Sizing a solar system for load-shedding, not for a sales brochure

Ask three solar installers to quote the same commercial building and you'll often get three different system sizes — not because they disagree on panel efficiency, but because two of them are selling a standard package and one is actually sizing against the building's load.

A standard package is easy to sell: pick a kW rating, quote a price, install fast. It's also frequently wrong. A retail unit with heavy refrigeration load has a completely different consumption curve to an office with the same floor area. A manufacturing site running three shifts needs a system sized against its overnight minimum, not its daytime peak. Sell the wrong size and you get one of two outcomes: an oversized system with a payback period nobody wants to explain to finance, or an undersized one that still needs the diesel generator every time load spikes.

Proper sizing starts with data most sites already have and rarely use: twelve months of utility bills, or better, interval meter data showing consumption by hour. That data reveals the shape of demand — the baseline load that never drops, the peaks, and how much of the day is actually covered by daylight hours versus needing battery discharge. From there, sizing an array and a battery bank is closer to engineering than sales.

The second most common mistake compounds the first: treating the inverter as an afterthought. A hybrid inverter is what actually decides whether a load-shedding outage is invisible to your operation or a ten-second scramble to restart a generator. The switching speed, the inverter's surge capacity for motor start-up loads, and how it prioritises circuits during a battery-only period all matter more than the brand of panel on the roof.

None of this is exotic. It's the difference between a solar quote and a solar design. When we scope a commercial or industrial site, the proposal includes the load profile we sized against, the expected output month by month, and the payback period based on that specific site's diesel offset — not an average across a brochure of similar-sounding buildings.