whats the best portable solar panel?

[CRJ]

Originally Posted by rubicon327

Something like this? All you need to do is splice in behind the controller and add a solar port thru the shell in a convenient location.

thanks for the diagram and tip on the Zamp equipment. I'll check it out.
There currently are MC4 splices up at the existing solar panel. I guess I could replace them with T type connectors but that would mean getting up on the roof to connect / disconnect which wouldn't be desirable.

[Jim Bennett]

Originally Posted by CRJ

thanks for the diagram and tip on the Zamp equipment. I'll check it out.
There currently are MC4 splices up at the existing solar panel. I guess I could replace them with T type connectors but that would mean getting up on the roof to connect / disconnect which wouldn't be desirable.

I definitely wouldn't do that with MC4 connectors. While you can take them apart, they are really not meant for a means of constant disconnecting. I thought about it more, and without moving the controller which would be a real pain, running wires up to in inside from a port to connect the portable panel would likely work the best, look the neatest and be easiest to use method.

[CRJ]

Originally Posted by Jim Bennett

I definitely wouldn't do that with MC4 connectors. While you can take them apart, they are really not meant for a means of constant disconnecting. I thought about it more, and without moving the controller which would be a real pain, running wires up to in inside from a port to connect the portable panel would likely work the best, look the neatest and be easiest to use method.

This definitely seems like the best approach. I'll pull the controller and figure out the best route for wiring. I just got the trailer and still need to learn more about the system. Like how to shut it down when not needed...... and I'm sure much more.

[richardr]

I am looking at 2 Renogy 100 watt solar panels HERE on Amazon. If I have a PWM controller that has an Absorption voltage of 14.4 volts, I calculate the following amount of power each panel will produce.

Regular Design: Optimum Voltage - 18.9, Optimum Current - 5.29 amps. So 14.4 volts with 5.29 amps = 76.2 watts

Slim Design: Optimum Voltage - 16v, Optimum Current - 6.25 amps. 14.4 volts with 6.25 amps = 90 watts

Are my above calculations correct, and the Slim Design will charge my battery by an addition of almost 14 watts or 18% power?

[Brian B-P]

Originally Posted by richardr

I am looking at 2 Renogy 100 watt solar panels HERE on Amazon. If I have a PWM controller that has an Absorption voltage of 14.4 volts, I calculate the following amount of power each panel will produce.

Regular Design: Optimum Voltage - 18.9, Optimum Current - 5.29 amps. So 14.4 volts with 5.29 amps = 76.2 watts

Slim Design: Optimum Voltage - 16v, Optimum Current - 6.25 amps. 14.4 volts with 6.25 amps = 90 watts

Are my above calculations correct, and the Slim Design will charge my battery by an addition of almost 14 watts or 18% power?

In ideal sun exposure, but below the optimal voltage (Vmp), the current will be somewhat higher than optimal current or Imp (but still less than short circuit current Isc). As a first approximation, guessing at a combination of optimum current and the lower voltage seems reasonable.

In practice, the shape of the voltage-current plot for the two panels may not be the same, and even if they are the same you're looking at two different points on it. It is rational to expect better output in ideal conditions from the panel with the better-matched voltage, but...

• in real sun conditions the target charging voltage may be too high for the lower-voltage panel, and
• even in ideal conditions picking the operating point of the panel's performance curve would provide a better estimate.

I assume that these are the panels:

1. Renogy 100 Watt 12 Volt Monocrystalline Solar Panel (spec sheet)
2. Renogy 100 Watt 12 Volt Monocrystalline Solar Panel (Slim Design) (spec sheet)

The downloadable spec sheets (linked above) include IV Curves. At 14.4 volts in ideal sun it looks like both panels would put out almost their short-circuit current (not just the max power point current), so the comparison would be

1. regular: 14.4 V * 5.75 A = 83 W
2. slim: 14.4 V * 6.45 A = 93 W

It would be great if they published these performance curves for lesser sun exposure conditions as well, to see how they would compare under more realistic conditions.

[thiggins]

We just bought the GoPower 120 portable...

[MBA80]

Check out the solar portable information in the attached PDF document. It shows the different Zamp Solar portables, their weight, dimensions both open and closed and their Amp hour rating on average. It also show the nice nylon ballistic case the portable comes in and the options you can purchase to extend the range (15 to 30 feet) and the Zamp Solar port which is best located near the battery compartment vent.

[richardr]

Originally Posted by Brian B-P

In ideal sun exposure, but below the optimal voltage (Vmp), the current will be somewhat higher than optimal current or Imp (but still less than short circuit current Isc). As a first approximation, guessing at a combination of optimum current and the lower voltage seems reasonable.

In practice, the shape of the voltage-current plot for the two panels may not be the same, and even if they are the same you're looking at two different points on it. It is rational to expect better output in ideal conditions from the panel with the better-matched voltage, but...

• in real sun conditions the target charging voltage may be too high for the lower-voltage panel, and
• even in ideal conditions picking the operating point of the panel's performance curve would provide a better estimate.

I assume that these are the panels:

1. Renogy 100 Watt 12 Volt Monocrystalline Solar Panel (spec sheet)
2. Renogy 100 Watt 12 Volt Monocrystalline Solar Panel (Slim Design) (spec sheet)

The downloadable spec sheets (linked above) include IV Curves. At 14.4 volts in ideal sun it looks like both panels would put out almost their short-circuit current (not just the max power point current), so the comparison would be

1. regular: 14.4 V * 5.75 A = 83 W
2. slim: 14.4 V * 6.45 A = 93 W

It would be great if they published these performance curves for lesser sun exposure conditions as well, to see how they would compare under more realistic conditions.

