Question I need help with

System
System Posts: 2,511 admin
in Off Grid Solar & Battery Systems #1
Ok, I have followed this forum for a long time and really appreciate the insight you guys provide. I have finally taken the plunge and am setting up a small system at my house.

My home is powered via the grid, but I am wanting to put up enough of a solar array to power some things in my man cave off grid (Probably around 1kw, but I want to leave some room to grow). I have everything figured out, but I don't know if I need to purchase a battery charger/generator or not?

I have the panels, charge controller, and batteries, but am confused as to what I need to look for in the inverter. Do I need to get an inverter/charger? Any help would be appreciated.

I have looked at the Xantrex ProWatt 2000, but I know it doesn't charge batteries so I don't know if it will meet my needs or not. To answer the question about why I don't grid tie, I want to do all the work myself and my power company requires contractors and UL products for grid tie.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #2
    Re: Question I need help with

    We'll say that you're basically experimenting with off-grid as a learning experience, okay? :D
    You've probably already learned how expensive it is. :cry:

    Now here's the thing: with utility power available, you would not need a generator for back-up of any kind. Sometimes you need a generator to back up the grid, but that's a different issue.

    Usually you design a system around the loads: maximum Watts used at any one time and total Watt hours used per day. That tells you how big an inverter you need and how big a battery bank is needed to power it. After that, the solar panels and charge controller are determine by the recharging needs of the battery bank. The final stage is where the generator comes in: what to do when the sun doesn't shine?

    Since your loads are basically "optional" and could be switched from inverter to grid there's no need for the generator. You may, however, want a battery charger so that the batteries are not left uncharged if the sun doesn't co-operate. It is never a good idea to leave batteries uncharged.

    Maybe we'd better start from the beginning with what you want to run and for how long?
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  • System2
    System2 Posts: 6,290 admin
    #3
    Re: Question I need help with

    Yes, this is certainly a learning experience. I know it isn't cost effective but I am learning a ton in the process and there is some value in that I suppose. Here is my plan, please critique it because I am a novice and need all the advice I can get.

    In the room I am going to try and power there are

    3 60W lights (18w really)
    TV which is a big one that pulls (230 W)
    Dish Box (75W)
    PS3 (194W)
    Laptop (50W)

    I have built a small turbine that handles my phone charger, shaver, and other small things.

    My array (home brewed) will consist of fifteen 60W panels plus whatever I generate from the turbine which won't be much because I don't live in a good wind area. I am thinking I will use a 12V system so I will wire the panels in parallel.

    For batteries I have some Napa Deep Cycle batteries that are 12v and rated at 200 AmpH that were given to me by the owner of our local Napa store since I do his taxes (I am a CPA).

    I believe I will need a 60 Amp Charge Controller since I will wire the panels in parallel.

    The inverter is whats got me confused a bit. I want to get one that will be big enough if I decide to expand a little, but since this is a learning experience more than anything I don't want to break the bank to get one. I have looked at the Xantrex ProWatt SW2000, which runs about $300 or so. Do you have any suggestions on an affordable inverter?
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #4
    Re: Question I need help with

    that is not a necessity to have an inverter/charger if you have a charger and just need an inverter. it doesn't hurt to get an inverter/charger though and keep the charger as a spare so to speak.
    totally up to you on that.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #5
    Re: Question I need help with

    I'll put some comments in bold within the quote.
    jrmarr wrote: »
    Yes, this is certainly a learning experience. I know it isn't cost effective but I am learning a ton in the process and there is some value in that I suppose. Here is my plan, please critique it because I am a novice and need all the advice I can get.

    In the room I am going to try and power there are

    3 60W lights (18w really) CFL's, right? They're usually 13 Watt for "60 Watt equivalent".
    TV which is a big one that pulls (230 W) If this is an LCD TV, put a Kill-A-Watt meter on it (about $30 and worth every penny) and see what happens when you change the display settings. I can take 100 Watts off my 42" Toshiba just by making that adjustment.
    Dish Box (75W)
    PS3 (194W)
    Laptop (50W)

    Maximum total: 703 Watts. So a 2000 Watt inverter would have plenty of "room to grow".

