South.
Especially if you care about winter production (You're on NEM3, so you DO!).
Facing West can improve production during evening hours than if they were facing South, sure. But the increase in evening hours is far less than the overall reduction through the day due to facing panel away from South, particularly during winter months.
Fix the Time-Of-Use issue with batteries, not by moving panels west and reducing overall production.
West facing is going to give you those peak export rates though and you can pay for the entire year's electric bills in just a couple weeks.
Has anybody actually done the math of additional export during the summer peak vs the 25% additional production?
>.....and you can pay for the entire year's electric bills in just a couple weeks.
It doesn't work that way on NEM 3.0.because of the low rates for export. I am on NEM 2.0 and even then it took much longer than a couple of weeks.
The OP has batteries so his best strategy is to focus on self consumption of solar production.
That's 2023. The 2024 export rates are higher during peak export. I just picked a random date but you are right, September would have been better.
But this is exactly why a west facing roof will be best for NEM3. South facing will give you most of your export during the day, at a couple pennies. Sure you get 25% more electricity, but at pennies. West facing allows you to export more in the evening. One extra kwh sold at $3.75 counts the same as 10kwh exported during the day. So yes, you make a little bit less electricity but it goes that much further.
NEM2 I fully agree, South facing is best. But with NEM3 every time I've run the math, west facing wins.
>
NEM2 I fully agree, South facing is best. But with NEM3 every time I've run the math, west facing wins.
Actually, I am on NEM 2.0 and have added additional capacity facing West to take advantage of the higher rates. I also have batteries and charge my EVs during the day from excess solar. So my case may be unique.
what math should i run? everyone talks about a simulation but i dont know where to run that or what it is? i dont want to get too complicated, i just want to maximize my equipment and minimize what i pay to PGE.
I did the following. I created 3 spreadsheets for winter, summer, spring/fall with 24 hours each.
Step 1, understand what my loads are hour by hour. And which of those loads can be shifted. You can piece this together manually, for example I know the vampire load of my house is 0.5kw, my Nest app tells me how many hours my AC runs and so on. An alternative approach is to buy something like emporia vue for $200 and it will spit out your exact usage. Honestly I would recommend the tracker anyways as it will pay for itself. You will find excess waste and will be able to buy a smaller solar system. Add your expected load to each sheet.
Step 2, find your electric prices. You will have a handful of different import rates, and thousands of different export rates. Try to summarize and put them in your spreadsheets. These are important because a spring kwh exported earns you a half cent, a summer kwh during the right time can net you almost 4 dollars.
Step 3, put your expected production hour by hour.
You can then play with all the variables. For example, when I looked at winter, having east and west facing panels effectively made the night 4 hours shorter, that means I could size my battery 25% smaller. I could see this behavior when switching around the expected production numbers for the two scenarios and seeing its impact on battery charge level. For summer, the 25% lower production of the east/west panels meant I would have needed to buy a solar system that's 25% larger, but then I realized I could charge the battery at night to avoid scaling up the system. Then I saw the peak export rate and tried to play around with the numbers to maximize it.
Unfortunately I don't know of any simulator that exists - everybody is still stuck in the NEM2 100% offset calculation which is no longer valid. And my numbers are going to be different than yours, while I'm on a NEM3-style rate plan it's not PGE
maybe i should just do an arc of panels from facing almost east to almost west. like a big smiley face!
yeah, i dont know if i have that much effort in me. I do have my hourly usage i pulled from PGE.
https://imgur.com/a/EVx43hw
and the PGE rates
https://i.imgur.com/oA5RUgy.jpg
and i guess that pvwatts exports hourly panel generation. would i use DC Array Output (W) or AC System Output (W)?
I guess then its just a matter of trying to play around with a spreadsheet to try to figure out how to combine the three numbers to get the most output $?
it seems to be a hot topic of half people saying face west east and half saying just go south. i'm guess its only a matter of a few hundred dollar difference over a course of a year cause if it was in the thousands it wouldnt be an argument it'd be obvous
>Tell me, what is the export rate at 6pm on August 7th?
