Portable Solar being set up - Please check my plans

[dewey02]

I will be installing a portable solar system and want to check with folks to see if the set up I have planned is correct. While this will be a home-built portable unit, I will be installing an electrical sub-panel inside the trailer (in the pass through) that the panels will connect to.

Our Situation:

We will NOT be installing panels on the roof, just a portable unit. We camp mostly in tree-covered areas. Our electrical use when camping is fairly minimal. I have replaced all lights with LEDs. We do not have (or ever intend to have) a television nor do we plan to use the microwave when boondocking. We do use an iPad, and a laptop that we use which will need to be recharged. We play the radio about 2 hours per day. We have the propane/DC refrigerator, toilet fan, kitchen exhaust fan, and two O2 Cool 12 volt window fans, and of course the water pump, and CO/Propane detector. We do camp when weather gets cold, so we use the propane/DC furnace in the fall.

What I have already purchased and will be using: (we will not revisit this as it is already purchased)

• Two 120 Watt 12 volt semi-flexible solar panels from Solar Blvd. I have built aluminum frames for each of these and they are connected like a solar suitcase. They are 12 volt (Vm 20V; Im 6.0A; Voc 22.8V; Isc 6.65A). I plan to run them parallel to keep voltage at 12 volts. I am using semi-flexible panels because of the great savings in weight vs toting around glass panels of equivalent wattage
• Two Energizer 6 volt golf cart batteries wired in series. 215 amp hours. Connection between the two batteries is 4 AWG wire. I’ve had these for two years now.

I plan to purchase the following from Amazon:

1. 30 ft of 8AWG wire with C4 connectors. Is this an adequate length? And is the gauge large enough? Or can I go with a smaller gauge and save some money? Link Here

2. Renogy CNCT-MC4Y Branch Connectors Solar MC4 Connectors Y connector in Pair MMF+FFM Link here


3. Grape Solar GS-PWM-40BT 40 Amp PWM Solar Charge Controller with Remote Monitoring (I intend to us my Apple iPad’s Bluetooth to access the remote monitoring). I plan to mount the controller in the pass through at the front of the travel trailer. Link here

4. Battery Minder EZ Connector. This will be the plug in to the side of the trailer and will connect/disconnect panel wires from controller. Wire size for this is 12AWG, but I will be only using these wires for very short distance (less than 1 foot).
Link here

5. Two RadioShack Gold-Plated Inline Fuse Holder with 40 amp fuses. Link here



6. Wiring run from Controller to Batteries – need help with gauge here. The run will be approximately 3 feet. What size wire should I be using?

7. Do I need a battery cutoff switch? Between which wires do I install it? What brand/type?

I don’t plan to install an inverter at this time, but will pre-wire the elect. Sub panel for the future.
I would appreciate your critique of the system and suggestions for wiring sizes, improvements, etc. Please avoid the “put it on the roof” and the “semi-flexible panels suck” comments, as those decisions are already made. I have numbered the items that I have not yet purchased, so that you can easily refer to each item. Thank you in advance.

[BFL13]

"
so around 1pm I suspect the output would have been noticeably higher, but by then the batteries were no longer in bulk mode charging but absorption and the charging current dropped below the panel output as expected"

Exactly. To test these things you need to jump and dance all over the place. EG to get the afternoon AH haul to match the morning haul (as it should by bell curve) you have to hold the battery voltage down steady by running a load.

It is tempting to just take the morning haul and double it. Especially if the low sea is to the East and there are mountains and trees to the West.

[dewey02]

red31 wrote:

dewey02 wrote:
They are 12 volt (Vm 20V; Im 6.0A; Voc 22.8V; Isc 6.65A)

I call em 6A panels. it ain't no 7A+ panel.
Just like I call my 3.85A Isc panel a 4A panel. it makes 4A at times! It don't make Isc no more, that would be 50 percent (C/2) and the batt just can't take that by the time the sun is right.

The OP has 'special' panels, 20v vs my 17v! your 'relationship' is bogus for such panels, and they likely will never make 120 watts!

OP here. Just to clarify, I purchased two Solar Cynergy Flexible 120 watt 12 volt solar panels from Solar Blvd. (for $119 each, they've gone up in price since then). The following link has their spec sheet.
Link here

[ktmrfs]

mike-s wrote:

ktmrfs wrote:
I've got in theory 60A total charging current. Now that's in theory, and today with the roof panels flat and being near 45 degrees latitude the sun angle limits the roof panels to around 20A total.

