On-grid domestic battery storage
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Hi
I like the idea, but doubt the economics of such a setup would really stack up ... it's far too close to the refrigerant based thermal panel heating systems pushed on these boards around 5 years ago to not be able to form an initial opinion on ... open to discussion if anyone's made a major technical advancement which conforms to various laws of physics and is relatively cheap, efficient & maintenance free compared to PV panels in unusual places/positions, but ....
HTH
Z
Doh! Yes, I just re-invented thermodynamic panels didn't I, damn. Oh well, the thought was there.Mart. Cardiff. 5.58 kWp PV systems (3.58 ESE & 2.0 WNW). Two A2A units for cleaner heating.
For general PV advice please see the PV FAQ thread on the Green & Ethical Board.0 -
The price includes fitting & vat (although the electrician was already on site to fit a new inverter to the pv).Hi
Is that 12kWh useable or gross and did it include installation, energy management ancillary equipment & VAT? ... anyway, for a complex issue I'll attempt to simplify the tipping point position without referencing performance models ....
I'd tend to look at the manufacturers net maximum capacity as they often lock out a proportion to help with lifespan, efficiencies etc .... for example, of a Powerwall2's 14kWh of batteries, only 13.5kWh is really accessible ... from what I've seen there's no particular standard that manufacturers follow to allow consumers to compare offerings ....
If your price is fully installed it looks like around 2.5x higher than the likely tipping point, which is probably somewhere around £150/kWh, which shouldn't be too hard to reach with battery packs currently trading at an average price below this already, (Average 2018 was supposedly around $175/kWh & expected to fall to below $95 within 5years) with some considerably cheaper, notably this is at volumes which are considerably lower than a major purchaser would be taking ... Tesla for example are already producing their own batteries at, or below, $100/kWh, which is probably somewhere around double the theoretical minimum cost for current cell capacities & technologies.
So, £150/kWh would place a Powerwall2 at somewhere around £2100 (~$2750) of which the current cell cost makes up around 50% ($1400) but is falling fast.
A user with PV resulting in (say) 1500kWh of remaining electricity imports would have a saving ceiling of around £225/year (1500*.15) if all of the energy could be delivered from battery stored PV generation. This in itself would equate to around a 10 year payback on a PW2 even at £2100, but with a typical array of 4kWp there would still need to be considerable imports, so we're starting to rely on equipment & storage lifespans considerably longer than typical design & test specifications would consider .... anything over £150/kWh just makes the calculation results & timespans worse!
HTH
Z
Last year's export was 2911 kWh so there's plenty of scope for savings.
Round trip losses are running at around 8% + 5.9% loss to the grid. I'll have an accurate figure for the round trip losses when I get round to fitting a bi-directional meter to the inverter.
Consumption appears to have dropped quite significantly as we now avoid wasting electricity that would have been exported. Initial indications are that this could be more than the round trip losses.
Both of the inverters came with Wifi dataloggers so there was no need for any additional ancillary energy management equipment. The additional meter that I'm fitting is totally unnecessary but I do like accurate figures for my spreadsheet.
12 kWh is the battery capacity. The maximum battery DOD is 90% but the minimum setting on the ME3000SP is 85% ~ 10.2 kWh usable.4kWp (black/black) - Sofar Inverter - SSE(141°) - 30° pitch - North LincsInstalled June 2013 - PVGIS = 3400Sofar ME3000SP Inverter & 5 x Pylontech US2000B Plus & 3 x US2000C Batteries - 19.2kWh0 -
HiThe price includes fitting & vat (although the electrician was already on site to fit a new inverter to the pv).
Last year's export was 2911 kWh so there's plenty of scope for savings.
Round trip losses are running at around 8% + 5.9% loss to the grid. I'll have an accurate figure for the round trip losses when I get round to fitting a bi-directional meter to the inverter.
Consumption appears to have dropped quite significantly as we now avoid wasting electricity that would have been exported. Initial indications are that this could be more than the round trip losses.
