A 3,000MW energy storage target, proposed in Arizona as part of a grid modernisation policy, recognises the role of the technology in reducing the need for fossil fuels to stabilise the grid, a consultant has said.

Yesterday, Andy Tobin of the state’s regulator, the Corporation Commission, presented a plan that includes a goal to generate 80% of Arizona’s power from renewable sources by 2050, a commitment to review the existing Renewable Energy Standard and Tariff (REST) policy, to use renewables to mitigate peaks establishing a ‘Clean Peak’ standard and to deploy 3,000MW of energy storage to “leverage low priced energy during the day”.

The Commission will vote on the proposal in the next couple of weeks. A final vote is expected which would make the regulatory proposal legally binding, within six months to a year, Lon Huber, vice president and head of consulting at Stratagen Consulting, told Energy-Storage.News.

The 3GW target would be the biggest established to date in the US – the first state to set a target, California, is calling for 1.35GW by 2024 and New York for 1.5GW by 2025. While the timeline for deployment is longer for Arizona than those two previous title-holders, Huber pointed out that relative to the state’s size, the figure pencils out at a far higher capacity deployed per capita than in the others.

Lon Huber said the establishment of the target is closely linked to known plans for development of new gas turbine facilities by Arizona’s major utilities, including Arizona Public Service, which is projecting that it will need 5GW of new gas plants by 2032. Huber said it was likely the 3,000MW figure was arrived at as “a fraction of the new combustion turbines in the IRP (Integrated Resource Plans) of the utilities”.

“I think the assessment of what could be cost-effective storage was probably based on the need for new peakers over the next 15 years, more than anything. I think the innovation here is that, depending on different states and how they do things, you could end up in a situation where you buy a lot of renewables but you still need a large fossil backup fleet.”

While renewables-plus-storage may not be ready to take over the role of large thermal generation plants – and in the case of Arizona, the US’ largest nuclear power plant – in providing baseload energy, Huber said that in the hierarchy of needs, peaker plants which are often only run on a part-time basis to stabilise the grid, come first. In a recent blog for Energy-Storage.News, Marek Kubik at storage system provider and integrator Fluence wrote about an academic study into Ireland's grid which showed the role batteries could play there in stabilising the grid using far less capacity than thermal generation.

Huber said Tobin and the Corporation Commission appear to have realised that ratepayers should not have to pay for both the renewables deployed and the fossil fuels used to stabilise their variable output onto the grid, with Arizona set to use “renewables to whittle down that fossil backup fleet, so that ratepayers don’t pay twice for resources”.

Essentially, with utility-scale solar prices lower than wholesale in Arizona, at as low as 2.5 to 3 cents per kWh on a 25-year PPA, the state has “super-cheap fuel” which it can now use for meeting peak demand, Huber said.