenhouse at University of New Hampshire (see the article about it here) to reduce their heat load, but our winter heat needs are much lower, so we would like to run numbers on whether a system like that would work for us to provide all of the heat we need to get that little bit of extra growth in the winter. Another neat system we have seen is the “Climate Battery” system that stores summer heat in the ground and pulls it out in the winter (You can read about that one here). If we get our grant funding, we will also run numbers on whether it is possible to use a really big water tank (like septic tank size) in the heat-pump system to do that kind of seasonal storage. We’ll keep you posted as to whether it works out!