Off grid system for remote cabin

Cariboocoot

Re: Off grid system for remote cabin

This is where I get lost, because wiring is second-nature to me. I can do it without thinking about it. Trying to explain it ...

Also, much of what you need to do will depend on your particular situation. The distance between components, for example, has a bearing on wire size: it has to be able to carry both the expected maximum continuous current and keep the Voltage drop acceptably minimal over the distance. Likewise circuit protection has to be size to suit the wiring & current.

The mechanical aspects of placement are another tangle. In some places you may want to use conduit, even though you don't have to meet code. It's about protecting exposed wiring from likely hazards. Then when you put wire in conduit its Ampacity rating goes down. Back to step #1 above!

You'll find you'll have to measure and place theoretically to begin with, maybe a few times. There are some limitations you can't get around: the array has to go here because that's where the sun is and the controller has to go here to keep it out of weather and that makes the distance between this much. Keeping batteries close to the inverter is necessary too (heaviest current flow & greatest Voltage drop problems).

There are four basic circuits involved, and they interact with each other:
1). Array to charge controller.
2). Charge controller to batteries.
3). Batteries to inverter.
4). Inverter to AC loads.

Each of these needs its wires sized according to the expected maximum continuous current and circuit protection accordingly (the NEC rule of current * 1.25 * 1.25 if no other specs are given by the manufacturer).

One good thing: just about every component you can think of has a manual available on-line. You can actually read through the installation manuals for inverter and charge controller before you even buy them and know what you're getting in to.

Photowhit

Re: Off grid system for remote cabin

There are some odd things you can choose to ignore if you have no inspection. DC wiring must be in conduit to the battery box. All accessable wire(under 10 feet high, running 30V or more,) must be in conduit, so if you have a ground mount array you have to fence it or run wire in conduit, which there aren't many panels with this provision any more.

Caveman

Re: Off grid system for remote cabin

I went with more of a scaled down system, with the plan to fire up the generator for times of higher demand. I've got most if not all of the equipment, but I haven't purchased any wiring, fuses, or connectors or anything. The PV panels are going to have to be 60' from the batteries, (I intend to build a compartment under the cabin for all the batteries, controller, etc.) and the batteries will have to be about 40' to the AC service panel. Anyone able to help me with wire size? I know the DC wiring is a different animal from the AC.

BB.

Re: Off grid system for remote cabin

AC or DC does not matter too much for our scale of systems... Volts, Amps, Resistance pretty much. The issue is usually DC may be 12-48 volt batteries vs 120-240 VAC for line power... About 10x the voltage and 1/10 th current for AC vs DC comparison (and this has confused more than a couple of licensed electricians on their first solar power installs who end up using to small of wire for an installation).

I use a simple voltage drop calculator and look at 1% to 3% wiring drop typically... But it really depends about what section of the system you are talking about (voltage drop is not as series an issue for wire from panels to charge controller--The drop from charge controller to battery bank should be very low to ensure the controller is measuring the "correct" battery voltage during charging, etc.).

What we really need to know is the Array specifications (how many panels, Vmp/Imp of the panels), brand/model of solar charge controller, battery bank voltage/AH/configuration, Inverter Brand/model/ratings, distances for each wire run, etc.

Regarding battery installation--make sure it is easy to get too... You will want to check the batteries physically every week or month (electrolyte levels, state of charge, corrosion, current balance if parallel strings, voltage readings of cells/batteries, etc... Basically looking for anything "going wrong" before something is permanently damaged.

-Bill

Caveman

Re: Off grid system for remote cabin

Here are the array specs
- 2 panels (12V 140 watt each)
- 2 6V golf cart batteries

Morning star Pro star 30 controller
Exel Tech XPX inverter

All the components and the batteries will be in a small cabinet with the cable runs being pretty short. I was planning on installing all the components right next to each other.

Cariboocoot

Re: Off grid system for remote cabin

Caveman wrote: »

Here are the array specs
- 2 panels (12V 140 watt each)
- 2 6V golf cart batteries

Morning star Pro star 30 controller
Exel Tech XPX inverter

All the components and the batteries will be in a small cabinet with the cable runs being pretty short. I was planning on installing all the components right next to each other.

