Explain why renewable energy resources such as solar and wind are not always reliable for large-scale electricity generation.

Solar energy cannot be generated at night or during bad/cloudy weather, so power output drops to zero or very low levels.
Wind energy is intermittent – electricity is only produced when the wind is blowing at sufficient speed.
Because of these limitations, the supply from solar and wind cannot always be generated on demand, meaning supply cannot always match demand.
In contrast, fossil fuels or other non‑renewable sources can generate electricity consistently at any time, making them more reliable for large‑scale supply.