"Are those EC fans really that much more economical?"

At the location where he himself lives, many storage facilities have been built over time and he stores around 4,000 tonnes of product. Another 1,400 tonnes of storage capacity is at a later purchased site across the road. Pretty much everything is stored loose in bulk with both semicircular channels and on a slatted floor. There are also 150 boxes in which product is stored. All storage cells have outside air ventilation and no mechanical cooling is installed. He stores most product until the April-June period when deliveries are made.

Basically, Grubben was used to not really paying attention to power consumption during storage. "My father always had the slogan that energy costs nothing. In the past year, of course, that has changed a bit." Fortunately, Grubben had already invested in solar panels on the roofs of the various buildings on the farm in 2010. And because, despite the substantial storage capacity, he is still a small consumer with his 2 x 80A power connection, he can just balance his consumption. Of course, this has resulted in considerable savings on energy bills in recent years. Especially since the fans in the storage facility actually run mainly at night when it is cold anyway. The direct consumption of solar energy for the fans is then only limited. "At the other location, solar panels will also be installed soon," says Grubben. "Especially this year with the various tax benefit schemes, that still pays off. Despite the fact that net-metering will be phased out in the future."

So a total of 5,400 tonnes of product is stored at two sites. "What struck me last season was the difference in power consumption between the two sites. At the home site there was a power consumption of 70,000 kWh with 4,000 tonnes of product and at the other site there was 50,000 kWh consumed with 1,400 tonnes of stored product. So with almost three times more product but one and a half times more energy consumption. At both sites, potatoes and onions are stored in roughly the same proportions. The difference between the two sites lies mainly in the fact that EC fans are installed at the home site. "I called the storage advisor at Tolsma-Grisnich again to see if this can really make that much difference" says Grubben. And it turns out it does. EC DC motors have 20% lower energy consumption at 100% speed and the big advantage is that the speed can be controlled. This makes the advantage even greater in those periods when the product can do with a little less air. At 80% speed, energy consumption is only 50% compared to normal AC fans. Especially when drying and storing onions, where a lot of hours are spent, this quickly saves money at energy prices of € 0.40 per kWh, which were sometimes quite normal in the past period.

In onion storage during the drying phase, Grubben's fans always run at 100% speed. After all, onions that are brought in with good quality and colour need to be dried in this first phase of storage so that they also remain good for the rest of the storage season. Grubben does post-drying at 80% rpm. "I have also sometimes gone down to 60-70% rpm, but then there were not enough hours available in the day to dry the product back to the desired relative humidity." The MH-treated onions are eventually cooled back to around 7°C with the relative humidity kept around 80%. "In itself, 70-75% is a nicer humidity, but because some varieties do have fragile skins, I keep them at 80%".

Looking back at the last few years in onion growing, Grubben is happy with how storage has gone. Even in the past year with high energy prices. He hasn't changed his strategy much. In doing so, he uses the Vision Control storage computer. "It's nice that you can log in anytime and anywhere. This allows him to keep an eye on the measured values and make some adjustments to the settings where necessary. Grubben does not yet use smart modules like energy management, for example: "You just have to run those fans when the product demands it. Not when the power is cheap". Nevertheless, Grubben thinks there is still some more for him to get out of the Vision Control to further optimise his storage efficiency. In summary, Grubben has a clear strategy around the trade-off between energy costs and storage efficiency: "Quality doesn't always pay better...... At the end of the day, it's about just having to have tonnes, that’s what you can sell".