Well those panels are likely 17.5 Vmp @ 8 Imp or close, so the most current you'll see to the batteries would be 16 Amps. Fairly easy to handle over short distances. The MS 30 controller is somewhat overkill unless you're planning on adding more panels later. If so, wire for the higher current now; it will save rewiring later.

That's just enough panel for recharging those batteries, btw. Could be a tad slim. As long as this is not a vital system or you have a back-up charging method (generator or grid plus charger) it should be okay. Golf cart batteries tend to be around 220 Amp hours +/-.

Exeltech makes all sorts of variations on their inverters. You'll need their specs on maximum current draw for the particular model you get to plan the wiring and fuse for it.

BB.

Re: Off grid system for remote cabin

Caveman wrote: »

Here are the array specs
- 2 panels (12V 140 watt each)

I guess those are Vmp~17.5 to 18.6 volt panels or so

- 2 6V golf cart batteries

Probably around 225 AH @ 6 volts each. Put together in parallel, 12 volts @ 225 AH

My equation for the range of battery bank that would work with a 5% to 13% rate of charge solar array:

• 2*140 Watt panels * 0.77 panel+controller deratings * 1/14.5 volt bat charging * 1/0.05 rate of charge = 297 AmpHour @ 12 volt battery bank maximum
• 2*140 Watt panels * 0.77 panel+controller deratings * 1/14.5 volt bat charging * 1/0.10 rate of charge = 149 AmpHour @ 12 volt battery bank nominal

• 2*140 Watt panels * 0.77 panel+controller deratings * 1/14.5 volt bat charging * 1/0.13 rate of charge = 114 AmpHour @ 12 volt battery bank minimum (cost effective vs array size)

Morning star Pro star 30 controller

Should be fine... Keep wire run from solar array to battery bank short and heavy (use a voltage drop calculator for 1% to 3% voltage drop maximum suggested).

Exel Tech XPX inverter

What size inverter? My suggestion for inverter sizing would be based on C/8 for continuous discharge and C/2.5 for maximum surge power:

• 12 volt * 225 AH * 0.85 inverter eff * 1/8 rate of discharge = 267 watts at 120 VAC max continuous
• 12 volt * 225 AH * 0.85 inverter eff * 1/2.5 rate of discharge = 918 watts at 120 VAC max starting surge

Note that AC inverters have a fairly large standby power draw (typically ~6-12 watts for the smaller inverters--So you should have a DC power on/off switch for the AC inverter power.

All the components and the batteries will be in a small cabinet with the cable runs being pretty short. I was planning on installing all the components right next to each other.

Keep good ventilation--All electronics will last longer if they are keep cool and from excess temperature swings/thermal cycling.

-Bill

Caveman

Re: Off grid system for remote cabin

Don't know why i missed this before, but here are the inverter specs:

Excel Tech XPX-1-1-6-1 ( 100703)

DC 12V (sys) 171 A @ 13.8V (nom)
AC 117V 17.1 A 60 Hz

That's what the label says on the side.
Here is my dilemma, the cabin is very shaded by large trees and I would like to keep it that way. The closest sunny area is at a detached deck I built about 60 feet away. It would be very convenient to mount the panels on the side of the deck (facing south). The deck is on a steep slope, so the downhill side has plenty of room for my 2 panels and more if need be. So far my plan has been to build the panels on a hinged framework to get the benefit of the sun's angle during the different seasons. Up until now I have been planning on building a little platform underneath the cabin and have kind of a "power control center" there Now I am gathering that there could be a problem with the 60' run from the panel to the batteries. I could build a little room underneath the deck, there's plenty of room for it. So it sounds like the better setup would be to have my "power control center" out underneath the deck, keeping my wiring to the batteries short, and also have the inverter out at the deck, and then I could run AC wiring to the cabin (I was thinking maybe 10/2 all the way to my main service panel). Any suggestions? Or am I going about this all wrong?
Thanks for all the help so far.

Cariboocoot

Re: Off grid system for remote cabin

There would definitely be a problem getting 16 Amps @ 12 VDC from the panels through 60 feet of wire to the charge controller. It would require 2 AWG wire to keep the V-drop below 3%. Pretty nasty expense.

