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Home batteries could inadvertently increase carbon emissions, study finds

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Large batteries installed in homes to store energy from the grid could actually increase carbon emissions under current policies, according to a new study.

It has been assumed that these storage systems, such as Tesla’s Powerwall, could be instrumental in lowering greenhouse gas-emitting energy sources.

However, a team of researchers at the University of California San Diego argue that deploying them today, without making fundamental policy and regulatory reforms, risks increasing emissions instead.

If residents use these systems to reduce their electricity bills, the batteries would draw energy from the grid when it is cheapest.

As the utilities don’t structure how much they charge with the goal of lowering emissions, the cheapest power more often comes from power sources that emit carbon, such as coal.

In addition, batteries do not operate at 100 per cent efficiency: as a result, households that use them draw more power from the electric grid than they actually need.

For the systems to actually reduce greenhouse gases, utilities need to change their tariff structures substantially to account for emissions from different power sources, the researchers said. They would need to make energy cheaper for consumers when the grid is generating low-carbon electricity.

“We sought to answer: what if consumers on their own or in response to policy pressure adopt these systems? Would greenhouse gas emissions from the electric power system go down and at what economic cost?” said Oytun Babacan, lead author.

This year, 2018, saw a substantial increase in installations of the systems compared to previous years, with sales tripling between January and September.

When they are set up to operate with the goal of cutting emissions, home batteries can reduce average household emissions by 2.2 to 6.4 per cent. The monetary incentive that customers would have to receive from utilities to start using their home systems with the goal of reducing emissions is equivalent to anywhere from $180 to $5,160 per metric ton of CO2.

“This is impractically high and very high compared to other emissions-reducing options that are available,” said Ryan Hanna, a postdoctoral researcher.

Most households adopting energy storage are likely to choose equipment vendors and operation modes that allow them to minimise electricity costs, leading to increased emissions, Babacan added.

“Thus, policymakers should be careful about assuming that decentralisation will clean the electric power system, especially if it proceeds without carbon-mindful tariff reforms that aim to reduce residential energy bills and energy consumption associated CO2 emissions,” he said.

Consumers could be encouraged to use the devices in an environmentally beneficial way by ensuring that system developers and equipment vendors favour clean energy use by tracking and adjusting to variations in marginal emissions across the bulk grid, the authors noted.

Although the systems do not encourage cost-effective emissions control at the moment, the research is quick to note that the advantages of batteries should not be overlooked.

“There is an enormous upside to these systems in terms of flexibility and saving households money,” the authors said. “While the increase in home batteries deployment is underway, we need to work on multiple fronts to ensure that their adoption is carbon minded.”

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