Report: Watt on a hot tin roof

by Mark Ogge

How rooftop solar increases reliability and reduces electricity prices

Rooftop solar generates best on hot sunny days, exactly the conditions that see gas and coal generation at risk of breakdown. This summer rooftop solar reduced demand peaks in the National Electricity Market by over 2000 MW, while a breakdown at a major coal generator contributed to wholesale electricity prices hitting $12,000 MWh. 

Hot days present the greatest challenge for the National Electricity Market (NEM) to supply our electricity needs.

There are two main reasons for this. Firstly, the highest demand for electricity occurs on hot days, due to increased use of air-conditioning. Daily peak demand can more than double – in Melbourne this summer demand on cooler days peaked around 4,000MW, but approached 9,000MW on the hottest days.

Secondly, gas and coal power stations are less efficient and break down more frequently in very hot weather.

Conversely, rooftop solar produces electricity best on hot days, as they are usually very sunny. They can directly contribute to powering air-conditioning (and other uses) reducing the demand for electricity from the grid. Rooftop solar consistently reduces the size of the crucial summer day demand peaks and delays the timing of the peak to later in the day. This reduces the amount of electricity needed from large-scale generators. As such it increases the reliability and resilience of the grid, providing power when gas and coal plants are most likely to fail, and when the consequences of those breakdowns would be most serious. 

Full report