Charging setpoints for wind and solar

wrdaigle
wrdaigle Solar Expert Posts: 65 ✭✭✭✭
in Off Grid Solar & Battery Systems #1
I need a little advice regarding setting my battery charging setpoints for my wind generator and solar charger.

First things first, here are the specs on my batteries...I have 12 trojan L16H's configured for 24V. Each individual 6V battery is rated at 435AH at the 20-hr rate, so my total battery capacity is 1305AH. Based on the spec sheet from Trojan:
Daily Charge: 29.6V
Float: 26.4V
Equalize: 31.0V

Solar: I have 1500W of solar connected to an Outback MX60 charge controller. The manual for the charge controller says to defer the battery specs when setting setpoints, but it defaults to 2 hours absorb time and 2 hours float time.

Wind: This is where I start to get a bit confused. I have a Bergey XL.1 (1000W). By default, it has a "regulation voltage" set at 28.1. Any time the batteries reach 28.1, the wind turbine first tries to divert energy to a dump load. If no dump load is installed, or the voltage is still too high even with the dump, the wind generator slow's itself down so the voltage drops by 1.5V. The problem is, during the day, my batteries are almost always above 28.1V, so the generator is always trying to dump. I burnt up the dump circuitry last year due to this. I sent the controller back to Bergey and they suggested not hooking up the dump load since it will self-regulate even without it. To further complicate the issue, the equalization voltage for the wind generator is set to be 2V higher than the regulation voltage. The regulation voltage is the only thing that can be modified and the slow mode voltage (-1.5V) and equalization voltage (+2V) are relative to the regulation voltage. The manual says 28.1V "...is appropriate for flooded-cell lead-acid batteries. We do not recommend changing this setting unless you have a compelling reason to do so. Improper voltage regulation settings can lead to either undercharging and shorter battery life or over-charging and shorter battery life."

My dilema is, during the winter I don't quite have enough solar to get my batteries through a full 2-hour absorb cycle at 29.6V. My wind generator isn't helping since it's not allowed to charge above 28.1V outside of an equalize cycle. It seems like I should be able to coordinate my wind generator and solar charger a little better than this.

Here is my suggested solution:

Bergey Regulation Voltage: 29.0V
Bergey Slow Mode Voltage: 27.5V (1.5V less than regulation voltage)
Bergey Equalization Voltage: 31.0 (2.0V above regulation Voltage)

Solar Absorb Voltage: 28.9V
Solar Float Voltage: 26.6V
Solar Equalization Voltage: 30.9V

Here is my logic. In raising the regulation voltage for the Wind generator from 28.1V to 29.0V I would maximize the wind generator during and equalize cycle (i.e. 29V + 2V equals 31V). Lowering the solar absorb voltage to 28.9V would ensure that I'm maximizing the wind generator during the day to finish the float cycle.

My main concern is that I will still have the potential to overcharge my batteries if I have a really windy couple of days. Worst case scenario if the wind is blowing really hard is that the batteries cycle between 27.5V and 29V (i.e. everytime the batteries hit 29 volts, the wind generator will go into slow mode until the batteries are below 27.5V for more than 13 minutes). Seem problematic to anyone?

One more question: Any suggestions for how long to absorb, float and equalize. I don't really have a good energy meter, but I estimate the I use about 4000 watt/hours ( about 160 AH) each day. I'm not even sure if this is pertinent. If not, what factors would you use in determining these times?
· Share on Twitter

Comments

  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #2
    Re: Charging setpoints for wind and solar

    Oh boy; the problems of wind just go on and on.

    First of all, don't fixate on Equalization. That is not something you want to do on a regular basis. It is something Trojan recommends you do "as needed" by checking the specific gravity of the battery cells and look for discrepancies between them. More than 0.010 and you should consider running an equalization cycle.

    As far as Absorb time is concerned, your MX60 will "run up the clock" as it goes through the Bulk cycle. How long that takes is how long it will run the Absorb cycle, up to the time limit. The time limit can be extended up to 4 hours. I'd recommend you set it to the max and keep an eye on the current until you get a feel for your "average" Bulk time. As a general rule, bigger batteries need longer Absorb times. But the depth of discharge will also be a factor. The Float time is irrelevant, as it will maintain Float until it can't maintain Float due to lack of sunlight.

    As for setting the Bergey's controller, I'd set it at 29.6 - the same as the MX60's Absorb set point. I'd also make sure there's a dump load available just in case. I'm not sure how they wire this, but if done properly the load and its wiring should never burn out no matter how long it is "on" for.

