Free Calculator
What Your Installer's Offer Doesn't Say About Payback
Read your offer, type in six or seven fields, and get its payback twice: once the way the installer divides it, and once with the lines it never mentions. Nothing you enter is sent anywhere.
Nothing leaves this page. Your figures are used by the calculation in your browser only. They are not sent, saved or logged. This tool shows arithmetic and questions to ask. It is not financial advice and it does not tell you whether to sign.
Step 1 (optional): pull the fields out of your offer
Offers come as PDFs. If you would rather not retype them, copy this prompt, paste it into an AI assistant you already use, then paste the text of your offer underneath. The assistant lists each field with the exact words it came from. Check those words against the document yourself, then type the values below. This page never sees your offer or the assistant's answer.
Step 2: type in what your offer says
The form starts on the worked example from our hidden-costs article (linked in the text below the tool) so you can see how it behaves. Replace it with your own numbers, or clear it first.
Sets the currency, and the retail rate and yield used when you leave those blank.
The price you would pay, after any incentive the offer already subtracts. For a lease or PPA you can leave it blank.
If the offer does not state one, leave blank and the market typical is used. The result says so.
Your current bill, not the offer's. Blank uses the market typical.
What each exported kWh earns. Blank means the offer does not say.
Share of production you use as it is made. The article cites around 30% for a house without a battery.
String inverters typically carry 10 to 12 years, panels 25 to 30. A replacement is counted at the end of the warranty.
Ranges used for the lines your offer leaves out
Defaults are the ranges quoted in the hidden-costs article, in US dollars. Replace them with local quotes if you have them. Set both ends of a line to 0 to leave it out.
What the arithmetic shows
| Price per watt in this offer | $2.60 per W |
|---|---|
| Payback tool's typical for Texas (USA) | $2.80 per W before incentives. A market typical, not a benchmark for your roof or for what your offer includes. |
| Annual production used | 10,080 kWh (from the offer) |
| Yearly value, every kWh at retail | $1,859 |
| Yearly value with the offer's export tariff | $1,263 |
Four lines to ask about
An offer normally states an export tariff and an inverter model. It rarely mentions insurance, property tax or operations at all. Each line below shows the range from the article and the question to put to the installer.
Export tariff and self-consumption
Found in your entries
Article range: Export value runs from full retail down to about 6 cents per kWh; around 30% self-consumption is normal without a battery.
The offer states an export tariff, so the second payback figure uses it.
Ask: What export rate does your estimate assume, and which tariff or contract is that rate from?
Inverter replacement
Found in your entries
Article range: About $1,500 to $2,500 for a string inverter swap, labour included. Warranty usually 10 to 12 years.
The offer names an inverter (Fronius Primo 8.2-1) and a 12-year warranty. The replacement cost itself is still not in it.
Ask: What is the exact inverter model and warranty length, and does the warranty cover shipping and the labour to refit it, or cap it?
Insurance and property tax
Not in your offer: ask
Article range: Insurance about $50 to $150 a year. Property tax depends on the state, and some exempt residential solar entirely. Together about $50 to $400 a year.
Not in the offer.
Ask: Does the array change my home insurance premium, and does my state or county add it to the assessed value of the house?
Operations: cleaning, monitoring, service
Not in your offer: ask
Article range: About $150 to $300 a year on a system this size.
Not in the offer.
Ask: Is monitoring free for the life of the system, and who pays for cleaning and service calls?
What this tool assumes, and where it will be wrong for you
- Savings are held flat: no retail price inflation and no panel degradation, as in the payback calculator.
- The inverter is replaced once, at the end of the warranty you enter. Real failures are not scheduled.
- Insurance, property tax and operations are one flat yearly amount. The article quotes insurance and property tax together as $50 to $400 a year, so the two are combined here.
- The article's ranges are US dollar figures from a US article. In other markets, use local quotes.
- Payback is counted from day one, with no financing cost. A loan changes the cash flow and is not modelled.
- None of this is a forecast or a recommendation. Taxes, incentives and utility rules change, and yours may differ.
What does this checker actually do with my offer?
It does arithmetic and nothing else. The price goes over the yearly value of the electricity, which gives the figure most offers print. Then it applies the export tariff your offer assumes, and then it adds the lines our article on what every solar ROI calculator leaves out walks through: an inverter swap, insurance, property tax and upkeep. For a lease or PPA it compounds the escalator over 25 years instead, because there is no purchase price to pay back.
The saving and payback maths is the same code that runs the Solar Payback 2026 calculator, so the two tools can't drift apart. Use that one when you have no offer yet and want a market-level answer. Use this one when you have a document in your hand.
Which costs does an offer usually leave out?
Four lines move a payback figure by years, and they don't arrive in the same condition. An offer normally names an export tariff, though not always, and it normally names an inverter model with a warranty. Those two you can read off the document. Insurance, property tax and operations almost never appear in it, because they aren't the installer's costs to quote.
- Export tariff: the article's example runs from full retail down to about 6 cents per kWh, and in that example this one line moved payback further than price per watt, degradation and panel efficiency combined.
- Inverter replacement: roughly $1,500 to $2,500 for a string inverter, against a warranty of 10 to 12 years on a panel warrantied for 25 to 30.
- Insurance and property tax: $50 to $150 a year for insurance, $50 to $400 a year for insurance and tax together, and the tax half depends entirely on your state.
- Operations: $150 to $300 a year for cleaning, monitoring and the odd service call. Our soiling loss calculator puts a number on the cleaning part for your tilt and climate.
Those are US dollar figures from a US article, and the checker says so wherever it uses them. Outside the US, treat them as an order of magnitude and replace them with local quotes. The assumptions behind the underlying arithmetic are laid out in how each assumption moves solar ROI.
Is it safe to paste my offer into an assistant?
That part happens outside this page. The prompt button only copies text to your clipboard. Where you paste it, and what that service does with your document, is governed by its own privacy terms, not ours. An offer carries your name, address and often your meter number. Delete those lines before you paste, or skip the assistant and type the fields by hand, which takes a few minutes.
If you do use an assistant, treat its answer as a draft. The prompt asks it to quote the exact words it took each value from, so you can check them against the PDF. Models misread tables. A figure you didn't verify is a figure you shouldn't type in.
Why doesn't it tell me whether to sign?
Because it can't know enough to. It doesn't see your roof, your tax position, your utility's rules, your credit terms or what else you could do with the money. A payback range is one input to a decision about a five-figure purchase, and this tool is built to make that input honest, not to make the decision. It isn't financial, tax or legal advice. If the numbers surprise you, the useful move is to take the questions above back to the installer and see how they answer.
Does a longer payback mean a bad offer? Not by itself. The article behind this tool makes the point that a 15 to 17 year payback on hardware warranted for 25 to 30 years still returns a decade or more of nearly free electricity. What matters is whether the figure you were told is the figure you'll live with. For the no-offer baseline, the solar payback period guide covers where the typical numbers sit in 2026.