Pioneers in balancing the grid with wind power

The fact that wind or solar radiation can vary at any moment, and therefore complicate forecasts of future available energy, has meant these technologies have for decades been seen as a problem in balancing the electricity system.

This view does not conform to reality, however, and ACCIONA recently reached a landmark by becoming the first company worldwide to provide adjustment services to the grid, by increasing wind power generation alone.

Such services are essential to the proper functioning of the grid, since electricity cannot be stored on a massive scale and, thus, all energy has to be produced the moment it is consumed. Any decoupling between offer and demand can, if it is not corrected on time, endanger the quality of the electricity supply. Renewable technologies can now participate, as of 10 February, in this kind of service via the system adjustment services managed by the System Operator — in this case, REE in Spain. The generating companies offer capacity or backup power that can be revised upward or downward — i.e., increasing or reducing existing output — to be managed the following day by the operator.

Historic day

In this context, on 28 February this year, an important landmark was reached in the management of the Spanish electricity system. ACCIONA participated in it as the first company to offer balancing services exclusively based on wind energy capacity, requested by REE to solve technical restrictions in transmission lines by providing additional power generation.

Instead of the usual situation, where wind farms are required  by the operator to limit their production, the opposite, a more complex scenario, came into play: within minutes, a series of wind farms managed by ACCIONA were told by REE to increase their generation capacity by a total of over 150 megawatts (MW). This was possible due to the technical capacity of the subsidiary, ACCIONA Green Energy Developments, which interacts with the market, and the ACCIONA Renewable Energy Control Center (CECOER), which remotely controlled the operation in constant coordination with REE.

ACCIONA to provide other adjustment services

As well as the service to resolve technical constraints, ACCIONA has also been accredited by REE for the provision of other system adjustment services, such as tertiary regulation and deviation management for winpower capacity of 999 MW (out of a nominal total of 4,735 MW in which ACCIONA currently participates in Spain).

Further down the line, the Company plans to set up other programming units based on wind power and to use other renewable technologies (outside of hydro power, which is already used for these services). As well as ensuring a greater penetration in the grid, the participation of renewable energies in system adjustment services will increase the level of competition in the markets, which will have a positive effect on the electricity price paid by consumers. 

Electricity programming, against the clock

The electricity system has to keep a constant balance between generation and consumption to preserve the security and quality of the supply. The operator of the system — in Spain, REE — programs the operation of power plants from data provided by the market operator (OMIE), the system operation processes and demand forecasts managed by REE. Then it gives timely instructions for production to be adjusted to real-time consumption.

This process is carried out every day and against the clock — through highly regulated and complex procedures — such that the forecasting of programmed production and consumption is adjusted the closer the operation gets to real time. These are the main steps in the process:

• Daily market (12h00). Production agents and sellers of electricity transmit their offers by computer for each hour of the following day. Following the marginal model adopted by the EU, the sale and purchase offers are matched, starting with the cheapest, until existing demand is met, at which the price is fixed for all the energy managed in this hour. 
• Daily Base Program. This is the result of the daily market, incorporating the energy corresponding to bilateral contracts (outside the market).
• Constraints-Solving Markets. Through these, the daily base program is adapted to the requirements of the electricity system.
• Daily Viable Program. The result of the previous process, a technically viable program for system operation for each hour of the next day.
• Intra-Day Markets. Buyers and sellers can readjust, during six daily sessions, their contract commitments up to around four hours prior to consumption.
• Final Schedule Program.  Programming established by REE after the intra-day market sessions.
• Secondary Regulation Market. Provides a band of available capacity to be later used automatically and in real time by REE.
• Tertiary Regulation Market. Repositions the secondary regulation energy used.
• Deviation Management Market. Established to resolve the differences between generation and consumption of over 300 MWh that can appear following the close of each intra-day market session.
• Operational Schedule Program (P48). The final result of the process. Through it, REE establishes the forecast for each hour, which is published 15 minutes before each hour changes. 

From this final forecast, as the system is operated, REE issues instructions to generators so that they increase or reduce production (adjustment services or real-time regulation) in order to maintain the balance of the system at any moment.