Pre-testing the Solar Panel System

Before installing the solar-panel system aboard Hunky Dory, I decided to temporary test the system at my home in Ohio.

For this test system, I placed two Renogy 175-watt flexible solar panels on my patio at home, connected them in series, and used a Victron 150/100 MPPT solar charge controller connected to the panels over 20-foot solar-panel extension cables. To provide a load (so I could test what the solar panels could do), I connected the charge controller to an older 12-volt battery with various other loads. For loads, I connected a 300 watt inverter to the battery (with enough lamps connected to total close to 300 watts when turned on) and several 12 volt higher current devices - with all of this totaling more than the combined specified wattage of the two panels (350 watts).

The testing allowed me to confirm the wiring and controller settings, learn how to monitor the system with the VictronConnect app, and see how sunlight, panel angle, shading, electrical loads, and the battery’s charging stage and load affected the amount of power produced by the solar panels.

Compared panel angles and tested partial shading

I compared the panels lying flat and also with them propped against the patio fence at different angles, each at different angles to the sun. I performed the comparison during near solar noon, when the sun for the time (September) and location (Ohio) was approximately 53 degrees above the horizon, and the outside temperature was about 82 degrees F.

The highest output from the panels occurred in full sun (no clouds) with the panels tilted approximately 40 degrees, placing them close to perpendicular to the sun. The controller briefly showed about 270 watts at that angle—approximately 12.5 percent more than the panels produced while lying flat. So, aiming the panels directly at the sun provided slightly more power. This was the highest output power measured.

I purposely shaded roughly one-third of one panel by merely standing between the sun and the panel. The reported output on the controller dropped to approximately 125 watts, demonstrating how significantly partial shading can affect panels connected in series.

Clouds eventually rolled by, which gave me an opportunity to check the effects on the power out of the panels. With the sun obscured by a cloud, the output power of the panels varied between approximately 40 and 140 watts

With this testing, to maximize power produced from the panels, I had plenty of load on the system - enough power draw from the lamps and other devices to exceed the panel total specified wattage. Power over and above what the panels were capable of producing was supplemented by the battery.

Lessons learned

• Testing the components at home made it possible to verify the wiring, controller settings, Bluetooth connection, firmware, and basic operation before beginning the permanent installation aboard the boat.
• Solar output cannot be evaluated from one reading alone. Cloud cover, time of day, panel orientation, shading, battery state of charge, and the controller’s charging stage all affect the displayed output.
• Tilting the panels toward the sun improved their output, although the approximately 12.5 percent difference measured during this test suggested that mounting them flat would still provide useful power.
• Partial shading had a much greater effect than panel angle. Because the two test panels were connected in series, shading part of one panel substantially reduced the output of the pair. (A parallel configuration can improve that with some applications.)
• A nearly charged battery may cause the controller to reduce production even when full sunlight is available. A controlled load or partially discharged battery is helpful when testing maximum panel output.
• The inverter test showed that an electrical load does not necessarily produce an immediate, matching increase in harvested solar power. The battery can temporarily supply the load while the controller adjusts.

Tips

• Assemble and test the major components before installing them in locations that will be difficult to access.
• Follow the controller manufacturer’s connection sequence and configuration instructions. Confirm polarity and panel open-circuit voltage before connecting the photovoltaic input.
• Use properly sized conductors, fuses, and disconnects appropriate for the controller, battery bank, and expected current.
• Disable the controller or cover the panels while making or changing photovoltaic connections.
• Use a known electrical load and begin with a partially discharged battery when evaluating maximum solar output. Solar panels only produce power when there is a load applied to them. So a fully charged battery with no load on the system will indicate zero or very little output power even on full sun.
• Allow the MPPT controller time to stabilize after changing panel angle, shading, or electrical load.
• Take screenshots of the monitoring app after each change and photograph the corresponding panel position. This makes later comparisons much easier.
• Test partial shading before selecting the permanent panel location, especially when panels will be wired in series.

References

• Victron Energy — Product manuals
• Victron Energy — VictronConnect app manual
• Renogy — 175-watt flexible monocrystalline solar-panel information and manual