Retrofit to Battery Back Up?

stoneunhenged
stoneunhenged Solar Expert Posts: 39 ✭
in Grid Tie and Grid Interactive Systems #1
My plan is to build a PV system that feeds into the grid but eventually add a battery back up system. How difficult would the retrofit be? What type of components should I buy now with the retrofit in mind? Thanks for your help.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #2
    Re: Retrofit to Battery Back Up?

    I'll suggest you look at SMA's Sunnboy GT inverters: http://www.solar-electric.com/smasugrtiein.html
    Then for battery back-up you can add their Sunny Island unit: http://www.solar-electric.com/suis5050waba.html

    Pricey, but designed to do just what you're after.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,439 admin
    #3
    Re: Retrofit to Battery Back Up?

    If you are going grid tied first, then hybrid later (with batteries)--You can either look at the Sunnyboy Marc suggested, or look at a pure GT inverter and later getting a XW or other Hybrid inverter that is compatible with your pure GT inverter (back feed the XW/Hybrid inverter to recharge your battery bank).

    I would be a little hesitent to make big plans this way... The hardware goes through an evolution about every 5-10 years--and it is possible that whatever you planned for today may not be available or totally different 5-10 years out.

    If you plans are closer in--You may want to save up and go Hybrid right out of the gate now. You probably will have more tax credits and rebates now than you will in five years.

    But--this is a big commitment. In general, if you are looking for emergency/backup power, a genset will probably cost you a lot less money and be easier to move from home to home (and just install a pure GT solar system for now--much cheaper and depending on where you live, you may actually save money).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Seven
    Seven Solar Expert Posts: 292 ✭✭
    #4
    Re: Retrofit to Battery Back Up?

    I went back and forth trying to find a way to do what you are talking about for two years. It is almost an impossible decision due to the nature of the lifecycle of electronics. Any way you go you will end up with some equipment you won't use down the road.
    My final decsion was to build an offgrid setup and get it operational and running a couple of rooms in my house. I will continue to buy panels with the gameplan being to get enough panels over the next couple/three years to do a hybrid system. This way I can buy the panels as money permits. As time passes my required number of panels can change so I am not locked in to a rigid layout. Once I get to the point I have the required panels, I will then look at the current batch of inverters to see what is worth buying.
    Getting similar panels is the most common problem of a long term build. They way my thinking goes is that my original panels for the offgrid setup could be used later in the tied setup if needed. The inverter,CC, and batteries can always take a different set of panels if I choose to keep them active, or they could be used to step down the hybrid batt bank and run a 12v or 24v sub system.
    Like said above, what you are actually going to do with the system will determine what is the best way for you to go.

    good luck!
    Seven.
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  • ggunn
    ggunn Solar Expert Posts: 1,973 ✭✭✭
    #5
    Re: Retrofit to Battery Back Up?
    stoneunhenged wrote: »
    My plan is to build a PV system that feeds into the grid but eventually add a battery back up system. How difficult would the retrofit be? What type of components should I buy now with the retrofit in mind? Thanks for your help.
    Unfortunately, a lot of the equipment requirements for the two different types of systems is different. Most grid tied inverters are built to handle high voltages from the PV array while inverters that deal with batteries are designed for low voltage input. Your best option may be to go with a SMA grid tied inverter (Sunny Boy) and add an SMA battery inverter (Sunny Island) and a protected loads panel later. It ain't cheap, though.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #6
    Re: Retrofit to Battery Back Up?

    "It ain't cheap, though."

    Boy is that ever right!

    But neither is buying a Xantrex MPPT80-600 which can take a high Voltage GT array and charge a battery bank, which would be another option (around $2,000 just for the controller & its associated bits).

    There's no cheap way to do solar and get good results. Every time someone tries to "save money" they end up on here saying "my system doesn't work: help!" :roll:
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  • Peter_V
    Peter_V Solar Expert Posts: 226 ✭✭✭
    #7
    Re: Retrofit to Battery Back Up?

    I assume this is to have backup power in case of a power outage?

    If so, then I'd recommend buying Enphase inverters and adding a cheap generator. The nature of Enphase micro inverters and cabling losses means that they work well with generators. When the sun is out the generator just idles and the inverters provide the bulk of your power. If the inverters are producing more power than you need they will shut down one at a time and regulate output power.

    Note: Enphase does not endorse using their inverters this way, but several people near me have tested this with no problems.

    The big problem with hybrid inverters, other than the large initial cost, is the cost of battery up keep. You waste power keeping the batteries charged up, you waste power going through the chargers/charge controllers, and even if you never use them you have to replace the batteries every few years as they die of old age.

    You can pick up a generator for substantially less than the cost of upgrading to a hybrid configuration and that's without including the cost of batteries.
    The cost of replacing your batteries every 5-6 years would buy a couple more generators.

    Unlike batteries, generators rarely die of old age when not being used.

    Oh yeah, if you're buying panels now and storing them for future use, I'd just save up the money instead. The price on PV panels has been plummeting lately, today they cost less than 1/2 of what they cost 2 years ago and it looks like they will drop even more.
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  • techntrek
    techntrek Solar Expert Posts: 1,372 ✭✭✭
    #8
    Re: Retrofit to Battery Back Up?
    Peter_V wrote: »
    If so, then I'd recommend buying Enphase inverters and adding a cheap generator. The nature of Enphase micro inverters and cabling losses means that they work well with generators. When the sun is out the generator just idles and the inverters provide the bulk of your power. If the inverters are producing more power than you need they will shut down one at a time and regulate output power.

    One problem with that is generators are very inefficient at idle, so you are wasting a lot of gas essentially duplicating the generating capacity.
    4.5 kw APC UPS powered by a Prius, 12 kw Generac, Honda EU3000is
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  • RCinFLA
    RCinFLA Solar Expert Posts: 1,484 ✭✭✭✭
    #9
    Re: Retrofit to Battery Back Up?
    Peter_V wrote: »
    If the inverters are producing more power than you need they will shut down one at a time and regulate output power.

    I have real doubts about this claim. The inverters would have to be shutting down based on overvoltage. Not a good way to run.

    Only an inverter/generator would likely provide suitable frequency stablity to even keep the GT inverters reliably on line.
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  • Blackcherry04
    Blackcherry04 Solar Expert Posts: 2,490 ✭✭✭
    #10
    Re: Retrofit to Battery Back Up?
    Peter_V wrote: »
    I assume this is to have backup power in case of a power outage?

    If so, then I'd recommend buying Enphase inverters and adding a cheap generator. The nature of Enphase micro inverters and cabling losses means that they work well with generators. When the sun is out the generator just idles and the inverters provide the bulk of your power. If the inverters are producing more power than you need they will shut down one at a time and regulate output power.

    Note: Enphase does not endorse using their inverters this way, but several people near me have tested this with no problems.

    The big problem with hybrid inverters, other than the large initial cost, is the cost of battery up keep. You waste power keeping the batteries charged up, you waste power going through the chargers/charge controllers, and even if you never use them you have to replace the batteries every few years as they die of old age.

    You can pick up a generator for substantially less than the cost of upgrading to a hybrid configuration and that's without including the cost of batteries.
    The cost of replacing your batteries every 5-6 years would buy a couple more generators.

    Unlike batteries, generators rarely die of old age when not being used.

    Oh yeah, if you're buying panels now and storing them for future use, I'd just save up the money instead. The price on PV panels has been plummeting lately, today they cost less than 1/2 of what they cost 2 years ago and it looks like they will drop even more.
    Please tell us more, with a little more detail. I'd like to give it a try. I am guessing you'd have to have 240 V / 60 hz reference voltage.
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