Solar Panels for greenhouse needs

[dubosegriffin]

Greetings from Charleston SC where we have on average around 25 days a year that drop below 30. We have an 100 square foot greenhouse that cools down to ambient at night. I am interested in using solar panels to power a small space heater during the winter. I need to be able to capture energy from the sun during the day and use this energy to run the heater at night. It would also be nice to run a fan in the summer and possibly a small water pump for misting plants. However, the winter heat is the most important. Is there any solution for me?

thank you!

[Sunking]

It is not possible to do what you want, well unless you want to spend 10's of thousands of $$$$. Using solar PV to heat air and water is just futile.

[Naptown]

As Dereck said PV is cost prohibitive for the application you want it for. That said I just finished up a 20KW system for a commercial greenhouse but not for heat. Ventilation fans and a few lights.
You want to add thermal mass to the greenhouse. consider putting some water barrels on the south side that will heat up during the day and transmit their heat at night. Perhaps some solar thermal to warm the floor or earth below the greenhouse and temper the swings from day to night.

[dubosegriffin]

Thank you for your replies. I already have a black plastic trash can with water but it does not really do anything. Can you explain thermal mass and solar thermal for ground? Thank you.

[Naptown]

You would need more than one can with water and make it a smaller tubular or oval shape to increase surface area to volume.
You could add some thermal panels and a loop or two of Pex buried in the ground to heat the ground during the day and radiate the heat at night.
However the best thing you could do would to devise some sort of moveable insulation that could cover the walls and roof at night and moved out of the way during the day.

[Whitebear]

Solar hot water

You could used hot water type solar collectors plumbed to a large, well-insulated storage tank then pump that hot water through radiators at night to heat the greenhouse. This would cost several thousand dollars--offset perhaps by Federal and State tax credits and utility company rebates.

Have you considered installing a wood stove?

[peakbagger]

If you roam around in the Home Power magazines archives there is a article about a large scale solar hot water system built for a greehouse application in the Green Bay Wisconsin area. I agree with the others that solar electric is not the way to go.

[SteveC]

I've been dealing with a greenhouse since the 80s and have tried and rejected a number of "heating" ideas. Your greenhouse is quite small [no offense: mine is only 300 sq. ft.]. This means your space is at a premium [as it always turns out to be in all greenhouses] and storing heated water, solar or otherwise, is quite difficult...you need lots of volume and there is not room for lots of volume in a small greenhouse.

If you can come up with an underground storage, that can work. However, now you are looking at a fairly major job to dig out a hole, build or buy and install a tank, build or purchase some solar water-heating panels, set up the pumps/controls/etc. for heating that water. Plus the plumbing/controls to get the heat from the water in the tank to the inside of the greenhouse, whether that be by radiators, etc. It is quite complicated for a small place.

The trouble is, to get enough heat back out of the water to bring the air temp's up to plant-friendly level, even if it is just a few degrees above freezing, is a lot of work. If this is a "labor of love," and you are doing it for fun, ok. Otherwise, you will likely find the project to be far more time-consuming and difficult to bother with.

I originally planned to build a big tank beneath the floor of my greenhouse, put it in before I built the greenhouse, in other words. Or build a big tank inside the greenhouse, on the floor, open on top like a big fish tank, then build racks and shelving above the water to hold my plants. This was done and written about in a number of publications back in the 70s and 80s. I don't recall how owners like the results, but I seem to recall disappointment. I blew it off.

I eventually put a tiny propane heater in the greenhouse, one that vents the burner to the outside to prevent sulfur compounds and other damaging byproducts of the gas flame for the health of the plants. Later, I removed the heater [though it worked, I hated spending the money on propane] and installed a small wood stove. It cannot be automated, but I live here and don't mind. I only have to light a fire in the stove maybe 20 nights a year, so for me it isn't a big hassle.

[dubosegriffin]

Switch to Mist Concept

Again, thank you for all the replies regarding heating. I would like to switch the topic to using solar power to run a misting or watering system. Again, small green house with two tables that are about 8 feet long. So, I was thinking of a misting system or a watering system. I guess I would need about 8 mist heads and there would be about 20 feet of line. I envision that I would have a submersible pump down in my trash can of water. This pump would be connected to a timer so that the misting would occur on some interval throughout the day, or morning/afternoon watering. I would love to power this pump with a solar panel outside the greenhouse. What are your recommendations and would you have a battery in this system or just water plants when the sun is out?

[jimcook888]

Solar Powered Misting

I am building a greenhouse (14x14). It will have solar powered fan, vents and I am planning a solar powered misting device. Google Sunjet Solar 150 Pump Water Fountain (www.1000fountains.com). This pump looks powerful enough to easily do your misting. All you have to do is connect it to a tubing over head that has misting nozzles in it. If you have difficulty let me know and I will let you know hoiw I came out. However that will be a while i haven't finished putting the polycarbonate sheets in the greenhouse yet.

[maple flats]

We also have a hobby greenhouse. Ours is 8 x 10. We heat it with a line voltage t-stat controlled 600 watt electric heater. It only heats when the temp drops to 40 degrees. Cycles on and off as necessary. This is what you need. PV Solar will cost you too much to have a system that will do the sob. It would take all of the fun out of eating the tomatoes if you paid about $150 per pound for them. As others have said, solar thermal can work for that application far better and cheaper. It still is likely to take a few decades to pay for the system, and several new greenhouse covers.