Use electricity when it is at its cheapest


The Elgevos research project shows, using a solar collector greenhouse, how much, by load shifting in accordance with the price fluctuations in the electricity market, minimum annual electricity procurement costs can be achieved. The project offers an on-line configuration tool for this purpose. Editor-in-Chief, Katrin Klawitter asked Dr Ingo Schuch from the Humboldt University in Berlin to explain.

Foto: Ingo Schuch

Are your results currently only interesting for companies that already have available a solar collector greenhouse and a heat pump or are thinking about purchasing these?

Dr Ingo Schuch: The use of heat pumps in greenhouses has already been investigated many times. However, a widespread use of this technology, which is quite common in other areas of heating technology, has so far failed because of the additional costs for the system equipment and operating energy.

As demonstrated in the Zineg project with the prototype of a solar collector greenhouse, the use of electric heat pumps for heating / cooling in tomato growing cannot only significantly reduce energy consumption but also lead to yield increases of up to 32 percent. However, whether higher prices can be achieved for horticultural crops from a CO2-neutral or resource-saving production is still an open question.

Which acquisition costs are we talking about here?

Dr Ingo Schuch: According to our estimates, the costs for equipping a one-hectare collector greenhouse are between 70 and 120 euros per square metre. These investments need to be offset by additional revenues and lower energy costs. Depending on the assumption of the costs for the solar system, the additional revenues and the development of energy prices, this results in a large variation in the amortisation period of three up to 15 years.

In the meantime, the price for electric power for driving heat pumps has become more expensive and it is difficult to predict where the development will go. Here, the flexible operation of the greenhouse with load management for power grid relief could create a win-win situation that also leads to lower electricity costs. Therefore, in the Elgevos feasibility study, the greenhouse operation was optimised according to the price fluctuations on the electricity market.

However, the use of lighting did not pay for itself, even in electricity-optimised operation. The additional costs for the electricity supply clearly exceed the revenue from the increase in the yield of tomatoes.

Are your results relevant to operations that grow other crops, such as ornamental plants?

Dr Ingo Schuch: Our studies focused on the greenhouse cultivation of vegetable crops. In principle, however, energy-intensive greenhouse crops are suitable, which also have a certain flexibility with regard to permissible heating, cooling as well as light / dark phase.

What importance do you envisage for load management in the future?

Dr Ingo Schuch: Until a few years ago, electricity in Germany was generated predominantly by fossil power plants, which were operated according to the electricity demand. In view of the on-going expansion of renewable energies, especially wind and sun, the need for flexibility in the electricity system will increase significantly in the future.

Consumers can also make a contribution here by adapting their behaviour to electricity generation, that is, via load management. In times of high electricity supply and low demand, then electricity prices on the spot market are low. However, adapting consumer behaviour is not always worthwhile at the moment because electricity prices are subject to high additional costs, such as taxes and surcharges. As a result, fluctuations in spot market prices are not passed directly onto consumers. The highest share of electricity costs lies in grid charges and the Renewable Energy Act (EEG) surcharge.

There are already various proposals to make load management more attractive in the future, for example, by making grid charges and the EEG surcharge more flexible. These previously fixed cost components would then be linked to the electricity price, so the price signals of the market would be strengthened. Low electricity prices would be associated with low additional costs, high corresponding with higher taxes and surcharges. Depending on how the other regulatory framework conditions are structured, this can be just as worthwhile for companies as it is for households.

A prerequisite for this is that companies can either (partially) shift their electricity demand in time or have a possibility of decoupling time-inflexible demand by storage of electricity extracted from the grid.