When you turn onto the Petersen farm in North Friesland, you enter an energy transition wonderland. Behind you, dozens of wind turbines are turning, on the left a fully electric fleet of vehicles from the local project developer GP JOULE is charging, and straight ahead a biogas plant is humming. "And behind the shed is Germany's first brownfield solar park in the megawatt class," laughs Sören Sönksen as he welcomes you. He takes care of the commercial aspects of the biogas plant - and thus also the sale of electricity.
“Since the plant was initially equipped with a CHP capacity three times higher than its biogas production, it was clear to us that the plant's electricity production should be as flexible as possible and aligned with daily electricity exchange prices.” With one or two stops per day, the biogas plant runs according to schedule - it produces electricity almost exclusively during the hours when power is traded at particularly high prices on the electricity exchange. Depending on the day of the week, the plant "only" operates at full load for four to twelve hours, during which it produces electricity and heat. For the remaining hours of the day, it continues to produce biogas and stores it for later conversion into electricity under the air roofs of the fermenter and digestate storage, while heat is supplied from the 500 cubic metre heat storage tank.
"At the beginning we were a bit nervous when we switched to scheduled operation," recalls Sören. But the additional work involved in both the initial changeover and the new day-to-day operation was manageable and the technical hurdles were easy to overcome. "In order to be able to operate even more flexibly, we later also made the feeding of the system more flexible. Contrary to the prophecies of doom of some experts, this did not have any negative effects on the biology in the fermenter.”
Next Kraftwerke's customer app plays a major role in the daily implementation of the electricity production schedule. "We receive the current electricity price forecasts for every quarter of an hour and a proposed timetable via the app every day. We regularly adjust this ourselves and send it back. Next Kraftwerke then uses remote control to switch the CHPs to the times we set. The app is damn good and works flawlessly," says Sören Sönksen with satisfaction.
Linking the power production to the intraday prices of the spot exchange does not lead to an increase of starts and stops when compared to a schedule which is based on day-ahead prices. "We use the intraday prices in the app to align the blocks of our electricity production as precisely as possible and to the nearest quarter hour to the highest spreads." Electricity traders refer to the price differences between the cheapest and the most expensive quarter hour of a day as spreads.
He is also satisfied with the financial side of the changeover. "When we started to operate our plant according to Next Kraftwerke's schedules about three years ago, our calculation showed an additional revenue of 1,000 euros per week compared to a base load operation. We quickly achieved this figure in real operation, which justified our investment in materials and labour. Since 2021, the electricity prices and correspondingly the spreads have risen sharply, so that over the course of the year we achieved additional revenue of 2,500 euros per week. Since December 2021, we have now achieved a weekly plus of around 6,000 euros compared to 24/7 operation, but in the meantime the plant has also been upgraded to provide even more flexibility. Now we are being rewarded for our first-mover commitment and courage."