Solar Panels- Wired in Series vs. Parallel question

mchero wrote:
4 250 Watt Hight Voltage panels up on the roof. 2 Panels in series then parallel

The man just wanted to know which one is better - series or parallel. Wattage, number of panels or series-parallel variants were not part of the question, so let's stick to the subject ;)

I have 4 250 Watt Hight Voltage panels up on the roof. 2 Panels in series then paralled using MC4 branch connectors down to a Midnight Solar Classic 200 Light. Panels FLAT on the roof. Last month in Quartzsite I saw 900+ watts!

Question with no details = Going in circles.

Building a high voltage systems in series makes sense if you want to use smaller gauge wire. If you had 1000 watts of solar you would need some pretty hefty wire to the controller in parallel.

400 watts and above = series wired with MPPT controller.
400 watts or less = parallel wired with PWM controller if using 12v panels.

smkettner wrote:
Yup. The more power the more is in series.

Adding more power sources (panels) adds power regardless of how they are wired. The amount of additional power depends on the capacity of the panels.....NOT on how they are connected.

And back to the original question, for most RV applications there is no good reason to do anything but 12 V; batteries (6 or 12) panels and controllers.

Building a higher voltage system just doesn't make sense....unless your power needs approach a medium size house.

Yup. The more power the more is in series.

smkettner wrote:
Home systems are typically 3kW to 20kW and are not really running on 12 volt batteries.

They are not running on 12V batteries - they are running on 6V :)
Sorry couldn't resist. A lot of offgrid bungalows have a bunch of either GC or L16. For a total 48V of course.

beemerphile1 wrote:
Saw a tv show about solar on houses and other buildings. The statement was made that a system with panels in series could be dragged down by a poorly functioning panel. A system with panels in parallel would not be affected by a poorly functioning panel.

Others may be able to explain the hows and whys of the statement.

In series the bypass diodes would allow current to pass through a defective or heavily shaded panel.

In parallel you still lose the power from the defective or shaded panel.

In some unlikely extreme case the series panel could open the circuit completely for no solar power.

Either way the defective panel gets replaced and it becomes a non-issue.

BTW anyone with a large enough system to power a home will have most panels connected in series to the voltage limit of the inverter or controller. Home systems are typically 3kW to 20kW and are not really running on 12 volt batteries.

Wiring 12V nominal panels in series and using a PWM controller with a 24V battery bank may be more efficient than a parallel wiring scheme.

When wiring in series, shade on one panel will limit the harvest current to the lowest of the multiple panels. When wiring in parallel, shade on one panel will limit the harvest current to the aggregate of the multiple panels.

Controller efficiencies and power handling differ. While one controller may accept and efficiently deliver the most current with higher voltage, another may produce less power with higher voltage, comparatively. In the most general terms, smaller RV sized controllers will gain in heat with higher voltages. Higher heat means lost power and may effect longevity.

For expandability, sizing a controller to handle the higher voltages of the initial system wired in series, may require a controller replacement if controller input voltage is exceeded by the addition of more panels wired in series.

IMO, wire sizing is a non-issue for nearly all RV solar installations. If the difference in size is based on cost, an owner could change to a lesser quality toilet tissue and recover the cost difference between barely adequate wire and larger cable within a month. YTPMMV.

For residential installations where series mounted strings are typical, there is a lot of sense in using micro inverters like the Enphase system.
Since the system will operate without the current drop when a module is lost//shaded/malfunctioning, it makes for good sustainability. I'm reading that the durability of some micro inverters is in question and replacement costs are significant.

beemerphile1 wrote:
The statement was made that a system with panels in series could be dragged down by a poorly functioning panel. A system with panels in parallel would not be affected by a poorly functioning panel.

Not exactly correct.

In a series arrangement, ALL the current flowing goes through ALL of the panels. If one goes partially open (gets a high resistance and low output), it might severely limit the total output well below the capacity of the remaining good panels.

In a parallel arrangement, one panel going totally dead only removes the capacity of that panel and leaves the others unaffected.