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On Sunday, 25 August 2019 14:50:37 UTC+1, Scott wrote:

I was watching an item on TV about use of batteries to balance the
national grid. I have also heard it said that the supply is likely to
become less reliable with increased dependence on renewables.

I have always assumed that an uninterruptible power supply must be
energy inefficient for the same reasons as stand-by uses electricity.
Is this a correct assumption or does a UPS not consume any electricity
at all unless it is brought into use?

The battery charger is not 100% efficient. Once fully charged the battery
is often then overcharged continually. Turning 12v or 24v back to 110/230v
is also not entirely efficient.


As an aside, could a power cut ever damage a modern computer (say if
you happened to be installing an update or defragmenting a disc when
it happened)?

For sure, your filesystem can be totally borked - though it
usually survives unharmed. NTFS has been much hyped as
more robust in this respect, but it's only a limited subset of
data that gets duplicated, so it's almost as vulnerable as FAT32.

Its easy to defrag so no mains failure will bork anything.

Roger summed it up very well with
"Yes, but only journalists who can't do sums, and battery manufacturers,
see a major role for batteries in solving this problem."

Even if UPSes were 100% efficient, they would still not be practical for
grid backup.

But they can be viable to help with when a wind farm drops
off the grid for whatever reason and provide a replacement
for that short term loss from the grid until it reconnects.

The costs, pollution, energy consumption in manufacture
and vast demand for lead would be problematic.

The dont supply the entire feed to the grid.