Electric Cars, Solar & Net Metering

SEP 12 2015 BY STAFF 34

Electric Vehicles, Solar Energy and Net Metering

It’s an interesting combination in more ways than one. As there are no production or transportation costs for solar, beyond initial installation, home solar/ EV driving makes for one of the most efficient way to drive electric. Further, costs of owning an EV as well as home solar is more affordable than ever.  In fact, roughly 1 in 3 EV drivers have a home solar.  As Elon Musk said at a recent press conference, “We have this handy fusion reactor in the sky called the Sun. You don’t have to do anything, it just works. It shows up every day and produces ridiculous amounts of power.”

Driving our i3 BEV for almost a year put us on a crash course of learning how electricity is quantified, produced, transported, and consumed. First to understand how electricity measured you need to know what a kWh is, think ten 100 watt light bulbs burning for an hour and that’s a kiloWatt hour.

The sun’s energy can be harnessed several ways but the most cost efficient for individuals and homes are solar panels. Solar energy systems produce direct current (DC), however households use AC. So, our solar system has two Sunny Boy 5000TL US-22 inverters which convert the solar energy captured by our 48 Canadian Solar panels from DC to AC which is then put into the breaker panel. Outside of some switching noises in the morning when the inverters turn on, they don’t hum or make noise. These inverters have continuous output display panels on them and are connect to the internet to allow us to track the production anywhere.



Next, figuring out how far the i3 could go on a single charge was a little more difficult because of varying driving conditions that effect efficiency. The i3 has a 22 kWh (kiloWatt hour) battery pack but its use able capacity is 18.8 kWh. Most months we are able to go about 5 miles per kWh which falls right in line with the as advertised 80-100 mile range on a single charge. However, we have found this to be rather variable depending on weather and how it’s driven.

Interestingly, the i3 is more efficient in the city stop and go traffic of less than 50 mph, than it is at 75 mph on an interstate, whereas “ICE” internal combustion engine autos are more efficient on the interstate. We experienced no difficulty getting around in the snow with our i3 while driving shod with snow tires, though the bitter cold, arctic winter can dramatically shorten the range of of the i3 and all electric vehicles. See here for winter driving review.

A little over a year ago, we had a 12 kW Solar system installed on our home. In 14 months, it has produced 17.58 MWh (megawatt hours) which has been more than we have consumed over the same period even factoring charging of our i3 BEV doing 1000 miles a month. Obviously we consume electricity when are not producing, namely at night, during storms or when covered in snow. So we still have a monthly bill to pay, but it’s not much. The amount of electricity in kWh we produce in excess of production is credited each month and then subtracted from our usage in kWh from the grid. This is called Net Metering and many utilities have it. They do not credit us 1:1 for each kWh we kick into the grid because of the costs of maintaining the grid, power lines etc. In the last 4 months, our electric bill has been $74 – $44 of which is a “customer charge” for being hooked up the the grid.

*Editor’s Note: The remainder of this post by Chuck Vossler appears on BMWBLOG. Check it out here.

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34 Comments on "Electric Cars, Solar & Net Metering"

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Solar and EVs, truly a match made in heaven. The owner saves money and with energy that is clean as possible, the environment wins. The only losers are the oil companies and the utilities who are beginning to wage war on their users with net metering agreements.

If I had it to do over again I think I would have gone with the Sunny Boy inverter instead of my Enphase micro inverters. The Sunny Boy inverters allow you to have solar power even when the grid is down unlike the Enphase units.

I’m pretty sure that is what that outlet is below the inverter in the picture. Also I believe this central inverter is more amenable to a battery back up like the Tesla power wall.

