Solar Panels with Batterys

[aptsys]

Originally somewhere around 230 miles on average, now maybe 150 miles which gets me 2 days of travel.

 

[Mr Chibs]

Blimey that's quite a battery depreciation. I wonder if the rate of decline will be the same in the next 3 year period.

 

[SpecialK]

I thought Tesla battery warranty guaranteed they could not to drop more than 80% in 8 years?

 

[bernardgreen]

could not to drop more than 80% in 8 years?

drop by 80% leaving only 20%

Or

drop to 80% losing only 20%

 

[MeldrewsMate]

This doesn't seem to be addressing the OP's query in any way.
He does't know his Kelvins from his kilos, nor his batteries from his battery's.
He doesn't see the difference between a kW and a kWh either, but he certainly didn't ask for an argument over the economics of battery storage, nor the past and predicted range of electric cars!
He wanted to know if adding a third battery pack (of 2.4kWhr capacity) would allow him to boil a kettle without import from the grid. The answer, it seems, is that the power delivered to the house from the battery pack is limited by the power rating of the inverter, and therefore the likely answer is no. The extra batteries (plural of battery) would not add to the (standard?) 48vdc storage potential. It would appear that the existing inverter may not be powerful enough to supply more than 2kW, so an inverter upgrade would be in order.

If you're still there OP, a simple test would be to load up the battery system with, say, a 1kW heater and note the amount of grid imported power (presumably nil), then add load until the system starts to import power. The figure obtained may well be the inverter's power limit, and correlate with the amount supplied when the kettle was on.

 

[HawkEye244]

Who knows if the OP is still around but that's a great answer Meldrews.

I do wonder then why larger inverters aren't fitted as standard in most domestic PV installations as surely this is quite a common problem ?

Is it to avoid batteries being fully discharged and thereby speeding up their depreciation ? Keep people dependent on the grid ? Account for the fact that battery storage technology is just not up to par ? A combination of all of these plus other reasons ?.

 

[JohnD]

I do wonder then why larger inverters aren't fitted as standard in most domestic PV installations as surely this is quite a common problem ?

I would have thought the inverters are sized to suit your array. When I bought mine I think the scheme was for houses with panels of 4kW nominal output or less, so the inverter is no bigger. Mine will run the tumbledrier or kettle on a sunny day. I have no battery.

If I had a battery capable of delivering more than 4kW, it would run flat rather quickly.

 

[ericmark]

I know my panels are rated at 6 kW and my battery 3.2 kWh and max charge is 2 kW and max discharge is 3 kW and also LUX. As to how much the inverter will handle I have not really looked, my display shows this

From 0.30 am to 7:30 am battery is being charged, so start the day with fully charged battery, but clearly over around 6 kW even in sunlight it will draw from grid, but this only happens when having a shower, so we were using cheap rate or solar until 9 pm today. The time from 9 pm to midnight we don't use much power, I have set tumble drier and washing machine with a 3 hour delay, so they will not start until I get into the cheap rate.

Solar produced 17.5 kWh's of which 11 kWh were exported, but costing is hard, it shows imported 12.2 kWh but it does not say what was at 8.85p per kWh and what was at 31.31p per kWh and the phone app is only showing total kWh not the use in £ so it is a bit hit and miss, we should get 15p per kWh for exported power, but not seen any payments yet.

So one battery should pay for its self, but a second one is uncertain as to if worth while, the inverters seem to be rated for maximum battery discharge rate there is a 4kW, 5kW and 6kW version, but my battery is limited to 3kW so it really does not matter what the inverter can do, in my case the battery is the limiting factor.

Since I should be buying at 8.85p per kWh and selling in the day at 15p per kWh it does not really matter if I start the peak time with a fully charged battery, and being fully charged means if we get a power cut central heating and freezers will continue working unless power cut between around 6 pm to midnight depending on time of year when battery may be already discharged. It holds back 10% but that would not last long.

My thoughts are battery live around 7 years, so any pay back has to be within 7 years, one battery no problem, but with two in heart of summer likely not needed and in winter not enough solar to fully charge them, so the gain is the over night charge only, and not really done the maths to date to if worth it.

