Factors That Determine How Many Solar Panels You Need
Factor 1 — How Much Solar Power You Need
The amount of electricity you use has the biggest impact. Most homeowners aim to cover all their electricity consumption.
Monthly Energy Consumption
Number of Solar Panels Needed
800 kWh
14
1,000 kWh
17
1,200 kWh
21
1,400 kWh
24
1,600 kWh
27
1,800 kWh
31
2,000 kWh
34
Assumes 400W panels.
Factor 2 — How Much Sunlight Your Roof Gets
Sunnier locations need fewer panels. One 400W panel in Arizona produces nearly 90 kWh/month while the same panel in Alaska produces only 36 kWh.
Region
Average Monthly Peak Sun Hours
Northeast
122–149
Southeast
152–179
Midwest
122–152
Northwest
152–198
Southwest
198–228
Factor 3 — Your Roof Characteristics
Sunnier locations need fewer panels. One 400W panel in Arizona produces nearly 90 kWh/month while the same panel in Alaska produces only 36 kWh.
South-facing roofs at 30–45 degrees are ideal. Other roof directions may require a few extra panels to meet energy needs.
Factor 4 — What Solar Panels You Use
Higher wattage panels produce more energy.
Panel Wattage
Panels Needed for Average Electric Usage
250W
26
300W
22
350W
19
400W
17
450W
15
Assumes 137 monthly peak sun hours.
5 Things That Can Limit How Many Solar Panels You Can Install
Roof Size and Design
A typical 7.6 kW installation covers about 334 sq. ft. Vents, chimneys, and skylights limit where panels can go.
Number of Panels
System Size
Min. Roof Space
10 panels
10 panels
10 panels
15 panels
15 panels
15 panels
20 panels
20 panels
20 panels
25 panels
25 panels
25 panels
30 panels
30 panels
30 panels
Assumes 400W panels.
Shading
Trees or neighboring buildings can reduce viable panel space. Trimming trees can help, but some shading may be unavoidable.
Personal Budget
Solar costs about $3.03 per watt, or around $14,000 after the federal tax credit. Installing fewer panels is an option to better fit your budget.
Net Metering Program
If your utility doesn’t offer full-retail net metering, consider installing fewer panels or pairing with a solar battery.
Utility Restrictions
Some utilities don’t credit excess energy beyond monthly consumption. Most allow installations up to 120% of annual energy usage.
Can Solar Panels Run an Entire House?
Yes, solar panels can power your entire home, but not always in the way you think.
Most home solar arrays only run your house during the day. Excess energy is sent to the grid in exchange for bill credits through net metering, which then offset the cost of electricity used at night.
