Moving to new house.. solar system sizing

[h2ofun]

Thanks all!

I'd love powerwalls to complete the system but I can't justify the $ for it because the payback isn't there (just based off of the Tesla's website of savings over 20 years). But, it seems with NEM 3.0 the math would all change and power walls would increasingly be favored.

My energy bill will not reflect my actual usage since I am not charging my car at home, will I receive any pushback if I want to an oversized system relative to my existing energy needs? I heard that PG&E will push back hard on allowing customers to get an oversized system as they don't want to be in the business of writing surplus checks.

Also, given TOU I heard that it may be advantageous to have the panels be west facing rather than south facing. South facing will generate the most kW but west facing will generate more power during the peak hours. Will Tesla walk through all the scenarios and create the best layout to optimize against the existing TOU plans? Or, will they simply put as many panels as possible south facing because that direction generates the most kW (without regards to west facing generating more energy during peak times)?

If one has excess power at true up time, since PGE only writes like 3 cents per KWH, no one ever would oversize to get money back!!!!

Even though I thought I had put on too large a system, things change. Now I find it is too small with my PW's. Luckily, I have put on 2 11.4K inverters so my wiring and stuff is all ready for as many panels as I can fit, which will not be enough to peg the inverters, but what the heck.

 

[Redhill_qik]

If one has excess power at true up time, since PGE only writes like 3 cents per KWH, no one ever would oversize to get money back!!!!

OP will be with San Jose Clean Energy, SJCE, for generation and would get back $0.0419 per surplus kWh at true-up, plus another $0.01 if they sign up for Total green. Not a massive incentive, but better than PG&E.

Thanks all!

I'd love powerwalls to complete the system but I can't justify the $ for it because the payback isn't there (just based off of the Tesla's website of savings over 20 years). But, it seems with NEM 3.0 the math would all change and power walls would increasingly be favored.

My energy bill will not reflect my actual usage since I am not charging my car at home, will I receive any pushback if I want to an oversized system relative to my existing energy needs? I heard that PG&E will push back hard on allowing customers to get an oversized system as they don't want to be in the business of writing surplus checks.

Also, given TOU I heard that it may be advantageous to have the panels be west facing rather than south facing. South facing will generate the most kW but west facing will generate more power during the peak hours. Will Tesla walk through all the scenarios and create the best layout to optimize against the existing TOU plans? Or, will they simply put as many panels as possible south facing because that direction generates the most kW (without regards to west facing generating more energy during peak times)?

I haven't seen any threads here about PG&E pushing back on oversizing. The PTO application has an automatic 10% added to your highest annual usage in the last 3 years , if you have it, and there is an entry for extra planned increases (getting an EV, switching from gas to electric, mining crypto ).

I had no issues with my PTO application that included another 23% (2,350 kWh) to my highest+10% which made the Production - Usage come out to -100 kWh.

On the solar placement, I think the best outcome is to fill the south facing roof to the maximum for best production all year and especially for the winter, then the west for the peak period before going to the east and lastly north.

My roof surfaces are horrible for solar, I have 6 on the SWS, 10 WNW, 3 ESE and 5 NEN. The original configuration was 4 SWS, 10WNW, and 10 ENE because that likely was the easiest to install. The change increased production estimate by 6.7%/723kWh.

 

[nwdiver]

Actually - under our Direct Energy Free Nights plan, we aren't charged TDU charges during free nights...

When projecting energy costs for a typical home, they are assuming customers have 45% free electricity and 55% daytime paid electricity.

With solar panels and energy storage, you should be able to do much better.

Before solar panels - we were using 68% of our electricity between 9AM-9PM. After adding solar panels and PowerWalls and shifting EV charging to overnight, we reduced daytime usage to 22%!

When we estimated long-term break-even, we assumed a fixed price 24/7 plan - at least until the utility companies start excluding solar/energy storage companies from free nights plans - we should be able to break-even faster than we had planned...

Interesting. I know that with TXU their free nights and weekends had TDU fees.

 

[tfan2018]

OP will be with San Jose Clean Energy, SJCE, for generation and would get back $0.0419 per surplus kWh at true-up, plus another $0.01 if they sign up for Total green. Not a massive incentive, but better than PG&E.

I haven't seen any threads here about PG&E pushing back on oversizing. The PTO application has an automatic 10% added to your highest annual usage in the last 3 years , if you have it, and there is an entry for extra planned increases (getting an EV, switching from gas to electric, mining crypto ).

I had no issues with my PTO application that included another 23% (2,350 kWh) to my highest+10% which made the Production - Usage come out to -100 kWh.

On the solar placement, I think the best outcome is to fill the south facing roof to the maximum for best production all year and especially for the winter, then the west for the peak period before going to the east and lastly north.

