One Year Experiment Of Living And Driving Two BMW i3s On Sunshine – The Wrap Up


Net Zero Energy Challenge Concludes

Net Zero Energy Challenge Concludes

Our one year experiment of living and driving on sunshine is over!

The idea is a simple one:

“Harvest endless sunshine from a small portion of a roof to provide 100% of the energy needed to power a home and the two cars in the garage, with zero utility cost, and zero gasoline cost.”

On May 15th, 2015 we concluded our year long Driving to Net Zero Energy Challenge. It’s hard to believe that our two BMW i3’s are already a year old and boy did time fly! I’ll have an overall wrap up post about the year on June 1st.

Before then, I’ll carve out a couple of sections and focus a little more in depth on various parts of the effort.

We believe we are the first household in the world to attempt this with full documentation. We also believe that there are dozens, perhaps hundreds of other households who have accomplished the exact same thing without going though the painstaking detail and very public process of sharing private and personal information.

*Editor’s Note: This post also appears on Peder’s blog. Check it out here.

Thank you to BMWi, ChargePoint, Stellar Solar and SDG&E, for following us and supporting us during this past year. It is because of a very efficient home, a great Solar PV system (installed in 2007) and the BMW i3’s, the most efficient cars sold in the USA, that we were able to attempt this effort.

We have also documented this effort at every turn, with our utility, our Solar PV generation, and with the ChargePoint CT 4000 charging station in the greatest detail possible. With the ChargePoint CT 4000, we are able to account for every kWh taken from the wall and used for the BMW i3’s.

ChargePoint Residential Charger

ChargePoint Residential Charger

Data is king, ChargePoint with the CT 4000 and soon their residential home charger the ChargePoint Home, allows the owner to see data on each charging session in detail, just like checking up on your bank account or your friends on Facebook.

A focus on the BMW i3’s powered by Solar PV.

Our BMW i3's in the garage

Our BMW i3’s in the garage

We’re loving our BMW i3’s and they have been a joy to drive all year. They have been trouble and maintenance free with the exception of one service visit for each car to update the software and replace the KLE.

The cars are a blast and spirited to drive, especially off the line, and are very practical for our semi-urban lifestyle. Every morning they await us with a full charge ready for the days adventure. One detail in particular that has been very impressive is that we have no door dings, dents or scratches after a year of duty on the roads. Typically for us we collect a few door dings and the occasional scratch every year. The carbon fiber construction and thermo-plastic skin appear to be a great advance in not only lightweight construction, but also in durability and appearance.

Just one funny anecdote. Of course we race our cars against each other! Julie and I both have the BMW i3 bev model, so we have to see who’s got the fastest car. In the first race Julie beat me by a long shot and I was sure that BMW had made her car just a little faster than mine. We swapped cars and did the same race again…and Julie beat me by a long shot. I have concluded that my extra 150lbs was the difference in both races πŸ™‚ Julie may be able to go 0-60 in 6.5 seconds, but it takes me a few ticks longer.

Using our stats we collected every month for the past year, here is in detail how our cars performed powered by Solar Energy. That’s the beauty of the challenge. These are all actual and real world numbers, not estimates or calculations.
Location is Carlsbad Ca.

  • A total of 5061 kWh of electricity was used to drive 21,477 miles in two BMW i3’s.
  • Julie averages 4.3 miles per kwh 11,862 miles / 2717kWh
  • Peder averages 4.1 miles per kwh 9615 miles / 2344 kWh
  • Our 8.5kw Solar PV system generated 13,546 kWh for the year. This equals 1593 kWh per kw system size
  • A 3.18 kw Solar PV system (3.18 times 1593) would provide the 5061 kwh of power for both BMW i3s driven 21,477 miles.
  • 37% of our overall solar generation was used by our BMW i3’s, 63% was used by our home
  • It would cost $9540 to provide the solar supplied energy to drive both BMW i3’s and subsequent cars, for 25 years (536,925 miles)
  • Two gas cars @25mpg (average fleet mpg) would use 859 gallons of gasoline to drive 21,477 miles
  • Current cost of gasoline in San Diego Ca is $3.93 a gallon using 859 gallons of gasoline is $3375
  • The total cost of the PV System is equal to buying gasoline for 2.82 years. An ROI of 35.4%
  • Driving the BMW i3’s powered by Solar PV, the cost per mile is $0.017 cents per mile.
  • If advantageous TOU rates are factored in, the Solar PV system size and cost would be reduced by 22%, the cost per mile would be $0.013 per mile.
  • Driving on Solar PV supplied electricity is 1/10th the cost of driving on gasoline.
Getting Expensive Again

