Speak EV - Electric Car Forums banner

21 - 34 of 34 Posts

·
Registered
Joined
·
1,405 Posts
I assume all manufacturers test and know the life of products then issue a warranty for something like 10-25% less of projected life. It would be very generous of them to allow a product life of 50%. more than warranty. I gather their 10 year warranty is for a remaining 70% efficiency but my payback allowance was for 100% efficiency over 20 years. I suppose dead is the wrong word for battery performance but if the battery falls below 50% then payback period doubles so the economic viability is dead.
How did Tesla test product life? The cells are not EV cells. The use-case is not in a car. The product delivers a maximum of 5kW charge and discharge power which is pretty light work for a 13.5kWh battery (my hybrid can generate 80kW from a 6.2kWh battery). I doubt the product life is as short as you predict.

Also, you appear to be saying that most fossil fuelled cars will be dead 40-45 months after they roll out of the factory - that’s 10-25% beyond their warranty period. My washing machine is still running after 20 years - that’s 1000% of the warranty period. Have I missed something?
 

·
Registered
Joined
·
13 Posts
Some more details:
1. One function of the Powerwall is to make the solar PV more effective at reducing grid consumption. It adds 70% to the impact of the panels.
2. Another function is to shift daytime grid consumption to nighttime. This represents 40% of all the electricity drawn from the Powerwall. The impact is lower, because we’re buying the electricity rather than generating it

Add the two together and the battery has an ROI roughly 85% that of the solar PV. Not as good, but not terrible.
I don’t wish to denigrate the idea of energy storage, am minded to do it and merely trying to explore and understand the relative options. Having now read the other forums on this subject I understand that Powerwall represents the leader in current viability but that a new Powerwall (13kwh) costs £7k to install and has a 10 year warranty for 70% efficiency so assuming it saves 1000kwh of solar generated elec exported to grid at annual value of £0.15 per kWh produces annual savings of £150 year so will take over 40 years to payback investment.
My original post was questioning whether an old leaf 24 kWh battery could deliver potentially better value as a power storage unit.
 

·
Registered
Joined
·
1,405 Posts
I don’t wish to denigrate the idea of energy storage, am minded to do it and merely trying to explore and understand the relative options. Having now read the other forums on this subject I understand that Powerwall represents the leader in current viability but that a new Powerwall (13kwh) costs £7k to install and has a 10 year warranty for 70% efficiency so assuming it saves 1000kwh of solar generated elec exported to grid at annual value of £0.15 per kWh produces annual savings of £150 year so will take over 40 years to payback investment.
My original post was questioning whether an old leaf 24 kWh battery could deliver potentially better value as a power storage unit.
You’re going to find it hard to answer that question if you reject the information from an owner about the value of a Powerwall. Your price is not what I paid, your assumptions are incorrect and your guesstimated returns are not what I’m telling you I actually generate. Good luck!
 

·
Registered
Joined
·
13 Posts
You’re going to find it hard to answer that question if you reject the information from an owner about the value of a Powerwall. Your price is not what I paid, your assumptions are incorrect and your guesstimated returns are not what I’m telling you I actually generate. Good luck!
I got the £7k Powerwall installation from this thread https://www.speakev.com/threads/powerwall-2.69913/ but would be interested to know what price you paid. Your table implies that your solar array produces 4039 kWh which is a bit above the 2500kwh per annum of the average 3kwP system. I note however that the 43% of generation your Powerwall apparently saves equates approximately to my guesstimate 40% or potential 1000 kWh annual export to the grid of a 2500 kWh system. The price of £0.15/kWh obviously varies but is reasonably. generous in terms of enhancing payback.
 