    Even with these two charge sources together coming up with enough power to charge 1305 Amp hours of 24 Volt L16's is going to be tough. That would be up to 130 Amps @ 24 Volts, or about a 4kW array. 2500 Watts is going to be pretty slim for that much battery.
    · Share on Twitter
  • Seven
    Seven Solar Expert Posts: 292 ✭✭
    #3
    Re: Charging setpoints for wind and solar

    He only has 1500w of panel. My math shows that to be good for 40a.
    · Share on Twitter
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #4
    Re: Charging setpoints for wind and solar
    Seven wrote: »
    He only has 1500w of panel. My math shows that to be good for 40a.

    And a 1000 Watt Bergey. ;)

    The most you could expect from the 1500 Watts on a 24 Volt system would be about:
    1500 * 0.77 = 1155 / 24 = 48 Amps max.

    Like I said, even with the Bergey that's going to be far short of what that big battery bank wants.
    · Share on Twitter
  • wrdaigle
    wrdaigle Solar Expert Posts: 65 ✭✭✭✭
    #5
    Re: Charging setpoints for wind and solar

    Where does the calculation of 130A come from? Do you think I would be better off I removed a set of batteries from the bank? I inherited the system. The previous owners thought the solution to all their problems was just to add more batteries, so they kept adding to the bank. Hence, some of the batteries are in better shape than others.

    One way or the other, it doesn't sound like I have to worry too much about overcharging my batteries even if I bump up the regulation voltage on the Bergey.
    · Share on Twitter
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #6
    Re: Charging setpoints for wind and solar
    wrdaigle wrote: »
    The previous owners thought the solution to all their problems was just to add more batteries, so they kept adding to the bank.

    That is precisely the wrong thing to do. :grr

    The 130 Amps comes from Trojan's recommended peak charge current of 10% of the batteries' total Amp hours. In this case 1305 * 0.10 = 130 Amps. To get that at 24 Volts from solar: 130 * 24 = 3120 at 77% typical efficiency = 4052 Watts of array.

    Step 1: resize your battery bank to suit your actual needs. Charge and equalize all batteries until you find the best of the bunch. Then see how your solar compares to the new bank size.
    · Share on Twitter
  • Ralph Day
    Ralph Day Solar Expert Posts: 1,022 ✭✭✭✭
    #7
    Re: Charging setpoints for wind and solar

    I seldom bother adjusting the settings on my SWWP H80 wind turbine. For a dump load I have my MX60 AUX relay power a solid state 120vac relay to an outlet where an electric heater is plugged in. The "divert" response is faster with the MX relay than with the H80 controller...less voltage swings. Not sure how this would work with a Bergey. I'm still waiting for the 48volt Bergey 1kw turbine promised for release in 2003.

    Ralph
    · Share on Twitter
  • ChrisOlson
    ChrisOlson Banned Posts: 1,807 ✭✭
    #8
    Re: Charging setpoints for wind and solar
    wrdaigle wrote: »
    Here is my logic. In raising the regulation voltage for the Wind generator from 28.1V to 29.0V I would maximize the wind generator during and equalize cycle (i.e. 29V + 2V equals 31V). Lowering the solar absorb voltage to 28.9V would ensure that I'm maximizing the wind generator during the day to finish the float cycle.

    It's really hard to use wind power to properly charge batteries, no matter what you do. We depend on wind here more than solar because in the winter time we barely get 7 hours of daylight, and during those daylight hours we're lucky if we get 1 hour of sunshine on average from the middle of December to the middle of February.

    I gave up long ago on using wind turbines to try to bulk/absorption/float the bank because they either make way too much power, or not enough, to hold the voltage and amperage where it has to be to properly charge the bank. After having lived off-grid for almost a decade it's my opinion that you use wind power only to reduce the generator run time. In the ideal world the turbines will keep the bank from getting sacked during a "dry spell" of no sun so you don't have to run the gen. And they'll keep the bank up enough so that when the sun comes out the solar panels can take the bank to 100% SOC in one good day - again without running the gen.

    It's my opinion that off-grid wind turbines should not have any sort of voltage regulating scheme built into them. Just let them run flat out all the time and use auxiliary loading on your system that uses the excess power for water or space heating. And if they still make too much power on a good wind day and the auxiliary loads can't keep up, then shut them down.

    We use about 20-22 kWh per day in our home and on any average day our turbines meet the loads so our bank neither gets sacked, nor fully charged. If the sun comes out our Morningstar MPPT controllers handle proper charging of the bank and if the voltage (because of wind power) tends to want to go over the set points of the MPPT controllers, then I have a RD-1 that runs on 240 volt water heating elements in stages to use the excess so the MPPT controllers can do their thing to the bank.

