Batteries and inverters are making load-shedding worse

[Nat Quinn]

Researchers found that the extra power drawn to recharge batteries in backup power setups without solar power generation negated the very thing load-shedding was set up to achieve.

Inverter and battery systems without solar generation effectively undermine the aim of load-shedding due to the extra electricity they draw from the grid to recharge after a power cut.

University of Johannesburg physics professor Hartmut Winkler told MyBroadband that most solar setups also draw extra power from the grid to recharge their batteries.

“All a battery does is to store electricity (i.e. it charges itself) at times when electricity is available to it, and then uses up that same electricity when the power supply is no longer there (as is the case during load shedding),” said Winkler.

“So the same amount of electricity is being used, despite Eskom’s efforts to curb electricity use by instituting load-shedding.”

The power drawn to recharge the battery after a power cut is significantly higher than it would be without the system.

“In practice, what happens is that when power cuts set in, the battery starts discharging, but the moment the power comes back on, the use of electricity goes up well above what it would otherwise be because the battery is no longer full, and extra electricity is needed to charge it,” said Winkler.

He explained that although a setup with solar generation is ideal, most still draw some power from the grid to recharge.

It is possible to set inverters to charge exclusively through solar power generation, but this puts the household at risk of being without power at times.

“The ideal is if the battery is only charged by the solar panels, as that then does not draw more electricity from Eskom,” said Winkler.

“The problem is then that you may not have enough in the battery to get you through the night, or through cloudy spells.

“This is why most people with solar panels still end up at least partly charging their batteries with the Eskom line.”

Research from Stellenbosch University’s Electrical and Electronic Engineering and Industrial Engineering departments revealed that these systems ultimately increased energy demand on the grid and negated the impact of load shedding.

The researchers tested the extent of the problem by simulating a group of 12,000 residential households to determine the impact of inverter and battery setups on load-shedding.

“We assessed the impact of domestic users installing battery backup solutions without solar and evaluated the impact of doing so for different penetration levels of such systems into the domestic market,” they wrote.

They found that with inverters only provided to households within the top 15% when it comes to usage, the effect of load-shedding was reduced by approximately 60% in summer and 70% in winter.

“The results show that with a mere 15% penetration, the intended effect of load-shedding will be curtailed by just over 60% in summer and just over 70% in winter when considering the whole day’s curtailment,” the researchers wrote.

“This is caused by the fact that when the power is returned for a zone that just experienced load shedding, all the inverters will begin to charge at the same time, which, consequently, pulls additional electricity from the grid.”

“Most importantly, a peak is formed at the start of the charging period,” they added.

They also found that the peak power draw either matched or surpassed the load-shedding draw when increasing the inverter penetration level and charging rate.

 

source:Batteries and inverters are making load-shedding worse (mybroadband.co.za)

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