Not solar again ?

[wanderingbob]

I ain't gonna do it , but I am Curious . In the course of a year I pull 3 different trailers and I was wondering : My pickup has a metal topper like the phone companies had in the past , if I put 3 or four hundred watts of panels on top of the topper to charge the 4 golf car batteries on the front of my trailer , where would I put the controller , close to the batteries or close to the panels . A portable suitcase panel would not work as we may leave the trailer all by its lonesome and I am to lazy to tote the suitcase . We work craft shows and sometimes the trailer and truck can not be near each other . Also would it hurt the panels when I unplug from the trailer for a day ? Where does all that electric that I ain't catchin , where do it go ?

[pianotuna]

Hi Perry,

The Victron 100/30 SCC is an excellent choice.

[PerryB67]

Duplicate post removed.

[PerryB67]

StirCrazy wrote:
the higher voltage at the controler has something to do with it. Ieven find this with my 24V panel in my caper. at 7am I will be fetting between 0.5 and 1amp of charge out of the 325 watt 24V panel but my 480 watt panels (12V's in parralel) will be putting nothing out for another hour at least. so low light/shading get better preformance as the voltage that does come through is high enough to start the charge. A MPPT charger is an important part of this equasion also in my opinion.

Read my post again. I find I'm getting what your talking about with today's modern panels.

I also have a Victron 100/30 SCC, so that's a moot point.

pianotuna wrote:
Perry Unisolar made panels with diodes between every cell. Wired in series parallel, they do work in leafy shade, and in rain too.

There is one other currently made panel that has this feature--but they are from Germany and I have been unable to find a source to buy them from.

In general, parallel is better, but with a good MPPT controller more watt-hours may be harvested.

So the panels you're talking about are unobtainium. I'm talking about current panels, that are easily obtained, that the sales person at Northern Arizona Wind & Sun recommended because of their superior light gathering ability.

Again, I already have a quality Victron 100/30 SCC.

Enjoy,

Perry

[pianotuna]

PerryB67 wrote:

CA Traveler wrote:
Another factor is serial panels with bypass diodes which most panels have results in better shade tolerance than parallel.

Why would you have better shade tolerance in series than parallel. Nearly as good, or as good, but I don't see better, Then again, sometimes I need to be educated.

Enjoy,

Perry

Perry Unisolar made panels with diodes between every cell. Wired in series parallel, they do work in leafy shade, and in rain too.

There is one other currently made panel that has this feature--but they are from Germany and I have been unable to find a source to buy them from.

In general, parallel is better, but with a good MPPT controller more watt-hours may be harvested.

[StirCrazy]

PerryB67 wrote:

CA Traveler wrote:
Another factor is serial panels with bypass diodes which most panels have results in better shade tolerance than parallel.

Why would you have better shade tolerance in series than parallel. Nearly as good, or as good, but I don't see better, Then again, sometimes I need to be educated.

Enjoy,

Perry

the higher voltage at the controler has something to do with it. I even find this with my 24V panel in my camper. at 7am I will be getting between 0.5 and 1 amp of charge out of the 325 watt 24V panel but my 480 watt panels (12V's in parralel) will be putting nothing out for another hour at least. so low light/shading get better preformance as the voltage that does come through is high enough to start the charge. A MPPT charger is an important part of this equasion also in my opinion.

[PerryB67]

CA Traveler wrote:
Another factor is serial panels with bypass diodes which most panels have results in better shade tolerance than parallel.

Why would you have better shade tolerance in series than parallel. Nearly as good, or as good, but I don't see better, Then again, sometimes I need to be educated.

Enjoy,

Perry

[CA_Traveler]

Perry, I agree and 500W tends to be the point to give more consideration to serial for wiring loss. Serial advantages for me: Less cost with 24V panels, didn't want to upgrade later, less roof space and easier installation. With my 3 serial panels I have 64' of 10ga with extremely low loss due to the increased voltage and lower amps to the controller. Another factor is serial panels with bypass diodes which most panels have results in better shade tolerance than parallel.

My 750W serial 24V panels with MPPT controller cost $100 more than parallel 12V panels with PSW controller in 2014.

[PerryB67]

CA Traveler wrote:
400W of solar suggests 30A. Parallel 12V panels would require large wire to the controller vs serial panels at about 8A. For the OPs application 10 ga wire at 8A would be ideal, maybe even 12 ga. There are tradeoff factors for any installation.

