Impact of Increasing Penetration of Renewable Energy Resources
By: Dilshan Subasinghe
Tags: Renewable Energy, Renewables, Energy, Impact

The problem of global warming and climate change has led to an increase in the use of renewable energy resources as a means to provide clean electrical energy whilst reducing CO2 emissions. The intermittent nature of renewable energy resources brings with it many challenges in relation to the stability of electricity grids. One particular challenge is the impact of renewables on frequency and voltage stability. In some cases, the addition of renewables may improve the voltage profile of a network, such as in times of high load demand, and in other cases may lead to overloading of the network for example, through excess generation. Some methods used to mitigate the problem of overloading are active curtailment and energy storage. Active curtailment is intentionally reducing the energy generated by renewables by for example, pitching the blades of a wind turbine to a sub optimal position although it may be argued that this defeats the purpose of including renewables in the generation mix. With energy storage solutions, excess generation can be stored during times of low demand and despatched at times of high demand. Increasing levels of electric vehicle penetration and the opportunities created by vehicle to grid schemes offer a possible solution.

In radial systems where generation occurs at one end of a line and the load is located at the other, a voltage drop is experienced along the length of the line and consumers located at the far end of the line can experience unacceptably low voltages in times of high demand if the system is not well designed. Injecting power from renewables at the far end of the line can help to raise the voltage as shown in Figure 1.

Figure 1: Voltage Along a Feeder With and Without Embedded Generation [1]

Situating renewable generation close to loads can help to reduce active power losses in the network. However, after a certain point, depending on the hosting capacity of the network, active power losses can begin to increase as the power not consumed by the load flows back to the grid, increasing the loading on feeders and therefore i 2R losses.

Much in the same way as voltage stability, the frequency stability of the network can be affected by renewables and system frequency may rise above acceptable levels if too much power is being generated from renewables and the frequency may fall below acceptable levels if not enough power is being produced by the system as a whole. Demand response is one possible solution to this issue where users are encouraged to use less or more power by being offered incentives by their utility depending on the situation. Coupled with traditional primary and secondary frequency response methods this can help to lessen the impact of renewables on the power system. Load scheduling may also be used to reduce strain on the network at times of high demand.

In addition to frequency and voltage stability issues, introducing renewables into the power system can affect fault current level and protection strategies may have to be rethought in order to avoid the unintentional tripping of system protective equipment.

References

[1] A. Sahito, Z. Memon, G. Buriro, S. Memon, M. Jumani, and A. Ansari, “Voltage profile improvement of radial feeder through distributed generation,” Sindh University Research Journal, vol. 48, p. 498, 2016.