How can a homeowner compare 20-year savings projections from different solar installers that use different assumptions about utility rate increases?

Comparing 20-year solar proposals with conflicting utility escalation rates (r r𝑟) can feel like comparing apples to spaceships. Because a higher assumed utility inflation rate makes solar look artificially more valuable, you have to level the playing field by stripping out their specific inflation guesses and running the numbers through a single, independent baseline.

Here is how to do it step-by-step:

- Ignore the installer's projected "cumulative savings" headline. Instead, grab the raw, unadjusted numbers from each quote: the total cash price (or net loan principal), estimated Year 1 production (in kWh kWh k W h ), the degradation rate (usually 0.5% per year), and the initial solar rate or payment structure.

- Throw out the 4%, 5%, or 6% annual rate hikes the installers might be using. Pick a conservative, historically grounded baseline. Historically, US electricity rates have averaged around 2.5% to 3% per year, though regional data varies. Apply one single percentage (e.g., 3%) across all proposals as your uniform variable r baseline r sub baseline end-sub𝑟b a s e l i n e.

- Build or project a 20-year table for each installer using the formula for future utility cost without solar:  𝐶u t i l i t y(𝑡)=𝐶y e a r 1×(1+𝑟b a s e l i n e)𝑡−1
- Subtract the projected solar costs (loan payments, maintenance, or remaining grid electricity with solar) from that baseline for each year t t𝑡 from 1 1 1 to 20 20 2 0.

- A dollar saved in year 20 is worth less than a dollar saved in year 1 due to inflation and the time value of money. Apply a discount rate (i i𝑖, typically 3% to 5%, representing what that money could earn in a safe investment) to calculate the **Net Present Value (NPV)** of each system:  

N P V=∑2 0𝑡=1 N e t S a v i n g s𝑡(1+𝑖)𝑡 - Comparing the NPVs using the exact same discount and utility inflation rates gives you a true apples-to-apples financial comparison.

- Divide the total cost of the solar system (over 20 years, including financing) by the total kWh kWh k W h the system is guaranteed to produce over those 20 years.
- L C O E=T o t a l S o l a r C o s t o v e r 2 0 y e a r s T o t a l 2 0-y e a r k W h P r o d u c t i o n
- The installer with the lowest LCOE LCOE L C O E provides the cheapest energy, regardless of how fast utility rates rise.

If you'd like, you can share:

• The utility inflation rates used by each installer
• The Year 1 solar costs vs. projected grid costs

I can help you build a quick mathematical breakdown or formula comparison for your specific quotes.

The key is to stop comparing the installers’ headline 20-year savings numbers until you put them on the same assumptions. A proposal using a 5% annual utility-rate increase can look dramatically better than one using 2%, even if the solar systems themselves are identical.

A good apples-to-apples method

1. Ask every installer for the underlying assumptions, not just the final savings figure:

• Starting electricity rate ($/kWh)
• Annual utility-rate escalation (%)
• Expected annual solar production
• Panel degradation rate
• Self-consumption vs. exported energy
• Net-metering/export-credit assumptions
• System price and incentives
• Financing interest rate and term
• Maintenance/replacement costs
• Discount rate, if they calculate NPV
• Whether figures are nominal or inflation-adjusted

DOE specifically cautions that solar savings depend on local utility rates and compensation for excess generation, and NREL notes that future electricity-price escalation is highly uncertain. The Department of Energy's Energy.gov NREL 2. Normalize the utility-rate escalation. Have each installer rerun the proposal using the same escalation rate—for example, 2%, 3%, and 4% annually. That turns the disagreement over assumptions into a sensitivity analysis.

For example, if today's electricity cost is $200/month, a simple 20-year model would project roughly:

• 2% escalation: $297/month in year 20
• 3%: $348/month
• 4%: $421/month

Those differences compound, so they can overwhelm relatively small differences between solar proposals. 3. Compare cumulative savings under identical scenarios.

