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My Plan to Achieve Energy Freedom - The Road to Zero Energy Bills
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At some point in the next few years, many of us will have batteries powering our houses. But what about now? And how will we know the point at which they cross the breakeven point? This post is to detail some thinking towards quantifying the costs and returns so we will know that point when it comes. The SEAI now have grants for both SolarPV and a home battery, and so I think this point may be coming relatively soon.
One reason for storage is this:
Solar produces most energy during the day. We consume most of our energy in the morning and evening outside of these peak solar hours. Storage allows us to store the peak daylight energy and use it later in the day and during the night. Furthermore, day and night electricity rates are different, so a battery allows you to charge at night and consume all of your energy at that lower rate.
It struck me that a good way to envision the types of energy amounts that we talk about here (always kWh!) is easily articulated in batteries. They hold an amount of energy:
The Tesla Powerwall 2 got a lot of press when it was announced at a retail price of €8,000 for 13kWh of storage. It currently offers a cost-per-warranted-kWh of $0.21. The 6.4kWh Powerwall costs about €4,000.
The Tesla Powerwall retails for €7,000. Unpacking the Home Battery Value Proposition does a good job of presenting the other advantages of battery storage aside from just economic value:- Energy Security: Electricity Grids black out from time to time. In a worst case scenario, some major problem could bring the grid down for a long time or permanently. Having Solar PV + Storage would give some continuous power even in this worst case scenario.
- Independence: Connecting to the grid means dependence on the grid infrastructure, the utilities selling you power, and the prices which the energy market commands. Price shocks happen from time to time and while connected the grid, this is a risk. PV + Storage negates this risk somewhat.
- Environment: Using the grid in an environmentally friendly way - low energy prices correlate to low emissions intensity, so you're reducing both your emissions and energy costs
How much battery storage do I need?
The easiest way to figure this out is to get a consumption meter (see previous post here) or look at your bill. If you get solar, you can estimate how much extra the solar will generate that you can store. In winter, you can also charge the battery with cheaper night rate electricity and use that to offset your daytime consumption.
How Much do Batteries Cost?
A 13.8kWh Powerwall system costs about €7,300. A Tesla 6.4kWh Powerwall costs about €4,000. A GivEnergy 8.2kWh battery costs €3,000. Battery costs are continuing to fall over time.
When will batteries cross the breakeven point?
Battery prices have been falling fast, and they continue to do so. The cost of battery storage fell 14% every year on average between 2007 and 2014, according to a report by the Climate Council, and it’s expected that prices will halve again within the next five years.
The falls go hand in hand with a reduction of cost of installing Solar PV:
Where the rubber meets the road
So we know they’re falling fast in price, and that they may well make sense at some point soon, but when? The battery makes money for us in two ways:- When we charge the battery with excess solar generation during the day, and use that to offset grid consumption in the morning, evening or at night
- When we charge the battery with cheap night rate electricity and use that to offset daytime consumption at the more expensive rate
So to understand the $ / kWh at which a battery breaks through to become a cost-positive asset, we just need to fill in the table with the number of kWhs of each type of arbitrage. I’m working on this at the minute for myself, and plan on installing a battery soon. But I wanted to publish a first post lookin showing everyone how to go about thinking whether a battery makes sense for you. I expect it if doesn’t now, it will at some point soon as prices continue to fall.
One other thing: once renewable energy is installed, it’s “fuel” (wind or solar energy) is free. That manifests itself in renewable energy lowering energy market prices when it’s generating. So there is a happy correlation between low energy prices and low Carbon emissions of electricity. It means that when you are charging a battery with low cost electricity, the odds are, you are also charging it with low emissions electricity too. So batteries tend to result in both a Carbon and Financial arbitrage at the same time.
This post was a lot of the research I've been doing over the last few months now that the SEAI have refreshed their grants for batteries and Solar PV (€2100 for 3kWp solar panels plus €600 for the battery system), heat pumps (€3,500), and insulation (€4,500), and also introduced a bonus grant for doing several of them at the same time. Spoiler alert: There will be a big post soon on this.. as we are currently doing some work!0 -
At some point in the next few years, many of us will have batteries powering our houses.
Good post and its worthy of more discussion and calculation.
Having done similar research myself I came to the conclusion that the battery was not worth it and I'm not sure it will in the medium term either.
