2022-04-11

Power line signalling thoughts (demand power management)

There are ways that things can communicate over power lines, notably Ethernet over power, which, IMHO, is crap. I am sure it has its place, but I would avoid like the plague.

However, I can see one area where some simple signalling would be very cool, and ideally in a really standardised way. Indeed, the idea that this could even signal incoming on your mains feed is not at all daft.

It actually sort of exists, it is frequency - when under 50Hz (UK) the power grid is struggling to meet demand, and when over 50Hz it has extra capacity. At present, few, if any, devices can detect or use that. Just using that could be useful, but I am thinking only a simple signal of 5 possible values.

What I am talking about is some signal that can tell a device :-

  • Right now power is effectively negative, please consume some power now even if it is going to waste
  • Power is cheap now, if you have a choice, now is the time to use it
  • Normal - use power as needed
  • Power is expensive now, if you have a choice, now is the time not to use it
  • Please shut down usage if at all possible right now

Not suggesting a complex set of signals by any means.

Now, if this was inherent in the mains supply, that could be useful of a lot of devices in the home. Ideally you need some signally (i.e. not frequency, really) so that you can isolate and run your own in the house. So for a house with solar and not a sane feed in rate, you can set this based on your solar/battery status in the home. But for most people not having this, the grid can set it.

I guess, it could be a standard that is frequency as the primary key and a secondary power signally for home override, maybe.

The point is that lots of kit really has a choice. At the simplest level, things like electric emersion heater, but in my case things like my hot tub. At present my hot tub heats based solely on temperature. With a very slight bias it could target that heating when we have spare solar. Just adjust target temp by say 0.5C depending on the signal on cost of power right now. Same for water heater. Same for heating or cooling a home, e.g. even aircon. Especially true for charging anything from a mobile phone, right up to a car.

It would need to be a simple standard and somehow in the chipsets for power supplies on any and every device. A world wide standard for this would be great.

11 comments:

  1. Would your idea accommodate existing electric clocks?

    https://en.wikipedia.org/wiki/Electric_clock

    "The accuracy of synchronous clocks depends on how close electric utilities keep the frequency of their current to the nominal value of 50 or 60 hertz. Although utility load variations cause frequency fluctuations which may result in errors of a few seconds during the course of a day, utilities periodically adjust the frequency of their current using UTC atomic clock time so that the total number of cycles in a day gives an average frequency that is exactly the nominal value, so synchronous clocks do not accumulate error.[12] For example, European utilities control the frequency of their grid once a day to make the total number of cycles in 24 hours correct.[13][failed verification] U.S. utilities correct their frequency once the cumulative error has reached 3–10 sec. This correction is known as the Time Error Correction (TEC)."

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  2. For scandinavian region price for current hour is available at: https://www.statnett.no/for-aktorer-i-kraftbransjen/tall-og-data-fra-kraftsystemet/
    Result of bidding for future hours are available somewhere. I have not looked for it...
    /hjj

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  3. Look up DRM (Demand Response Mode / Messaging?) in Australia. It is required that all inverters support it. (Although only an off and on mode). It is capable of telling stuff to ramp up generation or demand etc.

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  4. You can roughly do this using the National Grid Carbon Intensity API - https://carbonintensity.org.uk/. E.g. when carbon intensity is low, it's likely that plenty of juice is available. As others have mentioned, DSR (demand side response) is something that is being trialled/worked on in the UK, but at the moment theres no ability to individually participate AFAIK. https://www.nationalgrideso.com/industry-information/balancing-services/demand-side-response-dsr

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  5. It's a good idea from an engineering perspective, but I doubt it would survive contact with political reality.

    Given that the UK's approach to energy management seems to be to generate as little as possible while telling people to just stop using it, I suspect the signal would end up like the "terrorist threat level" — i.e. permanently stuck in the "emergency" zone.

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  6. Set your wayback machine to 2005 and weep:

    https://www.dynamicdemand.co.uk/

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  7. Another important point to note is that grid frequency is national across the UK, whereas there may be local factors to consider when implementing some kind of simple demand management scheme such as these. E.g. some parts of the electricity distribution network are already operating very close to capacity.

    On the other hand, this may be an ideal use for Vehicle-to-Grid technology. Charge your EV battery when electricity is cheap, use some of its stored charge to feed local demand when electricity is expensive. This from Nissan and ENEL in 2015:
    https://www.greencarcongress.com/2015/12/20151208-nissanenel.html



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  8. https://andrewback.net/works/Time-for-Tea

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  9. There is some commonality with this:

    https://www.bbc.co.uk/news/av/stories-61030903

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  10. New Zealand has "Ripple Control". There are two additional frequencies that the power company overlays onto the grid. There's a secondary meter that is turned one by one tone, and turned off by the other. This meter is charged at a much lower rate (typically about ⅓ the main meter). It's typically used for hot water from electricity, but can be used for anything (eg EV chargers etc).

    https://en.wikipedia.org/wiki/Load_management

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  11. You know this terrible white elephant call Smart Meters? Well, if you get one you can actually just use that to reference all import and export energy for both your solar and import usage.

    They actually measure a whole lot more than just kWh used in a specific timeframe too - you can see exactly what is sent to the DCC (and onto energy suppliers) here: https://www.smartdcc.co.uk/media/6106/con_u1_2_duis_31_ddmmyyyy_clean.pdf

    Thankfully you can get this little widget: https://shop.glowmarkt.com/products/glow-stick, which handily is a quick email to Hildebrand and they'll enable MQTT on the device itself, for you to have all the data available from the smart meter for your benefit.

    With the Reactive Power as well as Active Power, you can probably use NILM (https://github.com/nilmtk/nilmtk) to actually fingerprint each electrical device in your home, but more importantly you can measure pretty much everything you need to, using the billing meter.

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