Both of the inverters came with Wifi dataloggers so there was no need for any additional ancillary energy management equipment. The additional meter that I'm fitting is totally unnecessary but I do like accurate figures for my spreadsheet.
12 kWh is the battery capacity. The maximum battery DOD is 90% but the minimum setting on the ME3000SP is 85% ~ 10.2 kWh usable.
I understand what you're saying, however ...
The specification for the ME3000SP confirms the maximum efficiencies for charge as 94.5% & discharge as being 94% with a standby use of 5W, importantly this is battery chemistry & capacity independent ... I believe that you are using Pylontech modular batteries as your storage solution.
Why is this classified as being important? ... well, without knowing the battery chemistry, the matched storage capacity and the rate of charge & discharge, the term 'maximum' either means that the efficiency percentages either represent the inverter & transformer direct efficiency losses, or these losses plus the minimum battery internal resistance inefficiencies for the lowest possible storage configuration of the best battery technology option being charged at the minimum rate possible to ensure that internal cell resistance is minimised.
Take for example the effect of charge rate on a single Lithium-Ion (2850mAh/3.7V) cell's resistance based energy loss as heat ...
Each cell effectively stores a nominal ~10Wh(2.85x3.7) of energy, therefore a 12kWh system would be expected to contain 1200 batteries, probably weighing just under 60kg (raw cell), so we'll look at resistance losses at various charge rates ...
Charge at 3.7V cell at ~4V with an internal resistance of ~0.18 ohms ...
300W (0.25W/cell) = 0.3% loss
(0.06A(0.25/4) = ((0.06x0.06)*0.18)/0.25)
3000W (2.5W/cell) = 3% loss
(0.63A(2.5/4) = ((0.63x0.63)*0.18)/2.5)
... so charging the 12kWh battery bank at 300W results in 0.9W.t of heat being created whilst doing so at 3kW produces 90W.t of heat ... 10x the charge rate, 100x more resistance losses through heat .... this is exactly the problem seen when EVs fast charge on considerably higher power supplies ...
... of course, the losses here are simply those within the batteries, in your case the Pylontech units, which you must have 5 (2.4kWh), each having electronics & management systems consuming it's own energy, which the specs don't reference but based on ~2W/unit(?) is likely ~250Wh/day in total, which represents approximately 2% of a full 10.2kWh daily charge, 4% of a 5kW charge, or 10% of a 2kWh charge ....
So, we have a situation where we have stated "Round trip losses are running at around 8% + 5.9% loss to the grid", with inverter specifications, the application of laws of physics and reasonable assumptions for missing data suggesting ...
Charge & Discharge ...100*0.945(Inverter Charge)*0.985(1.5% battery charge resistance)*0.985(battery discharge resistance)*0.94(Inverter Discharge) = 86.2%
Running ... Likely around (((2W*5)+5W)*24) 360Wh/day but representing a variable percentage based on energy diverted to charge averaging an equivalent of ~3.5% based on an annual average of 5kWh of self generation being diverted to charge and daytime energy being non-diverted from household PV ...
So, excluding the variable of equipment baseload around 86% efficiency, but when including it more likely ~82% efficiency ....
Obviously this doesn't stack up with your figures, but it certainly does with published specs from many solution providers & what would be expected from inverters, including the very one you mention (ME3000SP) ... so it's hard to accept the data you're providing ...
Are you sure that the data you're looking at isn't simply derived from the change in battery status after charge & discharge has been applied and is supplied by the BMS ... ie the DC/AC inversion is being missed?
The only other thing that readily comes to mind is that your batteries are DC connected on the solar side of the TGM, therefore you'll not be able to access off peak charging, in which case we're talking at cross-purposes & the gap becomes smaller, but that opens up the question of why the ME3000SP in particular?
Hope this all makes sense!
Z"We are what we repeatedly do, excellence then is not an act, but a habit. " ...... Aristotle
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Hi
I understand what you're saying, however ...
