PowerSwitch

In the past, when electricity has been in short supply it has been in effect rationed by either imposing voltage reductions, or rota power cuts.
The idea being to reduce the load so as to match the available supply.

This was last done on a regular basis in the 1970s when coal miners struck and power stations ran short of coal.
More recently*, rota cuts and voltage reductions were imposed on a "one off" basis due to the very rare, near simultaneos breakdown of two large generating units.

The load reduction achieved recently by rota cuts and voltage reductions was much less than expected.

If rota cuts and voltage reductions become widespread, I fear that the savings will be far less than expected, and that therefore larger areas will have to be cut off for longer, than is being expected.

There two reasons for this
Firstly, an increasing proportion of the electrical demand is by appliances with switched mode regulating circuits.
Reducing the voltage to such loads saves nothing whatsover, indeed a very slight increase is likely.
Such loads include virtually all IT stuff, electronic lighting ballasts, and industrial motors on variable speed drives, and many other motors.
A lot of the remaing load is thermostatic water or space heating, this will consume less power for the first few minutes of any voltage reduction, but after about 10 minutes the load rises to the previous figure (due to each appliance running longer to give the required output)
The contribution from some embeded microgeneration would be lost as the grid tied inverters wont tolerate the reduced voltage.

Rota power cuts can also shed far less load than expected, especialy if repeated or prolonged.
If 10% of the national load is disconnected, then in the short term 10% less power is needed.
If however the emergency continues for some hours, then the savings become less. For example, after a few hours it would be the norm to reconnect those blacked out, and to blackout a different area, in the interests of fairness. Unfortunatly, when the supply is restored, virtualy every thermostatic heating or cooling appliance will draw power at it attempts to catch up.
Therefore the formerly blacked out area may consume 50% more power than normal for an hour or so, meaning that a larger area has to blacked out to compensate.
And of course ALL micro generation in the cut off area is lost, so for example cutting off 100MW of load might lose 5MW of embeded generation for a net saving of only 95MW.

If rota cuts become prolonged, then the savings are even less for several reasons. For example an electric bakery wont stop making bread, they will simply transfer production to the times when the power is on, and use exactly the same KWH in total.
If someone knows that the power will be off when they normally take a bath/shower, they MIGHT go without, but more likely will shower or bathe when the power is on, thereby useing exactly the same energy in total.

Also, in urban districts the areas cut off or turned on are fairly small in area, at any one time.
Those with homes or busineses on the boundaries will make arrangements to obtain power by private cable or even extension leads from premises still on, thereby increasing the load on such areas.

Not very encouraging is it !
To save 10% of electricity, a lot more than 10% of consumers would have to be disconnected.

*link to report
http://www.nationalgrid.com/NR/rdonlyre ... Issue1.pdf
Into exceptional loss of generating capacity leading to discconnections.
Edit to add link to report.

Adam, Its those pesky switch mode power supplies again.

I remember working and living through the 3-day week. Instead of working 5 8-hour days we worked 3 12-hour days. At home we left the immersion heater on all day and we had 2 car batteries on charge so they’d be ready to power fluorescent lights and a portable TV. Our house was heated by 2 gas fires, cooking was by a gas cooker with no electrical connection, and we had stored hot water. Most households would find power cuts much harder to cope with nowadays.

Indeed, allowing many industries to only work a 3 day week saved some fuel, but not as much as expected, since as you point out, many worked longer hours on the permitted days to partialy compensate.

Domesticly, the absence of hot water storeage in most homes would be problem. As you point out, an immersion heater, or a conventional gas boiler could heat water in the tank whenever the power was on, for later use.
Cant do that with electric showers and combi boilers!

I remember the number of extension leads strung accross high streets at high level, because each side of the street was cut off at different times.

I was a teenager at the time, and equiped our home with a 72 volt standby lighting system, rather an odd voltage but it had its merits.

Blimey adam2 that's iompressive. The best I could muster (admittedly aged only about 10, and with the help of my brother) was a morse-code "telegraph" from one bedroom window to the next, so the 2 of us kids could chat after bed-time .

