How to Evaluate Commercial Solar Proposals (A 7-Step Checklist for Property Owners)

When I first started reviewing commercial solar proposals, I assumed the cost per watt was the only number that mattered. Three projects and about 40 vendor comparisons later, I realized that approach was completely wrong. The lowest cost-per-watt quote often hid the highest total cost of ownership—bad site assessments, undersized batteries, or warranties that didn't cover what you'd expect.

This checklist is for commercial property owners, facility managers, and corporate energy buyers evaluating proposals for solar panel systems, battery storage, backup generators, or EV charging infrastructure. It'll walk you through seven steps I use in my own quality audits, plus a few red flags most people miss. There's no fluff here—just the process I've refined over four years of reviewing these deliverables.

Step 1: Validate the Site Assessment

Before you even look at pricing, check the site assessment. I can't tell you how many proposals I've reviewed where the solar irradiance data was pulled from a generic map instead of a site-specific tool. That's a problem.

Here's what to ask for:

• Shading analysis: Did they use a tool like Solargis or Helioscope? Generic satellite data doesn't account for nearby buildings or tree growth.
• Roof condition: When was the last structural assessment? If your roof needs replacement in 5 years, installing panels now means paying for removal and reinstallation later.
• Utility interconnection: Did they check with your local utility on capacity? Some commercial zones have limited interconnect capacity, especially for battery export.

Checkpoint: If the proposal doesn't include a site-specific shading analysis, ask for it. I've rejected entire batches of proposals—literally 12 out of 30 in one Q1 2024 audit—because they relied on generic solar maps for sites with partial shading.

Step 2: Verify the System Sizing Logic

Most people assume bigger is better. But from the outside, a 100 kW system looks impressive. The reality is oversizing creates problems: higher upfront cost, wasted generation during low-demand periods, and penalty charges for exporting excess power to the grid in some markets.

What you need instead is load-matched sizing. The vendor should have analyzed your 12-month utility bills to match the system size to your actual consumption pattern. If they didn't ask for your bills, that's a red flag.

For battery storage, the same logic applies. A powerwall 3 installed (yes, Tesla's offering gets a lot of attention) can handle 11.5 kW continuous output, but some commercial loads spike above that. The warranty on a powerwall 3 is 10 years or 37.8 MWh throughput—but those terms change based on installation temperature and discharge cycles.

Checkpoint: Request a load-matching report. The vendor should show you peak demand, base load, and how the system covers both. If they can't, move on.

Step 3: Audit the Equipment Warranty Stack

This is where the difference between residential and commercial proposals really shows. Residential warranties are straightforward; commercial stacks involve multiple components, each with its own terms.

Break down the warranty into three layers:

1. Solar panels: 25-year performance warranty is standard. But check the degradation rate—0.5% per year is good; anything above 0.7% means you'll lose significant output by year 20.
2. Inverters/battery: Powerwall 3 warranty is 10 years, but third-party batteries might be shorter. I've seen proposals where the inverter warranty was 5 years on a system expected to last 30—that's a future cost you'll eat.
3. Workmanship: Who covers the labor for replacements? Some vendors say "25-year warranty" but exclude labor after year 5. That's fine if you know it—bad if you don't.

Checkpoint: Ask for a warranty summary table with all three layers. The vendor who said "this isn't our strength—here's who does it better" earned my trust for everything else. A vendor who glosses over warranty gaps? I'd rather work with a specialist who knows their limits than a generalist who overpromises.

Step 4: Scrutinize the Financial Projections

This was accurate as of Q4 2024, but the solar market changes fast—especially with federal incentives and state-level policies. Verify current rates before signing anything. I learned this the hard way in 2022 when a client budgeted for a system based on 2021 incentive levels and came up short by $22,000.

Look for:

• Net metering assumptions: Are they assuming you'll get full retail credit for exported power? Many utilities have moved to avoided-cost rates or time-of-use structures that change the math.
• Degradation impact: A 0.5% annual degradation means your system produces about 88% of original output at year 25. If the financial model assumes flat output, it's optimistic.
• Operation & maintenance (O&M) costs: Panels need cleaning. Inverters fail. Batteries lose capacity. What's the annual O&M budget? I've seen proposals budget zero—that's not real.

Checkpoint: Run the numbers through a third-party calculator like NREL's SAM tool. If the vendor's payback period is more than 2 years shorter than SAM's, ask why.

Step 5: Confirm the Financing Structure

Vivint Solar and Sunrun offer a range of options: cash purchase, solar loan, lease, or power purchase agreement (PPA). Each has different implications for your total cost of ownership.

Key questions:

• Who owns the RECs (Renewable Energy Certificates)? In some lease agreements, the vendor keeps them—you lose that revenue stream.
• Is the lease escalator fixed or variable? A 2.9% annual escalator sounds small, but over 25 years it adds up.
• What happens if you sell the property? Can the lease be transferred? Some leases require buyer credit approval, which can kill a sale.

Checkpoint: Request a total cost comparison over the system's life, not just monthly savings. That $0 down lease might look good but could cost twice as much as a loan over 25 years.

Step 6: Check the Installation Timeline and Permitting

I used to think rush fees were just vendors gouging customers. Then I saw the operational reality of expedited solar permitting. Some jurisdictions take 6-8 weeks for commercial permits; adding EV charging infrastructure can double that timeline for separate electrical work.

Ask for a permitting roadmap with estimated durations for each step. If the vendor says "3 weeks from contract to install," they're either extremely experienced in your jurisdiction or oversimplifying. The latter is more common.

Checkpoint: Look up your local building department's average permit review time for solar. If the vendor's estimate is half that, ask how they achieve it—some have pre-approved designs that speed things up, which is legitimate. Others just haven't checked.

Step 7: Evaluate the Post-Installation Support

It took me about 50 commercial project reviews to understand that post-installation support matters more than installation speed. A system that's down for 3 weeks waiting for a service call loses you real money.

Ask about:

• Monitoring platform: Can you see real-time production and battery status? Some vendors charge extra for monitoring access.
• Response time SLAs: What's the guaranteed response time for outages? For commercial systems, 24-48 hours is reasonable; 5+ days is not.
• Service network: Who does the actual repairs? Subcontracted technicians may not have the same training as the original installers.

Checkpoint: Request a service agreement that spells out response times and escalation procedures. If they won't commit to SLAs, that's a risk you need to price into your decision.

Common Mistakes I Still See

Even after years of reviews, I see these same errors in proposals:

• Assuming all solar is the same: It's not. Panel efficiency matters for roof-limited sites. Inverter topology matters for complex shading. Battery chemistry matters for cycle life.
• Ignoring the inverter bottleneck: A 50 kW solar array paired with a 30 kW inverter will never produce more than 30 kW. I've rejected proposals where the inverter was undersized without explanation.
• Skipping the O&M budget: Budget 0.5-1% of system cost annually for maintenance. Over 25 years, that's 12-25% added cost—not negligible.

Three things: validate the site assessment. Scrutinize the warranty stack. Confirm the financing structure. In that order.

This was accurate as of January 2025. The solar industry and incentive landscape change fast, so verify current policies and pricing before making a final decision. I learned these evaluation criteria over four years of reviewing 200+ pieces of vendor content annually. Things may have evolved since I last checked—especially with new battery technologies like powerwall 3 updates.