REP - Certified Renewable Energy Professional Energy Storage and Grids Questions and Answers

Question 1

A utility is experiencing significant grid instability due to the high penetration of intermittent renewable energy sources. Which of the following energy storage services is most crucial for maintaining a balance between electricity supply and demand on a second-by-second basis?

Accepted Answer

Frequency regulation

Answer

Frequency regulation is the use of energy storage to inject or absorb power in milliseconds to maintain the grid's operational frequency, which is vital for stability when dealing with fluctuating renewable energy inputs. Peak shaving, black start, and energy arbitrage are all valuable services, but they do not address the immediate, rapid adjustments needed to counteract the intermittency of renewables.

Question 2

A remote island microgrid, powered primarily by a solar PV array, needs an energy storage solution to provide power throughout the night and ensure grid stability. The system must be capable of rapid charge/discharge cycles to smooth out passing clouds during the day. Which technology is best suited for this application?

Accepted Answer

Lithium-ion battery energy storage system (BESS)

Answer

Lithium-ion BESS is ideal for this scenario due to its high efficiency, rapid response time, and modular scalability, making it perfect for smoothing solar intermittency and providing overnight power. Pumped-hydro and CAES are better for large-scale, long-duration storage and have geographical constraints. Flywheels excel at very short-duration, high-power applications like frequency regulation but are not suitable for providing energy over several hours.

Question 3

Which of the following is a primary challenge associated with integrating large-scale renewable energy into traditional power grids?

Accepted Answer

Reduced system inertia

Answer

Traditional power grids rely on the rotational inertia of large, synchronized generators (like turbines in fossil fuel plants) to resist sudden changes in frequency. Renewable sources like solar PV and wind are often connected via inverters and do not inherently provide this inertia, making the grid more vulnerable to instability from supply or demand fluctuations.

Question 4

Compressed Air Energy Storage (CAES) is being considered for a large-scale, long-duration storage project. In a diabatic CAES system, what is typically required during the energy discharge (expansion) phase to increase the efficiency and power output?

Accepted Answer

Burning a fuel, like natural gas, to heat the air

Answer

In diabatic CAES systems, the heat generated during air compression is lost to the environment. To compensate for this and increase the energy output during expansion, the compressed air is typically heated by burning natural gas before it enters the turbine. Advanced adiabatic CAES systems aim to capture and store this heat for reuse, eliminating the need for fossil fuels.

Question 5

A grid operator needs a storage asset specifically for providing very fast, high-power bursts of energy to regulate grid frequency and improve power quality, with a very high cycle life being a top priority. Which technology is uniquely suited for this high-power, short-duration application?

Accepted Answer

Flywheel energy storage

Answer

Flywheel energy storage systems store kinetic energy in a spinning rotor and can respond almost instantly to inject or absorb power. They are characterized by a very long cycle life (hundreds of thousands of full depth-of-discharge cycles) and high power output, making them ideal for frequency regulation services.

(REP) Certified Renewable Energy Professional Practice Test

(REP) Certified Renewable Energy Professional Practice Test

REP - Certified Renewable Energy Professional Energy Storage and Grids Questions and Answers