East or West

If you cannot face panels south and have just the choice of east or west or combination of both, what’s best?

I thought I would offer some generation figures based on a friend’s and mine 4kW installations completed last November. We are located within 300 yards of each other in North Essex so no differences re weather etc.
My friend, Nick, has a split installation of 8 Suntech 250W panels facing east and 8 west, both 35degree roof elevation coupled to a SMA 4000 TL Inverter. As of this morning his reading was 977kWh.
My installation, which went live a week after Nick’s, is 16 Hyundai 250W panels facing due west again at 35degrees roof angle coupled to a SMA 4000TL. My reading this morning was 1136 kWh, up 159kWh on Nicks.
We will continue to monitor and compare and I will post again later in the autumn with the latest figures.
I would be very interested to read about any other west or east only and split 4kW installations to get comparisons

Thanks

To make the best savings you need to look at when the household is using their electricity and try and match the generation to the usage. My guess is that an East West split will be the best as you will have a more equal spread of power generated over the whole day.

West is always better as gets the sun for longer

I would split the system, for several reasons:

Firstly, there will be a more even supply of power during the daylight hours. My SE-facing panels produce far too much power between 9am-12noon, and far too little power in the afternoons and evenings.

Secondly, a system which does not face South is at risk of "missing out" on the sun if the sun is only out for half of the day.
West-facing systems will "miss out" if it is sunny in the morning and clouds-over at lunchtime. East-facing systems will "miss out" if it is cloudy in the morning and clears at lunchtime.
So a system which isn't South-facing will be increasingly erratic from one day to the next, the further its orientation is from South (South has a chance to catch at least some direct morning or afternoon sun, even if it's a bit off to the side of the panels).

In fact, it I was able to, I'd have a system as follows:
3.6kW inverter.
2kWp facing SouthEast.
2kWp facing SouthWest.

brightasaspark said:

If you cannot face panels south and have just the choice of east or west or combination of both, what’s best?

I thought I would offer some generation figures based on a friend’s and mine 4kW installations completed last November. We are located within 300 yards of each other in North Essex so no differences re weather etc.
My friend, Nick, has a split installation of 8 Suntech 250W panels facing east and 8 west, both 35degree roof elevation coupled to a SMA 4000 TL Inverter. As of this morning his reading was 977kWh.
My installation, which went live a week after Nick’s, is 16 Hyundai 250W panels facing due west again at 35degrees roof angle coupled to a SMA 4000TL. My reading this morning was 1136 kWh, up 159kWh on Nicks.
We will continue to monitor and compare and I will post again later in the autumn with the latest figures.
I would be very interested to read about any other west or east only and split 4kW installations to get comparisons

Thanks

Click to expand...

There are two notable differences:

1.
The make of panel (one is better than the other?).

2.
One string compared to two strings (cable losses?).


....and some unknowns:

1.
The size and length of cables.

2.
Any shading issues.

i was thinking of putting 4KW on my dads place, 8 east and 8 west and was going to runb through pvsol tonight. I cant se why with todays prices this wont be an efficient/ sound investment?

brightasaspark said:

If you cannot face panels south and have just the choice of east or west or combination of both, what’s best?

I thought I would offer some generation figures based on a friend’s and mine 4kW installations completed last November. We are located within 300 yards of each other in North Essex so no differences re weather etc.
My friend, Nick, has a split installation of 8 Suntech 250W panels facing east and 8 west, both 35degree roof elevation coupled to a SMA 4000 TL Inverter. As of this morning his reading was 977kWh.
My installation, which went live a week after Nick’s, is 16 Hyundai 250W panels facing due west again at 35degrees roof angle coupled to a SMA 4000TL. My reading this morning was 1136 kWh, up 159kWh on Nicks.
We will continue to monitor and compare and I will post again later in the autumn with the latest figures.
I would be very interested to read about any other west or east only and split 4kW installations to get comparisons

Thanks

Click to expand...

Your post is interesting, and in my opinion it is only real tests like this here in the UK that will give us real results.

That said, the important part of system performance is design, so lets assume your friend Nick has no shading, and that the install is of good quality, with a similar cable runs and sizes to your own, Why the big difference in performance? Suntechs are a good performing panel.

My thoughts are his inverter is oversized, When the sun gets onto your 16 panels, away it goes, full power from 16 panels.

But this will never happen to Nick's, 8 panels tickling away in the morning, then the other 8 take over in the afternoon, what has been your maximum peak output? around 3200w I would guess, and Nick's would be around 2500w.

So if Nick had a smaller inverter, maybe a 3000tl it would start up sooner and be running in its "sweet spot" instead of struggling to run a 4000tl, therefore producing him more power.

There are many installers that just because they are fitting 4KW to the roof, think they need a 4000tl inverter, this is not always the case.

These are just my thoughts on this, it would be interesting if he could fit a smaller inverter for a month or two and then see what happens to his generation figures compared to your own.

Earthstore said:

My thoughts are his inverter is oversized, When the sun gets onto your 16 panels, away it goes, full power from 16 panels.

But this will never happen to Nick's, 8 panels tickling away in the morning, then the other 8 take over in the afternoon, what has been your maximum peak output? around 3200w I would guess, and Nick's would be around 2500w.

So if Nick had a smaller inverter, maybe a 3000tl it would start up sooner and be running in its "sweet spot" instead of struggling to run a 4000tl, therefore producing him more power.

Click to expand...

Yes, a relative of mine has a 30-degree roof, with 4kWp split into two opposite-facing arrays. Coupled with a 3.6kW inverter (Aurora 3600 indoor). Power peaks around 3.1kW in ideal conditions (i.e. about 85-90% of maximum designed capacity).