A Feed in Tariff for your Solar PV excess is, imo, a much much more likely scenario for people in the near future than using a dedicated battery to power the house. You need to add that to your calculations and those figures are not yet available, but expected in the next year or so.
In addition to that we should/will also in time be able to use the EV battery to power the house. That tech already exists and being used, just not yet as a commercial consumer product.... but buying a dedicated battery wont make financial sense for a while yet (if ever), imo.
I'll happily have you prove me wrong!
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At some point in the next few years, many of us will have batteries powering our houses. But what about now? And how will we know the point at which they cross the breakeven point? This post is to detail some thinking towards quantifying the costs and returns so we will know that point when it comes. The SEAI now have grants for both SolarPV and a home battery, and so I think this point may be coming relatively soon.
One reason for storage is this:
Solar produces most energy during the day. We consume most of our energy in the morning and evening outside of these peak solar hours. Storage allows us to store the peak daylight energy and use it later in the day and during the night. Furthermore, day and night electricity rates are different, so a battery allows you to charge at night and consume all of your energy at that lower rate.
It struck me that a good way to envision the types of energy amounts that we talk about here (always kWh!) is easily articulated in batteries. They hold an amount of energy:
The Tesla Powerwall 2 got a lot of press when it was announced at a retail price of €8,000 for 13kWh of storage. It currently offers a cost-per-warranted-kWh of $0.21. The 6.4kWh Powerwall costs about €4,000.
The Tesla Powerwall retails for €7,000. Unpacking the Home Battery Value Proposition does a good job of presenting the other advantages of battery storage aside from just economic value:- Energy Security: Electricity Grids black out from time to time. In a worst case scenario, some major problem could bring the grid down for a long time or permanently. Having Solar PV + Storage would give some continuous power even in this worst case scenario.
- Independence: Connecting to the grid means dependence on the grid infrastructure, the utilities selling you power, and the prices which the energy market commands. Price shocks happen from time to time and while connected the grid, this is a risk. PV + Storage negates this risk somewhat.
- Environment: Using the grid in an environmentally friendly way - low energy prices correlate to low emissions intensity, so you're reducing both your emissions and energy costs
How much battery storage do I need?
The easiest way to figure this out is to get a consumption meter (see previous post here) or look at your bill. If you get solar, you can estimate how much extra the solar will generate that you can store. In winter, you can also charge the battery with cheaper night rate electricity and use that to offset your daytime consumption.
How Much do Batteries Cost?
A 13.8kWh Powerwall system costs about €7,300. A Tesla 6.4kWh Powerwall costs about €4,000. A GivEnergy 8.2kWh battery costs €3,000. Battery costs are continuing to fall over time.
When will batteries cross the breakeven point?
Battery prices have been falling fast, and they continue to do so. The cost of battery storage fell 14% every year on average between 2007 and 2014, according to a report by the Climate Council, and it’s expected that prices will halve again within the next five years.
The falls go hand in hand with a reduction of cost of installing Solar PV:
Where the rubber meets the road
So we know they’re falling fast in price, and that they may well make sense at some point soon, but when? The battery makes money for us in two ways:- When we charge the battery with excess solar generation during the day, and use that to offset grid consumption in the morning, evening or at night
- When we charge the battery with cheap night rate electricity and use that to offset daytime consumption at the more expensive rate
So to understand the $ / kWh at which a battery breaks through to become a cost-positive asset, we just need to fill in the table with the number of kWhs of each type of arbitrage. I’m working on this at the minute for myself, and plan on installing a battery soon. But I wanted to publish a first post lookin showing everyone how to go about thinking whether a battery makes sense for you. I expect it if doesn’t now, it will at some point soon as prices continue to fall.
One other thing: once renewable energy is installed, it’s “fuel” (wind or solar energy) is free. That manifests itself in renewable energy lowering energy market prices when it’s generating. So there is a happy correlation between low energy prices and low Carbon emissions of electricity. It means that when you are charging a battery with low cost electricity, the odds are, you are also charging it with low emissions electricity too. So batteries tend to result in both a Carbon and Financial arbitrage at the same time.
This post was a lot of the research I've been doing over the last few months now that the SEAI have refreshed their grants for batteries and Solar PV (€2100 for 3kWp solar panels plus €600 for the battery system), heat pumps (€3,500), and insulation (€4,500), and also introduced a bonus grant for doing several of them at the same time. Spoiler alert: There will be a big post soon on this.. as we are currently doing some work!
