BMW i3 Driving to Net Zero Energy – Powered By Sunshine


bmw i3 solar

Driving To Net Zero

The idea is a simple one: Harvest sunshine from the roof of your home to provide 100% of the power needed for your home and the two cars in the garage. That is our goal in this “Driving to Net Zero Challenge.”

The 12 month documented journey began May 15, 2014. Our first posting of data will be around July 1st containing tabulated data from May 15th to June 15th.

norby graph may

We will begin with May, the April information is used as an example only.

We will need to drive the most efficient cars to achieve our goal of net zero. We were very happy for BMW to learn that the BMW i3 is the most efficient production car in the world. The BMW i3 has a combined EPA rating of 124 MPGe.

Said another way, the BMW i3 is a car that drives on 1/5th the energy of a typical new gasoline car in the USA. So 4/5ths of the journey to net zero is efficiency savings, 1/5th will be energy generation via solar PV.

*Editor’s Note: This post originally appeared of Peder’s “Electric BMW” blog.  Check it out by clicking here.

It is this unbeatable combination of efficiency, luxury and performance that truly defines “premium” in an automobile in our opinion and why we choose to buy two BMW i3’s.

Even though the i3 is much larger in passenger space, leg room and cargo space than it’s prototype predecessor the BMW ActiveE, it weighs 1350lbs less than the ActiveE and is 25% more efficient.

BMW i3

BMW i3

We took delivery of our first i3 “Thor” on May 15th, our second i3 will arrive within the next few days. Our experience the past 5 years and 100,000 miles driving the BMW Mini-E and the BMW ActiveE, have demonstrated to us that the range of the i3 fits in very comfortably with our suburban lifestyle and location. Our home is in Carlsbad, CA , 30 miles north of San Diego. We realize that in a more rural environment, two i3’s may not be a practical answer.

BMW i3 And Solar Panels On Roof

BMW i3 And Solar Panels On Roof

In the above pics is our BMW i3 and six solar panels integrated into the roof of this small stone faced area of our home. If purchased today, these six panels would be 260 watts each for a system size of 1.56 kwh. The panels use 81 square feet of roof space and will generate 2,400 kwh per year. This amount of electricity will power the BMW i3 for 10,200 miles a year. (2,400 multiplied by 4.25 miles per kwh)

Just ponder that for a moment, 6 panels, 81 square feet of space producing electricity for over 25 years, powering a car for 250,000 miles of zero emission driving.


So how are we doing leading up to the start date of “The Drive to Zero?” Here’s a quick look at our March to April energy use for our home and two cars (ActiveE and Honda Fit EV.) With the BMW i’3s we will save around 1000 kwh each year thanks to the world leading efficiency of the car.

Screen Shot 2014-05-02 at 7.41.13 AMThought of the Month:   The Energy Grid

The energy grid serves us well. I have no desire to be “off the grid” or off any of the other grids in our lives such as our transportation grid, social grid, food grid, communications grid, or monetary grid, just to name a few.

These giant sharing systems (grids) are a far more efficient way to deliver services than if we’re all hoarding our money in our mattresses, had no place to buy food, had no shared transportation network, and had no utility grid.

Our goal is not to remove us from the energy grid, but rather to help reinvent the grid and make it a more equitable, more resilient and more accessible grid. A grid where a family or a business is not just a payer, but also can be a payee if they provide a net benefit to the grid, a grid that encourages more localized behind the meter efficiency savings and renewable energy production.

The key component in this re-imagined grid is smart data. When we can see how our home uses energy we can select more efficient appliances and adjust our energy use in a more favorable way. When we can see how much energy our cars are using and when they are using it, we can modify our charging times to optimize the savings, or to assist the grid by not charging during high demand times. The gathering and displaying of data in a connected house is a key component of getting to net zero. When we can measure it, we can improve it.

The energy grid to date has only been open on the income cash flow side to the big boys (utilities and power-plants,) but now over 100,000 of users are participating as owners of micro power-plants both benefiting the grid and themselves.