My roof surfaces are horrible for solar, I have 6 on the SWS, 10 WNW, 3 ESE and 5 NEN. The original configuration was 4 SWS, 10WNW, and 10 ENE because that likely was the easiest to install. The change increased production estimate by 6.7%/723kWh.

Good to know about no pushback on oversizing.. 8.16kw it is then!

Did you have to propose the configuration changes to Tesla? How did you arrive at conclusion that switching the configuration would yield more production?

I still don't know whether Total Green is worth signing up for or not... is it? The energy pulled from the grid costs 1 cent more, but surplus would also generate that additional 1 cent.

 

[Redhill_qik]

Good to know about no pushback on oversizing.. 8.16kw it is then!

Did you have to propose the configuration changes to Tesla? How did you arrive at conclusion that switching the configuration would yield more production?

I still don't know whether Total Green is worth signing up for or not... is it? The energy pulled from the grid costs 1 cent more, but surplus would also generate that additional 1 cent.

On the possible push back for oversizing, a 24 panel/8.16kW system is likely generating 10,000-13,000 kWh annually in San Jose, CA. PG&E will start with your home's sqft*3.32 and then you can justify any overage with your EV charging. BTW, if you aren't going to actually be charging your EV at home then choose the E-TOU-C rate versus the EV2A rate as it more cost effective.

I proposed the changes to Tesla including removing roof vents that were on their drawing, but not actually on the roof that prevent panel placement in a discussion with my project advisor after seeing the first drawing.

I concluded that switching would yield more production because I know that the sun is always south of my house and almost all of the panels were on the north facing roof slopes. I aIso used SunCalc sun position- und sun phases calculator with the satellite image overlay to look the sun path on the summer and winter solstices, 6/20 and 12/21, to see which roof slopes would be getting sun on the best and worst days.

I would only sign up for TotalGreen if you want 100% renewable for personal reasons or you know that you will be a net producer.

 

[ohmman]

I really like what Connecticut does for PV sizing - they look at the load that would be generated from the home, entirely transitioned to electric, plus 2 EVs. That's how much PV you can install. Groups will be pushing for something similar with NEM 3.0, especially if the "bad" stuff is looking likely (monthly true-ups, for instance).

 

[Ctein]

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?

Dear tfan,

Daly City Model X owner, here. Solar system, but no PowerWall (yet-- in six weeks).

We're missing two really important pieces of information. First, how many miles a day do you drive on average? Second, do you use your car to commute to work?

If the answer to the second is "yes," the solar system isn't going to do much for charging your car at all -- it'll be mostly generating power when the car isn't there! Unless you get a PowerWall, to bank KWh for use when you get home. That may or may not make it pay for itself -- you'll only be paid .05/KWh for your excess generation, and the off-peak (midnight to 3 PM) rate you'll be paying is 0.17. So, the PowerWall saves you money, the question is does it save you enough.

The miles per day matter, too. If you've got a ten-mile commute, you're using about 5 KWh round-trip. So banking car-power in the PowerWall isn't gonna save you more than about 60 cents/day.

(I have read that the PowerWall software will do what amounts to arbitrage: When you're on the Time-of-Day rate plan -- which you will be -- it can charge itself up when rates are low and feed your house off that stored power when rates are high. I do not know if that is true! )

My gut feeling is that with electric water heating and an induction stove, you're gonna need more than 4 KW... assuming you cook during daylight hours! (Or get a PowerWall.) Yes, they are efficient, but they're still using electrons instead of gas, and they'll eat up a lot of power over the course of a day.

But how much more you need depends upon your answers to my questions.

Yes, there is a minimum $10/month charge, which gets credited against your new usage. That is likely to go up over time because, in truth, we solar folk are not paying as much to PGE as it costs them to maintain our share of the grid. It's a compromise, because both the State and PGE want to encourage solar installation, but in the long run it's economically unsustainable.

Same reason your water rates go up when there's a drought. Less usage doesn't save the utility much on keep the pipes working!

If your partner isn't going to get an EV for 5-7 years, DON'T factor that into your decision. Panel prices continue to drop every year.

pax / Ctein

 

[flyboynwa]

I put in a 21.1 kw system with 3 power walls in Florida and am glad I did the largest I could. As for power walls they work 2 fold. if you don't have a poerwall you won't be able to use your solar during a power outage as the electric company will shut your system off to not allow back flow. Number 2 at night when most places charge you more for electricity you will not need to take electricity because you will power your house from the power wall
finally for my system and Powerwall and rebate etc I break even in 9 years.

 

[OldPro]

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?

