Commercial and industrial (C&I) solar is mostly a different sport from residential. Bigger systems, more complex tariffs, different financing options, different risk profile. This guide covers the specific things C&I buyers need to know.
Why commercial is different
A residential buyer mostly thinks about offsetting kilowatt-hours. A commercial buyer has to think about:
- Demand charges — often 30–50% of a commercial bill, based on peak 15-minute demand.
- Time-of-use rates — peak-hour electricity can cost 2–3× off-peak rate.
- Power factor penalties — not solar's main job, but related.
- Load profile — when you use power matters as much as how much.
- Depreciation and tax treatment — can shift ROI by years.
- Financing structure — cash vs loan vs lease vs PPA each have different implications.
The headline economics for C&I solar are often better than residential — 4–7 year paybacks are common — but reaching those numbers requires getting all of the above right.
The economic drivers
Self-consumption ratio
The most important number. It's the percentage of solar production you use on-site versus export to the grid. Higher is better because self-consumed solar offsets the full retail rate; exported solar is compensated at lower rates.
- Business operating 8am–6pm weekdays: typically 70–85% self-consumption.
- 24/7 operations: approaches 100%.
- Weekend-closed operations: 50–60% without battery storage.
Demand-charge reduction
If your peak demand happens during daylight hours, solar can shave that peak and reduce demand charges — sometimes worth as much as the energy savings. Requires careful load analysis during design.
Time-of-use tariff capture
Peak utility rates are often midday, which aligns perfectly with solar production. Offsetting peak kWh at peak rates is significantly more valuable than offsetting off-peak kWh.
Depreciation / tax treatment
In many jurisdictions, solar qualifies for accelerated depreciation, tax credits, or both. This can substantially improve after-tax ROI. Worth a conversation with your accountant before committing to a financing structure.
Structural considerations
Commercial roofs are more varied than residential and more likely to have issues that affect solar viability.
Roof age and remaining life
Solar systems last 25+ years. Installing on a roof with less than 15 years of remaining life costs you the re-installation fee when the roof is eventually replaced — typically 15–25% of the original install cost. Replace the roof first if it's close to end of life.
Roof type
- Metal roofs: Easy. Standing-seam clamps require no penetrations.
- Concrete / flat: Ballasted or mechanically-fixed mounting. Watch weight loading.
- Bitumen / membrane: Requires careful penetration detailing. More expensive to install well.
- Tiled or slate: Less common for C&I but works with appropriate flashing kits.
Weight loading
Solar adds roughly 15–25 kg/m² (panels + mounting). Most modern commercial roofs handle this, but older warehouses and structures with snow-load ratings should be assessed. Ballasted systems on flat roofs can add significantly more weight.
Available roof space
Usable roof area is less than total roof area. Skylights, HVAC units, roof access, fire setbacks (required in many jurisdictions), and shading from surrounding structures all reduce available space. Typical utilisation for a flat commercial roof: 40–60% of total area.
Financing structures
Cash purchase
Own the system outright. Best long-term ROI. Highest upfront capital. Makes sense for businesses with available cash and a strong tax position.
Loan
Finance the system, own it after paying off. Preserves working capital at the cost of some total return. Most financiers offer 5–10 year terms for solar.
Operating lease
Monthly payment, no ownership. Off-balance-sheet treatment in many jurisdictions. Moderate total return. Attractive when capex is constrained.
Power Purchase Agreement (PPA)
Third party owns and operates the system on your roof. You pay only for the electricity it produces at a contracted rate (typically 10–30% below grid rate). Zero capex. Provider captures most of the savings. Often the right choice when you can't commit capex or don't want to manage the asset.
The right financing structure depends on your cost of capital, tax position, balance-sheet preferences, and how long you plan to occupy the site. A business paying corporate tax in a jurisdiction with accelerated depreciation often does far better with cash + depreciation than PPA. A business without taxable income often does better with a PPA. Model both.
What a serious proposal looks like
A real C&I proposal should include:
- Load profile analysis based on 12 months of interval data from your utility.
- Yield model with monthly production estimates, not just annual.
- Self-consumption ratio analysis matched to your actual load pattern.
- Structural assessment of the roof.
- Full bill of materials with specific panel and inverter models.
- Annual cash flow table over 25 years, with inverter replacement year included.
- IRR and NPV calculations using realistic (not promotional) assumptions.
- Warranty schedule for all major components.
- Interconnection timeline estimate based on your specific utility.
A three-page PDF with a system size and a price is not a proposal. It's a marketing document.
Common traps
- Assumed self-consumption too high. Quote assumes 90% self-consumption; your actual pattern is 60%. Payback number is fantasy.
- No inverter replacement in the model. Ignoring a known ~10% of system cost at year 10–12 inflates ROI significantly.
- Unrealistic electricity rate escalation. Projecting 6%/year rate increases when historical data shows 3% doubles the 25-year value artificially.
- Skipped structural assessment. "We'll check during installation" means no responsibility for structural issues.
- PPA with punitive exit terms. Some PPAs lock you in for 20 years with high buyout costs. Read the contract.
- Hidden O&M responsibilities. Find out who's responsible for cleaning, monitoring, component replacement, and warranty claims before signing.