The specification for the ME3000SP confirms the maximum efficiencies for charge as 94.5% & discharge as being 94% with a standby use of 5W, importantly this is battery chemistry & capacity independent ... I believe that you are using Pylontech modular batteries as your storage solution.
Why is this classified as being important? ... well, without knowing the battery chemistry, the matched storage capacity and the rate of charge & discharge, the term 'maximum' either means that the efficiency percentages either represent the inverter & transformer direct efficiency losses, or these losses plus the minimum battery internal resistance inefficiencies for the lowest possible storage configuration of the best battery technology option being charged at the minimum rate possible to ensure that internal cell resistance is minimised.
Take for example the effect of charge rate on a single Lithium-Ion (2850mAh/3.7V) cell's resistance based energy loss as heat ...
Each cell effectively stores a nominal ~10Wh(2.85x3.7) of energy, therefore a 12kWh system would be expected to contain 1200 batteries, probably weighing just under 60kg (raw cell), so we'll look at resistance losses at various charge rates ...
Charge at 3.7V cell at ~4V with an internal resistance of ~0.18 ohms ...
300W (0.25W/cell) = 0.3% loss
(0.06A(0.25/4) = ((0.06x0.06)*0.18)/0.25)
3000W (2.5W/cell) = 3% loss
(0.63A(2.5/4) = ((0.63x0.63)*0.18)/2.5)
... so charging the 12kWh battery bank at 300W results in 0.9W.t of heat being created whilst doing so at 3kW produces 90W.t of heat ... 10x the charge rate, 100x more resistance losses through heat .... this is exactly the problem seen when EVs fast charge on considerably higher power supplies ...
... of course, the losses here are simply those within the batteries, in your case the Pylontech units, which you must have 5 (2.4kWh), each having electronics & management systems consuming it's own energy, which the specs don't reference but based on ~2W/unit(?) is likely ~250Wh/day in total, which represents approximately 2% of a full 10.2kWh daily charge, 4% of a 5kW charge, or 10% of a 2kWh charge ....
So, we have a situation where we have stated "Round trip losses are running at around 8% + 5.9% loss to the grid", with inverter specifications, the application of laws of physics and reasonable assumptions for missing data suggesting ...
Charge & Discharge ...100*0.945(Inverter Charge)*0.985(1.5% battery charge resistance)*0.985(battery discharge resistance)*0.94(Inverter Discharge) = 86.2%
Running ... Likely around (((2W*5)+5W)*24) 360Wh/day but representing a variable percentage based on energy diverted to charge averaging an equivalent of ~3.5% based on an annual average of 5kWh of self generation being diverted to charge and daytime energy being non-diverted from household PV ...
So, excluding the variable of equipment baseload around 86% efficiency, but when including it more likely ~82% efficiency ....
Obviously this doesn't stack up with your figures, but it certainly does with published specs from many solution providers & what would be expected from inverters, including the very one you mention (ME3000SP) ... so it's hard to accept the data you're providing ...
Are you sure that the data you're looking at isn't simply derived from the change in battery status after charge & discharge has been applied and is supplied by the BMS ... ie the DC/AC inversion is being missed?
The only other thing that readily comes to mind is that your batteries are DC connected on the solar side of the TGM, therefore you'll not be able to access off peak charging, in which case we're talking at cross-purposes & the gap becomes smaller, but that opens up the question of why the ME3000SP in particular?
Hope this all makes sense!
Z
The figures are currently coming from the data logger connected to the ME3000SP - Input power/charge power/discharge are the main ones I'm using for the calculation.
As I said previously, I'm fitting a bi-directional meter to the inverter to check those figures & provide accuracy.
FYI, yesterday's round trip loss was an indicated 14% which was high for a single charge/discharge cycle.
Anyway, once I get the meter fitted I'll let you know how close your predictions are.4kWp (black/black) - Sofar Inverter - SSE(141°) - 30° pitch - North LincsInstalled June 2013 - PVGIS = 3400Sofar ME3000SP Inverter & 5 x Pylontech US2000B Plus & 3 x US2000C Batteries - 19.2kWh0 -
HiThe figures are currently coming from the data logger connected to the ME3000SP - Input power/charge power/discharge are the main ones I'm using for the calculation.