Today, at solar noon in Portland (when you would get peak charging current), the solar altitude was about 62 degrees. That's 28 degrees off normal (perpendicular, AKA zenith angle) for a horizontal panel. cos(28)~=.88, so the panel would receive about 88% as much light as it would if positioned normal to the sun. It's a bit less than that due to thicker atmosphere at lower angles, but not much unless the sun is much closer to the horizon. To get only 1/3 the output is due to factors other than the sun angle. The sun would have to be closer to 20 degrees altitude (that's like 8-9AM) to produce that output based on sun angle (or clouds, haze, shadows, etc.).

my 60A was the total of portable AND roof panels, 30A each. the 3 roof panels were giving me around 20A while the 3 portables with even approx aiming would have maxed out the 30A portable controller. And I measured it around 11-AM PDT, which was about 10AM real time which puts the sun at a pretty low angle. I'd have estimated the sun angle to be around 45 degrees which would give me about 25A in theory. so I was pretty close to what I would have expected out of the roof panels. and at that time the solar angle was off in two directions relative to the panel, my panels would have needed to be tilted up and rotated counterclockwise to be perpendicular to the sun which further reduces the efficiency.

so around 1pm I suspect the output would have been noticeably higher, but by then the batteries were no longer in bulk mode charging but absorption and the charging current dropped below the panel output as expected.

[red31]

dewey02 wrote:
They are 12 volt (Vm 20V; Im 6.0A; Voc 22.8V; Isc 6.65A)

I call em 6A panels. it ain't no 7A+ panel.

Just like I call my 3.85A Isc panel a 4A panel. it makes 4A at times! It don't make Isc no more, that would be 50% (C/2) and the batt just can't take that by the time the sun is right.

The OP has 'special' panels, 20v vs my 17v! your 'relationship' is bogus for such panels, and they likely will never make 120 watts!

[BFL13]

It is all about your Declination (time of year) and your Latitude for what happens. It is rather like taking your noon sight to get your latitude. It is all about the Dec.

Zenith Distance (ZD) = 90- Sun's altitude above horizon.

Tilt = ZD

Say at 49N, at 21 Jun when Dec is 23N, and Alt is 64 at high noon.

ZD = 90- 64 = 26. correct tilt at high noon is 26 degrees--except that is not optimum (for a fixed pointing South panel)which is less than that to get more shoulder hour time early morning and late afternoon.

ZD + DEC = LAT so in this case 26 + 23N = 49N Lat.

Later, on 21 Sep Equinox, your Dec is zero. So now Lat = ZD (twice a year like a stopped clock twice a day) and 0 + ZD is 49N so tilt is still ZD or 49, way up from back in June at 26.

Sun is lower, so tilt is up. That is for high noon.

If you have a tilted twirler, then in the morning and late afternoon with it pointing at the sun, which is lower then, you want a higher tilt. As the sun comes around (at 15 degrees an hour) and gets higher, you want to lower the tilt to the high noon amount and then start raising the panel again for the afternoon while still keeping it aimed.

[mike-s]

ktmrfs wrote:
I've got in theory 60A total charging current. Now that's in theory, and today with the roof panels flat and being near 45 degrees latitude the sun angle limits the roof panels to around 20A total.

Today, at solar noon in Portland (when you would get peak charging current), the solar altitude was about 62 degrees. That's 28 degrees off normal (perpendicular, AKA zenith angle) for a horizontal panel. cos(28)~=.88, so the panel would receive about 88% as much light as it would if positioned normal to the sun. It's a bit less than that due to thicker atmosphere at lower angles, but not much unless the sun is much closer to the horizon. To get only 1/3 the output is due to factors other than the sun angle. The sun would have to be closer to 20 degrees altitude (that's like 8-9AM) to produce that output based on sun angle (or clouds, haze, shadows, etc.).

[BFL13]

"So the OP has 2 x 6A panels," No, No, a thousand times, NO!

He has two 120w 12v panels. With PWM, your expected amps is the panel Isc total. A typical 120w is 7.6a Isc. It is all proportionate--An 80w panel is 5.1, a 100 is 6.2, a 130 is 8.2 etc.

Pick a watts number and you can get your expected amps pretty closely by using say the 130 at 8.2.

EG a 120 would be 120/130 x 8.2 = 7.569

Never use Imp with PWM. And before going bananas on this again 🙂 ---
you get the "same as Isc amps" ---because as we all know, you can't get Isc with a connected panel. But you do get that same amps number.

Just aim the (say) 130w disconnected panel at the sun and read off the Isc with your meter. Say it is 9AM, and you get 5 amps. Connect up and you get 5 amps to the battery as seen on the Trimetric.

Do the same thing later at high noon, and now you get 8.3 or 8.4 on a bright sort of day (above Isc rating) and sure enough you get 8.3 to the battery when connected.