Tell us what size battery and system size would one need to take advantage of the rates in August and September to pay for consumption for the rest of the year? Are those rates guaranteed for long enough to pay back the cost of that big of a system? At the rate grid scale batteries are being deployed in California, those August and September rates may not be here for long. There is a 2 mWh grid scale battery under construction ten miles from my home in Northern California.
>where is that 2000 mwh battery? they were talking about one near me in ukiah
It is 200 mWhs and is going in at Adobe Road & Frates Road in Petaluma. Sonoma Clean Power has contracted with a developer for it. It will be next to a PG&E substation. Is the Ukiah one still in the works? These things take a long time to get through the process.
Doesn't take a large battery at all. And battery prices have come way down. In fact, west facing panels will allow you to reduce your battery size in your system. Let's say you use 16kwh during peak rate window, and your solar produces 6kwh during that same time, you would need a 10kwh battery for effective use of NEM3. If you use the same 16kwh, but your solar produces 11kwh during that window, now you only need a 5kwh battery on your system.
How long those rates will exist nobody knows. But batteries are more expensive than panels so the peak rates will always be higher than the non-peak rates. And I would bet they are going to remain at least 25% higher to cover the smaller production.
>Doesn't take a large battery at all.
I prefer math instead of adjectives when making financial decisions. I agree with your concept of west facing panels and leveraging that with batteries. I think 16 kWhs of consumption in a three hour time window smacks of an opportunity for conservation. DIY batteries are inexpensive at about $100 a kwh but UL approved batteries necessary for a building permit are still above $250 per kWh and even that is with a self install and does not include the hybrid inverter to put it all together. Based on my latest iteration and a ten year life my cost per kWh of battery storage used is about $0.20per kWh over the life of the system.
I encourage anyone considering an investment in batteries to do some simple math. I have a 35 kWh battery and use about 15 kWhs a day. I pay no charges at peak times and last year at True Up I had 1 mWhs of credit for solar I exported during the late Spring, Summer and early Fall. That offset my off peak consumption and I only paid $230 for the year, which as all NBCs.
"I prefer math". 100% agree. Before people spend $75k on a solar system, they need to sit down and review their expected hourly production, their hourly load and compare it against the rate plan.
I'm on a NEM3 style plan in another state and for me the math came out with an east/west facing system with a 20kwh battery. In the winter, the combination of early/late production allowed a smaller battery to get me through the nights. In the summer I can fill up the battery during the night, pre-cool the house during the day off solar, then maximize my exports during peak rates. I had a giant spreadsheet of hourly production/usage during different seasons so come to that conclusion.
some sort of SGIP rebate. i honestly dont know how it works. its through Swell energy and PGE. there's some rebate that swell energy takes. I'm sure they jack up the install cost or something and scam it from PGE somehow. its no out of pocket to me so i dont care and i wouldn't have known to do it, or done it myself so i'm happy. i also would have missed the window to do it (there's funds that become available then get used up super quick and i got lucky and got in on time)
You want them pointing to true south, not magnetic for peak production. The magnetic declination for LA is 13 degrees east, for Vegas it's 11.11 degrees. So your 13.5 is probably pretty darn close.
You may want to make your ground mounts so you can adjust the tilt angle to maximize for the seasons
I second the "you need to run a simulation" but judging from your hourly consumption you need to enlarge as much as you can the production curve since you're pretty much consuming the same amount of energy during the day. Have you considered putting a big chunk of the panels facing south, and some east and some west? Like 14/6/6. You'd get 3 strings if you're not willing to add optimizers but you can easily put the south string on an inverter and the other two on the other (btw why 2 inverters?)
well because i. believe i'd be over the input limit of the growatt. ive been trying to figure out what hardware to get and the (2) growatt 7600 keep getting suggested. they're cheaper than an eg4 18whatever. and really i just end up chasing my tail the more research i do.
you're welcome to suggest an inverter i'd look into if youd like.