The installer whose economics remain attractive under the conservative scenario is generally more compelling than one that wins only under an aggressive rate-escalation assumption. 4. Separate “bill savings” from investment return. Ask for:

• 20-year gross utility-bill savings
• 20-year solar-system costs
• Net savings
• Payback period
• NPV
• IRR, if provided

DOE recommends considering the time value of money rather than relying solely on payback. The Department of Energy's Energy.gov 5. Make sure they're modeling the actual tariff. A flat $/kWh assumption can be misleading if your utility has time-of-use rates, fixed charges, or different compensation for exported solar. DOE recommends reviewing the actual utility rate and available rate options; NREL has likewise emphasized that the value of PV depends on the actual tariff structure.

One particularly useful question to ask installers

“Please give me the 20-year cash-flow spreadsheet and rerun it using 2%, 3%, and 4% annual utility-rate escalation, keeping every other assumption unchanged.” That makes it much harder for an installer to win the comparison simply by choosing an optimistic escalation rate.

Also ask them to identify which assumptions are guaranteed by the contract versus merely estimates. DOE recommends getting multiple installer assessments and carefully reviewing proposals and contracts rather than comparing headline prices alone.

Bottom line: compare the installers on a common base case + sensitivity range, rather than accepting each company's preferred 20-year rate-escalation assumption. The most useful comparison is often “What happens if electricity prices rise only 2% per year?”—not “Which installer predicts the biggest 20-year savings?”

Comparing 20-year savings projections from different solar proposals is notoriously tricky when installers use conflicting inflation or utility rate escalation assumptions. If Installer A assumes a 4% annual rate hike and Installer B assumes 2%, Installer A's 20-year savings will look vastly superior—even if their hardware and pricing are identical.

To compare them on a truly apples-to-apples basis, use this step-by-step framework:

1. Standardize the Utility Escalation Rate

• Normalization: Pick a single, independent escalation rate to use for both proposals. The historical average for U.S. electricity prices over the last 20–30 years generally hovers around 2.5% to 3.5% per year (though local rates vary).
• Adjustment: Recalculate both projections using your chosen unified rate (3% is a common benchmark). If an installer's software doesn't let you change it, manually calculate the projected grid costs year-by-year using the formula𝐹𝑢𝑡𝑢𝑟𝑒_𝐶𝑜𝑠𝑡=𝐶𝑢𝑟𝑟𝑒𝑛𝑡_𝐵𝑖𝑙𝑙×(1+𝑟)𝑛 (where r is your uniform rate and n is the year).

1. Calculate Net Present Value (NPV)

• Time Value of Money: A dollar saved in year 20 is worth significantly less than a dollar saved in year 1 due to inflation.
• Discount Rate: Apply a standard discount rate (typically 3% to 5%, reflecting a safe investment return or inflation) to future cash flows.
• Formula: Convert the 20-year stream of projected savings into an NPV calculation to see what those future savings are worth in today's dollars.

1. Isolate the Cost of Energy (Levelized Cost of Energy - LCOE)

• Metric: Divide the total cost of the solar system (over 20 years, including financing, maintenance, and incentives) by the total kilowatt-hours (kWh) the system is projected to produce.
• Comparison: This gives you an effective price per $kWh for each proposal ( /kWh ), completely stripping out utility inflation assumptions. The system with the lowest LCOE provides the cheapest energy, regardless of how fast utility rates rise.

1. Check Production Estimates vs. System Size

• Verification: Look at the first-year kWh production per watt of solar installed (kWh/kW). Some installers inflate savings projections simply by overestimating how much sunlight your roof gets or by oversizing the system relative to your actual usage.
• Consistency: Ensure both proposals are modeling similar annual degradation rates (standard solar panels degrade by about 0.5% to 0.7% per year).

Would you like me to help you set up a simple calculation template or do you want to share the specific escalation rates and numbers from your quotes to run a comparison?

A homeowner should compare solar proposals by normalizing the assumptions, not by comparing the headline “20-year savings” numbers. The biggest differences often come from assumptions about future utility prices, because higher assumed electricity inflation makes solar savings look larger.