    I have built a small turbine that handles my phone charger, shaver, and other small things.

    My array (home brewed) will consist of fifteen 60W panels plus whatever I generate from the turbine which won't be much because I don't live in a good wind area. That is the #1 problem with wind turbines! I am thinking I will use a 12V system so I will wire the panels in parallel.

    15 * 60 Watts = 900 Watts. Normal efficiency derating of 77% leaves 693 Watts. That would recharge 488 Amp hours of battery - quite a lot, really. Nearly 3 kW hours worth. But you may have lower efficiency with homemade panels.

    For batteries I have some Napa Deep Cycle batteries that are 12v and rated at 200 AmpH that were given to me by the owner of our local Napa store since I do his taxes (I am a CPA).As above, about two in parallel, three could be managed. The rule-of-thumb charge rate is 5%-13% of the Amp hours, so 48 Amps could be used with up to 960 Amp hours (but I wouldn't recommend it).

    I believe I will need a 60 Amp Charge Controller since I will wire the panels in parallel.Yes, because your panels could put out 48+ Amps.

    The inverter is whats got me confused a bit. I want to get one that will be big enough if I decide to expand a little, but since this is a learning experience more than anything I don't want to break the bank to get one. I have looked at the Xantrex ProWatt SW2000, which runs about $300 or so. Do you have any suggestions on an affordable inverter?

    One caution: homemade panels have problems. You simply can not build a weather-proof panel that will stand up and perform as well a commercial panel. It's getting so they're not cost effective either.

    Fuses are essential. More than two panels in parallel and each should have a fuse on it. I don't know what the Isc of your homemade panels would be, or even the Vmp or Voc so it's hard to say what size fuses should be used.

    Probably the most inexpensive sine wave inverters available are the Samlex units: http://www.solar-electric.com/sasiwain1.html

    Again, no built-in charger so you have to consider that.
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  • System2
    System2 Posts: 6,290 admin
    #6
    Re: Question I need help with

    I completely understand the drawbacks to homemade panels. However, since I have the grid as a back up to my off grid setup, I plan on building a retractable awning to cover the array during bad weather. It may be tricky though because of the angle the array will be sitting. However, it will be fun coming up with a solution.

    Also, I don't expect the panels to hold up as long as commercial panels, but hopefully they can make it 5 years or so. Again, I am not doing this to save money. Rather, just to get my hands dirty and learn about the dynamics before spending the money required to do it the right way.

    I use Electricity for everything (heat/air, etc.) and with it only being 8.5 cents in my area it will be awhile before any alternative is cost effective. My biggest hope is that people in my community will see the turbine and panels and it will spark an interest in renewable energy.
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  • James
    James Solar Expert Posts: 250 ✭✭
    #7
    Re: Question I need help with

    Please keep in mind that the interest you spark may be that of your local inspector or neighbors that don't like the look of a wind genny. Sorry to sound negative, but it is a reality.
    Good luck with your project, it a great way to learn.
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  • blackswan555
    blackswan555 Solar Expert Posts: 246 ✭✭
    #8
    Re: Question I need help with
    3 60W lights (18w really)
    TV which is a big one that pulls (230 W)
    Dish Box (75W)
    PS3 (194W)
    Laptop (50W)

    Be a little careful with using watts, especially on CFL`s, Inverters work in VA (volts times amps) not watts, you have to take into consideration power factor,eg, Some CFL`s will use around double their watts,
    Do the VxA calculation (most things have it on) or measure with appropriate meter if you are using many inductive loads,

    Tim
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  • solarix
    solarix Solar Expert Posts: 713 ✭✭
    #9
    Re: Question I need help with

    I suggest the Xantrex PowerHub 1800. A nice package unit for powering your man cave. Comes with a built in box for housing your batteries, takes care of all the fusing stuff, and can be connected to your PV panels via your charge controller. It is msw though. I run my whole office on one like a big UPS. You should be able to find them online for under $750. Email me if you need some help.
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