Way too easy. Unreal how people still want to use Imp with PWM and get themselves all mixed up. 😞

MPPT expected amps is totally different, but if you have the panel watts you can do the PWM amps as the standard you should at least be getting, and then do the MPPT calculation to see if you get more or less than what you should get with PWM. You do not always get more with MPPT. Usually is is pretty much a wash. BTDT many times. My poor old multimeter and Trimetric get a good workout when we go camping. 🙂

Like previously mentioned, with my three 100w panels and my PWM Solar 30 controller, I got 18.6 amps showing on the Trimetric to the battery. Same as three Iscs worth. With my 20 Tracer MPPT same panels, series or parallel no diff, same place etc, never saw 19 or more amps. It disn't even hit the 260w/20amp limit of the controller. I was just as well off with the Solar 30 PWM for amps to the battery. And that is with my tilted twirler, so that is as good as it can get.

However, as stated I sometimes use my 255w 24v panel instead of the three 100s (swapping between 5er and camper) so the MPPT is required to run the 255w 24---but it doesn't make any diff for amps to the battery.

[red31]

the beauty of PWM with minimal wiring voltage drop is that Isc is on the rise (locally), Vmp drops like Voc and as long as the voltage at the controller is st pt or above, you're in business. It can get TOO hot for PWM but then the sun seems to go down.

[mike-s]

Lwiddis wrote:
Mike, are you trying to limit opinions? I like reading other posters thoughts.

Opinions are fine. It's when they're presented as facts that there's an issue.

[ktmrfs]

BFL13 wrote:
Here is how you calculate your "expected amps" to the battery. Use your own set-ups to get your own numbers but it all works the same way. (Panels aimed at the high sun to get full amps in each case)

PWM---you get the total Isc. (Imp has no meaning with PWM)
So my three 100s, each with 6.2Isc, get me 18.6 amps to the battery. Regardless of panel temperature etc etc.

MPPT- Panel temperature say 50C vs ambient 25C means 10% power drop.
So my 300w worth of panels becomes a 270W right off the top.

Wiring loss array to controller (based on Imp for the wire gauge) say it is 2% (which is pretty good) So now your power is 270 - 5.4 = 264.6w

Now the controller itself has an efficiency between input and output- less efficient when input is higher v than output v--eg 24-12 worse than 12-12. Typical 24-12 is say 95%. so now output watts is 264.6 x 95 = 251.4w (which is why I am ok with my 260w Tracer and my "300w" array.

Now you divide the output watts by battery voltage to get your amps to the battery. You get more amps with a lower voltage battery of course. (So the MPPT salesman always picks an example where the batts are low)

251.4/ 13v = 19.34 amps
251.4/ 13.5v = 18.6 amps (same as with the PWM)
251.4/ 14v = 17.96 amps

So there you see that you don't gain much in actual battery charging by spending big bucks on an MPPT controller. Lots of hype vs actual measurements tells the tale.\

Sometimes you do get a touch more with the higher voltage MPPT in low light but it is sort of trivial in the big picture. IE, in low light you don't get much anyway. A little more than not much is still not much!

I do have MPPT and PWM so I don't care. I just don't get any more amps with the MPPT, but I also have a 24v panel I use sometimes and you can't run that with a PWM, so I have the MPPT that can run it OR the 12s either way.

Isc should drop with temperature as well, so that will affect PWM max current vs temperature as well.

But I do agree, a good PWM controller is pretty much on par with a MPPT controller, but at noticeably lower cost. And MPPT controller only buys more amps when the battery can take it and when you have low IR drop in the cableing and when the MPPT controller has good efficiency. once you get near probably 80 percent charge if your panel sizing is reasonable both will start reducing current below what the panels could deliver anyway.

I've got 480 Watts of panels on the roof and 480Watts of portable panels. same panel mfg. same Voc, same Imp and the midnite kids can be set up as a master and slave and the roof controller becomes the master, and when adding in the portable I've got in theory 60A total charging current. Now that's in theory, and today with the roof panels flat and being near 45 degrees latitude the sun angle limits the roof panels to around 20A total. meanwhile one 160W portable panel angled was giving close to 11 A so I could get 30A out of the portable.

In this case the MPPT controller was giving me 10.5 A but Isc on the panels is 8.9A but I had only about a 10ft run of 10ga wire. In this case the MPPT was giving more than a 10 percent improvement over a PWM controller. But the cable run was short which helps a great deal.

so the angle does have a noticeble effect this time of year and in the fall. during the summer not near as much, and of course much less effect the further south one is. One noticeable advantage of portable panels. easy to get angled for max output.

[BFL13]

PT--"I get 16.9 amps from 256 watts of solar in a fixed flat installation. That works out to 230 watts, so my total losses are lower than 11%.

So your battery voltage is 230/16.9 = 13.6v. OK.

