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Neville
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# Posted: 19 Nov 2011 09:25pm
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Hi,
We've lived off grid for several years and so know what to expect from solar electricity, but now find ourselves needing a tiny system to provide minimal electricity to a very small cabin in a subtropical location.
My desire is to keep the system small and simple. There is a risk of theft and I'd like not to be out a huge amount of cash.
I am considering a rollable unisolar panel either the 68W or 124W, a tiny backup generator (a honda eu1000i, 900W). I want to charge a 12V battery or two. Have an inverter for VAC. And be able to run the generator into the charge controller to top out the batteries.
This is to be used to power a couple led lightbulbs, charge phones, some rechargeable handtools and small water pump. Naturally not all at once!
Thoughts on a relatively inexpensive charge controller that fits the bill (I realize the choices may be different for the 2 different panels)? Inverter recommendations are welcome as well.
Been poring over the choices online and am more confused than ever.
Any info appreciated!
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CabinBuilder
Admin
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# Posted: 24 Nov 2011 11:56am - Edited by: CabinBuilder
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The basic formula is: A=W/V, i.e. Current(Amper) = Power(Watt) / Voltage(Volt).
In case of your solar panel setup, the charge controller's max current should be at least 120W / 12V = 10A.
However, I don't think this calculation applies to the case of charging batteries using generator (the battery's resistance would play a role).
Check these related discussions on charging battery with generator.
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MtnDon
Member
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# Posted: 24 Nov 2011 03:08pm
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Quoting: Neville ...be able to run the generator into the charge controller to top out the batteries.
The DC output on the Honda EU1000 is only 8 amps at 12 VDC. That is not very much current to charge even a single battery. If the battery has a rating of 105 amp-hours, common RV/Marine capacity, and if it was discharged to 50% ((105/2 = 52.5)) it would take over 6.5 hours to recharge the battery and that is not taking charging inefficiencies into account; nor the fact that the last 10% or so of recharging takes longer than the first. ((52.5 / 8 = 6.5625)) And Honda recommends that the generator be run with the Eco-throttle Off so that means running at full throttle all that time.
There would be no reason to run the generator DC output through a charge controller with such low a charge rate. It would probably just extend the time required.
If you can afford an MPPT charge controller go for one of those. Otherwise a standard PWM type will work. Match the maximum volts and amps from the panel and any future additional panels to be within the design parameters of the CC. Make allowance for cold weather high voltage; multiply the Voc rating of the PV module by 1.56 for a quick safe rule of thumb for the maximum voltage rating of the CC.
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razmichael
Member
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# Posted: 24 Nov 2011 05:59pm
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Adding to what MtnDon states, the generator 12v output is not for charging batteries - even the manual states this. Not to mention that you should be using a smart charger of some type if you want to keep your batteries happy. hard to really suggest an optimum system without going into a better analysis of how often you will be using it, how much sun you expect etc. My system (currently used with my trailer until I finally build the cabin) was designed based on my expected use and the easy transfer over to a cabin. You need to decide how to balance battery capacity with solar recharge capability based on what you expect to use, how often and how long you will be at the cabin and what type of sun light you get. My Components:
-2x6v Trojan T105 batteries for about 220 amp hrs
Xantrex hf1800 Inverter - provides a auto switch over if I plug it into a generator, 3 way charging, remote control panel and 120VAC for the rare times I need it (generally turned off),
30amp PWM charge controller - nothing special with basic features,
90W solar panel,
Assorted cables (big ones connecting the batteries to the inverter), distribution panels, fuses and switches.
The batteries provide more than enough power to get through four or five days - even including my wife using her hair dryer on occasion. Add the Solar Panel in and I have never needed the generator unless I want to charge things right up in a hurry or am using power tools for a major project.
The Inverter is not cheap but provides a number of the functions of the system in one appliance.
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Neville
Member
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# Posted: 26 Nov 2011 12:02am
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Sorry to be late in replying.
Thanks for all the info!
I wasn't planning on necessarily using the 12v output on the Honda eu1000i. Was just looking for a way to top off the batteries in rainy times.
Some inverters (such as our Outback) have an AC input that will allow for battery charging. We wired a plug into it and are able to charge via our generator or use generator power during higher demand applications.
razmichael, it sounds like your Xantrex has similar features. I wasn't sure if this was a common feature or not. At any rate I don't want an inverter as expensive as the one we currently have for this new system. Think I'm on the right track now.
Thanks again!
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Rob_O
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# Posted: 26 Nov 2011 12:28am
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Quoting: Neville Thoughts on a relatively inexpensive charge controller that fits the bill
You're going to spend $50-$60 to get *any* name brand charge controller. For about $100 you can get a Xantrex C35 that will allow you plenty of capability for future upgrades.
How much 120V power will you need? Everything you listed can be run on 12V
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