 

[JohnD]

The purple line seems to be capped at 4. What is SOC?

What is the brown line?

You mention a power cut. Surely your inverter will close down? Or do you have an off-grid socket for the freezer?

 

[ericmark]

The purple line seems to be capped at 4. What is SOC?

What is the brown line?

You mention a power cut. Surely your inverter will close down? Or do you have an off-grid socket for the freezer?

Purple is power in the battery or state of charge (SOC) brown is what I am using.

With a power cut I have one FCU and two double sockets still powered, they feed the central heating and freezers only, did think about lights, but running in my living room 100 watt of lighting during a power cut is not really a good idea, so use plug in rechargeable touches which auto switch on in a power cut.

The inverter also connects neutral to earth during a power cut, so I have a TN-S supply, when there is power it is a TN-C-S supply.

So the inverter will island for essentials, but would loose most things, the main CU would go dead. If sun light then the freezers would likely work for weeks, the battery being charged in day to keep freezers running, but if it happened in the evening when battery down to 10% then clearly it would not last long. Uncertain what would happen when the sun came up, never tried it, but when smart meter was fitted the central heating was still running. Clearly the thermostat and every thing else to do with central heating needs to come off the one supply, using USB to power a thermostat is clearly not going to work.

I did not install it myself, one not into dancing on the roof, and two one needs the paperwork to get the money for exported power. And of course the compliance certificate. So not really a DIY job, as one needs the certificates.

 

[plugwash]

He wanted to know if adding a third battery pack (of 2.4kWhr capacity) would allow him to boil a kettle without import from the grid.

IF the OP wants to solve this "problem", he first question that needs to be answered is what is the topology of their solar/battery system? does each battery have it's own built-in inverter? do the batteries share an inverter with each other but not with the solar system? or does the system use one inverter to run both the solar and the batteries?

You seem to be assuming the last option, but given that the batteries were added later, I suspect that one of the former two options is more likely

There is also the bigger question though, of whether the problem is worth solving. You get into diminishing returns adding inverter capacity that will only be used for a few minuites per day.

 

[ericmark]

Solar system was installed back in 2011

Yes that was some time back, so yes

Were installed in Feb

Seems to show not part of same inverter, the

we get just over 60p per KW we generate and then another 4p for half of that as deemed export, the panels paid for themselves in FIT payments in under 10 years.

is very different today, the smart meters actually measure what is produced, I wish I could get 60p per kWh I produce, I only get paid for what I export as 15p per kWh, and it may well be those on the old deals get no benefit from having a battery? I can't look it up as no longer available.

Today one needs batteries to be able to feed in, and

When I put the kettle on it used to draw around 3KW , but since the batterys were fitted its around 1-1.2kw we are pulling in from the grid

That does not tie in with my solar panels, my kettle shows no movement of the smart meter. In fact only when having a shower does the smart meter show any import, the in house display (IHD) is next to useless as it only shows anything from 9 pm to 11:30 pm when it auto switches off.

 

[StephenStephen]

In terms of the kettle, I've had one of these for years - it draws less power, (and is much more efficient) so would likely not import from the grid in your setup:

 

[StephenStephen]

In terms of grid export later in the day in the summer:
You could do the maths to see if the 50% deemed export at 4p/kWh is worth as much as the much higher export rate you'd get for the smaller amount of actual export later in the day.
If you've not done so already, you might consider a TOU tariff, then you have the option of charging the battery at cheap rates and exporting it at higher rates.

I've not done the maths, but I would think it unlikely that adding more battery would make sense either financially or environmentally - you'd be using the extra less, so the return is diminished.

There's an environmental benefit you currently get from exporting to the grid later in the day - electricity tends to be dirtier and in short supply later in the day. You'd lose that benefit if you added more battery.

...and then there's DFS sessions...

I''ve just noticed the original post date! Oh well, no harm!

