Solar and Battery for a Food Processing Plant

What the client needed

A food processing plant in South East Queensland uses about 12 GWh of electricity a year, with refrigeration and process loads that peak in the late afternoon. Network demand charges had become one of the largest lines on its power bill.

The question they needed answered: What size of solar and battery makes financial sense for the site, and how much will it really save?

What we did

• Analysed 12 months of 30-minute interval data against the site's network demand tariff.
• Modelled rooftop and carpark solar, and batteries from 0.5 to 2 MW, dispatched to target the network peak window.
• Checked roof structure, switchboard capacity, protection and connection requirements.
• Compared solar-only and solar-plus-battery options on capital cost, savings and payback.

What we found

Each kVA of peak demand costs nearly $14 a month under the site's tariff. The late-afternoon peak alone was setting about $310,000 a year in demand charges.

2 MWp of solar produces about 2.9 GWh a year, all used on site, for around $500,000 a year in savings.

A battery discharging from 4pm to 9pm cuts peak demand from about 1.8 MW to 0.8 MW, worth around $165,000 a year. On its own it pays back slowly, but it also backs up critical refrigeration.

The constraint was the main switchboard, not the roof. It needs a new incoming section to take the battery inverter.

Demand charges are set by the worst half-hour each month. At 98% battery availability over about 22 peak days, there's roughly a 36% chance of missing at least one day, which can cut the expected demand saving by about a third.

What we recommended

• Install 2 MWp of solar now.
• If the battery goes ahead, base its performance guarantee on monthly peak demand achieved, not battery uptime.
• Hold a reserve state of charge before the peak window, and use load and weather forecasts to schedule the battery.
• Design the switchboard upgrade now either way, and re-run the numbers each year as tariffs change.