A practical approach:

1. Ask each installer for the exact assumptions behind the projection

Request a copy of the proposal’s assumptions page or model inputs, including:

• Current utility rate ($/kWh)
• Annual utility rate increase (the “escalator”)
• Solar production estimate (kWh/year)
• Panel degradation assumption
• System size (kW)
• Upfront cost and incentives included
• Financing terms (loan rate, lease/PPA escalator, fees)
• Net metering or export credit assumptions

Installers can produce very different savings estimates because they may use different assumptions for electricity rates, system output, financing, and incentives.

2. Put every quote into the same utility-rate scenarios

Instead of accepting one installer’s rate forecast, run all proposals under identical scenarios, for example:

The math is usually compound growth:

Future electricity rate = Current rate × (1 + annual increase)ⁿ

A small difference in the assumed rate can create a large gap after 20 years.

Example:

• Current electricity rate: $0.15/kWh
• 20 years at 2% annual increases: about $0.22/kWh
• 20 years at 5% annual increases: about $0.40/kWh

The installer using 5% will generally show much higher “savings” than the installer using 2%, even if the solar systems are identical.

3. Compare “bill without solar” versus “bill with solar”

Ignore the savings percentage at first. Compare:

Without solar

• What the homeowner would pay the utility over 20 years under the same rate assumption

With solar

• Solar payment (if financed)
• Remaining utility bill
• Maintenance or replacement costs
• Any escalator in a lease/PPA

The difference is the actual economic benefit.

4. Create an apples-to-apples spreadsheet

Use columns like:

This shows whether one installer’s advantage comes from a better system or simply a more optimistic forecast.

5. Pay attention to financing type

A cash purchase, solar loan, lease, and power purchase agreement (PPA) are not directly comparable. A PPA or lease may look better if the model assumes high utility inflation, because the savings depend heavily on the gap between rising utility prices and the contracted solar price.

6. Use a neutral baseline

A good comparison is to ask:

“What are the 20-year savings if we use the same utility escalation rate for every installer?” For example:

• Installer A’s system using a 3% escalator
• Installer B’s system using a 3% escalator
• Same electricity usage
• Same incentive assumptions
• Same financing assumptions

Then you are comparing the solar offers rather than the sales forecasts.

A useful rule: treat any 20-year savings number as a scenario estimate, not a guarantee. The most important number to compare is how the proposal performs under conservative assumptions.

5. Pay attention to financing type

A cash purchase, solar loan, lease, and power purchase agreement (PPA) are not directly comparable. A PPA or lease may look better if the model assumes high utility inflation, because the savings depend heavily on the gap between rising utility prices and the contracted solar price.

6. Use a neutral baseline

A good comparison is to ask:

The key is to normalize the assumptions before comparing the 20-year savings numbers. Otherwise, you may be comparing an installer using a conservative 2% utility-rate increase with another using an aggressive 5%, even if the systems themselves are identical. Different rate assumptions can materially change projected 20–25 year savings.

A practical way to compare them

1. Get each installer's assumptions in writing.

Ask for:

• Current utility electricity rate ($/kWh)
• Annual utility-rate escalation (%)
• Annual household electricity consumption (kWh)
• Expected solar production in year 1 (kWh)
• Panel degradation rate
• Net-metering/export-credit assumptions
• Expected utility charges that remain after solar
• Incentives/tax credits included
• Financing costs and loan payments

2. Put every proposal under the same utility-rate scenarios.

For example, calculate 20-year savings at:

• 2%/year — conservative
• 3%/year — middle case
• 5%/year — optimistic

You don't have to decide which forecast is "correct." The point is to see whether Installer A still beats Installer B when both are subjected to identical assumptions.

As a benchmark, EnergySage currently uses a 2.8% annual electricity inflation assumption in one of its national savings estimates, while its marketplace says its standardized quote methodology uses state-level historical averages. EnergySage EnergySage 3. Separate the solar system's performance from the electricity-price forecast.

