How much solar power can I fit on my roof in Missouri and Illinois?  How much will the solar system produce?

These are two of the most frequent questions that we hear about solar power in the St. Louis region.   Here are some simple guidelines for starters:

1. A solar panel’s DC power rating equals approximately

15 watts / ft2

2. Most viable roof areas allow approximately 70% of the space to be effectively used.

3. Three good rules of thumb for determining how much energy solar power systems in the St Louis region under good conditions (no shading and southern orientation) will produce on average for each rated KW DC of installed capacity.

1. 1 KW DC ~ 4 kilowatt-hours (kwh) of energy/day
2. 1 KW DC ~ 120 kwh/month
3. 1 KW DC ~ 10% of an average Illinois/Missouri home’s requirement of 1,100 kwh/month

So, let’s run through an example of a home that could be 2/3 solar powered:

Available roof space = 30 X 20 feet = 600 ft2

Usable roof space = 600 ft2 X 70% = 420 ft2

Solar on the roof = 420 ft2 X 15 watts/ft2 = 6,300 watts (6.3 kW round to 6 kW)

Production = 6 kW X 4 = 24 kWh/day = 8,760 kWh/year (estimate)

Average home usage/year = 13,200 kWh (1,100 kwh/month)

Percentage solar powered = 8,760 kwh/13,200 kwh = 66%

Number of modules = 24 x 250-watt or 20 x 300-watt

A typical 100% solar-powered house would require approximately a 9 KW array:

Production = 9 kW X 4 = 36 kWh/day =13,140 kWh/year (estimate)

Average annual home usage = 13,200 kWh (1,100 kwh/month)

Percentage solar powered = 13,140 kwh/13,200 kwh = 99.5%

Number of modules = 36 x 250-watt or 30 x 300-watt

Roof area covered = 9,000 watts/15 watts/ft2 = 600 ft2

[su_row][su_column size=”1/2″]5.9 KW Example (Missouri)

• 26 x 225-watt modules
• 5.85 KW x 4 hr/kwh = 8,540 kwh/yr
• 70% of 1,000 kwh/mo electric requirement [/su_column][su_column size=”1/2″]9.5 KW Example (Illinois):

• 38 x 250-watt modules
• 9.5 KW x 4 hr/KW = 13,870 kwh/yr
• 100% of 600 kwh/mo home electric + 1,000 miles/mo EV charging! [/su_column][/su_row]

##### Are you interested in a firm quote? Contact us for a free consultation.

[gravityform id=”24″ title=”false” description=”false”]