Unfortunately the regulations in pretty all countries prohibit the operation of a inverter in island mode. Although the manual states that you can use the SunnyBoy in Island mode, it is with it’s caveats. This mode is normally coordinated with a Sunny Island system over bluetooth to regulate feed in whilst charging the batteries connected to the sunny island. SMA has a turn key ernergy storage + solar inverter in the SMA Smart Energy 5000, it comes with a 2kWH Lithium battery to heighten the self consumption (but still won’t operate in island mode). If you need a true energy router, the Dutch Nedap Power Router is something you’d want. It’s sold a whole lot in Australia. It provides UPS functionality as well. The germans already have the sonnebatterie (= solar battery) system which also performs similar to the SMA solution but is a seperate device that improves the self consumption of the solar energy. So No, you don’t need to have a central inverter for these self consumption of solar power storage devices. What you do need is a seperate kWh meter for the consumption and the producing side so that the software in the energy storage device can… Read more »

That is not fully correct as I too have the SunnyBoy SMA inverters and I can produce 1500 watts per inverter as long as the sun is up. One does have to throw a switch to turn on the islanding capability. This is legal and has been inspected by the city and utility.

Yes, I too have 2 SMA 4000 watt Sunny Boys, and after it was inspected I put in my own SPS (Secure 1500 watt power system) on both inverters going to 2 separate recepticles.

Unfortunately, its not quite enough to start important loads such as the refrigerator, so I have to use the power to charge my 2 evs, and then use extra large inverters off the respective 12 volt batteries to start the motorized equipment.

Since I live in a locale with little sunshine, my 9120 watt (by solar panel tabulation) only produces what it should at 9300 kwh per annum, but thats what it should by me, and is still around double what I use so I get back $.03574 / kwh on the overage. This basically pays for ten months of $15.67 monthly bills (no $44 or $74 per month here!!) so I have free electricity for 10 months out of the year, or, as much electicity as I want for around $30 per year.

Yes Bill. That is a great way to pull power off an EV…..well I know it works on a Volt but I bet you could pull power of a Leaf in the same low cost way.


In other words, when theres a neighborhood power failure, I’m still using the sun to run my refrigerator. IIt just that ALL the juice got to charging the ev’s simultaneously.


The refridgerator is really one big problem for most people that want to go off-grid.

I get the feeling that changing to a fridge with low starting current could solve the problem for many… However it is nearly impossible to gain good information on what actually is the peak current a certain model has.

It would be really nice, if those companies selling household equipment could include that information into the spec-sheets.

What would be even nicer, would be if more companies produced fridges using a 12V/24V DC Compressor (those exist! and in theory are not more expensive…) However economy of scale seems to lead to hugely overpriced 12V/24V equipment prices. Furthermore those stuff is commonly seen as camping equipment… another factor rising the price…

Can please someone KICKSTART a project for CHEAP 12V/24V household equipment… (ideally with ethernet plug, so the fridge can communicate with the BMS) should not be too expensive.

My 25 cubic foot refrigerator (considered a large model) has a split-phase compressor, with the fans in the unit either PSC (efficient) or, running off the 2 phase generated incidentally by the running compressor. Starting current is around 30 amps for 2 seconds. I use a 2000/4000 watt inverter from harbor ‘junk’ (freight) tools that will even start it with the car off. Running the micro wave in addition to the refrigerator (it too is the largest available) makes things unstable but works if I turn the car ‘on’ to raise the 12 volts about a volt and a half. Its great that they sell those quite nice inverters so cheaply. I’m told the alternator replacement in the volt is somewhere around 150/175 amperes.

But I can run my refrigerator for hours on the battery alone, once started.

Yeah, some central inverters now have the ability to provide power for one outlet while in islanding mode. It’s a neat little feature that provides people with a way to power their refrigerator without having build a whole critical loads panel.

But if you really want to, you can build a system to make Enphase microinverters operate when the grid goes down. It is called AC Coupling. You’ll need a critical loads panel, a battery, and battery controller/inverter.

Here is an Enphase white paper on it:

It is not trivial though. I think I want to do something like that eventually, but I’ll wait until the Powerwall is widely available so I could build a system with it.

Our Outback Power system provides power to a selected set of circuits when the power goes out.

I don’t understand why it is so difficult or expensive to produce a switch/relay that automatically cuts the connection to the grid when grid power goes out. Bill?