·
Registered
Joined
·
1,405 Posts
I got the £7k Powerwall installation from this thread https://www.speakev.com/threads/powerwall-2.69913/ but would be interested to know what price you paid. Your table implies that your solar array produces 4039 kWh which is a bit above the 2500kwh per annum of the average 3kwP system. I note however that the 43% of generation your Powerwall apparently saves equates approximately to my guesstimate 40% or potential 1000 kWh annual export to the grid of a 2500 kWh system. The price of £0.15/kWh obviously varies but is reasonably. generous in terms of enhancing payback.
My advice:
1. If your solar PV system is 3kWp and your objective is to maximise ROI, don’t connect it to a 24kWh battery. Get someone to repurpose the battery into 3-6 modules then sell all but one of them plus what’s left of the car
2. Don’t tell me the product I bought is going to die before it achieves payback and then ask me how much I paid for it
3. Don’t assume that home batteries contain re-used cells unless the supplier tells you that’s the case
4. Don’t assume that a 1000kWh of power stored annually needs a 20kWh battery. The maximum that system will generate in a day is roughly 18kWh and you’ve assumed the house is consuming 60% of the power generated. For maximum ROI, you don’t size a battery to accept peak production
3. Don’t assume that the only thing the battery does is store power from solar. To maximise ROI, you should use the battery to time-shift your demand in the winter. From Nov-Jan, my ROI from the battery is better than my ROI from the solar PV
4. Don’t assume that the battery in a Leaf will outlast its warranty by more than 100% but the battery in a Powerwall will outlast its warranty by less than 25%
5. Don’t roll out your back-of-envelope calculations twice when someone who has direct experience of the product tells you they’re wrong the first time.

My Powerwall is on target to deliver a 12-year ROI assuming electricity prices don’t change (they probably will) and the FiT doesn’t increase with inflation (which it does). Who knows what will happen in the next 10 years, but I’m happy that I’m on track for the 11-year ROI my installer predicted.

It’s going to take a while for old EVs that aren’t V2G compliant to be valuable as static storage. Actually, the number of customers willing to park an old car next to their house probably means it’ll never happen. The hardware for V2G is still quite expensive. That’s changing, but I think it’s still several thousand pounds even if the car is already designed to support V2G. The way our economy works, mass producing something for a specific purpose will usually result in economies of scale that lead to a better ROI than repurposing something in lower volumes. Maybe that will change, but I doubt it will happen quickly.
 

·
Registered
Joined
·
13 Posts
Well I think you know you are misquoting me but I still I hope it goes well for you because change is needed and battery storage is the future. The powerwall installer in the Fully Charged video made the point a couple of years ago that he considered the payback period equated to the battery life but obviously that is not yet known. I raised my post to see if anything had changed - I see that my Energy Supplier ( Tonik) is offering on their website a Powerwall 2 installation for £9,400.
 

·
Registered
Joined
·
1,851 Posts
I don’t wish to denigrate the idea of energy storage, am minded to do it and merely trying to explore and understand the relative options. Having now read the other forums on this subject I understand that Powerwall represents the leader in current viability but that a new Powerwall (13kwh) costs £7k to install and has a 10 year warranty for 70% efficiency so assuming it saves 1000kwh of solar generated elec exported to grid at annual value of £0.15 per kWh produces annual savings of £150 year so will take over 40 years to payback investment.
My original post was questioning whether an old leaf 24 kWh battery could deliver potentially better value as a power storage unit.
I'm not sure I'm following your sums. We can provide a detailed payback calculation for our customers and we're typically looking at 10-15 year paybacks. Generally we would consider the Powerwall to be too large for the average UK home but using it as an example, i.e. assuming it's matched to a large solar array, then with your figures if you cycled it just once per day it could potentially save 13 kWh x £0.15p/kWh x 365 days = £700 per year, so a payback of 10 years. If we assume an average efficiency of 85% over that ten years then it's 11.5 years.

Where does your 40 years come from?
 

·
Registered
Joined
·
13 Posts
I'm not sure I'm following your sums. We can provide a detailed payback calculation for our customers and we're typically looking at 10-15 year paybacks. Generally we would consider the Powerwall to be too large for the average UK home but using it as an example, i.e. assuming it's matched to a large solar array, then with your figures if you cycled it just once per day it could potentially save 13 kWh x £0.15p/kWh x 365 days = £700 per year, so a payback of 10 years. If we assume an average efficiency of 85% over that ten years then it's 11.5 years.