Great post-
I was hoping to achieve what your looking for but even with an A rated house I couldn’t get near moving away from the grid.
The main barrier to that is my east/west orientation. From mid October to mid March my solar is pretty much useless, as are the 5kwh’s of battery storage that I have.
I was undoubtably sold a duck as the financial saving per year is working out at €400, the work was done for environmental reasons also- but costs have to be financially viable.
I’m waiting for some further data to come back and when I get a chance I’ll outline fixed totals, however at present I’m looking at an 18 year payback.
The sales lad was all talk of 70% savings on an electricity bill and they are still marketing this but it’s simply not true.
I never should have put out the extra for the battery as it’s not used in winter and not needed in summer.0 -
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The initial model for CRU is that the existing day time rate will continue as will the night rate BUT between 17.00 to 19.00 we will have Peak pricing looking at what has happened around the world this would be 3 to 4 times the day rate so 70ish cents a unit....We will all go back to eating our dinner in the middle of the day….This is the initial position and clearly laid out on the CRU website as stated though we may well get to Time of Use billing at some stage.Albeit I think there would be a lot of eeeem " Public Disquiet " seen as we are all gone left like
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Thanks for all of your replies. Apologies for the delay in getting back to reply.As above, re: financial payback of batteries, divide the cost of the battery by the saving per kWh of electricity to get the number of cycles before the battery will pay for itself. You'll nearly always get a very long period.
E.g. 13.8 kWh powerwall costs €7,400 (is this excluding installation?). Divided by your (best case) saving of 17c = 43,500 units. Tesla claim 100% depth of discharge so you would need to fully cycle the battery 3,152 times for it to break even.
Would you cycle a battery that size once a day - I wouldn't think so and even if you did it would take 8.5 years to reach break even point, by when your battery is probably knackered in any case. As I said before, If you don't fully cycle the battery every day, it takes longer. If the usable capacity of the battery is smaller, it takes longer. If the battery degrades, it takes longer. If you have to top-up the battery using night-rate or daytime electricity, it takes longer. If FIT is introduced, it takes way longer.
Great reply, thanks. It's always useful to work the upper and lower bounds. I'd see an 8.5 year payback best case scenario as not unreasonble for a technology still on the exponential-cost-reducing-curve. That means 4.25 years payback in 18-24 months at the current pace of cost reductions, at least on a product perspective. As you say, installation also costs money and the cost of that is not falling anywhere near as fast, if at all so that will have an impact. It simply comes down to incentives - if batteries give Irish people the ability to reduce their costs, their environmental impact and their contribution to a stable electicity grid, then they should be incentivised to the point that they make pure financial sense to everyone. In terms of working out the payback time, I know that most people use this as their main metric for investment, though I prefer normalizing it to a yearly ROI based on it's warrenty period, and then just invest in the thing that has the highest ROI % per year. That way you can compare it to your mortgage and other alternative investments. The return of €7,400 you estimate over 8.5 years would give an ROI of €7,400 / 8.5 = €870.58 per year, and so €1,305.88 of "profit" over the remaining 1.5 year warrenty period (Powerwalls look to have a 10 year warrenty period (https://www.tesla.com/sites/default/files/pdfs/powerwall/Powerwall_Warranty_USA_2-0.pdf). €1305.88 / 10 = €130.588 per year on a €7,400 investment is a 1.74% yearly ROI best case. Not good enough to justify when you're paying 3.5% on your mortgage, but it's a good baseline to have as prices fall.I'd wonder about that too. Environmentally its surely better to give it to the grid rather than a battery which has had all the associated mining, transport and the need to recycle at the end of its life?
The environmental (e.g. Carbon reduction) benefit of SolarPV is that it reduces the need for fuel in some power plant when the solar is generating and hence lowering demand. Because the power plants powering the grid change all the time (in Ireland, mostly as a function of how much wind is generating), so too does the CO2 reduction. This is encapsulated in the real-time marginal CO2 intensity figure for the grid at any time. You can see this for Ireland in real-time on the Eirgrid Dashboard (http://smartgriddashboard.eirgrid.com/).
