The answer
Which number matters most?
A commercial solar case rests on when your business uses electricity, how much of the array's output it can consume on site, and the full cost of installing and maintaining it. Roof area alone is not a financial case.
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Put solar output beside your meter data
Ask for half-hourly electricity readings covering ordinary weekdays, weekends, closures and the main seasonal changes. Then overlay the proposed array's expected generation. Where generation and demand happen at the same time, the site may avoid buying those units; the rest may be exported, curtailed or stored. A yearly total cannot show that split.
This matters particularly to offices that close at weekends, schools with holidays, warehouses with a large overnight base load and hospitality sites whose busiest hours may be later in the day. Model the real operating pattern. If a new heat pump, refrigeration plant or EV charging is planned, show today's case and a separate future case. Future loads should not be counted as guaranteed savings before the project is committed.
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Is the roof a safe long-term place for the array?
Establish the roof covering's condition and remaining life, structural capacity, penetrations, safe installation access and a maintenance route. If the roof is likely to need replacement soon, fitting panels now may create a later removal and reinstatement bill. Ask what the insurer requires and who is responsible for any roof warranty.
A tenant also needs to check the lease, landlord consent and rights to keep equipment in place long enough to benefit from it. The person paying the electricity bill may not be the person who owns the roof. Make that commercial arrangement explicit before treating a modelled payback as the tenant's return.
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What belongs in the financial model?
Show capital cost including access, electrical connection and design; ongoing inspections and maintenance; expected inverter replacement where relevant; finance costs; and the assumed life of the roof and equipment. Split avoided imports from export income and use the site's actual supply-contract terms rather than a generic domestic tariff. An export limit from the network operator can materially change the result.
Ask for at least a central and cautious case, varying future import prices, export payments, self-use and downtime. The result should show cash flow and assumptions, not just one payback number. A free commercial survey can establish whether the roof, connection and load pattern justify detailed investment modelling before the business commits to procurement.
Where this guidance comes from
Check the original guidance.
These primary sources support the technical or scheme points above. Rules can change; follow the current source before making a commitment.
Apply this to your property
Test solar against your site data.
A free commercial survey can connect roof feasibility to actual operating hours and electricity demand before a business case is presented.