[Closed] Going fully solar/electric

You won't be completely off grid in December unless you insulate to Passivhaus standards. You get about a quarter of the rated Summer output just when you need the most heat.

Have a look at your gas bill and work out how many kWhs of gas you use in December now. I think you might be surprised at how much energy you are using and that solar is only viable if you reduce that. That said if you heat with a heat pump, at current gas and electricity prices you may decide electric is viable even without solar. I'm against battery storage, the electricity suppliers can do the buffering for you and probably better than you.

bookmarking

I'd also ask what are your insulation levels like?

Insulation upgrade in the loft is my first job. It’s a 1930s build with cavity walls.

I know I will use some grid energy, but with the ability to charge the battery overnight at cheap rates, then empty it for morning heating, I reckon it should work.

Current energy price craziness makes it impossible to work out accurate pricings.

Obviously proper calculations will be needed eventually, but is this even viable?

It is possible.

Will it be cost effective? Unlikely.

Will you have to compromise in all sorts of ways? Yes.

Is it easy? No.

Is it worth doing? Likely.

Lets not forget that micro-generation (unless it is hydro) is pretty inefficient for all sorts of reasons. Large scale generation is much more efficient in other ways.

The best thing we can do is huge reductions, rather than just generate more.

I’m struggling to see any efficient technology for the masses to replace gas.

Whilst financial gain is part of it, I also want my domestic emissions reduced.

This is what I get from a 100% unshaded south facing 3Kwp system in N Wales - see what size system you can fit on your roof and scale up accordingly.

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I too would be sceptical about battery storage - just to expensive - but then I might be wrong.
You could look at solar thermal as well but it's a one-trick pony.

A stove would make a massive difference. We survived for the last two winters with just a stove in our kitchen/breakfast room/snug/dining rooms (approx 15m x 10m).

I’m struggling to see any efficient technology for the masses to replace gas.

If it's efficiency youre after then the answer is electricity - but the question is cost.
Get the price right and it's the answer..... but until then....

I have a wood burner too, but I’m not sure that will be acceptable in the future.

My other hope is the “much talked of” conversion of the natural gas network to hydrogen.

I would get someone knowledgeable to help look at things like construction, insulation and air-tightness first to give you an assessment of what you could achieve given the fabric of the building and potential EPC. You’d then be able to assess the options available for heating, solar, PV etc.

I wouldn’t go so big so quick. I’d maybe start with a 5kw system, with an inverter big enough to cope with any future improvements. There’s no grants, little in the way of FIT, so all that mass of solar panels will head back to the grid without you seeing a penny. A solar immersion control like the iBoost will give you a decent amount of hot water for a small outlay. Batteries IMO are a red herring. Wait 5 years and they’ll be half the price.

Something that an architect friend said to me always sticks in my mind. 'If you add together all the tiny gaps and cracks in your house where warm air can escape, you'll find it can easily be the same area as an open window or even a door'

I would get someone knowledgeable to help look at things like construction, insulation and air-tightness first to give you an assessment of what you could achieve given the fabric of the building and potential EPC. You’d then be able to assess the options available for heating, solar, PV etc.

Good luck with that. There is a gap in the market in that this role doesn't really seem to to exist.

A solar immersion control like the iBoost will give you a decent amount of hot water for a small outlay.

I have a combi - so I plumbed something similar into a 2kw oil radiator in the most used room in the house keep it warm during the day when we are not using the generated leccy for other things. Considerably less heat required when we get home.

Not a great use but the leccys there anyway and the house does need much less oil fueled energy to get to temp when we get home.

This video indicates around £4K +vat for a 8kw battery install and estimates ~4 yrs payback, might be worth a look.

Yep our holiday place has an Immersun that feeds the hot water tank first and when that's up to temperature it feeds a dedicated socket in the hallway that has a simple panel heater plugged in so any spare electricity turns into heat.

(An oil rad isn't quite as good as they take more power before they start emitting heat - cheap and cheerful panel heater throws out heat in seconds which is good for an intermittent supply)

Yes, Ive watched EVM's videos as part of my google research.

I’m struggling to see any efficient technology for the masses to replace gas.

Whilst financial gain is part of it, I also want my domestic emissions reduced.

You and me both. I've just installed a 5kW solar array and will have battery backup when Elon can make a Powerwall for me. I have an oldish gas boiler and I'm starting to wonder if I should replace it before the government bans the sale of them but like you I'm struggling to see how a heat pump is financially and practically realistic even in a well insulated, double glazed house constructed to normal building standards. Besides all that the sheer size and appearance of the things is off-putting and although its claimed modern ones are quieter I still worry about noise and vibration in the house and getting noise complaints from the neighbours.

