380watt 24V System.. does these components sound correct??

Re: 380watt 24V System.. does these components sound correct??

Welcome to the forum.

If you want to run a 12 Volt system with those panels you've got problems. First, you need an MPPT controller to down-convert the Voltage. Second, the MS 15 Amp won't work there. Fine for 24 Volt system, not for 12. Here's why: 15 Amps (output current limit of the controller) * 12 Volts = 180 Watts. So putting more than 200 Watts of panel on the input side is just wasting panel.

Realistically, for a 12 Volt system you'd be looking at about 24 Amps peak current from those panels through an MPPT controller. Which is good, but it means having to buy a bigger controller such as the Rogue http://www.roguepowertech.com/products/mpt3024.htm

Now the other thing is the amount of power that would be available. The panels would be capable of "harvesting" about 760 Watt hours AC per day, and would work well with a couple of golf cart batteries (6 Volt, 220 Amp hours wired for 12 Volt) and only 25% depth of discharge. You could go up to four but ... 24 Amps is only just 5% of 440 Amp hours and it would be very marginal for recharging, especially with loads drawing at the same time.

That 100 feet of M4 cable: is that 50 feet from the array to the controller? If so you are going to have problems with Voltage drop and will want to be able to wire the panels for higher Voltage to overcome this. Again that means MPPT controller, but it may also mean the Rogue is out if you have to put them all in series (exceeds the controller's input maximum). You may want to plan for bigger wire.

Fusing. If all panels are in series or there are only two parallel connections the array does not require fusing. The charge controller's output should be fused, as should the inverter's input. Can't say I'm keen on MSW inverters of any brand. Consider carefully what you plan to run on it before buying one. It could be a false economy. Samlex makes some fairly inexpensive sine wave inverters and Morningstar's 300W one is well loved by all its owners.

Once you get those details worked out and have the wire sized right you can pick the fuses. They really do have to be able to handle both the expected current and Voltage. 12 Volt systems have something of an advantage there, as many automotive/RV parts can be had for reasonable amounts of money.

Re: 380watt 24V System.. does these components sound correct??

ywhic wrote: »

So forgoing the 5 cu ft refrig.. and just say the 2 25w lights and 1 fan (12watts)..

What battery would be ideal with the 2 panel setup I outlined??

Would a single 12v battery be better than 2 6V batteries??

If you want to work it backwards ...
280 Watts of panel would support 180 Amp hours of 12 Volt battery. Possibly more if you use no daytime loads.
At a maximum that would be roughly 900 Watt hours AC, and that would be pushing things to the limit.

So two 25 Watt lights plus one 12 Watt fan is 62 Watts. Divide 900 by 62 and you get 14 hours of run time. And that's good because it means six hours of use per day is not an unreasonable expectation, provided you are willing to run your batteries close to 50% discharged.

If you have no more than 180 Amp hours of battery with the 280 Watts of panel you could probably run the laptop during the day without much loss of charging (based on 3 Amps @ 12 VDC).

It's all rather complicated and interconnected, isn't it?

Re: 380watt 24V System.. does these components sound correct??

Basically a 50% increase in array capacity is a 50% increase in power.

420 Watts would potentially yield:
420 * 77% efficiency / 12 Volts = 27 Amps, enough to support 270 Amp hours of 12 Volt battery. 810 Watt hours DC @ 25% DOD.
420 Watts * 4 hours equivalent good sun * 50% over-all system efficiency = 840 Watt hours AC per day. This is a pretty good balance.

Here's the problem, and it's a big one: if you keep adding panels in parallel to the array the amount of current the wire has to carry from the array to the controller goes up. So you run into this: 27 Amps @ 12 VDC over 30 feet requires 2 AWG wire to keep Voltage drop below 3%. If you price out that much 2 AWG wire you may instantly see the advantage in putting the money in an MPPT controller. I don't know how bad it is where you are, but around here it's very pricey.

I think you may have confused the 900 Watts running of the A/C and the 180 Amp hours of one of the battery choices with some of the power production figures. We've been tossing around a lot of numbers and configurations; it's pretty easy to get lost in them.

Re: 380watt 24V System.. does these components sound correct??

When using an MPPT controller you wire panels in series so that the Voltage goes up and the current goes down.
If we take the example of 18 Amps @ 12 Volts over 30 feet needing 4 AWG wire and up the Voltage to 24 thus lowering the current to 9 Amps the wire size changes to 10 AWG (both sizes chosen to keep V-drop under 3%).

You join them at the array, and send the higher Voltage down to the charge controller. That will lower the Voltage and increase the current. This is where you need to have the right controller, because their numbers are based on output current @ system Voltage. This means the 15 Amp Morningstar is not a good choice here, as you should be seeing current over its maximum output.

The Rogue 3024 is the probably the best in the low-power MPPT controllers. $325
The least expensive choice would be the Blue Sky SB2512i at $198, but naturally it has fewer features than the Rogue. You may find those features desirable. Blue Sky offers some add-ons and more advanced models, which of course increases the price.

Keep in mind that these have a maximum input Voltage around 60, which limits the total Voc of the array; you'd only be able to run two panels in series before you run the risk of exceeding the input maximum. But as noted above just going up to "24 Volts" (two in series, actual Vmp around 35) makes a big difference in the V-drop.