Going fully solar/electric

twrch and igm… looks like you are coming at it from two slightly different positions, both of which are correct, but aren’t quite the same thing. Bare with me here…

For domestic consumption, most of the large loads are essentially dumb, the amount of power they take will be based in the input voltage. So for cooking, showers, kettles and the like a slightly lower input voltage will lead to lower power consumption on those items, however there is a flip side… things also take longer to do, so a kettle takes longer to boil etc.

However there are also loads which don’t perform like this and will draw constant power regardless of the input voltage, up to the point where they just stop working.

In general the constant power loads tend to be the small items like TV’s, computers etc. However this is changing as more complex large loads are added to domestic supplies. EV’s being the obvious one as they’ll charge at constant power…

So, reducing the network voltage works in reducing both demand and losses, but only with ‘traditional’ loads, or complex power electronics loads designed to mimic those. Any constant power loads will just draw more current as the voltage drops.

Dropping all the way down to a low voltage DC domestic system does have all the problems with losses as all the ‘large’ loads would need power electronics to generate enough voltage to operate, and would then likely operate as constant power loads. This would lead to the scenario twrch was talking about.

Anyway, enough blether…

For the TLDR crowd… they are both right, but about slightly different things…

The losses avoided in converting PV DC to 230V AC and then back to DC for your LED bulb may well offset the I^2R losses in the cable. So not really just the ohmic I^2R losses.

You’d be surprised. With conversion at each end running at about 95% efficient (which is very realistic with current designs and components), any system over about 50W will be more efficient converting to 240V and back. I^2 losses are a b****! 😉

Nope. Technical efficiencies.

Grid voltage reduction is a way of reducing demand at peak times, when there is not enough supply. It relies on the fact that resistive loads on the network will draw less power when voltage is lowered, thus reducing demand.

twrch and igm… looks like you are coming at it from two slightly different positions, both of which are correct, but aren’t quite the same thing. Bare with me here…

Yep, I was answering someone’s questions about 12V systems being more or less efficient than converting to 240v. Grid voltage reduction is a complex and separate topic!

It is a new concept to me though – so it turns out one way to deal with excess demand is to supply less! Given that heat pumps are typically powered by a motor, transitioning more and more simple resistive heaters to such systems it going to cause issues when combined with grid voltage reduction. We will see!

Haven’t read the whole thread (I know, I know…..) but…..
We have 3KW PV panels and they don’t produce a load – certainly nowhere near considering battery storage. We’re not on mains gas and a new build well insulated house, so fully electric (apart from a small wood burning stove in the lounge, which gets far too warm if lit – should have sited it in the large open kitchen/dining area)

Was talking to a heating engineer/consultant recently who reckons if on mains gas, stick with gas as the replacement will be hydrogen, which will use the same pipes. Who knows if he’s talking sh1te?

Voltage reduction reduces both power (instantaneous) and energy (long term).

We found a 1.8% voltage reduction gave a 2.8% energy reduction. That’s empirical on a real distribution network. Other DNOs got similar long term results.

That wouldn’t be the case if the kettle simply took less power but longer to boil. There is something more interesting going on.

(OC6 is effectively a power reduction and is theoretically followed by a bounce back.)

If we have our sums right then the dynamic voltage optimisation we are trialling will reduce energy bills by around £600m per annum nationally.

gas as the replacement will be hydrogen, which will use the same pipes

Some of the network may be the same pipes but hydrogen brittling will become an issue for large chunks of the mains network (the stuff that comes to your house and likely down your street will be yellow polyprop…..which may also suffer molecule migration through(I’m not a plastics guy) but this is less of a concern as the numbers involved are tiny compared to a cracked iron work.

How ever -there are a couple of papers suggesting that they will be best to replace the iron work and pump hydrogen from a cost and infrastructure POV I did post some up in the tidal power thread but it turned out you need a journal subscription to read them.

Grid voltage reduction is a way of reducing demand at peak times, when there is not enough supply. It relies on the fact that resistive loads on the network will draw less power when voltage is lowered, thus reducing demand.

I thought that too when I started looking at voltage reduction. It’s true to some extent, but other things are going on too.

There’s a lovely report out there that details how different household equipment responds to voltage changes and it was the LED bulbs that caught my eye.

At the time the report was done, cheap bulbs (cheap GU10 as I recall) reduced power consumption as voltage fell, mid price ones held power steady, but expensive ones also reduced consumption with voltage reduction. Interesting. My theory is that was due to the different power electronics in the back of the bulb and what they were trying to do. If we repeated the study today you might get different results (in fact I suspect you would).

I think part of the load reduction is associated with the efficiency of a power electronics governed power supplies at different voltages. But I don’t know.