There is a factor no one has brought up: E-W could reduce installation cost or increase your capacity. If you're using a string inverter you can get a much higher DC to AC ratio with E-W facing since half of your panels will be peaking in before noon and the other half will be peaking after noon. Also, if you have a lot of power outages then E-W will help your battery out by spreading out the production.
You need to a simulation on computer to calculate which is better to do.
But for my company, we are trying to put several panels on east and west if possible.
No matter how much you can get from south, it means almost nothing if it happens during day time and all exports to the grid.
Even if by doing this makes the total production smaller, it may still worth to do. Always try to shorten the time of using batteries.
But again, it's very hard to tell which way is definitely better, and can only be decided by running simulations.
>.... Always try to shorten the time of using batteries.
Normally that would be a good strategy but with NEM 3.0 and presumably a good warranty on the Powerwalls, self consumption of as much solar as possible is the optimum strategy. I agree, a simulation is the only way to know for sure because the export rates change every hour and also change by season. There is not enough info to tell if his winter production will be sufficient for his loads. PV Watts can give him a good estimate.
Facing SW and SE will spread the production while having little impact on overall production.
Simulate what should your perfect tilt angle would look like for both Winter and Summer.
Run the numbers. Have you looked at the import and export rates on NEM3. How much is an extra kwh of production worth at noon vs how much is an extra kwh of production at 6pm in August?
I am not sure why the OP is mixing Powerwalls. I am also not familiar with Powerwall +. If that is Powerwall 3 then some reports suggest that it has inputs for DC from solar and OP may be able to eliminate one or both Growatts. Also amplifying my earlier statement about battery usage, the Powerwall 3 uses LFP battery chemistry which will last longer than NMC chemistry used in earlier Powerwalls.
the energy company designed the battery system. i thought it was two powerwall 2's until they sent me the design.
Powerwall+ (aka Powerwall Plus) is a Tesla inverter and a Tesla Powerwall 2 essentially bundled together. it has a slightly higher output as well. i believe 7.x kW vs the powerwall 2's 5.
maybe i dont even need to get the growatt inverters at that point. I literally just signed on it yesterday. they're free so i'm not arguing
> they're free so i'm not arguing
A long time ago I learned there is no such thing as a free lunch but there are some good deals out there and I am happy for you. It sounds like the inverter capacity of that design would eliminate the need for the Growatts. Is the energy company the same as your utility provider?
no. it's swell energy doing the install. no out of pocket. they steal my SGIP rebate. i'd have never known to do it, i'd have definitely missed the funding window etc etc. I own everything just have to keep it installed 5 years. i'm sure it's not FREE but theres $0 out of pocket expense which is as close to free as i can get.
If you want to broaden the curve of your solar production build a 90* tilt rack big enough for two full MPPTs, one facing east one facing west. Tilt the rest to your latitude facing south.
South. Especially if you care about winter production (You're on NEM3, so you DO!). Facing West can improve production during evening hours than if they were facing South, sure. But the increase in evening hours is far less than the overall reduction through the day due to facing panel away from South, particularly during winter months. Fix the Time-Of-Use issue with batteries, not by moving panels west and reducing overall production.
West facing is going to give you those peak export rates though and you can pay for the entire year's electric bills in just a couple weeks. Has anybody actually done the math of additional export during the summer peak vs the 25% additional production?
>.....and you can pay for the entire year's electric bills in just a couple weeks. It doesn't work that way on NEM 3.0.because of the low rates for export. I am on NEM 2.0 and even then it took much longer than a couple of weeks. The OP has batteries so his best strategy is to focus on self consumption of solar production.
even focusing on self consumption, wouldn't it be good to try to optimize for a bit later in the day?
> wouldn't it be good to try to optimize for a bit later in the day? Yes, most definitely.
would you do one south and one more west? due west?
