NorCal, Tesla 4kw + 1 powerwall

[Wannaretireearly]

I don't understand with your monthly electric bills that low how you plan to get a decent ROI? Are your e-bills expected to go up significantly in the near future? I had trouble rationalizing an $11K cash purchase on my very simple 6.6 kW grid-tie system and it had an estimated payback of 7 years. Depending on the estimates you shared you are between maybe 10-15 years payback? People move to a new home on average every 7 years right?

Good question. Yep. Without the fed rebate I am looking at a 10-12 year payback.

I'm banking on getting the 26% fed rebate next year which brings my total cost to around 13-14k (10k + 6k + 2k tax = 18k. 18k - 4k fed discount = $14k cost to me).

I think I'm down to 8 year ROI factoring Fed rebate.

Now, if I actually factor pge net metering and the $ benefit I get from using the powerwall during peak times, the roi looks better. I'll post a calc in another post that someone did for me on another forum...

[Wannaretireearly]

It looks like PG&E / Bay Area electricity has a lot of options / complications (e.g., time-of-use, tiers), so mervinj7's experience might be helpful to navigate the different electricity rates and net-energy-metering credits (e.g., Silicon Valley Clean Energy CCA). But here's an outsider guess looking at EV2-A (single meter) rate assuming NEM credits at retail:

https://www.pge.com/en_US/residential/r ... -plan.page

17¢/kWh from 12am - 3pm Off-Peak
37¢/kWh from 3pm - 4pm Part-Peak
48¢/kWh from 4pm - 9pm Peak
37¢/kWh from 9pm - 12am Part-Peak

As from VaR's production and consumption image of May 8th, production drops off around 5pm just after electricity jumps up to 48¢/kWh, and the higher rate also matches electricity usage going up in the evening when people return home. If we blend Part-Peak/Peak rates to be 43¢/kWh from 3pm - 12am, a 4kW system could produce up to 30kWh in the summer time with roughly 20kWh in 8 hours at Off-Peak 17¢/kWh for $3.40 and 10kWh in 4 hours at Peak-ish 43¢/kWh for $4.30. If we say your electricity usage is 10kWh Off-Peak $1.70 and 20kWh Peak-ish $8.60, this is a $10.30 daily cost that is reduced to $2.60, i.e., $7.70 savings generated by solar. Tesla's $7400 / $7.70/day = 2.6 years assuming this ideal summer day.

A battery pack allows you to shift your Peak electricity usage to look like Off-Peak, so charging 10kWh battery during Off-Peak and using that during Peak-ish makes the usage more match the 4kW solar production, so 20kWh Off-Peak $3.40 and 10kWh Peak-ish $3.40 results in an additional $2.60 saving for a $0 electricity charges -- i.e., $10.30 savings generated by solar + battery. Tesla's ($7400 + $6290) / $10.30/day = 3.6 years.

The breakeven time for solar is shorter than solar + batteries, but batteries do provide non-trivial ROI (about 1/3 of solar in this example) and also provide additional benefits such as protection from outages.

Also, an EV purchase in a couple years might have better vehicle-to-grid functionality which basically transforms the car into a mobile battery backup with much larger capacity (1 Model Y is more than 5 powerwalls). But that also has trade-offs of driving the car vs acting as a backup.

[Ampster]

..............

Also, an EV purchase in a couple years might have better vehicle-to-grid functionality which basically transforms the car into a mobile battery backup with much larger capacity (1 Model Y is more than 5 powerwalls). But that also has trade-offs of driving the car vs acting as a backup.

Whether vehicle to grid functionality ever comes about, an EV can allow you to leverage Time of Use rates. It is the classic load shifting scenario because you can plug in your car anytime and the timer turns on the charger whenever you program it. I have consumed more than I produced in the past several years and still only paid the fixed charges. In the summer for every kWh that I sent to the grid I could draw down 3 kWhs at off peak rates.

