Moving to new house.. solar system sizing

[tfan2018]

Yep, you're probly right about that. It also depends on the net metering details you have, and as ohmman pointed out the TOU details can change. Do you get paid full retail TOU rates for your surplus?

No, but slightly higher than PG&E:

• Our Net Surplus Compensation rate will be 25% higher than PG&E for customers that are annual net generators of power (set annually; currently $0.04190 per kWh)
• If you are a TotalGreen customer, the extra $0.01/kWh premium applies when you are drawing power from the grid as well as when you are generating power and sending it back to the grid.

Rooftop Solar - San Jose Clean Energy

We think it’s great that you’re powering your home with the sun’s power! We are here to help you get the most out of net energy metering (NEM).

sanjosecleanenergy.org

 

[tfan2018]

I'd appreciate it my solar design can be reviewed. It's an 8.14kW system. Left is west facing. Bottom is south facing. Right is east facing.

Not sure if there's way to put the panels that are east facing either south facing or west facing instead. It seems I am already constrained on the placement due to space. Would they be able to put some south facing panels on top of the garage that's on the low left of the design?

I'm wondering if I should remove those 8 east facing panels altogether.

 

[h2ofun]

I'd appreciate it my solar design can be reviewed. It's an 8.14kW system. Left is west facing. Bottom is south facing. Right is east facing.

Not sure if there's way to put the panels that are east facing either south facing or west facing instead. It seems I am already constrained on the placement due to space. Would they be able to put some south facing panels on top of the garage that's on the low left of the design?

I'm wondering if I should remove those 8 east facing panels altogether.

I have seen some analysis now that a persons east facing was better on their property than west facing, which they did not put any.
So depends on shading and other things. I always thought east was a no go but I learned something the other day. And something is better than nothing, so it also depends on how much one wants to spend.

 

[SaveOurPlanet]

I think orientation is always location and environment dependent, in my case a South facing roof may be ideal, but I only have East and West facing roof planes. West facing tiles would help me get more peak rate credit but there are a few big pine trees on the west side of my house up the hill so it would not work out. I am left with the East side, I am sitting on a ridge and I can see the SF Bay and sunrise after 6:30 most days. I am still waiting for PTO but I test my system from time to time when I am in town. Last Sunday, my generation started at 7:30am and stopped at 6:30pm, giving me production time of 11 hours, of course, the main productive hours are only between 9:00am and 3:00pm.

 

[Vines]

If you intend on having powerwalls in PGE territory on EV2-A, afternoon production between 4pm and later is worth tripple what other hours are worth.

There are certainly many factors to your evaluation.

 

[h2ofun]

If you intend on having powerwalls in PGE territory on EV2-A, afternoon production between 4pm and later is worth tripple what other hours are worth.

There are certainly many factors to your evaluation.

3 to 4 is close to triple also

 

[tfan2018]

Currently there aren't any shading limitations on any of the roof, luckily.

From what I read, south produces the most energy, while west will help generate more energy during peak. I don't really see any advantage of east facing panels... unless it is to offset energy usage in the morning? But since morning till 3pm is still off peak I don't think it makes a difference

 

[fishtaco]

PG&E (San Jose Clean Energy) customer. I will be moving into a new home in the next few months and want to install solar as soon as possible to start saving money on my energy costs. I've settled on Tesla solar panels and I currently already drive a Model 3 with 2 years of free supercharging.

In the next two years, I think 4.08kW system should cover most of my electricity needs, but should I install 8.16kW to future proof? I estimate that my energy bill will be approx $100-$130/month during the next two years. Based on Tesla savings estimation, 4.08kw will cover $92 of the estimated ($100-$130/month) energy bill each month. I plan to replace the gas wat/er heater with a hybrid heater and also replace the gas cooktop with induction. I will likely need to start charging at home once my free supercharging ends and my partner will likely get an EV 5-7 years from now. What would you do in my situation? 4.08kW will cover the majority of my energy needs while 8.16kW system will definitely be oversized but in 3-5 years my energy needs to increase due to two EVs. Not sure whether it makes sense financially to install 4.08kW and install add-on panels later on, or just go big at the beginning with 8.16kW. I'd love to get a powerwall but from ROI perspective it doesn't seem to save any money and more for backup power.

As I understand it, there is a minimum $10/month bill with PG&E even if I cover all my energy needs from solar. But San Jose Clean Energy also provide 4.19cents/kW for any excess (Rooftop Solar - San Jose Clean Energy)

Will the $ generated from excess energy generated be sent to me via a check or does it stay as a credit on the power bill and rolls over into future years until it can be consumed? If I receive a check, then technically the excess power I generate can pay towards the $120 annual minimum bill?

Should I submit an order for solar as soon as I move in, or wait a few months to see my energy usage trends?

