Going fully solar/electric

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. 😜