As I said previously, I'm fitting a bi-directional meter to the inverter to check those figures & provide accuracy.
FYI, yesterday's round trip loss was an indicated 14% which was high for a single charge/discharge cycle.
Anyway, once I get the meter fitted I'll let you know how close your predictions are.
I hope that the data you're referencing is energy as opposed to power ....
... Anyway, 14% losses would be spot on with the 86% round trip efficiency as calculated from the equipment specs & Li-Ion cell expectations yesterday and not far off what I've used as a default to model battery system performance, however, if the solar generation for yesterday where you are was similar to here, the power levels diverted to the batteries would have created little internal resistance heat within the batteries ... you'll probably not be able to get an idea of the efficiency spread until you've had an almost perfect generation day with a near depleted battery ...
As an aside, I did look at the battery module specs but couldn't find much in the way of self-consumption for the electronics (comms interfaces, BMS etc) so estimated ~2W for each module to add to the 5W for the inverter in a monitoring/standby/comms mode ... looking at the front panels, 2W (15W overall) doesn't seem excessive & may actually be on the low side, so does any of the paperwork that came with the Pylontech units give a clue what their individual or managed stack self-consumption is rated at?
To calculate the overall performance for your system for yesterday, you should really add the system consumption as an energy loss to your 'indicated 14%', especially so as the solar generation & battery diversion was low ... we generated 5.7kWh yesterday of which maybe around 2kWh could have been diverted, which would result in real 'losses' being double those indicated, (ie - if the battery wasn't there, neither would be it's load) ...
HTH
Z"We are what we repeatedly do, excellence then is not an act, but a habit. " ...... Aristotle0 -
Folks heres my 2p (well close to 10 grands worth).
I think a lot of you are getting bogged down in some of the minutiae of losses and economic return without looking at some of the other factors.
I have a 4kw east/west equal split solaredge system here in northern ireland.
Ive had it for almost 2 full years before putting in the me3000sp and initially 4.8kw battery. Maximum output was around 3.25kw so I decided when my garage was built to put 1.2kw in 4 extra panels south facing angled for best output feb-apr and sep-oct.
I added another 4.8kw of pylontech batteries in January.
I had the money for all of the above at times and so opportunity cost was the cost plus the ridiculous annual interest of about 1% or so which in real terms is loss but lets not go there...
Im not taking NI FIT into consideration but it should be roughly 400-500 quid a year so payback on the initial system in 10 years not including electricity costs. 8 years with electricity costs (at time of installation used about 6kWh per day on average - work from home, oil central heating and hot water, 1100l oil fill would do me about 11 or so months).
I went on a small generator seminar last summer and with the all ireland electricity market and brexit it scared the crap out of me so bought the battery system the next day. At 4.8kW it probably wouldnt pay for itself in 15 years so allowing for usual failure costs/upgrades etc it was more an environmental/lifestyle decision. I wired it to act as a UPS for the whole house (manual not automatic switch).
Since the solar installation I had changed the way I do things, cook during the day, slow cooker, bulk meals then freeze, use of 2nd freezer etc, washing machine and dishwasher alternate days at midday timed etc etc etc.
With the 4.8kW battery that changed a bit as say about now to late october it would only run down completely a couple of days. Part of the reason was that it peed me off putting the kettle on at 1kW generated and paying for the extra 200w at 16p a unit when in 30 secs I would be getting 4p a unit for exporting the excess.
I dont have an iboost etc because single household and considered it a waste of energy (and something that wouldnt ever pay back in my situation - Ive an immersion switch with 15 min setting).
The battery helped a lot and got me started on slow cooker overnight, dehydrator, stopping buying solar lights for the garden because all lights are now solar.... (are we learning yet ;-))
I started using the immersion for the shower and occasional hot water (4.8kw battery wasnt enough to stop sometimes importing - 9.6 is) so oil use has stretched by another month as Im not heating a tank of water morning every day now, just on demand.
