Need help to build my off grid solar kit

STEWPLATE · August 2015

Aloha! I'm so new at this , but determined to get this done! I want to build a custom off grid solar package to run 4x 5,000 btu air conditions. It's for a 3 bedroom home. To run the line to each air condition unit is approximately within 30 feet radius for 3 bedrooms and one other bedroom is about 50 feet away. Im more concerned about air condition cost savings, but hooking up a refridged would be nice to. What kind watts or amount of panels I need---What size invertor ?--- controller and other accesories do I need to get started? Of course how many deep cycle batteries do I need .

I would like to overkill so I can expand this package if I have to. As you can see I need help! I tried to set up but I get all confused. I orignally was gonna buy the grape solar kit but I think Im better off building my own kit to maximize the potential off getting more bang for my bucks, on inverters--and controllers I appreciate your help and assistance! thanks Al

BB. · August 2015

Before you buy anything--Do your research, planning, and a few paper designs first.

Air-conditioning takes lot of electricity. A well insulated building (lots of insulation, double/triple pane windows, weather stripping, heat recovery ventilator, etc.). And getting a very efficient A/C system that is Off Grid Friendly (no large surge current, low power modes)--A mini-split type system has been used by people here and been very happy with them (and with Heat Pump types--Even heating in winter is possible for sunnier locations).

Also, how you operate the mini-splits can help reduce energy usage/system size (i.e., run the A/C systems at low power during the day, vs running at high power in the evening when family returns home).

Have you picked your A/C system yet? Estimated how much they will operate (Watts * Hours of Use per day), etc.? Where will the system be installed (near what major city)? How much money are you willing to pay for the off grid power system?

How many months a year will the A/C system be used--If this was a weekend/seasonal system (few months during the summer)--Many times, a genset would end up being more cost effective.

-Bill

STEWPLATE · August 2015

Argh! I just saw how much watts you need to run 4 air condition units!! yikes! think Ill go to evaporater coolers. since Im running usually from july to sept , your right it's a seasonal thing. What you think of me buying solar panels that will give me about !,400 watts, and what kind of inverter and control charge I need. I want to put money into my inverter and charge controller so I can expand on it in the future. Am I making sense? thanks Al

STEWPLATE · August 2015

Im lookin to buy this:
[h=1]Kyocera KU265-6MCA 265 Watt Multicrystal Solar Module 5x to get 1,325 watts, so lookin for inverter and chrge regulater to expand up to 2,500 watts? am i doin this right?[/h]

BB. · August 2015

Ok... I will do a real quick set of calculations for an Off Grid system using "nominal" design rules... First we size the battery bank--But since we do not know your loads, but we have a solar array (note, 5x panels would limit you to a 12 volt battery bank and a MPPT type charge controller--All perfectly doable--But I would be suggesting 6x panels or other even number so you can have a 24 volt battery bank instead--Better for larger systems).

We recommend charging a battery bank at 5% to 13% rate of charge. 5% can be OK for a weekend/seasonal system. For a full time off grid system, 10% or higher rate of charge is recommended:

1,325 Watts * 0.77 panel+controller derating * 1/14.5 volts charging * 1/0.10 rate of charge = 704 AH @ 12 volt battery bank "nominal"

Next, how much power can your solar array supply... If you are in Honolulu, HI, using fixed array and the Solarelectrichandbook: [h=3]Honolulu
Average Solar Insolation figures[/h] Measured in kWh/m²/day onto a solar panel set at a 69° angle from vertical:
(For best year-round performance)

Jan
Feb
Mar
Apr
May
Jun

4.98

5.84

6.24

6.50

6.43

7.37

Jul
Aug
Sep
Oct
Nov
Dec

6.52

6.63

6.60

6.10

5.24

4.83

If you want the power available for July through September--Then 6.52 Hours minimum sun (you should plan on using ~65% to 75% of predicted daily loads to allow for variation in weather and loads.:

1,325 Watt array * 0.52 typical off grid system eff * 6.52 hours of sun per day = 4,492 Watt*Hours per day

And for the battery bank, recommend that you cycle roughly 25% per day (for two days, 50% maximum discharge):

704 AH * 12 volt battery bank * 1/2 days of storage * 0.50 maximum discharge = 2,112 Watt*Hours (over night, or during bad weather) per day

Regarding cooling--I am guessing you are in Hawaii--But you are taking about swamp coolers in another thread (I think)--Generally they only work well in very dry climates.

-Bill

BB. · August 2015

I should add that a 704 AH Battery Bank will support an AC inverter at C/5 for lead acid battery (C=20 hour capacity, C/5=> is discharging the battery flat in ~5 hours--About the maximum rate of discharge a flooded cell lead acid battery can sustain for a few hours):

704 AH * 12 volts * 0.85 AC inverter eff * 1/5 hour discharge = 1,426 Watt AC inverter maximum recommended

So--ideally, you should plan on drawing:

704 AH * 12 volts * 0.85 AC inverter eff * 1/20 hour discharge = 359 Watt AC power average (5 hours per night, 2 nights)
704 AH * 12 volts * 0.85 AC inverter eff * 1/8 hour discharge = 898 Watt AC power max continuous recommended (~4 hours to 50% discharge)

Note that it is not always easy/cost effective to "grow" an off grid system--For example, if you wanted to grow this system by very much--I would be suggesting going to a 24 volt system... At the very least that would need more batteries and a 24 VDC input AC inverter...