It ranges from 500 gCO2 emitted per kWh down to around 150 gCO2 / kWh over this monthly period. This was quite a clean time on the Irish grid - you can see the electricity sources for the last 30 days, and wind powered 53.1% of all electricity consumed in Ireland for the past 30 days:
So this is all just to say that it *when* you feed your power into the grid matters. If your solar generation coincides with the highest marginal CO2 intensity, then feeding it straight into the grid is better (from a CO2 perspective). However, if it doesn't, then it may prevent more CO2 emissions stored in a battery until a grid demand peak coindices with low wind and solar. If you only care about CO2 reduction, then it may also make sense to charge the battery at times of low emissions (usually times of high wind) and feed it back into the grid at times of low wind (and high emissions). Looking at the chart above, if you charged the 13kWh Tesla Powerwall at 150gCO2 / kWh (emitting 13 kWh * 150 gCO2 / kWh = 1.950 kg CO2 ) and then discharged it when the grid was emitting 500 gCO2 / kWh (preventing the release of 13 kWh * 500 = 6.5kg CO2), you would have a net negitive emissions impact of 6.5kg - 1.95kg = 4.55kg CO2. The average Irish person emits about 13,000kg CO2 per year for perspective. So if you managed to do this every day, you'd reduce your net impact by 4.55kg * 365 = 1,660kg CO2 a year. Lots of simplifications here, but just to give an idea of how time of use really matters with energy consumption and storage to optimize your emissions.My battery was end of commercial life (multinational data centre UPS), I got it for free. Methinks it's more environmentally friendly that I use it for another 5-10 years first before it will eventually be recycled, rather than it be recycled today. Reduce, re-use, recycle.
I agree - battery recycling processes are still emerging as the industry is still quite young. One would think that battery recycling will have improved a lot in 5-10 years' time. I've seen a few companies starting to tackle Lithium Ion battery recycling, such as this one. Lithium as a raw material will likely remain quite valuable, so you would expect a big recycling industry emerge to capture that resale value. Though as an aside, I hope that simpler energy storage technologies take off which don't need rare earth materials. This one for example, using simple gravatational storage at huge scale.The current case for an SEAI scheme installed battery in Ireland with our massive extra subsidy for battery systems is marginal at best. Even taking into account a rise in electricity prices and expecting the battery to last longer than the manufacturer's spec sheet, pay back is in the region of 15 years. At best. Throw in a feed in tariff in the next few years, even a very low one of say 5c/kWh and installing a battery system now will lose you money, not make you any. But of course people can still do it for environmental reasons, as a hobby or if they can implement a battery system for far lower costs than a taxpayer subsidised battery system. I'm in all those 3 categories myself.
This is a good point on the fact that the feed in tariff will effect the economics of home battery systems. It would seem like an unintended consequence however given Ireland's long term goals. Zooming out, a grid feed in tariff that disincentivises batteries doesn't solve the problem that to decarbonize the grid we'll need to: (1) Build lots of renewable energy generation capacity, solar on our roofs and otherwise (2) Build lots of energy storage to store renewables when they are generating for times that they are not. (1) is pretty straight forward. (2) is hard, and we will need to create incentives to build the something like 1,680GWh of storage (rough guess at what we'll need of 5GW * 14 days * 24 hours in a day) we'll need to store wind and solar for period of no renewables. A feed in tariff that disincentives adding distributed storage to our grid would be completely in the wrong direction so either that is changed at some point, or we fail in our decarbonization goals at great detriment to our collective future.
Yes, I would like to see this happen as we will need a lot of flexability in the system if we're to get to 100% decarbonised power. We're also going to see congesion on the Distribution Grid when people switch over to EVs in large numbers, which home batteries can help alleviate. However, some of the replies above make good financial arguements. We'll need better incentives to make batteries financially viable for everyone. Electric Cars will also represent a lot of flexability available to the grid if incentives are properly structured to allow people to get financial incentives to make their cars available to balance the grid, so if that was done properly, perhaps home batteries need not be manditory.Great post Conor. Wondering might future building regulations make the installation of a battery mandatory?Must say I like the idea of filling up a battery on the night time rate for use during the day. But the cynic in me thinks if that became widespread the electricity companies would either abolish the night rate it or at least find a way of increasing it beyond the discounted levels. Much the way the govt. is going to have to come up with new taxes to replace losses on petrol/diesel as people move to EVs.
