facing PV arrays: East/West, North or South

[ButchDeal]

ok, inverter capacity. no this isn't a problem.

the issue arose because a poco rep told me that the scaling is based on annual usage. the formula is ~ .86 * annual total = max allowable system size in kwdc. this has not been stated anywhere previously, so i want to add the final array for the best ROI.

Since you are limited in total size based on DC capacity your best return is going to be south facing unless there is some time of use.

[Jest Waitn]

image_9538.jpg


If you are running a string system, you can use those extra E-W panels to extend your hours of
production, without increasing the size of your AC inverter plant. Extras would also help under
clouds, since orientation is not critical under the dispersed light. This array might produce this
curve on a sunny day. The inverters are pegged out for 7 hours straight, but they may exceed 8
once I clear some shade problems. Bruce Roe
NSnview.jpg

that's real good output. good installation.

[bcroe]

image_9538.jpg

i constructed an initial south facing pv array this year and it is operational.
the next array is scheduled for next year. it can be faced south, but there is a fair amount of sunlight on the property at sunrise and sunset, which brings an east/west array to mind. a north facing array is also possible. any ideas?

If you are running a string system, you can use those extra E-W panels to extend your hours of
production, without increasing the size of your AC inverter plant. Extras would also help under
clouds, since orientation is not critical under the dispersed light. This array might produce this
curve on a sunny day. The inverters are pegged out for 7 hours straight, but they may exceed 8
once I clear some shade problems. Bruce Roe
NSnview.jpg

[Jest Waitn]

At some point, more south facing panels will start to be less cost-effective because you will begin to lose power to clipping mid-day. Eventually, the loss from clipping will exceed the loss you'd see from orienting the panels east or west. At that point, you could consider adding another inverter, but eventually, you'll max out the amount of backfeed your service panel can take. It isn't a scenario you are likely to run into, but I wanted to mention it as a qualifier just in case.

ok, inverter capacity. no this isn't a problem.

the issue arose because a poco rep told me that the scaling is based on annual usage. the formula is ~ .86 * annual total = max allowable system size in kwdc. this has not been stated anywhere previously, so i want to add the final array for the best ROI.

[sensij]

yes, grid tied.

what do you mean by 'max out inverter rating'?

At some point, more south facing panels will start to be less cost-effective because you will begin to lose power to clipping mid-day. Eventually, the loss from clipping will exceed the loss you'd see from orienting the panels east or west. At that point, you could consider adding another inverter, but eventually, you'll max out the amount of backfeed your service panel can take. It isn't a scenario you are likely to run into, but I wanted to mention it as a qualifier just in case.

[Jest Waitn]

You are grid-tied, right? All esle being equal, south facing will probably produce the most for you, but you can double-check with PVWatts. Once you max out the inverter rating that your service can accept, additional panels at less optimal orientations can help stretch out the production day.

yes, grid tied.

what do you mean by 'max out inverter rating'?

[JSchnee21]

Ha! I always wondered the same thing. So I decided to see for myself (attached).

For my current 12.2kW system:

Facing South: 16.754 MWh
Facing East or West: 14.609 MWh (12.8% less than South)
Facing North: 11.119 MWh (33.6% less than South)

NOTE: this is for a tilt of 20 degrees

Not as bad (for East/West) as I thought. But North takes a pretty substantial hit -- though its still "usable" if your install/add-on cost per Watt is low. But, given the cost per Watt, and these reduced yields, what impact does this have on your time to break even for this add on?

-Jonathan

[littleharbor]

Any northerly facing panels may produce in the summer season but in the winter would be pretty weak unless you are within the tropics. The tropics begin where on the summer solstice the midday sun is actually north of overhead, shining onto the north facing surfaces of vertical structures. Of course the opposite is true in the southern hemisphere.

[JSchnee21]

Clearly South will give you the best bang (kWh) for your buck as you get the longest and most intense sun hours per meter squared. But if you have time of use metering (in CA for example) a lot of folks seem to like to add Westerly or SW facing strings as well to spread some of their production into the late afternoon/early evening (when they get home from work) especially if their net metering terms aren't favorable with the TOU.

My raised ranch roof has one face that faces due South (175 degrees) and the other faces due North. But I find that I could potentially get a lot of sun on my Northern face (Only 20 degree pitch) in the mid to late afternoon. I don't have any panels there currently (and thus no data) but just from the impact of the solar radiation (heating) and duration, it seems SW/W/NW would be much better for me (in NJ) than Easterly facing.

But, if you are in a time of use market, I would do a differential cost analysis of adding storage vs. adding an additional string / array. To see which might give a better ROI.

PVWatts and/or the SolarEdge site designer (both free) should be able to give you fairly good production estimates for each of your various orientations.

-Jonathan

[sensij]

You are grid-tied, right? All esle being equal, south facing will probably produce the most for you, but you can double-check with PVWatts. Once you max out the inverter rating that your service can accept, additional panels at less optimal orientations can help stretch out the production day.

[Jest Waitn]

i constructed an initial south facing pv array this year and it is operational.

the next array is scheduled for next year. it can be faced south, but there is a fair amount of sunlight on the property at sunrise and sunset, which brings an east/west array to mind. a north facing array is also possible.

any ideas?