We bought two slim panels because I felt they would give us a higher charging current with our PWM solar controller. The down side is we have to be careful that we don't loose too much voltage in the wire from the panels to the controller.

I ran a test using an 8 foot 10 awg cable run and a 28 foot 10 awg cable run. There was a difference of almost 2 amps of battery charging with the two 100 watt panels (12+ amps down to 10+).

[Jim Bennett]

Originally Posted by richardr

I ran a test using an 8 foot 10 awg cable run and a 28 foot 10 awg cable run. There was a difference of almost 2 amps of battery charging with the two 100 watt panels (12+ amps down to 10+).

While that difference is substantial Rick, 10 amps in the sun 28' away is better than what you get in the shade 8' away. This is the main reason I have a portable panel, as so often in the past we seem to be camping in the trees, but go figure, since getting the 5.0TA and setting up the solar, we have mostly been in the bright sunshine.

[Mike Lewis]

I have three rooftop panels totaling 355W of power. A 95W panel was installed by ETI, later two additional panels were installed by AM Solar. They abandoned ETI's wiring and connected all three panels to a junction box of some kind on the roof. I assume they are connected in parallel. Nice fat #6 wire runs from the roof to the solar controller.

I recently installed a new MPPT controller and an SAE connector for a portable panel. The connector is wired in parallel with the panel wires from the roof. I'm a bit confused reading posts about needing to match portable panels voltage-wise with rooftop panels. My new controller shows that the rooftop panels vary in voltage, in bright sunshine they go up to 20V. So what do I need to look for in a portable panel? Thanks.

[Jim Bennett]

Originally Posted by Mike Lewis

So what do I need to look for in a portable panel? Thanks.

The manufacturer rated voltage is what I was told to look at by a local shop. Most all panels we would use are around 18V.

[rubicon327]

Originally Posted by Mike Lewis

I have three rooftop panels totaling 355W of power. A 95W panel was installed by ETI, later two additional panels were installed by AM Solar. They abandoned ETI's wiring and connected all three panels to a junction box of some kind on the roof. I assume they are connected in parallel. Nice fat #6 wire runs from the roof to the solar controller.

I recently installed a new MPPT controller and an SAE connector for a portable panel. The connector is wired in parallel with the panel wires from the roof. I'm a bit confused reading posts about needing to match portable panels voltage-wise with rooftop panels. My new controller shows that the rooftop panels vary in voltage, in bright sunshine they go up to 20V. So what do I need to look for in a portable panel? Thanks.

Your panels from AM Solar are most likely wired in parallel in the combiner box on the roof. That is the preferred method. This is a good video from AM Solar that goes over the basics of series vs. parallel arrays.

https://www.youtube.com/watch?v=Z1ur3kSHuBU

To the best of my knowledge with panels in parallel the maximum power voltage (Vmp) will be limited to the lowest Vmp rating of an individual panel. This is why you should try to match the Vmp of your panels as close as possible. Most "12V" panels will be 18Vmp +/- but can as high as 20Vmp +/- depending on the number of series connected cells on the panel. It is safe to say that AM Solar used 18 Vmp panels to match as close as possible with your existing Go Power 95W panel that literature shows is 17.2 Vmp. I also see Renogy makes a "24V" panel with a Vmp of 31.4 Vmp but that is a different animal altogether. As Jim said, look for an 18V +/- Vmp rated portable and you should be fine.

[fudge_brownie]

The general rule is: "Both in series and parallel connection, plugging a panel of a lower power rating to the array drags the whole output power down." The ideal solution is to add a panel identical to the existing panels.

However, this is a simplification. A good web site that discusses combining panels is this: https://solarpanelsvenue.com/mixing-solar-panels/. I like it because it has a lot of pictures.

I am sure AM Solar has done an excellent configuration, you will need to determine just how they wired things so you can add to it properly.

[John in Santa Cruz]

The self-taught EE in me isn't 100% sure about that rule of thumb that the lower voltage panel simply drags the higher voltage panels down to its output voltage. rather, I would expect the lower voltage panel to simply not contribute as much current to the total as the higher ones. when you parallel voltage sources into a low impedance load (for instance, the solar controller/regulator), you are creating a current 'adder'. this is, of course, a gross simplification of a fairly complex system, due to the nature of PWM or MPPT regulators.

those voltages are open circuit voltages. when the panels are under load, the actual PV voltage drops some based on the load. if any panels output is well below this *effective* voltage, then its simply not going to contribute any current, for instance, if one panel is shaded its not going to contribute anything but the unshaded panels should continue to contribute their full output.

in the ideal world, each panel would have its own MPPT style regulator, with the regulators all slaved together to coordinate the charging cycle... but I don't think anyone makes anything like this.

[Ron in BC]

Originally Posted by fudge_brownie

I like it because it has a lot of pictures.

Yes, a pretty clear illustration for us non-EEs.

I just realized that I have one possible advantage with my two 12 volt batteries isolated with a battery switch. If I do end up with a mis-matched panel for the new trailer, say the portable one, I could always feed it into the second battery.

Ron