If you contact Tesla now they can do an evaluation of need and benefit based on the power usage of the household that has occupied the home you are buying. You would have to evaluate if you think your family would have the same power needs + your Model 3 charging needs. I installed my Tesla/Solar City panels almost 6 years ago and it is one of the best financial decisions I ever made...with one EXCEPTION AND CAVEAT....At present 3 of the major California power companies are trying to get the PUC to change the rules and rates for excess power generated back into the system for NEW systems to be installed at some future date. (I have a profanity to describe this effort but will restrain myself) One of the 3 companies soliciting the PUC for this change is SDG&E which has reduced my savings by changing the rate structure for solar installation several times now thereby reducing my initial projected savings. Gee, thanks SDG&E! I'd get your system online to be installed ASAP. I'm waiting to get my Powerwall added until battery costs come down.

 

[TechnoMage]

When looking at getting solar do not forget the value the panels add to your house value. The payback is not just dollars saved on your electric bill, but the value added to your house, as well as the tax credits.

 

[h2ofun]

When looking at getting solar do not forget the value the panels add to your house value. The payback is not just dollars saved on your electric bill, but the value added to your house, as well as the tax credits.

Not everyone thinks panels add value. If leased, I know folks who walked about. If they are ugly looking at from street, I would walk away. So for me, I own everything. And I am trying to be very careful that one does not see a bunch of panels for my curb view value

 

[Ctein]

When looking at getting solar do not forget the value the panels add to your house value. The payback is not just dollars saved on your electric bill, but the value added to your house, as well as the tax credits.

Dear TM,

Well, the tax credits here get listed in when you order the panels, so it's not an surprise bonus. It's best to just think of that as a discount on the price. You order more than you really need, you're still out money you didn't need to spend. Just not as much.

Bay Area house prices are so high that solar doesn't materially change the asking price. By way of example, our Daly City house would sell for $1.3 *million*!!! We own our 4.5 KW system outright, no leases to be assumed. Last fall we were thinking about moving, so we brought in some realtors to discuss pricing, and we asked them directly if the solar would increase the asking price. The answer was no. It matters to some buyers, it doesn't to others, but it's just not a lot of money. Not compared to, say, a kitchen remodel (which has a much bigger impact on sales appeal around here).

Solar's a great investment... because of the reduced utility bills. Ours is going to pay for itself in about eight years (we're halfway there). After that, it's pure gravy. That's a nice ROI. Even if they change the rate structure a whole lot, we're still gonna come out ahead.

pax / Ctein

 

[SoCalSolarRoof]

If you contact Tesla now they can do an evaluation of need and benefit based on the power usage of the household that has occupied the home you are buying. You would have to evaluate if you think your family would have the same power needs + your Model 3 charging needs. I installed my Tesla/Solar City panels almost 6 years ago and it is one of the best financial decisions I ever made...with one EXCEPTION AND CAVEAT....At present 3 of the major California power companies are trying to get the PUC to change the rules and rates for excess power generated back into the system for NEW systems to be installed at some future date. (I have a profanity to describe this effort but will restrain myself) One of the 3 companies soliciting the PUC for this change is SDG&E which has reduced my savings by changing the rate structure for solar installation several times now thereby reducing my initial projected savings. Gee, thanks SDG&E! I'd get your system online to be installed ASAP. I'm waiting to get my Powerwall added until battery costs come down.

Which plan do you have now? I have a new install as of March and am trying to figure out which plan to use, DR2 seems like it gives me the most for my excess power during the day...

 

[jboy210]

Not everyone thinks panels add value. If leased, I know folks who walked about. If they are ugly looking at from street, I would walk away. So for me, I own everything. And I am trying to be very careful that one does not see a bunch of panels for my curb view value

Looks are a primary reason Tesla developed the SolarRoof. And one of the main reasons we bought one.

 

[mpstryker]

A Powerwall is a good investment for moving all energy consumption from the grid to off-peak times, in addition to completely preventing disruptions from the 4 power outages we have had in the Bay area since my system was installed. I got a 4kW system with one Powerwall in a house with gas heat, cooking, and hot water and one Tesla M3 to charge. My system provides 79% of the electricity I have used, averaged over a full year, and essentially all of the electricity taken from the grid is at off-peak rates. Payback time for the system at current electricity rates is < 8 years. Even so, I now wish I had installed an 8kW system with the one Powerwall to cover more driving in future (non-COVID) years and the last 20% of grid power. My Tesla contract in 2019 said that any additions or modifications would void the warranty. I have read that current NEM 2.0 customers will not be moved to the new NEM tariff.

 

[h2ofun]

Looks are a primary reason Tesla developed the SolarRoof. And one of the main reasons we bought one.

I would never put on, or buy a house, with solarroof

 

[tfan2018]

Dear tfan,

Daly City Model X owner, here. Solar system, but no PowerWall (yet-- in six weeks).

