‘Residential batteries are less profitable than selling excess power to the grid’

Although self-consumption of solar power is the optimal economic approach, the expense of household batteries at present outweighs the increased ability they offer to use electricity generated on the roof. Whether aggregated ‘virtual batteries’ offer better returns is an open question, due to lack of electricity company transparency.

July 1, 2021

A study by academics at Finland’s Lappeenranta-Lahti University of Technology (LUT) has concluded the expense of residential battery systems means they are less profitable than exporting unused electricity generated by household solar panels to the grid.

Researchers, in a paper published in Applied Energy, concluded the most valuable use of household solar electricity was for self consumption, as it avoids the taxes and grid charges associated with each kilowatt-hour of network electricity, as well as the wholesale cost of the energy.

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While residential batteries increase the amount of self consumption in solar households, the paper stated, their costs outweigh the benefits they bring, meaning the simple export of excess energy to the grid, at the wholesale price, offers the best returns at current battery price levels.

“We could roughly say that battery prices would need to drop to a third of their current level for them to be a viable investment for residential power systems,” said LUT researcher and lead author of the paper, Pietari Puranen, in a press release issued by LUT on Monday.

The academics also attempted to weigh the financial returns available to solar households who sign up to be part of ‘virtual batteries‘ set up by electric companies who aggregate groups of solar ‘prosumers’ – households which both consume and export solar power.

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However, the researchers were unable to come to a conclusion on the merits of such systems, with LUT associate professor Antti Kosonen frustrated in his attempt to calculate the economics. “In my opinion, virtual battery storage is not particularly transparent,” he said. “At least, regular prosumers may have trouble finding out about its advantages compared to selling excess electricity to the grid.”

The findings of the Techno-economic viability of energy storage concepts combined with a residential solar photovoltaic system: A case study from Finland paper, also published on the ScienceDirect website, were based on the electricity import and export data from two detached houses in Finland over a three-year period, and the corresponding electricity market prices.

The academics found the costliness of residential batteries rises with their storage capacity at a faster rate than the economic benefits they offer by increasing household consumption levels.

“Many still think batteries are the best, or even a necessary solution for deriving a profit from self-produced electricity,” said Jero Ahola, LUT professor of energy efficiency in electricity-driven systems. “However, current battery prices rarely make the investment profitable.”

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