off grid cabin/ home

wellbuilt

Re: off grid cabin/ home

Hi bill thanks for the reply , Im going to go with the 4/ 250 watt panels and the kid for the solar side of things .
Can I just run 2 panels in series and 2 parallel strings with out a combiner box or breaker of some kind ? What type of switch or breaker between the CC and the battery bank .

My new house will be off grid for 10 year +- after it is done , and I wanted to run a 48 volt system with 2 kids and 12 250watt panels .
Can I link 3 kid CC together for more power ?

Im guess The battery bank will need breakers on the + and - side
And breakers on the charger +
Im thinking about a samalex inverter 600watt to run a chest frig and other small loads .
I will need a 24v to 12v converter at 10 amps to run my 3.5 amp heater 5 15watt lights, radio

What do you think about charging , will a iota 24v 25 amp charger work for my 4 215 AH battery now ,
and latter on a 48volt system in my new home , if I add another 25amp iota @ 24 volts .
I would use the 2 iota chargers for back up , with a outback 48 volt inverter charger as the main power supply.
Thanks bill

BB.

Re: off grid cabin/ home

wellbuilt wrote: »

Hi bill thanks for the reply , Im going to go with the 4/ 250 watt panels and the kid for the solar side of things .
Can I just run 2 panels in series and 2 parallel strings with out a combiner box or breaker of some kind ? What type of switch or breaker between the CC and the battery bank .

You do not need a combiner box/fuses/breakers with just two parallel strings. Many people do like to put some sort of switch/combiner box on the array to allow easier servicing/debugging (if needed--Can turn off power during the day, shut down one string to debug wiring/panel problems).

The wiring should be sized to ~1.56 * Imp of the array, minimum.

Depending on the size/configuration of the array and the distance from the array to the charge controller/battery bank, to obtain a maximum of 3% to 1% of voltage drop may require a larger diameter cable.

And there is the whole planning ahead. Do you want to run heavy enough/extra wire for future expansion and/or bury larger diameter conduit or several in parallel (one trench, several conduits for future expansion)?

My new house will be off grid for 10 year +- after it is done , and I wanted to run a 48 volt system with 2 kids and 12 250watt panels .
Can I link 3 kid CC together for more power ?

12 * 250 Watts * 0.77 panel+controller derating * 1/59 volts charging = 39 amp minimum charge controller.

So, 2*30 amp rated MPPT charge controllers should be fine. If you ever plan in enlarging the array--A single larger controller would be nice.

Im guess The battery bank will need breakers on the + and - side

Yes--It is a good idea. The size of the main breaker(s) from the battery bank will depend on configuration (one or several parallel strings) and the maximum expected continuous current (AC inverter+loads, or charging current, etc.).

And breakers on the charger +

Generally, every + cable that leaves the common battery bus should be sized for 1.25x expected continuous loads (minimum) and for a minimum of 60 VDC. There are fuses and breakers that will work well--Fuses can be cheaper and smaller, but many times using circuit breakers is nicer--Both an On/Off switch and simple to reset the system after a short/overload (rather than having to replace blown fuses).

Im thinking about a samalex inverter 600watt to run a chest frig and other small loads .

If you are using a "standard" 120 VAC compressor on a refrigerator and/or freezer--600 Watts may be too small. If you are using a modern energy star refrigerator (frost free), you may need closer to 1,200 to 1,500 watts minimum.

I will need a 24v to 12v converter at 10 amps to run my 3.5 amp heater 5 15watt lights, radio

Assuming you get a larger AC inverter--You might want to look at 120 VAC LED lighting. It is much easier to send the power longer distances (vs 12 volts) and the 120 VAC bulbs may be less expensive than 12 VDC LED lamps (although, the 12 VDC/VAC MR 16 lamps have been popular).

If you already have the 120 VAC inverter--You can just run the lighting from it too. Overall, just about as efficient (inverter vs 24:12 VDC converters have similar losses).

What do you think about charging , will a iota 24v 25 amp charger work for my 4 215 AH battery now ,

That may be just small enough to be plugged into a Honda eu2000i (1,600 watt) genset (I like to keep smaller gensets to keep fuel usage "reasonable").

and latter on a 48volt system in my new home , if I add another 25amp iota @ 24 volts .

It can be difficult to "expand" systems over time--Often, it is better just to start out from scratch with a new system. About the only items that can be transferred with an upgrade are the solar panels (sometimes) and the higher end MPPT type charge controllers (12/24/48 volts). Everything else--either keep the older system as a spare or for powering a guest house, or sell the old components.

I would use the 2 iota chargers for back up , with a outback 48 volt inverter charger as the main power supply.

Yes, you can put two 24 volt chargers in series on a 48 volt battery bank--But it is usually not worth the wiring/fusing issues and can cause issues if one of the AC Chargers fails and you don't notice the failure (charge only 1/2 the 48 volt battery bank).

-Bill

wellbuilt

Re: off grid cabin/ home

hi bill , my panels will be mounted on a 12x16 deck roof in front of a travel trailer with only 10' of wire to the CC and maybe 10 feet to the battery bank .

