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This is not wholly related to EVs but extends the concept of off grid charging. It is really aimed at people with more scientific knowledge than I have.

Say a house in the UK countryside had enough land and outbuildings to allow for a serious wind turbine and solar panel array; enough to power a large house, at least in theory. The big problem is evening out supply and demand. That problem is increasingly being addressed by powerful battery systems. So, if you had a big enough battery bank, could you run a whole house, including say two EVs, with that setup? I assume the house would be heated, powered, and lit, electrically.

The biggest problem I can imagine is that it would not be practical to have batteries large enough to store summer energy for use in winter (even if they could hold a charge that long). So you would then have to have the turbine/solar panel array/battery pack big enough to cope with winter demand. Is that do-able or would the cost of installation be so high that no one in their right mind would attempt it? Could it become feasible with new developments currently on the horizon?
 

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Plenty of people do it, it would only be financially justifiable if you were looking at exorbitant costs to connect to the grid.
A CHP generator would compliment a large PV install nicely as you would typically need heat when the PV is performing poorly.
 

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Covering 90-95% seems to be readily achievable but the last 5% or so becomes uneconomic (batteries to last 3-5 days etc) that most off-gridders seem to have a small generator to cover these eventualities. If you size your renewable s for the last 5% you end up with far too much power for the rest of the time and with no grid connection there is no easy way to get rid of it.
 

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Personal wind turbine don't make sence if you can get a grid connection for a reasonble price, as the output increases so much for a small increase in height/size.
 

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Discussion Starter #5
Covering 90-95% seems to be readily achievable
If that is right, why aren't more people in this position doing it? Having to use a generator or even a grid connection to top up seems fine.

When you have one of those energy audits done as a preliminary to a grant for green tech, it almost always comes up with the recommendation to fit a wind turbine. So much so, that it is almost as if the audit had been designed by a wind turbine company. My understanding is that you have to have a lot of space, open countryside around you, and be prepared for a right mother of a beast towering above you, for wind power to make sense in most cases. But there are people (farmers, large landowners, etc) who do have the right conditions. In that circumstance, you'd think that the only reason not to do it would be if the figures just didn't stack up. Or is it just apathy?
 

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I think part of the problem is that it costs a significant amount to install most renewables, and the payback is measured in years if not decades. Many people don't want to spend many thousands or tens of thousands today for eventual payback in a decade. I've looked at battery storage for our PV, as the car charges at night while the electricity is produced during the day. At current prices we would just make a profit after 10 years, but we don't know if we'll be here that long...
 

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If you could choose your location, land etc. the best source of generation would by hydro-electric and a ground/water based heat pump system for heating a well insulated house. Just need to size the system at a little bit above normal usage on a winters day with a back up battery to smooth out the peaks and troughs, and a generator to use in emergency e.g if the water source freezes.
Regarding a wind turbine and solar PV, if you grid tie the system and have a small battery back up then you could select a size that normally provides you with most of the power (say >80% from it during the year) and the feed in tariff would more than pay for the times when you would need to import from the grid, but again a well insulated/designed and positioned house would not need that much heating even during the depths of winter.
 

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There are huge economies of scale with Wind turbines, so small "individual" turbines are a lot more expensive per kWh than grid-scale MW-class turbines. It is convenient that the average daily output of wind turbines and PV nicely complement each other, so you could go "mostly-off-grid" with a combination of wind and PV if you had a battery system that would smooth things out over roughly a day or so. But it makes far more (financial) sense to use a Grid connection than to invest in big enough batteries and (relatively) small wind turbines for most households.

My house is all electric (air-to-air heat pumps for main heat, immerser for hot water, electric oven and induction hob) with a ~9kW PV system. Before I got an EV, my annual electricity production was roughly equal to my annual consumption - but I produce more power in the summer and consume more in the winter, so still import substantially from the grid over the course of the year. I have Economy 7, so I could use more night-time electricity in the winter if I had a home battery (2 x 14kWh powerwalls should pretty much cover it), and thus save some day-to-day expenditure (and for several months each year we wouldn't really have to import any power from the grid on most days in that case either). But two powerwalls would cost me something like £12k or perhaps even a bit more - so it would take quite a while to "pay for itself" on electricity savings (which might be as much as £200-300 per year...)

Now that I have an EV (and planning to have a second in 2-3 years, we can't always travel together) we will be using an extra ~10kWh per day (on E7, yay!) I might still generate enough power on a good spring/summer day but no hope in the autumn and winter - I'd probably need a 5kW wind turbine (and that would probably require permission from the DNO since I'd in theory be able to dump ~13kW into the local grid on a bright, windy day).

A 5kW wind turbine would cost about £25k
 

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Most people in the UK will not save enough with a powerwalls to cover its cost before it needs replacing.... So would do a lot better using the money to reduce their morgage.

In other parts of the world. a powerwalls can pay for its self in under 5 years if someone has PV. In these locations, PV without a powerwall also pays for its self in under 5 years. Hence powerwalls are selling so well on the other side of earth.
 

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There's no reason to do it unless you have to, because the grid is so fantastically useful at 'buffering' your power (i.e. you can export a ton of solar energy to it in the summer, and then import it back again six months later) and because for most people the cost of getting and retaining a grid connection is very low.

The UK grid is also extremely reliable, so unlike remote parts of e.g. Australia there's very little advantage to independence - indeed an off-grid house is likely to have more power cuts (and certainly to have longer power cuts) than a grid-connected house. If your off-grid inverter fails then you're going to have no power for a few days while you organise a replacement, whereas when our local transformer failed UKPN delivered and installed a replacement diesel generator within 3 hours.

The only time it makes sense in the UK is when the dwelling is so remote that a grid connection is eye-wateringly expensive (and in extreme cases it can be many hundreds of thousands, or even millions, of pounds).
 

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solar output in the UK in winter is also woeful. You'd go months without enough generation to sustain your house especially with a car too.

Check out some of the tracking sites to see just how low peoples PV generation is in winter.

EG:

Cornovii Cloudbase 3.920kW | Monthly

Now ofcourse, you can scale the system up but lets look at an example....

I use on average 8000kwh a year, including charging one EV. If we assume thats monthly average of 666kwh and then look at that generation graph above you can see first of all, the peak output in any month is only 481kwh. If we double the size of the array, we now have a peak of 962kwh and for 5 months over summer, we now manage to meet that 666kwh target figure. but the other 7 months have nowhere near enough power to sustain 666kwh.

So you go EVEN bigger, and fit a 12kwp system, three times larger than the above... Theres STILL four months of the year were the generation is not even anywhere near close to covering 666kwh.

And there are further issues. Day to day variation isnt accounted at all. So now as well as your monster 12kwp system, you also need a battery thats big enough to store maybe a weeks worth of power, say 160kwh?. Furthermore, without any grid export, your 12kwp system is going to be massively over producing in summer and you cant do anything with the power. Theres no way to store it for months down the line, and even if you had some monster 1000kwh battery, it would spend most of the summer months near 100% charge, and then would be flat by the end of november and would stay that way until march...
 

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Solar PV is just not a good option for the UK or anyone living the UK, due to the "winter issue". The grants would have been spent a lot better building very large wind turbines. as they do give us power when we need it most.
 
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