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Just a thought but can a PV array not be used to run lighting and small power systems at 12V without the need to convert to 230v
Even if a PV array was running at 12v DC, there is a really good reason why homes are not wired to run lighting, etc, at 12v - you would need enormous (and expensive) cables, due to current losses. For a given power output, if you have lower voltage, you need to run higher amps. So, a light that draws 0.5A at 240v will need 10A at 12v. Power loss in cables is directly related to voltage (the losses rise at the same rate as the voltage), but is related to the square of current (that is, losses rise exponentially with current). Therefore, you want to run at high voltage/low current, and not high current/low voltage.
@twrch 1.5mm cable is rated to 14.5A, I don't think its as big a problem as you imagine. And in a typical house its not going to be a huge circuit.
I found this interesting
Seems quite thorough analysis of how to insulate a typical 1930s 3 bed semi.
why are phone batteries measured in mAH, but car batteries in KwH?
<vizletter>Can any of you so-called boffins explain that? </vizletter>
They're not, they're measured in AH.
My across the road neighbour has a 200w solar panel on pole which turns to follow the sun, and a homemade wind turbine (made from a washing machine motor) no idea of the power but about 3ft diameter, connected to some batteries. These between them do all the lights in his house, LED I think, and whatever it is he has running in two small sheds, lights and a 3D printer and a couple of other gadgets.
It can work.
He's an aircon engineer by trade and knows what he's doing which helps a lot...
I've often wondered why, if gas for CH is so 'bad', there isn't more of a push to go to electric boilers? (I think someone else mentioned this earlier.) I have no profound knowledge on this so please be gentle, however, having worked in B&Q a long time ago, even back then they were selling electric boilers. If we could sort out producing enough leccy from renewables, would they help to solve the problem?
Alternatively, we should just have thousands of water wheel generators in all sewer pipes - surely we get enough rain to make this work??? (Tongue in cheek)
An electric boiler is a bit daft though (especially for new builds) - it's not efficient to heat water up with electric and then pump it to rads around the house with all the losses involved.
Much more efficient to simply have programmable electric heaters in each room producing heat at pretty much 100% efficiency.
Instant heat, no leaks, no boiler maintenance (no boiler to go wrong!), much cheaper installation, less CO2, no noise and smaller heaters.
It would also be pretty easy to make the heating system smart with heaters that knew if a room was occupied and would switch on accordingly.
It all makes a massive amount of sense - it's just the cost of the electricity!!!
(it would/will also piss the plumbers off massively!)
1.5mm cable is rated to 14.5A, I don’t think its as big a problem as you imagine.
It's an enormous problem. Keeping it simple - the power you can get out of a cable run is calculated with V*I. If you run the maximum 14.5A at 12v, you can only draw 200W from the cable run. If you run that 14.5A at 240v, you get nearly 3500W.
The other issue with high-current, low-voltage systems is the voltage drop in the cables. That is calculated with I*R. The resistance of 10m of 1.5mm cable is 0.12 ohms, double that for the return run and multiply by your 14.5A, and you'll find there's a 3.5volt drop. Whatever you're powering will only see 8.5v.
It all makes a massive amount of sense – it’s just the cost of the electricity!!!
Electric heating makes as much sense as electric cars. My cynical mind says that there's a lot of money in selling EVs, and no money in selling cheap electric radiators. We can also just about get away with charging lots of EVs with our existing grid, but converting everyone to electric heating would bring the grid down immediately.
it’s not efficient to heat water up with electric and then pump it to rads around the house with all the losses involved.
My parents just got a "phase change" system installed - electric power is used a night to heat a "phase change material" (as far as I can tell, it's basically paraffin wax). It just means that the material gets melted, and that "phase change" from solid to liquid stores additional energy. That is then used to heat water during the day. They said that their hot water is now "not as hot as they expected"....
Is that a thermal store* then twrch? Interesting.
* a large tank traditionally filled with water I believe and heated via multiple sources (boiler/PV/Solar thermal). CH and hot water pipes then run through this tank and are heated by the 'contents' of the tank.
They said that their hot water is now “not as hot as they expected”….
The domestic hot water or heating water?
