How does solar and charging work?

[jboy210]

I am thinking about adding solar panels to my house, possible to offset some of my charging costs. Is anyone else doing this? Does it make sense? Do I need a powerwall?

FWIW, we pay $0.24/KWh in Northern CA off peak. We could receive $0.03 selling the power into the grid.

I want to do something in 2019 to try to capture the 30% credit.

 

[boaterva]

Depends where you are. It’s complicated in California, from what I hear. In Virginia, we have full net metering so everything goes back to the power company on a 1:1 basis for full credit.

3 cents seems like someone bribed someone a lot to screw everyone in the state. Good grief.

Anyone have pointers for calculations for California?

 

[woof]

Think of solar as an alternate power provider. If they can do better than $0.24/kWh, then yes, solar makes sense, even without a powerwall, or selling power back. For every solar kWh generated, thats one less grid kWh you pay for.

Adding a powerwall would allow for time shifting, so you can charge its battery from solar and use that instead of the grid during peak hours, thus reducing the price of power during those peaks. But that's often not worth the $$$ involved in a powerwall.

Selling power back to the grid only really matters if you produce more solar than you consume. With a $0.03 delta...probably just size the system so that doesn't happen...why pay for more solar than you need?

 

[Chicago_Teddy]

I just finished our solar install. We decided to go with Tesla’s solar panels for a few reasons. I am in Illinois so not sure how California works...but no need for a power wall here in Illinois based on ComEd (our utility provider). Hopefully in California they can be more help than in Illinois. Solar is so new it was hard getting help from the utility on what expectations may be.

But as Woof said...time shifting with a Powerwall may be helpful but depends on how California works.

FWIW, here in Illinois standard rate is about $0.07 / kWh, and hourly billing gets it down to about $0.03 overnight. I am expecting my first bill from ComEd soon but was nice to see that my normally ~$275 bill will be “expected to be about $38.00.”

 

[jboy210]

I just finished our solar install. We decided to go with Tesla’s solar panels for a few reasons. I am in Illinois so not sure how California works...but no need for a power wall here in Illinois based on ComEd (our utility provider). Hopefully in California they can be more help than in Illinois. Solar is so new it was hard getting help from the utility on what expectations may be.

But as Woof said...time shifting with a Powerwall may be helpful but depends on how California works.

FWIW, here in Illinois standard rate is about $0.07 / kWh, and hourly billing gets it down to about $0.03 overnight. I am expecting my first bill from ComEd soon but was nice to see that my normally ~$275 bill will be “expected to be about $38.00.”

$275 to $38 is great! How did you make that estimate? If I could achieve similar savings, that alone would be worth installing solar.

My plan is Time of Use. The off peak rate is $0.24. The Peak during the winter is $0.25, but will go up in summer. The peak is from 4PM to 9PM weekdays. All other times are off-peak.

I currently start my Model X charging at 12AM. My HPWC is wired at 240V @ 50A. That provides 10KW/h to the car. On a typical day it finishes charging in about an hour.

FWIW, there is a new law in California that requires solar on all newly constructed homes in 2020 unless there are site issues (shaded, etc)

 

[woof]

How did you make that estimate?

Contact a Solar installer, and get a quote. They'll give you those data.

 

[jboy210]

Thanks for the info. Does anyone know how solar power ebbs and flows during the day?

We work from home, so are here 24/7. That allows use to adjust our non-work related usage such as washing and drying clothes, and charging EV to optimize using solar provided electricity instead of grid provided electricity. Are there any sites that show when we would get the most solar provided electricity?

 

[Merrill]

I have a 6.5kW solar system and I have E6 tou with net metering, no Powerwalls yet. We are also with Sonoma Clean Power and our house is all electric. Our system is complicated by the fact that we have a second meter just for EV charging, over all we save about 70% of our bill. We cannot do more solar do to the fact that there is no room anywhere on the roof or even on the ground, we charge our cars after midnight at the EVB off peak rate. Overall the system works well and love that we charge the cars from the sun.

 

[Ulmo]

I am thinking about adding solar panels to my house, possible to offset some of my charging costs. Is anyone else doing this? Does it make sense? Do I need a powerwall?

FWIW, we pay $0.24/KWh in Northern CA off peak. We could receive $0.03 selling the power into the grid.

I want to do something in 2019 to try to capture the 30% credit.

I haven't taken detailed notes, but there are scores of well to do Tesla owners who got enough solar power to power all or most of their car charging needs. There is no uniform answer, unfortunately, since literally every single install is totally unique in about a thousand different variables, but there are some sort of patterns. I'll try to remember the most important patterns:

