Solar installation savings comparison tool

Comparing 20-year solar savings projections when installers use different utility rate escalation assumptions requires standardizing the data . Because a higher assumed utility inflation rate artificially inflates one installer's projected savings, you must strip away their unique inflation percentages and evaluate the systems under a common, realistic baseline.

Here is a step-by-step framework to normalize and compare the projections:

• Find the Year-1 Cost/Production Baseline : Look past the 20-year cumulative dollar savings and focus on Year 1. Compare the first-year solar production (in kWh), the estimated first-year bill with solar, and the offset percentage. If the first-year production estimates differ significantly for the same system size, ask the installers to justify their shading or efficiency assumptions.
• Isolate and Extract the Escalation Rate : Locate the specific percentage each installer used for annual utility rate increases (often ranging from 2% to 5% or more). Check the fine print of their proposals or ask them directly what rate they assumed.
• Apply a Standard Utility Escalation Rate : Recalculate (or ask both installers to run their models using) a single, neutral utility inflation rate across both proposals. A historical long-term average in the U.S. has typically hovered around 3% to 4% per year, though you can check your local utility's historical rate via the U.S. Energy Information Administration (EIA) data for greater accuracy.
• Account for System Degradation : Ensure both projections factor in solar panel degradation—the natural decrease in energy production over time, usually around 0.5% to 0.6% per year. If one installer assumes 0% degradation over 20 years, their production and savings numbers are over-optimistic.
• Compare Net Present Value (NPV) or True Cash Flow : Look at the cumulative out-of-pocket costs (loan payments or lease costs plus remaining utility bills) versus the status quo of paying the utility company entirely. Discounting future savings to present value (NPV) gives a clearer picture of what those future dollars are actually worth today.

Would you like help calculating a standardized 20-year projection if you share the:

• First-year utility bill or current electricity cost per kWh
• Proposed system costs and offset percentages from each installer
• Escalation rates they individually used

The fairest way to compare 20-year solar savings projections is to put every installer’s proposal through the same utility-rate assumptions, then compare both the standardized results and each installer’s original forecast.

A solar installer that assumes electricity prices will rise by 5% annually can show much larger lifetime savings than one assuming 2% annual increases, even if both proposals use the same solar panels, system size, and starting electricity rate. That difference doesn't necessarily mean one system is better; it may reflect different forecasts.

1. Standardize the assumptions before comparing proposals

Ask each installer to provide a 20-year cash-flow projection that separates the following inputs.

The key is to compare the same economic assumptions, not just the headline number labeled “20-year savings.”

2. Run three utility-rate scenarios

Rather than choosing whichever forecast sounds most convincing, ask every installer to run the same low, middle, and high scenarios. For example:

Low-growth scenario

1% annual utility-rate increase

Tests whether the investment still makes sense if electricity prices rise slowly.

Middle scenario

2.5% annual increase

Provides a common comparison benchmark, not a prediction or guarantee.

High-growth scenario

5% annual increase

Shows how much the economics depend on faster electricity price increases.

These are illustrative sensitivity scenarios, not forecasts for your particular utility. The Maryland consumer solar guide specifically recommends using a common utility escalation assumption to make competing bids easier to compare.energy.maryland.gov+1

3. See how much the assumption changes the numbers

Suppose your current electric bill is $200 per month, or $2,400 per year. The following example calculates the cumulative cost of utility electricity over 20 years if the entire annual bill grows at a constant rate.

Illustrative calculation: 20 annual bills starting at $2,400, with each year's bill increasing by the stated percentage. Figures rounded; no discounting or changes in electricity usage included.

That is a difference of roughly $26,300 in gross utility spending between the 1% and 5% scenarios. It is not a difference in solar savings: actual savings depend on how much grid electricity the solar system displaces, export credits, fixed charges, and system costs.

