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Comparing Electricity price plans -- there's not as much in it as you think

VanillaAir_UK

Well-Known Member
Jun 17, 2019
8,714
6,270
Surrey, UK
By shifting your load you are contributing positively to less "bad" electricity being needed during the peak hours. That's all good.
Is it? Most marginal power generation (ie what energy source has to increase when you use a bit of power) is gas, even in peak hours. Plus Powerwall has, last real world results that I have seen, around 20% round trip losses. So unless you are topping up with 0 carbon energy and the grid marginal is 0 carbon, then AC coupled Powerwall etc is far from an environmentally friendly option. Powerwall 1 was better as that was DC coupled so much less losses, so your own solar could top it up far more efficiently. But it still does not get away from fact that storing then using one electron, means that somewhere else, more than one electron (be it 1.1 or 1.2 electrons) is going to have to be created elsewhere to offset that and if that means using an extra 20% from energy generation schemes, then that is quite some impact. You cannot justify something like Powerwall on environmental grounds if you are on grid, even if you generate your own electrons, except for a tiny proportion of the year. The solution is to use less energy in the first place and what you do need to use, try and use it when grid marginal has least carbon impact. Its a very complex balancing act, made even more complex by the reduction of many high carbon energy sources - yay to that.
 

VanillaAir_UK

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Jun 17, 2019
8,714
6,270
Surrey, UK

im85288

Member
Aug 31, 2019
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72
Newcastle
Have you seen the YouTube Fully Charged regarding Powerwall 2 and Tesla Backup Gateway 2?, interesting, but they don’t talk money.

I had my system installed mid November (luckily I had agreed the price etc prior to October so as to benefit from only paying 5% VAT when installed with a PV system as opposed to 20% VAT after October) and as others have mentioned they now only come with the gateway 2. It allows you to decide what percentage of charge in the battery to keep for backup times. I have mine set at 5% and so far have only had one power cut lasting 28 seconds...which I obviously did not notice but was made aware by checking the app.

The price for mine (minus installation costs) was approx £7,300
 

Jason71

Active Member
May 8, 2019
3,190
3,255
Shropshire
The subject of the powerwall is an interesting one. I considered getting one earlier in the year but in the end I opted to add another 4kW of solar to my array. I felt that there is only a small environmental benefit in the powerwall at the moment as all it does it switch energy consumption from one time of day to another. I know that peak rate electricity has a higher carbon content so there is a benefit but its quite hard to quantify.

In the future when we have a smart grid which can adapt to customer demand and supply these types of technology are going to be important in smoothing out supply and demand.

Kudos to those who have done it but i think I am going to wait till the grid gets a bit smarter.

My home chargers app likes to tell me how much carbon has been used in each charge.
If I charge at peak it tells me 250+g/kwh
at Night it's more like 135g/kwh

No idea how its worked out but I guess that means the data is available from the national grid. I didn't realise it made quite such a difference and although I am paying the same at all times of day (still waiting on a smart meter for Octopus Go) it has prompted me to wait until the night time to charge even though there is no benefit to me.
 
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Glan gluaisne

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Sep 11, 2019
2,782
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UK
My home chargers app likes to tell me how much carbon has been used in each charge.
If I charge at peak it tells me 250+g/kwh
at Night it's more like 135g/kwh

No idea how its worked out but I guess that means the data is available from the national grid. I didn't realise it made quite such a difference and although I am paying the same at all times of day (still waiting on a smart meter for Octopus Go) it has prompted me to wait until the night time to charge even though there is no benefit to me.

Here you go, have a look at the live data from the grid: Live Carbon Dioxide (co2) monitoring of the UK electricity National Grid
 
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Fredneck

Member
Nov 8, 2019
478
293
Pennsylvania
The subject of the powerwall is an interesting one. I considered getting one earlier in the year but in the end I opted to add another 4kW of solar to my array. I felt that there is only a small environmental benefit in the powerwall at the moment as all it does it switch energy consumption from one time of day to another. I know that peak rate electricity has a higher carbon content so there is a benefit but its quite hard to quantify.

In the future when we have a smart grid which can adapt to customer demand and supply these types of technology are going to be important in smoothing out supply and demand.

Kudos to those who have done it but i think I am going to wait till the grid gets a bit smarter.

If used properly, the power wall allows renewable energy to be time shifted to maximize the usability. I know this is a UK/Ireland thread, but in some places the focus on PV solar is making a surplus during the middle of the day, then a steep rise in needed power in the evening hours. The power wall would be an ideal solution to mitigating that sort of issue.