For power-cuts we had an open fire, a paraffin heater, our camping-gaz cooker and hot water in the tank. Plus lots of torches and candles. We could, in theory (we were still too young) have done homework, but people couldn't today because so much of it relies on being on-line.

adam2 wrote:In the past, when electricity has been in short supply it has been in effect rationed by either imposing voltage reductions, or rota power cuts.
The idea being to reduce the load so as to match the available supply.

This was last done on a regular basis in the 1970s when coal miners struck and power stations ran short of coal.

It's been happening over recent years in South Africa, and numerous other places around the globe as reported in numerous posts by "seahorse" in this thread:
http://peakoil.com/forums/review-of-the ... t7291.html

Do bear in mind, that people will not be turning on their lights or boiling their kettles to create additional demand to compensate for their power-cuts. If the time constants for space heating are exceeded by the power-cuts then the additional "on" period won't compensate for the "off"s.

Bandidoz wrote: Do bear in mind, that people will not be turning on their lights or boiling their kettles to create additional demand to compensate for their power-cuts. If the time constants for space heating are exceeded by the power-cuts then the additional "on" period won't compensate for the "off"s.

True to an extent, when the power is restored after say 3 hours, not many consumers will use an extra 3 hours worth.
But there would be significant extra demand on restoration, almost every thermostatic heating and cooling appliance would run for perhaps the first 15/30 minutes, though not in most cases for longer than an hour.
There would probably be some extra boiling of kettles immediatly after restoration, by people who have been waiting for a hot drink.

UPS units are now more affordable and more widely used than in the past, therefore extra energy would be used to charge the batteries after a power cut.

RenewableCandy wrote:Blimey adam2 that's iompressive. The best I could muster (admittedly aged only about 10, and with the help of my brother) was a morse-code "telegraph" from one bedroom window to the next, so the 2 of us kids could chat after bed-time .

For power-cuts we had an open fire, a paraffin heater, our camping-gaz cooker and hot water in the tank. Plus lots of torches and candles. We could, in theory (we were still too young) have done homework, but people couldn't today because so much of it relies on being on-line.

A friend and I were keen electronics constructors. As well as many other very useful items, we built several radio transmitters so we could communicate between our houses. A distance may I add, exceeding one half mile!! On one evening, my friends radio transmission went abruptly dead. His father had heard his whole message downstairs on their music centre and feared that the GPO would be breaking down the door at any minute. One of my most successful designs, used a single valve oscillator, modulated by the output valve of an old radio that luckily had a microphone input. I must have been twelve or thirteen at the time and my parents should have been jailed for negligence.

Life is quite possible with a less than 100% available electricity supply.

The reliability of supply has improved here over the years mostly as a result of ESB replacing a lot of rotten old overhead line poles that previously fell over in high winds.

Despite this most households around here are well equipped with torches and candles for the odd outages however people's demeanour begins to change rapidly after supply has been off for a few days. I was told several lurid tales of loss of supply rage by a women who had to field calls from irate customers.

I well remember a Christmas about 10 years ago when we were off for 4 days and discovered we were the only folks in the street with a (bottle) gas cooker. More seriously the local water supply was just on the brink of running out and getting distinctly murkey when the pumps came back on.

There is no doubt in my mind that electricity has addictive properties on a par with opiates and the withdrawl symptons are just as dramatic and traumatic. It helps to have some experience of it to know what to expect.

Roger Adair wrote:There is no doubt in my mind that electricity has addictive properties on a par with opiates and the withdrawl symptons are just as dramatic and traumatic. It helps to have some experience of it to know what to expect.

Definatly, and perhaps a limited supply of 12 volt DC would help with the withdrawal symptons, just as methadone is used to help wean addicts of hard drugs.
They might become addicted to 12 volts DC, but that might be considered less harmfull.

the mad cyclist wrote:A friend and I were keen electronics constructors. As well as many other very useful items, we built several radio transmitters so we could communicate between our houses. A distance may I add, exceeding one half mile!! On one evening, my friends radio transmission went abruptly dead. His father had heard his whole message downstairs on their music centre and feared that the GPO would be breaking down the door at any minute. One of my most successful designs, used a single valve oscillator, modulated by the output valve of an old radio that luckily had a microphone input. I must have been twelve or thirteen at the time and my parents should have been jailed for negligence.

