This is how I am doing it this year. I only have enough room on my McSuburb parcel to have small-scale structures, so this year for experimentation one of the things I have is a 4 x 6 coldframe (walls insulated at ~R-5) with a below-ground insulated structure, a water-tubing subsoil heating system and ~30 liters of water for thermal mass. The glazing is 8mm twinwall polycarb at a 30º angle and at night I cover the glazing with an old sleeping bag. Further, I take some of the heated water and put it in the soil, which is insulated @ R-6 - down to 10" in a raised bed next to the house. Despite numerous days with highs in the single digits F (-15ºC ) and several lows well below 0ºF (-25ºC), last time I checked my soil was 64ºF in the sun and 58ºF in the shade (~18ºC and ~14ºC). Air temps during the day always need to be vented on sunny days and at night I have never dropped below 35ºF (2ºC), even on the night we hit -14F (-26C). So my dark-colored water and soil are my thermal masses. So, to reinforce anecdotally what is above, IMHO the original link had inadequate mass to keep from freezing for that volume. The glazing insulation is important. Any text on solar houses or solar greenhouses spend considerable time on solar access and solar mass, as well as insulating the glazing at night and opening the glazing to the sky as soon as the sun is up. For example, right now the coldframe has heated up ~4ºF in 3/4 of an hour's exposure despite cloud cover allowing only ~40% of the expected cloud-free solar radiation through. The sun is free energy. We must do more than just collect it to make it work for us. We must store it, distribute it, and insulate our glazing. Dan

nathanhurst I'm not going to get into an electronics lesson with you, but you (with all due respect) are complete wrong on how amperage, wattage and voltage work. Real quick. Using your idea of connecting the panels to get 120V is not correct. Two problems with your scenario 1) the heaters we are talking about are 120V AC. Your method only provided DC current. While the elements can handle DC, the fan cannot. There may also be other electronics that are running off of a power supply thatÂs designed for AC. You need an inverter to change DC to AC. While there does exist inverters that will convert, say, 120DC to 120AC, this is not widely used in the Americas. 2) Parallel or SeriesÂ. That is the question. What you first need to understand is that in order to increase AMPERAGE, you need to connect the panels in PARALLEL. To make things simple, letÂs say that a single panel is 15 watts (thatÂs approx. 1 amp at 12V)  (which each panel is in the kit aboveÂ. 3 panels make 45 watts, which is approx. 3 amps at 12Volts). And also, letÂs use small numbers just to get the point across here. 1 panel producing 12V = 15 watts = 1 amp To product 10 amps at 12V, you connect 10 panels together in a parallel manner (positive to positive, negative to negative). Now, if you take those 10 panels and connect them in series (positive from 1 panel to negative on the other panel and repeat for each panel you end up with 1 positive and 1 negative when done). That would make 120V DC, BUT, it would be 120V at 1 amp only. To be clear: - Connecting panels in parallel increases AMPERAGE (watts) but the VOLTAGE stays the same. - Connecting panels in series increases VOLTAGE but the AMPS (watts) stay the same. So using your idea, in order to product 1,500 watts (which is approx. 12.5AMPS) you would need: 10 panels in series = 120V at 1 AMP (letÂs call this 1 set). To make the MINIMUM 12.5 amps (we are not including startup amperage or other necessary things to take into account when configuring a system)Â. you need to connect 13 "sets" (rounded off) of the above connected in parallel. ThatÂs 130 panels (individual panels). AND THEN, that would ONLY product the required amperage ONLY in direct, full sun (we havenÂt calculated for dimmer light levels). You still need an inverter here, which of course, also costs in amperage loss. Hopefully, you now understand how this works. Ok ok, so IÂve been a technician for over 30 years! LOL I just hope that I explained it well enough. I admit, itÂs difficult for me to put my knowledge into short words. LOL But like IÂve said before, itÂs better to use a water heating system for a greenhouse rather than solar electric panels.

I still think the only way this would work (aside from having the hot tub in the green house, would be to capture lost heat. Now my hot tub is very well insulated, especialy above the tub. My hot tub is a self contained tub, the heater is contained in the tub enclosure. But I think this method would work even better with an inground hot tub. Idealy, if the hot tub is not installed yet, you could build an inground hot tub (the heater is seperate with an inground hot tub). Install the just the heater inside the greenhouse. Otherwise, the place I have found the most Waste heat with my Tub, is above the heater. So hputting some sort of heat exchanger above the heater to capture the heat lost from the heater would work very well.

