Variable Solar Storage with Batteries

[MikeGrahamT21]

Hi,

 

Aside from waiting for the price to drop a bit, I'm all set on getting a Sofar Solar ME3000SP battery AC inverter and a number of Pylon Tech 2.4Kwh batteries to go with it, in the last year a 4.8kwh package has dropped from about £3k to £2.3k, just wanting it to go sub £2k and then i'll consider it properly.

 

I've monitored our solar output throughout the year, and 5Kwh of storage seems fillable most of the year round. Obviously in spring summer and autumn we generate far in excess of this. We aren't on an Economy 7 tariff, i suppose we could move to one and charge batteries via grid on a night, but would mean us having a smart meter more than likely, which im not that bothered about.

 

Question is, if I say for example, bought 2 addition batteries to take us to 9.6kwh of storage, which would get used for majority of the year, to save the batteries sat being flat for months, could I unplug them when they were full, and leave them sitting fully charged until the higher output came again? The PylonTech stuff is pretty modular so allows this very easily, and aside from reprogramming the inverter, not much else would be needed.

 

Or should i just stick with the 4.8kwh which I can use all year round?

 

By the end of this year (Year 3), we will have earned around £1600 from the solar installation (not taking into account electricity savings, just from the FiT), and I plan to spend that money on the storage, obviously when the 2 meet in the middle (savings and cost). The plan is to do most of the house improvements in terms of energy saving, based on the money we earn from the PV, which seems a good way of doing it, and there should be more than enough to warrant it, especially when you take into account electricity savings.

 

Regards

Mike

[ProDave]

Lets work on 4.8 KWh of storage.  IF you fill and use that every day / night, you will save about 50p worth of electricity compared to importing.  So over a year, you will save about £182.50

 

Assuming you have managed to buy the kit for £2K the saving will therefore take you just short of 11 years to pay for itself.  What do you think the battery capacity will be like in 11 years?  I would say ready for new batteries some time very soon.  So the true cost of your "free" stored energy is not a whole lot less than the retail cost of importing power.

 

To me, it still does not stack up.  I keep on looking at batteries and the cost needs to fall, or true long life batteries like NiFe need to become popular.

 

Concentrate on more self usage in the day and dumping excess to water heating. And keep watching the prices.

 

 

[jack]

As Dave says, for us the numbers don't quite add up yet. From memory, we use around £900 of electricity per year (we have no gas, so that's heating, hot water, cooking - everything). We do have a nasty habit of using the dishwasher and washing machine overnight, so I'm sure we could reduce that, but I need to do some more analysis of what we produce compared to when and how we use it to figure out the price point that would make storage financially viable. 

 

For the moment, and for our family circumstances, I think an electric car is a more useful way of absorbing excess production. I reckon we can save well over £1000 a year in fuel and other costs by replacing our small car with an electric car. This does ignore capital costs - there's no doubt we'll need to pay more to get something we'd want to hang onto for a few years. 

 

I'd love it if someone would cobble together a system that let you use a proportion of your car's storage to provide time-shifted power to the house in the evenings. I know there are long-term smart grid ideas that take this concept further, but as a country we can't even manage a roll-out of basic smart meters, so I'm not holding my breath for smart grid functionality arriving in the next decade.

[MikeGrahamT21]

I totally agree with this, i really do, but there is something about more self sufficiency which can't be put into money terms. For example, having a UPS setup, for us would have key benefits.

 

Our electric rate is 12.8p,  on a 4.8 capacity thats 61.44p saving per day, however, in a day we could charge and use that capacity numerous times, so you can't just use 4.8 a day, and of course it would top up the generation if it wasn't quite enough, so I reckon the saving is actually a lot more than the simple calculation, but of course theres no way you could work that out. And of course, theres energy costs going up, over 10years, which could be a lot, and also might not be a lot, a bit of a gamble, but i'd say 18p a unit isn't unrealistic. Using 12.8p a kwh, gives a potential saving of £224 a year, so if the kit costs £1800 (which is what i'm aiming for), thats a £400 profit over the 10 years, not a lot i agree, but as said above, I think the saving potential is greater. Now if that electric cost went to the aforementioned 18p, that becomes a £1300 profit, even with the bare minimum saving.

 

Agree the batteries would be more or less useless after the 10 year period, but would still have some good potential even if only at 50% capacity, plus in 10years time, they'll have either broken under warranty (best case scenario), and of course new ones will be a hell of a lot cheaper by then, plus the tech will be a lot better.

