How solar panels work
Solar panels convert sunlight into DC electricity using photovoltaic (PV) cells. An inverter then converts that DC power into AC for your home. Excess energy flows back to the utility grid through your meter — most states credit you for this through net metering. On cloudy days or at night, you draw power from the grid as usual. A typical residential system includes panels (on your roof), a central or micro-inverter, racking hardware, wiring, and a utility disconnect.
How many solar panels does a house need?
| Home size | Monthly kWh | Panels (400W) | System size |
|---|---|---|---|
| Small (1,000–1,500 sq ft) | 500–700 | 12–18 | 4.5–7 kW |
| Medium (1,500–2,500 sq ft) | 700–1,100 | 18–28 | 7–11 kW |
| Large (2,500–3,500 sq ft) | 1,100–1,500 | 28–38 | 11–15 kW |
| Very large (3,500+ sq ft) | 1,500+ | 38+ | 15+ kW |
Assumes 5 peak sun hours/day and 20% system losses. Sunnier regions (Southwest) need 20% fewer panels; cloudier regions (Northwest) need 30% more.
Solar panel cost breakdown
| Component | % of total | What's included |
|---|---|---|
| Panels | 25% | Modules (monocrystalline most common) |
| Installation labor | 30% | Licensed electrician + roofers |
| Balance of system | 25% | Racking, wiring, disconnects |
| Inverter | 10% | String or microinverters |
| Permits & inspection | 10% | Permitting, interconnection, utility fees |
The US national average is $2.75 per watt installed. A 6 kW system costs $16,500 before incentives, or $11,550 after the 30% federal tax credit. Costs range from $2.25/W in low-cost states to $3.50+/W in high-cost areas.
Federal solar tax credit (ITC)
30% Investment Tax Credit available through 2032. Claim it by filing IRS Form 5695 with your tax return. You must own the system (not lease or PPA) and have enough tax liability.
Step-down schedule:
- 2022–2032: 30% credit
- 2033: 26% credit
- 2034: 22% credit
- 2035+: credit expires for residential installations
Unused credit rolls forward to future tax years. Many states and utilities offer additional rebates and SRECs (solar renewable energy credits) that stack on top.
Solar payback period
payback years = net system cost ÷ annual savings
The US national average payback period is 7–12 years. Fast-payback states (5–8 yrs): HI, CA, NY, MA — high electricity rates. Moderate (8–12 yrs): NJ, CT, MD, AZ, NV. Slow (12–15+ yrs): LA, WY, AR, KY — cheap power. After payback, the remaining 15–20 years of the system's life produce essentially free electricity.
Net metering explained
Net metering lets you sell excess solar production back to the utility at (or near) retail rate. When your panels produce more than you're using, the meter runs backward; when you need grid power, it runs forward. At month's end you pay only the net. 1-to-1 net metering (best): full retail credit. Net billing (common): wholesale rate credit (30–60% of retail). California switched to NEM 3.0 in 2023 with much lower export rates. Check your state's policy — it dramatically affects solar economics.
Panel efficiency and types
| Type | Efficiency | Cost/W | Best for |
|---|---|---|---|
| Monocrystalline | 20–22% | $2.75–$3.50 | Most efficient; sleek black; best for small roofs |
| Polycrystalline | 15–17% | $2.25–$2.75 | Cheaper upfront; blue hue; needs more roof space |
| Thin-film | 10–13% | $1.75–$2.50 | Flexible; lightweight; best for commercial/RV |
Factors that affect solar production
- Shading — even partial shade on one panel can reduce production across a string. Microinverters or power optimizers help isolate shaded panels.
- Roof orientation — south-facing is best in Northern Hemisphere; east/west loses ~15–20%.
- Tilt angle — optimal equals your latitude; most rooftops at 18–34° are close enough.
- Weather & climate — cloud cover reduces peak but not eliminated; snow briefly blocks panels.
- Temperature — panels are actually more efficient in cold weather; extreme heat reduces output ~10%.
- Age & degradation — panels lose ~0.5%/year; at 25 years they still produce ~87% of new output.
