Quick Answer
To calculate the energy needs of your off-grid greenhouse, consider the climate, size, and intended use of the space. Calculate the total watt-hours of energy required for heating, cooling, and lighting using a formula that takes into account the number of hours of operation and desired temperature. Use this information to select a suitable solar panel and battery system.
Calculating Energy Needs
To determine the energy needs of your off-grid greenhouse, you’ll need to consider the climate, size, and intended use of the space. For example, a small, unheated greenhouse in a mild climate may require significantly less energy than a large, heated greenhouse in a cold climate. A good rule of thumb is to estimate 1-2 watts per square foot of greenhouse space.
Determining Energy Requirements
To calculate the total watt-hours of energy required for heating, cooling, and lighting, use the following formula:
Energy (Wh) = (Number of hours of operation x Desired temperature x Greenhouse size in square feet) / Efficiency of system
For example, if you want to maintain a temperature of 70°F (21°C) in a 1,000 square foot greenhouse for 12 hours a day, with an efficiency of 0.5, the calculation would be:
Energy (Wh) = (12 x 70 x 1,000) / 0.5 = 1,680,000 Wh or 1,680 kWh
Selecting a Solar Panel and Battery System
Once you have an estimate of the total energy required, you can select a suitable solar panel and battery system. A good rule of thumb is to oversize the system by 10-20% to account for inefficiencies and unexpected energy demands. For example, if you need 1,680 kWh of energy per day, you would need a system that produces at least 1,900-2,000 kWh per day. This would require a solar panel array of at least 3-4 kW in size, paired with a battery bank of at least 4-6 kWh capacity.
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