Mixed Deck — All REP Topics Flashcards

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

Answer: Reduced system inertia

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.

A project manager is overseeing the installation of a rooftop photovoltaic (PV) system in the Northern Hemisphere. To maximize the total annual energy output, what is the generally recommended orientation for the fixed-tilt solar panels?

Answer: True south to maximize daily sun exposure

In the Northern Hemisphere, the sun travels across the southern part of the sky. Orienting solar panels to face true south ensures they receive the most direct sunlight exposure throughout the day and across all seasons, which maximizes the total annual energy production.

In a grid-tied PV system, what happens to power generation when the utility grid goes down (without a battery backup)?

Answer: The inverter shuts down to prevent islanding

Grid-tied inverters are required to detect grid loss and shut down immediately (anti-islanding protection) to prevent energizing lines that utility workers might contact.

In geothermal energy, what is the function of a 'separator' in a flash steam plant?

Answer: It separates steam from liquid brine after pressure reduction so steam can drive the turbine

In flash steam plants, the separator uses centrifugal force to separate steam from two-phase geothermal fluid after pressure is reduced, directing steam to the turbine and brine to reinjection or further flashing.

Which storage duration category is most appropriate for seasonal energy storage needed to balance renewable generation across months?

Answer: Ultra-long-duration (weeks to months)

Seasonal storage addresses multi-week to multi-month imbalances between renewable generation and load, requiring technologies like hydrogen, synthetic fuels, or large pumped hydro.

The 'mitigation hierarchy' in environmental management follows which priority order?

Answer: Avoid → Minimize → Restore → Offset

Best practice requires first avoiding impacts, then minimizing unavoidable ones, restoring affected areas, and only then offsetting residual impacts.

What is the typical temperature coefficient of power (Pmax) for a standard crystalline silicon PV module?

Answer: -0.5% per °C

Most crystalline silicon modules lose approximately 0.3–0.5% of rated power for every degree Celsius above 25°C (STC).

Cavitation in hydropower turbines is most likely to occur under which operating condition?

Answer: Low local pressure causing water to vaporize near turbine blades

Cavitation occurs when local pressure at the turbine runner drops below the vapor pressure of water, forming vapor bubbles that collapse violently and erode turbine components.

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.

What is the purpose of a SCADA system in a wind farm?

Answer: Real-time monitoring, data collection, and remote control of turbines

SCADA (Supervisory Control and Data Acquisition) systems provide operators with real-time turbine performance data, alarms, and remote control capabilities across the wind farm.

A hydropower project's 'hydraulic head' decreases by 20% due to drought-reduced reservoir levels. Assuming constant efficiency, how does this affect power output?

Answer: Power decreases by approximately 20%

Since power output is directly proportional to hydraulic head (P = ρgQHη), a 20% reduction in head causes approximately a 20% reduction in power output, assuming flow rate and efficiency remain constant.

Which metric represents the rate at which the present value of future cash inflows equals the present value of cash outflows, making NPV equal to zero?

Answer: Internal rate of return (IRR)

IRR is the discount rate that sets NPV to zero; if IRR exceeds the project's hurdle rate, the investment creates value.

The 'prudent investment' standard used by state utility regulators in rate cases evaluates whether a utility's capital expenditure on renewable projects was:

Answer: Reasonable and appropriate at the time the decision was made, even if outcomes were unfavorable

The prudent investment standard assesses whether a utility acted as a reasonable, prudent manager would have at the time of the investment decision, judged prospectively rather than by hindsight.

In the context of geothermal energy, what is 'reinjection' and why is it practiced?

Answer: Returning spent geothermal brine to the reservoir to sustain pressure and reduce surface disposal

Reinjection returns cooled geothermal brine back into the reservoir, maintaining reservoir pressure, extending field life, and minimizing surface disposal of mineral-laden fluid.

When comparing direct-drive wind turbines to traditional geared-drive turbines, what is a significant advantage of the direct-drive design?

Answer: Higher reliability and lower maintenance due to fewer moving parts

Direct-drive turbines eliminate the need for a gearbox, which is a complex mechanical component prone to wear and failure. By connecting the rotor directly to the generator, these turbines have fewer moving parts, leading to increased reliability, reduced maintenance requirements, and lower operational noise.

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.

What is the primary function of a bypass diode in a photovoltaic module?

Answer: Prevent reverse current flow through shaded cells

Bypass diodes allow current to flow around shaded or damaged cells, preventing hotspot damage and maintaining power output.

What is the primary purpose of a 'power purchase agreement' (PPA) in renewable energy project development?

Answer: To secure long-term revenue by locking in the price a buyer pays for electricity

A PPA is a long-term contract between a generator and a buyer that specifies the price, volume, and duration of electricity sales, providing revenue certainty needed to secure project financing.

In a vanadium redox flow battery, what component physically separates the two electrolyte half-cells while allowing ion exchange?

Answer: Proton exchange membrane

The proton exchange membrane in a vanadium flow battery allows proton transport between the positive and negative vanadium electrolytes while keeping them from mixing.

What does a turbine's 'power curve' depict?

Answer: Power output as a function of wind speed

A turbine's power curve is a graph showing electrical power output (kW or MW) at each wind speed from cut-in through rated to cut-out conditions.