Off-grid 24V system advice for newbee

Re: Off-grid 24V system advice for newbee

Welcome to the forum.

1). The size of the inverter governs the maximum load you can handle at any given time. Whereas there's nothing wrong with the Magnum 4kW unit, do you need that capacity? I run a refrigerator and two water pumps and, and, and ... most of the time my 3.5 kW Outback churns less than 500 Watts of power. The capacity is there for the motor start surges.

2). Your suspicion on the panels is correct: 30.1 Vmp is not going to work on a 24 Volt system. Given heat & wiring losses, the Voltage at the battery may well be below 28.8 which would be insufficient for charging. If you use flooded batteries EQ would be out of the question, as that is usually done at 31 Volts.

3). Have you got an actual Watt hour capacity in mind? If you can define your loads better to begin with it makes it much easier to calculate battery bank size and the amount of panel needed to recharge same. The four 380 Amp hour 6 Volts you have now would provide over 4 kW hours maximum, and that's nearly twice what I use. 760 Amp hours would require either an 80 Amp controller or two smaller ones. Maybe you'd like to stay with the existing controller if possible?

To that end, for the 380 Amp hour batteries you'd probably want an array of about 1200 Watts. The 760 Amp hours would want twice that. Also, if the first set of batteries is more than a year old you won't want to be adding new ones to it; they'll just get "dragged down" by the already aged batteries.

The 24 Volt system is a good idea. Depending on what kind of loads you've got and panels for recharging you may not have to add too much to your existing system. Mine runs on 320 Amp hours, but is getting an upgrade this year due to certain people not following instructions when they're there on their own.

Re: Off-grid 24V system advice for newbee

So you are building an entirely new 24 Volt system?

This Magnum http://www.solar-electric.com/maenms4040wa.html uses 25 Watts "running". This power consumption needs to be included with your calculations.

The search or stand-by mode is not necessarily a big power savings. I don't bother with it on my Outback because the 'frige runs 1/3 of the time (20 minutes out of every hour). During daylight hours it needs to be on all the time to supply the computer equipment, and into the evening for lights. Overall the difference works out to something like 10 Amp hours per day.

Coming up with the Watt hours used daily will be a big help. My system runs approximately 2.4 kW hours per day. This is roughly 100 Amp hours on 24 Volts, and 320 Amp hours gives me a 33% DOD. The plan for this year is to push that to 450 Amp hours, just in case.