My Dad bought me a book of electronic circuits when I was about 12, I soon cobbled up an FM transmitter built into an old calculator case and spent many happy English lessons jamming the radio that the teacher tried to make us listen to. Happy days.

Catweazle wrote:

the mad cyclist wrote:A friend and I were keen electronics constructors. As well as many other very useful items, we built several radio transmitters so we could communicate between our houses. A distance may I add, exceeding one half mile!! On one evening, my friends radio transmission went abruptly dead. His father had heard his whole message downstairs on their music centre and feared that the GPO would be breaking down the door at any minute. One of my most successful designs, used a single valve oscillator, modulated by the output valve of an old radio that luckily had a microphone input. I must have been twelve or thirteen at the time and my parents should have been jailed for negligence.

My Dad bought me a book of electronic circuits when I was about 12, I soon cobbled up an FM transmitter built into an old calculator case and spent many happy English lessons jamming the radio that the teacher tried to make us listen to. Happy days.

Cat obviously was scarred in his youth by the dulcet tones of big bruvva aka the British Brainwashing Corporation.

Perhaps a few CB radios powered by small PV panels and scrap car batteries might be usefull?

R

adam2 wrote:

Roger Adair wrote:There is no doubt in my mind that electricity has addictive properties on a par with opiates and the withdrawl symptons are just as dramatic and traumatic. It helps to have some experience of it to know what to expect.

Definatly, and perhaps a limited supply of 12 volt DC would help with the withdrawal symptons, just as methadone is used to help wean addicts of hard drugs.
They might become addicted to 12 volts DC, but that might be considered less harmfull.

Interestingly a local German Hippy here has been off grid for last 20 years and has been continually reducing the amount of AH battery storage and increasing the amount of wind energy his 2kW turbine and PV dumps into an (uninsulated) hot water cylinder that provides washing up water and also acts as a storage radiator in his very funky and aromatic smelling living room.

In the 20 years he has worked his way through several DC/AC inverters and 12V DC powered TVs all of which have eventually blown up.

My definition of a SMPS is somthing that does not live long enough and expires well before it's theoretical energy efficiency savings are realised.

I am on my fourth inverter, but the first two were cheap rubbish.
First good one was by studer, failed after some years of heavy use but was worth repairing.
Whilst awaiting repair I bought an old Trace 1255 inverter, still going strong.
I am nearly all 12 volts DC, and only use the inverter for A/C and power tools.

Switched mode power supplies are efficient, but not as reliable as one would hope.
They can fail with suprising violence !
Underloading only helps a bit, as many components are similary stressed even at part load.
A well designed linear power supply, with no components run too hot should last 100 years or more.
I am still useing a pre-war battery charger !

The vast majority of switch mode power supply failures are caused by ageing capacitors, normally on the high voltage side.

A stock of 220uF 400v and 2200uF 16v caps will allow you to fix many of them.

adam2 wrote:I am on my fourth inverter, but the first two were cheap rubbish.
First good one was by studer, failed after some years of heavy use but was worth repairing.
Whilst awaiting repair I bought an old Trace 1255 inverter, still going strong.
I am nearly all 12 volts DC, and only use the inverter for A/C and power tools.

Switched mode power supplies are efficient, but not as reliable as one would hope.
They can fail with suprising violence !
Underloading only helps a bit, as many components are similary stressed even at part load.
A well designed linear power supply, with no components run too hot should last 100 years or more.
I am still useing a pre-war battery charger !

I have a horrible feeling that adam and cat had incredibly similar formative experiences to myself. My first experiments in broadcasting involved the non linear characteristics of the geranium diode detector in a crystal set radio. I discovered that by modulating it with a battery and carbon microphone my dulcet tones could be heard downstairs on the b+w 405 line tv my parents were watching. The earth lead for my crystal set ran very close to the indoor tv aerial.

Many years later when I spent a period working at the other end of the broadcast tv chain I had my first intro to SMPS devices in the form of very lightweight chargers for the nicad battery packs for portable video cameras and recorders. These initially seemed a good idea until we discovered their short life and self destruct mode that managed to take out most of the components.

Thereafter they were replaced with somewhat heavier linear devices
sporting impressive moving coil ammeters and chunky transformers, diodes and linear regulators.