The energy regulator sets electricity pricing for consumers in Ireland so I wouldn't worry about electricity companies in this regard. Electricity retailers just have the option to provide discounts on the regulated tariffs. As some others have mentioned here, the EU has targets first for SmartMeter roll-outs, and then to real-time pricing so that is coming down the line unless something major changes. Real-time prices should benefit people with batteries as there will be greater arbitrage opportunities. There are also emerging grid services markets where battery owners will be able to provide "flexibility" to the grid as get get up towards 100% renewables. That would essentially pay you to feed power into the grid at times of frequency issues, congestion in your local area due to EV charging, etc. I think that will actually be quite a big financial opportunity depending on how it is rolled out.0 -
The environmental (e.g. Carbon reduction) benefit of SolarPV is that it reduces the need for fuel in some power plant when the solar is generating and hence lowering demand. ....
So this is all just to say that it *when* you feed your power into the grid matters. If your solar generation coincides with the highest marginal CO2 intensity, then feeding it straight into the grid is better (from a CO2 perspective). However, if it doesn't, then it may prevent more CO2 emissions stored in a battery until a grid demand peak coindices with low wind and solar. If you only care about CO2 reduction, then it may also make sense to charge the battery at times of low emissions (usually times of high wind) and feed it back into the grid at times of low wind (and high emissions). Looking at the chart above, if you charged the 13kWh Tesla Powerwall at 150gCO2 / kWh (emitting 13 kWh * 150 gCO2 / kWh = 1.950 kg CO2 ) and then discharged it when the grid was emitting 500 gCO2 / kWh (preventing the release of 13 kWh * 500 = 6.5kg CO2), you would have a net negitive emissions impact of 6.5kg - 1.95kg = 4.55kg CO2. The average Irish person emits about 13,000kg CO2 per year for perspective. So if you managed to do this every day, you'd reduce your net impact by 4.55kg * 365 = 1,660kg CO2 a year. Lots of simplifications here, but just to give an idea of how time of use really matters with energy consumption and storage to optimize your emissions.
I think you've missed a few key points and not really addressed my point at all.
Your representation above is all about feeding into the grid at a time of high emissions to reduce that burden and then taking it back out during low emissions.... sounds great... but the thing is that wind and Solar is relatively easy for Eirgrid to forecast at a national level and they provide those figures in advance already on their website and adjust their generators accordingly in advance.
You get the lower emissions either way. It doesnt matter if it reduces it from 500 to 450 or 200 to 150.... its still a 50g gain. I dont think your representation is accurate and certainly not practical as you can only charge/discharge a local battery as the sun shines and as you need it in the house... you cant really closely align it to any specific gCO2 figure from Eirgrid..... your needs as a human around your house take precedence.
And crucially, you havent mentioned the emissions from creating the battery in the first place which is my primary point. Letting it go to the grid is more environmentally sound, imo.
If you really want to support storage it is the like of Turlough hill and the new one they are creating in Tipperary that we need to support as taxpayers, not causing new Li-ion batteries to be mined from the other side of the world for questionable gain.
Large scale grid level storage is what we need to look at and incentivise, not individual level storage... particularly Li-ion batteries which have a finite life. Turlough hill only had to be built once and is running for decades.This is a good point on the fact that the feed in tariff will effect the economics of home battery systems. It would seem like an unintended consequence however given Ireland's long term goals. Zooming out, a grid feed in tariff that disincentivises batteries doesn't solve the problem that to decarbonize the grid we'll need to: (1) Build lots of renewable energy generation capacity, solar on our roofs and otherwise (2) Build lots of energy storage to store renewables when they are generating for times that they are not. (1) is pretty straight forward. (2) is hard, and we will need to create incentives to build the something like 1,680GWh of storage (rough guess at what we'll need of 5GW * 14 days * 24 hours in a day) we'll need to store wind and solar for period of no renewables. A feed in tariff that disincentives adding distributed storage to our grid would be completely in the wrong direction so either that is changed at some point, or we fail in our decarbonization goals at great detriment to our collective future.