Me either. A selector switch that runs a couple contactors. Done.

Prove it.

I’m sorry, but you guys obviously do not understand how a grid tied inverter works. It must dump its power into a solid 60 hz feed, and will trip on either frequency change or voltage excursion.

My SMA 4040 watt inverter will ONLY allow a 1500 watt load non-grid-tied-load. 1600 will trip it. Most grid tied inverters have NO provision for standalone operation.

Now it should be possible to ‘fool’ a grid tied inverter to ‘run freely’ without the grid. It would require a very stable ‘starter inverter’ and also many 300 watt light bulbs to use as a dump bank to prevent the voltage from going to high, with a mechanism to also remove the lightbulbs should the voltage go too low. And a 4 kw transformer since the output of the inverter is only 240, and my refrigerator is 115.

The author of the piece was very specific about the model of inverter and it is in fact one of the series equipped with the “secure power supply”, a special 15 amp circuit that is available when the grid is down. AFAIK this feature is only available on the US models and was introduced in response to events like hurricanes that can take out the grid for days. I do not think this inverter is compatible with batteries of any kind because, it’s inputs are specifically designed to get the most out of solar modules by using a particular algorithm that, works for solar panels but, not batteries. The manufacturer of this particular inverter has a separate product line for batteries. They do have a solar inverter with a 2 kWh battery that they sell in Europe, designed to reduce the amount of electricity that is sent to the grid (increase self consumption) but, that unit does not have the back up power supply. I think that it is a matter of time before more inverter manufacturers start to introduce models that handle solar panels and batteries and that can supply power in the absence of the grid, while still… Read more »

George, you can use Enphase microinverters when the grid is down as mentioned in my other message. But right now, it is not trivial.

I plan to to do it eventually but I’m going to wait until both the battery and battery controller market are more mature. Since I have a very nice net metering arrangement, I really dont’ get any benefit by adding batteries other than back-up.

Yes spec but it is pretty pricey. I’ll just stick with my micro’s.

Mark H is in the same problem. I think he has 24 micro’s and want to get a power wall.

Darn I forgot.
I came up with a way to get emergency power off our Enphase systems and forgot to link it:

Skip down to the chart that say’s :

Low Cost


I haven’t put this on my house yet in it is just thrown out as a suggestion.

Yeah, the current systems are not that great right now. However, I’m sure that someone will build a great AC coupled system eventually because there is a big market for it.

With all the existing microinverter systems, all the existing central inverter systems that don’t play well with batteries, and all places that would like to incorporate batteries without solar at all, there is a large demand for AC coupled battery systems.

Enphase is coming out with their own ‘AC battery’ product and IMHO, it stinks. It is too small and I don’t think it will allow the microinverters to work when the grid is down. Their stock price has plunged in recent months and I think the lack of a product in this space is a reason why, IMHO. So if they are smart, they will designed or OEM a battery-controller/inverter that will their microinverters to operate when the grid goes down.

Spec, If you’re the same person who used that handle in another place we both used to hang out, you are in California(LA?) if I am correct. I’m more familiar with south Florida where the “Secure Power Supply” will prove very useful after a hurricane. How often do you need backup power in your location?

If you can, you might take a visit to Solar Power International at the Anaheim Convention Center next week. There will be several new players in the battery space including Sonnebatterie, mentioned by Seth up top and who knows what else? I’ll be traveling from my island home to meet with several vendors, seeing as it’s a rare opportunity to meet with many players in the business in one place.

