Proposal A sales model
Proposal B sales model
| Review reference | Proposal A | Proposal B |
|---|---|---|
| Headline projected savings | $120,000 / 25 yr | $95,000 / 25 yr |
| Simple average headline claim / year | $4,800/yr | $3,800/yr |
| Proposal utility escalation | 4.00%/yr | 2.50%/yr |
| Gross no-solar utility baseline | $109,945 | $90,176 |
| Independent reference utility baseline | $90,176 | $90,176 |
| Proposal baseline vs reference | +$19,769 | +$0 |
| Claim share of gross baseline | 109% | 105% |
| Final-year average monthly bill | $564/mo | $398/mo |
| Escalation needed for gross baseline to reach claim | 4.64%/yr | 2.90%/yr |
The independent reference row applies the same 2.50%/yr escalation to the same current utility bill, but still uses each proposal's own savings horizon. The simple average headline claim divides claim dollars by years; it is a normalization reference, not annual cash flow.
Review before treating either savings number as comparable
- The proposals differ by 1.50 percentage points in annual utility escalation. That difference can materially change the modeled no-solar baseline over a long horizon.
- This comparison does not select a better installer or validate either savings forecast. Compare production, export compensation, financing, fixed charges, degradation, maintenance and the proposal's definition of savings separately.
Questions to ask both installers
These questions are generated deterministically from the numbers above and from common assumptions that a long-term savings model must define. They do not accuse or certify either installer.
- What exact starting utility bill or electricity rate does each savings model use, and how does it compare with my current average bill of about $220/month?
- Why do the proposals use different annual utility-rate escalation assumptions, and what source and date supports each rate? The current gap is 1.50 percentage points.
- Can you rerun the savings model using the same 2.50%/yr utility escalation reference for both proposals while keeping the other assumptions unchanged?
- How does the model handle fixed utility charges, minimum bills, time-of-use rates and other charges that may remain after solar is installed?
- How are exported solar kWh valued over time, and what current tariff, net-metering or net-billing rule is used for that assumption?
- What first-year solar production is assumed, what production model produced it, and what annual panel degradation rate is applied afterward?
- Does the headline savings number include tax incentives, financing cash flow, interest, dealer fees, maintenance, inverter or battery replacement, roof work, taxes, home-value changes or any benefit other than avoided utility purchases?
- Proposal A's stated savings exceed the simple gross no-solar utility baseline under its entered assumptions. What additional benefits or avoided costs are included in the savings definition, and can you itemize them separately?
- Proposal B's stated savings exceed the simple gross no-solar utility baseline under its entered assumptions. What additional benefits or avoided costs are included in the savings definition, and can you itemize them separately?
- Can you provide the year-by-year savings or cash-flow table behind the headline total instead of only the cumulative 20-, 25- or 30-year number?
- Which parts of the savings projection are contractual guarantees, if any, and which parts are estimates or assumptions that can change?
Why the same house can get very different savings headlines
Two proposals can use the same roof and still display very different long-term savings. One model may use a longer projection horizon, a faster annual utility-rate increase, different export compensation, different production degradation or a different definition of what counts as “savings.”
This comparison intentionally holds the current utility bill constant so the horizon and escalation assumptions remain visible. It does not attempt to recreate either installer's full proprietary cash-flow model.
What the independent comparison escalation does
The editable independent escalation applies the same annual utility-rate growth assumption to the same current bill for both proposals. Each proposal still keeps its own stated savings horizon, so the reference baseline answers a narrow question: how much of the difference in the proposal's gross no-solar utility baseline comes from using its own escalation instead of one shared scenario?
The Simple average headline claim / year is also only a normalization reference: stated savings divided by the stated number of years. It is not annual solar cash flow, and a proposal with uneven year-by-year savings should not be treated as if that average occurs every year.
Do not compare $120,000 over 30 years with $90,000 over 20 years as a simple $30,000 gap
When the projection periods are different, Home Solar Atlas withholds the headline savings-dollar difference. A longer horizon naturally creates more years in which avoided utility purchases or other modeled benefits can accumulate.
Solar savings comparison FAQ
Why can two solar proposals show very different 25-year savings estimates?
The proposals may use different starting utility bills or rates, annual utility-rate escalation, production forecasts, degradation, export compensation, financing, maintenance assumptions or definitions of savings. A different projection horizon can also change the headline total substantially.
Should I compare two solar savings headlines if the projection horizons are different?
Not as a simple dollar difference. A 30-year projection has ten more years to accumulate modeled benefits than a 20-year projection. Home Solar Atlas withholds the direct headline difference when the horizons do not match and instead keeps the horizons visible.
What is utility-rate escalation in a solar savings estimate?
It is an assumption about how quickly the modeled no-solar utility rate or bill increases each year. Because that baseline compounds over decades, the escalation percentage can materially change the cumulative avoided-utility-cost story. It is an assumption, not a guarantee that electricity prices will rise at that exact rate.
Does using one shared utility escalation make two solar proposals fully comparable?
No. A shared escalation reference isolates one important assumption, but the proposals can still differ in production, export credits, fixed charges, degradation, financing, incentives, maintenance and the definition of savings. Use the shared reference as a sensitivity check, not a complete model reconciliation.
Are installer solar savings projections guaranteed?
A projection by itself is not a guarantee. Only specific contractual language can establish a guarantee or remedy. Review the original proposal and contract to distinguish modeled estimates from any expressly guaranteed performance or savings terms.
What still needs separate verification
- First-year solar production and the production model used for the roof.
- Panel degradation and inverter or equipment replacement assumptions.
- Fixed utility charges and time-of-use billing.
- Export compensation, net billing or net-metering rules.
- Cash price, financing costs, lease/PPA payments and any escalator.
- Maintenance, taxes, incentives and any home-value assumption included in the proposal.