A properly sized solar system should offset most or all of your electricity usage without significantly overproducing. Oversized systems may not provide additional savings if your utility doesn't offer favorable net metering. Undersized systems miss potential savings. The goal is to match production to consumption.
Panel Sizing Methodology
Step 1: Determine monthly kWh usage (from bill or utility account)
Step 2: Calculate daily need: monthly kWh ÷ 30
Step 3: Account for sun hours and losses: daily kWh ÷ sun hours ÷ (1 – loss%) = system kW
Step 4: Panel count: system watts ÷ panel wattage
Step 5: Verify roof area: panels × 17.5 sq ft ≤ available area
Net Metering
Net metering allows you to send excess solar production back to the grid and receive credit on your bill. Policies vary by state and utility — some offer full retail rate credits, others offer wholesale or avoided cost rates. Check your utility's net metering policy before sizing your system, as it directly affects ROI.
Roof Orientation Impact
South-facing (ideal): 100% of optimal production
Southwest/Southeast: ~90–95% of optimal
West/East: ~75–85% of optimal (good for afternoon/morning peak)
North-facing: ~50–65% of optimal (not recommended)
Flat roof: ~85–90% with tilt-mount racking
ROI Calculation Basics
Average US system cost: $3.00/watt before incentives (~$18,000 for 6kW system)
Federal ITC: 30% tax credit through 2032 (reduces $18,000 to $12,600)
State incentives: Vary widely — SRECs, rebates, property tax exemptions
Typical payback period: 7–12 years in most markets
System lifespan: 25–30+ years with panel warranties
Degradation: ~0.5% per year — panels still produce ~87% at year 25
Peak Sun Hours by Region
Southwest (AZ, NV, NM): 6–7 hours
Southeast (FL, TX, GA): 5–6 hours
Midwest (IL, OH, MI): 4–5 hours
Northeast (NY, MA, PA): 3.5–4.5 hours
Pacific NW (WA, OR): 3–4 hours
Solar system sized?
Build the full proposal in BuildQuotes or invoice the job directly.