Question 186·Hard·Rhetorical Synthesis
While researching a topic, a student has taken the following notes:
- Grid-scale batteries and pumped hydro storage are two leading technologies for storing excess renewable energy.
- Batteries have response times measured in milliseconds, allowing them to balance sudden changes in supply and demand almost instantly.
- Pumped hydro facilities typically take several minutes to ramp up because water must be released from an upper to a lower reservoir through turbines.
- Batteries require less land and can be installed near urban demand centers, whereas pumped hydro needs specific terrain with two large reservoirs at different elevations.
- Although batteries remain more expensive per kilowatt-hour than pumped hydro, their costs are declining rapidly.
The student wants to add a sentence that highlights a primary advantage of battery storage compared with pumped hydro storage. Which choice most effectively uses relevant information from the notes to accomplish this goal?
For rhetorical synthesis questions like this, first underline the exact task (for example, “primary advantage of X compared with Y”). Then quickly scan the notes and mark every detail that is clearly an advantage of X over Y, ignoring disadvantages and neutral facts. Ask which of those advantages seems most central in the context given (here, operating the electric grid). Next, eliminate any choice that introduces information not in the notes, that focuses on the wrong thing (such as the competitor’s advantage), or that mixes in major drawbacks when the question wants an advantage. Finally, choose the option that most directly and completely reflects the strongest supported advantage and stays tightly linked to the notes.
Hints
Clarify what the question is really asking
Underline the words “primary advantage” and “compared with pumped hydro storage.” Ask yourself: according to the notes, what is the biggest benefit that batteries have over pumped hydro?
Sort the notes into advantages and disadvantages
From the bullets, make a quick list: what things are advantages of batteries, what things are advantages of pumped hydro, and what things are neutral or disadvantages of batteries? Focus only on the advantages of batteries when checking the choices.
Think about grid performance, not history or cost
Which battery advantages in the notes seem most important for balancing supply and demand on the electric grid—how quickly they react, where they can be placed, or how much they currently cost? Look for the choice that focuses on that major performance difference.
Watch for extra, unsupported details
Any correct answer must be fully supported by the notes. Eliminate options that add details about either technology that you don’t see mentioned in the bullet points.
Step-by-step Explanation
Understand the task and focus words
The question asks for a sentence that “highlights a primary advantage of battery storage compared with pumped hydro storage.”
Key points to keep in mind:
- It must be about batteries’ advantage, not pumped hydro’s advantage.
- It should reflect a primary (major, most important) advantage, not a minor detail.
- Every part of the sentence must be supported by the notes.
Pull out all advantages of batteries from the notes
Scan the notes and list what is good about batteries relative to pumped hydro:
- Batteries have response times measured in milliseconds, so they can balance sudden changes almost instantly.
- Pumped hydro takes several minutes to ramp up, so in comparison batteries are much faster.
- Batteries require less land and can be installed near urban demand centers, while pumped hydro needs specific terrain with two large reservoirs at different elevations.
- Batteries are currently more expensive, so cost is not an advantage (even though costs are declining).
The two genuine advantages from the notes are:
- Much faster response time.
- More flexible siting / less land / closer to cities.
Decide which advantage is most “primary”
Now think about which of those advantages is most central in the context of balancing supply and demand on the electric grid:
- The notes say batteries’ millisecond response times allow them to balance sudden changes in supply and demand almost instantly, and that pumped hydro takes minutes to ramp up.
- This directly affects how well each technology can handle sudden fluctuations on the grid.
- The location and land-use advantage matters, but it does not connect as strongly to immediate grid stability as the speed difference does.
So the primary advantage, based on the notes, is batteries’ much faster response time for stabilizing sudden changes.
Evaluate each answer choice against the notes and the task
Now compare each option to the notes and to the task of highlighting the primary advantage of batteries:
- Choice A mixes a cost disadvantage (batteries cost more) with a logistical advantage (no need for two elevated reservoirs). The sentence does not mainly emphasize a clear, primary benefit; it leads with a drawback and the advantage is secondary.
- Choice B focuses on location and land use (batteries closer to population centers). That is a real advantage from the notes, but it does not highlight the main performance advantage related to grid stability.
- Choice C ends by stressing an advantage of pumped hydro (widely deployed for decades), and that detail is not in the notes. It also fails to highlight any clear primary advantage of batteries.
- Choice D directly contrasts how long each technology takes to start releasing energy (minutes vs milliseconds) and connects batteries’ speed to stabilizing sudden fluctuations on the electric grid, matching the strongest advantage in the notes.
Therefore, the correct answer is:
D) Unlike pumped hydro facilities that can take minutes to begin releasing stored energy, battery systems can respond in mere milliseconds, making them ideal for stabilizing sudden fluctuations on the electric grid.