Three Solar Quotes, Three Different System Sizes: Which One Actually Makes Sense

You did the responsible thing and got three quotes. Installer A says 18 panels. Installer B says 26. Installer C throws in two batteries. Same house, same roof — and your first instinct is that somebody's lying.

Probably nobody is. But before you try to figure out who's right, there's a more basic question hiding under all three: are you even comparing the same thing? 

See, panel count isn't system size. Battery count isn't storage. And even the production estimate can mislead you.

Here's how to line the three up so they actually mean something — and why the winner usually isn't the biggest or the cheapest.

Are 18 panels and 26 panels even the same size?

Not necessarily — and this is the first trap. Panel count tells you almost nothing on its own, because panels come in different wattages. The number that actually matters is your system's DC size in kilowatts: panels × watts per panel. Eighteen big 440-watt panels (7.9 kW) can be a larger system than twenty-six smaller 300-watt ones (7.8 kW).

So the very first thing to do with three quotes is ignore the panel counts and write down each system's kW DC. Half the time, quotes that looked wildly different are closer than they seem — and quotes that looked similar aren't. You can't compare anything until you're comparing capacity, not headcount.

Why did three installers recommend different sizes?

Usually because they're working from different assumptions about your home — not because two of them are wrong. Different offset targets, different reads on your roof and shading, different guesses about future loads like an EV, different views on what your utility pays for exported power. Those are design judgment calls, and reasonable people land in different places.

One might size to cover 80% of your usage because your utility barely pays for the extra; another aims for 100%; another quietly built in the EV you mentioned once. None of that is a lie. The problem isn't that they disagree — it's that the assumptions are buried, so you're staring at three conclusions with the reasoning hidden under each one. Your job is to drag those assumptions into the open.

So which size is actually right for me?

The one that best fits your real usage, your goals, and your utility's economics — not automatically the biggest, and not automatically "100% of your bill." If your utility pays next to nothing for exported power, a system that overproduces past what you can use may just be extra panels you paid for and don't get full value from.

There isn't one mathematically "correct" solar system, which is exactly why "who's right" is the wrong question. There's a design that matches what you're trying to do. So ask each installer two things: what percentage of my usage are you designing to offset, and why does that make sense under my rate plan? A percentage with no reasoning behind it isn't a strategy — it's a default.

One flag worth knowing: if an installer sized your system off your home's square footage instead of your actual electricity usage, push back — for an existing home with a year of bills, square footage doesn't use power, your habits do. (New construction with no usage history is the fair exception; there, estimating from the home's appliances and loads is legitimate.)

👉 Got two or three quotes that don't seem to agree? Send them to us for a free second opinion — we'll normalize them and show you where the assumptions actually differ.

One quote is way cheaper — bargain or worse system?

Can't tell from the price alone, and "cheaper" usually hides why. Start by comparing cash price to cash price — never monthly payment to monthly payment — then check that the three quotes actually include the same scope: electrical work, permitting, roof work, monitoring, warranties. Cost per watt (cash price ÷ kW DC) helps once the systems are the same size.

Two things people get wrong here. First, a smaller inverter isn't automatically a corner cut. Solar systems are often designed with more panel capacity than inverter capacity on purpose, and a little clipping can be a perfectly rational tradeoff — the ratio is a clue, not a verdict. So don't ask "is the inverter too small," ask "how many kWh a year does the model expect to clip, and what would the next size up recover?" That turns a gotcha into an economics question.

Second, financing. The CFPB has found that some solar loans bake a large dealer fee straight into the loan principal — so the financed price can sit thousands above the cash price without that markup ever being shown to you plainly. Always ask for the cash price and the financing terms separately: amount financed, APR, term, total payments. A comfortable monthly payment can be hiding an expensive loan.

One installer says two batteries — who's right?

First, stop comparing battery count — "two batteries" isn't a spec any more than "18 panels" is. Ask what usable storage you're actually buying in kWh, and how much continuous power in kW, because two units from one product line aren't the same as two from another. Then ask what problem the battery is even solving.

A battery can earn its keep several ways — backup during outages, shifting your midday solar into expensive evening hours, making up for poor export rates, or dodging demand charges — and which of those applies depends entirely on your utility and how you use power. So "do I need two batteries" isn't something you settle by averaging three opinions. Ask each installer: what's this storage supposed to accomplish, and what numbers show this amount is right for my house? Storage should be modeled, not added out of habit.

So what single number settles it?

None — and that's the whole point. The most useful number in a proposal is estimated first-year production in kWh, but it's a model output, not a truth serum. Two quotes at 10,500 and 11,300 kWh look like B wins — until you find out B assumed less shading, or is a bigger (pricier) system, or makes its extra power in the hours your utility barely pays for.

So don't let one number end the argument. Line up a small set side by side and the real picture shows up: kW DC, first-year kWh, production per kW (kWh ÷ kW DC — this tells you whether a big number is just a bigger system or a genuinely better-producing one), offset target, and cash price. Put those next to each other for all three, and three confusing proposals finally become three comparable designs. There's a fill-in version of exactly that grid in the checklist below.

What should I ask all three installers?

The same handful of questions — and get the answers in writing. You don't need the salesperson to recite the math from memory; a smooth one can confidently tell you nonsense, and a good one might need to check with engineering. What you need is the assumptions on paper before you sign, not a confident tone in the room.

The short version: system size in kW DC; the usage and future loads they designed for; first-year kWh and the shading/loss assumptions behind it; the offset target and why it fits your rate plan; the inverter and its expected clipping; battery usable kWh and purpose if included; and the full financing terms next to the cash price. (Full checklist below — send it to all three.)

The bottom line

Three different quotes don't mean two installers are lying. They mean different equipment, different assumptions, different goals — usually some of each. So don't compare panel count, don't compare monthly payments, and don't let one production number end the argument. Make the quotes comparable first — same units, same assumptions, out in the open — then decide which one makes sense for your house.

The strongest proposal isn't the biggest or the cheapest. It's the one whose assumptions still hold up when all three sit side by side. And if a company won't put its assumptions in writing — ours included, hold us to the same standard — that's not just a sizing problem. That's your preview of how they'll handle everything else you can't easily check.

👉 Get a free IntegrateSun quote review — send us the proposals you already have and we'll line them up on the same terms, so you can see which design actually fits.