INTEGRATION OF FLYWHEELS IN THE ELECTRICAL SYSTEM WITH THE AIM OF MAXIMISING THE PENETRATION OF RENEWABLE ENERGY Paulo André EDA – Electricidade dos Açores, S.A. R, Francisco Pereira Ataíde, 1, 9500-535 , Açores, [email protected]

Flores Island has a big water resource. So, during winter I. INTRODUCTION the diesel engine online run only at 200 kW (<40% of rated This Abstract will focus the integration of Flywheels in the power), only to insure the frequency and voltage regulation, EDA electrical system, with the main goal of increasing the because of the slow response of the hydro’s. renewable energy penetration, mainly the wind energy. So, to sum it up, the main objectives were: • is a group of 9 islands on the North Atlantic Allow the increase on wind energy production; • Ocean. EDA, responsible for the electric supply on the Improve the efficiency use of the Diesel engines islands, runs 9 independent Power Systems, one in each (smaller spinning reserve vs. load > 40%); • Island, and the power production is mainly supported by Increase the grid stability. diesel. We run nine Diesel facilities (LFO and HFO), twelve small Hydro’s (80 to 1600 kW), eight Wind Parks and two Geothermal Power Plants. III. PROJECT IMPLEMENTATION Looking at the market solutions back on 2003, EDA found solutions based on a dynamic energy accumulation system, II. OBJECTIVES known as Flywheel. Those equipments are able to store The main goal was not only to increase the wind energy kinetic energy, and use AC/DC power converters to be production and the grid stability, but also to improve the interconnected in parallel to the grid, maintaining the control Diesel engines efficiency, running them over 40% of their and the power grid stability. rated power (minimum technical value for Diesel), and reducing spinning reserve, to improve the specific consumptions and the grid stability.

The biggest problem on small and isolated power systems is the instability caused by a large penetration of renewables, especially the wind energy.

So, EDA is trying to find solutions to maximize the energy production from renewable, mainly wind energy because EDA installed excess wind power capacity in some power The main advantages of the Flywheel solution were the systems. high charge and discharge cycles, with variable time intervals between them, compared to other energy storage We chose and Flores islands because of their grid systems, allowing to attenuate the instabilities on the grid size and their energy production sources. induced by wind energy production, making possible the increase in the penetration of renewables maintaining the The Graciosa island energy production is based on a wind- quality supply on the grid, complying with the standard EN diesel system, with two wind turbines of 300 kW (Enercon), 50160. two wind turbines of 100 kW (Nordtank), and six diesel engines from 600 kW to 810 kW (CAT). The peak power is around 2,2 MW.

The Flores island energy production is based on a wind- diesel-hydro system, with two wind turbines of 300 kW (Enercon), and a Power Station based on four small hydro generators from 250 kW to 600 kW and four diesel engines from 500 kW to 810 kW (CAT). The peak power is around 2 MW. EDA launched a public tender on September 2004. The contract was established with an Australian company named

POWERCORP for both Islands. This project was co- in order to react whenever an event occur, like load financed by the European Union, in the program named sheddings, engine failures, lack of wind, etc. The Flywheel PRAI (Regional Program for Innovating Actions). control system uses the droop mode of the engines to compensate the active and reactive load variations, The equipment delivered combines a low-speed flywheel maintaining the grid stability, transferring the load to the with solid state IGBT based converters to provide a high- diesel and hydro engines online, in order to avoid a power performance energy storage device. outage. In Graciosa we also installed a system that allows the automatically starting or stopping of a diesel generator, TYPE POWERSTORE doing the correct power steps. Therefore, it’s possible to Rated Voltage 440 V reduce the spinning reserve online, maintaining the security Max. Current 1312 A of the supply to the grid. Max. Power 1000 kW Continuous Power 300 kW Absolute Stored Energy 23,3 MJ IV. RESULTS Stored Energy at Max. Speed 16,5 MJ EDA conducted over the trial period some tests and Speed Range 1800 - 3390 rpm collected some events caused by failures on the power Permissible Ambient Temperature 0 ºC – 40 ºC system in order to obtain demonstrative results of the Relative Humidity < 95% solution applied. Those tests and events are shown bellow. Airflow 5000 m3/h We can first see the result of an event where the wind