We're missing two really important pieces of information. First, how many miles a day do you drive on average? Second, do you use your car to commute to work?

If the answer to the second is "yes," the solar system isn't going to do much for charging your car at all -- it'll be mostly generating power when the car isn't there! Unless you get a PowerWall, to bank KWh for use when you get home. That may or may not make it pay for itself -- you'll only be paid .05/KWh for your excess generation, and the off-peak (midnight to 3 PM) rate you'll be paying is 0.17. So, the PowerWall saves you money, the question is does it save you enough.

The miles per day matter, too. If you've got a ten-mile commute, you're using about 5 KWh round-trip. So banking car-power in the PowerWall isn't gonna save you more than about 60 cents/day.

(I have read that the PowerWall software will do what amounts to arbitrage: When you're on the Time-of-Day rate plan -- which you will be -- it can charge itself up when rates are low and feed your house off that stored power when rates are high. I do not know if that is true! )

My gut feeling is that with electric water heating and an induction stove, you're gonna need more than 4 KW... assuming you cook during daylight hours! (Or get a PowerWall.) Yes, they are efficient, but they're still using electrons instead of gas, and they'll eat up a lot of power over the course of a day.

But how much more you need depends upon your answers to my questions.

Yes, there is a minimum $10/month charge, which gets credited against your new usage. That is likely to go up over time because, in truth, we solar folk are not paying as much to PGE as it costs them to maintain our share of the grid. It's a compromise, because both the State and PGE want to encourage solar installation, but in the long run it's economically unsustainable.

Same reason your water rates go up when there's a drought. Less usage doesn't save the utility much on keep the pipes working!

If your partner isn't going to get an EV for 5-7 years, DON'T factor that into your decision. Panel prices continue to drop every year.

pax / Ctein

due to COVID WFH my miles driven has dropped drastically. pre COVID I would average 25 miles roundtrip for my commute (with my model 3). at work, they offer charging at 8.4 cents per kW via chargepoint. I have free supercharging for the next two years as well. based on my charging history, I needed about 55-65kW of charge per week for my car (pre COVID). it remains to be seen the frequency of commute to work when COVID is over.

 

[nwdiver]

they offer charging at 8.4 cents per kWh via chargepoint. I have free supercharging for the next two years as well. based on my charging history, I needed about 55-65kWh of charge per week for my car (pre COVID). it remains to be seen the frequency of commute to work when COVID is over.

kWh

 

[wjgjr]

Looks are a primary reason Tesla developed the SolarRoof. And one of the main reasons we bought one.

Yeah - while a small number of folks have strong opinions against the Solar Roof, I do think the looks would typically be a net benefit compared to panels, and for most people, there won't be concerns about roof access. Whether or not that translates into much value at the time of sale, I do not know, and I would generally not count on solar (roof or panel) to translate to higher resale - though I could hope it would. I do like that should I need to sell, there is a 25-year warranty that covers not just the solar generation but the roof itself, and from a company that seems more likely than other solar companies to be around for the entire time.

 

[Ctein]

due to COVID WFH my miles driven has dropped drastically. pre COVID I would average 25 miles roundtrip for my commute (with my model 3). at work, they offer charging at 8.4 cents per kW via chargepoint. I have free supercharging for the next two years as well. based on my charging history, I needed about 55-65kW of charge per week for my car (pre COVID). it remains to be seen the frequency of commute to work when COVID is over.

Dear tfan,

I get it. If you're back in the office every day, you're using about 6 kWH/day, five days a week. But you might not be. A full charge would run you for, what, about two weeks if you were full time?

If you have to buy power from the grid at home, you won't be able to beat 8.4 cents/kWH! If you're home enough to recharge off your solar installation when it's sunny, that's a slight win, since you'd only be paid 5 cents by PGE for the excess you generated. A net gain over charging at work of a whopping 3.4 cents/ kWH or about a penny per mile driven. A whole quarter a day!

This really doesn't sound like it should enter into your current decision about how much solar to install. Unless you're driving a whole lot more in 5 years, or your partner drives a whole lot more than you, it may not even be worth considering expanding then. 'Course the price for solar will continue to drop , as will battery backup (it's dropped three-fold since we first priced solar), so wait and see.

But for now, I think it's more important you make a good guess on how much juice you'll really be using at home. Me, I think the 4 KW array would hit the sweet spot, economically, based on what you've described. If you want to feel more future-proofed, go to 6; I'm not hearing anything from you that would justify 8 unless you invest in a PowerWall (and maybe not then).

One thing you might ask Tesla is whether you can change your mind and add more panels to the order before they do the installation, if you want to. It's going to take you a while to get installation after you put down your deposit; you'll probably have a couple of months of PGE bills to look at before they do.

pax / Ctein