    But I would not mess with the settings on your solar charge controller. It's the only thing besides the gen and inverter charger capable of properly charging your batteries. Set the turbine high enough so it doesn't interfere with what the solar controller does and use auxiliary loading (or "dump") to use the excess from wind. And whatever type of "dump" scheme you use make sure it doesn't pull the voltage down below the solar controller's set points for bulk and absorption charging.

    Edit: I wouldn't worry about float time too much. The batteries like to live at float. But if they make it thru the absorption stage and into float by the end of the day, that's usually "good enough". There's no set time that the batteries have to be floated, really, and they can go back to work after the absorption stage is done, without being floated at all, without having much of any adverse effect on battery life.
    --
    Chris
    · Share on Twitter
  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    #9
    Re: Charging setpoints for wind and solar

    Just as an editorial note, Chris, welcome to the forum. Your post is a Greg example of why this forum is so successful. Well written, informative , on topic and indeed unite useful. ( and backed up with a plethora of al world experience to boot!).

    I too second the notion that over worrying about float is a waste, in the real off grid world there is often a small load on the line all the time that prevents the ontroller from going into or remaining in float very much. I rely on the Tri metric to count AH/in AH/out to know where I am. I recommend to the OP that he get a good battery monitor.

    Thanks, keep in touch,

    Tony
    · Share on Twitter
  • ChrisOlson
    ChrisOlson Banned Posts: 1,807 ✭✭
    #10
    Re: Charging setpoints for wind and solar

    Thanks Tony. It seems when googling for information this forum pops up a lot and it usually has pretty good information and posts in it. So I thought I'd join and contribute what I know about, and hopefully learn what I don't know about (which is a lot more than I know about).

    That being said, when I see or hear about folks trying to maintain batteries with wind turbines, it concerns me a little. I'm somewhat of an expert on wind power, and in all my years of running off-grid turbines, I've yet to see one that can properly charge a battery bank. And that's no fault of most of the turbines - it's the wind. Even with a seemingly perfect installation, the wind is just simply not constant enough to extract power from it in the precisely regulated form that batteries require for charging.

    I always tell folks that if you live off grid and have only solar power and a backup gen, your batteries will live a long and happy life. If you live off grid and only have a wind turbine and backup gen, your backup gen will get a lot of hours on it every year, and your batteries will die an early death from not running the generator enough to properly charge them.
    --
    Chris
    · Share on Twitter
  • wrdaigle
    wrdaigle Solar Expert Posts: 65 ✭✭✭✭
    #11
    Re: Charging setpoints for wind and solar

    Thanks for all of your suggestions. I took all of them to heart. First, I plan to go do a good evaluation of my existing battery bank to find the best 8 batteries. This will give me ~800AH of capacity which should meet needs at least for the time being. Hopefully this will give my solar a better chance of getting the batteries through the absorb phase (particularly with a bit of help from the wind and/or backup generator). I realize the Bergey will never be the right tool for maintaining battery voltage. I would be satisfied if it could help with the bulk phase so the solar has a better chance of maintaining the absorb voltage during the middle of the day.

    I am also going to invest in a good meter. I do data management for a living, so it's driving me crazy not having access to the numbers. Right now I'm debating between a FlexnetDC and a Pentametric unit. Anyone have any experience/preferences or other recommendations?

    Once I get the dump load hooked up again, I will work on finding a good setpoint for the Bergey. If the sun's out and the wind is blowing, my batteries quickly rise above 28.1 which shuts the Bergey down. This just doesn't make sense to me.

    Luckily we live in a great location for both solar and wind. We're about 4 miles east of the Continental divide and live in a significant rain shadow. We only get 11" of rain per year, so cloudy/windless days are few and far between.
    · Share on Twitter
  • ChrisOlson
    ChrisOlson Banned Posts: 1,807 ✭✭
    #12
    Re: Charging setpoints for wind and solar
    wrdaigle wrote: »
    Right now I'm debating between a FlexnetDC and a Pentametric unit. Anyone have any experience/preferences or other recommendations?

    I only have experience with the Trimetric and it is a very good unit. I think the Pentametric does basically the same as the Trimetric with more bells and whistles.

    I know two different folks who have the Outback FLEXnet monitor and they both like it. I have no hands-on experience with it, other than looking at theirs. But it would seem to me that when you already have Outback equipment that the FLEXnet would be the logical choice.
    --
    Chris
    · Share on Twitter

Categories