Charging?

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System
System Posts: 2,511 admin
in Solar Beginners Corner #1
Noob question here -- is there a MPPT that will supplement battery charging with A/C power if there is not enough solar on a given day? I don't have a specific application at this point just wondering what would be the best way to handle keeping the batteries always ready.

Thanks
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,457 admin
    #2
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    Re: Charging?

    Not that I am aware of...

    Your couple of solutions:
    1. Get a good quality AC to DC battery charger/maintainer
    2. Get an Inverter/Charger--Basically acts like the electronics of a UPS. You just add the battery (and solar charger+panels if needed)
    There are other things you can do (AC vs DC gensets, Having a 24 or 48 volt battery bank and a second 12 volt battery bank; having a house and engine battery bank, etc.).

    Lots of options--But if you want to do it "right"--You really need to define your loads and needs; then look at what options will work best for you (most cost effective solution).

    Ideally, define your loads (watts peak, watt*hours per day). This defines the size of battery bank. Then you define solar panels + genset/AC backup charging to support the battery bank.

    And, conservation--It is almost always cheaper to conserve a watt than to generate a watt.

    A Kill-a-Watt meter is great for measuring simple AC loads. There are DC AH/WH meters too.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • System2
    System2 Posts: 6,290 admin
    #3
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    Re: Charging?

    So essentially you would connect the MPPT to the battery bank and additionally wire a AC to DC battery charger/maintainer too?

    At this point I'm considering this as a project to build up but in the back of my mind it would be nice to have a setup in place should a Florida storm roll through and I need quick emergency power for some essentials. As time and funds goes on I could add more batteries and panels...
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,457 admin
    #4
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    Re: Charging?

    Yes, you can parallel multiple battery chargers to one battery bank (several solar charge controllers, large AC battery charger, maintainer, etc.). They will not work in sync (one may stop charging before the other)--but that is not usually an issue (the "highest" voltage charger will "win").

    A big issue is your loads... If they are small, I would do it in this order:
    1. Honda eu2000i genset (~couple gallons of gas per day for lights and fridge--store 20 gallons with fuel stabilizer and change once a year--Or propane conversion genset for better fuel storage)
    2. Battery Bank + Inverter+AC battery charger or Inverter/Charger (sized to genset and loads)
    3. Solar Panels + Charge Controller
    It is actually pretty difficult to "grow" and off grid power system with respect to adding "power" (more batteries, more/larger inverters, etc.).

    Basically, a 1,200 watt peak power system can be done in 12 volts... Between 1,200 and 2,400 watt, you should look at 24 volt battery bank. And above ~2,400 watts, you should look at a 48 volt bank.

    As you increase bank voltage, you generally need new inverter and chargers.

    And mixing old+new batteries can be an issue (older batteries will fail and may take the other batteries down too). Mixing capacity/different brands/etc. is even more of an issue.

    Larger solar charge controllers (the expensive ones) are, many times, capable of 12/24/48 volt operation--so you can recycle those.

    Solar panels--The biggest issue tends to be trying to mix/match the correct Vmp/Imp panels together. Frequently, you cannot get matching panels (at a good price) a few years down the road--Many times, it is easier (and cheaper) to buy the best $$$/Watt solar panels and get a second charge controller to manage them (connect to the same battery bank).

    What ever you do--make a plan first. Buying stuff on sale, garage sale, etc. frequently does not save you any time or money in the long term (batteries age from the moment they are made--and need float charging or they will die in months, etc.).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • RandomJoe
    RandomJoe Solar Expert Posts: 472 ✭✭✭
    #5
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    Re: Charging?

    If you want an "integrated" system that will do all this, you can look at the Outback or Xantrex offerings (perhaps others?) - of course you will pay for those as well! :)

    In my case, I have the Outback system - charge controller, inverter, battery monitor and Mate interface. The Mate let me monitor and control all components of the system from one place. (Or can even be connected to a computer and that opens up a whole other world of possibilities.)

    I normally leave the charger turned off, and manually enable it when needed. Just a couple button pushes on the Mate. There are programmable limits so I can draw more current and charge faster when the system is plugged into the grid, or I can dial it down so it can run off my relatively small generator in an outage. The interface also lets you program other options - such as always charge if "grid/generator power" is available (just fire up the generator / plug into grid power and it starts charging), or even set some SOC limits and wire in a relay to the generator and it'll fire up the generator automatically to charge if needed.

