Rooftop solar will slow or reduce electricity demand in WA

Western Australia’s Independent Market Operator says it expects the state’s electricity demand to increase by nearly 2 per cent cent a year over the next decade, depending on the impact of rooftop solar on future market operations.

IMO has predicted that demand will increase by around 1.8 per cent a year over to 2024, compared to a forecast of just 0.3 per cent growth from the eastern states’ grid operator, AEMO.

But the WA grid operator has acknowledged that this forecast could be reduced dramatically if strong growth in rooftop solar uptake continues, and if energy efficiency and demand response mechanisms continue to be influential.

IMO modelling found that in a scenario where one-third of its customers had rooftop solar by 2023/24, forecast growth in peak demand could fall from 2.1 per cent a year to 0.8 per cent, or the equivalent of 710MW.

Already, the 336MW of rooftop solar installed in 2014 in the state’s main grid – the South West Interconnected System (SWIS) – has already shifted the afternoon peak from around 4pm to 5.30pm, and shaved back the peak over the last few years.

“Historically, peak demand in the SWIS has typically occurred in February, when commercial customers, schools and universities have returned from the summer break,” it says.

Now it occurs in January, and solar PV has cut demand throughout the day compared to other peak years. The ultimate peak had been deferred to the 5:30pm trading interval “largely because of the effect of solar PV generation offsetting demand during the afternoon.”

In its “expected outcome”, IMO says rooftop solar will continue to grow at around 5.8MW a month, as around 1,600 households install systems of at least 3.5kW each.

It says the installation rate could be higher, and under its expected and high scenarios, the amount of rooftop solar more than trebles to over 1GW by 2023/24. (see graph below). This would reduce peak demand by up to 300MW by 2023/24.

However, IMO also modelled a “high customer response” scenario, in which “saturation” of rooftop solar would occur within 10 years within the SWIS. It recognises that electric vehicle and battery storage could also have an influence, but did not model these.

Under this scenario, rooftops systems would be installed on 75 per cent of all suitable residential dwellings (defined as all detached dwellings and semi-detached dwellings, as well as 30 per cent of other dwelling types) and 90 per cent of all commercial properties.

The average system size would reach 3.5kW for residential (from 1.5kW now) and 26.5kW for commercial properties.

IMO says this level of uptake implies around 30 per cent of all customers could have rooftop solar within a decade.

“In light of ongoing technological advances and expected further increases in electricity prices, the drivers of customer demand response are not likely to abate in coming years,” it notes.

The difference between the expected case and high customer response scenario indicates a range of possible outcomes over the forecast period.

IMO says currently 15 per cent of residential customers have rooftop solar, helping reduce average electricity use (from the grid) per household by 6.6 per cent between 2007-08 and 2012-13.

Like AEMO, the IMO has also dramatically reduced its forecasts over recent years.

© 2014 Solar Choice Pty Ltd

Giles Parkinson