[solar_future]

It looks like PG&E / Bay Area electricity has a lot of options / complications (e.g., time-of-use, tiers), so mervinj7's experience might be helpful to navigate the different electricity rates and net-energy-metering credits (e.g., Silicon Valley Clean Energy CCA). But here's an outsider guess looking at EV2-A (single meter) rate assuming NEM credits at retail:

https://www.pge.com/en_US/residential/r ... -plan.page

17¢/kWh from 12am - 3pm Off-Peak
37¢/kWh from 3pm - 4pm Part-Peak
48¢/kWh from 4pm - 9pm Peak
37¢/kWh from 9pm - 12am Part-Peak

As from VaR's production and consumption image of May 8th, production drops off around 5pm just after electricity jumps up to 48¢/kWh, and the higher rate also matches electricity usage going up in the evening when people return home. If we blend Part-Peak/Peak rates to be 43¢/kWh from 3pm - 12am, a 4kW system could produce up to 30kWh in the summer time with roughly 20kWh in 8 hours at Off-Peak 17¢/kWh for $3.40 and 10kWh in 4 hours at Peak-ish 43¢/kWh for $4.30. If we say your electricity usage is 10kWh Off-Peak $1.70 and 20kWh Peak-ish $8.60, this is a $10.30 daily cost that is reduced to $2.60, i.e., $7.70 savings generated by solar. Tesla's $7400 / $7.70/day = 2.6 years assuming this ideal summer day.

A battery pack allows you to shift your Peak electricity usage to look like Off-Peak, so charging 10kWh battery during Off-Peak and using that during Peak-ish makes the usage more match the 4kW solar production, so 20kWh Off-Peak $3.40 and 10kWh Peak-ish $3.40 results in an additional $2.60 saving for a $0 electricity charges -- i.e., $10.30 savings generated by solar + battery. Tesla's ($7400 + $6290) / $10.30/day = 3.6 years.

The breakeven time for solar is shorter than solar + batteries, but batteries do provide non-trivial ROI (about 1/3 of solar in this example) and also provide additional benefits such as protection from outages.

Also, an EV purchase in a couple years might have better vehicle-to-grid functionality which basically transforms the car into a mobile battery backup with much larger capacity (1 Model Y is more than 5 powerwalls). But that also has trade-offs of driving the car vs acting as a backup.

another way of looking at is that the marginal payoff period of the battery is 6.6 years ($6290/$2.6/365). Plus with a battery you have power when the power goes out.

[Wannaretireearly]

Thanks for the responses. Appreciated...

[solar_future]

What does common sense have to do with it? I think you've been drinking the solar salesman Kool-aid.

Around here, few home appraisers give any value to having solar, even if the panels are owned free and clear. Solar on the home is often a bargaining chip for the buyer to get seller concessions because there is often a lease transfer involved.

The poster here is talking about purchasing a solar panel system. Let's say you have two homes which are exactly the same, except for the fact that home A has solar panel system and home B doesn't have solar panel. Let's say over the next 10 years you are going to pay $15k less in electricity bills living in home A. A rational buyer will pay more for home A with solar because they will have to make $15k fewer payments to the electric company. This is logic a third grader could understand.

Homes will solar sell for 4.1% more, on average in the USA, than homes without solar. https://www.zillow.com/research/sola...ll-more-23798/
Please show me any study which indicates that homes with solar don't sell at a premium, not just some anecdotal story.

[J.P.M.]

The poster here is talking about purchasing a solar panel system. Let's say you have two homes which are exactly the same, except for the fact that home A has solar panel system and home B doesn't have solar panel. Let's say over the next 10 years you are going to pay $15k less in electricity bills living in home A. A rational buyer will pay more for home A with solar because they will have to make $15k fewer payments to the electric company. This is logic a third grader could understand.

Homes will solar sell for 4.1% more, on average in the USA, than homes without solar. https://www.zillow.com/research/sola...ll-more-23798/
Please show me any study which indicates that homes with solar don't sell at a premium, not just some anecdotal story.