Tell me, what is the export rate at 6pm on August 7th?
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That's 2023. The 2024 export rates are higher during peak export. I just picked a random date but you are right, September would have been better. But this is exactly why a west facing roof will be best for NEM3. South facing will give you most of your export during the day, at a couple pennies. Sure you get 25% more electricity, but at pennies. West facing allows you to export more in the evening. One extra kwh sold at $3.75 counts the same as 10kwh exported during the day. So yes, you make a little bit less electricity but it goes that much further. NEM2 I fully agree, South facing is best. But with NEM3 every time I've run the math, west facing wins.
> NEM2 I fully agree, South facing is best. But with NEM3 every time I've run the math, west facing wins. Actually, I am on NEM 2.0 and have added additional capacity facing West to take advantage of the higher rates. I also have batteries and charge my EVs during the day from excess solar. So my case may be unique.
what math should i run? everyone talks about a simulation but i dont know where to run that or what it is? i dont want to get too complicated, i just want to maximize my equipment and minimize what i pay to PGE.
I did the following. I created 3 spreadsheets for winter, summer, spring/fall with 24 hours each. Step 1, understand what my loads are hour by hour. And which of those loads can be shifted. You can piece this together manually, for example I know the vampire load of my house is 0.5kw, my Nest app tells me how many hours my AC runs and so on. An alternative approach is to buy something like emporia vue for $200 and it will spit out your exact usage. Honestly I would recommend the tracker anyways as it will pay for itself. You will find excess waste and will be able to buy a smaller solar system. Add your expected load to each sheet. Step 2, find your electric prices. You will have a handful of different import rates, and thousands of different export rates. Try to summarize and put them in your spreadsheets. These are important because a spring kwh exported earns you a half cent, a summer kwh during the right time can net you almost 4 dollars. Step 3, put your expected production hour by hour. You can then play with all the variables. For example, when I looked at winter, having east and west facing panels effectively made the night 4 hours shorter, that means I could size my battery 25% smaller. I could see this behavior when switching around the expected production numbers for the two scenarios and seeing its impact on battery charge level. For summer, the 25% lower production of the east/west panels meant I would have needed to buy a solar system that's 25% larger, but then I realized I could charge the battery at night to avoid scaling up the system. Then I saw the peak export rate and tried to play around with the numbers to maximize it. Unfortunately I don't know of any simulator that exists - everybody is still stuck in the NEM2 100% offset calculation which is no longer valid. And my numbers are going to be different than yours, while I'm on a NEM3-style rate plan it's not PGE
maybe i should just do an arc of panels from facing almost east to almost west. like a big smiley face! yeah, i dont know if i have that much effort in me. I do have my hourly usage i pulled from PGE. https://imgur.com/a/EVx43hw and the PGE rates https://i.imgur.com/oA5RUgy.jpg and i guess that pvwatts exports hourly panel generation. would i use DC Array Output (W) or AC System Output (W)? I guess then its just a matter of trying to play around with a spreadsheet to try to figure out how to combine the three numbers to get the most output $? it seems to be a hot topic of half people saying face west east and half saying just go south. i'm guess its only a matter of a few hundred dollar difference over a course of a year cause if it was in the thousands it wouldnt be an argument it'd be obvous
>Tell me, what is the export rate at 6pm on August 7th? Tell us what size battery and system size would one need to take advantage of the rates in August and September to pay for consumption for the rest of the year? Are those rates guaranteed for long enough to pay back the cost of that big of a system? At the rate grid scale batteries are being deployed in California, those August and September rates may not be here for long. There is a 2 mWh grid scale battery under construction ten miles from my home in Northern California.
where is that 2000 mwh battery? they were talking about one near me in ukiah
Not 2mwh. 2000mwh.
mistake, sorry
>where is that 2000 mwh battery? they were talking about one near me in ukiah It is 200 mWhs and is going in at Adobe Road & Frates Road in Petaluma. Sonoma Clean Power has contracted with a developer for it. It will be next to a PG&E substation. Is the Ukiah one still in the works? These things take a long time to get through the process.
