Question

How much solar power will I need? We have a tiny cabin and want to get off-grid. We'd use 13,000 watts if everything runs at once.

Asked by John Soliz
Rising Star, TX

We also have a 1/2 HP well pump for our well. What wattage in panels & how many panels do we need?

Answer

John,

There is a lot to consider if you wish to be off the grid. If we were to design your system just based on the the amount of watts used which you had stated, you would need in the range of 59 solar panels each generating on average of 220 watts per hour.

To properly design your system you will need to look at a larger picture of your usage.

  • Look at a year's worth of usage and factor the average kilowatts per month, week and day. This will be your starting point.
  • For your home state of Texas, the average hours of usable sunshine, known as insolation, is between 3.5 (Southeast Texas) and 6.5 (Northwest Texas).
  • Take your daily kilowatt usage and divide it by the amount of insolation for your area.
  • This calculation will give you the amount of kilowatts you'll need to produce to power your house.
  • You can then divide that number by the watts produce by a solar panel (wattage varies per manufacturer) to determine the number of panels you'll need.

Now with that said, you are still not off the grid. To be fully off the grid, you will need to:

  • calculate the size of your battery bank to sustain independance thoughtout the evening hours, as well as
  • size the panel array on the roof to be able to charge those batteries during the day while powering the items under operation.

Hopefuly this does not discourage you from proceeding with you goal of being off the grid.

Consult with a green professional and do not be afraid to ask questions.

 

For more information:

Read "I want to help get my mom's house "off the grid." Where do I start?" a Q&A answered by Florian Speier.

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