Suppose:

• Installer A: $55,000 projected 20-year savings at 5% rate growth
• Installer B: $45,000 projected savings at 2% rate growth

You can't conclude A is better. A may simply be assuming much more expensive electricity in the future.

Instead, hold the rate escalation constant and compare the systems. This lets you answer: "Which proposal produces more value if both face the same future electricity prices?" 4. Compare cumulative cash flows, not just the headline "20-year savings."

For each year, calculate approximately:

Net annual savings = avoided utility bill − solar payment − remaining utility bill/fees − other solar costs

Then add those yearly amounts together. This reveals whether a proposal has:

• a faster payback,
• higher long-term savings,
• large financing costs early on,
• or savings that depend heavily on optimistic assumptions.

5. Run a sensitivity analysis.

A simple comparison might look like:

The spread between scenarios is important. If A only wins when electricity prices rise 5% annually, while B wins at 2–3%, B may be the more robust investment.

Also watch for other assumption differences

Utility-rate escalation isn't the only way a proposal can make savings look better. Installers can use different assumptions for production, degradation, electricity consumption, SREC values, and other factors.

In particular, make sure you're comparing the same:

• System size and expected production
• Panel degradation
• Electricity consumption
• Net-metering/export compensation
• Battery assumptions, if applicable
• Federal/state/local incentives
• Loan interest rate and dealer/origination fees
• Maintenance/replacement costs
• Solar payment escalators, for a lease/PPA

For financed systems, compare the cash price, APR, fees, total payments, and payoff period, rather than focusing only on the advertised monthly payment. Financing costs can substantially alter the economics.

The best question to ask each installer

"Please rerun your 20-year savings projection using a 3% annual utility-rate increase, and provide the year-by-year cash flows and all other assumptions you're using." Then give every installer the same rate assumption and the same electricity-usage/production assumptions where possible.

That turns the exercise from "Which salesperson's spreadsheet has the biggest savings number?" into "Which solar system gives me the best economics under the same assumptions?"

Comparing 20-year savings projections with different utility escalation rates is tricky because higher utility inflation makes a solar proposal look artificially better just by assuming electricity gets more expensive faster.

To make an apples-to-apples comparison, you need to neutralize their assumptions, normalize the data, and run the math under a single, unified baseline.

Step 1: Extract the Core Variables

Look at each installer's proposal and pull out these 4 critical data points for the 20-year span:

• Gross System Cost & Net Cost: The price after incentives (like the federal tax credit).
• Year 1 Production (kWh): How much energy the system is expected to generate in the first year.
• Annual Degradation Rate (%): How much production drops each year (usually between 0.5% and 0.7% per year).
• Assumed Utility Escalator (%): The annual percentage by which they assume your electric company raises rates (e.g., 2.5%, 3.5%, or 4.0%).

Step 2: Normalize the Utility Escalator

Do not trust their projected dollar savings ($) at face value because they are using different inflation formulas. Instead, pick a single, realistic utility escalation rate for all of them.

• Historically, US residential electricity rates have risen about 2.5% to 3.5% per year on average, though local regions vary. Check your local utility's historical rate hikes over the last 10 years on the U.S. Energy Information Administration (EIA) data portal.
• Re-calculate (or ask each installer to provide) what the savings would be if they all used the exact same escalator (e.g., a conservative 3.0% per year).

Step 3: Calculate Net Present Value (NPV) or Cumulative Cash Flow

A dollar saved in Year 20 is worth less than a dollar saved in Year 1 due to inflation. To compare them fairly:

• Sum up the estimated annual electricity bill savings over 20 years using your standardized utility rate.
• Subtract the net system cost (out-of-pocket cost after tax credits) from those total cumulative savings to find the net lifetime financial benefit.
• If you want to be financially rigorous, discount future savings using a discount rate (like 4%−5%) to find the Net Present Value (NPV) of each system.

