After reviewing hundreds of solar proposals on behalf of commercial and institutional clients, we've identified the issues that appear most often — and that cost property owners the most money when they go unnoticed. Here are the five red flags to look for before signing anything.
Production estimates based on industry averages, not your actual data
A credible proposal should be built on your 12-month utility interval data and a site-specific solar resource analysis (typically from NREL's PVWatts or equivalent). If an installer is quoting production numbers without having seen your utility bills or run a shading analysis, the estimate is a guess. Overestimated production is the single most common source of disappointment in solar projects.
Payback period calculations that ignore NEM 3.0
Any proposal for a new California solar installation that doesn't explicitly address NEM 3.0 export rates is either outdated or misleading. Under NEM 3.0, excess solar exported to the grid is compensated at roughly 5–8 cents per kilowatt-hour — not the retail rate. A financial model that uses retail rates for exports will dramatically overstate project returns.
System size that maximizes panels, not your return
Installers are paid per watt installed. This creates an incentive to recommend larger systems than your load profile justifies. The right system size is the one that maximizes your return on investment — which is often smaller than the maximum your roof can accommodate. Ask for the marginal return analysis: what does each additional kilowatt of capacity add to your savings versus its cost?
Vague or missing warranty terms
A complete proposal should specify: panel manufacturer warranty (typically 25 years product + 25 years performance), inverter warranty (typically 10–12 years, extendable), battery warranty (typically 10 years with a capacity retention floor), and workmanship warranty from the installer (minimum 10 years for commercial). Missing or vague warranty terms are a signal that the installer may not be confident in the equipment they're proposing.
No mention of interconnection timeline or utility approval
In San Diego, SDG&E interconnection approval can take 3–9 months for commercial systems. A proposal that doesn't address interconnection timeline, application fees, or potential upgrade requirements is incomplete. Some installers omit this because the timeline is long and the costs can be significant — but you need to know before you sign.
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The San Diego Solar Buyer's Checklist
Before you sign anything, read this. Our independent advisors put together the exact questions and red flags every property owner should know — completely free.
- Questions to ask every installer before signing
- How to spot inflated system size estimates
- What NEM 3.0 means for your payback period
- Red flags in financing and PPA agreements
- How to run a competitive bid process
- What independent consultants check that installers won't
- Key incentives available in California right now
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