Commercial solar sizing starts with a load profile

Start with when the business uses electricity

Two buildings with identical roofs can need very different solar designs. One may run refrigeration all week; another may be empty on weekends. Annual consumption gives scale, but it hides the timing that determines direct solar use. A commercial solar assessment should compare an interval load profile with a site-specific generation estimate.

Request interval data from the retailer or available metering system, preferably covering a full seasonal cycle. Record whether values are kWh per interval or average kW. For example, 10 kWh recorded over half an hour represents an average 20 kW during that interval. Mixing these units can double or halve an apparent load incorrectly.

An illustrative time-matching exercise

The following simplified one-hour periods assume no battery and no losses. Solar used on site is limited by whichever is smaller: generation or load. This is an educational calculation, not a generation forecast or savings estimate.

Do not calculate self-consumption from annual totals alone

A business that consumes more electricity annually than its array generates can still export heavily at midday and import after sunset. Sum the matched intervals instead. If solar already exists, grid-import data alone understates total site consumption because it omits solar used behind the meter. Reconstruct the load with suitable generation and storage data, and label any estimates.

Check the data before modelling

• Confirm the site, meter identifiers, time zone, interval duration and date range.
• Identify missing readings, estimated intervals and daylight-saving changes.
• Separate working days, weekends, shutdowns and seasonal operations.
• Record tenancy changes, production growth and equipment scheduled for retirement.
• Distinguish the network export allowance from inverter size and roof capacity.

Explain exceptional periods rather than deleting them silently. A long shutdown may be irrelevant to normal operation or may recur every year. The analyst should state which treatment was used. The monitoring data guide helps clarify measurement boundaries before combining files.

Energy offset and demand charges are different tests

Solar may reduce imported kWh without reducing the tariff’s highest-demand interval. A late-afternoon peak may remain after solar production falls. Read the commercial battery demand-charge guide for the separate power-and-duration test. Avoid adding energy and demand savings together unless the actual contract and modelling method support both.

If vehicles are being electrified, their charging times change the future profile. The fleet depot planning worksheet distinguishes energy needed per shift from coincident charging power. Model present operations and plausible future operations separately rather than treating future consumption as certain.

Ask for an auditable assessment

The output should show the data period, exclusions, load assumptions, generation method, export constraints and sensitivity to operating changes. Roof structure, electrical supply and approvals remain independent constraints. Use the project sequence guide to record who confirms each one. Roof area defines a physical opportunity; the load profile helps determine how useful that opportunity may be.