Building a power box with the controller, batteries, and inverter in it out where the panels will be (or somewhere along the way) and running the 120 VAC across the 60' distance to the cabin would work. You could do that with 10 or 12 AWG wire on the AC run.

BB.

Re: Off grid system for remote cabin

Your other option is to run the panels in series... The higher Vmp-array you can get, the smaller gauge wire you need.

For higher end MPPT charge controllers, they can run Vmp-array upward of 100 VDC (or even more for a few controllers).

So--it is a trade off. More money on copper wire, more money on charge controller, or having battery+equipment in cabin (security/heated environment in winter/easier to maintain batteries/allows use of DC power directly for lighting, car type electronics, etc.) for easy access vs 60' away in clearing.

If your system stays small, it might be better to keep everything at the array and just run 120 VAC wire back to the cabin.

The downside is that you probably want to turn the DC power to the inverter on and off--Even smaller inverters draw around 6 watts just on and idling. Trudging back and forth to the remote power station is going to be a pain for the longer term.

One option would be to change from the Exel inverter to the MorningStar 300 watt 12 volt TSW Inverter (600 watt 10 minute surge). It has both power save mode (search mode--pulse 120 VAC once a second to look for >6 watt loads) and a remote on/off switch (12 volt pair of signal wires you can attach a small on/off switch to). The MorningStar is probably the best 12 volt inverter out there right now because of relatively low price, rugged construction, and the power control options.

If you will be going with a larger system eventually, then go with the MPPT charge controller and higher voltage Vmp-array. And install the battery bank/power system in/under/next to the cabin (remembering batteries do out gas hydrogen and electrolyte fumes, and wire up for safety with fuse/breaker/etc. as needed--And I like to recommend sheet rock/concrete backer board for some additional fire proofing on walls and wood subfloors in case things go pear shaped).

-Bill

Caveman

Re: Off grid system for remote cabin

Thanks guys, I've got the generator side of the system up and running, with a manual transfer switch. I plan to use the generator to charge the batteries when needed.

If I run the panels in series, what size wire will I need to run the 60' from my panels to the cabin?

Looks like I bought way too much inverter, mine is the Exceltech XP 2000 watt. Ugg, ignorance strikes again.

I see what you are getting at with the maintenance hassle of a remote system, and the options for expansion, some things i'll be considering.

BB.

Re: Off grid system for remote cabin

You have a very good inverter--It is just so easy/cheap to buy a "big inverter" but then get into a money pit to support it with lots of battery bank, heavy cabling, and lots of solar array.

Lets go back to two x 6 volt 220 AH golf cart batteries--2-4 of those batteries are hard to ignore as cheap/reliable batteries for a first time system.

We start with a 5% to 13% rule of thumb for battery charging (good life, quicker battery charging). So picking 10% rate of charge (nice round number and good rate of charge):

• 12 volts * 220 AH * 1/0.77 panel+controller derating * 0.10 rate of charge = 343 watts of solar panel

Using the "Cheapskate" $$$/Watt listing from our host:

2x Kyocera KD215GX-LFBS panels is a nice price ($1.36 per watt + shipping--don't forget shipping+handling to your front door--different panels/suppliers can dramatically affect the delivered price).

[TABLE]
[TR]
[TD]Max Rated Power (Pmax)[/TD]
 		[TD]215 Watts[/TD]
 	[/TR]
 	[TR]
 		[TD]Voltage at Max Power (Vmp)[/TD]
 		[TD]26.6[/TD]
 	[/TR]
 	[TR]
 		[TD]Current at Max Power (Imp)[/TD]
 		[TD]8.09 Amps[/TD]
 	[/TR]
 	[TR]
 		[TD]Open Circuit Voltage (Voc)[/TD]
 		[TD]33.2[/TD]
 	[/TR]
 	[TR]
 		[TD]Short Circuit Current (Isc)[/TD]
 		[TD]8.78 Amps[/TD]
 	[/TR]
 	[TR]
 		[TD]Length x Width x Depth (inches)[/TD]
 		[TD]59.06 x 38.98 x 1.8[/TD]
 	[/TR]
 	[TR]
 		[TD]Weight of Panel (Pounds)[/TD]
 		[TD]39.7[/TD]
 	[/TR]
 	[TR]
 		[TD]Connector Cable Type[/TD]
 		[TD]MC4 Latching Cables[/TD]
[/TR]
[/TABLE]