Step 4: Compare Key Metric Benchmarks

Once the assumptions are leveled, evaluate the proposals side-by-side using these practical benchmarks:

1. Payback Period: How many years until your cumulative savings match the out-of-pocket cost of the system? (Lower is better, typically 6–10 years).
2. Levelized Cost of Electricity (LCOE): Divide the total 20-year cost of the solar system (including maintenance/financing) by the total 20-year kWh production. This gives you a per-kWh cost of solar ($/kWh) to compare directly against your current utility rate.
3. Equipment Quality & Warranties: Ensure the hardware differences aren't being masked by aggressive financial assumptions. A cheaper quote with an inflated utility escalator might just be using lower-tier panels that degrade faster.

If you want, share the numbers you have:

• The utility inflation rates each installer used
• The Year 1 savings or production estimates
• The net costs of the systems

I can help you re-normalize the projections to a single baseline rate.

Comparing 20-year solar savings projections with different utility rate increase assumptions (often called the rate of escalation) requires leveling the playing field. When installers use different escalation rates—say 3% vs. 5% per year—the one using the higher rate will project dramatically larger savings, even if their system costs or production estimates are worse.

Here is how you can systematically normalize and compare those proposals:

• Normalize the Escalation Rate : Pick a single, independent baseline utility inflation rate (historical averages typically range from 2.5% to 4% depending on your region) and plug all proposals into that same rate. Do not trust the installer's custom escalator; recalculate the 20-year avoided cost using your chosen uniform percentage.
• Calculate Net Present Value (NPV) : Savings 18 years from now are worth less than savings today due to inflation and the time value of money. Discount the projected yearly savings back to present-day dollars using a standard discount rate (like 4% to 6%) to see the true modern value of the cash flows.
• Isolate System Cost and Production : Strip away the utility inflation assumption entirely and look at the hard metrics: the gross cost per watt, total system size (kWh production per year), equipment quality, and the net cost after incentives (like the federal tax credit). A great physical system with a conservative savings projection is often a safer bet than an overpriced system propped up by an aggressive utility inflation guess.
• Evaluate the Contract Mechanism : Check how the savings are delivered. If it is a PPA (Power Purchase Agreement) or lease, look closely at the installer's own annual price escalator clause (e.g., a 2.9% annual increase built into your contract payment). If their contract raises your solar rate by 2.9% a year, but you normalize utility inflation at 3%, your actual long-term savings margin might be razor-thin.
• Run a Sensitivity Analysis : Test the extremes. Ask what the 20-year savings look like if utility rates only grow at 1% to 2% per year (a low-inflation scenario). If the installer's financial model completely collapses under low utility inflation, it means the proposal relies too heavily on skyrocketing power company rates rather than intrinsic system value.

If you'd like, share the current utility escalation rates and estimated annual production/costs used by your installers, and I can walk you through calculating a normalized comparison model.

The key is to normalize the assumptions before comparing the 20-year savings numbers. A proposal showing $120,000 of savings isn't necessarily better than one showing $90,000 if the first installer assumes much faster utility-rate increases.

1. Ask every installer for the same underlying inputs

For each proposal, get:

DOE specifically cautions that future utility rates are difficult to predict and that historical increases may not be a reliable forecast.

2. Recalculate all proposals using one rate-escalation assumption

Suppose:

• Installer A assumes utility rates rise 5%/year
• Installer B assumes 2%/year
• Both quote the same physical solar system.

Don't compare their headline 20-year savings. Ask both to rerun the proposal at, say, 2%, 3%, and 4% annual escalation.

This is essentially a sensitivity analysis. NREL itself uses multiple utility-rate-escalation scenarios—for example, 1.5%, 2.5%, and 3.5% in one analysis—to show how much the financial result depends on that assumption.