 

We can't do water heating, as we have a combi boiler and no water tank, so thats out the question. Electric car i've thought about, but they won't do the range i require for work, unless i buy a tesla, which is far too much money. Ive worked hard on self consumption, and working from home really helps that, but even with my best efforts, the bloody wash basket always fills ready for a cloudy day, and of course the battery would cover this, in terms of a top up.

 

It is a lot of ifs buts and maybes but I'm almost sure its a go-er.

 

EDIT: We would be able to consume the 4.8 relatively easily in a non generation time, we do use a lot of electric which is unavoidable.

Edited May 15, 2018 by MikeGrahamT21

[Jeremy Harris]

I agree, and have been watching the prices of battery systems closely over the past year or two.  We export a heck of a lot of energy, more than the 50% assumed export we get paid for, even with me charging my car up during the day. 

 

Like @ProDave, though, I can't make the sums add up yet - the capital cost would exceed the benefit, even without accounting for having all that capital tied up in a depreciating asset.

 

I approached the back up power desire from a different angle, and have a battery pack that runs our router, VDSL modem, switch and a RPi used as a file server, with some spare battery capacity (right now I can run this lot for at least 24 hours without power, perhaps a bit longer).  That gives us internet connectivity with things like tablets and laptops if the power goes off, which is useful.  This wasn't that costly to build, probably under £100 all in, and will probably last around 8 to 10 years I think.

 

I have been thinking about backup power for the house, but can't really justify the cost of a small generator just for the odd occasion when we might need it.

 

At the rate that battery technology seems to be improving, and prices dropping, I have a feeling that battery storage may well be viable within the next couple of years.  With respect to battery life, then I checked the lithium battery pack capacity that's in my car a couple of weeks ago, and can't measure any change from when it was new (it's now a bit over 4 years old).  That seems to indicate that battery life has improved a fair bit, as a few years ago the lithium battery packs I was using in my electric bikes had very noticeably lost capacity after three years.  It wouldn't surprise me to find that 15 years is now closer to the nominal 80% capacity remaining cut off than the 8 to 10 years that has been commonly quoted.  My car gets cycled a lot, too, it gets fully charged and discharged twice a day for five days a week, once a day on Saturday, plus the odd charge/discharge cycle on a Sunday, so it's probably done well over 2,000 full cycles by now, plus tens of thousands of lower capacity change cycles when it's running hybrid mode.

 

 

[ProDave]

Another thing people tend to do with FIT solar PV is optimise the panel orientation for maximum yield.  That is fine if your objective is to maximise payment.

 

But for a non FIT self use scheme, you don't just want a passive peak in the middle of the day that you are unlikely to be able to fully self use.  Instead my plan is some panels facing east, to get a much earlier start to useful generations levels and less facing south so the mid day peak will not be as large.  Also if I can manage some facing west would be good to extend generation into the evening, but that is harder to arrange here.  The total yield would be lower, but my feeling is you would generate more self usable power throughout the day.  One option I am looking at is making my east facing bank on a simple flip over mount so they would in effect be on a very basic tracker and those same panels could do the evening burst as well.

[richi]

Caution: EVs and hybrids never "fully" charge nor discharge their batteries.

 

Back in the 1990s, Toyota discovered that if you restrict the SoC to a swing of about 40% to 60%, the battery essentially lasts for ever (for the life of the car, anyway). This is why you see MY2005 Prius taxis at 300,000+ miles.

 

But that was NiMH chemistries. Lithium chemistries can stretch the point. For example, my Outlander PHEV uses around 25-95% SoC. I guess @JSHarris' plug-in Prius does a similar thing. And I guess his e-bike didn't ?

 

This also means you need to be careful when thinking about the battery capacity: If you want it to last 10 years, the usable capacity will be significantly less than the rated capacity (depending on how the specs are written). To use my PHEV example again: Most of the spec sheets say it has a 12 kWh battery, which is true, but it only uses about 70% of that (roughly 8.5 kWh).

[Jeremy Harris]

Yes, my electric bike BMS does the same as the system in my car, as I designed it to run the cells between 30% and 85% SoC, but the issue with lithium cells was never really cycle life, but the relatively rapid rate of degradation with age, the calendar life.  Lithium cells used to have a pretty poor calendar life, around 4 to 5 years even if you rarely ever cycled them, but this has gradually being improving, and newer chemistries seem to have a much longer calendar life, as do older chemistries with newer manufacturing methods. 