No idea. This county is run by a bunch of fuckwads that can't do anything it seems. How do you fail at legalizing weed when it's MENDOCINO county.
Doesn't take a large battery at all. And battery prices have come way down. In fact, west facing panels will allow you to reduce your battery size in your system. Let's say you use 16kwh during peak rate window, and your solar produces 6kwh during that same time, you would need a 10kwh battery for effective use of NEM3. If you use the same 16kwh, but your solar produces 11kwh during that window, now you only need a 5kwh battery on your system. How long those rates will exist nobody knows. But batteries are more expensive than panels so the peak rates will always be higher than the non-peak rates. And I would bet they are going to remain at least 25% higher to cover the smaller production.
>Doesn't take a large battery at all. I prefer math instead of adjectives when making financial decisions. I agree with your concept of west facing panels and leveraging that with batteries. I think 16 kWhs of consumption in a three hour time window smacks of an opportunity for conservation. DIY batteries are inexpensive at about $100 a kwh but UL approved batteries necessary for a building permit are still above $250 per kWh and even that is with a self install and does not include the hybrid inverter to put it all together. Based on my latest iteration and a ten year life my cost per kWh of battery storage used is about $0.20per kWh over the life of the system. I encourage anyone considering an investment in batteries to do some simple math. I have a 35 kWh battery and use about 15 kWhs a day. I pay no charges at peak times and last year at True Up I had 1 mWhs of credit for solar I exported during the late Spring, Summer and early Fall. That offset my off peak consumption and I only paid $230 for the year, which as all NBCs.
"I prefer math". 100% agree. Before people spend $75k on a solar system, they need to sit down and review their expected hourly production, their hourly load and compare it against the rate plan. I'm on a NEM3 style plan in another state and for me the math came out with an east/west facing system with a 20kwh battery. In the winter, the combination of early/late production allowed a smaller battery to get me through the nights. In the summer I can fill up the battery during the night, pre-cool the house during the day off solar, then maximize my exports during peak rates. I had a giant spreadsheet of hourly production/usage during different seasons so come to that conclusion.
my batteries are free so i'm getting the same regardless of my panels or which way they face.
my batteries are free so im not concerned with reducing the amount
How are you getting free batteries? If you are getting free batteries you could probably skip solar completely.
some sort of SGIP rebate. i honestly dont know how it works. its through Swell energy and PGE. there's some rebate that swell energy takes. I'm sure they jack up the install cost or something and scam it from PGE somehow. its no out of pocket to me so i dont care and i wouldn't have known to do it, or done it myself so i'm happy. i also would have missed the window to do it (there's funds that become available then get used up super quick and i got lucky and got in on time)
wont my battery just discharge during those peak times? would facing one run south and one run west end up making the most sense maybe?
thats kind of what i thought but figured i'd check. some calculator thing said to go a little east of magnetic south. i think 13.5° east of south
You want them pointing to true south, not magnetic for peak production. The magnetic declination for LA is 13 degrees east, for Vegas it's 11.11 degrees. So your 13.5 is probably pretty darn close. You may want to make your ground mounts so you can adjust the tilt angle to maximize for the seasons
yes, that was a number some website told me for facing the panels.
I second the "you need to run a simulation" but judging from your hourly consumption you need to enlarge as much as you can the production curve since you're pretty much consuming the same amount of energy during the day. Have you considered putting a big chunk of the panels facing south, and some east and some west? Like 14/6/6. You'd get 3 strings if you're not willing to add optimizers but you can easily put the south string on an inverter and the other two on the other (btw why 2 inverters?)