The daily power cycle in the UK is not as bad and PV solar is never going to be a huge factor, but a power wall can help shift wind power from off peak to on peak use times. The only question is how to control it. Cycling at the same time each day is not the right answer unless you are a bookkeeper. It needs to be more connected to supply and demand.
 

gangzoom

Active Member
May 22, 2014
1,375
1,231
Uk
Cycling at the same time each day is not the right answer unless you are a bookkeeper. It needs to be more connected to supply and demand.

As with all things in life that's a very easy thing to say but trying to implement in real life horrifically complicated. Just look at Austria now, actually on the face of its an ideal country for solar PV + battery every where and they can be coal free for electricity generation, but the real life facts are in regards to electricity generation is almost the opposite.

Our car is set to charge from 1am, and PW from 1am also, with 'peak' time been from 730am to midnight. You can see using this simple schedule we've pretty much shifted our entire electricity use to off peak period. Yes more fine tuning could make it match wind generation, but the effort that requires is massive compared to the current schedule.

49242760771_f83243f0ea_b.jpg


49242977327_8d9937fa9b_b.jpg


Looking at our meter we have used:
  • 18kWh of 'Peak' electricity last 31 days.
  • 968kWh of 'Off peak' electricity last 31 days.
It wouldn't take many house holds to do the same to really help reduce/remove any concerns people have about adding EV charging to the grid interns of meeting peak demand.
 

Glan gluaisne

Supporting Member
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Sep 11, 2019
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UK
The daily power cycle in the UK is not as bad and PV solar is never going to be a huge factor, but a power wall can help shift wind power from off peak to on peak use times. The only question is how to control it. Cycling at the same time each day is not the right answer unless you are a bookkeeper. It needs to be more connected to supply and demand.

Here in the UK we have a very pronounced day/night demand cycle, that does make using scheduled night charging of home battery storage (or cars) a pretty good initial approach. For example, this is the data for the last month from our national grid (so the whole of the UK):

upload_2019-12-20_8-14-3.png


And this is the data from the last 24 hour period (again for the whole of the UK):

upload_2019-12-20_8-15-37.png


Most of our renewable generation tends to come from wind, and as shown for yesterday's generation, it tends to be fairly even at the scale of 24 to 48 hours or so. We have the advantage of wind generation being distributed around the country a fair bit, and as it's all interconnected it tends to even out, except on windless days across the whole country, and they don't often seem to occur when demand is high.

Our biggest variable, in terms of generation, is our CCGT (gas) generators, that are used as the primary demand response generation provision. Short term fast response tends to be from a combination of pumped hydro, plus some battery storage that's being installed at wind generation locations (at their shore connection points for offshore).
 
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VanillaAir_UK

Well-Known Member
Jun 17, 2019
8,714
6,270
Surrey, UK
There are giant batteries being built into the grid all over the world (the latest announcement in Alaska) to provide load shifting, so I assume yes.
No. Look at the brown CCGT area on the last graph. You flick a switch, and very quickly the CCGT will adjust to handle that change - other mechanisms, offsets, frequency adjustments and predictions are used to handle the instantaneous effect of flicking that switch. It only becomes a 0 carbon effect when that marginal response is handled by 0 carbon sources and CCGT is effectively 0 - effectively as some sources effectively run on tick over as it can take such a long time to come online. Coal/wood very slow, CCGT response is quite quick, hydro even quicker and battery quicker still. But latter 2 are very finite resources so only used for instantaneous response (to keep frequency inline) leaving CCGT as the mainstay of marginal generation. Nuclear basically runs flat out, wind and solar are quite well balanced so actually quite predictable. Interconnects are often contractual - not unusual to see us generating and exporting - when you might think that we would generate less and reduce export. But we are not really there yet when battery and EV charging come truly out of non marginal generation for extended periods of time - average carbon may be lower, but an individual usage instance will eventually come out of CCGT most of the time.
 

rotor2k

Member
Sep 16, 2019
524
293
London
No. Look at the brown CCGT area on the last graph. You flick a switch, and very quickly the CCGT will adjust to handle that change - other mechanisms, offsets, frequency adjustments and predictions are used to handle the instantaneous effect of flicking that switch. It only becomes a 0 carbon effect when that marginal response is handled by 0 carbon sources and CCGT is effectively 0 - effectively as some sources effectively run on tick over as it can take such a long time to come online. Coal/wood very slow, CCGT response is quite quick, hydro even quicker and battery quicker still. But latter 2 are very finite resources so only used for instantaneous response (to keep frequency inline) leaving CCGT as the mainstay of marginal generation. Nuclear basically runs flat out, wind and solar are quite well balanced so actually quite predictable. Interconnects are often contractual - not unusual to see us generating and exporting - when you might think that we would generate less and reduce export. But we are not really there yet when battery and EV charging come truly out of non marginal generation for extended periods of time - average carbon may be lower, but an individual usage instance will eventually come out of CCGT most of the time.
You seem to be saying "it would just be a drop in the ocean so it's not worth doing".
I'm not arguing for PowerWall (I won't be buying one any time soon). But I think it's pretty well understood that we need to even out the load to fully get rid of Coal and Gas. That requires storing either electricity or energy that can directly and quickly generate electricity.
My understanding of those giant batteries is that they pay for themselves in ridiculously short timeframes (for the size of the investment).
 