    I went a different route and connected the Mate to a computer - now I can control the system from anywhere I can connect back to my home network! :) This also lets me implement much fancier programming and control strategies if I wish than the Mate has built-in.
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  • System2
    System2 Posts: 6,290 admin
    #6
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    Re: Charging?

    RandomJoe that is exactly what I want to do too. Is it the Outback VFX-3648 inverter/charger what actually allows the grid input?

    I do like BB's suggested approach too of figuring batteries/load, inverger, and grid charger. Once everything is going well then add the MPPT and panels. So can I use the Outback VFX-3648 inverter/charger with grid power to charge the batteries and later add the pannels?

    Thanks again
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,457 admin
    #7
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    Re: Charging?

    Yes, you can add solar panels + charge controller later.

    One thing to watch for--Some of the Outback inverters with AC input require very tight input frequency (grid frequency +/- 0.5 Hz or so) vs what you may need for a genset (+/- 5 Hz or so).

    A Honda or some other inverter/generator can be accurate enough to power those models of Outback Inverters--But regular AC gensets probably not.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • RandomJoe
    RandomJoe Solar Expert Posts: 472 ✭✭✭
    #8
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    Re: Charging?

    Yes, the VFX-3648 does the charging.

    BB mentioned the tight frequency requirements, that would be the grid-tie capable versions. I was tempted to get one "just in case" sometime in the future I wanted to go grid-tie, but they are very finicky about frequency and I knew I wanted to be able to use it with a generator.

    The non-gridtie versions (no "G" at the beginning of the model number) are more forgiving, as the input is actually intended to be used as a generator input.

    Yes, you can do what you want with the Outback system. In fact, if you want to start out with what is essentially a large-scale UPS, you can get just the inverter, batteries, and the Mate (it'll plug directly into the inverter). Wire them up and the inverter can keep the battery bank at full charge 24x7, passing power through to a subpanel that distributes power to your "backed up" loads. Then when the power goes out, the inverter immediately switches to battery and the items downstream never know anything happened!

    Then, when you are ready to add the solar, you get the charge controller and a hub (it isn't Ethernet, you need Outback's hub) and you plug in the inverter, Mate and charge controller to the hub so they can all talk to each other. Now you can set the inverter up so it doesn't use grid unless necessary. You can also get the FM-80 battery monitor, it gives you more detailed info on the state of the battery bank - again through the Mate interface.
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  • RandomJoe
    RandomJoe Solar Expert Posts: 472 ✭✭✭
    #9
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    Re: Charging?

    Thought I would add a bit...

    You ought to be able to do the same thing with Xantrex's system, I had solar from the beginning so didn't look for that. There may also be other systems available now, mine's been in for a few years now.

    The *primary* reason I chose Outback was because I could connect it to my computer and they offered a PDF of the communication protocol so I could write my own programs to interface with it. I actually had a slight preference for the Xantrex system at the time, but I couldn't get the comm protocol info. (As easily - I might have been able to get it if I signed an NDA, but no thanks.)

    Were I picking my equipment *now*, I'd really be interested in the Midnight Solar charge controller - again thanks to its communications capabilities. I haven't looked to see if they have the other pieces of the system or not. On the other hand, because it has so many comm options, I could also "integrate" the various pieces myself and might even enjoy that! :)

    But I do that sort of stuff for a living and a hobby! For most people, who aren't going to do such oddball things with their systems as I do, that probably isn't going to be a primary consideration. So definitely look closely at the various offerings and compare. Most (all?) have PDF downloads available of the installation, programming and operating manuals so you can get a pretty good idea what they are capable of and how flexible they are.
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  • bluewickedburner
    bluewickedburner Solar Expert Posts: 78 ✭✭✭✭
    #10
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    Re: Charging?

    Look at how some higher end motorhomes are setup, they already do this except for the solar component. You setup the genset for battery bank charge, any high draw loads you want to consider and the inverter/charger and genset all work in unison to keep power available regardless of loads and insure your battery bank doesn't get depleted.

    I'm going to install a Midnight controller and it will account for genset power generation.

    At that point, you don't even have to be there to think about it.

    For example, if I am somewhere it is hot and AC use is likely, that is one of the loads I set for auto gen start. AC thermostat detects temp threshold and sends a start signal to the genset and a delays the AC until the genset builds up power. When I plug into grid power, the genset is automatically disabled unless I start it manually in which case it disconnects the grid power or there is a gridpower failure in which case the inverter comes on automatically and the genset goes into loads monitoring and battery bank charge detection.

    No computer, just a single panel to set parameters.

    The Midnight charge controller I'm installing will get setup to monitor the genset source too.
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