I think stopping the use of gas for domestic heating is going to be a much harder nut to crack than moving from ICE vehicles to EVs. For a start electricity is cheaper than petrol but its five times the price of gas. Now we could make electricity cheaper by moving the renewable levy onto gas but someone struggling financially to heat their house with gas is not going to be able to afford to heat their home on electricity even if its a bit cheaper let alone afford a new heat pump.

This video indicates around £4K +vat for a 8kw battery install and estimates ~4 yrs payback, might be worth a look.

I was going to link to this one as well. However his man maths only works out if overnight cheap tarriff stays at 5p per kWh which I bet it won't.

He does make the good point that unlike a solar array its a lot easier to take your battery with you when/if you move.

Whenever I look into to cheap night tarifs they end up more expensive given the higher standing charge and punitive day-time tarif that goes with them.

The best thing we can do is huge reductions, rather than just generate more.

Having to generate all your own electricity is a good way of reducing though.

An oil rad isn’t quite as good as they take more power before they start emitting heat – cheap and cheerful panel heater throws out heat in seconds which is good for an intermittent supply)

Arguably a panel heater flattens out the hysterisis which is why I went for an oil heater. I am not needing instant heat I want to heat a volume to release the heat over a period

But net energy out is near as damnit net energy in in either case.

With batteries and storage, I can see changes shortly.

Might we have house by house or Street by street alternative storage? I'm talking thermal, chemical or mechanical...

Think mini versions of Cruachan, with a tower on each street...(etc)

OK.
My theory, though, is that with a potentially intermittent power supply of rather take what heat I can when it's there.
🤔

A panel heater will also just keep producing heat whist I think an oil rad will switch off when the oil reaches a certain temperature.
This is good when using mains power but I want to use every last watt of solar power.

Oil rad over 99% efficient in tests.

If I'm producing 2kw long enough in winter to reach the thermal cut off of I'll consider that but it's doubtful that'll ever happen .

A dehumidifier does better than 100% as you get the latent heat from condensing the water. I worked it out for mine but can't remember the exact numbers, of the order of 130% IIRC.

But it also needs a minimum /sustained input to set it going & frequent emptying

Convinance is king.

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 via an inverter and incur the losses that must arise from this?
Lighting and certain appliances can easily run off 12V DC so I've often wondered why we don't replace wiring systems for DC installations to utilise PV rather than rectifying it to 230v?
Most nights if it's just me and the wife in we only have a lamp or two on and probably just watch a laptop or tablet for TV or movies so aside from cooking and the washing machine running we are not generally pulling much electrical load from the supply. Pretty sure a half decent leisure battery could be charged to handle this for about 4 hours a night? Also wonder if PV wouldn't be enough to run my pc and monitor during the day, and a single 10W led lamp as that's pretty much all I run when WFH. 400w running load??

frequent emptying

They have a pipe outlet you can connect to the bathroom plumbing.

Edit to elaborate. Using either a heat recovery ventilation system or dehumidifier to keep humity down not only keps your house dry but also makes it feel warmer because damp air feels colder. Other things that make you feel cold are cold surfaces. Standing in front of a cold surface will feel colder than a warm surface for a given air temperature. Insulated walls and triple glazed windows don't feel cold to stand in front of so you feel warmer with a lower air temperature. Put the two factors together and you feel comfortable when the thermometer tells you it's a couple of degrees colder.

They have a pipe outlet you can connect to the bathroom plumbing.

Some do your also Assuming everyone haz a pipe near the area you want heating/sorry I mean drying....

And solar PV isn't 12v it's 500v DC peak

Mine is 700v DC peak IIRC, it depends how many panels you connect in series.

Even if you don't plumb in the dehumidifier it's not much of a chore to empty it once a day.

Lots of interesting chat in this thread. I too am looking at options for leccy only. A good friend is in the middle of getting PV+battery with enough storage to run the heat pump he is also trying to get (stock in high demand). We are having the house extended in 18 months and the boiler would have to be moved. I'd rather replace it with something more future proof as it would mean we don't have to worry about accommodating it in the design either.

Ah...right, to be honest I was kind of going by the single panel my mate has on the roof of his boat so wrongly assumed a home or commercial PV array was 12V stepped up to mains voltage. Ok so any form of charging/storage will require a level of marshalling equipment then which may ultimately mean that running low voltage systems is not beneficial? Still...high load appliances aside a PV array might be ok to power (via marshalling equipment and some storage) general small power and lighting to a small dwelling for a few hours each night plus direct usage of say a pc, monitor and lamp through the day??

