Residential Solar, Properly Explained

1. What "residential solar" actually is

A residential solar system is roughly five components: modules (the panels on your roof), racking (the aluminum hardware that holds them down and resists wind uplift), an inverter or set of inverters (which convert DC from the panels into the 240V AC your house uses), a monitoring system (so you can see what each panel is producing), and the balance-of-system: conduit, wire, the rapid-shutdown device required by NEC 690.12, the production meter, and the interconnection to your main panel.

A typical 2026 install is 16–22 panels in the 400–450W range, totaling 7–10 kW DC. That covers roughly 80–110% of the U.S. average home's 10,500 kWh/year usage (EIA Residential Energy Consumption Survey 2024). Modules carry a 25-year performance warranty (typically 86% retained output at year 25); inverters carry 10 years for string-style or 25 years for microinverters.

2. How a PV system actually works

Photovoltaic cells are silicon wafers doped with phosphorus on one side and boron on the other. When a photon with enough energy hits the cell, it knocks an electron loose; the dopant junction creates an electric field that drives the freed electron through an external circuit. That's it — sunlight directly displaces an electron. No moving parts, no fuel, no maintenance other than occasional cleaning if you live somewhere dusty.

Each cell produces about 0.6V at low current. 60–72 cells wired in series form a panel ("module") at 30–40V open circuit, ~400W peak. Panels are wired in series into strings (boosting voltage to 400–600V for the inverter input) or paralleled at lower voltage if you use microinverters. The inverter handles maximum power point tracking, anti-islanding (it disconnects in milliseconds if the grid goes down, per UL 1741), and DC-to-AC conversion at 96–98% efficiency.

3. How to size your system

Pull your last 12 months of electricity bills. Add up annual kWh. Divide by your state's specific yield (kWh per kW DC per year — varies from ~1,100 in Washington to ~1,700 in Arizona; see NREL PVWatts for your ZIP). The quotient is the kW DC you need to offset 100%.

Example: a Massachusetts home uses 11,000 kWh/year. MA specific yield ≈ 1,300 kWh/kW/yr. 11,000 ÷ 1,300 = 8.5 kW. Round up to 9 kW for a small reserve, or down to 7.5 kW if your utility's NEM successor pays poorly for exports (more on that below).

Two common sizing mistakes: (1) under-sizing to chase the lowest sticker price, then realizing you bought a system that meets 60% of your needs and discovers a heat pump or EV is coming next year, and (2) over-sizing past 110% on net-metering-successor tariffs where exports earn 4–6¢/kWh instead of retail. The calculator on this page warns when you're sized past 110% of stated usage.

4. Inverter architecture — string, optimizer, or microinverter

String inverters (SMA, Fronius, Sungrow) are one centralized box, usually wall-mounted near the main panel. Cheapest at the bid line. Trade-offs: any shaded or dirty panel drags the whole string down, and one inverter failure takes the entire array offline.

DC optimizers (SolarEdge) put a small power-electronics box behind each panel that does per-panel maximum power point tracking, then feeds a centralized string inverter. Shade-tolerant; per-panel monitoring. Costs about $0.10/W more than a plain string system.

Microinverters (Enphase IQ8) put a full grid-tied inverter behind each panel. Each panel is its own independent AC source. Most shade-tolerant; longest warranty (25 yr); easiest expansion later. Costs about $0.20/W more — roughly $1,400 on a 7 kW system. If your roof has any shade at all, or you plan to add a battery later (Enphase's ecosystem integrates tightly with their IQ Battery), microinverters typically pay for themselves through better lifetime production.

5. The net-metering successor problem (CA NEM 3.0 and friends)

For 25 years residential solar economics rested on net metering: any kWh your system exported to the grid earned the same retail rate as the kWh you imported at night. That was the deal in nearly every state.

That deal is ending. California moved to NEM 3.0 in April 2023, paying exports at the Avoided Cost Calculator rate (4–8¢/kWh, time-varying) instead of the 25–55¢/kWh retail rate. Massachusetts SMART, New York Value of Distributed Energy Resources (VDER), Arizona's export rate, and Hawaii's Customer Self-Supply program all moved similarly. The mechanics differ but the direction is the same: exports are worth dramatically less than imports, which makes solar-only systems less attractive in those states and makes paired battery storage essential to recover the previous economics.

