Introduction

A homeowner may collect two or three quotes and assume that the lowest monthly payment, the largest system size, or the longest warranty tells the full story. It usually does not. The real differences are often buried in the assumptions: how production was modeled, what utility rate increases were used, whether roof condition was considered, what equipment is included, who performs the installation, and what the warranty actually covers.

A good proposal should make the financial case clear without obscuring variables that could affect the outcome. A weak proposal may still look polished, but leave out the details needed to evaluate whether the system will perform as promised.

Here is what to review, what to question, and how to tell the difference between a solar proposal built for accuracy and one built to close the sale.

Start With the Production Estimate, Not the Price

The first number most people look at is the cost. That's understandable, but it's the wrong place to start.

The more important number is the estimated annual production, usually expressed in kilowatt-hours (kWh). This is the system's prediction of how much energy it will actually generate for your home each year.

Every other number in the proposal flows from this one. If the production estimate is inflated, the savings projection is inflated. The payback period is wrong. The return on investment is wrong. The whole financial picture is built on a number that doesn't reflect reality.

What to ask:

• How was this production estimate calculated?

• Was it based on a precise shade analysis of my specific roof, or an industry average?

• What software was used? (PVWatts, Aurora, and Helioscope are common, each with different accuracy levels)

• What shading losses were assumed?

The most rigorous solar proposals model your home specifically, accounting for your roof's pitch, orientation, any nearby trees or obstructions, and your local weather patterns. A proposal that uses regional averages instead of site-specific data is almost certainly optimistic.

Look Closely at the Degradation Rate

All panels lose a small amount of efficiency each year. This is called degradation. Most quality panels degrade at roughly 0.5% per year or less. Lower-tier panels can degrade at 0.7% to 0.8% annually, and older or lower-grade modules can exceed that.

On a 25-year projection, that difference adds up significantly. A proposal using optimistic degradation assumptions will show more lifetime savings than you'll actually see. Ask specifically:

• What annual degradation rate does this proposal assume?

• Is that rate supported by the panel manufacturer's performance warranty?

• Can you show me what the production looks like in year 10, year 15, and year 25?

Read the Warranty Language Carefully

"25-year warranty" appears in almost every proposal. What it covers varies enormously.

There are typically three separate warranties to understand.

Product warranty covers defects in the panel itself. Standard is 10 to 15 years, though premium manufacturers increasingly offer 25-year product warranties.

Performance warranty guarantees the panel will still produce above a certain output percentage after 25 years. This is where degradation guarantees live. A solid performance warranty guarantees at least 80% output at year 25, while top-tier manufacturers typically guarantee 86% to 92%.

Workmanship or installation warranty covers the installation work itself: the wiring, the mounting hardware, and the roof penetrations. This is separate from the panel manufacturer's warranty and is issued by the installer. Some companies offer 10 years. Some offer 2. Some subcontract the work and offer nothing.

What to ask:

• Who is backing each of these warranties: the manufacturer or the installer?

• If the installer goes out of business, what happens to the workmanship warranty?

• Does the workmanship warranty cover roof leaks caused by the installation?

Ask Who Is Actually Doing the Work

This is the question most homeowners never think to ask, and it's one of the most important.

Many solar companies don't employ the people who install your system. They use subcontractors who may be working on multiple projects for multiple companies with varying quality standards.

Subcontracting isn't inherently bad, but it changes the accountability structure significantly. When something goes wrong, like a roof leak, a monitoring issue, or a panel that underperforms, the company you signed with and the company that did the work are two different entities.

What to ask:

• Are the people installing my system your employees or subcontractors?

• If subcontractors, how are they vetted?

• Who do I call if there's a problem with the installation two years from now?

Check the Electricity Rate Assumptions

Almost every savings projection assumes that electricity rates will increase over time, typically 2% to 4% annually. That assumption significantly affects the projected savings over 25 years.

If a company assumes 4% annual rate increase and electricity rates stay flat or increase more slowly, the savings projection will be too high. This isn't necessarily dishonest; it's modeling an uncertain future, but the assumption should be disclosed, and you should understand its impact. Three numbers worth requesting:

• The annual escalation rate the proposal assumes

• The savings projection was recalculated at 0% escalation

• Your own actual average utility rate over the past three years

Understand the Financing Terms Completely

If you're financing the system rather than paying cash, the loan terms deserve as much scrutiny as the system itself.

What to ask:

• Is there a dealer fee built into this loan, and does it inflate the system price?

• What is the interest rate if I don't apply the tax credit within the promotional window?

• What is the total cost of the system if I make minimum payments for the full loan term?

• Who is the actual lender, and what are the prepayment terms?

A Note on Proposal Pressure

A legitimate company will give you time to review a solar quote carefully, ask questions, consult with others, and compare. High-pressure tactics like "this price is only good today," "we have limited installation slots," or "the incentives are disappearing" are common solar company red flags, regardless of whether any of those claims are technically true.

The incentive landscape has changed. Urgency-based selling has always been a feature of this industry, and it has often been used to prevent exactly the kind of careful evaluation this article describes. The Federal Trade Commission reported that consumer complaints referencing solar companies increased fourfold over a recent multi-year period, a pattern regulators attribute in large part to high-pressure sales tactics and misrepresented savings claims.

You should feel equipped to make this decision, not pressured into it.

What a Trustworthy Proposal Looks Like

A proposal worth trusting will show you a site-specific production model rather than a regional average, disclose the degradation rate assumed and tie it to the performance warranty, break out all three warranty types clearly, tell you who is doing the installation and how they're employed, explain the financing terms in plain language including worst-case scenarios, and give you time to review it without pressure.

None of this requires you to become an expert. It requires you to ask the right questions and to pay attention to which companies answer them directly and which ones don't.

Great Sky Solar has operated in Massachusetts since 2013. Every home we work with receives a site-specific production model. Every installation is performed by our own salaried employees. If you have questions about a proposal you've received, from us or from anyone else, we're happy to walk through it with you.

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