DC or not DC

My previous article reminded me of something that has been on my mind in the past.
Electronic devices, ones that do very little mechanical work, generally operate best with DC power supplies. In mobile devices such as phones or notebooks, the input power is used to charge the battery and it is the battery which supplies the actual electronics. But even in a desktop computer there is an internal power supply which changes the input AC power into various DC voltages before passing it on to the different components.
This is obvious with devices which are charged through a transformer (technically a SMPS). The transformer is commonly a little black box on the power plug which makes it impossible to fit in the socket next to any other device (who designs these things?).
While ideally there is as little as 5% loss of energy in per device, it may actually be significantly higher. And each one is wasting power.
Now AC is supplied to homes because this is the most efficient way to transmit electricity over long distances. Devices which draw large amounts of power – such as whitegoods or power tools – also built make use of the full amount available. But smaller devices need to drop power to reduce it to usable levels and this basically wastes the energy as heat.
An alternative, hinted at above, would be to have a single transformer which converted the input supply to some standard DC voltage for use within the home. As car chargers are common amongst the devices in question, a 12V supply would seem to be appropriate.
It would even be fairly easy so set up such a system. All you need is a couple of car batteries, a trickle charger and a bank of sockets to plug in the device chargers. A competent electrician should be able to do it in an afternoon.
I imagine that the best option in most houses would be a single supply point where mobile devices could be charged, but there is no reason why multiple points could not be spread throughout the house. It would mean a secondary wiring job but DC is a lot easier to deal with than AC and the concept of twinned supply already exists with grey water systems.
Another extension to the concept would be to wire in solar panels (which naturally supply DC) so that the secondary system is fully self-contained.

Big battery

I just caught a news item about a town in Texas which is building the world’s biggest battery. The intent is to maintain power supply when the single line from the national grid goes out – as it regularly does.
Now I don’t know how much wastage there is in storing power in this way, but the idea is great from a theoretical point of view. The normal pattern for electricity is for a central point of supply with failure prone transport to the point of usage. The risk of failure in transport is (usually) mitigated by using multiple redundant pathways – the electricity grid. This mechanism fails in the case mentioned in the article because there is only the single line into the town.
There are several known problems with the standard way that power is supplied. One of the biggest is that the grid is built around large scale centralised feed-in to the network and storage is apparently not practical at that scale. Hence electricity is generated to match demand – increasing production as more is drawn from the grid and dropping when usage falls. The possibility (probability) of under or over supply is obvious.
Balance is managed by using several sorts of power generation, at least some of which can quickly and easily brought on- or off-line. Even petrol powered generator may be included occasionally to meet short term peaks. At the other end, power is shed (read wasted) when supply outstrips demand.
In other words load balancing is done with methods which are quite expensive from both monetary and environmental points of view.
Storing (relatively) cheaply generated power during slack times and drawing against high demand would seem to make a great deal of sense. I assume that this is not possible at the national scale and so cannot be used in the central power plants. Given the fact that a town-sized battery is such big news, I guess that even storing at the sub-station level would be difficult.
But let’s take the concept further; how about power storage at the street or house level? Could each office building, which already have maintenance staff, include some electrical storage mechanism?
There may be maintenance concerns around having a bank of batteries behind the switch-board in every property – especially since traditional technologies use a number of toxic chemicals. But battery technologies have progressed fairly far in the last decade, riding on the back of the green movement and electric cars. At the same time the environmental and financial drivers for such a strategy are becoming stronger.
The idea ties in very well with the local generation of power. The input to the storage device need not be the national grid, it could just as easily be solar panels or a wind turbine placed on top of the house.