How much solar on roof to power a Tesla for a year?
- Thread starter nursebee
- Start date
nwdiver
Well-Known Member
250s aren't very common anymore. ~300w is the low end of what's currently manufactured. 10 300w panels would definitely do it
I believe that there's more information that would be needed to calculate the amount needed. Things like which way does the roof point, roof angle, tree blockages, etc.
Also, to figure out how much energy that you will use, we need to know which car and your driving habits. If using a Model 3 and you meet the EPA driving numbers, then you are about 4 miles / kWh. Which for a Model 3 means about 3,750 kWh. For a S, it may be as much as 7,500 kWh.
You will, of course, generate more energy in the summer than the winter, so if you want to charge your car directly, you would need the worse case capability, if you are just trying offset the energy, that's another.
And then you may also need a battery to time shift the energy.
Also, to figure out how much energy that you will use, we need to know which car and your driving habits. If using a Model 3 and you meet the EPA driving numbers, then you are about 4 miles / kWh. Which for a Model 3 means about 3,750 kWh. For a S, it may be as much as 7,500 kWh.
You will, of course, generate more energy in the summer than the winter, so if you want to charge your car directly, you would need the worse case capability, if you are just trying offset the energy, that's another.
And then you may also need a battery to time shift the energy.
SageBrush
REJECT Fascism
Figure 4,000 kWh a year. As for how many panels it takes to generate that amount of energy, ewoodrick covered the important variables. As one example, a 15 degree pitched roof without shading issues in NC will produce ~ 1.6 kWh/watt annually so 4,000 kWh would require 4000/1.6 = 2.5 kW
I don't know particulars about NC but in general is makes good sense to size your PV to cover your home+cars. If you are already planning to cover your home then just add on 4,000 kWh to your annual consumption.
I don't know particulars about NC but in general is makes good sense to size your PV to cover your home+cars. If you are already planning to cover your home then just add on 4,000 kWh to your annual consumption.
2012MS85
Member
Jaws comes to mind...You’re gonna need a bigger boat (solar system)! 10 panels @ 250 watts each is only 2.5 kw gross (before limitations of the inverter). But before we talk about solar production (supply), let’s start with energy consumption (demand)...
The answer depends on many variables, but here’s a ballpark estimate based on my 3 years experience owning 3 Teslas (two S, one 3) and 60 solar panels. My lifetime consumption for my 2012 P85 (with 50k miles) is 400 watts-hours per mile. So ignoring vampire losses and 10-15% AC-to-DC energy conversion losses, you get 2.5 miles for every kWh produced. So you’d need to produce 6 MWh (15,000 miles / 2.5 miles/kWh = 6,000 kWh) per year to charge an S at home before the aforementioned losses. So up to 7 MWh factoring in losses. If you have an X, it’ll require a bit more, maybe 8 MWh annually. With an ultra efficient LR 3, it could be half that (4 MWh per year, if it were just over 200 watt-hours per mile).
My actual annual solar production has averaged 18.5 MWh from my 16.1 kw (gross) ACPV system. My enphase micro-inverters have a net of 14 kw, but I’ll stick with gross kw because that’s what most folks reference. So my Midwest (Iowa) generation amounts to 1,149 for each kw gross of panel capacity. So if you install 2.5 kw, you could generally expect about 2.9 MWh per year of solar production. That’s about 75% of what a Model 3 might use annually. If you have net metering that cashes out annually, perhaps that’s a good size. But if you have an S or X, you might need 20 panels (double) or more. Good luck!
10 panels @ 250 watts each is only 2.5 kw gross (before limitations of the inverter). But before we talk about solar production (supply), let’s start with energy consumption (demand)...The answer depends on many variables, but here’s a ballpark estimate based on my 3 years experience owning 3 Teslas (two S, one 3) and 60 solar panels. My lifetime consumption for my 2012 P85 (with 50k miles) is 400 watts-hours per mile. So ignoring vampire losses and 10-15% AC-to-DC energy conversion losses, you get 2.5 miles for every kWh produced. So you’d need to produce 6 MWh (15,000 miles / 2.5 miles/kWh = 6,000 kWh) per year to charge an S at home before the aforementioned losses. So up to 7 MWh factoring in losses. If you have an X, it’ll require a bit more, maybe 8 MWh annually. With an ultra efficient LR 3, it could be half that (4 MWh per year, if it were just over 200 watt-hours per mile).
My actual annual solar production has averaged 18.5 MWh from my 16.1 kw (gross) ACPV system. My enphase micro-inverters have a net of 14 kw, but I’ll stick with gross kw because that’s what most folks reference. So my Midwest (Iowa) generation amounts to 1,149 for each kw gross of panel capacity. So if you install 2.5 kw, you could generally expect about 2.9 MWh per year of solar production. That’s about 75% of what a Model 3 might use annually. If you have net metering that cashes out annually, perhaps that’s a good size. But if you have an S or X, you might need 20 panels (double) or more. Good luck!
gjunky
Trifecta: Solar and both cars are EVs
As mentioned before, count 4miles/kWh for the Model 3 and 3 miles/kWh for the Model S or X and compare to your install and NET production from there. It sounds like you are on some net-zero plan which means you probably don't have to use batteries to offset you use (all depends on the plan you are on).
We had our X for about 2.5 years and it used up (according to the car), an entire year's production of our 11Kw system and we are in Arizona. It starts to add up (in kWh). Now we have two Teslas but I charge the model 3 at work most of the time.
We had our X for about 2.5 years and it used up (according to the car), an entire year's production of our 11Kw system and we are in Arizona. It starts to add up (in kWh). Now we have two Teslas but I charge the model 3 at work most of the time.
