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Hawaii, Bangalore confident grids can handle more rooftop solar; Australia, not so much

image credit: Photo 118900679 © Trong Nguyen | 
Peter Key's picture
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  • Jul 16, 2021

One concern about rooftop solar generation becoming a major power resource is the ability of local distribution grids to deal with the amount of electricity that a lot of rooftop solar units can provide.

Recently, a U.S. state and an Indian city have made moves to promote solar development that show that they don’t share that concern. The agency charged with decarbonizing Australia’s grid, however, said in its most recent report that multiple approaches will be needed to ensure that the amount of solar generation coming online in the island continent doesn’t disrupt grid stability.

The state that apparently doesn’t believe that rooftop solar can overwhelm its distribution grid has the potential to produce a lot of it. Hawaii’s Public Utilities Commission recently approved a program meant to boost consumer-level solar generation and energy storage pairings in the hope of replacing much of the generation capacity that will be lost on Oahu when a 180-megawatt coal-fired generation plant there closes next year.

Under the program, Hawaiian Electric will pay Oahu homeowners who either install solar+storage units or add storage to their existing solar units as long as they let the company draw from their storage units during its peak hours, which generally are from 5 p.m. to 9 p.m.

“We’re talking thousands, not dozens or hundreds” of new or expanded solar systems, Public Utilities Commission Chairman Jay Griffin told Honolulu Civil Beat.

Griffin said the program will go a long way to determining whether Oahu can replace the coal plant’s output with additional rooftop solar capacity.

That’s what we’re putting to test in real terms,” Griffin said. “But we’re not going to be putting all our eggs in one basket.”

That’s also true for the state’s long-term goal of getting all its power from renewable sources by 2045. Isaac Moriwake, a staff attorney with Earthjustice in Honolulu, told Honolulu Civil Beat that the state will need big renewable projects to hit that goal. But he said it also will need to cover all rooftops in the state with solar units, which means the state’s distribution grid will need to be ready.

Hawaii isn’t the only place with an ambitious goal for rooftop solar addition. India’s Ministry of New Renewable Energy (MNRE) wants the Bangalore Electricity Supply Company (Bescom) to expand the capacity of rooftop solar in the city to 300 MW, up from 155.8 MW at the end of May.

To help the company reach that goal, the MNRE is providing subsidies that range from 20 percent to 40 percent of the costs of rooftop solar projects. Consumers also can finance the projects through long-term, low-interest loans that they pay off as part of their monthly electric bills.

Some impressive technology also is going into the project, according to The Hindu. An Indian think tank called the Center for Study of Science, Technology and Policy last September launched its Rooftop Evaluation of Solar Tool, which enables consumers to virtually assess their rooftop’s potential to generate solar energy for their own consumption, as well as Bescom’s grid. To allow consumers to see the solar generation potential of their rooftops, the center used LiDAR to calculate it for every rooftop in the city.

If Bescom is concerned that the rooftop solar capacity it’s supposed to add will strain its grid, it didn’t say so in The Hindu’s article. The government agency charged with helping Australia decarbonize its grid, however, does have some concerns about the proliferation of rooftop solar on the island continent.

In its most recent “Quarterly Carbon Market Report,” the Clean Energy Regulator estimated that 792 MW of small-scale solar capacity was installed in the land down under in the first quarter — an increase of 28 percent over the 628 MW of small-scale rooftop solar capacity installed in the same quarter last year. At current rates, the agency said it expects 3.5 to 4 gigawatts of small-scale rooftop capacity will be installed this year, exceeding the 3 GW figure it had given as the lower bound of its estimates in the "Quarterly Carbon Market Report" for the last quarter of last year. “With an upper bound estimate of 4 GW of added capacity and no sign of decreasing rooftop solar growth, Australia could add another 20 GW of rooftop solar by 2025,” the Clean Energy Regulator said in its most recent report.

That pace of rooftop solar addition could pose a challenge to Australia’s entire grid, not just the distribution systems to which the new solar units are being attached.

“In a system rapidly changing with high penetration of renewables, multiple approaches are needed to ensure grid stability,” the Clean Energy Regulator said in its most recent report.

One approach being tested is deploying community batteries to soak up excess capacity from rooftop solar units. The government of Queensland said in March that it will try a pilot deployment of five grid-connected batteries that can collectively store up to 40 megawatt hours to soak up excess capacity generated by rooftop solar units, which are on nearly one of every three detached homes owned by electricity consumers in the state. Ausgrid in New South Wales and the state of Victoria also are testing community batteries.

In South Australia, the Australian Renewable Energy Agency and hot water heater manufacturer Rheem have launched a project that will test the feasibility of shifting the charging of hot water heaters to midday, when solar generation is peaking, as well as aggregating their load to provide grid services.

Similar programs have been around in some form in the U.S. since at least 2014 and new ones are still being offered.

Itron Inc. said late last month it had successfully deployed a grid-interactive hot water heater program for Fort Collins Utilities, which provides electricity, water, wastewater and stormwater services in the City of Fort Collins, Colorado.

Arizona may be getting in on the action, too. Arizona Public Service Co. last month issued a request for proposals for products that aggregate distributed technologies to provide systemwide capacity resources from 5 to 40 MW and locational resources of 1 to 5 MW. It said the RFP is open to all eligible distributed demand-side technologies, including such products as batteries, smart thermostats, managed electric vehicle charging stations and connected water heater and pool pump controls.

No matter how big programs using electric water heaters as DERs get in the U.S., however, few will get written up with better headlines than this one from The Fifth Estate in Australia: “South Australians to hit the showers to solve solar duck curve.”

The picture of a woman soaking in a bathtub that accompanies the article is a nice touch, too.


Peter Key's picture
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Matt Chester's picture
Matt Chester on Jul 16, 2021

A good example, indeed, of how energy systems across the world-- or even across a single country-- don't have one-size-fits-all solutions. Cater to the geography and needs and resources in the localized region for best results

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