Thanks John,
I'd considered using small PVs to sample the light at different array locations for another reason, a couple of years ago, but I hadn't looked at it again since then because I'd found what I wanted to know by other means. I hadn't thought of using a Zener to mimic a battery and hold the voltage. That's a good idea; thanks.
If I use bigger PVs, around 34W, then the only calculation needed would be to move the decimal point 2 places, and add the 2 values together. I could probably use a shunt on the DC supply to the inverter and use my data logger to monitor that and the solar samplers, and then do the calculations. But I'm probably getting ahead of myself, as that's more of a challenge type project for when I've finished the system upgrade.
Partial shading is only a problem in the summer and before about 10am. It's caused by a huge gum tree about 50m from the arrays, so the transition when it occurs doesn't last long. The shadow moves down the array relatively quickly.
David,
Alas, the Xantrex MPPTs can give me relay outputs for all sorts of condition - except float charging! It's a ridiculous omission. Everything else about them, I like. My previous Outback MPPT had a float signal available. But I could use one of my original Plasmatronics regulators to monitor battery voltage and provide a float output signal.
Rockabye,
My built-in test equipment works fine. I know the system well enough that I have a pretty good idea of when the batteries should have reached float just by the prevailing weather. It's the others who don't seem to understand. I installed a large LED voltmeter in the kitchen about 4 years ago, but it didn't seem to help. And then when I added the 24V regulator to solve the problem of marginally designed fluoro inverters periodically dying, it became useless unless I rewired that part of the house. (The easiest place to install the regulator was in the battery shed, so all the meter now sees is regulated)
Anyway, after the upgrade, we'll have all the system controls and instrumentation available in the kitchen. At present it's all still in the battery shed with the rest of the system. I put a trench and conduits through to the house a couple of years ago to bring remote controls and readouts to the house, but I since decided to completely relocate everything and do it properly, starting from scratch. As I said, it's a very old system that has simply evolved. The time has come to start again with a clean slate and do it the way I want it.
I will certainly have a prominent voltmeter and battery SOC indicator in the house when the renovations are finished. And based on all this helpful input, I think the best way to convey the system status to the household is an indicator that shows when the batteries have reached float, and another that shows the estimated available power using the little solar sampling PVs. The full calculation system can wait until I have spare time and feel in need of a challenge.
Using this arrangement, if the float indicator is OFF, then you don't use anything heavy duty. If the float indicator is ON, then you can see what's available from the arrays and see if they can handle what you want to use. If the float indicator goes OFF again, then you cease using that appliance unless it will only be brief.
Float will come much earlier in the day once the new arrays go up, but I'm also planning to add air-con later so what initially may appear to be overkill in array sizing will be less so later on.
Thanks for all the input and grey matter prodding.
Posted Thursday 8 Jan 2015 @ 12:06:42 am from IP
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