2012MS85
Member
I don’t mean to disagree, but every estimate I received online and from a half dozen solar installers all over-promised what my annual output would be. My annual solar generation - in Iowa - was forecast to be 1.3 kWh/watt. Reality these past three years has averaged only 1.15 kWh/watt. And the wintertime results have been plain horrible. I had zero output for 12 straight days during the recent sub-zero cold snap with over a foot of snow that froze solid on my solar panels until our heat wave ~40F this past weekend finally melted all that dang snow!
Depends on your location, plus you have to figure charging and discharging inefficiencies like vampire drain. I'd estimate ~500 watts per mile at the panel for something like a model 3, more for an S or X. That works out to be about 6KW around here near NYC. So my estimate is about 2.5x yours.
SageBrush
REJECT Fascism
Locations vary. My array produced 1.92 kWh/watt*year so far.
PVWATTS is a fantastic tool to start, but you have to be able to figure out your home shading.
Two "tricks" to consider:
1. Buy 1.2x or so panels above your inverter spec.
2. Avoid AC micro-inverters to reduce high current losses.
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favo
P3D+ owner
My 5.5 kW system (20 panels x 275W) produces about 6.5 MWh in Durham, NC. My P3D is averaging about 330 Wh/mile since the end of August. I am generating more than the car uses, but less than car + rest of my usage. I used to be a net generator, but no more. Another thing to consider is how much of your annual miles will be on trips and will, most likely, be handled by Supercharging.
I run 7.8kWp and a 30kWh LiFe storage in Austria. I drive 22.000km per year with a Zoe that takes around 16kWh/100km. From April to September this is able to run the car plus most of my household needs. From October to March, no chance. During December and January the frequent cloud cover plus few sun hours and low angle means almost zero energy production. And no amount of extra panels would change this, sadly. Just the way things are.
Johann Koeber
Active Member
Lots of good answers here. I vote for a somewhat oversized PV system; many here have found enjoyment in driving the Tesla more than they ever drove other cars. Due to the car, but also due to the trips being virtually 'free', thanks to 'free' fuel.
Personally I'm on my third Tesla and the M3 is on its way. We drive more than 60,000 miles per year, charging at home and at superchargers. The power usage of the house has surged from ca. 5,000 to 12,424 kWh for the last 12 months. The 30 kW PV array on the garage provided for 24,820 kWh, of which 4.668 kWh came from the grid. 16,502 kWh were delivered to the grid.
Personally I'm on my third Tesla and the M3 is on its way. We drive more than 60,000 miles per year, charging at home and at superchargers. The power usage of the house has surged from ca. 5,000 to 12,424 kWh for the last 12 months. The 30 kW PV array on the garage provided for 24,820 kWh, of which 4.668 kWh came from the grid. 16,502 kWh were delivered to the grid.
gjunky
Trifecta: Solar and both cars are EVs
You might be surprised that my top performing month is the month of May. I assume that it is because of the heat in later months lowering the efficiency of the panels.@gjunky What is your average annual solar production in sunny AZ from your 11 kw system? You have the best case scenario given the ideal location for solar
My yearly production is roughly 16mWh. We are going on four year now.
SageBrush
REJECT Fascism
Yep. I think my peak is in April.
By the way, AZ is no match for Colorado. As you point out, heat reduces performance.
2012MS85
Member
Thanks for your response and actual solar production data. I’m not surprised at all about May being your best month, as all my record days of 100+ kWh of solar production also occur in the cooler spring days of April and May. Most folks don’t realize that extreme heat is the enemy of solar due to the efficiency loss you referenced. My best total monthly output in 2018 occurred in July, but that’s because more days are sunny (and longer) and we have few rainy or cloudy days in the summer. See my attached snapshot by month for all of 2018.
2012MS85
Member
Agreed 100%. My record solar production day occurred April 19 with 107 kWh. Given rain and clouds the day before, my solar system appears to be bi-polar (with only 10 kWh produced on April 18). I include this daily graph for the OP so he understands just how volatile one’s solar output is from day to day. Hawaii won’t get the snow and ice Iowa just experienced, but I went 11 straight days with less than 1 kWh per day of solar production (a foot of snow and ice had fallen and frozen on my 60 panels, completely blocking the sunlight until temps warmed from sub-zero to 40F). So had I been off-grid, I would have needed 42 Powerwall2s (at a cost of over $250k) just to feed my 50 kWh per day that my household consumed during these extreme temps. We use electric heat to supplement our 96% ultra-high efficiency natural gas zoned furnaces that are our primary heat source. So being off-grid would never work for us. Also, even battery back up systems fail (like my friend’s system that didn’t turn on during his electric utility outage, where his 5-year-old backup battery failed exactly when he needed it).
I had 30 300 panels installed on my house and was selling too much back to the power company (at 3 cents a KWH) so I bought a Model S 85. I am driving it 8,000 miles a year and STILL am selling too much power back (my house is all electric), so I think 10 panels would do just fine.
SageBrush
REJECT Fascism
"What size, in kw, is needed to power tesla for a year?"
The same size, in kW, needed to power a Tesla for a day.
The same size, in kW, needed to power a Tesla for a day.
Zeronet
Member
I am in Arizona, so that makes it easy. I have 18 panels in an area just a little larger than my two-car garage. The system produces about 5.5 kW. My house is ridiculously insulated, all bulbs are LEDs, etc. I added the Tesla charger last fall and STILL have produced 30% more electricity than used by the house and Tesla (averaging 10,000 miles/yr) combined. It looks like I'll have to get a couple more Teslas.
If Arizonan's could just get the power companies to allow unrestricted solar, nobody would ever buy gasoline here again.
