Bought an off-grid home last June, all PV electricity (major appliances propane). Need to increase capacity and replace mod. sine wave inverter with pure sine wave. I have already acquired additional panels to increase my array size 50% (these are 17V panels) and 24 new 12V AGM batteries for a much larger bank. The house is wired for both 12V (DC service panel supplied directly by batteries) and 120V supplied by inverter. My question is: would I be better off leaving everything wired 12 volt and getting the highest output 12V pure sine inverter I can find, or wire the panels and batteries in 24V series pairs for a 24V pure sine inverter? If I went 24V, how would I convert to 12V to supply the DC service panel and my 12V circuits? Thanks for your suggestions.

Go with 24 or 48 volts DC. The higher the voltage the lower the losses from heat. (I squared R losses)

What kind of Charge controller do you have? What is the total panel wattage?

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You are pretty much stuck with a 12 volt system unless you want to spend big bucks.

Option 1 is go to 24 or 48 volt battery system with an inverter to match. Then buy a 48 volt to 12 volt DC-to-DC converter. Problem is the converters are very expensive, and if we are talking about something more than say 100 to 200 watts does not exist and would be a custom manufacture meaning really big money.

Option 2 is same as option 1, except replace all your 12 volt gizmos to match the system voltage. Problem with that is most of the gizmos do not exist in 24 and 48 volt units.

Option 3 is probable the best option. go with a 24 or 48 volt system, get a larger inverter, scrap and replace all your 12 volt gizmos with 120 volt AC gizmos to run off the larger inverter.

I do have a couple of more ideas, but I have not and will not run the numbers so I am just throwing out the ideas as food for thought.

1. Build two systems. build one for the AC inverter and run the battery voltage at 24 or 48 volts. The second is a 12 volt battery system to run your 12 volt gizmos.

2. Is build one 24 or 48 volt inverter system. Then buy one of the high power 12 volt switch mode power supplies made for HAM radio operators and bench technicians. Run that off the inverter. They are available up to 12 volts at 50 amps or 600 watts.

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Dereck, PE, MSEE
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IMHO

Might be the best way to go. I like being able to turn the inverter off at night (or whenever not needed) and still have a 12v light to get around by.

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FWIW I would can the AGM battery idea because they cost several times more than their flooded lead acid Brother for a given specification. AGM is only justified in mobile applications where spillage or mounting orientation is an issue, or in extreme arctic cold temperatures. Otherwise they offer no advantage in stationary applications, and/or moderate climate conditions.

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Dereck, PE, MSEE
Moderator

Using AGM does have one advantage, no watering of batteries. This plus not having to vent them is why I used them.

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Um AGM batteries also have the advantage of being able to put them in the shack were your generator is and not have to worry about hydrogen gas popping off.

Gassing is not much of a problem unless your have batteries in a tightly sealed room or container with no ventilation.

AGM batteries are very expensive and best used in extreme cold, or when mounting orientation or spillage is a concern. Otherwise there is really no reason to use them unless you have money to burn.

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Dereck, PE, MSEE
Moderator

Great suggestion. I prefer doing all I can everywhere 12 volt. The biggest contributing factor to success with any of these systems is leaving the inverters off. You learn that quick living with one. Think of it as a running appliance.

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The generator shack where my batteries sit is fairly well ventilated and is not at all heated. Those batteries will see temperatures that are below zero on a regular basis in the winter.