The trailer/deck will be junked when the house is built .

The chest frig ive been testing dosent surge more then 557 watts It is a 4'wide unit from Home depot, I only gave 140 bucks for it because it was a floor model .
The unit im looking at for the trailer is the same , but half the size 30" wide 34" tall .
At 557 watts I was thinking the 600watt inverter should work NO ?

I could get the 1000 watt if it would be better.

Im planning to wire all my 12v loads to my battery bank with a new panel to test the converter , would this be a good test .
What about lightning , I would hate to get fried .
I lived on a sail boat , for what it was worth we would hang heavy chain off the rigging to ground the boat to the water.
We just hope for the best , Ive seen a few people get hit , but mostly they had electrical problems with out real boat damage .
I have trees around me but im still exposed .
My well guy called and he is planning to drill my well next week , I hope it happens some water would be nice .
Thank bill

BB.

Re: off grid cabin/ home

600 Watt inverter may work. It is close, and I really don't have any better data. Perhaps somebody else here can help. How did you measure the surge power/current? You really need a current clamp meter that has peak detect/hold. Most meters are not fast enough, and peak Watts is not really the issue but peak VA (volt amps)--Because of the inductive nature of AC motors, they draw more VA than Watts, especially when starting (AC current is "out of phase" with AC voltage--The inverter needs to supply the current or VA. VA is always equal too or larger than Watts).

Power = VA * Power Factor (which is typically around 0.6 to 0.8 or so for induction motors).

Much of the issue with 12 volts is sending the power any distance. You have about 0.5 to 1.0 of voltage drop to work with (perhaps a little more since you are using a DC to DC converter and not a "real" 12 volt battery bank that will drop voltage as the battery discharges).

Using a generic voltage drop calculator, 14 awg wire will carry 10 amps about 10 feet with 0.6 volt drop. At 120 VAC and 1 amp, you can go ~300 feet with ~1.8 volt drop.

Lightning protection--Are you going to drive a 10' ground rod or two?

And with all the trees in the area, is the solar array going to be free of shade most of the day? Any shading will kill much/most of the array output. Electrical solar panels just do not work well with ANY shading.

-Bill

Alaska Man

Re: off grid cabin/ home

I don't mean to thread jack here, but I need to ask BB, why is that when you derate (Pane+Controller) you (* 1/0.77)? Wouldn't that make it 1 X larger before accounting for the inefficencies. I used your formula ( Thank You by the way) to figure an array size, but was a bit confused about that particular function.

BB.

Re: off grid cabin/ home

Alaska Guy.

The 77% eff:

• 0.81 panel derating (hot under sun, dust on panels, etc.) * 0.95 MPPT Controller+wiring efficiency = 0.77

The reason I use * 1/0.77 vs *1.2987 -- I am both lazy--I only have to remember 0.77 derating number vs also remembering/using *1.30 and explaining it is the inverse of 77% efficiency (1/efficiency = inefficiency ??? or call it 1/derating = over-rating ???).

Also when you look the equations with their "native values", it is easier to see how "adjusting" a value can affect the other all end results:

• 30 amps controller * 1/0.77 panel+controller derating * 29 volts charging = 1,130 Watt array

Looking at the maximum array size--Increasing controller current or battery voltage will increase the array size. Having a more efficient panel (colder weather) or more efficient controller (0.77 vs 0.80 derating), you don't need as large of solar array.

Is this your question?

-Bill

BB.

Re: off grid cabin/ home

There is also the difference between how how a MPPT controller and a PWM controller works...

A MPPT controller is a constant power converter: Power In * Efficiency = Power Out

A PWM controller is a simple On/Off switch that only takes the Imp-array in = Ibattery out (with very little losses).

It turns out, that if you do the Vmp of the panel (12 volt panel with Vmp~17.5 volts) and a typical battery charging voltage:

14.0 volts average charging / 17.5 volt array = 0.80 -- Add a little dust and such--And the two types of controllers (MPPT vs PWM), they work out to roughly the same efficiency (from "marketing numbers")--So for the two controller types on well designed systems on warm summer days, have very similar efficiencies--Close enough for our work (any solar system predictions vs actual results that are withing ~10% or better of each other--Is pretty much "the same").

-Bill

wellbuilt

Re: off grid cabin/ home

Hi bill , I am just using a watt meter but the VA was 620 ?
I am on rock I have at most 16" of soil in areas but at the trailer I mite have 3" of dirt.
could I burry a ground rod horizontally 20' ?
ground to a well casing ?
My well guy could drill in a well casing 6" x 20' deep for grounding at the house site .
As far as shade at the trailer site I get good sun from 10 am to 2pm now , but if we cut a few trees I can get sun till 430pm / 530
The house will get full sun with the panels on the roof facing south all day .
Im getting a well drilled over the week end .

inetdog

Re: off grid cabin/ home

wellbuilt wrote: »

Hi bill , I am just using a watt meter but the VA was 620 ?
I am on rock I have at most 16" of soil in areas but at the trailer I mite have 3" of dirt.
could I burry a ground rod horizontally 20' ?
ground to a well casing ?
My well guy could drill in a well casing 6" x 20' deep for grounding at the house site .
As far as shade at the trailer site I get good sun from 10 am to 2pm now , but if we cut a few trees I can get sun till 430pm / 530
The house will get full sun with the panels on the roof facing south all day .
Im getting a well drilled over the week end .