 

I did a stack of measurements a few years ago on some test cells of different types (but all lithium ion exchange cells), holding them at the best life long term storage open circuit voltage and cycling them once every few months to measure the capacity loss, and it was then between 5% and 10% per year, so for most applications calendar life was more critical than cycle life.  The worst cell type in terms of calendar life degradation was the first generation LiFePO₄ cells, they lost capacity more quickly than the older (and potentially more dangerous) LiCoO₂ cells.  The newer LiCoO₂ cells I  bought around a year ago seem to be significantly better in terms of much reduced capacity loss with age, so I'm guessing the manufacturing process has improved.

 

Cycle life is highly non-linear with SoC range for pretty much every cell chemistry, massively so in the case of some lithium cell chemistries, like LiFePO₄, where 10% to 95% may only give 1000 cycles, but restricting operation to 30% to 90% SoC may well give well over 20,000 cycles. 

[jack]

1 hour ago, MikeGrahamT21 said:

Our electric rate is 12.8p,  on a 4.8 capacity thats 61.44p saving per day, however, in a day we could charge and use that capacity numerous times, so you can't just use 4.8 a day, and of course it would top up the generation if it wasn't quite enough,

 

I think these calculations need thinking about. Our winter generation is at times virtually zero for days on end (edited to add: we have an 8.5kW system]. 

 

I'm also less sure that there will be a lot of days where you can recharge several times. Unless I'm missing something, the only way that can happen is for you to charge up, then use some of what's been charged, in time for there to be further charging. However, the chances are that if you'd just consumed the PV-generated energy as you went, you'd get the same benefit. 

 

It's hard to really model how you'd do without a year or two of good generation and consumption data, maybe on an hour to hour basis.

[ragg987]

26 minutes ago, ProDave said:

But for a non FIT self use scheme, you don't just want a passive peak in the middle of the day that you are unlikely to be able to fully self use.

My measurements for a full 12 months show I exported 3% back to the grid. South-facing array 4kWp, positioned to maximise yield. Using a PV diverter to my 300l DHW. For me it makes no sense to have east and west-facing panels to lengthen the generation period. Also, in winter you will take a bigger hit having East / West panels.

[Jeremy Harris]

8 minutes ago, jack said:

 

I think these calculations need thinking about. Our winter generation is at times virtually zero for days on end (edited to add: we have an 8.5kW system]. 

 

I'm also less sure that there will be a lot of days where you can recharge several times. Unless I'm missing something, the only way that can happen is for you to charge up, then use some of what's been charged, in time for there to be further charging. However, the chances are that if you'd just consumed the PV-generated energy as you went, you'd get the same benefit. 

 

It's hard to really model how you'd do without a year or two of good generation and consumption data, maybe on an hour to hour basis.

 

Our 6.25 kWp system behaves much the same; plenty of winter days with virtually no generation at all.

 

I wholeheartedly agree with the difficulty of trying to model how a storage system might perform, too, even with a lot of data on consumption.  The only way I could try and make some sort of reasonable case for battery storage was to ensure there were no large loads on during non-generation periods, and use a battery capacity that would meet the house baseline demand overnight and for part of the following day.  The combination of load limiting (just by not using things like the dishwasher or washing machine during the evenings or overnight) plus a relatively low capacity (and hence cheaper) battery system came closest to breaking even for us, but even then I think we'd have been losing money overall, compared to just using grid energy.

[ragg987]

1 hour ago, MikeGrahamT21 said:

in a day we could charge and use that capacity numerous times

I don't see how that would work. On a sunny day you would charge up your 4.8kWh and that is it done. When the sun goes down you use it until it is depleted.

 

Our 4kWp is capable of generating 25kWh per day, though the mean is 11kWh. The mean is meaningless (!) in the context of ability to charge a battery - I have the daily data someplace of actual daily generation so this might help to model your annual saving, though of course just because you generate 4.8kWh on a given day does not mean your battery will fully charge as you home will consume a background load.

 

Without doing the modelling, I fail to see how this could save you more than around £100-£150 per year (for a 4kWp array and 4.8kWh battery).

[jack]

As an example, here's the daily generation for January this year on my 8.5kW system:

 

 

There were 14 days that generated less than 4.8kWh, and that's ignoring charge/discharge inefficiencies, SoC limitations, and the fact that at least some of what was generated will have been consumed and therefore not available for storage.

 

I just checked, and December was worse, with 19 days that generated less than 4.8kWh.

