Different Panels and wattage, same controllers? System big enough for portable cooler?

Re: Different Panels and wattage, same controllers? System big enough for portable cool

msndave wrote: »

Thanks for your help. I’ve been reading other posts, but I have a pretty low tech, low wattage question. Can I combine two different panels with two different watts by using two of the same charge controllers to the same battery bank? I already have the Kyocera and batteries; I can add an Instapark 30 and an extra controller for not much money. Also, the Kyocera has been discontinued.

You can add the two panels in parallel--Even to one charge controller (assuming controller is large enough to manage the total current--see specifications). These panels are ~17.5 to 17.9 volts Vmp--They are fine to parallel.

You may also want to look at a single ~140 Watt solar panel like one of these:



Module
Single Module Price
Single Module per $/Watt


Solartech SPM130P-S-N 12V
$285.00
$2.192


Solartech SPM130P-WP 24V
$351.00
$2.70


Solartech SPM140P-S-N 12V
$305.00
$2.179


Kyocera KD140SX-UFBS
$285.00
$2.036


Kyocera KD140GX-LFBS
$265.00
$1.893


Eoplly Solar EP125M-72-190
$218.50
$1.15



Panels less than ~140 Watts can usually ship with traditional shippers (UPS/Bus/etc.)... Larger panels usually need to come by truck. It is usually nicer to install/more reliable (and overall cheaper $/Watt) if you get larger panels.

However, shipping to Alaska may blow the pricing all to heck.
Here are the details of what my system would look like:

(x1) Kyocera KC 40 Panel -- 43 watts – 17.4 volts – 2.48 amps
(x1) Instapark 30W Panel – 30 watts – 17.5 volts – 1.68 amps
(x2) SunGuard/Morningstar 4.5 amp Charge Controllers – I use Morningstar chargers because I heard they are better for sealed batteries?
(x3) UB 12350 Sealed Lead Acid Battery 35 Ah (total of 105 Ah) – I got these batteries because they were offered with free shipping to rural Alaska – anything larger is very, very expensive to get here. Also, these sealed batteries can be legally shipped via USPS flat rate boxes for around ten bucks.
(x1) Wagan 400 watt Power Inverter (works but loud fan runs all the time)

I would like to see you get a single 105 AH battery--Paralleling batteries is usually a bit of pain. You should connect them something like this to make sure all the batteries charge/discharge the same.

Again, you know your shipping costs better than I (us moderators are volunteers--We are not connected to our host NAWS in any other way).

I would also suggest you look at a DC Current Clamp DMM--Very nice for debugging and DC power system.

Morningstar makes nice smaller controllers... Yes, you need one that does not overcharge AGM batteries. They have some larger controllers with an AGM jumper you can set too.

As a side, my current setup is for lights, laptop for movies, etc for a rec cabin in the woods. We only use the cabin in the summer and we get around 13 – 15 hours of sun per day depending on the month. The KC40 is working well but we’d like to add some capacity for a portable beverage cooler to store some meat/cheese. Would this system be big enough for a cooler that draws 4 amps at 48 watts? Thanks again for your advice. – Dave

In reality, you really don't get 15 hours of "noon time equivalent sun"--Especially with a fixed array. Using PV Watts for Fairbanks, fixed array tilted to 50 degrees from horizontal (for summer use), we see:

Month    Solar Radiation
(kWh/m 2/day)
1      0.68     
2      2.19     
3      4.36     
4      5.91     
5      5.50     
6      5.62     
7      5.43     
8      4.55     
9      3.40     
10      2.09     
11      1.02     
12      0.34     
Year      3.43      

About 5 hours of noon time sun per day... A 70 watt solar array would output around:

• 70 watts * 0.52 system derating * 5.0 hours of sun = 182 Watt*Hours per day (long term average)

Your cooler runs at 48 Watts--Typically 24 hours per day... Just running the cooler would eat up your total power production in less than 4 hours.

Bringing ice/pre-frozen food/etc., using a propane fridge, etc. is going to be way more cost efficient vs using a Peltier based cooler.

And, we recommend 5% to 13% or so rate of charge for a "happy" battery bank. For a weekend summer cabin, 5% is OK (we usually like to see 10% or more rate of charge for daily use full time off grid):

• 70 Watts * 1/14.5 volt battery bank * 0.77 panel+controller derating * 1/0.05 rate of charge = 74 Amp*Hour @ 12 volt battery bank...

So, 105 AH @ 12 volt of AGM batteries is pushing it--But it will probably work OK.

Your thoughts?

-Bill

Re: Different Panels and wattage, same controllers? System big enough for portable cool

Yes, it will work as you want.

You can wire the second controller to the batteries--A parallel connection with the first controller. They will do fine charging the battery bank (assuming the controllers are working fine).

-Bill

Re: Different Panels and wattage, same controllers? System big enough for portable cool

In general, for PWM controllers (the type you have) are simple on/off switches. On, current flows to battery. Off, current stops. The solar panels just need Vmp in the range of 17.5-18.6 volts.

Below ~17.5 volts Vmp (on a 12 volt battery bank), on a hot day, the Vmp of the panel falls, and may not generate enough voltage to recharge the battery bank.

If the voltage is over ~18.6 volts, the relatively efficiency of the panel begins to fall (i.e., a ~35 Vmp panel with a PWM controller charging a 12 volt battery bank will only deliver ~1/2 of its power to charging the battery bank because of voltage miss-match).

As long as the controllers are working correctly, they will each make a decision on how much charging current the battery bank needs. The controller with the highest voltage setpoint will "win". At lower voltages (i.e, battery significantly discharged)--Both controllers will turn on and charge the battery bank.

For AGM batteries, you typically do not want over ~14.2 to 14.4 volts maximum--Or the batteries will overcharge, out-gas, and have an early death.

Just make sure the charge controllers have short (and heavy enough) cables between the controller and the battery bank. The cables should all connect to the battery common bus (per the Smartgauge website suggestions above).

You want the charge controller to accurately measure the battery voltage during charging.

-Bill