-Bill

STEWPLATE · August 2015

Ok 6x 265 watt panels----going to a 24 volt system, so I will need 24 VDc input AC inverter--how many 24volt batteries will I need. In hawaii seems they sell only marine batteries? do they come 24 volts? and would you recommend marine batteries? Alson I need a charge regualter? what would you recommend Thanks Al

STEWPLATE · August 2015

BY THE WAY B.B I APPRECIATE YOUR TIME AND EFFORT. THANKS A LOT FOR YOUR HELP! AL

STEWPLATE · August 2015

WILL THIS WORK? Wagan 2482-4 Slim Line 2000W 24V Power Inverter

solar_dave · August 2015

You will find that conservation is much cheaper than more solar, more insulation and better windows are the first step. Also the high efficiency mini-split with a high seer rating would be a better bet than four 5000 BTU window rattlers. They do come with a single outdoor unit and individual controlled wall units for the inside.

I thought most parts of the islands stay in a pretty comfortable range year round.

BB. · August 2015

Battery wise--Marine Batteries are not really good for full time off grid use... They do not deep cycle as well as a true deep cycle storage battery. "Golf Cart" batteries (typically around 6 volt @ 200 AH--for an 800 AH @ 24 battery bank, you would need 4x 6 volt batteries in series for 24 volts, and 3x200 AH battery string in parallel for 600 AH capacity. 12 batteries total--And this would be the largest 24 volt @ ~600 AH battery bank I would suggest for use with golf cart batteries--More than 3 parallel battery strings is something I would avoid if possible).

The Wagan Inverter is a MSW (Modified Square Wave) unit... That would not be my suggestion. MSW is not great for induction motors and some AC appliances. TSW/PSW (True/Pure Sine Wave) is usually a better choice, but also much more expensive).

But you are also putting the cart before the horse. You really need to decide on how much load you need to support... Or, as an alternative, pick something (like Battery Bank AH/Voltage rating, how bif of solar array, total cost of system, size of AC inverter, etc.) first. Otherwise it is like trying to pick a vehicle without any sort of idea of what you really want (motor cycle, Smart Car, station wagon, van, pickup truck, semi-tractor+trailer). All perfectly reasonable transportation devices--But they are nowhere near "similar" in cost/capabilities.

-Bill

oil pan 4 · August 2015

Another vote for no modified sine wave.
I tried powering my laptop off one of my modified sine wave inverters and it would power the computer but refused to apply any charge to the battery.

STEWPLATE · August 2015

Because of financial limitations, Im lookin to purchase a grape solar 200 watt kit. Im gonna buy 2 extra panels to get up to 400 watts . it says my inverter --charge controller should handle the extra 2 panels. Am I correct to say 2 golf cart 6 volt batteries = 12 volt. I have 4 100 watt panels so gonna get 8-6 volt batteries. ?? Does it make sense?

STEWPLATE · August 2015

with this 400 watt kit I just want to charge batteries use for some emergency lights and possible small tools,

BB. · August 2015

OK... 400 Watts of panels--The standard rate of charge is 5% to 13% with solar. And if you are fully time of grid, I would suggest 10%-13% rate of charge. Weekend/seasonal, you can get away with as small as 5% rate of charge (Numbers are approximate--Anything within ~10% is "the same" in solar):

400 Watts * 1/14.5 volts charging * 0.77 panel+controller derating * 1/0.05 rate of charge = 425 AH @ 12 volt largest suggested battery bank
400 Watts * 1/14.5 volts charging * 0.77 panel+controller derating * 1/0.10 rate of charge = 212 AH @ 12 volt nominal battery bank
400 Watts * 1/14.5 volts charging * 0.77 panel+controller derating * 1/0.13 rate of charge = 163 AH @ 12 volt minimum suggested battery bank

So, 2x 6 volt @ ~220 AH golf cart batteries would be a nice fit with your array. You could go with as many as 4x golf cart batteries if weekend/emergency/possibly RV use.

Inverter wise, the largest "useful inverter" on such a battery bank would be:

212 AH * 12 volts * 0.85 inverter eff * 1/5 hour discharge = 432 Watt rated AC inverter max "useful" for 212 AH @ 12 volt flooded cell battery bank
212 AH * 12 volts * 0.85 inverter eff * 1/8 hour discharge = 270 Watt rated AC inverter typical recommended max size

My personal suggestion is a MorningStar 300 Watt TSW 12 VDC AC inverter--Reliable and has remote on/off and "low power search mode". Very rare for such a "small" AC 12 inverter.

For a very nice charge controller--The Midnite MPPT 30 Amp controller would be very nice (not cheap) pick. Get the Remote Battery Temperature sensor option (always nice to have). The Wizbang Jr. is a nice item too (integrated battery monitor function).

MidNite Solar The Kid MPPT Solar Charge Controller

Or, for a less expensive controller, look at the MorningStar TS or PS series (roughly 30 amps or larger):

Standard PWM Charge Controllers

MorningStar also makes nice MPPT controllers too.

You typed about integrated Inverter-Charger -- There are inverters with integrated AC battery charger, and there are other (typical less expensive) Inverter-DC Solar Battery chargers. Make sure you understand what type of inverter-charger you are looking at (I am, in general, not a big fan of integrated function controllers--Although there are some very nice integrated inverter-AC battery chargers out there).

-Bill

Need help to build my off grid solar kit

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