You might see something like:

genui{"chart":{"chartType":"line","meta":{"title":"Illustrative effect of utility-rate assumptions","description":"Example only: cumulative solar savings under different annual utility-rate escalation assumptions.","footer":"Illustrative numbers, not a forecast."},"xKey":"year","xAxisLabel":"Year","series":[{"dataKey":"rate2","label":"2% escalation","axisLabel":"Cumulative savings","valueFormat":"compact","valuePrefix":"$"},{"dataKey":"rate3","label":"3% escalation","axisLabel":"Cumulative savings","valueFormat":"compact","valuePrefix":"$"},{"dataKey":"rate4","label":"4% escalation","axisLabel":"Cumulative savings","valueFormat":"compact","valuePrefix":"$"}],"data":[{"year":"1","rate2":1000,"rate3":1000,"rate4":1000},{"year":"5","rate2":5500,"rate3":5600,"rate4":5700},{"year":"10","rate2":12000,"rate3":12500,"rate4":13000},{"year":"15","rate2":19500,"rate3":21000,"rate4":22500},{"year":"20","rate2":28500,"rate3":31500,"rate4":34500}]}}

The exact numbers aren't important here—the point is that compounding makes the assumed escalation rate increasingly important over 20 years.

3. Don't overlook the utility's actual rate structure

The comparison shouldn't simply be "current cents/kWh × escalation." Solar savings depend on the utility's actual tariff and how exported solar is compensated. DOE notes that savings depend both on electricity rates and on what the utility pays/credits for excess generation.

For example, check whether each installer is modeling:

• Time-of-use rates
• Fixed monthly charges
• Tiered rates
• Net-metering/export credits
• Future changes to the applicable tariff
• Battery charging/discharging, if applicable

4. Compare cash flows, not just "20-year savings"

I'd ask each installer for a year-by-year table containing:

Year → utility bill without solar → utility bill with solar → solar payment → maintenance/replacements → incentives → net annual savings → cumulative savings.

Then compare:

• Year-1 savings
• Simple payback
• 20-year cumulative nominal savings
• 20-year net savings after all costs
• Net present value (NPV)
• Internal rate of return (IRR), if available

DOE points out that payback alone isn't a complete financial comparison; the opportunity cost of the homeowner's money over the planning horizon also matters.

5. Run a "same assumptions" test

A very useful question to send every installer is:

"Please rerun your proposal using a 3% annual utility-rate escalation, the same current utility tariff, the same panel degradation assumption, and the same treatment of incentives and financing. Please provide the annual cash flows for years 1–20."

That turns competing sales presentations into something much closer to an apples-to-apples financial model. DOE's solar PV cost-proposal guidance likewise recommends standardized inputs specifically to facilitate apples-to-apples vendor comparisons.

6. Then run a conservative/base/optimistic case

Rather than trying to determine the one true future utility-rate increase, I'd evaluate three cases:

• Conservative: low rate escalation
• Base: your best reasonable estimate
• Optimistic: higher escalation

The important question becomes:

Does Installer A still beat Installer B under the same conservative assumption?

If one proposal only looks attractive when it assumes 5–6% annual utility inflation, that's a materially riskier investment than one that works well at 2–3%.

And if you're in a particular utility territory, use the actual current tariff and export-compensation rules as the starting point rather than accepting the installer's "average utility inflation" assumption. DOE recommends checking current local utility rates when evaluating solar economics.

If you give me the two installers' 20-year savings figures and their assumed utility-rate increases, I can show you how to normalize them and determine which proposal is actually stronger.

Comparing solar proposals with different utility rate escalation assumptions can feel like comparing apples to spaceships. If Installer A assumes utility rates rise at 2% a year and Installer B assumes 5%, Installer B's 20-year savings projection will look vastly superior simply because of their math, not their hardware.

To make an apples-to-apples comparison, you need to strip away their customized inflation guesses and run the numbers using a standardized baseline.

• Step 1. Normalize the escalation rate by picking a single utility inflation percentage (the historical US average is roughly 3% to 4% per year, or you can look up your local utility's historical 10-year average) and recalculate or ask both installers to run their projections using that exact same number.
• Step 2. Compare the cost per kWh over time by looking at your current rate versus what you will pay the solar company (if leasing/PPA) or your projected cost of self-generated electricity (LCOE, or Levelized Cost of Electricity) for purchased systems.
• Step 3. Analyze the net present value (NPV) or cumulative cash flow year-by-year rather than trusting a single cumulative savings dollar amount at the bottom of a sales page, since money saved in year 20 is worth less than money saved in year 1.
• Step 4. Scrutinize system degradation rates and make sure both installers are using realistic panel degradation assumptions (typically 0.5% to 0.7% loss in production per year).
• Step 5. Evaluate the baseline utility tariff they used to start the calculation—ensure both used your actual current utility rate and tier structure, not an inflated starting point.

