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Energy Transition in Greenhouse Horticulture

Optimal integration of various energy sources

Zeppelin Power supplied and installed 1250 solar panels at the cherry tomato nursery Sweet Lions in Grubbenvorst. The challenge of this project was not the solar panels themselves, but the total integration of various energy assets connected to a single grid connection: in addition to the solar panels, also a CHP. These must not only work flawlessly together to cover the business load but also export and curtail energy: dim during a negative electricity price or up to the max of the grid connection.

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Eco-conscious cherry tomatoes under the Limburg sun

Anyone driving through North Limburg Grubbenvorst cannot miss it: the California greenhouse horticulture area dominates the landscape here. Among all those greenhouses, Sweet Lions' glass fortress takes a prominent place. Since 1993, a unique line of cherry tomatoes has been grown here in an eco-conscious and maximally organic way. Solar energy is the primary energy source for this company; it shines directly through the glass to nourish the plants naturally, but is also converted into energy via the solar panels on the roof.

When the sun doesn’t or barely shines, they have other resources in Grubbenvorst, namely three CHPs with a combined capacity of nearly 5 MWh. The CHPs not only provide energy and heat but also CO2, which is extracted from the exhaust gases and used as nourishment for the tomato plants.

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The challenge lies in the dynamics

Gerdo Rutten was until 2025 project manager at Zeppelin Power and was involved in integrating the CHP and solar panels into a single grid connection: “We were dealing with a limited grid connection of 2 MW here, on which a maximum of 1750 kW of power can be exported. This applies to both the CHP and solar panels together. The challenge was to neither draw too much power in nor export too much, as optimally and efficiently as possible.”

“In this project, our power management was crucial because the CHP and solar panels together exceed the maximum power that Sweet Lions is allowed to return. If we applied static power management, we would set the three inverters to always stay below the maximum limit. But by making the power management dynamic, we optimize power production based on real-time data. We dim the solar power very precisely and only when necessary, instead of switching off a large part of the solar field. This way, we utilize much more solar energy than with static power management.”

“Because we write the software custom-made, our PPEMS knows how to react as profitably and efficiently as possible to different inputs.”

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No smart system without our PPEMS

The Zeppelin Power Energy Management System (PPEMS) plays an essential role in the dynamics, efficiency, and profitability of the system. This PPEMS effectively operates based on quarter-hour data of trade prices from the electricity imbalance market and adapts the system’s dynamics accordingly. Nico Olsthoorn is Team Lead Engineering at Zeppelin Power and knows everything about the PPEMS: “Because we write the software custom-made, our PPEMS knows how to react as profitably and efficiently as possible to different inputs. How much energy is needed within the greenhouses, what is the current electricity price, and how much solar energy do the panels currently provide? Based on a calculation that is never over, the CHP is turned on or off, and the solar panels are dimmed or not.”

Gerdo: “If you stand in the right spot at Sweet Lions, you can hear the inverters hum and the CHP turn on and off. Our PPEMS regulates everything, and no one notices anything further. The only thing that matters is a continuous and reliable power supply for the company, always with optimal values on the energy export side.”