A Renogy Compact or HQST 100 watt panel only has an IMP of 5.3 and a Renogy Eclipse 5.7. So even with four Eclipse panels you'll only get 22.8. We have 465 watts of solar on our roof (three 100 watt Renogy Compact panels and one 170 watt GoPower) and yet when I run the numbers using either Will or another site (can't use affiliates) both have my amps at 25 in parallel. We use 10 awg and it works just fine. Our roof is full though. If there was more room, plan to add panels in the future, and keep with parallel, I'd go with 8 awg.

Enjoy,

Perry

[valhalla360]

CA Traveler wrote:

BFL13 wrote:
Solar on the truck and move some of the batteries from whichever trailer is in use to the truck during the day to get recharged somewhat. Put the batts back in the evening. Move the other batts to the truck next day for their turn at some solar.

Sounds like fun - :S

I'd opt for a very small gen. 🙂

The idea is good but easier to just set it up so you can merge the battery banks easily by connecting a cable.

[Gdetrailer]

CA Traveler wrote:

BFL13 wrote:
Solar on the truck and move some of the batteries from whichever trailer is in use to the truck during the day to get recharged somewhat. Put the batts back in the evening. Move the other batts to the truck next day for their turn at some solar.

Sounds like fun - :S

I'd opt for a very small gen. 🙂

Or just stay home?

My hats off to folks that want to camp/live/work without commercial power and be willing to go to all of this backbreaking work shuffling panels, wires, controllers and yes hundreds of pounds of batteries.. You guys put way to much work into camping, I would rather put that energy into sitting back in my camp chair sipping on my favorite beverage enjoying watching other folks labor..

If I was in this situation with three different trailers all needing some means of charging I would personally dump the single one panel array idea on the back of a truck.

Instead put the (invest) money into enough panels to populate each RV reasonably well enough to to help assist with charging. Then fill in any additional charging with a portable gen. Solar is reasonably inexpensive now days, 100W 12V panels often can be had for $80 each new.. So, you invest $320 in 4 100W panels for each trailer, install on the trailer off and be done with it.

Expensive up front? You bet.

Much easier to deal with? You bet.

Less backbreaking work?, You bet.

Less chance of something stupid happening like connecting things backwards or forgetting to disconnect wiring before moving the truck or someone snagging your wire damaging your panels and wiring with a bicycle, motorcycle, quad or just walking through your site? You bet.

[CA_Traveler]

BFL13 wrote:
Solar on the truck and move some of the batteries from whichever trailer is in use to the truck during the day to get recharged somewhat. Put the batts back in the evening. Move the other batts to the truck next day for their turn at some solar.

Sounds like fun - :S

I'd opt for a very small gen. 🙂

[BFL13]

Solar on the truck and move some of the batteries from whichever trailer is in use to the truck during the day to get recharged somewhat. Put the batts back in the evening. Move the other batts to the truck next day for their turn at some solar.

[Skibane]

CA Traveler wrote:
400W of solar suggests 30A. Parallel 12V panels would require large wire to the controller

Agreed - Attempting to run 12-16 volts at 30 amps for any significant distance is going to require thick, expensive wire.

Connecting all 4 panels in series would give you 48-64 volts at only 6-8 amps - which could be done with much thinner, cheaper wire.

Naturally, you'll end up spending some of that wire savings on a more expensive charge controller that can charge your 12 volt batteries from 48-64 volt power.

[Gdetrailer]

CA Traveler wrote:
Practically I agree, but this isn't proof. As soon as you connect a voltmeter there is a load and hence amps flowing even if it's extremely small.

Not sure how to "prove" it, any ideas?


Actually 2 checks are commonly used in full (or close) sun: Voltmeter and compare to Voc (open circuit) spec and ammeter and compare to Isc (short circuit) spec.

Typical DVMs will have input impedance of 1-10 megohm if not much greater, comparable to the olden days of VTVM (vacuum Tube volt meters) then the FTVM (FET transistor voltmeter) that replaced the VTVMs.

DVM will present a nearly immeasurable load than the lower impedance of the solar panels unless you have some access to laboratory quality picoamp meters.

Lets just say that the average cheap DVM isn't going to drop the open circuit voltage enough to be measured by even the best Fluke meter..

I mean if you really wish to get crazy you can buy lab quality meters which have GigaOhm impedances.. Like THIS which is rated 70 GigaOhm input impedance..

But reality is a DVM does not present enough "load" to alter your reading of a 18V panel so why make such a fuss?

A DVM simply PROVES that the panel is generating a output voltage (panel has no internal circuit damage).

And as you mentioned, the OTHER test is to use a short circuit test which is done by placing a ammeter across the terminals (standard ammeter looks like a short but also has a resistance). So one would have to use a very large ga wire to create the short then read with an indirect ammeter if you wanted to nitpick things this far.