Ive just bought one of the cheap chinese air source heat pumps and when I get time Im going to install it in the hall in my bungalow and this should from about now through to perhaps november supply heating/cooling. Again if that stretches oil purchase by another 4 months or so payback from that alone will be in 1-3 years depending on price of oil. This wouldnt have been feasible without the battery.
With the battery installed (in my spare room which now never really has heating on as those losses you all talk about go into heating the room), it gives you the opportunity to think a bit wider. I like to work on cars so rather than buying battery powered tools I can just go for the cheaper mains ones as I have a huge big battery in the house....
Back to electric lawn mower rather than petrol one...
Single use kettle, increased insulation and converting almost all the house and exterior lights to LED. Adding another chest freezer to the garage allows me to do a lot more cooking and storing which I wouldnt do otherwise. By the time winter comes round Ive a massive supply of home cooked microwave meals... again just thinking differently..
In my office from about Feb on Ive had a 90W tube heater under my desk for heating.... 9.6kw runs that for a long time, the south facing, clear access panels help.
The original intention was to move a couple of the east/west panels to the south but things progress and again Im not seeing it all as a fixed cost due to maintenance, upgrades etc. My solaredge inverter can cope with 20% extra loading so by my calculations I might just top that out a couple of days this year if we have a summer like last. If we dont and have a summer like the year before Im basically not paying for electricity from feb to nov.
Ive just had my last quarters electric bill in at just over 20 quid. Thats 20 quid total, for the quarter.
I changed suppliers last year with a 75quid sign up bonus. My entire electricity bill for the year was something like 150 quid. Down from around 4 or 5 times that. So add that cost into the fit and all of the above and its borderline 'payback' in around 10-12 years for everything provided no more maintenance, extras etc etc.
I have plans for perhaps another two panels, this time moved from e-w to put on sliding mounts to optimise for dec-jan and return to shoulder month level, but I'll take that from this years data with the system in stasis for 7 months.
I have a campervan with a couple of leisure batteries so will get a 100w solar panel for that along with a pure sine converter. Why? Well I have a charging point for it in the garage which is isolated from the house but if I throw the main switch into the house it might be possible to connect that up and mimic the grid so that even on sunny day with power cuts I can use the solar panels to keep the batteries charged.... Or maybe just use some of the export to keep those charged through the inbuilt mains charging system and kick over when I need... I have to add I have a degree in electrical engineering and masters in electronics so dont try this at home yourself kids...
Whilst I appreciate all the talk about losses, roi etc etc sometimes you just have to take a real world view and then take the end user approach and see the possibilities and opportunity costs of those possibilities as part of the equations.
Oh yeah Ive an inflatable hot tub and an infra red sauna now too... amazing what you can do when your running costs are effectively zero... oh hold on, the system is probably costing me more money than its saving...
So just to recap, rather than talking about 80 or 90% round trip losses and 2w or 5w background usage per piece of kit I'll repeat my electricity bill for the quarter was 20 quid and I'll likely not pay for electricity again until November.
Im down to only looking at my solaredge online monitoring and solarman online battery monitoring maybe 6 times a day now ;-)
Try not to think of the battery or solar in isolation but as part of a system, it can change the way you do things. If I didnt live in Northern Ireland then an electric moped would make a lot of sense now to replace a lot of the short town runs in the car....0 -
HiFolks heres my 2p (well close to 10 grands worth).
I think a lot of you are getting bogged down in some of the minutiae of losses and economic return without looking at some of the other factors.
I have a 4kw east/west equal split solaredge system here in northern ireland.
Ive had it for almost 2 full years before putting in the me3000sp and initially 4.8kw battery. Maximum output was around 3.25kw so I decided when my garage was built to put 1.2kw in 4 extra panels south facing angled for best output feb-apr and sep-oct.
I added another 4.8kw of pylontech batteries in January.
