You just got three solar bids back. One’s $28,000, another’s $19,500, the last one’s $23,000. The cheapest one looks tempting. But here’s what nobody tells you: they might not even be quoting the same system. Different panel brands, different inverter types, different warranty terms, different assumptions about your roof’s actual usable space. Without a framework, comparing solar bids is like comparing grocery receipts where one store lists items by weight and another by volume. Apples to mangoes. Installers know this.

I’ve watched homeowners pick the lowest bid and end up with an undersized system, a lien on their house from unpaid permitting fees, or a warranty that disappeared when the installer closed shop two years later. None of them were dumb. They just didn’t know what questions to ask. Let me fix that.

What a Complete Solar Bid Should Actually Contain

A professional solar proposal isn’t a one-page flyer with a big number at the bottom. If that’s what you got, ask for more. Walk away if they refuse. Here’s the bare minimum you need in writing before signing anything.

System specifications. The exact panel model and manufacturer. Wattage per panel. Total number of panels. Total system size in kilowatts-DC (kWdc). A quote that says “approximately 8kW system using premium panels” isn’t a quote. It’s a placeholder.

Inverter details. String inverters, microinverters, and DC power optimizers behave differently, cost differently, and have different implications for shading, monitoring, and future expansion. The proposal should name the exact type, exact model, and exact manufacturer. An Enphase IQ8 microinverter is not the same product as a generic Chinese string inverter at half the price, and swapping them out later will cost you.

Production estimates. Every proposal should include projected annual kilowatt-hour (kWh) output for your specific roof, location, and orientation. Many installers use PVWatts, a free tool from the National Renewable Energy Laboratory (NREL). Ask how they calculated it. If they can’t explain it, that’s a red flag.

Breakdown of costs. Equipment, labor, permits, inspection fees, utility interconnection fees, electrical panel upgrades, all itemized separately. A lump sum isn’t a breakdown.

Warranty terms. Panel warranties (usually 25 years product and performance), inverter warranties (10-25 years depending on type), workmanship warranties (typically 5-10 years from the installer). Know who backs each one.

Timeline and permits. Who pulls the permits, which jurisdiction gets them, installation timeline from contract to activation.

How to Normalize Bids for an Apples-to-Apples Comparison

Recommended Emporia Vue Gen 2 Home Energy Monitor 16 Sensors

Monitor 16 circuits in real time with solar and net metering support to optimize your solar ROI.

Check Price →
FactorBid ABid BBid C
Total price$28,000$19,500$23,000
System size (kW)10.26.58.5
Cost per watt$2.75$3.00$2.71
Projected annual output (kWh)13,2008,20011,100
Offset % (based on 11,000 kWh usage)120%75%101%
Inverter typeMicroinverterStringOptimizer
Workmanship warranty10 years5 years10 years

This is where most homeowners get lost. A bid in hand looks simple. But you can’t compare them straight up. You need to normalize them.

Step 1: Calculate cost per watt. Divide the total system cost by the total system wattage. A $23,000 bid for an 8.5 kW system (8,500 watts) is $2.71 per watt. A $19,500 bid for a 6.5 kW system is $3.00 per watt. Suddenly the cheaper bid isn’t cheaper. This single calculation catches more bad deals than anything else.

Step 2: Check offset percentage. Look at your last 12 months of electric bills. Add up your annual kWh consumption. Then look at the production estimate in each bid. Divide projected production by your consumption. If you use 11,000 kWh per year and the system produces 8,500 kWh, your offset is about 77%. Are all three installers proposing similar offset percentages? If one quotes a system that only offsets 60% of your usage without explaining why, ask.

Step 3: Normalize for panel quality. Panels are rated by efficiency and degradation rate. A 400W panel from a Tier 1 manufacturer like Qcells or Panasonic degrades at roughly 0.3-0.5% per year and carries a real 25-year performance guarantee. Generic panels may degrade at 0.7-0.8% annually. Sounds small. Over 25 years it’s meaningful. Ask each installer if their panels rank on the Bloomberg NEF Tier 1 list.

Step 4: Account for inverter monitoring. Some systems include robust monitoring apps and hardware. Others charge extra. Enphase’s Enlighten app gives you panel-level data. A string inverter without optimizers gives you system-level data only. If one bid includes detailed monitoring and another doesn’t, factor that in.

Step 5: Read the fine print on production guarantees. Some installers now offer production guarantees. If the system doesn’t hit a specified annual output, they’ll credit you. That has real dollar value. Most won’t offer it. If one bidder does, weight it accordingly.

