I have a 5m x 5m x 2.5m greenhouse, with plastic sheeting (not glass) and I need to keep the ambient temperature to 10c or 15c during the night.
There's currently a 2000w fan heater in, which raised the temp by about 2c - 3c during the night, but it was still 4c this morning and some plants have some "frostbyte". So I need to go and buy at least two more, but 6kw for 10 - 12hours will cost a small fortune to run on Eskom. So I need something more cost effective.
I have considered putting in some black water pipes, full of water, but don't yet have a workable solution for a heat source, during the night. Will a solar collector and circulation pump, during the day, heatup the water in the pipes warm enough to sustain some heat during the nights?
I prefer not to burn any wood or gas inside.