I had the money for all of the above at times and so opportunity cost was the cost plus the ridiculous annual interest of about 1% or so which in real terms is loss but lets not go there...
Im not taking NI FIT into consideration but it should be roughly 400-500 quid a year so payback on the initial system in 10 years not including electricity costs. 8 years with electricity costs (at time of installation used about 6kWh per day on average - work from home, oil central heating and hot water, 1100l oil fill would do me about 11 or so months).
I went on a small generator seminar last summer and with the all ireland electricity market and brexit it scared the crap out of me so bought the battery system the next day. At 4.8kW it probably wouldnt pay for itself in 15 years so allowing for usual failure costs/upgrades etc it was more an environmental/lifestyle decision. I wired it to act as a UPS for the whole house (manual not automatic switch).
Since the solar installation I had changed the way I do things, cook during the day, slow cooker, bulk meals then freeze, use of 2nd freezer etc, washing machine and dishwasher alternate days at midday timed etc etc etc.
With the 4.8kW battery that changed a bit as say about now to late october it would only run down completely a couple of days. Part of the reason was that it peed me off putting the kettle on at 1kW generated and paying for the extra 200w at 16p a unit when in 30 secs I would be getting 4p a unit for exporting the excess.
I dont have an iboost etc because single household and considered it a waste of energy (and something that wouldnt ever pay back in my situation - Ive an immersion switch with 15 min setting).
The battery helped a lot and got me started on slow cooker overnight, dehydrator, stopping buying solar lights for the garden because all lights are now solar.... (are we learning yet ;-))
I started using the immersion for the shower and occasional hot water (4.8kw battery wasnt enough to stop sometimes importing - 9.6 is) so oil use has stretched by another month as Im not heating a tank of water morning every day now, just on demand.
Ive just bought one of the cheap chinese air source heat pumps and when I get time Im going to install it in the hall in my bungalow and this should from about now through to perhaps november supply heating/cooling. Again if that stretches oil purchase by another 4 months or so payback from that alone will be in 1-3 years depending on price of oil. This wouldnt have been feasible without the battery.
With the battery installed (in my spare room which now never really has heating on as those losses you all talk about go into heating the room), it gives you the opportunity to think a bit wider. I like to work on cars so rather than buying battery powered tools I can just go for the cheaper mains ones as I have a huge big battery in the house....
Back to electric lawn mower rather than petrol one...
Single use kettle, increased insulation and converting almost all the house and exterior lights to LED. Adding another chest freezer to the garage allows me to do a lot more cooking and storing which I wouldnt do otherwise. By the time winter comes round Ive a massive supply of home cooked microwave meals... again just thinking differently..
In my office from about Feb on Ive had a 90W tube heater under my desk for heating.... 9.6kw runs that for a long time, the south facing, clear access panels help.
The original intention was to move a couple of the east/west panels to the south but things progress and again Im not seeing it all as a fixed cost due to maintenance, upgrades etc. My solaredge inverter can cope with 20% extra loading so by my calculations I might just top that out a couple of days this year if we have a summer like last. If we dont and have a summer like the year before Im basically not paying for electricity from feb to nov.
Ive just had my last quarters electric bill in at just over 20 quid. Thats 20 quid total, for the quarter.
I changed suppliers last year with a 75quid sign up bonus. My entire electricity bill for the year was something like 150 quid. Down from around 4 or 5 times that. So add that cost into the fit and all of the above and its borderline 'payback' in around 10-12 years for everything provided no more maintenance, extras etc etc.
I have plans for perhaps another two panels, this time moved from e-w to put on sliding mounts to optimise for dec-jan and return to shoulder month level, but I'll take that from this years data with the system in stasis for 7 months.
I have a campervan with a couple of leisure batteries so will get a 100w solar panel for that along with a pure sine converter. Why? Well I have a charging point for it in the garage which is isolated from the house but if I throw the main switch into the house it might be possible to connect that up and mimic the grid so that even on sunny day with power cuts I can use the solar panels to keep the batteries charged.... Or maybe just use some of the export to keep those charged through the inbuilt mains charging system and kick over when I need... I have to add I have a degree in electrical engineering and masters in electronics so dont try this at home yourself kids...