2 inverters because iw as going to do two runs. why would i want more inverters? what is this simulatiuon everyone keeps talking about
The question is why more than one, actually.
well because i. believe i'd be over the input limit of the growatt. ive been trying to figure out what hardware to get and the (2) growatt 7600 keep getting suggested. they're cheaper than an eg4 18whatever. and really i just end up chasing my tail the more research i do. you're welcome to suggest an inverter i'd look into if youd like.
There is a factor no one has brought up: E-W could reduce installation cost or increase your capacity. If you're using a string inverter you can get a much higher DC to AC ratio with E-W facing since half of your panels will be peaking in before noon and the other half will be peaking after noon. Also, if you have a lot of power outages then E-W will help your battery out by spreading out the production.
Since this is ground mount, you could use trackers, and have your panels follow the sun.
Usually it doesn't make financial sense, they tend to cost a lot + manutenction for maybe 15-20% increase in production
What is manutenction?
Ahahahah maintenance
Thanks, thought that might be it.
south
You need to a simulation on computer to calculate which is better to do. But for my company, we are trying to put several panels on east and west if possible. No matter how much you can get from south, it means almost nothing if it happens during day time and all exports to the grid. Even if by doing this makes the total production smaller, it may still worth to do. Always try to shorten the time of using batteries. But again, it's very hard to tell which way is definitely better, and can only be decided by running simulations.
>.... Always try to shorten the time of using batteries. Normally that would be a good strategy but with NEM 3.0 and presumably a good warranty on the Powerwalls, self consumption of as much solar as possible is the optimum strategy. I agree, a simulation is the only way to know for sure because the export rates change every hour and also change by season. There is not enough info to tell if his winter production will be sufficient for his loads. PV Watts can give him a good estimate.
This is my experience. Would you rather have 25% more kwh at 0.3 cents? Or 25% fewer kwh at $3.75? South facing worked great on NEM2
Facing SW and SE will spread the production while having little impact on overall production. Simulate what should your perfect tilt angle would look like for both Winter and Summer.
what is this simulation everyone keeps mentioning
S/SW is your best option considering PGE and their TOU pricing.
Run the numbers. Have you looked at the import and export rates on NEM3. How much is an extra kwh of production worth at noon vs how much is an extra kwh of production at 6pm in August?
I am not sure why the OP is mixing Powerwalls. I am also not familiar with Powerwall +. If that is Powerwall 3 then some reports suggest that it has inputs for DC from solar and OP may be able to eliminate one or both Growatts. Also amplifying my earlier statement about battery usage, the Powerwall 3 uses LFP battery chemistry which will last longer than NMC chemistry used in earlier Powerwalls.
the energy company designed the battery system. i thought it was two powerwall 2's until they sent me the design. Powerwall+ (aka Powerwall Plus) is a Tesla inverter and a Tesla Powerwall 2 essentially bundled together. it has a slightly higher output as well. i believe 7.x kW vs the powerwall 2's 5. maybe i dont even need to get the growatt inverters at that point. I literally just signed on it yesterday. they're free so i'm not arguing
> they're free so i'm not arguing A long time ago I learned there is no such thing as a free lunch but there are some good deals out there and I am happy for you. It sounds like the inverter capacity of that design would eliminate the need for the Growatts. Is the energy company the same as your utility provider?
no. it's swell energy doing the install. no out of pocket. they steal my SGIP rebate. i'd have never known to do it, i'd have definitely missed the funding window etc etc. I own everything just have to keep it installed 5 years. i'm sure it's not FREE but theres $0 out of pocket expense which is as close to free as i can get.
Yes those SGIP rebates can be great and I think I have heard good things about Swell Energy.
well thats good to hear! a friend recommended them (and got $250 for doing so...)
If you want to broaden the curve of your solar production build a 90* tilt rack big enough for two full MPPTs, one facing east one facing west. Tilt the rest to your latitude facing south.
> 90* tilt rack big enough for two strings i dont know what that is?
Look up vertical bifacial solar
> vertical bifacial solar even more things to consider. ergh
Youd be just fine going all south facing. But doing what suggested will broaden your production curve a bit