How Much Off Grid Solar Do I Need?

How Much Off Grid Solar Do I Need?

How much energy will my solar panels generate in a day? A 50 watt panel doesn’t put out 50 watts all day long. You might get 15 watts around breakfast, 45 watts at lunch, and 20 watts with dinner. This isn’t new info to most people 😁. So how do you figure out total energy (kWh) for a day if power output moves with the sun

This is a key question for sizing your off-grid system. On a sunny day, solar power output will look like the bell curve in the photo. You only get full power for few moments at the top of the curve. To make things easy, we can chop off the skinny sides of the curve, flip them over, and add them to the middle part. As a result, you can treat a day’s worth of inconsistent power as "just a few hours” of fixed, full sun production. Pretty cool eh? 

So now the real question: How many hours is “a few”? It depends on where you live. Check out the map. Find your solar zone to figure out the “full sun hours” for that area. Multiply these hours by the size of your solar array in kilowatts (1 kilowatt is 1000 watts) and you’ll get an idea of how many kilo-watt hours (kWh) your array will capture on average. These numbers are for SUMMER production. Winter will give you between 25% to 50% less! 

Example: A 150 watt panel in Los Angeles would be 0.150 kilowatts, multiplied by 4.5 hours. That would give you about 0.675 kWh of energy per day. See how that compares to your battery size. Keep in mind: this is an average for a sunny summer day and it doesn't take into account efficiency losses. Add a 25% "safety factor" to account for power lost in the controller and batteries. Confused? Shoot me an email:

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