I'd like to see the numbers behind the numbers on that info from Zillow.

Believe it or not, and for various reasons, not all folks who might want to buy a home are interested in PV. Maybe I'm wrong here, but seems to me that would reduce the size of the pool of potential buyers. If so, and if supply/demand still works, that probably won't help increase the price.

Not that it matters, but I wouldn't consider any home w/ existing PV on it, particularly a system that's, say, 10 years old, and additionally, not sized to my load. Suppose the system only generates $10K in offset revenue ? How many prospective buyers even know their annual usage much less how how to determine an existing system's output.

The way system prices are coming down, if I was interested in a property and it had a PV system on it, even if I was positively inclined toward the system, I'd use it as a bargaining point and say something like: I like your home, but not the PV. Besides, I can get a new system sized to my needs for less. Here's the deal: I'll buy your lovely home if your either remove the system and make the roof whole, or leave it and lower your price by $15K.

To some, your logic is the type only a third grader would come up with because only a third grader couldn't see through it. Peddlers love it.

But all that's of topic.

[solar_future]

I'd like to see the numbers behind the numbers on that info from Zillow.

Believe it or not, and for various reasons, not all folks who might want to buy a home are interested in PV. Maybe I'm wrong here, but seems to me that would reduce the size of the pool of potential buyers. If so, and if supply/demand still works, that probably won't help increase the price.

Not that it matters, but I wouldn't consider any home w/ existing PV on it, particularly a system that's, say, 10 years old, and additionally, not sized to my load. Suppose the system only generates $10K in offset revenue ? How many prospective buyers even know their annual usage much less how how to determine an existing system's output.

The way system prices are coming down, if I was interested in a property and it had a PV system on it, even if I was positively inclined toward the system, I'd use it as a bargaining point and say something like: I like your home, but not the PV. Besides, I can get a new system sized to my needs for less. Here's the deal: I'll buy your lovely home if your either remove the system and make the roof whole, or leave it and lower your price by $15K.

To some, your logic is the type only a third grader would come up with because only a third grader couldn't see through it. Peddlers love it.

But all that's of topic.

There are multiple studies that suggest home buyers understand 3rd grade logic and zero studies that support your bs argument. It's odd when people have a financial interest in the utility sector they all of a sudden can't understand 3rd grade logic that runs counter to their financial interests.

"As of the second quarter of 2016 more than 1.1 million solar photovoltaic (PV) homes exist in the US. Capturing the value these PV systems add to home sales is therefore important. Our study enhances the PV-home-valuation literature by analyzing 22,822 home sales, of which 3,951 have PV, and which span eight states during 2002–2013. We also, for the first time, compare premiums with contributory value estimates derived from the present value of saved energy costs (income approach) and, separately, the replacement cost of systems at the time of sale (cost approach) to examine market signals. We find home buyers are consistently willing to pay PV home premiums across various states, housing and PV markets, and home types; average premiums equate to approximately $4/W or $15,000 for an average-sized 3.6-kW PV system. We find that a replacement cost net of state and federal incentives is a better proxy for premiums than gross installed costs, and that the income approach is a good signal if it accounts for tiered volumetric retail rates. Other results include detailed premium analyses for PV home sub-populations"

[Ampster]

I had an appraisal done on my home after I installed solar and the appraiser added 50% of the cost of the solar to the value. The only questions he asked were, do you own it and when did you install it.

[RichardCullip]

Getting back to the original discussion about a 4kW solar installation with one PowerWall in northern California, I would caution the OP to not base the analysis on a theoretical best day performance of 30kWh. Based on my 16 months of history with a 4kW system in Poway, CA, I have yet to see a single day produce 30kWh. The best single day I've seen just barely touched 29kWh of solar production. Down here in Poway, the best months I've experience are averaging 26kWh/day while in the worst month I couldn't even produce 14kWh/day. For my first full year, I've averaged 20.4kWh/day. If the back of the envelope economic analysis is built on a 30kWh/day production I suspect the OP will be sorely disappointed in his actual performance. I also doubt that he will have enough excess solar to keep a PowerWall charged during anticipated times of power shutdowns.

