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Solar PV battery options
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I don't see any sums there, maybe I'm missing something
But seriously, go on go for it. Show us some assumptions and maths. If not for yourself or myself, then for any other person reading this thinking if they should or should not buy cells and build a battery and are unsure if they make financial sense.0 -
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I wouldn't be obsessed about batteries paying for themselves tbh. If they can great, but if I get 75% value out of a battery I'd be happy enough.
Not grabbing units from the grid gives me much better satisfaction tbh
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Saying that, my install was decent value and the battery after grant was cheap. I'll probably get another 2.4 pylon if can get an ok price.
Btw, some of those battery systems look great lads. Fair play.0 -
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I wouldn't be obsessed about batteries paying for themselves tbh. If they can great, but if I get 75% value out of a battery I'd be happy enough.
And what if you only ever got 50% - half your investment - back? Or 30%, or less? Would you not care?It's clear that the best you'll likely save with a 2.4kW Pylontech is 30c per day for maybe 300days a year, so €100 at best per year I reckon, and therefore €1000 over 10 years (which is the expected lifespan I believe)
I assume that the larger the battery, the less likely it will all be used (and/or refilled) each day
How did I do @unkel ???
As good as a simple sum goes I guess. But that 30c seems quite optimistic and the 300 days even more so
The good thing about the Pylontechs is that most people got most of the extra install cost of the battery for free (courtesy of the Irish tax payer), so their pay back time will likely be within the lifetime of the battery (and inverter) 0 -
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I don't think the 30c is optimistic though the 300 days may be. With my 4.8kW install and a single Pylontech in 2020 I got an output of 1050 kWh from my battery and so far this year the number is 588kWh. With the 16c I pay for the day rate that's about 160 EUR though I guess about a third of the load can be shifted to night time. So let's call it 125. Of course working from home means you make better use of solar in general and the battery in particular.
Glad you came up with the actual savings in units. That's a better start than most guesstimates people would go for!
It can be argued that the part of the load that can be shifted to night time has no added value (running through the battery) as it diminishes the life of the battery. We have done the sums for that before. So we'll stick to the €160 * your two thirds guesstimate = €107. You overpay on your day rate, you should pay no more than 13c, so that brings the figure down to €107 * 13/16 = €87
And we are not taking into account the alternative use of the units you send to your battery. If you have an immersion diverter or if we get a feed in tariff both worth say 5c per unit, then these 1050kWh * your two thirds from the battery would have generated 1050 two thirds * €0.05 in other savings or over €35. So the real savings (before any maintenance and losses) is really only a pittance of like €50 per year
And there you have a decent estimation of your savings. With a very small battery. Double the size of your batteries and you might get another 50% savings (unless you have a huge base load). Double the battery again, maybe another 25%. Double it again (what Dr. Phil has) and you get maybe 10% more
So with a 20kWh battery you might have a saving of €50 (1 + 0.5 + 0.25 + 0.1) = €90 per year
Unless, I'll say it again, you run a massive base load, so you do use up a lot of your battery units yourself and they can be valued at the higher rate (minus opportunity revenue). You can increase the revenue of the battery somewhat by peakshaving. But only really if the difference between day and night rate is fairly substantial (i.e. if you have the Energia EV plan where the peak rate is 16.8c and the night rate is 4.8c/kWh incl VAT). If your difference in rates is only 8-9c, again we have done the sums on that before and it turned out to be only marginally better than not doing it at all (mainly because of losses and battery cycling costs iirc)
And of course we are only discussing the current financials. The FIT might not happen for another few years. The price of electricity is likely to go up. The price difference between day and night rate is likely to go up very significantly. And there is the self-sufficiency and cover against problems with supply
And it's an interesting hobby 0 -
And it's an interesting hobby
That it is!
Another advantage of the hobby is being able to load shift.. or peak shave.
So when the kettle is put on, the battery will make up the difference between solar and demand.
It's a way you can eek a bit more out of it.
Now in summer I'm letting it discharge at night rate. Otherwise it would never drop below 70%!
When the days get shorter & not getting enough solar to charge during the say, night time use will be restricted and will start charging at night again0 -
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Buying a hybrid inverter and a 2.4kWh Pylontech and using that to peak shave makes no financial sense TO ME
It doesn't. But if you got the €2400 extra subsidy to spend €2400 extra on buying the Pylontech and the hybrid inverter over the standard inverter and the extra hour installation charge (or in other words the tax payer paid for your battery in full) then it does make sense
And for the record, no I did not get a cent subsidy for any of my own PV / battery installs. I am not a fan of subsidies as they invariably end up where they weren't intended and they invariably are inefficient use of tax money, but if there is a subsidy available, by all means, go and grab it!0 -
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Glad you came up with the actual savings in units. That's a better start than most guesstimates people would go for!