- System losses — inverter, wiring, dirt, mismatch: plan on 15–25% loss between panel rating and actual AC output.
Frequently asked questions
How many solar panels do I need for my house?
Most US homes need 15–25 panels (5–10 kW system). Calculation: monthly kWh ÷ 30 days ÷ peak sun hours ÷ (1 − 20% losses) = system kW. At 400W panels, a home using 900 kWh/month in a 5-hour-sun region needs about 22 panels / 8.9 kW. Use our calculator for a precise estimate based on your bill and location.
How much do solar panels cost?
The US national average is $2.75/watt installed, or $16,500 for a 6 kW system before incentives. After the 30% federal tax credit, net cost drops to about $11,550. Costs vary by state: $2.25/watt in low-cost states (TX, FL, AZ), $3.50+/watt in high-cost areas (NY, CA, MA). Total cost for a full house system typically runs $15,000–$30,000 before incentives.
What is the federal solar tax credit?
The federal Investment Tax Credit (ITC) is 30% of your solar installation cost — available through 2032. In 2033 it steps down to 26%, then 22% in 2034. To claim: install the system, file IRS Form 5695 with your tax return. You must own the system (not lease) and have tax liability to claim. Unused credit can be rolled forward to future years. State credits and rebates may stack on top.
How long do solar panels last?
Modern solar panels last 25–30 years. Most manufacturers offer a 25-year performance warranty guaranteeing at least 80–85% of original output at year 25. Actual degradation is about 0.5% per year, so at 25 years, panels still produce ~87% of original output. Inverters typically need replacement around year 10–15 ($1,500–$3,000). Panels themselves rarely fail outright — they just slowly lose efficiency.
How much can I save with solar panels?
Average US homeowner saves $1,200–$2,500/year on electricity. Over 25 years (with 3% annual rate increases), total savings typically range $40,000–$90,000. Savings depend on: your electric rate (higher rate = more savings), system size, local sun, and net metering policy. Homes in CA, MA, NY, and HI save the most because of high electric rates. Factor in the tax credit and payback typically hits at 7–12 years.
What is the payback period for solar?
Most solar systems pay for themselves in 7–12 years. Formula: net cost after incentives ÷ annual electricity savings = years. Example: $15,000 net cost ÷ $1,800/yr savings = 8.3 years. Fast-payback states (5–8 years): HI, CA, NY, MA — high electricity rates. Slow-payback states (12–15+ years): LA, WY, AR — cheap power. After payback, you have 15–20 years of essentially free electricity.
Do solar panels work on cloudy days?
Yes, solar panels still produce 10–25% of peak output on cloudy days (diffuse light still reaches panels). Even on overcast winter days, production continues, just reduced. Snow briefly blocks panels but slides off tilted arrays quickly. Annual production figures already account for cloudy and rainy days — the peak sun hours number (e.g., 4.5 hrs/day) is an all-weather average over the year.
What direction should solar panels face?
In the Northern Hemisphere, panels should face due south for maximum annual production. South-facing produces 100% of the rated output; southeast or southwest produces ~92–95%; east or west about 80–85%; north-facing is not recommended (produces only 50–60%). If your roof isn't south-facing, solar can still work — it just needs more panels to produce the same kWh.
What is the best angle for solar panels?
The optimal year-round tilt angle equals your latitude. For New York (40.7°N), use 40° tilt; for Miami (25.8°N), 26°. For seasonal optimization: summer = latitude − 15°, winter = latitude + 15°. Most rooftops have fixed tilt dictated by roof pitch (usually 4/12–8/12, or 18–34° — close enough to optimal for most of the US). Adjustable ground mounts gain 5–10% annual production.
Is solar worth it in my state?
Solar is most financially attractive in states with: (a) high electric rates, (b) good sun, (c) strong net metering. Best ROI: CA, HI, MA, NY, NJ, MD, RI, AZ, NM. Moderate: TX, FL, CO, IL, OH, NC, VA, OR. Lowest ROI: LA, WY, AR, KY, ND, WV (cheap power + weaker incentives). Even in 'worst' states, solar still pays back within the system's lifetime — just slower. Check your state's solar incentives database (DSIRE) for specifics.