Of course I could be wrong....

[azdave]

Please show me any study which indicates that homes with solar don't sell at a premium, not just some anecdotal story.

My situation was not anecdotal. It was first-hand experience. I had a home appraisal done for a refi and the appraiser said the panels added no value to the home. I showed him it was a fully paid for system that I owned and also had documentation from the utility showing zero net energy costs for well over a year. He said that didn't matter. I then showed them that the contract with the local power company still had 17 years remaining, could not be cancelled and that it was fully transferable to any new owner of the property at no cost. He still refused to increase the appraisedvalue by even a penny and his boss agreed with that appraisal.

[J.P.M.]

Getting back to the original discussion about a 4kW solar installation with one PowerWall in northern California, I would caution the OP to not base the analysis on a theoretical best day performance of 30kWh. Based on my 16 months of history with a 4kW system in Poway, CA, I have yet to see a single day produce 30kWh. The best single day I've seen just barely touched 29kWh of solar production. Down here in Poway, the best months I've experience are averaging 26kWh/day while in the worst month I couldn't even produce 14kWh/day. For my first full year, I've averaged 20.4kWh/day. If the back of the envelope economic analysis is built on a 30kWh/day production I suspect the OP will be sorely disappointed in his actual performance. I also doubt that he will have enough excess solar to keep a PowerWall charged during anticipated times of power shutdowns.

Of course I could be wrong....

Richard and I are ~ 15 miles apart with mostly similar weather and somewhat similar array orientations.
FWIW:
my zip: 92026
System size: 5.232 kW.
P.T.O. date: 10/17/2013
Array orientation: 195.75 deg. azimuth, 18.75 deg. tilt.
System has ~ 3.5 % total production penalty from tree shade that occurs daily from ~ 1530 hrs. onward.

Total system production since startup: 61,068 kWh. No dropouts, no downtime. That total is from the system monitor but adjusted downward by 0.0051% to account for disparity between monitor and SDG & E meter.
Approx. max. possible system production including shading loss since startup with same weather but with/if 100 % clear skies every day: 75,495 kWh.
Average running 365 day total annual production after 1 year of operation: 9,068 kWh/365 days, minimum, 8,716 kWh/yr., max. 9,571 kWh/yr., population std. dev. : 191 kWh.
Average system daily production: 24.81 kWh/day. Maximum: 35.47 kWh/day. Minimum: 0.66 kWh/day, population std. dev. : 7.80 kWh/day.
Average system daily production per installed STC kW : 24.81kWh/day/5.232 kW = 4.74 kWh/(day*installed STC kW).
I estimate system production degradation at roughly 0.30 %/yr. to maybe 0.40 %/yr. Published from data sheet says 0.40 %/yr.

I'd expect Richard's system to do a bit better/STC W than mine at least partially due to it being in service for a shorter time.

All that is to agree with Richard's statement about analyses based on best (and so non typical) production and some possible example/info on why it may not be a good idea to not plan things on optimum production numbers.

Take want you want of the above. Scrap the rest

[Wannaretireearly]

Thanks Richard and JPM! Good questions for me to ask the vendors, max system production vs. Avg expected system production...

[solar_future]

I had an appraisal done on my home after I installed solar and the appraiser added 50% of the cost of the solar to the value. The only questions he asked were, do you own it and when did you install it.

that seems like a reasonable appraisal.

[PVAndy]

Thanks Richard and JPM! Good questions for me to ask the vendors, max system production vs. Avg expected system production...

As a certified Tesla installer who has designed numerous Powerwall systems I would suggest that you request your installer use a Gateway 2. This Gateway has a 12 slot internal panelboard option that can hold 3 full size 2 pole breakers or 6 Eaton Quad breakers. It can be configured to be either a unbacked up heavy load panel or an essential load panel.

Andy