Glan gluaisne

Supporting Member
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Sep 11, 2019
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UK
There are two distinct issues with the grid and generation/demand management.

The really big one is keeping the grid frequency stable, especially when there are major generation disconnection events (like the ones that occurred in August when the Hornsea wind farm and parts of the Great Barford power station tripped offline). Preventing this from causing the grid to shutdown, due to low frequency load shedding, requires fast reacting generation that can come on line in seconds (what's called Fast Frequency Response generation, FFR). One consequence of the the privatisation of the generation market has been that providing FFR generation capacity is expensive, as it isn't often used, so there's been a tendency to reduce the level of it that's been contracted for. This is being fixed, and there are now battery installations being installed at wind generation sites, to store excess wind generation and be able to provide FFR generation if there is a frequency dip. In the slightly longer term (tens of seconds,rather than seconds) we have pumped hydro, primarily Dinorwig, which can spool up in a bit over a minute. The plan is that very short term FFR can maintain the grid frequency until pumped storage spins up, then CCGT can ramp up over the next 30 minutes or so to take over the generation gap. If it looks like the generation gap may be longer, we can spool up the coal plants, but that takes hours, rather than minutes.

The smaller scale problem is micro generation, and increased local LV grid demand variation. The LV grid is the local distribution network that supplies homes and smaller businesses, either with 415 VAC 3 phase or 230 VAC single phase. The main issue the LV network has is the supply impedance, in effect, and the impact this has on voltage regulation. If there are lots of homes with solar panels generating, then it's pretty easy for the local distribution network to hit the upper voltage limit, 253 VAC, at which point solar inverters will start to shut down, or limit. Likewise, with lots of heavy loads, like car charging, all being turned on at the same time, there's a chance that the local network voltage could dip below the lowest allowable limit, of 216.2 V. This is one reason that the government wants smart chargers to be used, as they can be commanded to reduce charge current, or shut off, if the local network looks as if it might be close to being overloaded.

Home battery storage is a fairly neat way around the local grid stability problem. With enough of it, some of the peak solar generation can be stored, so reducing the chance of the local grid voltage reaching the upper voltage limit, and this stored energy can then be fed back to the local grid when the demand is high, mitigating the risk of the voltage dropping to the lower limit.

In practice I'm not convinced that we can deploy enough home battery storage to make this work, plus the losses are such that home battery storage really works best for local offsetting, within the same home as the battery is installed. There is a case for considering local network battery storage, when the costs of alternative network reinforcement is high, although I've not yet heard of this being done.
 
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rotor2k

Member
Sep 16, 2019
524
293
London
There was a Fully Charged episode last week where they addressed some of the EV myths, and one of them was "if all ICE cars were replaced with BEVs, would the grid cope", and the answer was that nationwide we consume 16% less electricity than we did in 2010 (I think), and adding all those BEVs would add 10% to today's numbers, so "we'd be fine". I have to assume that 16% of the generation capacity got permanently switched off in the intervening years, so *would* we be fine?
 

Glan gluaisne

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Sep 11, 2019
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2,912
UK
There was a Fully Charged episode last week where they addressed some of the EV myths, and one of them was "if all ICE cars were replaced with BEVs, would the grid cope", and the answer was that nationwide we consume 16% less electricity than we did in 2010 (I think), and adding all those BEVs would add 10% to today's numbers, so "we'd be fine". I have to assume that 16% of the generation capacity got permanently switched off in the intervening years, so *would* we be fine?

This plot shows how demand has been dropping steadily over the past ten years or so (taken from the DUKES data, here: https://assets.publishing.service.g...ads/attachment_data/file/820708/Chapter_5.pdf):

upload_2019-12-20_10-44-15.png
 
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VanillaAir_UK

Well-Known Member
Jun 17, 2019
8,714
6,270
Surrey, UK
You seem to be saying "it would just be a drop in the ocean so it's not worth doing".

Not at all. What I am saying is that you cannot justify something like Powerwall based on time shifting, which was your original comment.

rotor2k said:
By shifting your load you are contributing positively to less "bad" electricity being needed during the peak hours. That's all good.