As above, it needs to be large scale grid level, not private individuals UNLESS some new low impact battery tech appears... Li-ion is not it.Yes, I would like to see this happen as we will need a lot of flexability in the system if we're to get to 100% decarbonised power. We're also going to see congesion on the Distribution Grid when people switch over to EVs in large numbers, which home batteries can help alleviate. However, some of the replies above make good financial arguements. We'll need better incentives to make batteries financially viable for everyone. Electric Cars will also represent a lot of flexability available to the grid if incentives are properly structured to allow people to get financial incentives to make their cars available to balance the grid, so if that was done properly, perhaps home batteries need not be manditory.
Again, I'd strongly disagree with your view here from an environmental perspective if its based on current battery tech.
We should not incentivise batteries any further and governemnt policy is also against you in that regard as they have recently reduced the incentive for batteries and increased it for the panels.... which I agree with.
What is needed is Vehicle-to-Home and Vehicle-to-Grid tech being developed and commercialised, not creating new batteries, which to be fair you have said in the latter half of your statement but you seem awful keen to get a battery installed anyway!
V2H and V2G already exist and are catered for in current EV standards/protocols, we need to develop that technology not mine,create, install another Li-ion battery that has a finite life.0 -
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I think you've missed a few key points and not really addressed my point at all.
I'm not trying to dodge your point. I really do want to be kept honest on the maths here, so let me have another try! I take the main point of your reply is that batteries cause more Carbon in their manufacture than they prevent through emissions arbitrage, so let's take a stab at the numbers to see whether this is case. I'll take a stab at the math on the Carbon impact, while acknowledging there are other concerns about batteries on human rights where the metals are mined that are harder to measure.
A 2019 Emissions From Lithium-Ion Battery Production report says carbon emissions from battery manufacture range from a low of 61 kilograms per kilowatt-hour to a high of 106 kilograms per kilowatt-hour. So a 13kWh Powerwall will release between 793kg and 1,378kg CO2. The manufacture CO2 footprint fell from 200kg / kWh in 2017, so presumably the mining and manufacturing footprint is on a downward trajectory. We need to figure out the emissions we can save with a battery to calculate the emissions "payback time" so see below for that.Your representation above is all about feeding into the grid at a time of high emissions to reduce that burden and then taking it back out during low emissions.... sounds great... but the thing is that wind and Solar is relatively easy for Eirgrid to forecast at a national level and they provide those figures in advance already on their website and adjust their generators accordingly in advance. You get the lower emissions either way. It doesnt matter if it reduces it from 500 to 450 or 200 to 150.... its still a 50g gain. I dont think your representation is accurate and certainly not practical as you can only charge/discharge a local battery as the sun shines and as you need it in the house... you cant really closely align it to any specific gCO2 figure from Eirgrid..... your needs as a human around your house take precedence.
I think you would be surprised by how inaccurate forecasts for wind and solar generation currently are. Solar generation is ultra local - a cloud floating across the sky can temporarily decrease a solar farms production. Predicting PV generation with accuracy requires real-time geo-stationary satellite data coupled with ultra local knowledge of the location of PV farms. Wind generation is similarly difficult to predict at a local level as it is so influenced by minute changes in wind speed and direction and local topography. You can build a macro inference between weather and renewable generation and then forecast generation based on weather forecasts alright, but it is not accurate to the granularity it would need to be to remove the need for real-time balancing. Also, you would need to accurately predict demand to a similar granularity. Supply and demand need to be exactly equal or the frequency of the system drops or increases. If these were possible, we would only have a day ahead power market. But in reality, SEM-O who operate the power market in Ireland, implement a day ahead market, as well as a balancing market where some power plants are finely adjusted on a minute by minute basis such that generation exactly meets demand. This fine balancing can and does happen in response to changes you make to either increase or decrease your consumption and that is the reason that a battery does have an emissions impact. It has an emissions arbitrage between the marginal CO2 of the energy you stored in the battery (solar from your roof, which has a marginal CO2 intensity for each additional kWh generated of 0 gCO2) and whatever the marginal power plant is on the grid at that time. If that is a gas plant, that's about 400 gCO2 / kWh. If it's a coal plant such as Moneypoint, it is about 900g CO2 / kWh.