I'm based in the SE too so a bit more sun compared to my hometown of Manchester! I have a Tesla Powerwall solution on both the house and garage - it powers the home (i still have a gas boiler though, but watch this space!) and charges my car still with plenty left in the battery so i don't have an electricity supplier at all (other than the sun!). Even on cloudy days its surprisingly efficient and the cells aren't an eyesore. You can get a Powerwall expert to come round and talk to you about it. Worth looking in to in my humble opinion.
Yep, it's a thermal store. The benefit of the "phase change" material is that as well as storing energy by raising the temperature of the material, you store additional energy in the material by melting it.
The domestic hot water or heating water?
They have electric radiators, so the domestic hot water. I think part of the issue is that they were very enamoured with an apparently high-tech solution for going all electric, and did not fully think through what that would mean for energy usage and electric bills, and how and when hot water is available (even though their previous system was an electric immersion tank).
Forgot to add another issue with low-voltage wiring. The power losses in the cable are determined by the current and the resistance of the cable, and not the system voltage. Therefore, the lower your system voltage (eg, 12v DC), the higher the losses are in proportion to the total power.
The formula is I*I*R (ie, it's exponentially related to I).
In the 14.5A / 1.5mm cable example above, the loss in 10m of cable would be 50W regardless of what your system voltage is. If you're pulling the max 200W at 12v DC, a quarter of that would be lost in the cable!
why are phone batteries measured in mAH, but car batteries in KwH?
Because no-one gives the correct units when measuring mobile phone batteries. The correct unit is watt-hours (ie, stored power), not amp-hours. You still need to know the battery voltage to know how much power is stored in a battery when the value is given in mAh (which is milliamp hours, or 1/1000th of an amp-hour).
Mobile phones tend to have around the same battery voltage, so you can still make a comparison using mAh. EV batteries have all sorts of different system voltages, so they have to be specified in kWh to make any kind of meaningful comparison.
@twrch not a spark so thanks for the refresher.
As for PCM, that's usually a salt solution, it's a glorified hand warmer really. Is it a Sunamp unit your folks have? I was looking at those in my project...
When the time comes to ditch gas boilers you can be sure the government will have to subsidise a viable alternative.
Why jump now?
Dehumidifier nonsense aside my folks have gone all electric with 2 heat pumps and a 240l +270 l tank valved in.
One is solic 200 thermodynamic controlled and one is heated off the heatpump circuit.
The heatpump alone despite being the size of a double divan bed cannot heat up water quick enough for turnaround from empty it needs 12 full hours to get back to temp (@ ambient of 17deg outside- not gonna get any better mid Jan is it) Does keep the house warm though.
The whole lots run off 6 KW solar -3kw on fixed South facing 40 degree and 3kw tracking the sun .
Given the age and size of the house they are largely pleased and the costs are no more than oil heating (in France where they live ) the boiler needed replaced anyway as the internal tank had split.
The French government largely funded the install in a manner that made it worth doing. In the UK financially it makes no sense.
I’m based in the SE too so a bit more sun compared to my hometown of Manchester! I have a Tesla Powerwall solution on both the house and garage – it powers the home (i still have a gas boiler though, but watch this space!) and charges my car still with plenty left in the battery so i don’t have an electricity supplier at all (other than the sun!). Even on cloudy days its surprisingly efficient and the cells aren’t an eyesore. You can get a Powerwall expert to come round and talk to you about it. Worth looking in to in my humble opinion.
Go on then, how much did two Powerwalls cost?
We're in the process of finishing off a new-build. The developer has made it partly as a sort of sales brochure to showcase their construction method and encourage more eco developments.
Much easier to do some of these things from the beginning than retro-fit obviously. It's a timber frame with lots of hemp insulation, triple glazed and air-tight. There's a 10kW worth of PV panels and hopefully at some point soon, there'll be a 10kWh battery in the garage - apparently these are in short supply at the moment.
Heating is electric underfloor downstairs and there's a ventilation/heat recovery air pump that should circulate the warm (dehumidified) air around the rest of the house.
Decided to go for a "smart" water tank from Mixergy. Supposedly learns your routine and only heats the water you need, but you can also set it up as a sort of heat-storage battery if you have excess power.
