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Solar system capacity


Chris Kitson

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Hi all. We are battling with the capacity of our guest cottage solar system.

System is..

4 x 200ah Ritar gel batteries

5 kva Riosun 48v inverter charger

6 x 420w poly canadian solar panels

It was installed last year October with guests staying from late December. It started fine but seems to have lost capacity. Its a basic cottage that had a kettle, toaster, microwave, 2x gas electric geysers (70w when engaged ), led lighting, 2 ceiling fans ( 70w at max ) and wifi. We have since removed the kettle. 

Problem is the batteries will be fully charged ( 57v ) quickly but then come 5pm theres a quick drop to around 52v if something is used like the microwave for a short period. Then its a steady decline from there even if theres an average of 50 to 100w usage from lights or a ceiling fan. Then usually by 4am the system is depleted and trips. 

My questions...

Are there enough batteries to keep the house powered through the night?

Why is there such a quick drop early evening?

Is there possibly a weak battery?

What can we do to resolve? We have been told to increase the battery capacity we would need to add 4 batteries because its a 48v setup. 

I have added photos that show consumption and battery between 5pm and 6pm and 4am and 7am. 

Thanks

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2 hours ago, Chris Kitson said:

4 x 200ah Ritar gel batteries

Stop right there! Systems built around lead/acid batteries (and I include gels in that) are designed to cope for occasional outages, not for daily load shedding.

Those batteries can't take regular deep discharges (in this case "deep" is > 50%). 

You have about 2.5kWh, of which you can only use 1.25 kWh without compromising the batteries. 

In the long run it is going to be cheaper to buy a lithium battery. You can charge it quicker, discharge it quicker and more deeply. You will find it has an order of magnitude greater life cycle (the number of times you can discharge/recharge).

The quicker charge is important because when load shedding numbers get high, your current batteries may not get enough time to fully recharge between sheds.

I know it's not my money, but a 5kWh lithium battery will make a world of difference here. Because you can discharge it down to at least 80%, you will end up with over 3 times the useable capacity.

Edited by Bobster.
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6 minutes ago, Bobster. said:

The quicker charge is important because when load shedding numbers get high, your current batteries may not get enough time to fully recharge between sheds.

Your inverter has a 60A maximum charge current. So 3000W. So a bit under 2 hours to charge a 5kWh battery from flat, and probably enough to get it charged up again between sheds even if there is no solar available.

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Bob thanks for the replies. The cottage is offgrid so no issue with charge time. What Im getting is that our capacity os too little. 

Next quick question, we have 3 x 3.3kwh lithium batteries at our house. We can survive off 2 so can we take 1 and place it in the cottage?

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1 hour ago, Chris Kitson said:

Bob thanks for the replies. The cottage is offgrid so no issue with charge time. What Im getting is that our capacity os too little. 

So how does that work? You have to get enough solar in there during the day to make it through the night? So once the sun goes down, the gels have to get you through until sunrise - with no grid backup. That's not enough. The gels, then, are being discharged for whole nights, every night.

1 hour ago, Chris Kitson said:

Next quick question, we have 3 x 3.3kwh lithium batteries at our house. We can survive off 2 so can we take 1 and place it in the cottage?

Well... a single 3.3 kWh battery can be discharged by about 2.9 kWh before the BMS shuts it down as an act of protection. So you have more outright power and nearly twice the useable power. It has to be an improvement. But what if it's an overcast morning? Now your battery has to stretch even further. Still, either that single 3.3 or the 5.0 that I suggest is going to stretch further.

NB! You reduce your protection in the main home. It sounds like you'll probably make it most of the time, but think of  that worst case scenario I described. I assume your main house has grid, but you'll still have to stretch the battery further.

Edited by Bobster.
spelin
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If budget is tight, start with the 3.3 from main house into cottage - run like that for a while, and take particular care on cloudy days (although your panel setup should mostly charge even on cloudy day), until you've figured out where you stand - from the limited info I'd say your 3.3 should suffice for the cottage, and two 3.3s may suffice for the house. If after running like this for a while you find its too tight (you wouldn't want cottage to discharge to 30% every night for example) then add the 5kwh (swap around again).

Unless the budget allows to just splash on the 5kwh from the start - but running it "closer to margin" for a while will also give you a better understanding of the system and your / the cottage's needs.

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Just my 2c, just trawling spec sheets. If it's 4x 200Ah Ritar batteries at 12V, that means you had approx 9.6kWh of battery capacity (call it 10kWh), and if you discharged to 50%, you should have had 5kWh available. This battery is supposed to give 1200 up to 1500 cycles at this discharge capacity, and up to 15 years of standby usage. My thumbsuck, you could have been able to see at least 4 years of light usage, say 100W of lights and a fan each night, but reality turned out to be different.

Just speculating, but I think it's more likely that you (or your guests) exceeded the 40A charge/discharge limit on the battery, ie. had loads in excess of 2kW connected, for example a combination of the kettle or microwave or toaster or goodness knows what your guests used, and that this may have overloaded the batteries. On top of that, yours appears to be a transformer-based inverter with 300% surge capacity, but it's less likely this would have been reached.

It's water under the bridge now, and it's better just to get a lithium battery that'll be better protected by a BMS, but the 3.3kWh battery I don't think will give you better capacity than the 4 Ritar batteries as new, especially if it's a 0.5C. Personal take would be to get a 5kWh Greenrich 1.5C battery or similar, just to be better prepared for whatever could be thrown at it.

Edited by GreenFields
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@Chris Kitson

It is pretty norm for lead acid to drop from the level you see while the charger is pushing power to them. So your drop to 52 from 57V is what is expected. A fully charged lead acid in good condition without load and rested after charge shows about 12.8V.

As you indicated the voltage under charge picks up fast shows loss of capacity as was explained by @GreenFields

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57v float charge  seems a bit high as I have been float charging at 54v and bulk charge at 57v  and battery settle in the evening at 51.8 and 4 year old + gels are still doing well with these setting 

So it's just my understanding that 57v is a bit high for float charge. 

Best is to check each battery or cell with an multimeter as one could be bad as your volts do drop to low volts under low loads 

 If you not going to go lithium any time soon best is then to get an  balancer as an out of balance cel will reduce the performance of the battery pack . 

I have spent the money on a lithium and only used it for 2 weeks and it far out performs these gels but as my gels are still going strong decided to uses them till they can't take the normal loads any more . 

Edited by GMAC
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5 hours ago, GreenFields said:

Just my 2c, just trawling spec sheets. If it's 4x 200Ah Ritar batteries at 12V, that means you had approx 9.6kWh of battery capacity (call it 10kWh), and if you discharged to 50%, you should have had 5kWh available.

Yes. My "calculations", if one may dignify them with that term, we're out by 100%, and so I gave @Chris Kitson bad advice. Apologies to Chris, and I need to do better. 

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31 minutes ago, Chris Kitson said:

Thank you for all the helpful replies. One last question. I cant add another 1 or 2 gels to the current system? Would be ideal. My understanding is the system is 48v. 

You can only add 4 at a time to connect the 4 in series and then in parallel with what you have. 

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As said your system is 48v so you can only add a minimum of 4 cells (batterys) at at time . This will give you more run time but then the problem comes in can your inverter charge that amount of storage quick enough and gel batterys does take longer to charge than lithium .

looking at what you want to spend now on gels you could just as well start looking at lithium .

 

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