Rest assured WPD, ENWL and ourselves (NPg) all got similar results from voltage reduction trials – results that cannot be explained by simple resistive load reductions (particularly when loads like ovens and fridges have thermostats – yes I know a fridge isn’t resistive )

@igm

Interesting concept.

I found this report by Western Power: https://www.westernpower.co.uk/downloads-view-reciteme/2444

“The trial found that the demand reduction delivered via a 3% voltage re-duction varied considerably. Results ranged from 0% to 2.7%, with an average reduction in demand of 1.5%. “

I’d be interested if you have a report from your own company that you could link, if you got different results.

It’s also an interesting use of the term “efficiency”. Grid voltage reduction is essentially forcing people to use less power, by supplying them with less power. I suppose you could argue it’s “operational efficiency”, in that it makes an entire section of consumers live their lives using less power.

It’s also going to be a real problem as more non-resistive loads get added to the grid, like EV chargers and heat pumps. They can draw more current as the voltage drops, causing transformers and lines to get hot (those darn I^2 losses!)

Also – if this becomes a widespread idea, how long before white goods manufacturers also start taking liberties with the allowed voltage tolerances? They could easily start producing goods that are trimmed to draw more power, to make up for the reduced supply.

The real reason no-one does low voltage domestic power distribution is simply that our houses haven’t got that wiring in to do it. Get a quote to rip down ceilings, rip up floors, channel into walls and blockwork to install new power networks in your house and get back to me 🙂

My house is a typical late 1980’s build and originally just had a single socket in the living room! Persumably for your CRT B&W telly and that was that…… lol

BTW, one thing i did run the calc’s on was using solar pv to transfer low grade heat to a bulk water store, that a heat pump then uses to drive that heat store into the house.
This works because in the UK, our heating loads are mostly during the hours of no or low sun, and often we are not at home during the middle hours of the day. So 2,000 litres of water in an insulated hole in the ground, simple immersion elements from solar PV panels for 100% energy capture (resistive elements convert ‘lecy to heat at 100% efficiency) and that store heats up a bit during the day, which means your heat pump system can operate at a better CoP when it heats the house in the evening, and is much less susceptable to low air temps driving down CoP.
The beauty of the system is that you store heat at a very low temperature above ambient if you have lots of water, so you don’t lose much of it. And of course, the surface are to volume ratio scaling laws make it better and better as you use a larger volume of water

It also works because we tend to want a relatively fixed, short period energy source for our heating, ie we get home at 6pm, turn the heating on for say 3 hours, and pump say 12kWh into our house, but then the system turns off and we go to bed. The bulk thermal store means that whilst it runs the heat pump can leverage a short term artificially low deltaT, and hence run at an artificially high CoP

1,000 litres of water holds roughly 12 kWh when it’s temperature is changed by just 10 degC

@twrch
Try these.

https://www.northernpowergrid.com/asset/0/document/5985.pdf

https://www.northernpowergrid.com/asset/0/document/4117.pdf

But in the mean time “efficiency”. It’s not that we are giving people less power – brutally we don’t really care, particularly as it doesn’t really change network utilisation much because as you note the current changes less than the power. It’s that if peoples appliances run at a lower voltage they run more efficiently and need less power.

And as for appliance manufacturers cottoning on, in practice they probably already have. A CE marked appliance will have its efficiency sweet spot somewhere around the perceived usual voltage, and even with voltage harmonisation, GB voltages are higher than average in Europe. So probably the sweet spot will be tuned a bit lower than we see in this country.

As for EV chargers, they probably are constant power devices (though they don’t have to be, that can be designed in or out), but they probably aren’t constant efficiency devices.

Taking a silly example, and EV chargers will be far more complex, if I put 220V into your phone charger do you think it will run hotter or cooler than if I put 250V in? I don’t know, but I suspect it will be cooler at 220V. That’s energy that was never charging your phone.

Is that the whole of the efficiency gain, I doubt it, but it’s more convincing than the resistive load that although it runs at a lower power runs for longer. My suspicion is that the long run energy reduction from lower voltages into resistive loads is actually negligible, due to thermostats, bimetallic strip switches and people simply letting things run longer. It’ll work for OC6 load reduction though as that is about power not energy.

@maxtorque the concept of a massive thermal store + heat pump sounds interesting. Do people actually deploy such solutions?

I’d be wary of burying such a thing because of future maintenance issues, probably because of my chemistry teacher’s story of a buried HCl pipeline that leaked at the papermill he used to work out that nearly took out the town’s main water main…

I haven’t read this whole thread but please don’t make the mistake of thinking you can use solar pv generation for heating your house, even with batteries. For the months you need to heat a house you generate bugger all with pv and batteries won’t store from September to February. And whoever just built a new house with electric ufh. I’m so sorry for you but you were given terrible advice, passive house or not.

