Why Commercial Solar Proposals Are Harder to Compare

A residential solar proposal is relatively straightforward to evaluate: panel count, system size, production estimate, equipment, price, warranty, incentives. For commercial projects, the variables multiply. System size is larger, roof engineering is involved, utility rate structure affects the economics, and tax treatment may be material to the investment case.

Business owners comparing commercial solar quotes need a structured approach — otherwise it's easy to compare on sticker price alone and miss important differences in what each proposal actually includes.

What a Complete Commercial Solar Proposal Includes

Building and Load Analysis

A credible commercial proposal starts with your actual utility data — typically 12–24 months of billing history — not a guess at your consumption. The proposal should show the installer understands your current load and, if relevant, any planned changes to it.

Energy Efficiency Assessment

Installers who only sell solar panels may skip this step. A thorough commercial proposal should address whether your current energy load reflects an efficient building, or whether efficiency improvements could reduce the system size and cost. An installer who sizes solar around an inefficient building's consumption is not serving your long-term interest.

Detailed Production Estimate

The production estimate should be based on your roof's actual orientation, tilt, shading (from rooftop equipment, adjacent structures, or trees), and local solar data. Ask the installer what tool they used for production modeling and what assumptions were made.

Utility Rate Analysis

Commercial electric bills often include both energy charges (per kWh) and demand charges (based on peak kW). The proposal should specify how solar addresses each component of your bill. A proposal that only shows energy savings without addressing demand charges may overstate the economic benefit for some commercial customers.

Roof Structural Assessment

Commercial roofs — especially flat roofs — require structural analysis to verify the roof can support the system weight. A credible proposal will specify whether ballasted mounting (no roof penetrations) or mechanically attached mounting is planned, and whether a structural engineering review is included.

Equipment Specifications

Panel manufacturer, model, wattage, and efficiency. Inverter type and brand (string inverter, microinverter, or power optimizer with inverter). Mounting system. All equipment should be specified, not described in vague terms like "tier 1 panels."

Complete Warranty Terms

  • Panel manufacturer's product warranty (typically 10–25 years)
  • Panel performance warranty (production degradation guarantee)
  • Inverter warranty
  • Installer workmanship warranty on the installation itself

Understand which warranties are manufacturer warranties (dependent on the manufacturer's continued operation) versus installer warranties.

Incentives with Verification Guidance

The proposal may reference the commercial Investment Tax Credit, MACRS depreciation, and Illinois Shines program benefits. These should be presented with appropriate caveats — tax benefits depend on your business structure and tax situation, and program benefits should be verified with your CPA and with the current program enrollment status. Be cautious about any proposal that presents specific tax savings as guaranteed without this context.

Project Timeline

Commercial projects involve engineering, permitting, utility interconnection, and potentially structural work. A realistic timeline for commercial permitting and interconnection in Illinois is longer than a residential project. The proposal should give you a realistic timeline, not a sales-optimistic one.

Red Flags in Commercial Solar Proposals

  • No efficiency assessment — proposal sized around your current inefficient load
  • Production estimates that seem high relative to comparable commercial projects
  • Tax benefits presented as specific savings without recommending CPA consultation
  • No structural analysis included or planned for a flat roof
  • Vague equipment descriptions ("tier 1 panels," "commercial inverters") without specific models
  • Pressure to decide quickly ("this price expires," "ITC deadline" — the deadline is real, but a reputable installer doesn't rely on pressure tactics)
  • No utility rate analysis — doesn't address demand charges for a commercial account
  • Crew and subcontractor situation not addressed — ask if the installation crew is direct employees or subcontracted

Questions to Ask Every Commercial Installer

  1. Did you review my actual utility bills, including demand charges, before sizing this system?
  2. Does this proposal address my building's efficiency, or is it sized around current consumption?
  3. What tool did you use for production modeling, and can you show me the assumptions?
  4. Is a structural engineering review included for roof loading?
  5. Who will perform the installation — your direct employees or subcontractors?
  6. What is the specific inverter model and its warranty terms?
  7. What is the realistic timeline from contract to interconnection, including permitting and utility review?
  8. How should I engage my CPA regarding the ITC and depreciation, and what documentation will you provide?
  9. What monitoring system is included, and what does the ongoing service relationship look like?
  10. Can you provide references from commercial customers in Illinois with similar building types?

How to Compare Proposals Once You Have Them

Create a comparison table across proposals covering: total installed cost, system size (kW), annual production estimate (kWh), cost per watt, equipment models, warranty terms, estimated first-year savings, projected payback period, and what incentives are included in the economics.

Lowest price per watt is not the right selection criterion. A system that produces less, uses lower-quality equipment, or skips an efficiency assessment that would have reduced the required system size can be "cheaper" while being more expensive in total.

SPM provides commercial proposals that include load and efficiency analysis, utility rate review, and equipment specifics. Learn about SPM's commercial services or schedule a commercial site assessment.