charge controller and inverter recomendations

10 Posts

May 30, 2008 07:58 am

I'm putting together a small'ish system, I already have panels, eight Mitsubishi 125 watt panels (17.3 max volts, 7.23 max amps). Keeping in mind my plan is to expand the system over time with the addition of more panels. I'm not interested in going grid-tie at this time, I know I'll have no problem using up the little bit of power I'll produce.
So I am looking for recomendations of charge controllers and inverters. How should I wire the panels? I wanted to just make one series string of 138.4 volts, but it looks like I would be limited on charge controllers that can handle that voltage. My hope is to add another 1000 watt string of panels next summer.
What if I can't get panels with the same specs or voltage? Would that be a problem? It would be nice to get a charge controller that would handle additional panels without having to add a second one or upgrading.
How big of a battery bank could I realistically charge? my thaught was eight 6 volt cart batteries, I know someone that can give me a good deal on some.
I'm not looking to supply all of my energy needs, just suppliment, I'm looking at this kinda like a new hobby...
Thank you in advance for any advice.

Thomas Allen Schmidt

679 Posts

May 31, 2008 12:44 pm

Re: charge controller and inverter recomendations

My first piece of advice would be to get ready to dig deep into those pockets of yours. If your are planning to seek any government incentives then plan on seeking a licensed electrical contractor because there will be permit(s) and inspection(s).

Something important here is to thoroughly and completely read and understand the specification sheets with any electrical device you are considering. Know there limits and ratings by UL standards. Familiarize yourself with the NEC, in particular Article 690.

http://photovoltaics.sandia.gov/docs/John_Wiles_Code_Corner.htm

The NEC gets "re-furbished" every three years, but the above site will "get your feet wet before the plunge" so to speak.

One thing you did not mention was, region.
Personally, to achieve, what I think you are wanting to achieve, I would install a back-up load center (breaker panel) and move those circuits I wished, from the existing panel to the back-up panel. For example; lights, refrigeration, communications, media, security. You will have to do a load calculation in order to size (spec. sheet) the inverter correctly. The inverter would be fed 120 vac from the existing grid fed panel by way of a dedicated circuit, it would then pass through the inverter to those back-up loads and maintain a charge on the battery. During a "black out," or you could turn that breaker off, the inverter would make 120 vac from the nominal vdc battery and send power only to those loads, not back onto the grid.
One example of the inverter you might be seeking could be the Xantrex 4048.
Oh man! I could go on and on with this stuff! I'll move on to the charge controller.
Again, read and understand those spec. sheets.
With the 1000 watt array you have and knowing you want to expand, you could look at the Out Back MX60. It would allow you to wire your PV modules at a much higher voltage (spec. sheet) while being able to charge at the battery banks nominal voltage.
The spec. sheets can be found at most RE dealers or the manufacturers web sites. Thats about it. Without more specific question, this is all I can tell you.

Thomas Allen Schmidt

679 Posts

May 31, 2008 01:08 pm

Re: charge controller and inverter recomendations

Oops! you wanted to know about batteries also.
Sizing for the future is a lot like forecasting the weather you know, but a "rule of thumb" for off grid systems that I go by is to size the anticipated load (and any future load) in watt hours or kilowatt hours then divide that by the battery banks anticipated nominal voltage. This will give you amp hours of capacity. Then multiply that by a factor of 5.
What your "connection" has is probably 220 amp hour batteries (spec. sheet) at 6 volts each. With 8 of them you could have; a 48 volt nominal bank at 220 amp hours or a, 24 volt bank at 440 amp hour or a, 12 volt bank at 880 amp hours.
Basically what amp hours means is, for example, it will supply 220 amps for one hour or 1 amp for 220 hours or any computation in between. Do you see the logic?
Something else to familiarize you with electrical calculations is Ohm's law. Basically volts times amps is watts and so on and so forth. If you like - http://www.elec-toolbox.com/main.html
I feel like one of the best investments I made when starting out was a subscription to the Homepower magazine.
Knowledge is power!

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charge controller and inverter recomendations

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