Demand charges change everything
Most commercial tariffs bill two things: the energy you used, and the highest rate at which you drew it during the billing period. That second charge is the demand charge, and on many commercial bills it is a large share of the total.
It means a commercial project is often not primarily about generating kilowatt-hours. It is about shaving the peak, and that is a different design objective with a different answer — frequently involving storage, because a battery can flatten a peak that solar alone cannot.
A design produced without reading an actual interval-data bill is not a design.
The tax position is genuinely different
Businesses and homeowners sit under different sections of the federal tax code for solar, and businesses have access to depreciation treatment that homeowners do not.
This is the single most consequential difference in the financial model, and it is also the one where general advice is most dangerous. The value depends on the entity type, its tax position, and whether it has liability to offset.
Get this from a tax professional who has seen your accounts. Not from a solar salesperson, and not from this page.
Different roofs, different engineering
Commercial roofs are typically large, flat or low-slope, membrane-covered, and structurally different from a residential pitched roof.
- Ballasted racking. Flat roofs often allow arrays held down by weight rather than penetrations, which avoids puncturing the membrane — but adds significant dead load.
- Membrane warranty. Roof warranties on commercial membranes frequently have strict conditions about what may be attached. Check before designing.
- Structural capacity. Ballast is heavy. A structural engineer, not a solar designer, signs this off.
- Wind uplift. A large flat array is a large sail. Engineering for uplift is a serious part of the design.
Procurement works differently
Residential solar is sold. Commercial solar is procured.
That means a request for proposal with a defined scope, multiple bidders responding to the same specification, comparable pricing, and contract terms that are negotiated rather than presented.
It also means an owner’s engineer or independent consultant is worth the fee on any project of size — someone whose only job is to evaluate the bids on your behalf.
Ownership structures you will not meet as a homeowner
Beyond cash and loan, commercial projects commonly use power purchase agreements where a third party owns the system and sells you the output, and various lease structures.
Which is best depends heavily on whether your business can actually use the tax benefits of ownership. A business with no tax liability to offset may be better served by a structure where someone else takes that benefit and passes part of it back in a lower rate.
How the work runs
- Pull interval dataTwelve months of it from the utility. Demand peaks are invisible in a summary bill and they drive the whole design.
- Establish the tax positionWith an accountant. This determines which ownership structure makes sense before any design work.
- Roof and structural surveyMembrane condition, remaining life, warranty conditions and load capacity.
- Define the objectiveEnergy offset, demand reduction, resilience, or a sustainability commitment. They lead to different systems.
- Write a specificationSo that competing bids are actually comparable. This is the step most often skipped and most often regretted.
- Competitive tenderMultiple bidders against one specification, evaluated on more than headline price.
- Interconnection studyCommercial-scale interconnection frequently requires a utility study, which takes time and can impose conditions.
- Contract and constructionNegotiated terms, defined milestones, and a commissioning standard agreed in advance.
What moves the price
We do not publish a national average and present it as your price. These are the variables that separate two quotes for the same job — run your own numbers with the cost guides and calculators, and check what incentives you actually qualify for.
| Factor | Why it moves the number |
|---|---|
| System scale | Cost per watt generally falls with size, which is the main structural advantage commercial has. |
| Roof condition and remaining life | A membrane near end of life must be addressed first, exactly as with a residential roof. |
| Ballast vs penetration | Structural capacity decides this, and the answer changes both cost and roof warranty position. |
| Storage for demand management | Frequently the component that makes the business case work, and frequently a large part of the budget. |
| Interconnection requirements | A utility study can impose equipment or upgrade costs that were not in anyone’s first estimate. |
| Ownership structure | Cash, loan, lease and PPA produce entirely different cash flow profiles for the same physical system. |
What to ask before you commit
Take this list to the conversation. A professional who answers these directly is telling you a lot; one who deflects is telling you more.
- Have you analysed twelve months of our interval data, and what does it say about our demand peaks?
- What proportion of the projected saving is energy, and what proportion is demand charge reduction?
- What does our roof membrane warranty say about attachments, and have you read it?
- Who is performing the structural assessment, and are they independent of you?
- What happens to the projected returns if the interconnection study imposes upgrades?
- Which ownership structure suits our tax position, and have you spoken to our accountant?
Common questions
How is commercial solar different from residential?
Different tariffs including demand charges, different federal tax treatment including depreciation, flat roofs allowing ballasted racking, competitive procurement rather than direct sales, and interconnection processes that often require a formal utility study.
What is a demand charge and why does it matter?
A charge based on the highest rate at which you drew power during the billing period, rather than total consumption. It can be a large share of a commercial bill, and reducing it — often with storage — is frequently the main justification for a project.
Should we buy, lease, or use a PPA?
It depends principally on whether your business can use the tax benefits of ownership. A business without sufficient tax liability may do better under a structure where a third party takes those benefits and reflects them in a lower rate.
Does our roof need replacing first?
Same principle as residential, higher stakes. A commercial array has a life measured in decades; if the membrane does not, replace it first rather than paying to remove and reinstall a large array later.