Where does your 40 years come from?
Thanks Trevor my Energy supplier Tonik has this statement on the website “Tesla Powerwall allows you to capture the excess solar energy you generate during the day rather than letting it go to waste.” Tonik’s offer is £9,400 for a Powerwall 2 installation of 13.5 kWh battery storage. I was an early adopter of Solar PV so got the highest FIT over 25 years achieving a payback just under 6 years but only have a 3 kwP system which has averaged 2500 kWh annually. I have two EVs so export less than 50% to the grid which suggests there is potentially 1000 kWh available excess solar energy that could be saved to powerwall which at £0.15 kWh would provide £150 annual savings or £3000 after 20 years ( at 100% efficiency)
I understand however that if I purchase a Powerwall with solar PV I can avoid the 20% Vat rate and have spare SW facing roof area that could accommodate perhaps another 5 kwP solar array. Obviously most of my Solar energy is produced in Spring/Summer and typically we get perhaps a week of sunny weather averaging say 15 kWh/day offset by Winter weeks of less than 3 kwh /day. In summer therefore we have an excess of energy and winter a shortage so one idea I’m considering is introducing an air source heat pump to generate hot water supply with excess energy from powerwall. In the Winter perhaps the powerwall could import energy under Economy 7 rates.
 

·
Registered
Joined
·
1,851 Posts
Thanks Trevor my Energy supplier Tonik has this statement on the website “Tesla Powerwall allows you to capture the excess solar energy you generate during the day rather than letting it go to waste.” Tonik’s offer is £9,400 for a Powerwall 2 installation of 13.5 kWh battery storage. I was an early adopter of Solar PV so got the highest FIT over 25 years achieving a payback just under 6 years but only have a 3 kwP system which has averaged 2500 kWh annually. I have two EVs so export less than 50% to the grid which suggests there is potentially 1000 kWh available excess solar energy that could be saved to powerwall which at £0.15 kWh would provide £150 annual savings or £3000 after 20 years ( at 100% efficiency)
I understand however that if I purchase a Powerwall with solar PV I can avoid the 20% Vat rate and have spare SW facing roof area that could accommodate perhaps another 5 kwP solar array. Obviously most of my Solar energy is produced in Spring/Summer and typically we get perhaps a week of sunny weather averaging say 15 kWh/day offset by Winter weeks of less than 3 kwh /day. In summer therefore we have an excess of energy and winter a shortage so one idea I’m considering is introducing an air source heat pump to generate hot water supply with excess energy from powerwall. In the Winter perhaps the powerwall could import energy under Economy 7 rates.
Fair enough. But it's always going to be hard to get payback on a battery that costs £9.4k. Maybe the sums would be better with a smaller system, say 4.8kWh for £4k or 7.2kWh for £5k which is more typical of what our customers buy.
 

·
Registered
Joined
·
276 Posts
Can you import low cost electricity from the grid to the Powerwall 2 or does have to rely on solar generated? I only ask as it will impact on the calculations
 

·
Registered
Joined
·
13 Posts
Can you import low cost electricity from the grid to the Powerwall 2 or does have to rely on solar generated? I only ask as it will impact on the calculations
There is another thread which implies that you can https://www.speakev.com/threads/powerwall-2.69913/
In my posts I’ve tried to question what the powerwall installation costs and what the payback period is. Seems to me it would have to optimised by savings on Economy 7 useage.
 

·
Registered
Joined
·
1,405 Posts
Can you import low cost electricity from the grid to the Powerwall 2 or does have to rely on solar generated? I only ask as it will impact on the calculations
Yes, you can.

There are three settings:
1. Only charge from solar
2. Only charge from solar and don’t use the battery during off-peak periods
3. Charge from solar and off-peak

There’s a machine learning algorithm controlling the whole thing, so it doesn’t do exactly what you ask it to, but I think the algorithm has been upgraded recently and it’s not too bad. It used to take a couple of days to respond to a change between the three settings, but it seems to do it immediately now.
 

·
Registered
Joined
·
276 Posts
Yes, you can.

There are three settings:
1. Only charge from solar
2. Only charge from solar and don’t use the battery during off-peak periods
3. Charge from solar and off-peak

There’s a machine learning algorithm controlling the whole thing, so it doesn’t do exactly what you ask it to, but I think the algorithm has been upgraded recently and it’s not too bad. It used to take a couple of days to respond to a change between the three settings, but it seems to do it immediately now.
I have only used linked to solar so assume you do this via the customise option? I am waiting to get on the Scottish Power EV tariff and hope to charge my car and top up the battery when solar isn’t generating enough.
 

·
Registered
Joined
·
1,405 Posts
I have only used linked to solar so assume you do this via the customise option? I am waiting to get on the Scottish Power EV tariff and hope to charge my car and top up the battery when solar isn’t generating enough.
Yep. Customise, “Advanced - time-based control”.
 
21 - 34 of 34 Posts
Top