Getting Expensive Again – Average price of gasoline on 5/22/15

sun gasYou can live and drive on Sunshine πŸ™‚

Cheers and thanks for reading and commenting.

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18 Comments on "One Year Experiment Of Living And Driving Two BMW i3s On Sunshine – The Wrap Up"

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“It is because of a very efficient home, a great Solar PV system (installed in 2007) and the BMW i3’s, the most efficient cars sold in the USA, that we were able to attempt this effort.”

It is also because of the nice climate year round (and the convenient nat. gas supply?)

Nevertheless it is fantastic and a great feat to keep track of, document, and share your experience.


Without a doubt, a temperate climate is a big part of the picture.

Well done, Peder. But . . . of course I have to nit-pick . . . πŸ˜‰ β€œHarvest endless sunshine from a small portion of a roof to provide 100% of the energy needed to power a home and the two cars in the garage, with zero utility cost, and zero gasoline cost.” I guess it is a small portion of the roof. My array probably is like 1/5 of the roof surface area. But we do generally use the best part of the roof so using the rest won’t be linear increase. You have a 8.5kw Solar PV system . . . that’s a pretty big system. Nearly twice the size of a typical residential system. And you live in San Diego which is great latitude-wise and probably good weather wise, so you (and I in Northern California) have an advantage over most people in the country. Also, you do have a third car parked in that garage which you put a fair number of gasoline miles on. But we won’t talk about that. πŸ˜‰ You should add this sentence since it really highlights the savings on gasoline: It would cost $84,375 to provide the gasoline supplied energy to… Read more »

What surprises me is that a public servant and a teacher can afford such a nice house, two i3’s, and an i8 in San Diego…. Maybe I should move there.


May 28, 2015 at 2:42 pm

LOL. You’ve seen Breaking Bad, right? (Just kidding! πŸ˜‰ )



Would it help to ease your suspicions a bit if you knew that I purchased my first house in Carlsbad at 19 years of age, my first business at 21, sold 5 businesses to Pepsico at 35 years of age, and basically retired at 35 a very wealthy person?

That I went to work at 2am working until 5pm 6 days a week for over 15 years to build those businesses?

That my public service is just that, public service to the county that I love?

That my wife is a proud Teacher of 5 years, a Principal, managing a site with 400 kids, 300 parents and a staff of 65, for 22 years, and now an Administrator in charge of curriculum and instruction and several school sites for over 2000 kids?

The “just a teacher’ inference always bugs me the most.

Hope this helps with your suspicions and thanks for reading.

Dave K.

Most people are just in it for themselves, you Peder, are obviously not. Hence their suspicious nature. Good for you, I think it’s really a big accelerator for solar when you add the EVs as this makes the payback so much faster. You (and others like you) deserve our thanks, you see your money as a tool to improve the world not an end in itself.


Hi Speculawyer,
I appreciate your nitpicking and comments:)
I’ve mentioned both the Nat Gas usage and the BMW i8 in a few of my past post and will touch on them both on the final piece coming around June 1st. In short, from a cost basis I have zero, but from a utilization basis, I am not zero overall energy use including the cars, although the home is a net zero home (Gasoline offset produced by the house, is much higher than natural gas use)

Yes, the system at 8.5kw system size is approximately twice the size of most residential systems. Many/most residential systems offset only a portion of an utility electric bill and are not used to power cars.