Going off the grid may be the right answer for some. For us, understanding and sharing is a good thing 🙂

We appreciate you following us on this 12 month journey to net zero energy use. We enjoy the dialog of different opinions and ideas in the comments as we all try to improve mobility and transportation for ourselves and future generations.

*Editor’s Note: This post is part of an ongoing monthly series.  To check out the first post in this series from April, please click here.

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46 Comments on "BMW i3 Driving to Net Zero Energy – Powered By Sunshine"

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Where is the cost of the solar panels in this calculation?


Hi there,

Good idéa. Congratulations.
I’m not sure, but I think you need 12 additional panels.
Home (+-500Kwh) + 2 cars (+-300Kwh)=800 Kwh/month.
Your 6 panels should give you +-250Kwh/month.
This is a good start anyway!!


scott franco
Sure, but the “net zero energy” is a financial and regulatory gimmick. You are not creating the power the cars and your house uses. You are selling power to the power company in the daytime, when you are not there, then buying it back in the nighttime at “net zero” (same price) terms. Net zero pricing was imposed on the utilities by regulators. They don’t like it, and want it gone. And in many states they are making progress. They claim net zero is a made up pricing model, that the idea that the grid is “storing” or “offsetting” your power is imaginary. Their probably correct, but the exact economy of power is impossible to determine, mainly because the regulators have distorted the pricing model of power so much. Until then, live the dream. The warning I would give to people who want to live the “net zero” dream is that: 1. The utilities are eventually going to overturn net zero metering. It is just a matter of time. 2. That grid tied system you are paying so much for cannot be converted to a battery backed system. The two types of systems, grid tied and battery backed, are fundamentally… Read more »
Mike I

@scott franco

I think you’re mixing up your terms.

“Net Zero Energy” means that over a given period of time, typically a whole year, the total net consumption and generation of kWh or equivalent is zero.

“Utility Net Metering” is a utility billing scheme where you only pay for the net kWh that you take from the grid during the billing cycle. This is sometimes combined with Time Of Use (TOU) billing so that prices are different during various times of the day. Places that don’t support Net Metering have different ways of handling distributed generators. For example, in Europe, they frequently have a separate meter for the generating system and you are paid for your generation according to their “Feed-in Tariff”. The house would continue to be billed for its usage as if there was no on-site generation.

So, one can have a Net-Zero home regardless of how the utility bills you or pays you for energy. It’s not a gimmick at all, it’s a personal goal for a homeowner to balance their usage and generation.

scott franco

I think you are misunderstanding. “net zero energy use”, (from the grid), or the idea that you are offsetting the energy used FROM the grid with energy provided TO it is a fiction. They are not storing your power and giving it back to you, or using to offset power generation, or anything else.


It is not fiction, it is accounting. It is ‘loaning’ and ‘paying back’. No one is claiming that the grid is ‘storing’ the energy. (Although California is going to start adding some more storage to deal with the evening peak issue.)

Mike I

Actually, “offset power generation” is actually the best description of the benefit of solar to the grid. When my solar system produces more energy than my home is using, the energy goes into the grid where it is used by my neighbors. That means that a utility scale generator does not have to produce the power that that neighbor is using. Distributed generation like residential solar also decreases grid transmission losses and peak loads.

Uh . . . what is your point? No, it is not ‘storing’ . . . it is loaning electricity during the day and it is returned at night. And this is a good thing . . . we humans use a massive amount of power during the day while working and at night demand drops off a cliff as everything is turned off. Thus, the PV systems are providing valuable power during peak demand and the EVs are providing valuable electricity consumption at night when the utilities have lots of excess electricity. Both HELP the utilities. Now sure, the utilities are not happy with it because they lose a paying customer. Well boo-hoo, buggy-whip makers were not happy but progress moves forward. Any attempt to stop net metering should be met with fierce resistance. I pay ~$5/month for distribution costs plus the utility sells my excess power during the day to my neighbor at peak rates and pays me back at night with cheap excess energy they have so I am not a ‘drain’ on them . . . they actually make money off me & my system. Just not as much money as they made when I was… Read more »
Rick Danger



That’s not really true. Our peak usage is generally in the late afternoon or evening, when people come home from work, have their air conditioners on, do chores, are watching TV, turn on lights, etc, all the while solar output is near or equal to zero.