So--two of those in series would be ~Vmp-array=53.2 volts and 8.09 amps

Using a generic voltage drop calculator and playing with numbers (3% of 53.2 volt drop = 1.6 volt max; 1% drop would be 0.5 volt drop):

• 60 foot one way run, 8.09 amps => 10 awg + 1.2 volt drop
• 60 foot one way run, 8.09 amps => 6 awg + 0.5 volt drop

Either of those wire gauges will give you a satisfactory system with a 430 watt array.

Rogue is coming out with a new MPPT charge controller--We have to wait and see if Marc will have a good solution/price point for this system (March?).

Otherwise, you are looking at:

Morningstar TriStar 45 amp MPPT Solar Charge Controller for $410 + options (LCD Meter, remote bat temp sensor, etc).

Or for a much larger/more features at $400-$600+ for the Midnite Classic series.

I always like to push the Battery Monitor (like the Trimetric or similar) as a great way to monitor a battery bank for spouse/kids/guests who you don't want taking specific gravity readings from your bank...

Good thing this is not my money. Hope this helps (information is a "starting" point--You are welcome to adjust, change vendors/suppliers/etc. to better meet your needs...).

-Bill

Caveman

Re: Off grid system for remote cabin

Yes it does help, and thanks again, but I'm still not clear (bear with me) if I should try to return my inverter for a smaller one or if this one will work with the stuff i bought. I already purchased the panels, controller, and batteries as well.

I was planning on making this a 12V system, if I install the panels in series, will it be a 24V system?

BB.

Re: Off grid system for remote cabin

Caveman wrote: »

Yes it does help, and thanks again, but I'm still not clear (bear with me) if I should try to return my inverter for a smaller one or if this one will work with the stuff i bought. I already purchased the panels, controller, and batteries as well.

Larger inverters consume more power when operated at light loads (i.e., 10-20 watts just "turned on"). If you can use a 300 watt TS Inverter (600 watt surge), the MorningStar is hard to beat... Plus it has the remote on/off and "search mode" to reduce power usage without spending a lot of extra money on large DC switches, etc.

If you need more power, then the larger inverter is nice (run a refrigerator)--But then you are looking at a larger battery bank--Which then means a larger solar array--And then a larger charge controller--And then a larger backup battery charger+genset, etc...

It is a vicious circle. So, based on what you know now--How much power (watts, Watt*Hours per day, etc.) do you want to run (from batteries/inverter). That will drive the rest of the equipment and make your choices more obvious (probably not ea$ier).

I was planning on making this a 12V system, if I install the panels in series, will it be a 24V system?

PWM charge controller are "simple" on/off switches. If you run a "24 array" (really ~Vmp=35 volts) through a PWM controller into a 12 volt battery bank, you will be "wasting" 1/2 the energy from the solar array. (current into the controller=current out of the controller).

MPPT charge controllers are "DC Power Down Converters"... Usually built around a DC Buck Mode Switching Power Supply (think the DC equivalent of a variable AC transformer). Power IN = Power out. For example:

• 2*140 watt panels = 280 watts = 17.5 volts * 16 Amps = 35 volts * 8 amps = 14.5 volts * 19.3 amps Batt Charging

Of course, the MPPT charge controller is only ~95% efficient, and solar panels only output around 81% of rated power, so the output will be less than name plate ratings.

For a first approximation, with a MPPT charge controller, you could put the two panels in parallel (Vmp=17.5 volts) or in series (Vmp=35 volts). And the battery bank will see the same charging current (power).

The difference is the current in the 60' of wire going to the solar array/charge controller will be 1/2 also--Allow you to use smaller gauge wire to carry the power.

If you can use your existing Inverter and PWM charge controller--We have to get back to the loads you want to power, and your expectations.

To send 16 amps 60' with less than 0.5 volt drop (Vmp=17.5 volts), would require around 3 awg.

To send 8 amps 60' with less than 1.0 volt drop (Vmp=35 volts) would require around 8 awg wire (~0.7 volt drop).

-Bill