Whilst I appreciate all the talk about losses, roi etc etc sometimes you just have to take a real world view and then take the end user approach and see the possibilities and opportunity costs of those possibilities as part of the equations.
Oh yeah Ive an inflatable hot tub and an infra red sauna now too... amazing what you can do when your running costs are effectively zero... oh hold on, the system is probably costing me more money than its saving...
So just to recap, rather than talking about 80 or 90% round trip losses and 2w or 5w background usage per piece of kit I'll repeat my electricity bill for the quarter was 20 quid and I'll likely not pay for electricity again until November.
Im down to only looking at my solaredge online monitoring and solarman online battery monitoring maybe 6 times a day now ;-)
Try not to think of the battery or solar in isolation but as part of a system, it can change the way you do things. If I didnt live in Northern Ireland then an electric moped would make a lot of sense now to replace a lot of the short town runs in the car....
No problem with anyone deciding to be an early adopter at all ... as long as passing readers are aware of realistic performance expectations it's their decision on how they justify their own purchasing decisions & what they do with their own money ...
However, there has recently been a considerable amount of information on this & other boards as well as elsewhere that tends to employ, shall we say, 'unethical' means in order to improve the economics of installing domestic battery solutions ...
Regarding automated diversion to DHW ... I take it that you are aware that the difference between your manual switching & such a solution could be multiple kW of power load above that of an automated proportional diversion system? ... before batteries it was probably a missed opportunity and with batteries it's not worth looking at now ... but as your justification for extending the battery capacity with additional modules was DHW for showers, you must be aware that proportional diversion would have been a less costly path! ....
On the kettle front ... I do understand what you're saying, but wouldn't the solution that a number of PV owners on this thread use be just as valid as a stop-gap (until battery system prices become more realistic) energy import saving solution when only generating 1kW .... a 1kW kettle!!
On the £20 for the last quarter eletricity bill .... great you're doing very well, at something like 20p/day standing charge for 90 days, leaves around 12kWh of total usage for the whole quarter at the 16p/kWh you mentioned! ... those batteries must be quite good & the sun must have been shining much more in NI than it has been here ... both January & February were terrible months for generation ...
Another issue could do with clarification if you would .... you went on a seminar last summer (2018) and as a result you purchased a battery system to add to a PV system you'd installed 2 years previously, so 2016, yet with your maximum 3.25kW system (4kWp?) you expect to be paid £400-£500?, so the 10 year payback on this would suggest somewhere around £4500 for the initial install, which you've since increased capacity by ~25% to 5.2kWp with 4 additional panels to feed the batteries ....
.... expanding on this, we (like many other PV owners) struggle to generate anywhere near an average of 1kWh/kWp per day in January, and this year we ourselves achieved around half of that, but what you're describing is that if your solar PV system effectively balanced your consumption (within £20-standing charge) then your usage must be that low that <1kWh/kWp covered your daytime usage & battery charging in January, therefore the extended logic would imply that you would have huge amounts of excess generation being exported in March & April .... else there's a large degree of smoke & mirror accounting being employed involving sign-up bonuses etc .... electricity bill of £150 (41p/day) for the whole of last year with some exceptionally good PV generation months, but only £20 (22p/day) in a winter quarter where January's generation was severely impacted by cloud ... unless there's an undisclosed reason such as a long period where the property was unoccupied, the figures simply don't seem to stack up to logical scrutiny ... can you help with reasoning/details behind the quandary the supplied information has created in order to clarify this for myself & other readers ??
HTH
Z"We are what we repeatedly do, excellence then is not an act, but a habit. " ...... Aristotle0 -
I can't comment on January due to an inverter failure, but this was my best February with 117% PVGIS.... those batteries must be quite good & the sun must have been shining much more in NI than it has been here ... both January & February were terrible months for generation ...