 

Remember, this is an 8.5kW system. A 4kW system would have generated less than half what's shown above. In fact, a 4kW system at my location (Hampshire/Surrey borders) would only have managed 5 days above 4.8kWh in January, and only 1 (and only barely!) day in December. 

[MikeGrahamT21]

52 minutes ago, richi said:

Caution: EVs and hybrids never "fully" charge nor discharge their batteries.

 

Back in the 1990s, Toyota discovered that if you restrict the SoC to a swing of about 40% to 60%, the battery essentially lasts for ever (for the life of the car, anyway). This is why you see MY2005 Prius taxis at 300,000+ miles.

 

But that was NiMH chemistries. Lithium chemistries can stretch the point. For example, my Outlander PHEV uses around 25-95% SoC. I guess @JSHarris' plug-in Prius does a similar thing. And I guess his e-bike didn't ?

 

This also means you need to be careful when thinking about the battery capacity: If you want it to last 10 years, the usable capacity will be significantly less than the rated capacity (depending on how the specs are written). To use my PHEV example again: Most of the spec sheets say it has a 12 kWh battery, which is true, but it only uses about 70% of that (roughly 8.5 kWh).

 

Specs for the Pylon Tech batteries have just been improved to 90% DoD with a full 10 year warranty, used to be 80%, however their materials have improved I believe.

[MikeGrahamT21]

30 minutes ago, jack said:

 

I think these calculations need thinking about. Our winter generation is at times virtually zero for days on end (edited to add: we have an 8.5kW system]. 

 

I'm also less sure that there will be a lot of days where you can recharge several times. Unless I'm missing something, the only way that can happen is for you to charge up, then use some of what's been charged, in time for there to be further charging. However, the chances are that if you'd just consumed the PV-generated energy as you went, you'd get the same benefit. 

 

It's hard to really model how you'd do without a year or two of good generation and consumption data, maybe on an hour to hour basis.

 

Yeah the winter generation can be pathetic, i monitored it this winter and we averaged about 2kwh a day, so clearly wouldn't be getting full battery use.

 

I think maybe to think about this less as the full charge and discharge cycle, the major benefit for me is the ability to top up existing generation, which rarely is enough. For example on a hot sunny day in summer, we'll generate a reasonably static 2.2-2.6kwh, which barely scrapes running things like oven, washing machine singly. The ability to provide another 3kwh from the battery on top of this 2.2-2.6, gives a lot more scope for flexibility, and of course it costs nothing from the grid.

[MikeGrahamT21]

30 minutes ago, ragg987 said:

My measurements for a full 12 months show I exported 3% back to the grid. South-facing array 4kWp, positioned to maximise yield. Using a PV diverter to my 300l DHW. For me it makes no sense to have east and west-facing panels to lengthen the generation period. Also, in winter you will take a bigger hit having East / West panels.

We are further north than you, but out of curiosity how many kwh did you generate last year?

[MikeGrahamT21]

17 minutes ago, ragg987 said:

I don't see how that would work. On a sunny day you would charge up your 4.8kWh and that is it done. When the sun goes down you use it until it is depleted.

 

Our 4kWp is capable of generating 25kWh per day, though the mean is 11kWh. The mean is meaningless (!) in the context of ability to charge a battery - I have the daily data someplace of actual daily generation so this might help to model your annual saving, though of course just because you generate 4.8kWh on a given day does not mean your battery will fully charge as you home will consume a background load.

 

Without doing the modelling, I fail to see how this could save you more than around £100-£150 per year (for a 4kWp array and 4.8kWh battery).

As said above, the fact that most of the appliances use more power than the solar pv can provide, even at its best, the battery will get heavy use. Even when we do have the oven on, we rarely just have that on.

 

There is several fridges (cerca 200W each) for medical storage, oxygen concentrator (500W), my work equipment (100W), background load (up to 100W), boiler in cold times (2-300W), so we will use more than the current 4Kw solar PV we have, hence why i believe the storage would be a good thing to have, to top us up during the day, and provide the background load during the night.

[ragg987]

1 minute ago, MikeGrahamT21 said:

how many kwh did you generate last year?

Approx 4Mwh. (Measured 3,860kWh from 24 Jan to 31 Dec 2017. Did not connect monitoring until 24 Jan)

[MikeGrahamT21]

8 minutes ago, ragg987 said:

Approx 4Mwh. (Measured 3,860kWh from 24 Jan to 31 Dec 2017. Did not connect monitoring until 24 Jan)

We have the infamous east west split, and we did around 3250kwh both 2016 and 2017. The west ones don't do so much in the winter. We do have south facing space for those (2kw) now, but its almost impossible to find anyone who will move them.