I have to admit that I’ve somewhat reversed my stance on the implications of this, because we’ve reached a point where 4-hour storage (able to recharge during solar’s peak output) is as cheap as natural gas peakers (i.e. 4h * $250/kWh = $1/W, plus cost of energy).

But still, zero net energy usage doesn’t mean your share of the grid cost is zero. If net metering stays, there are only two options as more people take advantage:
A) jack up the price on non-solar customers
B) move to a separate, fixed grid charge

Only a complete disconnection from the grid justifies you paying $0 if your net energy is zero.

As it is, if your solar electricity is reducing your bill by 30c/kWh, and your utility was only paying 4c/kWh for wholesale electricity before you went solar, then you can be damn sure that the difference winds up on the bills of others.


There are two peaks . . . a mid-day peak and an evening peak. Solar helps with the mid-day peak but is not so great for the evening peak.

However, as you noted, we just need a little bit of storage for that second peak. This can be done many different ways: pumped water storage, demand-response, battery storage, solar thermal systems that can operate after the sun is down due to thermal storage, etc.

I don’t pay zero. I pay ~$5/month for distribution. And the utility makes money off of my PV system. They get my electricity for free and sell it to my neighbor for 30 cents/KWH. They then repay me with cheaper electricity at night. So they get money from me in 2 different ways.


They don’t get your electricity for free. They are getting 30c/kWh less revenue from you to save on wholesale electricity purchases at 4-5c/kWh.

That’s a net loss of 25c/kWh for every kWh you produce. None of your disingenuous spin will ever change that.

You can argue that they shouldn’t have been charging you 30c/kWh in the first place, but that high rate pays for the grid maintenance, lets the poor pay lower rates, etc.

Unless a company has huge net margins (and grid operators do not), the *only* solution for a loss in revenue without a matching reduction of costs is higher prices. Otherwise the company bleeds until bankruptcy.


They are getting 30c/kwh less revenue for electricity THEY DID NOT SUPPLY TO THAT CUSTOMER. None of your disingenuous spin can convince me that any solar producer should have to pay for something he did not use.


Put another way, they get 30c less revenue for supplying me nothing, but they gain power they can sell for 4 cents/kwh. Sounds to me like a net GAIN for them.


“That grid tied system you are paying so much for cannot be converted to a battery backed system.”

You really don’t know what you are talking about. The racks, PV panels, conduit, etc. would all remain the same. You’d just add batteries and swap out your current inverter with an inverter that has a charge controller.

Rick Danger

That’s what I thought too, Spec.

Seems someone thought we needed some Solar FUD today.


It would be a little harder for microinverter based systems. They would need to pull some PV wire from the PV panels to a central inverter location but it still wouldn’t be all that hard and the Racks, PV panels, conduit would remain.


Or install an “AC coupled” conversion, which is batteries and an oscillator to trick the standard inverter into thinking the grid is still up (plus the requisite isolators from the grid lines). All in all it’s EXACTLY what Mint said was impossible.


I have a 2 Megawatt-hour surplus with my PV & EV system. But I only have 1 car and I only commute a couple days a week.


I am no expert but I concur with Spec9 regarding the grid tied vrs the battery back-up.


Thanks to Texas regulations, I cannot have more than 10kWh of panels on my house. Fortunately, I have a small house and a small car so it should be adequate. For larger homes, it might not be.


A 10KW system is pretty darn big. If you need more than that then you have a really massive or very wasteful house. Such a house could be improved with insulation, weatherstripping, switching to LED lighting, switching to natural gas for heating tasks (hot water, clothes dryer, stove/oven, etc.), installing a heat pump, etc.


Hi there,

10Kwh? Great!! It’s about 50 panels.
Nearly double size of Peder his installation.
Other solution for the car?
Tesla and use the supercharger for free!!



