reduce energy on standby

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fred55

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Just thought Id share my latest addiction - reduce energy usage. Concerned about my constant electric usage with things on standby so I've bought a clampmeter (£12) which will register current through a cable amongst other things - it clamps onto the live cable so I made an extension lead where the live is accessible for clamping around. I can now plug in the extension to feed an appliance to test the standby usage. Using the old formula V x A = power (W). Surprise and shocked how much is used by my standby equipment - microwaves ( x 2 ) garage door remotes ( x 4 ) TVs ( x 3 ), sky box, wireless router, yes I'm tight, but most of these things don't get used every day, they still use energy !! Conclusion Unplug or switch off.
 
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Sideways

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I've just installed solar panels and some Myenergi smart controls.
The system includes current transformers (equivalent to your clamp meter) on the 2 solar inverters to see what is being produced, and on the meter tails to see what is coming in from the grid or being exported to it.

These show that the house is using about 200W all the time. (cooker and microwave clocks, fridge, TV, desktop PC, routers, phone chargers etc etc).

Now these sensors aren't designed to measure small currents with high precision, but even if the number is only 100W, that's 2.4kW / day, 876kW / yr and £185 / year. It does make sense to investigate which devices are the worst offenders.
 

Spectric

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Using the old formula V x A = power (W).
That holds true in Ac circuits providing both current and voltage are RMS values. Multiply this by Sin Theta to get real power and by Cos Theta to get reactive or imaginary power which you may or may not be charged for.

Reactive power was really only of concern to large industries with machinery and lots of motors where there was a high percentage of inductance, but now it seems households are seeing more reactive power though capacitive loads as in switching power supplies and modern technology.

When looking at energy suppliers it is important to bear in mind their daily standing charge, so if you turned off both your gas and electricity you will still get a bill. High energy users can accept slightly higher standing charges for cheaper unit rates wheras low energy uses may accept the slightly higher unit rates for lower standing charges.
 

fred55

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Thanks Sideways my house was constantly drawing 650 W which is why I needed to check - and solar panels is my next project - how many! what storage ! maybe a link off for electric car ! excess to a hot waster tank ! ooow my brain starting to hurt. !! any recommendations for good company.
 

deema

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@Sideways is always very thorough in researching things very methodically, I’m hoping he will do a thread on his experience. I’m very impressed with how much power he’s generating on dull days.
 
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deema

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@Phil Pascoe don’t mock the afflicted with a comprehensive education🤪. You should feel sorry for the poor sole whose teachers thought getting the ideas down was more important than spelling or punctuation.
It’s been an acute source of embarrassment all my life, but I get by. I actually appreciate my billy do’s being highlighted, only way to try and improve…..I’ve edited it so nobody else will know how bad it was🤩
Apple predictive text doesn’t help….I often can’t see the difference between what I wanted to put and what it’s inserted.
 
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Spectric

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You need to differentiate between the academic and the skilled, two examples are 1) A guy with good degree in electronic's but could not solder or build prototype circuits to save his life and another person I worked with who was not very academic and very down to earth but who could produce some incredable work on his old lathe and mill.

This is the big problem we have today, education wants everyone to have a degree even if it is in drama or flower arranging but we really need the technical colleges to deliver hands on skills, all we have now is a skills shortage and many degrees not worth the paper they are written on.
 

guineafowl21

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Further to Spectric’s point, I quickly rigged up this setup:
6B0DE516-4AAB-4F64-A2EE-DAC2B6EE7807.jpeg

This is a simple 230V to 12V transformer left unconnected on the output. The meter is measuring 0.054A. Given a voltage of 245.2, we would expect: 245.2 x 0.054 = 13.2W of power usage.

8CF62C5C-ED34-4149-978F-A7318D64FA74.jpeg

However, the power meter only measures 4.3W, a third of the expected value. This is what is charged for by a domestic meter.

The reason is to do with power factor, which is a big subject, but involves a certain amount of power bouncing back and forth between source and load, which is not charged for in domestic properties.

In a nutshell, by doing P=VI you are measuring apparent power, units VA, and not real power, units W. You will be significantly overestimating electricity costs.
 
