Batteries on the Grid (OT)

In message <rPCdnYRa-OD8 snipped-for-privacy@brightview.co.uk>, Max Demian <max snipped-for-privacy@bigfoot.com writes

Some recently converted green friends put one on their roof. The only time I was there on a windy day, the house had a noticeable low frequency vibration. I have an idea the *barrel* type might be better but there won't be one on my roof.

Solid state devices took over from mercury arc rectifiers in about 1975 according to this

While I understand how to rectify AC to DC via a bridge rectifier and reservoir capacitor, I am struggling to understand how DC at several GWs is converted to AC?

I can only assume a big huge Inverter like an APC UPS!

It's all here in the link given by Fredxx

OK, thanks for the link but another question....

Whats the point behind converting from AC to DC and then converting back from DC to AC?

Surely there would be conversion losses in both the rectifier and in the inverter?

S.

They were still using them in the Royal Opera House to supply DC to the ex-WW1 submarine motors that operated the stage machinery until the major refurbishment just before the millennium.

For overland transmission, nothing to be gained at all. But undersea transmission, such as the interconnectors between the UK and Europe, there's quite a lot to be gained, because AC cables loose energy to the conductive sea water via capacitance losses. It may be acceptable over short distances, where cable losses and converter losses are not too different and it's a toss-up which works out the more efficient, but it's not acceptable over long distances. See

As the article suggests the losses are very low.

The original reason for AC to DC and back to AC is principally the systems are not locked in frequency, where the frequency will be slightly different and a wandering phase relationship.

A secondary, and perhaps now more important, reason is that transmission of DC is more efficient than AC, where dielectric strength and dielectric losses become significant factors with AC undersea cables.

JOOI do you know of any livestock farmers who make use of the energy readily available to them by living in a house-barn? (When I used to listen to the Archers I thought it would have appealed to Pat; but perhaps not so much to Susan Carter.)

No. Deep litter, yarded cattle dung is not hugely smelly but animals are noisy! I will shortly have some about 50m distant but we are double glazed and upwind.

In principle, yes.

You can create a sine wave by chopping DC with a variable pulse width high frequency square wave, and feeding it to a big transformer or filtering it with L and C..

Transmission losses and phase lag.

DC cables don't have extra circulation current due to capacitance to ground and/or extreme phase lag due to length Both of these limit a 50/60Hz AC grid to about 1600km in air and a lot less in sea water...

I'm don't think wind turbines have any effective spinning mass. AIUI they generate DC which is then converted to AC synchronised to the grid.

Actually synchronising a wind turbine to the grid would be a nightmare.

Andy

Presuambly it must be highly efficient else you'd have a shitload of heat to get rid of at each end. Even 99% efficient would mean 20MW of heat loss - at each end. How you gonna lose that? Ergo - it's much better than 99%.

and it wasa wind farm taht caused all sorts of problems last year when it went off line.

Prezactly.

Well conversion to DC is little more than some mercury arc rectifiers, and bloody big bungalow sized chokes......or was when I visited the very first link to France. Our party of schoolboys took the background

I think mercury arc valves were also used to chop the DC at 50Hz (or whatever te mains was at that time) and smooth it through yet more chokes and bus sized capacitors.. These days its all solid state. Good article here

How interesting! Am I right in thinking that the Science Museum still has some hydraulic lifts, although they had to put in local supplies after 1977.

Very very short duration overloads. Battery storage capacities are always quoted in MWatts which is largely irrelevant.