By definition a passive house requires so little heating it really doesn’t matter what type of heating you choose:

The Space Heating Energy Demand is not to exceed 15 kWh per square meter of net living space (treated floor area) per year or 10 W per square meter peak demand.

For a 100m2 that’s 1500 kWh per year or 1kW peak demand.

In terms of cost electric ufh would cost you £225 at 15p/kWh. In terms of being able to power that with pv in December you’d need about 30 high output panels angled for Winter sun, fewer if they were sun tracking. The rest of the year you’d be exporting leccy.

Edit: Our house requires about double the passivhaus standard of heating. Partly because it’s retro-insulated and still has a few thermal bridges where internal walls meet external walls, but also because Madame won’t put up with 18°C when sitting working. It require’s about 3000kWh a year which means a couple of m3 of wood or one oil-filled radiator, just one for the whole house.

You can’t heat a house on pv as most of the time the sun dosnt shine in the winter in the uk and if it is shining you won’t actually need to add extra heat. I do actually live in a passive house and I am also a passive house consultant. Direct electric heating isn’t considered sensible in passive houses, maybe in tiny flats in some instances. It is a mistake to only look at the heating load in a passive house. You still need to heat hot water so why not use that source to also heat the house?

I’m interested in this notional amazing house that is only 100m2 yet somehow has roof space for 30 solar panels that can produce power in the middle of the night to keep up with the 1kw heating load.

You know how much the temperature of a house varies once it’s well insulated? Not very much at all. We never ever heat at night. I rarely, very rarely heat in the day before 17:00. It’s currently (12:57) 18°C having not heated since yesterday evening, I’ll have a burn when Madame gets home and that will get it up to about 20°C. When it’s below zero outside I refill once or twice in the evening.

Hot water? The solar thermal provides for our needs for 6-7 months. The rest of the year the solar thermal tank feeds a normal electrical tank which takes the water up from tepid to shower temperature. The solar thermal divides domestic hot water heating electricity demand by about four. It thermo-syphons so requires no pumps, electrics or maintenance beyond a twice yearly panel clean and once a year fluid top-up.

Not my house, but you get the idea. 30 panels is achievable on many houses. I’ve only got 14 but will add some more when the current feed-in contract ends.

Not my house, but you get the idea. 30 panels is achievable on many houses.

That house isn’t 100sqm.

Mines 130sqm I’ve got 12 on my roof. Might get another 2 on if I pushed it ….

That house is an irrelevant example. It is clearly much bigger than 100msq and does not have a roof design you would normally find in uk housing stock. Lots of uk houses are unable to even fit 3.7 kw of solar, which generate almost nothing on dull winter days.

Mine’s 68m2, I’ve got 14, there’s space for another one and space for another 10 on the garage.

For some people it’s possible for others it’s not.

What is possible for the vast majority of households including you Trail-rat is vastly upgrading insulation standards.

The roof is the only thing most households get anywhere near acceptable standards.

A insulated cavity wall is about R=1.5. You can get to R3.5 with 10-12cm of insulation on the inside of a wall which will have none of the risks of insulating the cavity (you’ll complain about losing living space until you realise that removing radiators will gain you that space back). Current double or triple glazing will drop uw to 0.9-1.2. Insulating under thee floor is often not done at all. If you have sanitary space it’s easy to get to R=3 for the floor. Secondary double glaze doors or fit double doors and insulate what you can.

Insulating under thee floor is often not done at all. If you have sanitary space it’s easy to get to R=3 for the floor. Secondary double glaze doors or fit double doors and insulate what you can.

This is next weeks job for me and son no.1, suspended floors (thankfully the house was built on a concrete slab and there’s enough room to crawl about) with no insulation currently. 200mm loft insulation with a breathable membrane will be going in next week. Loft is already 300mm thick and previous owner had cavity wall insulation carried out.

Back to your strong assumption game there I see.

You are aware I removed the back of my house and rebuilt it 3m further away with 150mm insulation in the wall and the roof.
And 150mm (maybe more can’t remember and can’t tell from the build photos)in the floor tbh if all I’m aiming for is your heating outlined above then I’m already there. Our oil heating hasn’t used 1 bar the whole year (140l)

For me the next move to reduce the dependence on oil is to fit a thermal store/water tank of some kind and use the immersion dump for that.

And once cost come.back down I’ll get the front windows modernised to match the rear.

You’ll stop dissing EVs one day. 🙂

Did you miss the thread where I’m looking at buying outright twizzy for my local usage /client visits once they start up again ?

No, I didn’t. Only fools don’t change their minds, eh!