We don't move in for a couple of weeks so I don't know how much extra power we'll need from the grid. I've been told the background baseline power will be about 100W, but there must be a lot of assumptions and caveats in that so will be interesting to see how it really works.
Lowering voltages increases losses / reduces efficiency?
Well sometimes, I’d agree.
We’re not dropping to 12V, nor anything like that, but our wee trial linked below is going to reduce voltages to reduce energy use. And before anyone says V^2/R, it’s not that simple with power electronics and thermostats looking after things, with induction motors and with kettles.
https://www.northernpowergrid.com/innovation/projects/boston-spa-energy-efficiency-trial
Beware simple physics around efficiency and losses. It can be difficult to model what’s really happening accurately.
I’ve been told the background baseline power will be about 100W
Licks finger and sticks it in the air!
Define baseline.
Do they know what temperature you want the underfloor to run at, what fridge freezer and wifi system (mesh or not, etc) you're having?
Sounds rather optimistic!
House sounds great though.
I’ve been told the background baseline power will be about 100W
Given a house generally averages 400W and has a minimum of 250W without any heating load, that’s impressive if true. Or is that just the heating portion - even then though.
250W minimum with no heating load is a lot.
Our house idles at 96W (120W when the fridge kicks in periodically).
The constant loads are:
4 node mesh WiFi
Router
Modem
2xRaspberry Pi's
A bunch of ESP8266 temperature and humidity sensors and some power monitoring smart plugs.
TV on standby
I think its a very rough estimate. I think the HRV is roughly 20W, but up to 70W depending on how high it's cranked up.
Just looked at the fridge/freezer - looks like about 50W average. The router only uses 5W.
I'm sure there'll be all sorts of hidden little bits here and there that add up to a lot more overall, but I think they'll all be dwarfed by oven, hot water - not to mention car!
Was gonna say when my house is over 200w I start looking for what's been left on......
Given your average house is doing 10kWh a day, most of you are averaging 400W.
Some of you may be well under 250W at minimum, but not many I suspect. Let me check the data.
Are you suggesting folks are using 10kwh at standby ? Your math suggests you might be saying that.... That seems quite incredible.
I thought 10kWh was average general usage.....
250W base load does seem a lot:
.25 x 24 x 365 = 2190kWh
We rarely get to that even with an electric car and no gas.
I thought 10kWh was average general usage…
Ahh. Wasn’t clear. Yes in the UK (sorry Edukator) 10kWh per day is the typical domestic usage (in round numbers, in a typical year) not standby use.
It has dropped a fair amount over the last decade or so but Covid increased it (though overall electricity use dropped).
If it helps for a typical / average house roughly 15kW peak, 1.5kW ADMD (diversified peak), 400W average and 250W minimum.
Based on the draw on the electricity network (and a few assumptions about PV).
Back in the 1970s ADMD was probably 2-2.5kW.
I would imagine that led lights and non-crt TVs are the biggest power savers since then.
But of course we now have stuff on standby, WiFi, routers, speakers, various things being charged, etc.
Yep. Though I suspect takeaways might also be something to do with it as people stop cooking in the home and also diversity in when they get home and eat (the ADMD figure depends on when you use the power).
Beware simple physics around efficiency and losses. It can be difficult to model what’s really happening accurately.
Unless your wee trial is using non-ohmic conductors, there isn't any way around "simple physics". As far as I can tell, the efficiency gains in that trial are financial efficiencies gained from not buying higher-voltage transmission equipment. Yes, I understand that efficiencies come from many sources and meanings, and a complex system may have many ways to achieve efficiency gains, but we were previously very specifically talking about ohmic losses in cables.
Nope. Technical efficiencies. Actually does very little with regard to higher voltage equipment. A bit, but negligible really.
Google conservation voltage reduction, or Grid Code OC6.
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.
And to be fair I might have sounded a bit smart alec, my point wasn’t that you could avoid physics, my point was that physics isn’t simple in real world situations.
PS - always happy to argue the toss on this sort of thing. It’s what I do for a living and some of the best ideas come from the creative chaos of these sorts of arguments. And no you can’t have a percentage if s good idea comes up. 😜
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 )
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