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guineafowl21

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That holds true in Ac circuits providing both current and voltage are RMS values. Multiply this by Sin Theta to get real power and by Cos Theta to get reactive or imaginary power which you may or may not be charged for.
Not that it matters too much to the OP, but I believe it’s the other way around:
Real power is VA.cos(theta)
Imaginary is VA.sin(theta)
 

deema

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This takes me back to my degree in electrical and electronic engineering….yep I have one of those😝

Imaginary power is usually referred to as reactive power. For inductive loads such as motors and transformers, the induced phase change is in one direction, and for capacitors it’s in the opposite direction. To minimise power usage you want the phase change to be to be zero, or the power factor to be 1. However, this is normally only the case with resistive loads, and for commercial consumption more often than not banks of capacitors are added into the system to ‘pull’ the phase change back towards zero to give you a power factor (PF) of as close to 1 as possible. There is requirement on industry by the generators to keep loads within a certain PF band, which is why capacitors are often mandatory. Now I could be terribly mistaken, but I understood that all meters read VA, or as it’s known apparent power.

This is a nice summary without too much technical mumbo jumbo for anyone interested.

 

guineafowl21

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Most domestic meters measure only in real power kWh (not kVAh or kVARh) and charge as such, eg this one:

This three phase one from the same manufacturer measures kWh and kVARh, for industrial/commercial places:
 

Sideways

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I also believe that electricity meters - which will all be subject to a British Standard - measure real power, not apparent.
The imaginary or reactive component is only of concern to the electricity company who have to provide for the component that flows in and out but which is not consumed nor paid for.
For this reason - in a commercial setting - the power factor is subject to monitoring and the electricity company can (and do) charge a substantial premium if the power factor moves too far away from 1.0
I once followed a visiting inspector around an overseas factory as he made his monthly tour of the plant's meters noting both the readings and the PF (power factor) for this purpose. If I recall correctly, a PF below 0.9 was the trigger for the surcharge.
Here's a brief mention of the subject on the IET forums. A great source of reliable info on questions like this.
 

Sideways

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In practice, domestic installations have very little reactive power. The main non resistive loads (in terms of power consumption) are electric motors and fluorescent lights (because of the ballasts) so would have little to worry about even if they did have to pay for it.
 

guineafowl21

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In practice, domestic installations have very little reactive power. The main non resistive loads (in terms of power consumption) are electric motors and fluorescent lights (because of the ballasts) so would have little to worry about even if they did have to pay for it.
Certainly true, and why domestic suppliers don’t (yet) bother charging for it. But for devices on standby, as per the OP, it will have significance for the way he’s measuring power. Standby often involves a switching supply running at a very low level, taking little gulps of current at the peaks in a very non-sinusoidal fashion.

Take the example of my Panasonic microwave, at idle, from the other thread:
83.55 VA at 88.77deg
83.53 VAR
1.8 W

If I measured current, and multiplied by voltage as the OP is doing, I would think my microwave is using 83.55’W’ at idle. That is way off from the 1.8W that is being charged for, and arguably not worth bothering with.
 

Richard_C

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This is all really useful, but talk of clamp meters, extensions and guineafowls set up, I wonder how long it will be before a tabloid runs with the headline "homeowner electrocuted trying to save power consumption". (Do the suppliers charge you for the jolt that gets you or is that one free?)

We do need to think of these things though: a smart meter (not got one) will tell you what is being used but not what is using it. Iterative switching on and off is needed I suppose but even then I wonder if it will 'see' the impact of low current items. Its hard to work out the effect of lots of things. I know what the power of my oven is, but if the oven is on for 2 hours the thermostat will be cutting in and out so I can't simply say 2 x whatever KwH and some is used to drive the fan which runs all the time. Same with hob and with most appliances.

Next time I do a roast should I sit there and time the red light on/off durations? Wouldn't change anything, would still cook but at least I would know. It could get to be an obsession ......
 

Ozi

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I've just installed solar panels and some Myenergi smart controls.
The system includes current transformers (equivalent to your clamp meter) on the 2 solar inverters to see what is being produced, and on the meter tails to see what is coming in from the grid or being exported to it.

These show that the house is using about 200W all the time. (cooker and microwave clocks, fridge, TV, desktop PC, routers, phone chargers etc etc).

Now these sensors aren't designed to measure small currents with high precision, but even if the number is only 100W, that's 2.4kW / day, 876kW / yr and £185 / year. It does make sense to investigate which devices are the worst offenders.
My worst offenders are children. Minimum draw downstairs 34W min upstairs 240W which includes my clock radio and all their standby. If I look at my smart meter I can tell who is awake in the house, oldest sons room often drawing 1.5 kW.

Never again will they make the mistake of telling me they can't get jobs because of all the old people like me hogging them.
 

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