If the house has concrete footings with rebar, what is called a Concrete Encased Electrode (CEE) or Ufer ground (after the guy who invented) it will be your best bet for getting a good ground. The requirements for a CEE are described in the National Electrical Code, so do some research.
Even if you do not have concrete footings, burying the required bunch of concrete may be as effective as the drilled well.

On second thought, I suppose blasting a footing sized ditch (if it is really solid rock) will be harder than drilling a well..... I wonder if a 6" casing will really be enough better than a 4" casing to make the difference worthwhile? Also, if there is any kind of aquifer within that depth, you do not want to let ground water into it unimpeded.

wellbuilt

Re: off grid cabin/ home

Hi dog thanks for the reply , Im a builder in NY NJ area and we are required to ground our footings and concrete floor with #4 wire and run to water pipe at the main + grounding rod at service but I never liked doing it , dosent seem like the thing to do .
At the trailer site there is no dirt , but there is a mound of dirt 20' around x6' left from when they built the road, up in the 80s.
could I burry the ground in the mound ?
I have some large concrete blocks 2'x2' x 6' with 1/2" RR in it could I burry 2or3 in the mound ?

At the house site I have some dirt about 50' from the service panel down over a rock ledge with 6' drop .
a 1000gal septic tank will be placed there and buried I do have 30" of dirt in that area .
I was going to sink 2 6" well cases in the stone about 16' with 4' sticking out for a
solar panel pole mount just incase I want to go that way .
Im meeting the well guy this morning , we are pulling the well rig up to the site .
Hope I get water the easy way . Ill be back in a few days John

Alaska Man

Re: off grid cabin/ home

BB. wrote: »

Alaska Guy.

The 77% eff:

• 0.81 panel derating (hot under sun, dust on panels, etc.) * 0.95 MPPT Controller+wiring efficiency = 0.77

The reason I use * 1/0.77 vs *1.2987 -- I am both lazy--I only have to remember 0.77 derating number vs also remembering/using *1.30 and explaining it is the inverse of 77% efficiency (1/efficiency = inefficiency ??? or call it 1/derating = over-rating ???).

Also when you look the equations with their "native values", it is easier to see how "adjusting" a value can affect the other all end results:

• 30 amps controller * 1/0.77 panel+controller derating * 29 volts charging = 1,130 Watt array

Looking at the maximum array size--Increasing controller current or battery voltage will increase the array size. Having a more efficient panel (colder weather) or more efficient controller (0.77 vs 0.80 derating), you don't need as large of solar array.

Is this your question?

-Bill

Yes, Thank you. I set up an Excell sheet so I can enter the AH and C/R wanted to get the array size using your formulas.

BB.

Re: off grid cabin/ home

If you are doing a spread sheet or engineering calculator--You may have to put (_) around the 1/xx to ensure that you get the proper operational order:

30 amps controller * (1/0.77) panel+controller derating * 29 volts charging = 1,130 Watt array

As opposed what could happen (wrong):

30 amps controller * (1/0.77 panel+controller derating * 29 volts charging) = 1.34 (wrong results)

-Bill

Alaska Man

Re: off grid cabin/ home

Yes, I figured it out by adjusting the operators sequence until I got your results and then tested it. Works good. ;-)

Cariboocoot

Re: off grid cabin/ home

BB. wrote: »

If you are doing a spread sheet or engineering calculator--You may have to put (_) around the 1/xx to ensure that you get the proper operational order:

30 amps controller * (1/0.77) panel+controller derating * 29 volts charging = 1,130 Watt array

As opposed what could happen (wrong):

30 amps controller * (1/0.77 panel+controller derating * 29 volts charging) = 1,130 Watt array

-Bill

Or you could just avoid mixing fractions and decimals:

30 Amp controller / 0.77 panel & controller derating * 29 Volts charging = 1,130 Watt array.

Or even put the operation in the logical sequence:

30 Amp controller * 29 Volts charging / 0.77 panel & controller derating = 1,130 Watt array.

Why yes; I have spent way too much time writing stuff like this. How did you guess?

Alaska Man

Re: off grid cabin/ home

This site needs a "Like" button. ;-)

wellbuilt

Re: off grid cabin/ home

Up date , My well drilling is not going to good we are down 680 feet , We are taking it 100/200 foot more and bust .
The driller Is thinking about hydro fracking?
I have never seen this done , Has any one here had this done ?
I hope I don't end up with a long ground rod .
We will be drilling more in the next few days .

Photowhit

Re: off grid cabin/ home

Sorry to hear that, good luck!