How to Read a Solar Proposal Without Getting Lost

The Proposal Isn't as Complicated as It Looks

Most solar proposals are long because installers include a lot of marketing material. The actual decision comes down to a handful of numbers. Here's how to find them.

The Three Numbers That Matter

• System size (kW): How much power the system generates at peak. A typical home needs 6–12 kW.
• Annual production (kWh): How much electricity the system will produce per year. Compare this to your current annual usage from your utility bills.
• Net cost after incentives: The price after the 30% federal ITC and any state credits. This is your real out-of-pocket number.

Production Estimates: How Reliable Are They?

Installers use software (PVWatts, Aurora, Solargraf) to model your roof's production. These estimates are generally accurate within 5–10%, but ask:

• What weather data source did you use?
• Does the estimate account for shading from trees or neighboring structures?
• What degradation rate did you assume? (Panels lose ~0.5% efficiency per year.)

Equipment: What to Look For

• Panel brand and wattage: Tier-1 manufacturers (Qcells, REC, Panasonic, SunPower) carry better warranties and more reliable performance data.
• Inverter type: Microinverters (Enphase) or power optimizers (SolarEdge) perform better in partial shade. String inverters are cheaper but less flexible.
• Warranty terms: Look for 25-year panel performance warranty and at least 10-year product warranty.

Red Flags in a Proposal

• No shading analysis included
• Production estimate that perfectly offsets 100% of your usage (suspiciously round numbers)
• Pressure to sign before the proposal expires
• No itemized equipment list

Get at Least Three Quotes

Prices vary significantly between installers — sometimes by 20–30% for equivalent systems. Bestin.Solar connects you with multiple vetted installers so you can compare apples to apples.