@Aaron, if that’s any indication, a 6 kW system (two dozens modules) offsets all of my family’s electricity consumption + the 14~15kmiles/year I drive.

That’s for northern California, which gets about as much sunlight as Texas, but needs less air conditioning.
To get a better idea of what a PV system would get you, you can check out
or peek at some existing systems (although unfortunately with little specifications)


I think you are missing some parts of your calculation. Based on the (paltry) electricity use in your house, can we assume that you use natural gas for heating, water heating, and cooking (stove/oven)?

If so, then you will never be able to attain “zero net energy”.

For this reason, our house (two actually, main residence and granny unit) is full electric (passive heat/cooling design – no HVAC, electric stoves and on demand electric water heaters).

And trust me, 8 panels wouldn’t come close to generating that. We typically use 50 kWh a day now (with the addition of the Leaf in the garage) and our 28 panels generate a max of 48 kWh during the summer months.

On a yearly basis, I estimate we are generating about 2/3 of the power that we use…. another 15 panels going up on the gazebo this summer to try and fix that.

But the point is, I think you’re not as close as you are claiming unless I missed something?

“Thus, the PV systems are providing valuable power during peak demand and the EVs are providing valuable electricity consumption at night when the utilities have lots of excess electricity. Both HELP the utilities.” I don’t understand why you would want to do that assuming you are grid-tied and have access to natural gas. Yeah, you can install enough panels and then say you are ‘net energy zero’ . . . but you would be generating more CO2 emissions than if you just used natural gas. If you burn the gas directly, you’ll be able to capture and use most of the heat. But instead, you are having utility burn the gas (or worse, coal), generate electricity with it (losing a lot of energy in the conversion), transmit the electricity to you, and you then turn that electricity back into heat with an electric stove. This causes much more natural gas to be burned than if you just had a natural gas stove. Instead of switching things to all electric, use gas where it is more efficient. And if you want to “pay for” that usage of gas, just put up some extra PV panels and put that extra energy out… Read more »

Ack. I meant to quote your statement of:
“For this reason, our house (two actually, main residence and granny unit) is full electric (passive heat/cooling design – no HVAC, electric stoves and on demand electric water heaters).”


OK, so Peder cleared up my confusion in another post – this system is much bigger than indicated in the article.

As to Spec9 – it’s not just about the money. I wanted to use ZERO fossil fuels in the house. And propane is a by-product of fossil fuels and not something I can produce myself (we do not have NG lines out here).

So this gives me the ability to control my own energy production/consumption. I’ve chosen to be “clean” at my end of the wire… and we can let the other side move towards being clean at their end where it’s technology can be applied easier.

BTW, most of our power here is Cali is nuclear… 😉


Propane is a fossil fuel. But I think you will produce less emissions if you were to use propane for some heating tasks instead of having some far off power plant burn a fossil fuel to create electricity, transmit the electricity to you, then you turn the electricity back into heat. But I guess, as you point out, you can hope that the other end uses more green energy.

Oh . . . and if by ‘Cali’ you mean California . . . then, no, we don’t get most of our electricity from nuclear. We are actually down to a single nuclear power plant in the state (Diablo Canyon). Perhaps some of the imported electricity is nuclear. But most of our electricity is natural gas. Nuclear is around 20%. The rest is hydro, solar, wind, geothermal, etc.


We’re 20 miles from diablo, I’d bet we get most of it… 😉


@Kosh, congrats on your dedication re zero fossil fuels.
As alternative (or complement) to more PV, have you checked how practical it’d be in your situation to add a solar water “pre-heater” to reduce the energy consumption of your tankless?
I ran the numbers for my home, and a simple batch heater aka ‘integrated collector-storage’ or ICS, feeding mostly hot water to the existing heater, was the most cost-effective.

@Spec9: at least in California, burning NG/propane for heat isn’t better than using electricity, assuming it’s not just dumped into a resistive heater.