Practical implications: in NEM 3.0 states, size for self-consumption (60–80% of annual use) rather than 100% offset. Add a battery to time-shift midday production into evening peak hours. Ask your installer specifically which tariff your system will be enrolled under, and have them model production hour-by-hour against your load shape — not just annual offset percentage.

6. Should you add a battery?

Three reasons to add a battery:

1. Resilience. Your roof solar disconnects during a grid outage unless you have a battery (or a grid-forming inverter with manual transfer switch). A 13.5 kWh Powerwall-class system carries an average home through 12–24 hours of essentials.
2. NEM successor economics. In CA NEM 3.0 territory, storing midday excess and discharging at the 4–9pm peak captures the retail-rate import you'd otherwise pay, instead of accepting a 5¢/kWh export.
3. Time-of-use arbitrage. In states with steep TOU rates (CA, MA, AZ, FL), a battery can save $400–$800/year just by shifting consumption from peak to off-peak windows.

Cost: a Powerwall-3 (13.5 kWh, integrated inverter) installs at $13,000–$17,000 in 2026. Enphase IQ Battery 5P comparable. The federal 25D credit covers 30% of battery cost including labor for standalone storage ≥3 kWh — that's a meaningful change post-IRA. Payback on the battery alone is 7–15 years depending on tariff structure; resilience value is harder to quantify but matters in hurricane and wildfire regions.

7. What it actually costs in 2026

Here's how the per-Watt math works. LBNL's Tracking the Sun 2024 reports a median installed cost of $3.40/W for residential PV, with the 20th percentile at $2.70/W and the 80th at $4.30/W. EnergySage's Q4 2024 marketplace median was $2.92/W. NREL's 2024 benchmark study for a 7.15 kW residential system was $3.06/W modeled cost.

Component shares (NREL 2024 benchmark): modules 14%, inverter 9%, racking + balance-of-system 14%, installation labor 7%, permitting + interconnection + inspection 8%, sales + marketing + overhead + profit 48%. That last category is why high-pressure sales operations charge $4.50+/W on systems that should be $3.00/W — door-knock and lead-gen costs land in your contract.

Concrete examples (mid-band, before incentives):

• 7 kW simple shingle roof in Texas: ~$22,000 gross → ~$15,400 net after federal 25D.
• 9 kW complex multi-plane shingle roof in Massachusetts: ~$33,000 gross → ~$23,100 net.
• 10 kW tile roof in California with shade: ~$42,000 gross → ~$29,400 net.
• 12 kW ground mount in upstate New York with one Powerwall: ~$55,000 gross → ~$38,500 net plus an NY-Sun upfront payment.

8. How to read a solar bid without getting taken

Get 3 quotes from independent local installers, not door-knockers. Compare line-by-line:

• $/W installed. Total contract price divided by DC kW × 1,000. The number that matters. National median is $2.90–$3.40/W; anything over $4.50/W needs a justification.
• Module make and model. Tier-1 brands (Q-Cells, Silfab, REC, LG (residual), Panasonic (residual), Hyundai, Trina). Avoid no-name modules — warranty is only as good as the company surviving 25 years.
• Inverter type and warranty. Confirmed in writing. String 10-yr, microinverters 25-yr.
• Production estimate in kWh/year with an explicit performance guarantee (e.g., "We guarantee 11,500 kWh in year 1, with degradation per panel warranty"). Reject vague "save up to X" pitches.
• Roof penetration warranty. Separate document covering leaks from racking attachments. 10-yr workmanship is standard.
• Critter guard (mesh under the array perimeter). Squirrels chew DC wire. Get this included.
• Tariff enrolled. Which net-metering successor program your interconnection paperwork will file under, and the per-kWh export rate.
• Main service panel work. Many systems need a 200A panel and a load-side breaker; verify your existing panel supports the back-feed breaker per NEC 705.12.
• Sales pressure. If they want a same-day signature, walk. Reputable installers give you 30 days to decide.

For the federal 25D credit, save: the installer's invoice with cost breakdown, the permission-to-operate (PTO) letter from your utility, and the IRS Form 5695 prepared for the tax year you got PTO (not the year you signed the contract). The credit is non-refundable but unused portion carries forward.