Light-Weight Solar Panels

[Davidasailor26]

The panels put out significantly less power than I expected. My panels are located on top of my dodger so they are shaded by the boom and mainsail.

The biggest drawback of serial wired panels is their susceptibility to shading. If one panel is shaded that will limit its output current, and the whole array’s output will be limited to that lower value. Parallel configurations are more shade tolerant, and having multiple controllers can be even better.

 

[dlochner]

Fusing rules are actually pretty simple, fuse to protect the wire and fuse close to the unregulated power source, i.e., battery.

Look to the ABYC Ampacity tables for guidance. First determine the temperature rating of the wire. Boat wire will specify the temperature rating. Next determine the expected load on the wire. If the load is expected to 30 amps, then look at the table under the appropriate temp rating (Most Boat wire is 105°.) The chart indicates that 14ga wire outside of the engine room is rated for 35a, thus the minimum maximum size fuse (or breaker) for this circuit is 35a. If the circuit is from a a regulated power source such as a solar panel that will produce less than 35a and is not connected on the other end to an unregulated source then no fuse is needed because the wire can handle the maximum current available.

In real life we typically have a large main source of power that branches out in successively smaller circuits with smaller wires. In this case every time the wire sized is reduced it needs its own individual fuse.

When selecting wire size it is necessary to consider both the amps it will carry and the round trip wire length. That is the length of the wire from the battery to the device and back to the battery. The longer the wire run the larger the wire needs to be to over come the resistance of the wire. Remembering Ohms Law, as the resistance increases the amps that can pass through go down at a constant voltage. In real life, this resistance turns precious electricity into heat instead of doing the job you hoped it would do.

The Ampacity tables provide guidance on the correct wire size. Look at the table for Conductor sizing, they come in2 flavors a 10% and a 3% voltage drop. using the 30 amp load again, the chart for a 10% drop shows 14ga wire is only suitable for short wire runs of under 10 feet. Longer runs will require successively bigger wire. If less line loss is desired, look at the 3% chart, a 10 ga wire is required for a 10 foot run and a 15' run requires 8 ga. (Be careful when reading the charts that you are reading the correct voltage chart as there are 12v and 24v charts.

So what's this mean for your proposed solar install. Each panel produces about 5 amps the 3% loss chart for 12 volts indicates that 10ga wire is adequate for a run of 60 feet. At 24v, closer to the actual output voltage 10 ga cable is good for about 120 feet.

On my boat, I generally use wire that is larger than needed to reduce line loss. Electricity doesn't come cheaply on a sailboat and I hate to waste it on heating wires. Most of the wiring that I install is 10 or 12 gauge for that reason.

Edit: Corrected an important word, changed minimum to maximum in the sentence fuse size.

 

[GeneraiT001]

Fusing rules are actually pretty simple, fuse to protect the wire and fuse close to the unregulated power source, i.e., battery.

Look to the ABYC Ampacity tables for guidance. First determine the temperature rating of the wire. Boat wire will specify the temperature rating. Next determine the expected load on the wire. If the load is expected to 30 amps, then look at the table under the appropriate temp rating (Most Boat wire is 105°.) The chart indicates that 14ga wire outside of the engine room is rated for 35a, thus the minimum size fuse (or breaker) for this circuit is 35a. If the circuit is from a a regulated power source such as a solar panel that will produce less than 35a and is not connected on the other end to an unregulated source then no fuse is needed because the wire can handle the maximum current available.

In real life we typically have a large main source of power that branches out in successively smaller circuits with smaller wires. In this case every time the wire sized is reduced it needs its own individual fuse.

When selecting wire size it is necessary to consider both the amps it will carry and the round trip wire length. That is the length of the wire from the battery to the device and back to the battery. The longer the wire run the larger the wire needs to be to over come the resistance of the wire. Remembering Ohms Law, as the resistance increases the amps that can pass through go down at a constant voltage. In real life, this resistance turns precious electricity into heat instead of doing the job you hoped it would do.

The Ampacity tables provide guidance on the correct wire size. Look at the table for Conductor sizing, they come in2 flavors a 10% and a 3% voltage drop. using the 30 amp load again, the chart for a 10% drop shows 14ga wire is only suitable for short wire runs of under 10 feet. Longer runs will require successively bigger wire. If less line loss is desired, look at the 3% chart, a 10 ga wire is required for a 10 foot run and a 15 run requires 8 ga. (Be careful when reading the charts that you are reading the correct voltage chart as there are 12v and 24v charts.

So what's this mean for your proposed solar install. Each panel produces about 5 amps the 3% loss chart for 12 volts indicates that 10ga wire is adequate for a run of 60 feet. At 24v, closer to the actual output voltage 10 ga cable is good for about 120 feet.

On my boat, I generally use wire that is larger than needed to reduce line loss. Electricity doesn't come cheaply on a sailboat and I hate to waste it on heating wires. Most of the wiring that I install is 10 or 12 gauge for that reason.

Many thanks Dave. I will not scrimp on wire thickness

 

[BarryL]

Hello.

This is very interesting information. With the Victron controller, I can monitor the solar output in real time. I saw situations where the 2 100W panels were generating only 20W. One panel was in the sun, the other heavily shaded. I thought that one panel was bad. I would disconnect one panel and the power would jump up. But later the situation would be reversed.

Now I understand what is happening.

Thanks!
Barry

The biggest drawback of serial wired panels is their susceptibility to shading. If one panel is shaded that will limit its output current, and the whole array’s output will be limited to that lower value. Parallel configurations are more shade tolerant, and having multiple controllers can be even better.

 

[DArcy]

Another consideration when deciding on parallel vs. series panel configuration is the rated input voltage to your MPPT. Mine cannot handle the higher voltage of solar panels in series so I have mine in parallel. I haven't looked at Victron controllers, they may well be able to handle the higher voltage.
While shading of one panel can reduce the total output in series, the voltage is higher in series so you do get marginal improvement in low light situations such as overcast and dusk/dawn.