12@ 334watts is too small. that is max power which you wont get and i average 5 or 6 good hours of sun a day going to the panels here in san diego wjich doesnt help

 

[tfan2018]

I'd also like to add that Tesla calculated the 8.16kw based on the design above to be generating 11k kWh annually. Is this within expectations?

 

[ohmman]

But since morning till 3pm is still off peak I don't think it makes a difference

...still "currently" off peak... I wouldn't be surprised if the early mornings eventually get added back to peak or part-peak.

The benefit of east facing panels is early production for recharge of batteries. In a decent sized PV system, batteries are there mostly to get you through the night. But when you wake, the problem is that you've depleted some portion of the storage, and you're not going to be generating anything worthwhile until 11am. East facing panels do take some of that worry out.

 

[papab]

I'd appreciate it my solar design can be reviewed. It's an 8.14kW system. Left is west facing. Bottom is south facing. Right is east facing.

Not sure if there's way to put the panels that are east facing either south facing or west facing instead. It seems I am already constrained on the placement due to space. Would they be able to put some south facing panels on top of the garage that's on the low left of the design?

I'm wondering if I should remove those 8 east facing panels altogether.

Can you put more panels on the south facing roof? Unless you're offgrid and need the morning charge as ohmman mentioned, I think the return on investment for the east facing panels will be pretty small. East & West facing will have the same solar gain but if you're on TOU net metering that makes the west way better. That could be complicated if you have regular morning or evening clouds. I assume it's too late to change the roof design?

 

[tfan2018]

Can you put more panels on the south facing roof? Unless you're offgrid and need the morning charge as ohmman mentioned, I think the return on investment for the east facing panels will be pretty small. East & West facing will have the same solar gain but if you're on TOU net metering that makes the west way better. That could be complicated if you have regular morning or evening clouds. I assume it's too late to change the roof design?

Not too late to change the design, the installation itself won't happen for another 2-3 months due my specific circumstances.

I do agree the 5 panels on the south was fewer than expected. Morning is overcast 30-50% of the time so it's best that I avoid east or just give up those east facing panels.

 

[papab]

I meant the design of the actual roof, to get more south facing area.

 

[tfan2018]

No, the roof itself wouldn't be changed/re-designed. It is what I have to work with.

 

[Ctein]

I'd also like to add that Tesla calculated the 8.16kw based on the design above to be generating 11k kWh annually. Is this within expectations?

Dear T,

Our system is a 4.85KWDC/4.25KWAC system. IOW, a bit bigger than half yours. Our panels are entirely south facing, but since we're in Daly City, which has a higher fraction of time under the marine layer, it's probably roughly comparable to your situation. In the first three years of run, we averaged 6,500 kWH/year of production. If that 8.16KW is the DC panel output, then that scales up to almost exactly 11MWh/year. If that's your usable AC, then 12.5MWh/year.

So, yeah, sounds like a realistic estimate.

As I recall, you said you weren't getting a PowerWall at this time, so other people's comments about recharging that really don't apply. Given that, I'd drop the 8 east-facing panels. It's adding 50% to your cost for considerably less power generation than that (Is there a base installation fee or is it entirely proportional? You do the math.) That pesky morning marine layer, plus much less power from those east-facing panels after 3PM in the afternoon, when rates jump up. It doesn't sound cost-effective to me, unless you use lots of power in the morning.

Removing that third of the panels will still likely leave you with more than 8MWh/year real production.

pax / Ctein

 

[tfan2018]

Dear T,

Our system is a 4.85KWDC/4.25KWAC system. IOW, a bit bigger than half yours. Our panels are entirely south facing, but since we're in Daly City, which has a higher fraction of time under the marine layer, it's probably roughly comparable to your situation. In the first three years of run, we averaged 6,500 kWH/year of production. If that 8.16KW is the DC panel output, then that scales up to almost exactly 11MWh/year. If that's your usable AC, then 12.5MWh/year.

So, yeah, sounds like a realistic estimate.

As I recall, you said you weren't getting a PowerWall at this time, so other people's comments about recharging that really don't apply. Given that, I'd drop the 8 east-facing panels. It's adding 50% to your cost for considerably less power generation than that (Is there a base installation fee or is it entirely proportional? You do the math.) That pesky morning marine layer, plus much less power from those east-facing panels after 3PM in the afternoon, when rates jump up. It doesn't sound cost-effective to me, unless you use lots of power in the morning.