It can be argued that the part of the load that can be shifted to night time has no added value (running through the battery) as it diminishes the life of the battery. We have done the sums for that before. So we'll stick to the €160 * your two thirds guesstimate = €107. You overpay on your day rate, you should pay no more than 13c, so that brings the figure down to €107 * 13/16 = €87
And we are not taking into account the alternative use of the units you send to your battery. If you have an immersion diverter or if we get a feed in tariff both worth say 5c per unit, then these 1050kWh * your two thirds from the battery would have generated 1050 two thirds * €0.05 in other savings or over €35. So the real savings (before any maintenance and losses) is really only a pittance of like €50 per year
And there you have a decent estimation of your savings. With a very small battery. Double the size of your batteries and you might get another 50% savings (unless you have a huge base load). Double the battery again, maybe another 25%. Double it again (what Dr. Phil has) and you get maybe 10% more
So with a 20kWh battery you might have a saving of €50 (1 + 0.5 + 0.25 + 0.1) = €90 per year
Unless, I'll say it again, you run a massive base load, so you do use up a lot of your battery units yourself and they can be valued at the higher rate (minus opportunity revenue). You can increase the revenue of the battery somewhat by peakshaving. But only really if the difference between day and night rate is fairly substantial (i.e. if you have the Energia EV plan where the peak rate is 16.8c and the night rate is 4.8c/kWh incl VAT). If your difference in rates is only 8-9c, again we have done the sums on that before and it turned out to be only marginally better than not doing it at all (mainly because of losses and battery cycling costs iirc)
And of course we are only discussing the current financials. The FIT might not happen for another few years. The price of electricity is likely to go up. The price difference between day and night rate is likely to go up very significantly. And there is the self-sufficiency and cover against problems with supply
And it's an interesting hobby
What the fudge! This is utterly ridiculous math.
We are trying to gauge the payback from the battery. So you cannot exclude the night rate savings by saying they reduce the life of the battery. The battery is paid for. It has a finite number of cycles plus age. Use it or lose it. If I wasn't using the battery to say do the washing that solar would be going back to the grid. So I definitely count the night rate savings. You cannot double count the battery cost vs the night rate shifted usage and vs the rest. We've been through this once before - you just love to double count the costs.
Put it another way. If I am saving 7c per unit and my amortised battery cost per unit is 6c, yes I save only 1c but more importantly I am paying off cost of the battery.
16c is a bit high but I get a very cheap gas rate in the package from Bord Gais and due to solar PV I use way more gas than I use electricity from the grid. Bord Gáis Energy
Best Dual Fuel - Gas and Electricity
Electricity Charges
Day rate 16.07 cent
Night rate7.96 cent
Standing charge€242.06
Gas Charges
Unit rate3.371 cent
Standing charge€96.94
But your 13c number is nonsense. Checking bonkers the best day rate on a day/night plan is 14.9c. But at the end of the day 16c is what I pay for my electricity and that's what I save per kWh from my battery.
I don't have a diverter and though I do manually divert electricity to my hot water tank its a small tank and gets hot in an hour. So that alternative uses argument does not hold water. In the summer I will have enough to charge the battery even if I had a diverter. Now if you are making the argument that I should spend a 1000 euro to get a bigger better tank and diverter in order to save 0.05 euro per unit then well...
As far as FiT is concerned, I will believe it when I see it. Meanwhile I've been saving with the grant paid battery for the last two years. That is money in my pocket.
I do have an EV and a Zappi but the car is not always at home and when at home doesn't always need a charge. A mere 3 or 4kWh in a day won't make much of a difference. Didn't you say you don't bother to plug in if you are not taking in at least 10-20kWh?
And I'm not sure why you are bringing our past discussion about peak shaving and night charging the battery in here. I have not applied any of those savings here. My actrual battery use was 1250kWh but I deducted 200kWh because that was a generous estimate of night charging last year. I only started in November.0 -
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Let's say the day/night rates are 20c/10c. The battery cost 1200 Euro and it saves you 500 kWh of day and 200 kWh of night. Note that that excess solar would have gone to the grid otherwise. Assume no diverter, no FiT and a zero discount rate for simplicity. Do you think the payback is 10 years or 12 years?
10 years...
...I'm all for simplifying sums. The sole reason I post any of this in here is to prevent fools (very obviously not you!) from parting with their money thinking they will save money but they will actually loose money. The likes of FB pages are full of these eejits. Problem is that the above calculation is not that simple. It would be if the battery has eternal life. It doesn't. The battery we have been discussing is your Pylontech. It has a design life of 10 years (or 4500 cycles). If you use the battery like above, throwing away a considerable part of its life only saving night rate, your battery will have paid for itself in 10 years alright as per your example. But it then will also be end of life (or nearing it)
Is that what one should plan to do? Pay thousands up front (and again, I'm all for simplifying sums, but we did not take into account opportunity costs of money here either - never mind some people take out loans to install PV!)? And by the time it has paid for itself, it will pay for you no more?
Maybe that gives a little bit more of an angle into why I would not recommend charging your car / running your dishwasher on your battery, ever. Even with supercheap DIY AE batteries like a lot of us in here now have & enjoy 0 -
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