Energy Matters Forums

[amongstmyselves]

Howdy all,

Our system is a fully off grid setup with generator to do backup and battery management when the sun isn't around long enough. Our batteries are SLA, the inverter is a Sunny Island 6.0.

During Winter the generator is used numerous times to do Boost Charges when the sun can't manage this. The system is configured so that the batteries must achieve a full boost charge every 10 days. If it doesn't then it will call upon the generator to do this. This is all fine.

My problem with the system is that it isn't smart enough to kick in the generator to finish off a charge which has been started via Solar. It appears the day counter is aligned to when the last EQ charge happened which is meant to happen every 30 days. Instead what will generally happens is once the 10 days has exactly clicked over then the generator will start any time of night. Then it will proceed to do a 6 hour charge.

The noise of the generator isn't really an issue given our remote location but it's the waste of fuel that bothers me. Why couldn't the system be configured that once solar input had reduced to a point for a certain period and given the time of day, then engage the generator to finish off. Often the finishing off time is only a couple of hours at most.

During Winter I did start to monitor the day count when a Boost did complete but the counter that is displayed is for doing an EQ charge and not Boost so it doesn't reset once a Boost Charge has been achieved. I wish the counter shown was the Boost counter.

I'd really appreciate any ideas for fixing this issue or some suggestions.

Steve.

[Gordon-Loomberah]

Hi Steve, automated systems often aren't quite as smart as we'd like, how much hassle would it be to manually manage the generator? Human smarts are way better than a battery management system I think.

I have reasonably high energy use for a couple of aquaponics systems I run and manually start a generator in cloudy periods of weather to prevent the LiFePO4 battery from discharging too deeply.
Recently I bought myself a new 3.2kW generator (only runs a battery charger) with remote (2 wire) start, and use a relay operated via a small wall charger output through a TP-Link remote switch to turn the generator on whenever I want, from anywhere- no need to be physically present. I have a small laptop with a data logger monitoring my system, so that I can see charging rates, discharge rates and battery voltage, and can log on remotely to check if needed, so that informs me of any need to run the generator when I am not at home.

I am planning to add a bit of automation to this arrangement with my Morningstar relay driver, which could start the generator at a certain battery voltage, with a programmed time delay- without the need for 240V.

[amongstmyselves]

Howdy Gordon,

I'm a bit of a tinkerer, so a more manual system might have been something I could have dealt with. Alas, when we bought the property it came with an old Outback system which needed an upgrade for several reasons but I would have probably preferred that arrangement with the new batteries and panels that we now have.

The issue I am having is related to having SLA batteries instead of a Lithium compound battery which as you'd know need a lot more maintenance than LiFePO4's.

Steve.

[Gordon-Loomberah]

It's almost 6 years since I had a Lead-acid battery, but I used to EQ manually, rather than use the Outback FM80's programmable setting. EQ really only needs doing if the battery hasnt been having its regular absorb time at least a few days per week, and cell voltages drift apart. EQing when cell voltages are equal and absorb duration has been reasonable really only shortens battery life.

[amongstmyselves]

I do a manual EQs before and after Winter but I've probably only done it a dozen times in the 30 months we've had the system. There's been some other small issues that the installer has suggested an EQ for. The system has also done a few, but not many, automatic EQs as well. Apart from the stupid generator issue our system is working very well. Given that the batteries have only had 60 cycles in 30 months, we should get a very good life out of them as well. Who knows what sort of battery chemistry will be around when they need replacing. Exciting times !

[australsolarier]

your battery only had 60 cycles in the last 30 months?

do you by any circumstance mean: 60 equalisation cycles?

[amongstmyselves]

Actually I was thinking about that last night and I'd add in another year for some reason. The system is only 18 months old.

I don't know how the system works this figure out. It's not as though they are Lithium batteries which can be drained fully. Not that you'd want to do that given the sudden lack of house power.

The figure is what the system shows. 60 battery cycles in 18 months. On average the batteries don't go below 80% State of Charge. We use on average 8kWh of power per day and the battery storage is 38kW. There are 6.3kW of solar panels. The system was specified to deliver 12kWh in Winter and 14 in Summer. But this included air conditioning which hasn't been installed (as yet).

[Helipos]

It might be that the system has used 60x the AH capacity of the batteries in discharging over the last 18 months. Quite possible if the nightly discharge is pretty light.

[amongstmyselves]

Ah that's an interesting idea Helipos.

[davidg]

Lead Acid and Lead Acid Carbon cells cycles equate to DOD ie if you are typically using only 20% DOD then then life cycle might be say 7500 cycles and less cycles for a DOD of 50%.