should i consider pointing my panels a bit east and a bit west?

Hedges said:

The old powerwall was battery only. Do no models include PV MPPT?
I don't think so, and you need PV inverter if you have PV.
Powerwall by itself acts as UPS for house (maybe requires external transfer switch). But long power outage will drain it. It should AC couple to Growatt or other PV inverter, let you keep running indefinitely.
However, if loads exceed PV, it can't keep up. Will need to disconnect heavy loads. Battery can't charge without AC, and your loads could overload and shut off AC. (my system has a load-shed relay. And some loads direct on grid, not on battery.)


NEM 3.0 will force you on a different rate schedule, so have to consider the pricing.
DIY GT PV hardware will make power for about $0.025/kWh (amortized over 20 years), fast payback compared to $0.40 ~ $0.60/kWh utility rates.

Exact orientation and tilt could be optimized for different purposes, summer vs. winter best production, etc.
Partly a SWAG, partly preference for how yo want it to behave. Everything is a guess or predition.

To the first order, I assume the area presented to sun based on geometry determines production.
Due East and due West would give more flat production during summer, much less in winter.
I oriented 100% of my panels toward 2PM summer sun, for NEM 1.0. I've since added panels due East because peak times now later in the day. A bush now shades one array so I want to orient South East, more power than shaded and charge batteries earlier.

It is nice to have something that works well when grid is down.

Click to expand...

the grid here doesn't seem to go down much. other than when the fire came through. of course saying that, it will probably change.

i have quite good sky exposure and space so i can face the panels however is best. its getting too confusing and complicated and i dont care too much if there isn't a super clear advantage of thousands of dollars difference.

The Powerwall+ is a step up from its predecessor, the Powerwall 2, and comes with an integrated solar inverter, which is a significant upgrade.

The Powerwall+ should take the place of at least one Growatt maybe both. I think it can sent 7.6kW of PV to the grid, probably simultaneously charge battery with the remaining power.

Perhaps what Powerwall+ sends to grid can, up to 5kW, charge Powerwall2 battery. Consider not using Growatt at all.

Modest orientation changes won't make much $$ difference. North or due East/West could make bigger difference.
I would do approximately SE and SW for good year-round NEM 3.0 & offgrid performance. If I needed lots of A/C in summer then I might do something different.

Consider enough panels for 2 MPPT inputs for now, maybe max out the other 2 MPPT later, overpaneling for better production in poor weather/seasons. You probably won't find same panels, so would go on separate MPPT.

We've been seeing new panels for $0.17 to $0.27/W (some brands, from Santan and Inxeption among others.)
Used panels $0.10 to $0.27, including premium brands.
The 30% tax credit on new purchases helps influence the choice.

Utility rates and policies change. We are going to start having a higher fixed monthly cost, reducing benefit from PV. But building it cheap you should still save money.

Hedges said:

The Powerwall+ should take the place of at least one Growatt maybe both. I think it can sent 7.6kW of PV to the grid, probably simultaneously charge battery with the remaining power.

Perhaps what Powerwall+ sends to grid can, up to 5kW, charge Powerwall2 battery. Consider not using Growatt at all.

Modest orientation changes won't make much $$ difference. North or due East/West could make bigger difference.
I would do approximately SE and SW for good year-round NEM 3.0 & offgrid performance. If I needed lots of A/C in summer then I might do something different.

Consider enough panels for 2 MPPT inputs for now, maybe max out the other 2 MPPT later, overpaneling for better production in poor weather/seasons. You probably won't find same panels, so would go on separate MPPT.

We've been seeing new panels for $0.17 to $0.27/W (some brands, from Santan and Inxeption among others.)
Used panels $0.10 to $0.27, including premium brands.
The 30% tax credit on new purchases helps influence the choice.

Utility rates and policies change. We are going to start having a higher fixed monthly cost, reducing benefit from PV. But building it cheap you should still save money.

Click to expand...

I bought these panels new for $0.22 I believe. I can get more till they're gone. I went off a couple solar proposals from companies to match my usage and increased it by about 30-40%.

The powerwalls seem stupid. From what iw as told, if the grid goes down and they're fed more than 10kw from solar, that the powerwalls shit down the inverter and just run off the battery power. So if that's the case overpowering may be a bad idea. I'm trying to figure out the Max input for the Tesla inverter. A lot of those numbers don't.mean much to me.

I'm unfamiliar with the quirks of Powerwall.
If that is the case, use them within their limits.

Having PV array of two orientations will probably keep peak power below that 10kW limit, while extending hours.
So I'd try to make it a Tesla only system, no Growatt.

Do you know about the Backup Switch? Needed to feed backup loads when grid down. Is that Tesla Proprietary?

Hedges said:

The old powerwall was battery only. Do no models include PV MPPT?
I don't think so, and you need PV inverter if you have PV.
Powerwall by itself acts as UPS for house (maybe requires external transfer switch). But long power outage will drain it. It should AC couple to Growatt or other PV inverter, let you keep running indefinitely.
However, if loads exceed PV, it can't keep up. Will need to disconnect heavy loads. Battery can't charge without AC, and your loads could overload and shut off AC. (my system has a load-shed relay. And some loads direct on grid, not on battery.)


NEM 3.0 will force you on a different rate schedule, so have to consider the pricing.
DIY GT PV hardware will make power for about $0.025/kWh (amortized over 20 years), fast payback compared to $0.40 ~ $0.60/kWh utility rates.