Tonight I've had a look at usage for the first 2 months of battery ownership. As I said earlier, batteries change behaviour in the same way that panels do when you first install them.
For example.....
Dishwasher - Eco instead of 65C
ASHP - Eco for maximum COP
Computers - put to sleep when I leave my desk
Tumble drier - replaced with a heat pump model rather than repair
Lights - not left on unnecessarily during the day
Washing machine - Eco program when possible
None of the above affect lifestyle one iota & previously would have used energy that would otherwise have gone to the grid.
These are the figures for import + solar usage for this Feb & March compared to last year.....
Feb -5.9%
March -9.8%
The usage figure includes round trip/standby losses so the actual domestic consumption will have dropped by slightly more. The figures are also skewed negatively by the fact that we had a gas hob last year & an induction one this year.
It's still early days, but if the next couple of months show a similar pattern then this phenomenon is worth consideration when assessing the viability of batteries.4kWp (black/black) - Sofar Inverter - SSE(141°) - 30° pitch - North LincsInstalled June 2013 - PVGIS = 3400Sofar ME3000SP Inverter & 5 x Pylontech US2000B Plus & 3 x US2000C Batteries - 19.2kWh0 -
Folks heres my 2p (well close to 10 grands worth).
I think a lot of you are getting bogged down in some of the minutiae of losses and economic return without looking at some of the other factors.
Thanks for the post, really interesting and informative.
But, just to be clear, you seem to be coming to a similar conclusion as myself regarding the payback period of a suitably sized battery, around 10-20yrs.
Personally, for education, hobby and general interest, I'm fine with that, but I'm reluctant to talk about it positively on here as it's a money saving site and those payback periods are outside of the warranty lengths.
I suspect the kit will last well beyond warranties, if (again) suitably sized and used sensibly, but I'm walking a tricky line when you take the three factors here into account - money saving, green and ethical, and fun/enjoyment.
Please don't think anyone is being negative, just boringly realistic so as not to mislead.
I think your post got the balance just right, and I'm loving all the incoming info from those doing, whilst I'm just talking. :TMart. Cardiff. 5.58 kWp PV systems (3.58 ESE & 2.0 WNW). Two A2A units for cleaner heating.
For general PV advice please see the PV FAQ thread on the Green & Ethical Board.0 -
I think there's a strong argument that it's now possible to get back your investment in batteries & eventually make a profit. The only real question is how long that takes.Martyn1981 wrote: »Thanks for the post, really interesting and informative.
But, just to be clear, you seem to be coming to a similar conclusion as myself regarding the payback period of a suitably sized battery, around 10-20yrs.
Personally, for education, hobby and general interest, I'm fine with that, but I'm reluctant to talk about it positively on here as it's a money saving site and those payback periods are outside of the warranty lengths.
I suspect the kit will last well beyond warranties, if (again) suitably sized and used sensibly, but I'm walking a tricky line when you take the three factors here into account - money saving, green and ethical, and fun/enjoyment.
Please don't think anyone is being negative, just boringly realistic so as not to mislead.
I think your post got the balance just right, and I'm loving all the incoming info from those doing, whilst I'm just talking. :T
As you rightly point out, payback is currently north of 10 years (probably around 14 in my case), but that timescale is constantly being eroded by decreasing battery prices & energy price inflation. While interest rates remain at historic lows, using capital doesn't add too much to the overall cost. I'm still of the opinion that borrowing money to buy batteries is inadvisable.
I Agree that if this was purely a "money saving" forum then advocating batteries would be inappropriate. However, when you add "green & ethical" to that it's probably not. More so when you consider that batteries remove the "use it or lose" mindset that surplus pv generation encourages.4kWp (black/black) - Sofar Inverter - SSE(141°) - 30° pitch - North LincsInstalled June 2013 - PVGIS = 3400Sofar ME3000SP Inverter & 5 x Pylontech US2000B Plus & 3 x US2000C Batteries - 19.2kWh0
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