New research questions priority dispatch for solar PV during peak loads

Researchers from the Bern University of Applied Sciences (BFH) have proposed a series of measures to help solar PV increase its share in a given country's energy system without the need for building additional, costly distribution infrastructure.

In the “Discussion paper: Solution approaches for the grid integration of solar power,” the scientists explained that expanding the European grid, for example, would not solve the problem of having too much solar power injected into grids during load peaks, which may not be absorbed by the grid nor sold to consumers, due to the lack of enough demand.

“If we want to supply Italy with wind electricity from the North Sea, of course, we must increase the transmission capacity,” the research's lead author, Christof Bucher, told pv magazine. “However, at least in Switzerland, a lot of costs are associated with the distribution grid expansion to host more PV, which we think is the wrong way to push grid integration.”

The research group proposed a series of alternative measures that consumers and grid operators could employ to avoid grid expansion. They said a general incentive approach to grid-serving behavior should be encouraged.

For example, they claim that priority dispatch for PV may be avoided during peak times, thus forcing the PV system operators to use surplus solar power for batteries or electric vehicle (EV) charging. Priority dispatch has been an important tool to facilitate renewable energy integration into power systems in the past. It consists of prioritizing the injection of power produced by clean energy sources while offsetting conventional power production. 

“There should be no right to feed load peaks into the grid when they are not relevant in terms of energy but are challenging and uneconomical for the overall system,” the paper notes.

Increasing self-consumption by PV system owners should also be encouraged. “However, one thing technical is missing: Self-consumption does not necessarily reduce stress on the grid – that’s why many grid operators don’t agree with current regulations, which throughout Europe typically support self-consumption,” Bucher stated. “If you do self-consumption for 95% of the time, but one week per year you are on vacation and do not do any self-consumption, then the whole grid infrastructure must be dimensioned for this one week. It would be very easy to avoid this situation, but currently there are no incentives to do so.”

The researchers also warned that PV curtailment will be unavoidable in the future. “Curtailment should be used, but not too much,” Bucher explained. “Anyway, it should be an economic decision of every individual PV system operator. My guess is that today, 50% of distribution grid reinforcement investments are spent for maybe 10% of the additional solar energy. This is far from the economic optimum.”

According to him, encouraging a free market vision and reducing subsidies may be only part of the solution. “I guess it will not be sufficient as a free market would not necessarily give a price to the infrastructure,” he added. “Therefore, our short-term vision is rather a shift from kilowatt-only based feed-in tariffs (FIT) towards higher tariffs for systems that avoid injecting power peaks. As system operators don’t.”

He also explained that, by not injecting 50% of power, most systems lose less than 5-10% of energy, with self-consumption being taken into account. “If PV system operators are offered a 20% higher FIT for this sort of system control, they should take this offer,” he said. “And, of course, this could be implemented cost-neutral, with those who inject more power getting a lower FIT.

“In the view of the authors, it is more expedient to invest in the decentralized handling of power peaks than in the expansion of the distribution grid,” the paper concludes.