Removing that third of the panels will still likely leave you with more than 8MWh/year real production.

pax / Ctein

thanks pax! Originally I was not going to purchase the powerwall, but I figured it’s now or never so I am going to buy it as a hedge against future TOU changes and “complete the system”. My goal/dream has always been solar + powerwall. PW may have a long payback but buying it will make me much happier. And there’s been a TON of good info I’ve received in this thread alone and the whole forum.
Thanks for the suggestion regarding removal of the 8 east facing panels. I think between your previous analysis on a 6kw based on my usage and now the addition of powerwalls I am all set

 

[Ctein]

thanks pax! Originally I was not going to purchase the powerwall, but I figured it’s now or never so I am going to buy it as a hedge against future TOU changes and “complete the system”. My goal/dream has always been solar + powerwall. PW may have a long payback but buying it will make me much happier. And there’s been a TON of good info I’ve received in this thread alone and the whole forum.
Thanks for the suggestion regarding removal of the 8 east facing panels. I think between your previous analysis on a 6kw based on my usage and now the addition of powerwalls I am all set

T, that's great!

It's really difficult to figure out the economic value of a PowerWall, and we're not getting ours for another 5 weeks. So, all I know is what I've gleaned from reading about it. But I *think* it'll be a break-even proposition over its life. And, what with rate increases being a sure thing, that means better than break-even.

But, as you said, the big thing is it'll make you happier. That's why we're getting ours, so all the important parts of the house will have a UPS the next time(s!) a blackout hits.

Let us know how your installation goes.

pax / Ctein

 

[h2ofun]

T, that's great!

It's really difficult to figure out the economic value of a PowerWall, and we're not getting ours for another 5 weeks. So, all I know is what I've gleaned from reading about it. But I *think* it'll be a break-even proposition over its life. And, what with rate increases being a sure thing, that means better than break-even.

But, as you said, the big thing is it'll make you happier. That's why we're getting ours, so all the important parts of the house will have a UPS the next time(s!) a blackout hits.

Let us know how your installation goes.

pax / Ctein

It is amazing we live in a third world country in California and need to basically make our own power plants.

 

[bob_p]

For us, our PowerWalls provide us two benefits.

First, they allow us to operate off-grid during shorter (minutes to hours) unplanned outages and longer emergencies (hurricane, winter storm). For this use, the cost savings of the PowerWall is the cost of installing a comparable whole home generator that can provide power during grid outages. When we estimated our break-even when planning our solar panels/PowerWall system, we deducted the projected cost for a generator from the system cost - because the PowerWalls provide value equivalent to a generator.

Second, we're using a "free nights" plan, that provides completely free electricity between 9PM-9AM. By configuring the TEG, we are able to maximize solar/PowerWall power usage during the expensive 9AM-9PM period and have cut our daytime grid power to only 22% of our total grid power usage, increasing our cost savings by using solar/PowerWalls.

But, if we had been operating on a "buyback" plan - where the utility is paying us for excess electricity, our electric bill would have been much higher, since our solar/PW system was only providing us 59% of our power usage - so we would have had to pay for 41% of our electricity.

And if the grid is on almost all of the time, instead of storing power in the PowerWalls, the power would essentially be stored on the grid - and providing little cost savings for having the PowerWalls.

So the PowerWalls likely only provide noticeable payback if operating under a TOU plan, using the PowerWalls to shift grid usage to the least expensive (or free) periods.

 

[h2ofun]

For us, our PowerWalls provide us two benefits.

First, they allow us to operate off-grid during shorter (minutes to hours) unplanned outages and longer emergencies (hurricane, winter storm). For this use, the cost savings of the PowerWall is the cost of installing a comparable whole home generator that can provide power during grid outages. When we estimated our break-even when planning our solar panels/PowerWall system, we deducted the projected cost for a generator from the system cost - because the PowerWalls provide value equivalent to a generator.

Second, we're using a "free nights" plan, that provides completely free electricity between 9PM-9AM. By configuring the TEG, we are able to maximize solar/PowerWall power usage during the expensive 9AM-9PM period and have cut our daytime grid power to only 22% of our total grid power usage, increasing our cost savings by using solar/PowerWalls.

But, if we had been operating on a "buyback" plan - where the utility is paying us for excess electricity, our electric bill would have been much higher, since our solar/PW system was only providing us 59% of our power usage - so we would have had to pay for 41% of our electricity.

And if the grid is on almost all of the time, instead of storing power in the PowerWalls, the power would essentially be stored on the grid - and providing little cost savings for having the PowerWalls.

So the PowerWalls likely only provide noticeable payback if operating under a TOU plan, using the PowerWalls to shift grid usage to the least expensive (or free) periods.

Now, whether batteries, generator, nothing is SO personal dependent.

I sure am hoping that going 100% off grid during the 3x peak, and putting what solar I am generating during this time back to PGE at 3x cost, will help reduce my bills. I still am looking at more panels so I can charge the batteries faster, and send more 3x cost power back to my PGE battery for the winter use.