I have 3.75kWp - all SouthEast facing - and the Aurora 3600 indoor. In prolonged sunny spells it runs at 3.7kW (i.e. 100-105% of maximum designed capacity) and I do wonder whether that will shorten its lifespan by pushing it to the maximum.

Earthstore said:

Your post is interesting, and in my opinion it is only real tests like this here in the UK that will give us real results.

That said, the important part of system performance is design, so lets assume your friend Nick has no shading, and that the install is of good quality, with a similar cable runs and sizes to your own, Why the big difference in performance? Suntechs are a good performing panel.

My thoughts are his inverter is oversized, When the sun gets onto your 16 panels, away it goes, full power from 16 panels.

But this will never happen to Nick's, 8 panels tickling away in the morning, then the other 8 take over in the afternoon, what has been your maximum peak output? around 3200w I would guess, and Nick's would be around 2500w.

So if Nick had a smaller inverter, maybe a 3000tl it would start up sooner and be running in its "sweet spot" instead of struggling to run a 4000tl, therefore producing him more power.

There are many installers that just because they are fitting 4KW to the roof, think they need a 4000tl inverter, this is not always the case.

These are just my thoughts on this, it would be interesting if he could fit a smaller inverter for a month or two and then see what happens to his generation figures compared to your own.

Click to expand...

Correct you don't see peak output as high on east west but it should start and end a bit earlier.

I have an east west split 90 degree azimuth, first day of feed in 26th November, has very little shading ( a tree but not in winter) late on the west aspect.

The inverter is oversized and at its worst is probably only 92% efficient which will be winter time, early morning and late evening.

It has 16 Suntech STP240S-20Wd panels 8 east and 8 west and a Sunnyboy 4000TL. in Essex (The same setup as Nick but 240Wp less).

It has produced 1047kWh so taking into account we don't know exact install dates and this is a smaller system its very close.

I have seen Instantaneous peaks of 3760W and on a sunny day five minute average peaks as recorded by the inverter over 3000W

split between the 2 on 2 strings every time.
Just been back to a customer for some electrical work we did this for in Oct last year and production is well above SAP, and likely to get better still over the summer.
It's a mute point, but I am about to install 4.5kW this way on a 20 panel system, 10 on each roof. We will use a 3.6kW inverter. The net capacity is, therefore, 3.6 kW for the purposes of FiT so gets the higher rate. This will maximise production throughout the day and in less than ideal conditions but due to the E/W split shouldn't exceed the max capacity of the inverter even under ideal conditions. This is, I believe the way to make an E/W system economically viable
First one I have done this so should be interesting!!

FB. said:

Yes, a relative of mine has a 30-degree roof, with 4kWp split into two opposite-facing arrays. Coupled with a 3.6kW inverter (Aurora 3600 indoor). Power peaks around 3.1kW in ideal conditions (i.e. about 85-90% of maximum designed capacity).

I have 3.75kWp - all SouthEast facing - and the Aurora 3600 indoor. In prolonged sunny spells it runs at 3.7kW (i.e. 100-105% of maximum designed capacity) and I do wonder whether that will shorten its lifespan by pushing it to the maximum.

Click to expand...

Now this is my opinion here, firstly, your inverter will be fine, the panel performance will drop off just a little in a couple of years, so it will peak at maybe 97-100%, perfect, and very well matched I would say for optimum perfrormance.

As I wrote before, and this confirms my assumptions on the original post (thanks) that your relative could produce more from a smaller inverter,maybe a 3000, yes it may miss a couple of peaks, but the rest of the time the system would be producing more, as the inverter would be running at it's "sweet spot" so it is all down to system design.

I've pondered how solar panel performance might degrade as time passes.
I would think that after several months, there would be an equilibrium between muck landing on the panels and rain washing it off.

So the next stage will be panel malfunctions. I would guess that a malfunction would knock out a whole subsection of a panel (one-third of the panel), causing the bypass diodes to be permanently active, allowing the functional two-thirds of the panel, plus the undamaged panels, to continue almost normally.

So with 15 panels in my array, and with three subsections on each panel (total of 15 x 3 = 45 subsections), I would expect to lose 1/45th of my input (2.2%; from 3.75kWp to 3.67kWp) at the first malfunction.

As for whether that malfunction occurred after six months or three years; we could not predict in advance.
I might be lucky and have no malfunctions for five years and continue to operate at 3.75kWp, or I might be unlucky (or have poor quality panels, or just a bad batch) and find that I lose one panel's subsection per year, so that I'm down to 3.33kWp after five years.

Frankly, I'm not sure if I could tell the difference between 3.75kWp and 3.67kWp with a partial panel failure, given the variability in weather and temperature - and how panels can sometimes perform above their nominal rating if conditions are especially favourable. My 250Wp's manage 270Wp in ideal conditions (even after several months of muck accumulation probably at equilibrium) and that would be enough to mask the loss of three subsections, or one entire panel failure.

Some real world data from two systems less than a mile apart in Worcestershire.

1 10 kWp single phase (2 x SMA SB 5000TL) 37 Degress Dues south, slight shading midday.
1 9.88 kWp 3 pahse (SMA STP8000TL) 15 degree slope roof 18 panels on the East, 20 Panels on the West, slight shading in the morning first thing on the East facing panels, and slight shading very late pm on the west

We have a third 10kWp system going in about 2 miles from these systems (45 degree 15 degrees East of South) in a couple of weeks we'll add that data as well then.

The fact that the east / west split one is only at 15 degrees is clearly having a beneficial effect, we are monitoring them every five minutes for a whole year.