[MikeGrahamT21]

56 minutes ago, JSHarris said:

Yes, my electric bike BMS does the same as the system in my car, as I designed it to run the cells between 30% and 85% SoC, but the issue with lithium cells was never really cycle life, but the relatively rapid rate of degradation with age, the calendar life.  Lithium cells used to have a pretty poor calendar life, around 4 to 5 years even if you rarely ever cycled them, but this has gradually being improving, and newer chemistries seem to have a much longer calendar life, as do older chemistries with newer manufacturing methods. 

 

I did a stack of measurements a few years ago on some test cells of different types (but all lithium ion exchange cells), holding them at the best life long term storage open circuit voltage and cycling them once every few months to measure the capacity loss, and it was then between 5% and 10% per year, so for most applications calendar life was more critical than cycle life.  The worst cell type in terms of calendar life degradation was the first generation LiFePO₄ cells, they lost capacity more quickly than the older (and potentially more dangerous) LiCoO₂ cells.  The newer LiCoO₂ cells I  bought around a year ago seem to be significantly better in terms of much reduced capacity loss with age, so I'm guessing the manufacturing process has improved.

 

Cycle life is highly non-linear with SoC range for pretty much every cell chemistry, massively so in the case of some lithium cell chemistries, like LiFePO₄, where 10% to 95% may only give 1000 cycles, but restricting operation to 30% to 90% SoC may well give well over 20,000 cycles. 

This is very interesting, I'll have a read of the manual for the ME3000SP, and see if it allows you to choose these type parameters as part of the setup.

[MikeGrahamT21]

Pylon Tech is 6000 cycles at 90% DoD, apparently one of the best available, but that is according to their own documents!

 

Seems to be plenty of settings, like minimum voltages which stop it from totally draining the battery, so I reckon the 6000 could be improved upon.

 

The 6000 Cycles, if charged fully and used fully would provide 28800 Kwh of power, in its rated life time, worth at 12.8p, £3686. At 18p that would be £5184.

 

Obviously this isn't linear, and we won't get 6000 clear cycles, but i do remember reading an article which suggested you worked out the total amount of capacity in its life time, and take that from the installation cost, if you are still +ve, then you are in profit, but not sure how accurate that calculation is.

 

Does this have any impact on peoples feelings above?

[readiescards]

2 hours ago, ProDave said:

Another thing people tend to do with FIT solar PV is optimise the panel orientation for maximum yield.  That is fine if your objective is to maximise payment.

 

But for a non FIT self use scheme, you don't just want a passive peak in the middle of the day that you are unlikely to be able to fully self use.  Instead my plan is some panels facing east, to get a much earlier start to useful generations levels and less facing south so the mid day peak will not be as large.  Also if I can manage some facing west would be good to extend generation into the evening, but that is harder to arrange here.  The total yield would be lower, but my feeling is you would generate more self usable power throughout the day.  One option I am looking at is making my east facing bank on a simple flip over mount so they would in effect be on a very basic tracker and those same panels could do the evening burst as well.

 

I have panels SE and SW facing and wish I could re-position a few of panels to be NW and EW facing as it is frustrating when it is a sunny morning or sunny evening but my panels are not illuminated and I'm buying electric at 3 times the cost of what I'm paid to export it.  A battery would change all this but in the meantime I think extending the generation period would have been better than maximizing generation for me.

[Jeremy Harris]

 

49 minutes ago, MikeGrahamT21 said:

Pylon Tech is 6000 cycles at 90% DoD, apparently one of the best available, but that is according to their own documents!

 

Seems to be plenty of settings, like minimum voltages which stop it from totally draining the battery, so I reckon the 6000 could be improved upon.

 

The 6000 Cycles, if charged fully and used fully would provide 28800 Kwh of power, in its rated life time, worth at 12.8p, £3686. At 18p that would be £5184.

 

Obviously this isn't linear, and we won't get 6000 clear cycles, but i do remember reading an article which suggested you worked out the total amount of capacity in its life time, and take that from the installation cost, if you are still +ve, then you are in profit, but not sure how accurate that calculation is.

 

Does this have any impact on peoples feelings above?

