How to make renewables to be dispatchable through ancillary services

Among the objectives of the Integrated National Energy and Climate Plan (INECP) sent to the EC in March 2020 by the Government of Spain are to increase the share of renewable energy in the electrical market up to the 74% by 2030, a decrease of 23% of greenhouse gas emissions —with respect to 1990— and the 19% reduction in energy costs. With these goals in mind, will it be possible, therefore, to set up a stable electrical system with 67 GW of additional renewable power as well as increase its generation capacity by 154%?

Although we talk about renewable energies, the system stability implies that we should be able to deal with powers. The term energy is used in system planning (matching of generation and demand of supply and demand in different markets: day-ahead, reserve, etc.). However, in order to make the system feasible —broadly speaking, on snapshot generated in day-ahead markets—, it is required to have real-time operation mechanisms, also called ancillary services, which are those that guarantee the system stability.

We know that the importance of renewables in the energy mix continues to increase today. In 2018, it had a share of 26% (wind and photovoltaic energy), but its participation in ancillary services barely reached 6%. According to this data, it seems that a greater participation of renewables in those services will be necessary, and thus we should make them more manageable, if we want to reach a participation in the system mix close to 70-80%.

«A greater share of the renewables could be a double-edged sword»

Nowadays (2019), the impact of asynchronous generation in the electricity system in comparison with the total generation park is 34% (specially wind and photovoltaic energy). Within the scenarios foreseen for the system, this impact could be 75-80% in 2030. Therefore, this landmark would have a double impact regarding the system stability. The first is related to the firming of the generation, which would decrease significantly. Not surprisingly, these renewable energies are called variables, and thus would make planning much more difficult even in the very short term. The second one refers to the inertia of the system, which would decrease drastically.

From a technical point of view, the greatest requirement for renewables to participate in the stability of the system is included in the recent EU regulation 2016/631, which compels all new generations, — renewable or not—, to a stricter and more homogeneous operation and control than those determined by the previous operating procedures (PO12.2.). In this sense, renewables have to compensate power for frequency deviation and be able to receive voltage or reactive setpoints from the system operator or TSO. Moreover, it is optional at the moment for the asynchronous (renewable) generation to emulate inertia and primary regulation to provide stability to the system.

Additionally, renewables can already participate in tertiary and secondary services. However, its impact here is not so significant at the present time due to technical difficulties in the regulation of generation (variable) and the price obtained for these services. In this case, the incentives to participate in them are expected to be increased thanks to the incorporation of the PICASSO platform for the secondary regulation at the European level. Unfortunately, photovoltaic energy is not enabled to provide secondary services yet, although it is expected to be one of the fastest-growing technologies in the system.

A greater share of the renewables could be a double-edged sword. By entering at 0 marginal cost and having priority in all energy dispatching, the system costs associated with generation will decrease, as well as those of ancillary services. Therefore, the remuneration for renewables will also decrease on the one hand —a phenomenon also known as price “cannibalization”— while, on the other hand, the curtailment will increase due to grid constraints.

«Integrating renewables into the system and making them dispatchable can be a challenging in a context of changes, not only technological, but also regulatory ones»

Storage will definitely be a decisive factor of action to increase the technical capacity of renewables for primary and secondary regulation, as well as the deviation restoration and voltage control (ancillary services). Similarly, it will serve to reduce the curtailment and increase the captured price  from the renewables. A well-managed storage profile will indeed avoid significant discharges at low prices in the high generation of renewables. Moreover, it will make it possible for energy to be poured out when the system allows it —with less renewables and better prices— and thus increasing both the captured price  for its retribution and the energy supplied to the system. It should be added that the operating procedures associated with storage (Balance OPs) are expected to come into force at the end of 2020.

Certainly, integrating renewables into the system and making them dispatchable can be a challenging in a context of changes, not only technological, but also regulatory ones. Fortunately, there are technological solutions focused on reality and foresight that have been analyzed before. An example of this could be the AGC System developed by Isotrol, which will make possible an exclusive secondary regulation zone for wind energy and, in the near future, for photovoltaics and storage.

Currently, our Local Control Systems (in particular the PPC) allow the renewables to comply with the EU regulation 2016/631 and have the frequency compensation functions they require. Moreover, our Reactive Power Control system is fully compatible with the new secondary and tertiary voltage control service that the REE (corporation which operates the national electricity grid in Spain) will provide shortly, and where the participation of renewables will be mandatory to provide stability to the system. In fact, our control system is already being used to manage the distribution of reactive energy at nodes affected by a significant number of plants. In addition, our Active Power Control allows not only the integrated dispatch of the active power in these nodes, but is also compatible with the new power reduction service that the REE is also going to implement shortly, which will control the power and dynamics of it.

Regarding storage, as it has been mentioned before, we know that it will affect the firmness of renewable generation, the participation in secondary regulation, the one in the reactive and voltage support service, and to the increase in the captured price from renewables on the market. Having this in mind, Isotrol has already developed its first EMS to control the state of charge of batteries, whether they are isolated or in hybrid plants.

Consequently, it is possible to ensure the dispatchability of the renewables in such uncertainty context, in which their power is controlled and in which they can participate in ancillary services to increase their remuneration. Overcoming this challenge successfully not only depends on the capabilities of the selected technological partner, but also on their ability to analyze the different scenarios and develop solutions with high added value for both the renewable industry and the electricity system.

Source: Spanish Wind Energy Association (AEE)

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