Even if you don’t plumb in the dehumidifier it’s not much of a chore to empty it once a day.

It's enough of a chore if you have a full time jobs and a child they are also noisy when working while the heater sits there doing it's thing silently day in day out with zero issues it's also portable.

(Having lived in a rental flat that needed two running all the time I won't be going back to that regardless of efficiencies)

A PIV on the other hand.

Ive just had solar installed with a battery. 10 panels on the roof 4kwh, 3.3 kwh battery. So far it seems great when the sun shines. Not looking in going totally electric yet, but hoping to in the future. The system came with the iboost but i haven't got an immersion so couldnt be fitted.
I also have a catalogue from a company called Fischer Future Heat, they have some interesting stuff like electric boilers and radiators etc. Not sure on prices though. Phone number: 01162425533 or 08001032705, email: info@fischerfuture.co.uk

Anything that goes against your idea that oil-fired central heating is the perfect solution for you gets you coming out with some remarkably tenuous justifications, Trail_rat.

Six seconds to empty the dehumidifier in the bathroom if not plumbed in, I've just timed it. It also takes 6 seconds to plug it in, turn it on and select 60%.

How long do you spend on this forum a week?

some remarkably tenuous justifications

And the noise ?

And for the record. As you state.... The perfect solution for ME. I'll decide what the perfect solution for me is. There are some on here who's advice I'll heed.

As I said I've lived with your solution in the past. Its an informed decision. It was used to patch up a house with inadequate ventilation.

Well the perfect solution for you isn't the perfect solution for some others or the objective of reducing carbon emmission and the Op asked sensible questions so I provide sensible suggestions. Suggestions that are science based, make for comforatbale living and may help people to reduce their carbon footprint.

I know you're into oil fired central heating and diesel cars, Trail_rat, you've contributed to enough threads extolling their virtues. But some peple are trying to get away for that and starting future looking threads such as this one. I know that if one of your posts follows one of mine it'll be to slag off my post. You've been doing it for years.

I hope that so much negativitiy about a device as simple, effective and usefula as a dehumidifier provides entertainment for other members if nothing else. Anyhow my explanations are there for all to see and they stand up to examination.

I switch mine on in the ventilated bathroom after a shower because it clears the damp air and provides some very efficient heating at the same time. Noise? Not an issue ofr me.

Actually forget it.

Your so predictable.

*Goes back to reading oil fired heating monthly*

Batteries IMO are a red herring. Wait 5 years and they’ll be half the price.

Unlikely unless there is a technological revolution, the manufacturing is pretty efficient I doubt the price of the raw materials will fall much due to the nature of the work involved in extraction.

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 via an inverter and incur the losses that must arise from this?
Lighting and certain appliances can easily run off 12V DC so I’ve often wondered why we don’t replace wiring systems for DC installations to utilise PV rather than rectifying it to 230v?

I found myself wondering something similar the other day, but mulling whether or not you could combine sources i.e. solar PV and a small (vertical axis?) wind turbine, if you only wanted to run some LED lighting and a lower powered PC/laptop during daylight hours it might be a practical idea for a low cost/carbon footprint WFH setup? Dunno...

TBH trying to address household heating requirements with home generated leccy sources feels like a bigger, harder task than I would feel able to tackle today...

@trail_rat @donks a battery can run at 12V though and doesn't need to be huge just to run a lighting circuit. A leisure battery size would probably cover it.

Might actually be a cheap way to harvest and use winter power if heating is already covered.

I've got 9 PV panels and 1 solar thermal panel. On a south facing roof in what seems to be an unusually sunny location.

Its a system the previous owner installed a few years back, so I'd have to go into manuals to find the ratings etc...

I'd echo comments about winter generation being about 25% of that in summer.

Solar thermal is great from March to Sept on a sunny day....not so fab when cloudy. If a sunny winter's day, you can get a tank of hot water out of it. It recently cost me £200 to get a service-I'd been quoted more-which you need to factor in.

All-in tho' my PV pays for all my Elec, Oil and Wood costs throughout the year (I'm on the old FiT).

If anyone thinks that mains gas is expensive, try not been on mains gas...

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.

https://peter-wurmsdobler.medium.com/improving-the-thermal-performance-of-uk-1930s-semi-detached-houses-6f64c6514565

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.

@twrch

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. 😜