I size commercial solar around useful electricity, not simply available roof space. The important information is how much power the business uses, when it uses it, what may change in the future, and what the site and network will allow.
Annual electricity use is only the beginning
Two businesses can use the same amount of electricity over a year and still need very different solar systems. The timing of that usage changes how much solar can be used directly and how much may be exported.
The information I use
- Electricity bills and annual kWh
- Interval data for larger or more complex projects
- Operating hours and weekend use
- Electricity tariffs and demand charges
- Existing solar production and exports
- Roof area, direction, shading and condition
- Electrical supply and network limits
- Expected business growth
- EV charging and electrification
- Whether battery storage is being considered
Self-consumption matters
If a business can use most of the solar power while it is being generated, the system may replace grid electricity at the customer's retail rate. A system that exports a large share of its output can have a different financial result.
Bigger is not automatically better
A larger system can make sense where daytime usage is high, energy use is growing, EV chargers are planned, storage will absorb surplus generation, or exports have useful value. A smaller system may be better where daytime consumption is low or network/export conditions restrict the benefit.
Future demand should be included
I do not want to size a system only for yesterday's bill if the customer is about to add machinery, extend operating hours or electrify part of the business. Reasonable future demand should be built into the comparison.
Network limits can change the design
The local network may limit system capacity or exports. A business with strong onsite consumption may still use a larger system even when exports are restricted, but the expected result should be modelled rather than assumed.
Battery storage can change the solar calculation
If a battery is part of the project, there may be value in producing additional daytime energy to charge it. But solar and battery capacity should be considered together. A large battery with too little surplus solar may be underused.
Why I often compare several sizes
For a commercial customer I may compare a conservative system, a recommended system, and a larger growth option. If storage is relevant, I can then compare solar-only against solar plus battery. Seeing price, generation, self-consumption, exports, savings and payback side by side makes the recommendation easier to understand.
The aim
The objective is not to install the most panels. It is to find the system size that gives the best combination of useful energy, financial return, practical performance and future flexibility.
Solar and battery performance and savings are estimates that depend on the individual site, electricity use, tariffs, equipment, installation and assumptions used. Current incentives and network requirements should be checked for the specific project before a proposal is finalised.
Want to look at your actual situation?
You do not need to know the system size first. Start with your electricity use, existing system and what you want to achieve.