This illustrates why a large 20-year savings claim should never be evaluated without seeing the underlying rate assumption. The FTC warns that future utility rates are difficult to predict because many factors influence them.consumer.ftc.gov+1

4. Compare net savings, not just avoided utility bills

For each scenario, have every installer calculate:

\begin{aligned}
\text{Net savings} ={}& \text{Avoided utility costs}\\
&+ \text{Export credits}\\
&- \text{Solar system costs}\\
&- \text{Financing and upkeep costs}
\end{aligned}

Use a year-by-year cash-flow table and ask for cumulative net savings at years 5, 10, 15, and 20. If you are financing the system, include loan interest and payments; if you are leasing or using a power purchase agreement (PPA), include the payment schedule and any contractual escalator.

Also compare the assumptions that utility-rate standardization won't fix, especially system production, degradation, net-metering or export-credit rules, and the definition of savings. The Federal Trade Commission recommends comparing installation costs, ongoing fees, production expectations, warranties, and contract terms.energy.maryland.gov+2

5. Questions to ask every installer

You can use these questions directly when requesting revised proposals:

• What annual utility-rate escalation percentage did you use, and what evidence supports it?
• Can you rerun the full 20-year model at 1%, 2.5%, and 5% annual escalation, keeping the other assumptions constant?
• Does your savings figure subtract the complete system cost, loan interest, ongoing fees, and maintenance?
• Are future export credits, utility fixed charges, and solar production degradation included?
• Which numbers are contractual guarantees, and which are estimates?
• Can I see the year-by-year cash flows rather than just the headline savings figure?

For an independent starting point, the FTC's Solar Power for Your Home guide explains what to check in solar offers. You can also try this solar savings comparison tool to organize two proposals' stated escalation rates and projection horizons. Treat third-party calculators as screening aids, not validation of an installer's complete financial model.

Bottom line: Choose the proposal that offers the strongest economics under comparable assumptions and remains attractive under conservative scenarios—not necessarily the installer advertising the largest 20-year savings number.

Yes. There are calculators specifically designed to help homeowners compare solar installers’ long-term savings claims when they use different utility-rate inflation assumptions.

The key is to normalize every proposal to the same annual utility-rate escalation, over the same 20-year period, rather than accepting each installer's headline savings number at face value.

Best calculators I found

1. Solar Savings Claim Checker

(Best for your question)

Compares an installer's projected savings, projection period, and utility-rate escalation assumption against an alternative scenario. It is designed to expose how different assumptions inflate long-term savings claims.

Important limitation: it does not fully recalculate the installer's solar savings using the new inflation rate.

Open the calculator ·www.homesolaratlas.com

2. Compare Solar Savings Claims

Best when you have two or more quotes. Enter each installer's claimed savings, projection length, and annual utility escalation, then compare them against one common utility-bill baseline.

Open the comparison tool ·homesolaratlas.com

3. GoSolarVA Compare Quotes

Useful if you're comparing residential solar proposals in Virginia. It lets you compare system prices and production estimates using a shared utility-rate growth assumption, with modeled payback and long-term net benefit.

Open the calculator ·www.gosolarva.com

How to normalize 20-year savings estimates

Suppose two installers give you these estimates:

These are illustrative numbers, not actual quotes. Installer B's higher figure might partly reflect its more aggressive inflation assumption rather than a better solar system.

For a fair comparison:

1. Ask both installers to rerun their projections at the same utility-rate escalation, such as 2%, 3%, or 4% annually.
2. Keep system production, solar-panel degradation, export-credit rates, financing, and other assumptions consistent.
3. Compare net savings after system costs and financing, not just avoided utility bills.
4. Request a year-by-year cash-flow table so you can verify the 20-year totals.

One important distinction: simply adjusting a savings figure by the ratio of two inflation assumptions is not mathematically reliable. Utility-rate escalation compounds over time, and solar savings depend on production and the portion of your bill that solar actually offsets.

My recommendation is to start with the Compare Solar Savings Claims tool, then request recalculated projections from the installers using identical assumptions.

If you share the 20-year savings totals and annual utility inflation rates from your quotes, I can also help you work through a side-by-side normalization.