“Save $85 a Month, Every Month”
You'll see them in solar ads constantly: specific monthly savings numbers. “Save $85 a month.” “Cut your bill in half.” “Save $1,000s every year.” The specificity is the point. Concrete numbers feel verifiable in a way vague promises don't. They feel responsible, even understated.
They aren't data. They're cohort averages dressed up as personal forecasts.
Any savings number a solar ad shows you is the output of a model with inputs. Those inputs include: system size in kilowatts, household consumption pattern (annual kilowatt-hours and time-of-day distribution), utility rate schedule, time-of-use exposure, the utility's compensation policy for solar exported back to the grid, the system's financing structure, the assumed annual escalator on utility rates, the assumed annual degradation on the panels, and the system's assumed lifespan. Change any one of those inputs and the savings number moves — sometimes by a lot.
The savings claim is real for someone. It's the average of a specific cohort: a particular system size, on a particular utility, in a particular state, under a particular rate structure, for a particular household consumption pattern. The ad doesn't tell you what cohort. It tells you a number and lets you assume the number applies to you.
Austin makes this worse than most markets. The local utility, Austin Energy, doesn't use net energy metering (NEM) the way California and most other sun-belt utilities do. Instead, Austin Energy compensates customer-exported solar at the Value of Solar (VoS) tariff — a per-kilowatt-hour rate set by AE that's typically lower than the retail rate you pay for grid electricity. So a “save $85 a month” claim generated on California NEM math doesn't apply to an Austin homeowner under VoS. The Austin homeowner's monthly savings would be smaller — sometimes materially — because the export side of the math is structurally different.
There's a regulatory backdrop. The FTC requires substantiation for any specific quantitative claim in advertising — the advertiser has to be able to demonstrate the claim is true for the average consumer who would reasonably interpret it. In practice, savings claims survive substantiation by being narrowly true for the cohort the advertiser modeled, with the broader applicability buried in disclaimers most readers don't open. Technically defensible. Functionally misleading for the customer evaluating their own situation.
We don't quote specific monthly savings numbers in our ads. Not because we're allergic to math — the math is the whole point — but because we can't responsibly tell you what your savings will be without seeing your bill, your roof, your rate schedule, and your consumption pattern. The proposal is the answer. Our proposal includes the inputs and the assumptions, so you can see exactly what we modeled and push back on any of it. An ad number is a forecast for a household that isn't yours.
When a specific number is useful and honest
Specific savings numbers carry real information in a few places:
In a proposal tailored to your home, where the inputs are visible: your bill history, your roof's estimated solar production, your specific utility rate schedule, the assumed escalator, the assumed degradation. You can see the assumptions and push back on them.
In testimonials from named customers describing their own systems, with enough context — system size, utility, system age, household profile — that you can compare to your situation.
In academic or market research reports about cohort averages, when honestly framed as cohort averages and not as personal forecasts.
In utility-published incentive documentation, like Austin Energy's residential solar rebate eligibility and payment schedule. The utility's own numbers are the utility's own numbers — no extrapolation, no modeling, no cohort.
If a competitor's ad has gotten you anchored on a specific savings number — “$85 a month,” “save $1,000s,” “cut your bill in half” — the question to ask the salesperson is the one their ad is structured not to surface: what household, what system size, what utility, and what rate schedule generated that number — and how do those inputs compare to mine? If the salesperson can't show you the model, the number was for someone else's house.