Numerical answer
Four of the five sentences below, labelled 1-5, form a coherent paragraph. Identify the ONE sentence that does not fit and enter its number.
1. As solar and wind power generate electricity intermittently, depending on weather and time of day, storing surplus energy for later use has become a central challenge for renewable grids.
2. Lithium-ion batteries, while dominant in electric vehicles, remain relatively expensive for grid-scale storage compared with some emerging alternatives.
3. Pumped-hydro storage, which moves water uphill during periods of surplus power and releases it through turbines when demand rises, currently accounts for the large majority of the world's grid-scale storage capacity.
4. The Wright brothers' first powered flight in 1903 lasted only twelve seconds but marked the beginning of practical human aviation.
5. Newer approaches, including large-scale flow batteries and compressed-air storage, are being piloted as utilities look for cheaper ways to store energy over longer durations.
1. As solar and wind power generate electricity intermittently, depending on weather and time of day, storing surplus energy for later use has become a central challenge for renewable grids.
2. Lithium-ion batteries, while dominant in electric vehicles, remain relatively expensive for grid-scale storage compared with some emerging alternatives.
3. Pumped-hydro storage, which moves water uphill during periods of surplus power and releases it through turbines when demand rises, currently accounts for the large majority of the world's grid-scale storage capacity.
4. The Wright brothers' first powered flight in 1903 lasted only twelve seconds but marked the beginning of practical human aviation.
5. Newer approaches, including large-scale flow batteries and compressed-air storage, are being piloted as utilities look for cheaper ways to store energy over longer durations.
Show answer and solution
Answer: 4
Sentences 1, 2, 3 and 5 together discuss the challenge of storing renewable energy and the various technologies (batteries, pumped-hydro, flow batteries) used to address it. Sentence 4, about the Wright brothers' first flight, is on an entirely unrelated topic (aviation history) and breaks the paragraph's coherence.
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