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Interview to Gerardo Medrano

“There are emerging technologies that will allow renewables to work as grid forming systems just using negligible storage capacity

We go on with our 2020 editorial line about climate challenges. This time we have interviewed our colleague Gerardo Medrano, an expert in electrical systems and control theory. He has explained to us how renewable generation can take part in the control system.

Could you explain to us what is electrical generation control? Why is it necessary to control the electrical system?

The electrical systems complex dynamics tend to instability and the elements that take part in them must be directed towards stable conditions, despite the existing uncertainties.  Renewable energies depend on the availability of the natural resource in a certain moment, so the have more associated uncertainty. However, the use of advanced prediction and control systems have help us to be close to manage them as a conventional resource.

From a technical point of view, to what extent do renewable energies already take part in the control of the electrical system?

Renewable energies, specially wind and hydro power, take part in the control of the systems by offering frequency and power regulation services, inertial response and reserve, voltage regulation and grid support in case of overvoltage or voltage spikes. How they do it, if it is compulsory and its remuneration depends on the regulation of each country.

In Spain, the services that allow the Grid Operator to guarantee the stability of our electrical grid are remunerated in the so-called balancing markets. These markets were opened for renewable energies in 2016 and they have encouraged participants to take part to a greater extent in the control of the electrical system. Moreover, we are converging to a common European grid code (ENTSO-E) and the Spanish grid operator, REE, has just adapted its operational procedures so the connection of new renewable generation is now more demanding. Wind power in Spain represents around 6% of the adjustment services provided by all technologies. It is a business with a huge potential growth as the latest technology developments have increased a lot the controllability of these kind of systems. Hydro generation leads the market with a 30% share.

The regulatory scenario is complex. Our colleagues Ignacio de Lis and Marc Bellon are specialized in Grid Studies and offer consultancy services for clients interested in connecting renewable energy.

Why is a greater presence of renewables a challenge to the system?

Because the system was conceived to work without them. We have discussed about it in depth in another post: renewable energy does not add up to the inertia of the system, so it becomes more sensitive to changes, less controllable. In Spain, the Renewable Energy Control Centre (CECRE) is in charge of facing this challenge every day, maximizing the renewable MW that the system can admit in each moment. There is no doubt that future grid connection requirements and storage-based renewable systems, will bring along an unprecedented share of renewable generation.

Clearly, storage will play an important role in the integration of renewable energy, is there anything more that renewables could provide the system with to reduce the need for storage?

Renewables will have to improve their response times -that are already good-, so that large generation groups can respond to setpoints within the second. As renewables do not depend on fuel, they are the only generation technology which costs will continue to decrease. This will lead to oversize scenarios where nominal capability will be constrained which will allow maintaining power reserves, making the renewable resource more manageable. Besides the costs and response times, there are control strategies that have not been standardized yet that would allow to increase the share of renewables in very weak systems. The complexity of these strategies and the absence of a market to stimulate them entails they are not used in practice.

There are emerging technologies that will allow renewables to work as grid forming systems just using negligible storage capacity, making 100% renewable scenarios feasible. I think it would be possible in large geographical extensions with high hydro power generation. In the Power Electronics Department at Norvento we have started to work in this business line, and we have already developed our own grid forming equipment we use in microgrids. It is not unlikely that we have the opportunity to put this technology to use in future projects along with our nED100 wind turbine or PV systems.

Have you found it interesting? Read the next interview on the acceptation of the impact of renewable energy in the landscape.

Gerardo Medrano

Gerardo is an industrial engineer specialized in electrical systems and control theory. He forms part of Norvento’s Power Electronics Department where he collaborates in the development of converters for batteries and wind turbines. He had also worked with other manufacturers in Spain, Germany and Australia performing grid connection and design tasks.