If you'd like, share:

• The utility inflation rates used by each installer
• Whether the proposals are for a purchase (loan/cash) or a lease/PPA

I can help you break down how to mathematically true-up their projections.

The key is to separate the installer’s solar/financial assumptions from its assumption about future electricity prices. A 20-year savings number can look dramatically better simply because one installer assumes utility rates rise faster.

NREL itself uses different utility-rate escalation scenarios—for example, 1.5%, 2.5%, and 3.5% annually in one residential analysis—showing how consequential this assumption can be.

A good apples-to-apples method

1. Ask every installer for the underlying 20-year cash-flow spreadsheet, not just the headline "20-year savings."

   Get:

   • Year-1 electricity rate ($/kWh)
   • Annual utility-rate escalation
   • Solar production by year
   • Panel degradation assumption
   • Net-metering/export-credit assumptions
   • System price and incentives
   • Financing interest rate and loan term
   • Maintenance/replacement costs
   • Any battery assumptions
   • Their definition of "savings"

2. Put all installers under one utility-rate assumption.

   For example, if Installer A assumes 5% annual utility inflation and Installer B assumes 2.5%, don't compare their resulting savings directly.

   Instead, recalculate both using, say:

   • Low: 1.5%
   • Middle: 2.5%
   • High: 3.5%

   Those aren't necessarily the correct rates for your utility; they're useful sensitivity cases. NREL has used essentially this kind of low/base/high framework.

3. Compare cumulative cash flows, not just the 20-year total.

   A useful comparison is:

   Metric	Installer A	Installer B
   System price after incentives	$	$
   Year-1 utility bill without solar	$	$
   Year-1 solar bill	$	$
   Year-1 savings	$	$
   Break-even year	—	—
   20-year savings @ 1.5% escalation	$	$
   20-year savings @ 2.5%	$	$
   20-year savings @ 3.5%	$	$
   Net present value	$	$

   This tells you whether one system is genuinely better or merely benefits from a more optimistic forecast.

4. Check whether "escalation" is actually being double-counted.

   This is particularly important. Some modeling systems distinguish inflation from an additional electricity-price escalation rate. For example, NREL's SAM documentation says electricity-bill escalation can be an increase in addition to the financial-model inflation rate.

   So if an installer says "3% utility escalation," ask:

   "Is the 3% the total annual increase in the electricity price, or 3% on top of your assumed inflation rate?"

5. Use the same production estimate where practical.

   If Installer A predicts 12,000 kWh/year and Installer B predicts 14,000, the difference isn't attributable to utility escalation. You want to isolate the variables.

   NREL's PVWatts Calculator can provide an independent production estimate for a proposed system. It estimates grid-connected PV production, although NREL cautions that actual production has uncertainties and depends on the inputs.

The most revealing calculation

I'd actually ask each installer to provide three versions of the same proposal:

"Please rerun the 20-year savings using utility-rate escalation of 1%, 2.5%, and 4%, while keeping every other assumption unchanged."

Then compare the results.

If Installer A's system still wins under all three scenarios, that's strong evidence that the economics are attractive independent of the rate forecast.

If A shows $80,000 of savings versus B's $45,000, but A's advantage disappears when both use the same 2.5% escalation, you've discovered that the forecast—not the solar system—is driving the apparent advantage.

One more important distinction

Don't automatically choose the installer with the largest projected savings. Also compare cost per watt, system size, production per kW, degradation, equipment warranties, financing cost, export compensation, and contract terms.

The cleanest decision is essentially:

Same electricity-price forecast + same production methodology + same incentives + same financing assumptions → then compare the systems.

That turns a salesperson's "20-year savings" projection into something you can actually audit.