East facing array

[Bluedog225]

I had the chance to sit, drink coffee, and watch the sun this weekend.

I’ve been thinking about how best to implement an east and west facing array (in addition to a main southern array) to fatten the curve of production and minimize hours on battery. None of this is built yet.

I focused on the east array and I ran a few scenarios through the PV Watts calculator. But only a few. It’s a bit of a pain on an ipad.

My hypothesis was that facing due east would not be the way to go given the weak early morning sun. And that a southeast array would pick up more power.

It looks like the south east array picks up 6.3% more watts at 10 am. There’s a tradeoff between picking up early morning sun earlier and giving up total production.

For me, picking up 1500 watts or so as early as I can and maintaining it until the southern array kicks in would allow me to run the air conditioner as early as possible. And for a couple of months a year, this can be important.

I’m still trying do decide how early is too early to point a few panels at the sun.

Someone smarter that me and handier with a computer could figure out how to graph production curves find the optimal azimuth and tilt to maximize morning production and allow the easterly facing array to ramp up and meet the southern array smoothly without a dip between the two. And similarly for the westerly array.

Anyway, I thought someone might find this interesting. Cheers.

 

[SilverbackMP]

A YouTuber (don’t remember the name( did a deep dive on this and came to same conclusions you did.

 

[Warpspeed]

So many different factors to consider.

East/west panels, each elevated to look 60 degrees above the horizon will give a pretty constant output from sunrise to sunset.
Basically if you have 2Kw facing east, and 2Kw facing west, you get a very constant 2Kw all day long.

If you face all 4Kw facing due south, you get more than double the totak Kwh over a full day, but its in the form of a a MASSIVE peak centred around mid day with very little early morning and late afternoon.
That might be more useful, or maybe not, depending if all that concentrated power over a very few hours can be utilized.

I have both here, east/west, plus a large third array facing solar noon.

 

[TorC]

If you want to play with some numbers for up to three arrays in an off-grid setup, take a look at this thread. It's something I put together at a time when I was looking at a certain number of panels possibly going on either a south roof or split into a E/W arrays on a gable with ridge running north/south.

My conclusion from writing it and running some numbers was that the limit of performance is rainy days when every watt counts, and shortening battery hours didn't make up for the lessened production on said rainy days.

 

[Warpspeed]

Have to agree that the limit on performance is those totally grey sky days, where you cannot even see where the sun is supposed to be.

The light is totally diffused, and it makes pretty much no difference which way the panels are oriented. The key factor is the total number of panels in operation, not the direction. It makes hardly any difference, but the optimum position is pointing straight up ! The more sky the panels can "see" the better they work in a totally grey sky. You might only be getting five or ten watts per panel, but its better than nothing I suppose.

 

[JJJJ]

One thought would be to focus most of the panels south (northern hemisphere) and one or two facing east and west just to catch a few rays at the beginning and end of the day.

 

[Warpspeed]

When I first built my east/west arrays, I assumed that performance in winter would be pretty poor, because the sun is mostly low in the sky to the north, and the days are very short (southern hemisphere).
I was pleasantly surprised that in very poor cloudy conditions it contributed just as much as the direct north facing panels.

If you arrange your panel support into an equilateral triangle, looking up sixty degrees above the horizon east and west, it fits neatly onto a flat roof.
Its also structurally very strong, and wind loading either pushes downwards, or blows between the panels.

This has now been working for just over five years, and very happy with it.
I have since extended it to 8+8 panels instead of 6+6 panels.

 

[TorC]

Very interesting @Warpspeed, and good to know on the east/west panels. Maybe the insolation calculator I pulled data from gives more weight than observed to sun direction on cloudy days. I'd looked at all equator vs ±90° even split on 5:12 roof ≈ latitude. It's also possible the semi-sun days in winter were just so far off with the east/west that they couldn't make up the difference, whereas full cloud didn't matter, but is so low to begin with it doesn't do all that much.

 

[Warpspeed]

Sixty degrees elevation is optimum for all sun elevations from sunrise to sunset over the full 180 degrees.
The output varies only a few percent throughout the whole day with a clear blue sky.
As soon as the sun disc is completely above the horizon you are at full output.
Only one set of panels will be working though.
At solar noon you get each contributing exactly 50%.

 

[Warpspeed]

I use only one solar controller for this, and the east and west panels are combined with diodes into that single controller.
Its at its very best in mid summer where the sun passes directly overhead.
Its as good as an active tracker for consistency of output throught the day, but you only get 2Kw for 2Kw + 2Kw worth of panels.
With no moving parts and less to go wrong I think its a very good tradeoff as panels have become so cheap these days.
It has to be more robust in a storm than an active moving tracker flapping about. The wind cannot really get underneath it to create lift.

 

[RV10flyer]

I have 7.6kW facing SW at 64°, the remaining 24.4kW facing due South at 45°. For those of you that have poor morning weather, hill blocking the sun until about 9 to 10 AM and use the most power doing supper and dishes in the evening will like it this way better. I am going to add a little SE facing array this year, to catch the winter SSE sun. After adding SW, no more pulling 100-200A out of my battery in that 4-7 PM timeframe. I would not do a due E or W array.

 

[efficientPV]

I have some east facing panels and it is the best money I ever spent. Just what you need in the morning to recover from over night. I have a washer that operates directly from these panels without battery from 9am to 12. Domestic water heater also turns off by10am and we can use the dishwasher then. It is power when you need it.

 

[Bluedog225]

Curious if they are directly east facing?

 

[Gavin Stone]

My medium sized array is southeast facing. Definitely worth it. My larger array is directly south. And my smallest is facing almost directly west. Trying to gather what I can, when I can.

 

[Warpspeed]

East is particularly good for battery charging, because very early in the day is when you will be bulk charging, and everything you can get will be used.
Later in the day, there may be excess power available that goes completely to waste, because by then the battery is full.

The exception to that might be air conditioning, where you need a LOT of power in the afternoon and early evening.
What is best for you, can change a whole lot depending upon particular circumstances.

 

[JRH]

I had the chance to sit, drink coffee, and watch the sun this weekend.

I’ve been thinking about how best to implement an east and west facing array (in addition to a main southern array) to fatten the curve of production and minimize hours on battery. None of this is built yet.

I focused on the east array and I ran a few scenarios through the PV Watts calculator. But only a few. It’s a bit of a pain on an ipad.

My hypothesis was that facing due east would not be the way to go given the weak early morning sun. And that a southeast array would pick up more power.

It looks like the south east array picks up 6.3% more watts at 10 am. There’s a tradeoff between picking up early morning sun earlier and giving up total production.

For me, picking up 1500 watts or so as early as I can and maintaining it until the southern array kicks in would allow me to run the air conditioner as early as possible. And for a couple of months a year, this can be important.

I’m still trying do decide how early is too early to point a few panels at the sun.

Someone smarter that me and handier with a computer could figure out how to graph production curves find the optimal azimuth and tilt to maximize morning production and allow the easterly facing array to ramp up and meet the southern array smoothly without a dip between the two. And similarly for the westerly array.

Anyway, I thought someone might find this interesting. Cheers.

I wish I knew the answer.. … I would t have to work anymore…… but I don’t ….sry.