power station tripped with 450 kW caused a frequency drop In the technical point of view, this equipment is able to of only 0,8Hz. On the past, similar events would have caused take or provide 500 kW for a period of approximately 30 a frequency drop of about 2 Hz. sec., with a ramp-up time of approximately 4 ms to change from 0 kW to +/-500 kW, which can store 16,5 MJ, approximately 5 kWh.

The following graph shows the 250 kW charge and discharge test.

On a case of a distribution line fault we were able to maintain the grid stability, avoiding load shading or a low frequency trip of the wind turbines. The system is using a

control software module called “ride-true” to prevent a The systems was installed on 20 feet containers, to ensure flywheel trip by overload of the power electronics. an easy and fast installation. The containers were assembled and full equipped in Darwin, Australia.

We also installed a control system, referred as Integration Package, which allowed an easy integration with the existing equipments on the Power Stations. This system is able to always know which engines are online, their power status, and the flywheel status. Therefore it can control the flywheel

Nevertheless, we are facing some problems on the old On the next example, it is shown that after a Flywheel Nordtank wind turbines installed on Graciosa Island, and collapse, the grid stability is compromised (frequency and because of that it’s not been possible to compensate the voltage stability). power losses of the Flywheel system running on the last three years.

In Flores Island it’s already possible to run the system in a diesel off mode, using only the wind and hydro and the flywheel for the frequency and voltage regulation. This can be seen on the following load diagram (recorded on the 24th

2.000 kW

1.800 kW

1.600 kW

1.400 kW

1.200 kW

1.000 kW Wind Diesel 800 kW Hydro 600 kW Comparing two different events, in this case an hydro 400 kW generator trip, with similar conditions, we can see the main 200 kW difference on the frequency stability. 0 kW

0:00 1:00 2:00 3:00 4:00 5:00 6:00 7:00 8:00 9:00 0:00 10:00 11:00 12:00 13:00 14:00 15:00 16:00 17:00 18:00 19:00 20:00 21:00 22:00 23:00 52,0000 of December of 2010). 51,5000 51,0000 That represents 54,5% of Hydro, 33,4% of Wind and only 50,5000 Série1 12,1% of Diesel. EDA had on that specific day above 14 50,0000 Série2 hours straight without a Diesel engine online on Flores 49,5000 Island. 49,0000

48,5000 Because of that, it is possible to accomplish one of the 48,0000 -10 1 2 34 5 6 78 910 most exciting and defying objective of this project, which is to achieve a diesel off mode, and to be able to supply the grid only with renewable energies. Nevertheless, the reverse side of the coin is the system’s efficiency as we have a lot of equipments spending energy. V. CONCLUSIONS To sum up, in the last years EDA invested in renewables trying to use the endogenous resources of Azores Islands (hydro, wind and geothermal). This allows a reduction on fossil fuels use and consequently CO2 emissions.

In 2010 EDA managed to reach 28,1% total in renewable energy on all Islands (48,6% in Flores Island and 44% in São Miguel Island).

EDA experienced around 11 kW of continuous losses that The know-how that EDA is trying to obtain will provide represent around 97 MWh each year. We also need to add sustainable energy sources for the future. the consumption of the air conditioning system, increasing those numbers to 143 MWh each year.

VI. REFERENCES In both islands, the increase in wind production was achieved as expected, being possible to obtain an annual [1] www.eda.pt average of more 160 MWh in wind energy in each islands. [2] www.pcorp.com.au That shows that it’s possible to obtain a positive liquid result (after deducting the losses) of around 600 MWh of wind energy, less 160.550 liters of diesel and less 427 tons of CO2 emissions on the last five years on both islands.