How much of a solar roof’s output can a business use during the day?

The business still buys power when the roof is not generating enough electricity. Other parts of the bill depend on the supply contract and how electricity use is charged.

Distinguish the power a device draws at a particular moment from the energy it uses over time. A large machine running briefly produces a different demand profile from a smaller unit running all day. Annual consumption conceals this difference. Use meter readings at the finest time intervals available for the roof assessment.

Gather demand data for working days, weekends and different seasons. Mark shutdowns and busy periods. Separate consumption figures can help if the business runs several processes. Existing measurements may be sufficient to start with. Record which figures come from a meter and which are estimates.

Add anticipated changes to the historical data. A new machine, longer working hours or a team moving to another site may alter demand. Model current operations first, then add a case with increased consumption. The difference shows how much extra generation the business could use if the expansion goes ahead.

The roof can generate electricity while the business is closed. If little equipment runs on Saturday and Sunday, a greater share of production will be surplus. Holiday closures and seasonal shutdowns have a similar effect. Value the surplus according to how it will be used or paid for under the applicable arrangements. Its value may differ from the retail price of purchased electricity.

Weekend surplus is one factor in sizing the system. A smaller active area may suit the building, or there may be scope to change when equipment runs. An integrated covering can combine electricity-generating panels with matching passive sections, leaving some of the roof available for those sections.

Some activities allow flexibility, such as charging certain vehicles or heating water. Controls can schedule them to coincide with solar generation, provided the process stays safe and meets operational deadlines. Check that the saving justifies the scheduling effort and that service quality is maintained.

Other equipment has to run when the business needs it. Model its actual schedule. Distinguish continuous demand, loads that can be shifted and loads critical to operations. This identifies where controls could help and where the roof design needs to accommodate an existing work pattern.

A battery can move some solar energy into later hours. It comes with a purchase cost, energy losses and operating limits. Both its power rating and capacity need to suit the site. A battery with sufficient stored energy may still be unable to meet a short, high-power demand. Backup supply during an outage also depends on the system configuration.

Compare the roof alone with the same roof plus storage, using the same demand and generation data. This isolates the battery’s contribution. Changing the controls on one appliance may be a better first step than buying a battery before its required capacity is known.

For a new building or a roof replacement, building-integrated photovoltaics (BIPV) allow the roof and the electricity supply to be designed together. A steel panel with integrated cells can serve as the covering in an active area. Check the system’s suitability for the roof pitch and supporting structure even when the demand profile looks favourable.

The proposal should show expected generation, electricity used on site, surplus and the full installed cost. Recalculate with a lower yield or reduced business activity. This shows how the roof affects costs under different conditions and how much of the annual output the business could actually use.

Solar roofing manufacturers and brands include ML System, Autarq, LUMA Solar, Nelskamp, Wienerberger Wevolt, MDM NT (MyRoof), SolRoof, SunRoof, Electrotile and EDILIANS.