Plenty of little and not so little things we can all be doing to help. But justifying them based on incorrect assumptions is not a great way of doing them.
 

rotor2k

Member
Sep 16, 2019
524
293
London
Not at all. What I am saying is that you cannot justify something like Powerwall based on time shifting, which was your original comment.



Plenty of little and not so little things we can all be doing to help. But justifying them based on incorrect assumptions is not a great way of doing them.
Sorry, I seem to not be understanding. How else do you justify the PowerWall?
My original comment was "I have not seen any economic analysis of the PowerWall and I don't understand how it can be justified".
 

rotor2k

Member
Sep 16, 2019
524
293
London
Is it? Most marginal power generation (ie what energy source has to increase when you use a bit of power) is gas, even in peak hours. Plus Powerwall has, last real world results that I have seen, around 20% round trip losses. So unless you are topping up with 0 carbon energy and the grid marginal is 0 carbon, then AC coupled Powerwall etc is far from an environmentally friendly option. Powerwall 1 was better as that was DC coupled so much less losses, so your own solar could top it up far more efficiently. But it still does not get away from fact that storing then using one electron, means that somewhere else, more than one electron (be it 1.1 or 1.2 electrons) is going to have to be created elsewhere to offset that and if that means using an extra 20% from energy generation schemes, then that is quite some impact. You cannot justify something like Powerwall on environmental grounds if you are on grid, even if you generate your own electrons, except for a tiny proportion of the year. The solution is to use less energy in the first place and what you do need to use, try and use it when grid marginal has least carbon impact. Its a very complex balancing act, made even more complex by the reduction of many high carbon energy sources - yay to that.
Octopus Go cheap rates (as indeed the market rates) are 1/3 of the daytime rates, so even with a 20% loss, it still makes economic sense at some scale to do this (if you can get a cheap enough battery). And as far as using one electron means 1.2 electrons has to be created... that is literally how shifting is going to work. There are losses everywhere; storing cheap low carbon electricity at a 20% loss to use it during peak is a perfectly acceptable trade-off, as long as it makes economic and environmental sense (which it does).
The question I was asking, which I am pretty sure of the answer: does the PowerWall make economic sense, and the answer seems to be a resounding no.
 

Fredneck

Member
Nov 8, 2019
478
293
Pennsylvania
As with all things in life that's a very easy thing to say but trying to implement in real life horrifically complicated. Just look at Austria now, actually on the face of its an ideal country for solar PV + battery every where and they can be coal free for electricity generation, but the real life facts are in regards to electricity generation is almost the opposite.

I'm sorry, but I don't follow your reasoning. You are looking at what is being done now which is far from optimal, but suited to the needs of today. I am talking about what will be needed to make full use of renewable power. Car charging is usually done at night to suit the homeowner but also the utility which in most locations has excess capacity at night.

In some locations, like California in the US, there is a virtual surplus of electricity during the day when residential generation is at a max. Car charging can be done then but scaled back on days when the sun is blocked. The point is the time of car charging is largely flexible and can be adapted to suit the needs of the utility network. The way to do this is to have users provide their goals (such as needing 100 miles of range for today) and let the network work it out.

Some people seem to get worked up and start talking about the "smart grid" as if it was some hugely failed thing!!! The point is we have the technology and can make this work. It doesn't matter if some misguided efforts of something unrelated failed in the past. This is clearly not rocket science.
 

Fredneck

Member
Nov 8, 2019
478
293
Pennsylvania
Here in the UK we have a very pronounced day/night demand cycle, that does make using scheduled night charging of home battery storage (or cars) a pretty good initial approach. For example, this is the data for the last month from our national grid (so the whole of the UK)

I'm very familiar with the UK grid demand curve. Worst case is 50% variation from day to night. You don't seem to have much of a peak in the AM, rather it ramps up in the morning and is level most of the day until it peaks in the late afternoon/early evening.

Here in the US much of the country has two peaks, one in the morning and one in the late afternoon. These tend to be more pronounced than the UK usage. That's what I was referring to.

With the addition of lots of PV solar some parts of the country have a surplus of power at the mid day peak. EVs are a natural to load shift to match the power generating peaks of the various power sources. Some have even suggested EV batteries can be used like a powerwall to use for additional reservoir capacity. I don't think this will ever happen, but certainly the charging can be timed to suit generation.
 

Fredneck

Member
Nov 8, 2019
478
293
Pennsylvania
Sorry, I seem to not be understanding. How else do you justify the PowerWall?
My original comment was "I have not seen any economic analysis of the PowerWall and I don't understand how it can be justified".

The power wall can be used to store PV solar and allow you to use your own power rather than use the utility for storage. Some states are redoing their laws regarding this and making it much less economically viable to install PV solar and use the grid as storage.
 

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