Heat pumps (for water or space heating) commonly have EFs of 2 and higher, so even if 2/3 of the electricity comes from fossil fuels, with plants+transmission ~35% efficient, you’re still ahead.
Same thing for cooktops, as induction is over twice as efficient as gas (and a joy to use, I might add).

Mike I

Be careful using solar hot water in front of a tankless NG fired water heater. Most are not designed for it in that they cannot modulate the flame low enough and they automatically turn on when there is any water flow. You have to make sure you check the specs to see the maximum inlet water temperature allowed.


Thanks for the warning. Mine is a tank heater, and @Kosh mentioned his tankless being electric (which I assume can be modulated down to zero), so we’re good.

A tempering valve is typically added after a solar heater to prevent overly hot water from reaching fixtures. In my case, it’s on the outlet of the tank “backup heater”; in Kosh’s case, I’d imagine it’d go before the on-demand heater, thereby also protecting it from excessive temperatures.


I really don’t think this can be stressed enough . . . the combo of EVs and grid tied PV systems are MUCH better for the utilities than if such customers went off grid.

The PV systems generate valuable power during peak demand systems and thus reduce the need of the utilities to build expensive and rarely used ‘peaker plants’. Also, the PV electricity is generated right where it is consumed so there is no need for transmission lines. The PV systems also help with frequency regulation.

The EVs charge up during the middle of the night and thus are providing valuable much needed electricity consumption at a time when the utilities have lots of excess electricity generation capacity.

Both of these technologies help ‘flatten’ the supply/demand imbalances inherent in most utility grids and thus make them much more efficient.



Thank you for letting the world know about this – it is the way of the future.

My brother and his wife each drive and EV (iMiEV and Leaf respectively) and they have a 6.37kW system (27 x 240W) that produces up to ~28kWh on summer days. They are coming up on their 1st anniversary with the PV system, so we’ll see what they pay on an average month, but it is probably in the range of $20-25. (Previously, it was $80-170/month + $1,000/year for an oil fired hot water heater.)

That is with a new heat pump hot water heater and A/C in the house, and electric stove. They heat with wood pellets. Almost (fossil) carbon free – only when he needs to drive his Tacoma do they buy any gas.

Even without SREC’s they will probably pay for the PV system in under 10 years. With SREC’s it will likely be 5-6 years.

Before the PV system, their EV’s cost 2-3¢ / mile each. Now, it is probably 1¢ / mile for *both* cars.


Peder, good luck. We’ve been net-zero w/ 2 cars for about 14 months now with a Volt and RAV4 EV. Between the two cars we drive around 23-24k miles, and our house is around 2,800 sq ft, built in 1974 w/ awful original windows. We planned the system without careful calculations, going with the shock and awe method of solar installation: we have 15.3kW, 66 Sunpower panels. Even w/ both cars and a pool pump, we still overproduce enough to zero our bill each month. It’s very gratifying to know that your fuel bills are essentially zero after making the initial investment, and what a great investment in our collective futures:) Beautiful house, BTW.


Thanks again Peder for your write-ups, for helping spread that “solar+EV” virus that many of us here enjoy already.

I completely share your point of view re the grid btw, to the point that I’m about to add modules to a system which already covers slightly more than all of my needs + driving. My excuse? Not all neighbors have solar yet… 🙂


I am in the process of preparing to install a 20kW system, which is huge, and will basically cover my entire roof. I already have a 9.6kW Leviton EV charger that I installed in garage (about $1,000 self-installed and bought on Amazon), but no EV or PHEV at this point (I have been driving an Escape Hybrid SUV for 10 years in October, and if I drive the speed limit I still get from 31 to 36mpg). My system will be grid-tied and use 64 e-20 327w SunPower panels, 64 p400 SolarEdge optimizers, and two SolarEdge 10kW inverters.

My first pick is the i3 REX, but have seriously been considering the Mitsubishi PHEV Outlander – which has a few things going against it: it will rust, like my Escape has – it’s not available for possibly another 18 months in the USA. The i3’s major issues for me are: 1) size (not big enough), 2) range.