 

[ericmark]

it draws less power

I did try to find details, it seems it is still 2.8 kW or there about, so uses same power to heat as my kettle both can save energy, but if they use more that the battery can deliver still means it draws from the grid. There are kettles designed for caravans which only use 750 to 1100 watts, however clearly they take longer to boil, my pre-solar method was to use two cup boilers in the TV adverts to made two cups of coffee and give time for other things. I now try to use one boiler twice so as not to exceed the time the adverts run, but not exceed 3 kW, since they only boil just enough that can still be done.

However the question arises should we become slaves to the solar panels and batteries, and completely alter our living habits to suit when power is cheap? As yet resisted moving meal times, we still have an evening meal, but clearly it would be cheaper to cook mid day or after mid night.

I suppose I could keep tree cuttings dry them and then cook on an open fire, or even hang washing out, however I feel having a solar panel means I am still using sun light to dry cloths even if using a tumble drier. However since paid for export more than over night import costs, money wise better to dry over night. Dryer at moment using 648 watt, it does vary through the cycle, but since low it will be covered by solar easier.

Bring back the hot and cold fill washing machine, yes I know you can still get them, seems two reasons why now rare, one is items soiled with things like egg are better washed cold first, and second is the way the government set out the energy rating resulted in it being hard to get a hot and cold fill to get into energy ratings permitted. The same goes for fridge/freezers, to have a small fridge and large freezer would not help the energy ratings, so they vanished, so we now have a fridge/freezer and a freezer running.

Governments seem to forget we don't all live in large cities. For me to shop local, means a walk up a steep hill with shopping, as no parking at the shop, and a very restricted option of what I can buy, so we travel 8 or 12 miles to larger towns. So to reduce travel we have three freezers, the chest freezers is so handy, we can put whole bags of shopping in it, and then latter sort it out into the upright models. When we get home just want to sit down.

However this means high back ground power usage. This is an unusual over night power usage as intend to go out for a day or two, used 7.9 kWh over night, charging battery and doing washing. The in house display shows 9.44 kWh and cost £1.93 which includes standing charge. As to why the IHD and the solar software do not tally not a clue.

Yesterday looked at the UV forecast to see likely sun shine, this morning bright sun light, so this forecast, does not really help working

out likely sun shine. Which is why for me having a battery is important, one can't work out ahead what the day is likely to be like. Only 1.3 kW at moment, but that is due to angle and direction of roof, it gains more from evening sun. So for me having the battery charge over night is good, but for others it may not be so beneficial.

But at an average of £2.50 a day for electric, which includes the standing charge, is it all worth it? Before solar average was £4 a day, so they are saving approx £1.50 a day so around £550 a year, that's 22 year pay back time not 7 years as I was told. If I pay nothing that's 8.7 years, so only way it can pay is when counting the exported power.

But the deal the early people were getting for solar panels was very different to what it is now. And I have no idea as to if they can change tariff without loosing the very generous payment they get? It did seem crazy at the time, they were being paid in essence for being guinea pigs. No one was really sure how it would work out.

I know with my iboost+ when first fitted it was not really matching the export point, and it required some tweaks, the point at which it switched on/off was changed, I would guess the same applies to add on batteries? I note through the day my IHD will flit from import to export and it seems the software for the inverter has a small delay in adjusting. Often in the evening when solar has stopped the IHD will show export of maybe 20 watt. Although today the IHD shows I have used more than the solar software shows, the reverse has also been noted. I do have three ways to view export, smart meter, export meter, and inverter software, I will admit I have not compared them much. Until around September last year it seems the electric providers would go by what my meter said had been exported, then it changed, and for new customers they needed a smart meter.

I suspect having a smart meter would reduce the payments to those who were on the old deals when solar first was being promoted. Seem to remember a guarantee they would be paid for 25 years? This is why the iboost was so good, it allowed them to use the power and be paid for it. Today as I have now realised the simple time clock would be better than the iboost+ I had fitted.

So to advise we need to be very careful, as if what is done cancels the old deal, then he could be worse off? My panels are rated at 6 kW, I seem to remember the deal had a limit, and if the solar panels exceeded a set amount then the payment reduced. So the old solar panels may be a lot smaller than fitted today, mine are only on one side of the roof, and even on that side we could easy add another 4 panels to the 14 already fitted. It would not help as inverter not big enough, but the output per panel has been going up year by year.