Exact orientation and tilt could be optimized for different purposes, summer vs. winter best production, etc.
Partly a SWAG, partly preference for how yo want it to behave. Everything is a guess or predition.

To the first order, I assume the area presented to sun based on geometry determines production.
Due East and due West would give more flat production during summer, much less in winter.
I oriented 100% of my panels toward 2PM summer sun, for NEM 1.0. I've since added panels due East because peak times now later in the day. A bush now shades one array so I want to orient South East, more power than shaded and charge batteries earlier.

It is nice to have something that works well when grid is down.

Click to expand...

Actually, my experience with the east/west split showed no difference between the 'all north' neighbours installation and our 'half east/half west' of ours between summer and winter...
Yes, the sun track moves north at midday (correct here in the southern hemisphere) but still rises and sets in the east and west, so while the midday production drops on the split, the morning and afternoon gain in production still makes up to that lost midday peak...
That is what showed in our data between the two otherwise identical systems....

(we used to have 'races' lol- seeing if either system 'won' in daily production in the same conditions- and there was literally no difference between them in summer or winter (both made about 32kWh a day in summer, about 27kWh a day in winter- the only time we saw a major difference was in full, all-day overcast, where our split won hands down, usually 5kwh a day ahead of his 'all north'- I put this down to the entire sky becoming a 'diffuse' light source, and his panels could only see about 'half' the sky, where ours between them could 'see' almost all of it- hence the higher output...)
(we could look at the inverters display screen to see the total daily generated power in kWh)

This was the first days output- 31.8kWh from the 6kw of array- we had it installed in late December 2016 (our christmas present to ourselves), and that was the first full days production on the then brand new system in the middle of summer...

Bop raises an interesting point.

On total cloud days when its not even possible to see where exactly the sun is, solar output will be pretty pitiful.
But what matters most is the total area of exposed panels, and it does not seem to matter in which direction they face.
Pointing straight up is probably very slightly better, but not by much.
So if you have some unused roof space on the southern side (in the southern hemisphere) and you can get some cheap used solar panels, it can make a very worthwhile difference in mid winter.
This is counter intuitive, sun low on the northern horizon in mid winter, fitting south facing panels ?
But it definitely contributes on the worst solar days if you have unused roof space, and an abundance of low cost solar panels.

I have four groups of panels. Due east, due west, north, and pointing virtually straight up.
All contribute at various times in various ways, and it seems to balance out rather well in highly variable conditions throughout the year.
So don't get too bogged down with theory.
Its not as super critical as many people believe.
Its a simple case of more is always better....................

Hedges said:

I'm unfamiliar with the quirks of Powerwall.
If that is the case, use them within their limits.

Having PV array of two orientations will probably keep peak power below that 10kW limit, while extending hours.
So I'd try to make it a Tesla only system, no Growatt.

Do you know about the Backup Switch? Needed to feed backup loads when grid down. Is that Tesla Proprietary?

View attachment 212898

Click to expand...

i dont know about the backup switch, the installer will take care of that.

Warpspeed said:

Bop raises an interesting point.

On total cloud days when its not even possible to see where exactly the sun is, solar output will be pretty pitiful.
But what matters most is the total area of exposed panels, and it does not seem to matter in which direction they face.
Pointing straight up is probably very slightly better, but not by much.
So if you have some unused roof space on the southern side (in the southern hemisphere) and you can get some cheap used solar panels, it can make a very worthwhile difference in mid winter.
This is counter intuitive, sun low on the northern horizon in mid winter, fitting south facing panels ?
But it definitely contributes on the worst solar days if you have unused roof space, and an abundance of low cost solar panels.

I have four groups of panels. Due east, due west, north, and pointing virtually straight up.
All contribute at various times in various ways, and it seems to balance out rather well in highly variable conditions throughout the year.
So don't get too bogged down with theory.
Its not as super critical as many people believe.
Its a simple case of more is always better....................

Click to expand...

Most gridties struggle with cloudy days (although the new higher voltage ones (with 1000Vdc PV limits, rather than the older 600v or 500v ones) are dramatically better...) the biggest issue for the older gridties is the voltage ratio between the DC coming in (often only 400v or so) and the AC going out (230v AC, DC equivalent is 360vDC) means they simply don't have much extra to play with, it doesn't take much cloud to cut your exports to practically zero...

My offgrid system (even with its tiny 1.5kw array) gives me amply power to run the van and shed, because its using a high voltage (3 series 38v Voc panels) to the MPPT controllers to charge a 12v nominal battery bank- Literally at dawn, its already at 50V from the array and starting to put current into the bank (with no direct sunlight on the panels at all, shaded by trees)
This is at the old campsite, while building the shed- at dawn, and already the panels are at 52v, with half an amp flowing into the battery bank at that time...

Cloudy weather also means the high voltage arrays work better- this is at 8AM, 100% cloud cover with showers all day, the suns still down behind the trees still (there's an arrow pointing at it- the bright disc in the trees, just to left of the tree by itself in the middle and again- its already over 10% of its normal output under those conditions at 4.4A...

On days like that, I get 40%-50% of normal power made (even with 100% grey cloud cover and showers all day...) so by simply having more panels than I really need, even on days like that I can still charge the battery bank fully...
'Ye old PWM' or even MPPT with a 18v parallel array likely wouldn't put a single picoamp in all day under those conditions...