Mushroom farm: growing cells in a power cut, and the peak

Keep the cell fans, the cooling and the climate computer on one backed-up circuit. A battery takes over within milliseconds, and a generator that starts by itself carries a long cut. Business battery systems pay for themselves when they also cut the cooling peak and store solar power. Our guide to an emergency power supply for your business compares UPS, generator and battery in general. This article applies it to growing cells.

You know the moment. A cell was filled yesterday, the compost is working, and the alarm goes at four in the morning. The fans are silent and the climate computer is dark. How long before the crop in that cell suffers? And a month later, the network bill shows a peak from the week three cells needed full cooling at once.

One grower on a solar forum put it plainly. His farm needed 114 kVA, "for a mushroom farm that requires a lot of cooling". Your climate installation is the biggest load on the site, and it is the one load that cannot stop. A heavier connection for that peak is expensive. A generator alone leaves a gap of seconds in which every fan stops.

A farm in Tielt shows the logic we build on. Its connection was too small to grow, and the next step would have been medium voltage. A battery system of 45 kVA and 123.2 kWh now gives the site more power, so a heavier connection was not needed. A smart control sends surplus solar power to the boilers. It is not a mushroom farm, but the problem is the same: more power than the connection gives, at the moments you need it.

What does a mushroom farm use its electricity for?

Mostly for cooling, ventilation and air circulation in the growing cells. Heat usually comes from a boiler. Electricity keeps the climate that the crop needs, day and night, for the whole cycle.

The Irish farm advisory service Teagasc describes the standard. Growing rooms are computer controlled at a constant 18 to 25 °C and 90 to 95% relative humidity. A crop takes about six weeks from filling to the end, with three flushes. The climate computer steers temperature, humidity and CO2 all that time.

Wageningen University & Research compared the most energy-efficient Dutch mushroom farms in 2019. At three comparable farms, electricity for cooling was 55 to 65% of the total energy use. An Italian study of a Dutch-type farm measured 0.22 kWh per kg of mushrooms, of which 0.18 kWh for cooling.

The load is not flat. After a cell is filled, the mycelium grows through the compost and the temperature rises, so the cell needs a lot of cooling. Wageningen describes fans at 100% after filling and during harvest, especially the first flush. Outside those moments, growers turn them back to 30 to 50%, which saves up to 80% of the fan electricity.

In Belgium, the sector is small and concentrated. VILT counted 33 mushroom farms, 17 of them in West Flanders (article updated in 2020). Many farms therefore sit in the same grid area, on connections that were sized long ago.

What happens in a growing cell when the power goes?

Everything that keeps the climate stops at once: fans, cooling, humidification and the climate computer. The air in the cell is no longer refreshed or circulated, while the compost keeps living.

CO2 is the first issue. Penn State Extension notes that when pins form, CO2 in the room should be 0.08% or lower, depending on the variety. Without ventilation, that level is not held. Heat is the second issue: a cell full of freshly filled compost produces warmth that the cooling normally removes.

How fast the damage comes depends on the phase. A cell that was just filled, or a cell in its first flush, asks the most cooling and air. A cell at the end of its cycle is more forgiving. We give no general figure in minutes, because it depends on your cells, your compost and the weather outside.

Which loads must stay on in a power cut, and which can wait?

Put the climate of the growing cells on the backed-up circuit, and leave the rest off it. The smaller that circuit, the longer any reserve lasts and the smaller the inverter can be.

For the cold room with the picked mushrooms, our article on cold rooms in a power cut shows how long the cold lasts. Livestock farms face a similar problem with barn fans, explained in ventilation in a barn during a power cut.

Battery, generator or both: what keeps the cells running?

For short cuts a battery alone is enough; for long cuts, a battery plus a generator that starts by itself. The battery closes the gap, the generator brings the hours.

A battery system that can run as an island takes over without a gap. According to Victron, a MultiPlus-II does this in less than 20 milliseconds. A generator needs a few seconds to start, so every fan in every cell stops and restarts.

With both, the battery carries the first minutes and a Victron GX control can start the generator automatically, for example when the battery gets low. How the switchover itself is wired is explained in our article on the generator transfer switch.

How big must the battery be: power for the starts, energy for the hours?

Power (kVA) sets whether everything starts; energy (kWh) sets how long it runs. The grower on the forum learned the same rule. Size the inverter on the highest apparent power. Size the battery on the average real power multiplied by the hours.

Power first. Electric motors draw two to twelve times their running current for a few seconds when they start, according to Auburn University. After a cut, all fans and compressors want to start together. Fans on frequency drives start softly, which lowers that moment a lot.

Then energy. Divide the usable kWh by the average power of the backed-up circuit in kW. The result is the number of hours. Measure that average in a freshly filled cell on a warm day, because that is when the cooling runs hardest.

With a generator behind it, the battery only has to bridge the start and a safety margin. Without a generator, it must cover the longest cut you want to survive. That second choice quickly makes the battery large, which is why most growers combine both.

Why does the cooling set your peak every month?

Because cells are filled in rotation, the heaviest cooling moment comes back again and again. It does not come once a year, like the harvest in a fruit cold store.

In Flanders, the capacity tariff counts your highest quarter-hour of each month, and you pay on the average of the last twelve monthly peaks. Our article on the capacity tariff for businesses explains the calculation. A peak that returns every month weighs fully in that average.

The peak builds when several cells need full cooling and full fans at the same time. Hot afternoons add to it. So does the restart after a cut, when every motor starts together. In Wallonia the rules differ: see our article on grid tariffs in Wallonia and Brussels.

What you can do without a battery: spread the filling of cells over the week, and let the climate computer ramp fans up in steps. Wageningen also notes that compost that stays a day or two longer in the tunnel needs less cooling in the cell.

Can one battery guard the cells and also cut the peak?

Yes, if you split its capacity. A fixed reserve stays locked for the power cut, and the part above it works every day.

In a Victron system this is the minimum state of charge "unless the grid fails". Below that level, the battery is only used when the grid is gone. Above it, peak shaving keeps your grid offtake under a limit you set, and surplus solar power is stored for the evening and the night.

That daily work is what makes the battery pay, not the few cuts a year. Our article on peak shaving with a battery shows how it works in practice. The general causes of peaks are in peak demand in a business.

Greenhouses face a related choice with lighting and CHP. See a battery in a greenhouse or nursery if your farm grows other crops too.

When is a battery not the right answer?

When your connection is large enough, your peak costs little and cuts are rare. Then an alarm, a standby generator with automatic start and a tested routine may be enough.

A battery is worth studying when one of these applies. The connection limits new cells or more cooling, the monthly peak is high, or a gap of seconds already caused problems. It is also worth it if you want to use more of your own solar power.

Whatever you choose, test it for real. Switch off the grid once a year with a freshly filled cell on the back-up, and watch the log. For the question of who pays when a cut damages your crop, see what you can claim after a power cut.

What happens when you ask us to secure your growing cells?

We start from your measured consumption, not from a catalogue. Our business battery page lists the steps: analysis and sizing, technical design, installation and commissioning, then monitoring and support.

• Analysis: a short measurement of your site, including a freshly filled cell, shows the real peak and the average load of the climate circuit.
• Design: which circuits go on the back-up, the inverter power for the starts, the reserve in kWh, and whether a generator joins.
• Installation: business systems range from small SME installations to modular systems up to 1 MW.
• Monitoring: in the app and the VRM portal you follow consumption per phase and get a notification when the battery runs low. See our energy management software.

How long such a project takes from start to finish is explained in the steps of a business battery project.