Solar Panel Placement

Clark

I am in the process of mounting 1000 watts of solar panel on the shed roof at the cottage. I have space for 480 watts facing south. Should I place the remainder on the southeast facing side of the roof or place some panels facing west? Suggestions anyone?

Cariboocoot

Re: Solar Panel Placement

Welcome to the forum.

A lot depends on your particular location and how you use your system. But most of all you should know that having panels facing in different directions divides them into different arrays, and each array should have its own controller for maximum benefit. With an array that size you are probably considering an MPPT type controller. If you divide the panels into two or three separate arrays you might be better off over-all buying a separate PWM type for each array (especially financially as three MPPT controllers would cost a lot of money).

So you have the potential here for a "fixed tracking" set-up, where you have panels facing East, South, and West (or there about). In such a case the "East array" is usually made largest, as it starts the charging in the morning and is the primary power source for the Bulk stage. Then the "South array" will come in to play, along about Bulk end to Absorb begin and will take the battery bank through the Absorb stage to Float. Finally the "West array" will keep the Float going for as long as it is able. This would maximize the power available from the battery bank over night.

A lot of other things enter into this, such as the shading that might affect the arrays (especially early/late) throughout the year. Also you have to consider local weather conditions: do you get morning fog, high midday temps, or afternoon thunderstorms? All these things have to be looked into, as well as if the "East array" will be large enough to provide enough current to perform the Bulk charge adequately.

You can run some simulations with PV Watts: http://www.nrel.gov/rredc/pvwatts/ See what each array might output for your location throughout the year and determine if there's any big advantage to dividing the panels up as I described.

I'm sure others will have some insight on this as well.

RandomJoe

Re: Solar Panel Placement

I have my panels divided between south-facing and west-facing, tied to the same charge controller, and haven't seen any problems. I might get a little more out of them separated, but they run right at the wattage I expected during the peak of daytime sun so I'm not complaining. I have limited south-facing roof, but lots of west-facing. (East too, but there's a huge tree in front (east) of the house!)

Of course the one thing you must do is only PARALLEL panels on different faces. My south panels are one string, and my west panels are a string. (And I just recently added more west-facing for two more separate strings, four total strings now.) All of those parallel together coming down to the charge controller. Don't connect panels facing different directions in series!

As the sun rises, the south panels start up first. They also produce the most per-panel during winter. The west panels stay up in power later in the day than the south ones. I lose some winter with them due to the angle of the sun on them but actually produce more in summer.

As for whether to use SE or W, use the PVWatts link Coot gave. It is what showed me I'd actually get more overall (but less in winter) for west-facing panels, which surprised me.