• The larger the solar installation, the more likely that most or all of the charging needs of the cars will be met. I've usually seen the solar systems that can achieve this starting at 10kWp and going up from there, usually somewhere between 10kWp and 25kWp, but there are many forum posters who have reported on much larger systems than that. Obviously they had much better financial situations (or in some less restrictive jurisdictions allowed jacks of all trades to do more DIY for far lower cost; regulatory compliance is the most expensive part of any home solar install in most jurisdictions (amounting to about 40% to 70% of the cost (which means Democratic governments are the largest impediments to clean energy in existence (although they simultaneously make it socially popular))), California most of all).
• The solar installation has to be much larger to fully power cars and house compared to the size of solar system necessary to just power a home.
• The solar installation size necessary to fully power cars and home will increase for every increase in use you do: more EV's, further commutes, faster driving, more heater or A/C use in the car, more home A/C's, more home electric heaters, more pools, etc. Commute distance (or more accurately, how much energy you use in your EV) has a huge effect on this. Also, electric heaters in your home have an outsized effect on this, as well (but it is rare that you use an electric heater and haven't already taken advantage of an easy conversion to a heat pump, but there are cases where people have gone that route and saved a lot of energy).
• Battery backup is the holy grail of the clean energy movement to shift daytime solar into nighttime use, but that is not ready for average income prime time. My two PowerWall 2's are only half of what I need for a modest home and no current EV, and I know from when I owned an EV that I would probably need 6 PowerWall 2's AND double my solar installation size to make more sense for where I live if I regained one person with an EV; even more batteries and solar would be required if I had two or more people with EVs; I calculated that literally the only way I could afford this would be to DIY, but I think that requires me to first inherit (& buyout other inheritors) the home and change insurance providers, so that's not happening for some decades yet. PowerWalls (and/or LG Chem RESU10H or similar) batteries would allow you to shift daytime sunlight into nighttime car charging (but for instance, that LG I just mentioned fully maxed out wouldn't even be enough to get you a 10 mile commute plus a modest home). I logically ask the somewhat obvious question this raises: where will our EVs be parked during the sunlight hours? I have been pushing the concept that people should try to find situations where they can install the solar power necessary to charge their cars where their EVs will be parked in the daytime, but that is a long sell, since it often entails employers installing industrially adequate solar farms in their parking lots with EV charge stations, and getting that right is a whole project unto itself. But compare that long sell to the long sell of expensive PowerWall/other battery installs, or the long sell of offsetting $0.25/kWh electricity with a $0.03/kWh backfeed tariff, and suddenly all the different long sells look relatively slightly less unattractive. Above all, be realistic for your financial and use case; don't take my pie in the sky pipe dreams as reality.
• Here's a prime example of a thousand variables coming to matter: what if your commute is such that you can charge your EV on the weekends? Could you top-up a bit on Wednesdays somehow, such as having an errand on Wednesday that brings you by a nice SuperCharger that you like and works well? Does your work offer affordable charging plans in their parking lot or a near parking lot? Do you own your own business? Do you work from home? Do you have to drive uphill in freezing cold headwind winters with heater set to high a fairly long distance? Does your homeowners insurance cover DIY solar installs (none do, but that would be a great way to save 70% of the cost of solar, allowing you to install WAY bigger solar for your budget)? Do you have God-provided Life-worth-it-making Redwood Trees soaring your mind to the heights of the heavens giving you splendor and love and the much better income and health that brings, but shade your roof? Are you coastal (that means fog and clouds where I live which means less solar, and it also means colder winters and less air conditioning in summers, and that means how much sun warms your home in winter and how much shade you have in summer and whether your building was built with the bathrooms in the downwind direction of the prevailing winds (to properly exhaust the ... gases) and a bunch of variables that no one can guess)? In Central Valley, how well your home is insulated makes a huge difference. I'm sure it makes a difference everywhere. I'm sure I forgot a lot of variables and don't even know of a bunch of other variables.
• Get a lot of solar quotes. Prices vary considerably.
• Tesla, unfortunately, has not invested any time making good software programming in their EVs and EV chargers to align their cars with available solar power in charging situations fed by solar installations; this is a totally gross omission by Tesla, and I consider it unacceptable. But, there is a sort of lame excuse they can use: to limit Tesla's charging speed to solar power availability would be to limit it to below what is safe to charge most Tesla batteries in most solar installations, since most solar installs are too puny to properly supply the wattage necessary to charge a Tesla car sufficiently. Teslas charge best at 6kW to 15kW, and most solar installs net out at around 2.5kW (which is under the minimum to charge a Tesla) during most of the sunlight hours with rare peaks higher than that; the solar install necessary to provide enough wattage for two Teslas would be an outrageous 50kWp (or more) install which is something only millionaires can afford, and even then, it wouldn't be charging their cars unless they are so much their own boss they can park at home when the sun is shining or dole out the extra cash for an irrational PowerPack purchase or two (uber expensive), or for more modest uber-wealthy people, very large PowerWall installations (7 to 10 PW2's). In some situations, uber-wealthy people like that would be forced to get PowerPacks/large PW installs to own EVs since their neighborhood utility grids would not be sufficient to charge their cars; this is actually a coming problem, and hopefully home battery prices plummet in price to reach the middle class and start helping out in this regard, and work employers start installing work solar charging stations rampantly. Anyway, Tesla should start supporting limiting car charging to only available solar power in software, even if the current use case is rare, but currently, Tesla does not do this. As I proofread this, it occurs to me that a modest commute family with two EV's and some PowerWalls could offset their grid use with a far more modest solar install of approximately 15kWp to 20kWp, and while they'd end up using some utility power to charge their cars, the numbers start coming into focus more realistically.
• For most (moderate income) people, EVs charge at night during lowest utility rates, and their solar installs just cover daytime (home) use and PowerWalls just cover a portion of their evening home use. For this group, everything else I said above is pie in the sky stuff.

I hope that gives some ideas.

 

[boaterva]

To get a general idea of how much ‘solar power’ you have available, this site can be useful;

PVWatts Calculator

 

[Silicon Desert]

Does anyone know how solar power ebbs and flows during the day?
Are there any sites that show when we would get the most solar provided electricity?

I have software that allows you to determine that. So do all solar installation companies. Easy to know in advance about how the system will perform.