FactorBid ABid BBid C
Total price$28,000$19,500$23,000
System size (kW)10.26.58.5
Cost per watt$2.75$3.00$2.71
Projected annual output (kWh)13,2008,20011,100
Offset % (based on 11,000 kWh usage)120%75%101%
Inverter typeMicroinverterStringOptimizer
Workmanship warranty10 years5 years10 years

Bid A is the largest system and makes sense if you’re planning to add EV charging. Bid B looks cheapest but leaves 25% of your bill unchanged and uses a simpler inverter. Bid C is well-sized for current usage at a competitive price per watt.

Contractor Vetting: The Stuff That Doesn’t Show Up in the Bid

The proposal is only as good as the company behind it. I’ve seen beautifully formatted proposals from fly-by-night outfits and messy bids from excellent local installers. Don’t judge the company entirely by the paper.

Check the license. Every state has a contractor licensing database. Your installer needs to be licensed in your state. In California, that’s the CSLB. In Texas, TDLR. Look them up. It takes three minutes.

Verify NABCEP certification. The North American Board of Certified Energy Practitioners certifies solar installers the same way electrical boards certify electricians. It’s not required everywhere, but it’s a meaningful quality signal. Ask if the lead installer on your project holds a NABCEP PV Installation Professional certification.

Check how long they’ve been operating. Six years in business means they’ve survived long enough to stand behind their work. Fourteen months means they might be excellent, or they might fold before your inverter warranty expires. That’s not automatic disqualification, but it’s reason to scrutinize their warranty backing. If your company closed tomorrow, who honors the workmanship warranty?

Pull their permit history. Your local building department has public records. A contractor who routinely gets permits pulled is doing things right. A contractor who claims they “handle the permits” but has no history in your jurisdiction is a problem.

Talk to references. Not the ones they hand you. Search Google, Yelp, the Better Business Bureau. Look specifically for complaints about post-installation service. That’s where bad installers always crack.

Understanding Financing Terms Buried in the Proposal

If you’re financing the system, financing terms are part of the bid whether they’re clearly labeled or not. Two bids might show identical cash prices but vastly different loan costs.

Dealer fees are the ugly secret here. When an installer uses a third-party solar loan (GreenSky, Mosaic, Sunlight Financial, etc.), the lender charges the installer a dealer fee, often 15-30% of the loan amount. Many installers quietly add that fee to the financed price. So the $23,000 cash price becomes a $28,000 financed price with 9.99% interest. Ask directly: “Is the financed price the same as the cash price?”

Power Purchase Agreements (PPAs) and solar leases don’t show a system price. They show a monthly payment. They can make sense for some homeowners, but you don’t own the panels, you don’t get the federal tax credit (the installer does), and selling your house gets complicated. The U.S. Department of Energy has a solid breakdown of ownership versus leasing tradeoffs that’s worth reading before you sign.

If you’re comparing a loan-financed bid against a PPA bid, you’re comparing two fundamentally different financial products. Treat them separately.

Red Flags Worth Walking Away From

Some things just tell you to close the folder and call the next company.

High-pressure closing tactics. “This price is only good today.” Solar equipment prices don’t change by day. A legitimate installer holds a quote for at least 30 days.

No site assessment before quoting. A professional installer looks at your roof, your electrical panel, and your utility bill before giving a final number. Remote quotes using satellite imagery work for ballpark estimates. A final proposal without a site visit means they haven’t verified your roof condition, your panel capacity, or your shading situation.

Pushing for permits in your name. Some installers ask you to pull permits yourself “to save money.” What they’re really doing is shifting liability onto you. Don’t do it.

Vague production estimates. If a company says your system will “offset most of your bill” without giving an actual kWh number, they’re either incompetent or deliberately vague. Either way, move on.

No physical address. If the company’s address is a PO box or a residential street that shows up as somebody’s house on Google Maps, they may not have a legitimate business location. That matters when you need someone to show up three years from now for a warranty repair.

Getting three bids and picking the middle one is a strategy. Just not a good one. The process I’ve laid out here takes two or three extra hours, but it’s the difference between a system that earns you back $1,200 a year for 25 years and one that underperforms, causes headaches, and loses you money. If you want to go deeper on your own system’s production estimates, the NREL’s PVWatts Calculator is free and accurate. Use it to sanity-check every production number an installer hands you. If their estimate is more than 10-15% higher than PVWatts for your address and roof orientation, ask why. Keep asking until you get a real answer.

Sources

Disclosure: As an Amazon Associate, we earn a small commission from qualifying purchases at no extra cost to you. We only recommend products that genuinely support the topics covered in this article.

Disclosure: As an Amazon Associate, we earn a small commission from qualifying purchases at no extra cost to you. We only recommend products that genuinely support the topics covered in this article.