There are four key factors in figuring out solar capacity for a greenhouse:
- the area of your greenhouse,
- the wall material,
- the average low temperature outside,
- the temperature you want to maintain inside.
January is the coldest month in Bangor, Maine where Andrew lives. The average low during the month is 7ºF, while an optimal temperature for the plants starts around 60ºF. Andrew had to find a way to heat up his 50 ft² greenhouse in the winter. His father helped pick the systems for heating and heat distribution — the equipment would use about 2300 W. Together they calculated that a greenhouse made of 5/8" polycarbonate would consume around 100 kWh in January.
Solar panels get around 3.5 peak sun hours a day in Maine, and the days are mostly clear and sunny. Three 500 W solar panels would produce a little over 5 kWh in a day. This system would give Andrew over 150 kWh per month: the extras were just a safety margin. The battery would keep the heating system working at night.
Andrew decided that ground-mounted installation would fit his situation the most. The space was abundant, but the roof of the house didn’t have the proper inclination and angle. To provide solar power for greenhouse they opted for 440 W bifacial Aptos modules
, a 3600 Wh KiloVault battery and a MidNite Classic charge controller. The whole lot cost them around $4,500. They mounted solar panels on a pole with the help of friends who had experience in installing solar.
Usually, a solar system requires an inverter to turn DC from panels to AC. Andrew didn’t need one because all he used his solar energy for was a DC heating system and lighting. That’s not the most common scenario, and If your equipment or appliances demand AC, add an inverter that matches your system type