 

 

Predicting real world life for any cell of any chemistry is pretty damned difficult, and cycle life is very far from being the only, or even the primary, consideration.  As mentioned before, the massive variability in cycle life with cell SoC variability from cycle to cycle (which is not the same as the apparent DoD available from the BMS, that is often quoted) has a major impact on cycle life, but calendar life is also massively variable too, being highly dependent on things like temperature and the mean cell voltage.  If a battery pack has a high mean cell voltage, higher than the storage open circuit cell voltage, then calendar life is reduced pretty dramatically (this is the primary reason laptop batteries fail early on machines that spend a lot of time plugged in to the charger, for example).  Also, if the mean cell voltage in a pack is lower than the optimum long term storage voltage then calendar life is also adversely affected.

 

In practice, house systems may be slightly better than electric vehicle systems, in terms of the mean cell voltage through life, as a lot of electric vehicles will spend most of their life with a fully charged pack (mine does, for example, it sits fully charged for at least 3/4s of every day).  Taking any 3.7V nominal lithium chemistry cells as an example, most will be at around 100% SoC with an open circuit cell voltage of around 4.15 to 4.2 V, and will be close to 0% SoC with a terminal voltage of around 3.2 to 3.4 V per cell.  Best storage voltage is around 3.9 V per cell, but this is only around 50 to 60% SoC, plus open cell voltage off charge is a very unreliable indicator of SoC, the BMS has to actually measure the energy that goes into and out of the pack to control SoC accurately.

 

Most battery management systems for lithium chemistry cells tend to use "top balancing", where cells are periodically charged to the 100% SoC voltage, where the terminal voltage of every cell in the pack is the same.  They are then cycled between the defined limits (typically this might be 10% to 90%) for a defined number of charge/discharge cycles, before the balancing system kicks in again to bring all the cells up to 100% SoC.  The reason for this is that there will be gradual drift over time between cells in the pack, due to the tolerance on cell capacity from one cell to the next, slight variations in internal resistance, temperature variations across the cells in the pack etc.

 

Needless to say, the manufacturers don't give much away about how their systems actually work (except Tesla, who make pretty much all the details available as a matter of policy).  Anyone who drives a plug-in hybrid, or just a normal hybrid, car will notice (if they are observant) that the behaviour of the car changes periodically, with the engine running when you might otherwise expect it not too.  Prius owners started noticing this right from the time the first cars went on sale, and some owners managed to reverse engineer things to discover what was going on.  In my case I bought a CANBUS reader in order to be able to set some of the non-user changeable functions (like the audible seat belt alarm, the reversing beeper etc) and as a side effect this will show a lot of information from the battery management system.  It's clear that once every few weeks the battery management system goes into cell balancing mode, where it takes the cells up to maximum SoC.  My guess is that the frequency it does this is dependent on several factors relating to the way the car has been driven and the environmental conditions, as it's not a fixed time period as far as I can tell.

[billt]

If it's of any interest I've been monitoring our consumption and production for several years and have modeled the performance for a battery system. The results are not very impressive.

 

The system has just under 13kW of solar panels, facing SSW at 45 degrees. Nominal battery capacity 14.4kWhr, DOD limited to 80%. Average daily consumption is about 21kWhr, so annually about 7700kWhr.

 

2012 shortfall of 1370 kWhr (3 months with zero import)

2013 shortfall of 1510 kWhr (5 months with zero import)

2014 shortfall of 1180 kWhr (4 months with zero import)

2015 shortfall of 1410 kWhr (4 months with zero import)

2016 shortfall of 1410 kWhr (4 months with zero import)

2017 shortfall of 1320 kWhr (4 months with zero import)

[MikeGrahamT21]

Just now, billt said:

If it's of any interest I've been monitoring our consumption and production for several years and have modeled the performance for a battery system. The results are not very impressive.

 

The system has just under 13kW of solar panels, facing SSW at 45 degrees. Nominal battery capacity 14.4kWhr, DOD limited to 80%. Average daily consumption is about 21kWhr, so annually about 7700kWhr.

 

2012 shortfall of 1370 kWhr (3 months with zero import)

2013 shortfall of 1510 kWhr (5 months with zero import)

2014 shortfall of 1180 kWhr (4 months with zero import)

2015 shortfall of 1410 kWhr (4 months with zero import)

2016 shortfall of 1410 kWhr (4 months with zero import)

2017 shortfall of 1320 kWhr (4 months with zero import)

Do you have any data to suggest what the battery is doing? So we can see total generation from PV, and total battery consumption, with grid consumption also. Gives a better idea to how much the battery storage actually adds to the setup.