For us it’s about 5.25kw for the home and 3.25 (rounding off) for the cars.



“The total cost of the PV System is equal to buying gasoline for 2.82 years.”

Awesome !!


Great I hope to copy paste this with a new house and model s quiet soon.

Mister G

Thanks for sharing.

I was inspired by your project so I kept track of the electricity used to charge our two EVs (85 kWh Model S and BMW i3 BEV) since our 3.5 kW Solar PV system went live. Until we get our home remodel under way, we are limited to using a standard wall outlet (with a Belkin WeMo to monitor usage) to charge the cars at home, but I have access to a ChargePoint station at work and we always use the bank of free ChargePoint stations at the San Rafael Target when we shop there. For 22 days in May, we generated 449.5 kWh from solar, used 419.7 kWh to charge the cars at home and 99.7 kWh from ChargePoint for a grand total of 519.4 kWh for EV charging. So we ended up offsetting 86% of the EV electrical usage with solar which isn’t too shabby. Things won’t look as good in the winter since there is less sunlight and the EVs use more energy per mile in colder weather. But once the remodel is over and we know exactly where the new skylight is going, we may add some more panels to get more than 3.5 kW. And… Read more »

Nice job Peder. We have achieved what you set out to achieve for 3 years running now. It comprises of an all-electric home, a Chevy Volt (96% EV), a Ford Focus Electric and a 11.8 KW solar array. There is currently a yearly surplus of about 2000 kWh. All charging is done at home. Consumption patterns are similar – the home is in the Bay area. More details are here:


Great document with a clear pathway.


Well, Peder, I’ve written this before and since you are wrapping up, I’ll write it again…until you have ditched the NG, you haven’t finished yet. If we can dump the propane in NY, converting to all electric (with highly efficient heat pumps and secondary combustion fireplace insert for heating in NY) at both FL & NY residences…you certainly can ditch the NG in Southern California! Between heat pump (or solar) water heating and induction cooking, there is certainly little reason to keep the last of those fossil fuels in your life. So, Peder, any final words on dumping NG???


From what I can infer from Peder’s data he needs another 2000 kWh yearly and he needs to swap out his NG water heater and cooktop with electric versions. The GE water heaters have now reached energy factor 3.1. So another 1.2 KW or 4 or 5 panels is all he needs to really get to complete net zero. He has enough roof area remaining to accommodate the panels even if they are not completely south facing.

Bill Howland

Well congratulations Peder..

I too have 2EV’s charging for the past year totally on Sunshine (9120 watt system making about 8700 kwh due to the poor sunshine in BUffalo, plus snow covered the entire months of January and February).

The ev’s are the big power consumer: anything requiring heat runs on Natural Gas (I have eight gas appliances).

I will have an overage of Solar Power production, so people have said why not convert some gas appliances to electric to keep from giving the electric utility an overage for the year. I shoot back that the pidlly 3 cents / kwh I expect on the overage is more money than the gas costs at 2 – 2 1/2 cents / kwh by heat content.

So even though
the electricity is free, the gas is free-er.
I’ve replaced the BEV with a PHEV, so now I’ll probably use less electricity next year.

But the 2 cars, when they run electrically, will be ‘sun powered’.


Peder’s efforts are not about saving money. He is too well off for that. It is about showing a better, eco-friendly and sustainable way of doing things. It is a window into the future. Though NG is cleaner than gas, it is still a fossil fuel and causes pollution. It is not sustainable and ways should be explored to eliminate it from the future energy mix. Currently PV coupled with heat pumps can compete in running costs with NG in many areas in the US. This is because heat pumps have now reached almost 400% efficiency (loosely speaking). Current PV rates are about 7-8c per kWh LCOE in CA. Divide by 4 and voila you beat NG which has appliances running at 60-90% efficiency.