Solar upgrade

Trappfarmer · 01-09-2021, 06:47 PM

It seems like the rend is toward adding solar panels for charging batteries and maintaining batteries when not on a trip.
We have a 100w system that came with the unit from FR. Thinking of adding 1 or 2 or even 3 more.
Would like to here some comments from those that have done this.

TitanMike · 01-09-2021, 07:04 PM

How lsrge is your battery bank? The larger it's amp hour capacity the more panels that are recommended.

A 100 watt panel will deliver around 6-7 amps of charge current. A 50% discharged 100 amp hour battery will need 50 amp hours replaced. That would take 8+ hours if the system was operating at max efficiency and the battery stored every bit of power it received.

Since we know that neither happens it's best to go large with solar. Put the largest number of panels on the roof that can be supported by both the roof size and your budget.

Especially if you enjoy off grid camping.

Trappfarmer · 01-09-2021, 07:22 PM

Aren’t we already over budget just owning one of these things?

Sunvalley ID RVer · 01-09-2021, 08:01 PM

Mine came with a 100W solar panel. It's basically an adder to feel green. A 100W isn't much and might be verily enough to power some of the electronics that are always on like the precision plex or wifi stuff. I was told you should not walk on them. So if you put more on your roof be becareful about accessing all the stuff on the roof.

**Flybob** · 01-09-2021, 09:10 PM

You can add more panels if you have room, remember you will likely need a new controller and have to upgrade the wire gauge. There are some good tutorials online to help configure systems. Check out Renogy.com as one.

richp · 01-09-2021, 09:17 PM

I have flat mounted Renogy 600 watt panels feeding two Trojan T-105s, and have lived for months at a time without ever touching the generator. That includes TV/DVD use evenings, no constraints on the (all LED) lighting, spring/fall furnace use, and a 2000 watt inverter powering a sewing machine and computers. (One year out at Quartzsite, it included inumerable hours of weekend football playoffs using a Tivo.) No A/C use, but pretty much normal living.

Flat mounting means less than optimal solar exposure. So I upped from 300 watts on my first generation installation to the current 600.

With the right hardware properly installed, and if you monitor your use and battery status with a decent controller/monitor setup (Trimetric is my choice) solar can be really functional.

Rich Phillips

TitanMike · 01-10-2021, 04:05 PM

Quote:

Originally Posted by Trappfarmer

Aren’t we already over budget just owning one of these things?

Very true. I just like to toss that in so nobody thinks I'm "spending their money" with my recommendations.

TitanMike · 01-10-2021, 04:11 PM

Quote:

Originally Posted by richp

I have flat mounted Renogy 600 watt panels feeding two Trojan T-105s, and have lived for months at a time without ever touching the generator. That includes TV/DVD use evenings, no constraints on the (all LED) lighting, spring/fall furnace use, and a 2000 watt inverter powering a sewing machine and computers. (One year out at Quartzsite, it included inumerable hours of weekend football playoffs using a Tivo.) No A/C use, but pretty much normal living.

Flat mounting means less than optimal solar exposure. So I upped from 300 watts on my first generation installation to the current 600.

With the right hardware properly installed, and if you monitor your use and battery status with a decent controller/monitor setup (Trimetric is my choice) solar can be really functional.

Rich Phillips

Quartzsite is definitely a place where Solar carries the day.

When I went there I was able to keep my batteries charged with only a 160 Watt portable system (LiFePo4 batteries). No sewing machine but lots of evening movies and some furnace use on cold mornings (it was January).

Solar can need some help up here in the Pacific NW even in mid-summer when it's overcast. Even larger roof mounted panel systems can struggle to keep up.

Maingler · 01-10-2021, 06:17 PM

The 100w panel you have is a 24v panel. You can add up to 575 Watts 24v panels without changing your controller.

Trappfarmer · 01-11-2021, 08:35 AM

This is the controller we have.

rk06382 · 01-11-2021, 10:14 AM

Quote:

Originally Posted by Trappfarmer

This is the controller we have.

That is a 30a MPPT controller that can have upto 100v coming from the solar panels. (30a x 14.3v = 430 watts)

My Victron SmartSolar MPPT 100/50 is a 50a controller.

richp · 01-11-2021, 10:25 AM

As a related aside, for various reasons flat mounted panels will rarely, if ever, actually send full rated power down the line to the controller.

