Batteries – Falling Flat Or Charging Ahead?

On 15th November 2017 by good2us

Elon Musk is best known for re-usable rockets and electric cars, but his core activity is batteries. But are they really capable of storing sufficient energy in a cost effective way?

In 2016 the state of South Australia suffered an energy crisis as a result of storm damage to electricity transmission infrastructure on 28 September 2016. The cascading failure of the electricity transmission network resulted in almost the entire state losing its electricity supply.

In response to a challenge on Twitter from an Australian software billionaire, Mike Cannon-Brookes. Mr Musk said he could install 100 megawatt hours (MWh – one million watts used continuosly for one hour) of battery storage in the state of South Australia in 100 days to help solve an energy crisis it faces, or it would be free of charge.

The problem with renewables is that the sun doesn’t always shine and the wind doesn’t always blow. The conventional approach to this problem is to have coal, gas or nuclear-powered power stations in reserve to fill any gap.

This poses an expensive problem since any power provider is rewarded when the power they generate is used. Wind or solar power has a zero marginal cost, once the wind turbines and solar panels are installed they produce power that is effectively of zero cost, That means the grid will take this power first as it is by far the cheapest.

This poses a financial problem for those funding the construction of the backup power stations as their revenue stream may be weak and so not justify the cost of building the power station unless the price they are paid when the power is required is high.

A gas-fired power station costs, typically, £0.5m/MW to build, whilst nuclear could be as much as £6.9m/MW. However, the gas costs do not include running costs, i.e. the cost of gas. And even if there is no requirement for a conventional power station’s output it has to be kept running albeit with no load that makes the amount of gas used lower than when there is a load.

Taking into account all costs, including fuel and carbon taxes, the average lifetime cost of a new gas-fired power plant opening in 2024 is slightly higher than that of Hinkley Point C, based on the UK’s Department of Energy and Climate Change’s central assumptions for gas and carbon costs, at an estimated £94/MWh. The lifespan of a gas-fired power station being typically 30 years and a nuclear one 60 years.

Simulations of Lithium-ion battery usage show that the life of Lithium ion batteries is variable and depends on temperature, depth of discharge before recharging occurs (DOD) and number of recharging cycles, typically 5000.

In the case of no thermal management and the battery temperature varies with an outside   ambient   temperature, heat   generation   and   heat dissipation rate. The impact is that cell temperatures swing from 5oC in the winter to 35oC in the summer; then it is only possible to get 7 years life out of the battery using it within a restricted 47% DOD operating range.

If a thermal management system were added to maintain battery cell to maintain  temperatures within a 20-30oC operating range year-round, the battery life is extended from 4.9 years to 7.0 years cycling the battery at 74% DOD. Life is improved to 10 years using the same thermal management and further restricting DOD to 54%.

Whilst battery prices have plummeted Elon Musk’s price, of about $250 per kilowatt hour (kWh), is relatively cheap. But the total cost (including building the plant, for example) would be about $500 per kWh to hook the batteries up to the grid. A 100MWh facility would cost $50m or nearly the same price as a gas-fuelled power station, $0.50 per MWh.(£0.38 per MWh). It would also need to be replaced every 7-10 years. In fact, in order to have a 100MWh backup battery facility that lasted 10 years operating on a par with a gas-fuelled power station, i.e. able to deliver 100MW for one hour, would require a 200MWh facility so that DOD would not fall below 57%. Increasing the initial construction cost to £0,76 per MWh. This makes the total construction cost of a battery installation that will last 30 years (the life-cycle of a gas-fuelled power station) of $3.0/£2.28 per MWh plus the costs of a thermal management system.

Batteries need to be charged and then re-charged. So, just as with gas, fuel is not free. The electricity required to charge and then re-charge cannot be sold to the grid so the lost revenue represents the cost of fuel. In addition, the thermal management system will require power.

With the cost of a battery installation being over 4 times that of a gas-fuelled power station unless the running costs of Lithium-ion installations (cost of temperature management systems and re-charging batteries) are radically less than those of a gas-fuelled power station, unless gas prices rise considerably such installations look a poor investment.



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