Last winter I followed advice in Elliot Coleman's book (Winter harvest handbook) and had great luck in *harvesting* fresh vegetables all winter. They did most of their growing however in the fall (I started them all in late September or later) and then later in the very early spring as in the winter months they barely grew (although they did a tiny bit). My set up: Hoop house - It was an existing (built by me and my husband a handful of years ago for season extention) 12x16 plastic covered hoop house. We made it out of plastic conduit and the only thing we modified for the winter is that we swapped out the flat 4 way fittings at the roof peak with adjustable angle fittings. I found that 45 or 90 degree fittings didn't work (too sharp an angle) and I didn't want to not have an angle for the snow load so I went with manually setting the angle as steep as I could with the adjustable ones. (You can find them by googling "PVC 1" Adjustable Ell Fitting 3 Way" or "4 way"). We never removed snow off the top of it - By design or by luck the snow would shed off the side. (Although I hear brooming it off is good practice.) I sealed the window and door with weatherstripping. I also added ~ 800 gals of water - some large tanks (which were a royal pain to get in) and lots of single gallon containers. against the north wall. I also added 1" foam insulation along the north wall - including covering 1/2 the "ceiling" on the north side (taped to the conduit frame in some areas). I dug the foam insulation ~ 6" deep around the perimeter. I then planted in two 18" rows separated by a small 1ft step path - all under a 4ft wide floating row cover (the row cover hovered on smaller plastic conduit hoops). Under the row cover in the small 1ft step path I put as many gallon jugs as fit leaving me with step spaces. I also put a few 1L and 2L bottles on the outside edges under the row cover. I also put one strand of old-fashioned (ie not LED) christmas lights suspended from the conduit as my "emergency" heat source. I put my thermostat for my lights outside my row cover and set it to turn on at 28*. I also grew a few earthboxes full of veggies but I found that anything in a box didn't grow nearly as well as things in the ground. I think the roots get too cold and they stop growing much, much earlier (but they didn't die - just didn't grow as much) even though they were under the same row cover but they didn't die. The last thing I did was put a small muffin fan attached to a tiny solar panel under the row cover for air circulation. I had my window/door always closed (ie I disconnected my autovents) for the winter months (Dec-Mar). I also never went in to harvest except during the day (almost always a sunny day) when opening my row covers wouldn't release any trapped heat that was vital for the night. I weighed down one side of the row cover with cylindrical bags of sand that I could easily remove and then the other side with soil/rocks piled on top. Watering was mostly a non-issue, but I'd carry in my water in jugs on sunny days and water by hand. I think I had to do this maybe 3-5 times all winter (ie monthly). With this set up I successfully grew: kale, leaf lettuce, carrots, beats, chard, mache VIT, bok choi, spinach, etc. For most plants I would harvest outter leaves and leave the inner leaves to continue growing. With that set-up each plant continued to provide until the late spring heat caused them to bolt (which was fine since I needed the space for the next round of crops). The temperature inside the row cover was much more stable than in the hoop house in general. The temp in the row cover never dropped under I think 25 - even after multiple cloudy/stormy days. In addition my hoop house is drafty so perhaps with a more sealed-tight environment no extra energy would be needed and/or maybe more ventilation. Oh and my hoop house is on the north side of my property and has mature trees ~ 50 feet away from it on the east side which did shade some in the morning (but not so bad because they didn't have leaves) and then we have evergreen trees that would shade the late day sun as well. I still think it's worthwhile but it depends on how much sun you get. I'm planning on building a "real" greenhouse (twinwall, etc) and am spending this winter scouting for the right location (best sun). I plan to use an earthen floor due to my experience of growing in pots vs in the ground, but am still doing my research for that as well. I've read that wherever possible you want to insulate in the ground to keep from losing heat that way. I plan to do that with my final greenhouse. Also wherever you are realize that both snow and a kneewall (if you have one) will shade part of your greenhouse floor in the winter due to the low sun angle so you may lose "significant" growing space that way.