There is a lot of research on this area, so you don't have to take my word for it. ElectricityMap are an NGO who analyse electricity markets in Europe in real-time to make available the 5-minute marginal CO2 intensity in gCO2 / kWh so that companies (or people like us) can optimize the emissions of electricity consumption. "When a consumer is asking for more electricity, that additional electricity will come from the cheapest power plant that still has spare capacity at that time. This power plant is called the marginal power plant. Typically the marginal plant is a system that can react quickly to changes in electricity demand, such as a gas turbine. It however cannot be a wind turbine or solar cells, as you can’t command them to produce more (unless you command the weather that is):
As a consumer, when you decide to charge your electric vehicle at a given time, you are causing the marginal plant to produce more, and therefore, are responsible for the carbon emissions associated to it. Those emissions are called marginal carbon emissions. It is the quantity that should guide our choice as flexible consumers. For example, it is better to charge your electric vehicle when a hydro dam provides the additional electricity, compared to when a gas turbines does (as the latter has much higher emissions). Note that long-term effects exist (e.g. the depletion of a hydro reservoir that would causes coal plants to supply electricity once it’s empty), but we here focus on short-term effects."
You can see where Ireland fits into Europe for our average marginal CO2 intensity, about 510gCO2/kWh :
So now we have the figure we need to calculate the emissions return of a Tesla Powerwall. Best case, it's manufacture released 793kg. Best case, we cycle it once per day charging it with solar and discharging it at the average marginal emissions intensity of 510gCO2 / kWh. That's 510g per kWh * 13 kWh so 510 * 13 = 6.630kg per day. So it takes 793kg / 6.630kg per day = 119.6 days for the battery to break even best case. Worse case, the manufacture releases 1,378kg CO2 and we can only manage to time our discharging to achieve say, 50% of the possible emissions arbitrage. So we save 6.630 / 2 = 3.315 kgCO2 per day in emissions arbitrage, and so our battery takes 1,378kg / 3.315 kg per day = 415.6863 days, or 415.6863 / 365 = 1.1 years to become Carbon negative.
That's a useful range to have even if it is back of the envelope and best case - a stationary lithium ion battery in your house can become Carbon positive within a year, and is warrantied for 10.V2H and V2G already exist and are catered for in current EV standards/protocols, we need to develop that technology not mine,create, install another Li-ion battery that has a finite life.
Definitely agreed that Vehicle to Grid is better than stationary batteries. Using a battery in an EV that would have manufactured anyway rather building another additional stationary battery is clearly best. But I think this will take longer to bring the amount of storage we'll need to be brought online at the distribution level through V2G to add the flexibility we'll need to get to 100% decarbonised electricity. EV manufactures are currently preventing V2G from materializing by removing warranties if cars are used in this way. I think it's a matter of time, but stationary batteries are available now and their specific purpose is for charge and discharge to and from the grid so they can fill the gap in the meantime.As above, it needs to be large scale grid level, not private individuals UNLESS some new low impact battery tech appears... Li-ion is not it. V2H and V2G already exist and are catered for in current EV standards/protocols, we need to develop that technology not mine, create, install another Li-ion battery that has a finite life.
Yes, I agree that large scale storage, particularly pumped hydro is the best option for macro level storage of renewables to tide us over for a few weeks of low renewable generation. The solution(s) also have to address local distribution system congestion however - when everyone's charging their electric cars, and your local substation is maxed out, it doesn't matter if we have spare pumped hydro capacity in Tipparary at that moment, you can't get any more power through the substation. The extra power needs to come from *below* the substation. That is where local batteries can help deliver stored renewable power in a way that is cost effective - they remove the need to double the size of all of our substations in response to the inevitable roll-out of electric vehicles at a large cost to tax / electricity bill payers. That is why I think that incentivising home batteries is a good long term approach for us environmentally and financially. One part of the many solutions we'll need.0 -
Just to add to the arguments
I agree grid storage would be very useful but another reason for me to have my battery storage is backups for power cuts, out in the countryside myself, prone to a few through the year. (More storms = more power cuts)
Also on that, with the removal of fireplaces and the switch to A2W as your sole heating source for new builds I really think PV plus battery back up would be needed in the event of an extended powercut.0 -
Just to add to the arguments I agree grid storage would be very useful but another reason for me to have my battery storage is backups for power cuts, out in the countryside myself, prone to a few through the year. (More storms = more power cuts)
Also on that, with the removal of fireplaces and the switch to A2W as your sole heating source for new builds I really think PV plus battery back up would be needed in the event of an extended powercut.
isn't there some issue with using the batteries when the grid is down - thought it had been mentioned earlier in the thread.0 -
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