I islandboy, and yeah, it is me. Yeah, those SMA inverters with the SPS are pretty neat. That is a clever addition to their inverter that sounds like it would be a decent way to keep your refrigerator operating during the day provided you have good sun (though Bill Howland seems to indicate that it didn’t work well for him but he is in Rochester, NY). I’m in Northern California, otherwise I would definitely go to SPI. I’m pretty certain that someone will provide a good AC coupled battery system that handles isolating from the grid and keeping microinverters operating eventually. There are some systems but they are a bit kludgy, use lead-acid batteries, and expensive as you noted. I pretty much have no need since the grid in the middle of Silicon Valley is pretty good. But I’d still like to do it as a fun project and to allow my system to operate when the ‘Big One’ (earthquake) hits. But for now, I’ll wait until their are better products available. It is not like one could buy a Tesla Powerwall even if you wanted, they are not available yet and when they start delivering, I’m sure SolarCity will… Read more »

Spec, Good to see you still active in the blogosphere as ever! I hang out with a lot of our old compatriots from that other place, at Darwinian’s new joint but, insideevs is mandatory daily reading for me.

I attended training for the inverters with SPS near Sacramento about a year ago and the trainer said that it was good enough to run their fridge. There are many factors to consider when using the SPS which include, available sunlight, a big difference between the Sacramento area and Rochester NY, especially in the winter. The short term load characteristics matter as well with the modern, high efficiency, “soft start” or “inverter” refrigerators being much easier to cope with than the older units.

I guess EV charging would not exceed 15 amps at 110 volts, so that should not be a problem.

Since you’re up north of LA, Intersolar back in July, at the Moscone Center in SF would have been the show for you. I’ll let you know if I see anything interesting.

Ok First off guys I’m in Buffalo not Rochester.

Second, it wont work in arizona either. The SPS limitation is 1500 watts, period.

Third, its not 15 amps but around 12 1/2.

At my house I can have 2 – 1500 watt loads but I cannot combine them otherwise since in this mode the inverters are not synchronized
as they are when tied to the grid.

My refrigerator draws over 3 kva when starting and will trip everything except my 12 volt to 2000/4000 watt harbor freight inverter.

Therefore I charge my cars off the panels, then use the inverter to run the refrigerator with the car providing the link.

$74 customer charge? That is at least half of most people’s utility bill! What utility company do you have?

Chuck wrote: “In the last 4 months, our electric bill has been $74 – $44 of which is a “customer charge” for being hooked up the the grid.”

Is $74 the total for all four months or a monthly average? I’m guessing the former.


Yeah, that sentence is quite vague. I’m guessing he means that the total of the last four bills is $74 . . . and most of it is a grid connection fee of $11/month (thus $44 for 4 months.

I pay a $5/month ‘distribution fee’ for PG&E, Northern California.


Right, mine is also only ~$5/month from PG&E plus any GAS usage..

Municipal utilities like Austin Energy only charge a ten dollar line fee to solar customers and pay a premium Value of Solar of 11.4 cents/kw.

Shareholder utilities have a large profit motive and excess executive compensation ratepayers are made to cover.

I’d like to see all utilities be made non profit.

We do a lot more solar and solar ownership here, not just leasing.

On the other hand, these utilities charging high rates are providing a lot of people with a big incentive to install solar PV on their homes. 😉

“First to understand how electricity measured you need to know what a kWh is, think ten 100 watt light bulbs burning for an hour”

A 100 Watt bulb? What’s that? Haven’t seen one of those in years. 😉

I drove like an old man my whole life…I brake so gradually that my 1993 Roadmaster did not need a brake job until 110 K miles. [Yeah, even an old man car] I never did a jack rabbit start in my life…until I had my Volt (after already having the solar on the roof). When you burn nothing but photons, THAT’S when the fun begins.

…that is, as long as I am not expecting to run out of charge. I still drive like an old man in that case.

Seems like the ideal setup (to me) would be solar panels large enough to collect enough energy for daily use, plus extra to store for later, and a really large battery. So say a 10kW system with 3 powerwalls. Then just forget about the grid. Put a gas generator in for backup if needed.

presuming you have a NG line, I can recommend considering a NG generator as well, quieter and effortless at a Price.

On Kickstarter I noticed a project to build a solar BMS designed to be used off-grid with a Lithium-Ion battery.
That project was successful & the designer is now producing a larger version for a 3kW PV array and 3kW load.