Meanwhile a PWM at 13.6 with 12v panels is not down from Isc hardly at all by IV curve, so using the standard 🙂 method-- 256/130 x 8.2 = 16.15 amps.

That is with panels aimed. but yours are flat. Diff between flat and tilted and aimed varies by latitude and time of year. Let's give you only 10% loss for being flat-- that means your equivalent amps to 16.9 is 110/100 x 16.9 = 18.6 so your MPPT with amorphous panels vs poly also, is 18.59/16.15 = 15%--looks good! (at 13.6 battery)

[red31]

Lwiddis wrote:
Mike, are you trying to limit opinions? I like reading other posters thoughts.

not so, pwm can do 24v charging with '24v' panels but is very wasteful to use 24v panel for 12v charging, that is just not how to wire PWM.

PWM, use 12v panels in parallel.

Use them in series requires MPPT to harvest max energy to charge 12v batt.

So the OP has 2 x 6A panels, in parallel use 10-12A for voltage drop and since the Vmp is so high for flex panels (OP's spec is 20v Vm) then one can have 1-2v of drop, note these are not Poly/mono, these panel have a high Vm (Vmp). Vm does not drop as fast for flex panels as mono/poly with heat. My 17v Vmp panel would suffer in the heat with 2v drop, it might not be able to get to set pt voltage!

of course with a MPPT they can be used in series for 6A x 40A (Vm x 2), with MPPT any voltage drop is loss of power. Voltage drop calc can be done with 6A, half of parallel PWM.

I like the PWM Grape controller, I can check overnight min voltage from my kitchen with the controller in the garage 30 or so feet away, landscape lighting system 3 hrs/night. EPSOLAR ViewStar VS 1024 BN PWM Solar Battery Charge worked great but no Bluetooth and not available for free shipping to the local home depot.

[pianotuna]

Hi BFL13,

Those are your calculations.

I get 16.9 amps from 256 watts of solar in a fixed flat installation. That works out to 230 watts, so my total losses are lower than 11%.

Now, what does the PWM do when the battery bank is at 14 volts? Oh...it Pulses faster and faster (way faster than any meter can measure), and the width of the pulse is shorter and shorter. So what REALLY is going into the battery bank?

Of course, this is meaningless--because once you are out of bulk charging mode, MPPT controllers change over to PWM to prevent battery over charging. So most of those losses you talk about--don't exist, or are identical between the two types of controllers.

That said, there have to be good reasons to switch to MPPT from a PWM controller, especially with the Grape 40 amp having all the features a person could dream of.

I'm just happy that after 3 grey days that my battery bank was in float by high noon. So nice to see only 3 amps going into 556 amp-hours of bank (and the parasitic load of 1.4 amps taken care of)

BFL13 wrote:
Here is how you calculate your "expected amps" to the battery. Use your own set-ups to get your own numbers but it all works the same way. (Panels aimed at the high sun to get full amps in each case)

PWM---you get the total Isc. (Imp has no meaning with PWM)
So my three 100s, each with 6.2Isc, get me 18.6 amps to the battery. Regardless of panel temperature etc etc.

MPPT- Panel temperature say 50C vs ambient 25C means 10% power drop.
So my 300w worth of panels becomes a 270W right off the top.

Wiring loss array to controller (based on Imp for the wire gauge) say it is 2% (which is pretty good) So now your power is 270 - 5.4 = 264.6w

Now the controller itself has an efficiency between input and output- less efficient when input is higher v than output v--eg 24-12 worse than 12-12. Typical 24-12 is say 95%. so now output watts is 264.6 x 95 = 251.4w (which is why I am ok with my 260w Tracer and my "300w" array.

Now you divide the output watts by battery voltage to get your amps to the battery. You get more amps with a lower voltage battery of course. (So the MPPT salesman always picks an example where the batts are low)

251.4/ 13v = 19.34 amps
251.4/ 13.5v = 18.6 amps (same as with the PWM)
251.4/ 14v = 17.96 amps

So there you see that you don't gain much in actual battery charging by spending big bucks on an MPPT controller. Lots of hype vs actual measurements tells the tale.\

Sometimes you do get a touch more with the higher voltage MPPT in low light but it is sort of trivial in the big picture. IE, in low light you don't get much anyway. A little more than not much is still not much!

I do have MPPT and PWM so I don't care. I just don't get any more amps with the MPPT, but I also have a 24v panel I use sometimes and you can't run that with a PWM, so I have the MPPT that can run it OR the 12s either way.

[Lwiddis]

Mike, are you trying to limit opinions? I like reading other posters thoughts.

[2oldman]

mike-s wrote:
there are lots of people who will jump in without reading the provided info first and understanding it.

This is no different from getting advice from your buddies. Some know what they're talking about, some don't.

Absolutely take everything you read here with a grain of salt, and RTFM!