Solar powered electric help for winter roof garden?

Question

Winter is coming.

It's getting cooler here in the Bronx and I've been planting kohlrabi, peas and other winter veggies. But my garden is in pots and I fear the roots will freeze. But then I had and idea... what if I took some of the solar panels that I salvaged and have not yet found a use for and made some kind of "winter plant helper" ? I could collect light all day then artificially extend the sunlight with a few extra hours of UV light. Or I could put in a thermostat and heat pads ...

but maybe it makes more sense to try to find some bales of hay (impossible in the city without a car, but I'll try) or build a cold frame.

Is there any logic to my idea for winter electronics for plants? Is it worth a shot?

Answer 1

Plants, like us, need a specific amount of daylight and nightlight, rest and adjustment to seasons. You will be putting a strain with the extra light on your plants, in addition to their attempts to survive and adjust to the winter.

You are better off building a green house for them, and put the panels to good use to regulate the temperature inside. Or use hay. Nowadays, there are all manner of drop off services, so you could just have someone drop off the hay for you.

Answer 2

If you're worried about freezing, keep them warm somehow (heat mat/cold frame/both). If you want to boost photosynthesis use lights (not UV, but red and blue). So the first thing is to decide what you'd like to achieve. Attempting to warm the plants using lights is unlikely to work unless you use incandescent lights all night in a greenhouse -- they don't deliver the heat to the right place very effectively because of convection. The batteries you would need for this are huge.

Freezing wil affect the survival of (some) plants while insufficient light will affect their growth, but it's not just the roots you have to worry about. In fact if they weren't in pots I wouldn't worry about the roots freezing at all. If you use an insulated cold frame or greenhouse, you may not even need to use batteries -- simply warming under the pots during the day would use the pots/soil as a heat store. This may be enough depending on how hard your winters are and how tender your plants are. In addition plants feel wind chill, so just keeping the wind off them will help.

Answer 3

Sunlight at 100 watts per square meter for 8 hours is a wild overestimate for cloudy NY winters. 50% efficient photocells are likewise an overestimate. 85% inverter, for conversion to 120v AC is about right.

With those numbers, a 1 square meter array will give you 100X8X.5X.85 = 340 watt hours of AC. You'll need a deep cycle marine battery or two to store it in the daytime, and those are not cheap, and do not like cold. At best you'll get an extra hour of expensive, dim light.

Of course, you could go for a 100 square meter array, but $$$$$.