off grid cabin/ home

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

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

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

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