Lazy Daze Owners' Group

That depends upon your current solar power system. Let's take a simple case: suppose your solar panels on the roof are wired in parallel, and they're putting out about 18 V (Vmpp). The Goal Zero "Boulder" 200 W suitcase also puts out 18 V. So you could simply wire the two sets of panels in parallel.

But your solar charging controller will have to be rated to handle the amperage coming from both sets of panels combined. If it isn't, you'll need to upgrade to a beefier controller. (Alternatively, if you now have a Victron Smart Solar controller, you could add a second controller--a $65 Victron 75/15 would work for the GZ suitcase's roughly 12 A maximum output--and network the two controllers together.)

By the way, the Goal Zero "HPP" connector appears to be just a garden-variety Anderson connector pair, with a rubber boot for weatherproofing. Anderson connectors are available all over the place. Or you could buy a GZ HPP cable and cut off one end to tie it into your system.

That's a simple example. If your roof array is wired to put out more than 18V, you can still do this, but in that case you'll definitely need a separate controller for the GZ suitcase.  That's what I've done for my homemade 200 W suitcase, because I wired its two panels in series in order to cut voltage drop in half in the 20' cable I sometimes use. Its output voltage is enough different from my roof array that I used a separate Victron 75/15 for the suitcase.

That should give you an idea of what's involved. In any case, I'd suggest adding a breaker where the suitcase connects to the LD, so that you can cut off the power from the panels before disconnecting them. Otherwise you can get arcing and pitting in your connectors.

"I don't think the solar suitcase comes with a charge controller but they are available from GZ for a hundred bucks."

The Goal Zero 96110 charging controller has two advantages: it's waterproof and only an inch thick, so you could glue it to the back of a solar panel and have a self-contained unit that could hook up directly to a battery bank. And it uses GZ's modified Anderson connectors, so it's a plug-and-play solution if you want to charge a Goal Zero power station.

Here are the drawbacks:

1. It's a PWM (pulse-width modulated) controller rather than MPPT (maximum power point tracking). PWM is inefficient. Most modern controllers--even relatively inexpensive ones--use MPPT circuitry, which can get 15%-25% more power from a given panel than PWM. That alone is a reason not to buy the GZ controller. Why throw away power?

2. It can only accept 15-22 volts from solar panels. OK, but most panels put out around 18 V, so why is this a drawback? Because if you want to set out more than one panel (two 100 W panels on the ground are a common setup), having a higher voltage is a big advantage. Here's why.

When designing any solar power system, you're always thinking about minimizing voltage drop--power lost in the wires leading from the panels to the charging controller. In a permanent installation with roof-mounted panels, that means keeping your cable runs as short as possible, and sizing your wire to keep voltage drop below one or two percent, if at all possible.

But with ground-based panels, you may want to park in the shade and put the panels fifteen or twenty feet away. (I carry ten-foot and twenty-foot cables.) Unless you use massive wire, that can mean significant voltage drop at 18 volts. But if you connect your two panels in series for 36 volts--or buy a single 30 volt panel--the voltage drop is cut in half. That makes long cables much more practical.

3. The GZ controller is overpriced. You pay a hundred bucks for an inefficient controller that can't handle multiple panels in series. By contrast, sixty five bucks will get you the Victron 75/15 that I mentioned in an earlier post. So let's talk about that.

First, let's get the drawbacks out of the way. It isn't waterproof, so it'll have to be mounted indoors. And it doesn't have GZ-type terminals, so you'll have to strip wires and insert them into its screw-clamp terminals.

But that said, it's an efficient MPPT controller that will get more power out of any solar panel than GZ’s PWM controller. It can handle up to 75 volts of input--plenty to allow series-connected panels,a which will minimize voltage drop in a long cable from your rig to your panels. It has Bluetooth built in, so you can monitor it from anywhere nearby. And it costs a lot less than the GZ controller.

The Victron 75/15 controller isn't the only possibility, of course. Suppose you just want a single outside panel, and you want a controller that you can mount on or near the panel. Well, you could buy this $38 Bateria controller. It's an MPPT type, it's waterproof, and it's simple--no fancy Bluetooth features. I haven't used this one myself; I just mention it as an example of a simple, nearly plug-and-play*, efficient MPPT controller that's a lot more affordable than the GZ controller.

* It uses SAE connectors, which you can get in any auto parts store, so you would have to do some cutting and butt-splicing to attach them to your panel.

I recommend the Victron 75/15 because it's versatile, efficient, and reasonably priced. I've used several of them over the years and have had zero problems with them. But if you want a cheap solution that will work better than the GZ controller, there are plenty of choices, such as the Bateria model I just mentioned.

OK, I've gone on long enough. :-) I hope this gives you some ideas for the best ways to implement a supplementary solar panel.