East/West PV Array with 1 mppt?

[Hedges]

Voltage is nearly the same whether direct sun or oblique.
Just do the math for 4s. That is, max Voc on record coldest temperature for your location not exceeding max allowed voltage input, and min Vmp on a hot day with panels hotter than ambient not below min MPPT operation.

If you will have shading, the voltage of a panel or diode-bypassed portion of panel will drop off. If that would be below minimum MPPT, would cause further loss of power.

 

[Andy_Knowles]

Voltage is nearly the same whether direct sun or oblique.
Just do the math for 4s. That is, max Voc on record coldest temperature for your location not exceeding max allowed voltage input, and min Vmp on a hot day with panels hotter than ambient not below min MPPT operation.

If you will have shading, the voltage of a panel or diode-bypassed portion of panel will drop off. If that would be below minimum MPPT, would cause further loss of power.

My voltage with 4 together exceeds the startup requirements.
All 8 panels will be in sun for the majority of the day - no chance of shading beyond there being clouds.

My roof is 22.5 degrees, I'm not sure if 8S will actually be better then 4S2P

 

[Hedges]

I'm not saying 8s; I don't have your numbers to check if that is OK.

If you have 4 panels facing East and 4 panels facing West, you want 4s2p not 8s.

Exceeding startup when cool may not mean being above minimum MPPT when hot. You have to run the numbers. I think the assumption is PV panels will be about 20 degrees C above ambient.

I had inverters with 24s (12V) panels. When one inverter died I rearranged several inverters as 16s2p. That worked fine except when shade hit a panel, because 15s or 14s was too low a voltage.

Your inverter may have voltage vs. efficiency curves. If 4s is allowed and 8s is allowed, likely inverter efficiency is lower at the higher voltage of 8s. But you may make up the difference in wiring loss.

 

[Andy_Knowles]

I'm not saying 8s; I don't have your numbers to check if that is OK.

If you have 4 panels facing East and 4 panels facing West, you want 4s2p not 8s.

Exceeding startup when cool may not mean being above minimum MPPT when hot. You have to run the numbers. I think the assumption is PV panels will be about 20 degrees C above ambient.

I had inverters with 24s (12V) panels. When one inverter died I rearranged several inverters as 16s2p. That worked fine except when shade hit a panel, because 15s or 14s was too low a voltage.

Your inverter may have voltage vs. efficiency curves. If 4s is allowed and 8s is allowed, likely inverter efficiency is lower at the higher voltage of 8s. But you may make up the difference in wiring loss.

Thank you for the reply, both configurations are within the tolerance of the controller.
8S is nowhere near the limit of the input voltage.
4S2P is only a few volts above the starting voltage - but to keep the mppt on it needs to remain above 120v (which it should easily)
Shading is definitely not an issue (I am out in the countryside and have taken down all nearby trees!

 

[Hedges]

I found your posting of PV and inverter data, looks OK to me.

Growatt 5000 ES in 2p4s with 400w panels

Hi all, I'm building my first system, and am just looking for advice really, This is for a garden office, with a East/West roof - I want to put 4 panels on each side - so running 2 parallel sets of 4 in series. I wanted to do them in two sets so that I won't get big losses in the morning and...

diysolarforum.com

Max allowed PV input voltage is 20% above Voc of 8s. Without having temperature coefficient of panels (on data sheet not label) and your location's record coldest temperature, I'll assume 16% rise. So not "nowhere near the limit", but sufficient margin.

Likewise startup and MPPT voltage vs. 4s x Vmp. String will be 12% above high-tolerance spec for startup voltage, and 22% above min MPPT. (All using nominal panel specs.)

Good enough.
I'll post a couple comments on the other thread.

 

[Hedges]

Are your roof faces due East and due West?
Have you used an insolation calculator to determine Wh production on the Winter Solstice? It may be quite low.

 

[Andy_Knowles]

Are your roof faces due East and due West?
Have you used an insolation calculator to determine Wh production on the Winter Solstice? It may be quite low.

Haven't done any calculation on that side, I think the west panels will get more time in the sun than the east as I'm at a bit of an angle (not perfect east west)

 

[TomC4306]

Not roof mounted but the same theory.
I sacrifice peak power for a wider production window.
Into a single MPPT.
Works great!

 

[Hedges]

Haven't done any calculation on that side, I think the west panels will get more time in the sun than the east as I'm at a bit of an angle (not perfect east west)

Tom's panels differ about 90 degrees in orientation, not 180 like yours.

But yours don't look as bad as I thought. For San Jose:
West South West with 68 degree angle from vertical gives 2.72 hours December, 6.56 hours June.
It won't let me evaluate East North East for the other four panels.
Repeat with your latitude.

Solar Irradiance Calculator

www.solarelectricityhandbook.com

 

[Andy_Knowles]

I think it will be fine, I'll start with a split of 4S2P
if in winter it turns out to be rubbish then i'll try switching the cabling to make a 8S and see if that helps... obviously it may make it worse!
Thanks for the info!

 

[Hedges]

8S won't help in the winter, maybe make it a bit worse pushing current past bypass diodes.
Another 4S aimed direct South and tilted would be best. (but avoid exceeding max PV current; suitably steep tilt may take care of that.)

 

[Andy_Knowles]

I'm using pretty much every square inch of space on the roof, so in at maximum panel capacity with the 8 panels total

 

[Hedges]

Depends on winter consumption.
South wall? Tilted up at the North edge of roof, hanging down at South edge? Portable ground mounts?
(Only if you determine you need more)

 

[Andy_Knowles]

I'll see how I go with what I've got, the see.

 

[Warpspeed]

It will work fine for you with either two controllers, or one controller.
If you decide to use just the one controller, suggest you fit series diodes where east and west connections are paralleled.
I originally had 3S 2P east and the same west on my garage roof. Its now 4S 2P east and the same west. Works extremely well.

 

[Andy_Knowles]

It will work fine for you with either two controllers, or one controller.
If you decide to use just the one controller, suggest you fit series diodes where east and west connections are paralleled.
I originally had 3S 2P east and the same west on my garage roof. Its now 4S 2P east and the same west. Works extremely well.

Thanks for the info, I did exactly that!
And yes it's working well, though I haven't got the battery yet, and it's winter, I've seen 2500w a couple of times when kettle and toaster on at once, not bad for an east/west 3200w array in winter!

 

[Warpspeed]

Yes, its a great way to do it.
Pretty much constant power from dawn to dusk without the usual giant peak at mid day, and it also works well in a dull grey cloudy sky.
Its perfect for a no battery system because power is almost constant throughout the day. That is how I started out as well.
I later added four more panels to increase the voltage, and that made a big difference as you would expect.
Just took this picture a few moments ago, its spring down here, about an hour and a half after sunrise. Full power right now coming off the east bank.

 

[Andy_Knowles]

Looks great! I start getting power nice and early and it runs out around 7:30pm in the winter - though a few months to go yet.
My battery should arrive soon, so I'll be using it properly then, but even now I can put the underfloor heating on for free!

 

[Warpspeed]

I have three separate groups of panels, north, up, and east/west.
Of the three, the east/west works best.
There is less maximum power than the north facing panels, but usable power is there for many more hours each day.