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Off-Grid Sizing Calculator

How Big Should Your Off-Grid System Be?

If you are moving from a utility-connected home in the 'burbs' to an off-grid home in the boonies, you will have the opportunity (perhaps necessity) of downsizing your electricity usage. In order to calculate how large your home power system needs to be, run the Off-Grid sizing calculator below.

  • Run the System Sizing Calculator with with figures from working through the Load Evaluation Calculator, (PDF) based on the energy efficient lighting and energy efficient appliances you will choose for your new off-grid home.
  • Use our Appliance Electrical Consumption Table for average appliance electrical usages.
  • Once you have a good idea of what size system you are going to need browse our Off Grid Systems. Or call us at 1-800-472-1142 and we can design any size system to fit your needs.

1. What's the most electricity you might use in a month?

Use the actual watt-hours per day at the end of your Load Evaluation Calculator OR (PDF). You can do this by consulting our Appliance Electrical Consumption Table below or by measuring the power usage of each appliance with a Kill A Watt Meter for a more precise measurement.

* If you want a quick ballpark number, look at your past electric bills and find the month with the highest usage (often summer or winter, depending on cooling/heating needs in your area). The bill should show you the number of kilowatt-hours (kWh) used that month. Put this number in the space below.

Wholesale Solar Load Evaluation Calculator
Appliance Quantity Watts
(V x A)
Mult. * 1.5 for AC conversion
Hours On per Day Watt Hours per Day

Total Watt Hours per Day:

Watt Hours Required Assuming Inherent Efficiency Loss:

* Use these estimates to provide a general watt value for your appliances.
For example:

Blender - 500 Watts

2. What percentage of your house/business power do you want to generate with solar power?

If you want to produce 100% of your electricity, leave 100.

3. How many Peak Sun Hours do you get per day?

Look at the Solar Map to find this number.

This gives you the annual average. If you will use your system during the winter, subtract 1.5 hours from the annual average to account for decreased sunlight during those months. This ensures your system will be properly sized to provide year-round power, even during darker months.

Sun Hours/Day
Minimum System Size:
Approximate Solar Panel Wattage:

Approximate Number of Solar Panels Needed:

* For 20 Astronergy 270-watt solar panels to produce 5,400 watts..... 5,400 divided by 270(watts per panel) = number of solar panels needed.
NOTE: These figures are approximate and do not take into account the variable efficiency ratings of solar panels and off grid inverters. Please work with experienced Wholesale Solar staff to design a system which fits within your budget and can be expanded as needed.

To get a ballpark idea of what your system might cost:

Click the button on the right to view our off-grid ballpark cost table.

Last updated: 01/21/2018

System size (kW) Daily Production Estimate Example panel configuration Approximate Price Range (before 30% federal tax credit)
1.08 kWSummer 4.5 kWh
Winter 2.0 kWh
4 × 270 W$8,000
1.62 kWSummer 10.5 kWh
Winter 5.0 kWh
6 × 270 W$9,800 - $10,500
3.24 kWSummer 14.5 kWh
Winter 7.0 kWh
12 × 270 W$12,500 - $13,900
4.05 kWSummer 18.0 kWh
Winter 9.0 kWh
15 × 270 W$13,500 - $14,900
4.86 kWSummer 21.5 kWh
Winter 10.5 kWh
18 × 270 W$18,100 - $19,500
6.48 kWSummer 29.0 kWh
Winter 14.5 kWh
24 × 270 W$24,100 - $27,000
7.08 kWSummer 31.5 kWh
Winter 15.5 kWh
24 × 295 W$26,000 - $28,900
8.1 kWSummer 36.0 kWh
Winter 18.0 kWh
30 × 270 W$26,100 - $29,000
8.85 kWSummer 39.5 kWh
Winter 19.5 kWh
30 × 295 W$27,800 - $30,700
9.72 kWSummer 43.5 kWh
Winter 21.5 kWh
36 × 270 W$33,200 - $35,800
12.15 kWSummer 54.5 kWh
Winter 27.0 kWh
45 × 270 W$41,500 - $44,100
13.28 kWSummer 59.5 kWh
Winter 29.5 kWh
45 × 295 W$45,000 - $47,600
14.58 kWSummer 65.5 kWh
Winter 32.5 kWh
54 × 270 W$44,300 - $46,900
15.93 kWSummer 71.5 kWh
Winter 35.5 kWh
54 × 295 W$47,600 - $50,200

These figures are based on complete solar power systems that Wholesale Solar sells. Prices are approximate. Prices do not include freight, tax, or installation.

Why are smaller systems sometimes more expensive than larger ones? Because higher-efficiency panels cost more. For example, to get a 10 kW system, you can either use 35 285W panels or 39 260W panels. Even though you need more 260W panels (they are less efficient), economies of scale actually make them more affordable. So when would you want to use higher-efficieny panels? Only when you're limited on roof/ground space and need to squeeze the most power out of every available square foot. In other words, more efficient panels cost more but can generate more power per square area. If you're not limited by space, we suggest you go with the best price per watt instead.

Click the button on the right to check out our pre-designed systems that closely match your current calculated off-grid needs. *

* Pricing on these systems does NOT include batteries.

Take your calculated numbers and explore the Off-Grid Systems.
Or give us a call at 1-800-472-1142. We are here to help!