I suppose it's similar position to the petrol regulations (https://www.hse.gov.uk/fireandexplosion/petrol-storage-club-association.htm) - it's seems you can only (easily) store 30 litres "at home" (e.g. in a garage in cans) but a couple of cars could easily hold three times that.

   - Andy.

Hi Andy, 

The new guidelines advise domestic Battery Energy Storage Systems to be installed outside if possible but if within a garage or outbuilding the conditions mentioned must be met. In addition if an EV is kept in the same space it's kWh value is counted in ie. added to the value of BESS units and the total must not exceed 80 or 40 kWh (depending on the garage/outbuilding being attached or detached from the domicile.

Regarding the example of my neighbour, obviously with the storage capacity of his two EV's he could not have any separate BESS installed within the garage space, but should anyone have EV's with +40/80 kWh capacity kept in the same space (the PAS is not a Regulation and will be revised in 2 years time). 

Is that somehow worse than parking internal combustion engine vehicles in a garage, given that only 1 litre of diesel holds about 10kWh?

the difference, and it is a biggy, is that we have many centuries of experience with hydrocarbon fires and in all cases, either cooling or removing oxygen quenches the fire and stops the production of heat and we know we can be confident that once extinguished, the fire stays out.

The problem with a battery fire is that when the battery is charged, it provides its own source of (resistive) heating and re-ignition, making it far harder to put out, and once out there is a significant risk of re-ignition.

Mechanical damage to the battery that allows the plates to move and then touch inside leaves it in a 'could trigger at any moment' state which is hard to make safe until is has been made flat, slowly and safely.

In a great many cases it is not just the energy that needs to be compared - consider if you like that a small stick of dynamite, and a mars bar - both store about the same chemical energy and release one megajoule when oxidised fully , but the nature and rate of the energy release makes them the solution to quite different problems.

Mike.

the difference, and it is a biggy, is that we have many centuries of experience with hydrocarbon fires and in all cases, either cooling or removing oxygen quenches the fire and stops the production of heat and we know we can be confident that once extinguished, the fire stays out.

The problem with a battery fire is that when the battery is charged, it provides its own source of (resistive) heating and re-ignition, making it far harder to put out, and once out there is a significant risk of re-ignition.

Mechanical damage to the battery that allows the plates to move and then touch inside leaves it in a 'could trigger at any moment' state which is hard to make safe until is has been made flat, slowly and safely.

In a great many cases it is not just the energy that needs to be compared - consider if you like that a small stick of dynamite, and a mars bar - both store about the same chemical energy and release one megajoule when oxidised fully , but the nature and rate of the energy release makes them the solution to quite different problems.

Mike.