The salesperson sits at your kitchen table, spins a laptop around, and shows you a chart: "You will save $47,000 over 25 years." The number glows. It feels specific. But behind it are assumptions about your electricity usage, your utility's future rate increases, panel degradation curves, and whether you actually qualify for every incentive in the model. Change any one of those inputs and the savings number reshapes dramatically. That projection is not a lie, exactly. It is a forecast built on optimism — and you are the one signing the contract.

Beneath the savings pitch sits a hardware and installation quote. That is where the real money decisions live, and it is where this guide focuses.

Cost per watt: the only number that matters for comparison

Every solar proposal lists a system size in kilowatts (kW) and a total price before incentives. Divide the total price by system size in watts. That gives you cost per watt ($/W) — the single metric that allows a genuine apples-to-apples comparison across installers, regardless of how they format their proposals or structure their financing.

2025 benchmarks: Residential solar in the US averages $2.50-$3.50/W before the federal tax credit, depending on region and equipment tier. A proposal at $4.00+/W for a standard rooftop system with no battery storage needs justification — premium panels, complex roof geometry, or main panel upgrades. Without one of those factors, you are overpaying.

If the proposal does not show a $/W figure, calculate it yourself. Takes ten seconds. Installers who obscure this number are usually above market and hoping the monthly-payment framing keeps you from noticing.

System sizing: oversized systems cost you money upfront

A system sized at 120% of your annual consumption sounds like smart headroom. In practice, it means you are buying panels whose extra production you may never capture — unless your utility's net metering policy is generous enough to make the math work. Often, it is not.

  • Check your utility's net metering policy. Full retail credit (1:1) makes oversizing less painful. Avoided-cost credit (wholesale rate, often $0.03-$0.05/kWh) means every excess kWh you export earns a fraction of what you paid to generate it. At those rates, oversizing is just buying expensive electrons for your utility.
  • Match the design to your actual usage. Ask the installer which 12 months of electricity bills they used for sizing. If they used a "standard home profile" instead of your real consumption data, the system size is a guess dressed up as engineering.
  • Watch for round-up sizing. An installer might size you at 8.4 kW but propose a 9.6 kW system because it fills the roof with a clean grid of 24 panels. Aesthetically tidy. Financially, that extra 1.2 kW costs $3,000-$4,200 and may not produce proportional savings.

Panel and inverter selection: tier matters

"400W panels" is not a spec. It is a category. A proposal that stops there — no manufacturer, no model, no efficiency rating, no warranty terms — is incomplete in a way that should make you uncomfortable, because you are committing to equipment that will sit on your roof for a quarter century.

What a complete spec looks like: "24x REC Alpha Pure-R 430W (10.32 kW), 22.3% efficiency, 25-year product warranty, 92% output guarantee at year 25. Inverter: Enphase IQ8M microinverters, 25-year warranty."

Panels from Tier 1 manufacturers (REC, LG, Panasonic, Canadian Solar, Qcells) carry bankable warranties because the companies behind them are financially stable enough to honor claims two decades from now. But be careful with that label. The Bloomberg Tier 1 list is based on bankability, not panel quality, and some low-quality manufacturers have landed on it. A brand you have never heard of calling itself "Tier 1" tells you nothing useful.

Red flag: A proposal that does not name the panel manufacturer and model number is hiding the equipment tier. Budget panels with shorter warranties, faster degradation, or both — that is what vague specs typically conceal.

Battery storage: separate the value from the upsell

Batteries are the most emotionally compelling part of a solar proposal. Backup power during outages. Energy independence. The pitch practically sells itself. But "makes sense for peace of mind" and "makes sense financially" are two very different claims, and the installer is counting on you not to separate them.

  • Cost per kWh of usable storage is the comparison metric. A Tesla Powerwall 3 at ~$12,500 installed with 13.5 kWh usable capacity costs ~$926/kWh. An Enphase IQ Battery 5P at ~$6,000 installed with 5 kWh usable costs ~$1,200/kWh. Bigger batteries have better unit economics.
  • Backup vs. arbitrage. If your utility has time-of-use rates with a spread of $0.15+/kWh between peak and off-peak, batteries can genuinely pay for themselves through rate arbitrage. If your rates are flat, a battery is an insurance policy against outages — not a savings device. Price it accordingly.
  • Warranty cycles. Most battery warranties guarantee 70-80% capacity after 10 years or a specific number of cycles (typically 4,000-6,000). Daily cycling burns through 3,650 cycles in a decade. If your intended use pattern exceeds the warranty's cycle count, the guarantee expires before the timeline does.

Dealer fees, adders, and the gap between gross and net cost

Every solar proposal shows two numbers: the gross cost and the net cost after the 30% federal Investment Tax Credit. The space between them is where fees hide — charges that inflate the gross cost before the incentive calculation, quietly making the system more expensive while the net number still looks reasonable.

  • Dealer fee / origination fee — If financing through the installer's lending partner, a dealer fee of 15-30% may be baked into the loan. A $30,000 system financed with a 25% dealer fee means you are actually paying $37,500. That "low monthly payment" the salesperson highlighted? It hides a $7,500 fee.
  • Permit and interconnection fees — Legitimate costs, usually $500-$1,500. But they should be itemized, not folded into the equipment cost where they inflate the per-watt figure without explanation.
  • Roof warranty exclusion — Some installers void your existing roof warranty by drilling through the membrane. Others use ballasted or rail-less mounts that preserve it. The proposal should specify which approach is planned and whether roof leak coverage is included for the life of the system. If it does not, ask — because a new roof costs more than the solar panels sitting on it.
Red flag: Any proposal that shows a monthly payment without disclosing the total financed amount, APR, loan term, and dealer fee is engineered to sell on cash flow, not on value. Demand the total cost of ownership over the loan term and compare it to a cash purchase price. The gap will tell you exactly how much convenience is costing you.

Production guarantees and what happens when panels underperform

Most installers include a first-year production estimate measured in kWh. Some guarantee it. That distinction is the difference between a contractual commitment and a marketing slide.

Ask specifically: "If the system produces less than the estimated kWh in year one, what is the remedy?" A production guarantee means the installer compensates you — credit, check, or additional panels. A production estimate with no guarantee means the number carries zero contractual weight. It is a projection, not a promise.

Check the irradiance data source, too. Proposals generated from satellite-based design tools (Aurora Solar, Helioscope) with site-specific shade analysis are generally reliable. Proposals built on "regional averages" are guessing — and your north-facing dormer or neighbor's oak tree is not part of the average.

What to do before you sign

Get three proposals. Compare them on $/W before incentives, equipment specs, warranty terms, and total financed cost. The 25-year savings projections? Ignore them. They depend on utility rate assumptions that no one — not the installer, not the utility, not the regulators — can reliably predict over that horizon.

The proposal that deserves your signature is the one that shows its work: named equipment, transparent fees, honest sizing, and a production guarantee with teeth. Everything else is presentation.

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