So it would seem that a little overage on panel vs. controller capacity is not a bg issue -- until you decide to further beef up the array on the roof.

Rich Phillips

rk06382 · 01-11-2021, 10:49 AM

Quote:

Originally Posted by richp

As a related aside, for various reasons flat mounted panels will rarely, if ever, actually send full rated power down the line to the controller.

So it would seem that a little overage on panel vs. controller capacity is not a bg issue -- until you decide to further beef up the array on the roof.

Rich Phillips

I have ten 100w Renogy solar panels but max out at 730 watts from my 50a MPPT. (50a x 14.6v = 730w) Battle Born LiFePO4 Bulk/Absorption stage is 14.2-14.6v.

I have a 60a circuit breaker going to the panels as per Victron manual.

I did a thread on oversizing in Aug 2018:
Solar panel over sizing with rigid roof mount

richp · 01-11-2021, 12:02 PM

Hi rk,

Your other thread kind of affirmed my choice a while ago to double the flat panels and forget about risking my old bones going up top.

Rich

Trappfarmer · 01-11-2021, 01:51 PM

Wow! This is the reason for forums. Great answers and comments. I’m waiting on the quote for adding 1,2,or 3 100w panels.
Will revisit after the job is completed.
Thanks to all!

DogFather · 01-12-2021, 01:35 PM

Quote:

Originally Posted by richp

Hi rk,

Your other thread kind of affirmed my choice a while ago to double the flat panels and forget about risking my old bones going up top.

Rich

X2!

Agreed, going extra on the panel count has meant to me:

Less time on the roof
Have tilt capability, but haven't needed it
Less frequent dusting/cleaning/de-leafing
Better production on cloudy/overcast days
Better production when camping near trees
On good days, quicker recovery

gordonsick · 01-12-2021, 02:21 PM

A big problem for us with RV solar panels is that the cells on part of one or more panels can become shaded by a tree or some other obstruction. When a solar cell becomes shaded, it behaves like a resistor and becomes a "hot spot". That is, it switches from producing electricity to consuming electricity. Since the panels consist of many cells hooked in series, the shaded cells produce a voltage drop that eats up the power produced by the cells that are in the sun.

The solution is to have a shunt diode across each cell in the panel. The diode essentially shorts out the resistance of the hot-spot cell and allows the current from the other cells to bypass it.

While the problem has been known for some time, it is only recently that solar panel manufacturers have started installing shunt diodes with each cell on the panel. Since this is a "hot" issue, you can be assured that any manufacturer that has the shunt diodes will make sure to advertise it in their literature. If a panel manufacturer does not mention shunt diodes, it is probably best to assume that they aren't installed.

As an early 2015 adopter with my two 100W Go Power flexible solar panels, I'm pretty sure that I don't have shunt diodes, despite the high price I paid. I plan to install my own shunt diodes across the panel output wires in the future. I'll strip the installation off and install one or more diodes in series with each other and in series with the panel. I'll make sure that I don't put the diodes in backwards, since that will short out the panel. To make sure I've got it right, I'll put my multimeter in the mode to measure DC resistance. It will measure high resistance when I put the positive lead on the negative end of the diode and low resistance when it is lined up with the positive end. Then, I can measure the DC voltage of my panel. It will be positive only when I have the positive lead attached to the positive lead from the panel. Then, I'll connect positive to positive and have a shunt diode for the whole panel. I'll make sure that the diode can carry the full rated current of the (other) panel.

My fix will not be perfect, since it will only prevent the whole panel from becoming a hot spot. If I buy more panels, I'll make sure they have diodes on each cell, so that I get more power when some cells are shaded.

–Gordon

DogFather · 01-12-2021, 03:44 PM

Thanks, Gordon, that's very good info.

I don't think my panels have the diodes, but I'd like to add them as you discussed.

Do you have a diode spec or link to other info on this?

Trappfarmer · 01-12-2021, 03:47 PM

If I add 3 panels to the roof do I have to add battery capacity?

DogFather · 01-12-2021, 04:00 PM

You don't have to, but to avoid wasting some output from the panels, advisable. IOW, if battery capacity isn't increased, after the panels top off the existing battery, for the rest of the sunny day there's nowhere for the juice to go other than feeding current loads - your reservoir would be full.

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