Practice Test Geeks(REP) Certified Renewable Energy Professional Practice Test
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Storage and Grids Flashcards

7 cards from real REP practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.

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  1. Which grid service involves an energy storage system automatically responding within seconds to stabilize grid frequency deviations?

    Answer: Frequency regulation

    Frequency regulation requires fast-responding assets (often within 4 seconds) to correct imbalances between generation and load, maintaining grid frequency near 60 Hz.

  2. A battery energy storage system (BESS) has a round-trip efficiency of 85%. If 100 MWh is stored, how many MWh are available for discharge?

    Answer: 85 MWh

    Round-trip efficiency represents energy out divided by energy in, so 100 MWh × 0.85 = 85 MWh delivered to the grid.

  3. What term describes the practice of charging storage systems during low-price periods and discharging during high-price periods to capture wholesale electricity price spreads?

    Answer: Energy arbitrage

    Energy arbitrage exploits time-of-use price differentials by storing cheap off-peak energy and selling it back during expensive peak hours.

  4. Which interconnection standard governs the technical requirements for connecting distributed energy resources, including storage, to the utility grid in the US?

    Answer: IEEE 1547-2018

    IEEE 1547-2018 sets the technical requirements and testing procedures for interconnecting distributed energy resources (DERs) to the electric power system.

  5. In a pumped hydro storage facility, which factor most directly determines the amount of energy that can be stored?

    Answer: Volume of upper reservoir and head height

    Stored energy in pumped hydro equals mass × gravity × head height, so both reservoir volume (mass of water) and elevation difference (head) are the primary determinants.

  6. What grid condition is described when voltage levels at distribution nodes fall below acceptable thresholds, often during peak demand?

    Answer: Undervoltage (voltage sag)

    Undervoltage or voltage sag occurs when demand exceeds local generation or reactive power support, causing voltage to drop below the standard range (typically ±5% of nominal).

  7. Which storage technology is best characterized by very high cycle life, fast response, and suitability for short-duration, high-power applications like UPS and frequency regulation?

    Answer: Supercapacitors (ultracapacitors)

    Supercapacitors can deliver very high power for short durations with hundreds of thousands of charge/discharge cycles, making them ideal for rapid-response grid stabilization.