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

Mark Grubben is an arable farmer in Swifterbant where he stores products at two locations. The products he grows and stores himself are 25 hectares of consumption potatoes and 45 hectares of red and yellow seed onions. In addition, other crops are also grown, such as cereals.

Over the years, many storage facilities have been built at the location where he lives and he stores around 4.000 tons of product. Another 1.400 tons of storage capacity is available at a later purchased location across the road. Almost everything is stored in bulk with both semi-circular channels and on a slatted floor. There are also 150 boxes in which product is stored. All storage cells are equipped with outside air ventilation and no mechanical cooling has been installed. He stores most products until the period April - June in which deliveries are made.

In principle, Grubben was used to not really paying attention to power consumption during storage. "My father always had the slogan that energy costs nothing. That has of course changed a bit in the past year." Fortunately, Grubben had already invested in solar panels on the roofs of the various barns on the farm in 2010. And because, despite the considerable storage capacity with its two 80A power connections, it is still a small consumer, it can simply balance. This has of course resulted in considerable savings on energy bills in recent years. Certainly also because the fans in the storage actually mainly run at night when it is cold. The direct absorption of solar energy for the fans is then only limited. "Solar panels will soon be installed at the other location," says Grubben. "Certainly this year with the various tax schemes, it still pays off. Despite the fact that netting will be phased out in the future."

A total of 5.400 tons of product is therefore stored at two locations. "What struck me last season was the difference in power consumption between the two locations". At the home location there was a power consumption of 70.000 kWh with 4.000 tons of product and at the other location 50.000 kWh was consumed with 1.400 tons of stored product. So with almost three times as much product but one and a half times as much energy consumption. Potatoes and onions are stored in approximately the same proportions at both locations. The difference between the two locations is mainly that EC fans are installed at the home location. "I called Tolsma-Grisnich's storage advisor again to see if this can really make that much of a difference," says Grubben. And that indeed turns out to be the case. EC DC motors have a 20% lower energy consumption at 100% speed and the big advantage is that the speed is adjustable. This makes the advantage even greater in those periods when the product can do with less air. At 80% speed, the energy consumption is only 50% compared to normal AC fans. Especially when drying and storing onions, where a lot of operating hours are made, this quickly generates money at energy prices of € 0,40 per kWh, which were sometimes quite normal in the past period.

When storing onions during the drying phase, Grubben's fans always run at 100% speed. After all, onions that have arrived with good quality and color must also be dried in the first phase of storage in such a way that they remain good for the rest of the storage season. Subsequent drying is done by Grubben at 80% speed. "I have also dropped to 60-70% speed, but then there were not enough hours in the day to dry the product back to the desired relative humidity." The onions treated with MH are finally cooled down to about 7 degrees, with the relative humidity being kept at about 80%. "In itself, 70-75% is a nicer humidity, but because some varieties go bald faster, I keep them at 80%."

Looking back on the last few years in onion cultivation, Grubben is satisfied with how the storage went. Also in the past year with high energy prices. His strategy hasn't changed much. He uses the Vision Control storage computer for this. "It's great that you can log in anytime, anywhere." This gives the opportunity to monitor the measured values ​​and adjust the settings where necessary. Grubben does not yet use smart modules such as energy management: "You just have to run the fans when the product asks for it. Not when the electricity is cheap". Nevertheless, Grubben thinks that he can still get more out of the Vision Control to further optimize his storage efficiency. In summary, Grubben has a clear strategy for the trade-off between energy costs and storage efficiency: "Quality does not always pay better... In the end, you just have to have tons."