How are you tracking solar harvest vs load?

unyalli
unyalli Solar Expert Posts: 121 ✭✭
in Off Grid Solar & Battery Systems #1
Hello, my little sunsaver mppt shows me power harvested from my array, power sent out the charging circuit after the mppt thing, and power consumed by load. After subracting load power from charge power I have battery power consumption so the whole story. After watching my system for a few months now I realize it's not big enough. I have 220ah of battery in two 6 volt's connected in series. My understanding from all the great help I've received and great information I've read here is I need to produce 26 amps of charge current to properly charge and equalize these batteries. With this I'm looking at bigger charge controllers (and of course a bigger array) and can't find any way of tracking them with the detail I get from the little sunsaver. What say you guys?

For instance, the Bogart Engineering Trimetric 2025 simply watches current go into and out of the batteries. It's a battery monitor not a full solar system monitor. The Morningstar Tristar's show solar harvest via the modbus interface just like the sunsaver but not system load.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #2
    Re: How are you tracking solar harvest vs load?
    unyalli wrote: »
    I have 220ah of battery in two 6 volt's connected in series. My understanding from all the great help I've received and great information I've read here is I need to produce 26 amps of charge current to properly charge and equalize these batteries.

    Well, no. Not exactly. The peak charge current rule-of-thumb is a shortcut to getting an array that is probably the right size. Most of the time it works, but it is not an absolute.
    It would be 22 Amps @ 12 Volts less 77% panel & controller derating: 343 Watt array +/- a bit.

    What tells you if the batteries are getting charged is A). specific gravity, B). charge controller reaches Float stage, C). resting Voltage attained, or D). battery monitor.
    For instance, the Bogart Engineering Trimetric 2025 simply watches current go into and out of the batteries. It's a battery monitor not a full solar system monitor. The Morningstar Tristar's show solar harvest via the modbus interface just like the sunsaver but not system load.

    The only reason you get to see system load is because you're using all DC out the controller's LOAD terminals. The majority of us manage without that. If you go with a really complex system like Outback FlexNet you can have multiple shunts and get readings for in/out. The Pentametric can do this too; watch two shunts, one for power out of the charge controller and one for power to the loads.

    Personally I think it may be just a little bit obsessive.
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  • westyd1982
    westyd1982 Solar Expert Posts: 85 ✭✭
    #3
    Re: How are you tracking solar harvest vs load?

    I added more charging capacity to my system last year. In planning it, I looked at all kinds of options like changing out the charge controller with a larger Morningstar or a Midnight Classic. However, I didn't want to give up the load monitoring provided by my SunSaver MPPT for DC loads, and I didn't want the issues of different panels on one charge controller. Also, I monitor my AC loads with the data from my SureSine-300.

    As part of working through all the options and what I wanted for my system, I contacted Morningstar about adding additional charge controllers instead of replacing my SunSaver MPPT. They said all of their MPPT products should play nice together. All of their MPPT products provide the same monitoring data for the charging. The 45 & 60 just don't have the load monitoring. I ended up buying an extra 250W panel as part of my grid-tied system purchase last year and I just bought another SunSaver MPPT. I got it installed in November, and they seem to work well together. To make the monitoring work correctly, I had to buy a MeterHub (see: Morningstar-MeterHub-(Hub-1)-Works-with-MODBUS - also has a photo of my setup). Overall, I've been really happy with my additional SunSaver MPPT and on sunny days my system gets into absorption before noon. BTW - a 250W panel works great with the SunSaver MPPT.


    This is my data graph from a couple of days ago (yesterday was cloudy and my panels are covered with new snow this morning):
    Attachment not found.

    - Tom
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  • unyalli
    unyalli Solar Expert Posts: 121 ✭✭
    #4
    Re: How are you tracking solar harvest vs load?

    Hey there Tom hows it going, I'm having fun monitoring my system with your code.:D So you have both Sunsavers connected in parallel to the same battery bank?
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  • westyd1982
    westyd1982 Solar Expert Posts: 85 ✭✭
    #5
    Re: How are you tracking solar harvest vs load?
    unyalli wrote: »
    So you have both Sunsavers connected in parallel to the same battery bank?

    Yes. Both SunSaver MPPTs are independently wired to my battery bank. Basically each PV panel has its own charge controller that connects it to the battery bank. It was the most cost effective way for me to add another panel to my system without having to completely redo the charging side. The SunSaver is nice and small so I had space to mount it in my current arrangement. I also had all the conduit and space for another breaker. I just had to pull another set of wires. It seems to work really well so far, and now I've got more than double the charging power on most days.
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  • unyalli
    unyalli Solar Expert Posts: 121 ✭✭
    #6
    Re: How are you tracking solar harvest vs load?
    Cariboocoot wrote: »
    The Pentametric can do this too; watch two shunts, one for power out of the charge controller and one for power to the loads.
    Thank you for bumping this thought in my head. Every time I would go to Bogart their write up on the pentametric put me off. I finally went deeper and there it is. The PM-5000-U is the brains of the outfit and will monitor three shunts. It will measure solar array power, battery bank, and system loads. Then you need some way of controlling/monitoring it and you don't have to use that ugly PM-100-D display. They have three units that allow monitoring/control via PC and RS232, USB, or TCP/IP. Thank you cariboocoot.
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