Charging my Cars and Battery Backup

My solar system was initially set up with Net Metering: energy produced was valued the same as energy consumed.  When charging my car, I would plug in at night during the off-peak rates and “use” the energy I generated during the day at peak rates.  With Net Metering, I was able to nearly break even on my yearly driving needs (until I added a second EV).  In order to expand my solar system, I was forced to switch from Net Metering to Net Billing, where energy produced is valued at wholesale rates.  To make solar more practical with Net Billing, the recommendation is to add a storage battery that allows the energy produced during the day to be consumed at night.

When determining the battery storage I would need, I considered the size of my car’s battery.  Clearly, a 12KWh house/solar battery would not meet the charging needs of my car’s 30KWh battery, so I opted to double the solar battery storage.  Now, if I charge the car when the charge level drops to 35%, I will use 19KWh of battery storage.  This allows me to charge every three days using only electricity generated by my solar panels.  This is useful because the car is usually not available for charging until after sunset.  (Unfortunately, the winter solar performance is a small fraction of the energy generated in summer, so I end up buying electricity to fill the gap.)

Charging during the day using battery and sunlight.

I liked the 2017 BMW i3 so much that I wanted to upgrade it.  The 2019 model includes a 42KWh battery, capable of driving 150 to 180 miles on a charge.  I also work from home now, so the newer BMW i3 spends a lot of time parked in the driveway during the day.  Because this car’s battery is so much larger than the house battery, I needed a different charging strategy.  On sunny days, the sun will generate up to 3.5KW of power from 10:00am to 3:00pm.  That amounts to over 17KWh of electricity generation.  If the house battery is already full, then the power bleeds onto the electrical grid at wholesale rates.  Instead, I plug in the newer BMW i3 and feed the excess electricity into the car’s battery.  The 17KWh from the panels and 19KWh from the house battery nearly fills the car’s battery nicely.  Unless I’m planning to drive a longer distance, I usually unplug around 80% charge, leaving more energy in the house battery for cooking dinner, lighting, and cooling the house.  If I wasn’t working from home, I’d have to use a different charging approach, such as more frequent short charges providing just enough energy to power my car through a day’s needs.

More Solar Capacity and an End to Net Metering

 I first installed solar panels on my new garage roof in 2009.  The six panels met the needs of my house by Net Energy Metering standards.  The NEM program credits you for any electricity you feed into the grid based on the rate you would pay if you drew energy from the grid at the same time. So, if I generated electricity during peak pricing hours, I would get a credit for that amount.  Then I would do laundry on the weekends during off-peak hours and get to use nearly two KWh for each KWh I generated.  This allowed me to bank excess power during the summer and draw against it during the winter.  My net electric bill for the year was under $50. 

In 2012, I bought the purple Mitsubishi i-MiEV and needed to generate more electricity to power the miles I would be driving.  I did some rough math and estimated four more panels would essentially cover most of my home EV charging needs.  The NEM program was still in effect, so again I was able to bank summer electricity for use in the winter.  My yearly cost for powering the house and charging the car with the new system remained under $100 and included nearly 10,000 miles worth of driving.

My original solar panels (in yellow) and my upgraded panels (in green)

In 2018, I bought the blue BMW i3 and passed the Mitsubishi onto my partner.  Between the two of us, we were driving nearly 20,000 miles a year.  In 2019, I replaced the main inverter on the original solar panels with microinverters, which improved their afternoon energy production by about 10%.  (I have a power/telephone pole next to my garage that casts a shadow across some of the panels.)  Still, I was running over my production by $600 to $800 a year.  So, I planned to add to the solar panels.  But my garage roof was now full, and I would have to put the panels on the main house roof.  But the house roof was installed in 1997 and had exceeded 25 years of age, so I would have to replace the roof before installing the new solar panels. 

Alas, I waited too long to get started on the roof replacement, so my NEM program was terminated when I upgraded my solar system.  Under the new solar program, I am credited the wholesale cost of any energy generation (not transmission), which is about 15% of what I pay for electricity.  I had eight new solar panels installed, each generating up to 410 watts.  (The original panels generate up to 230 watts.)  I also had to buy battery storage for the excess electricity I generate during the day to use after sunset.  The original recommendation was to install one house battery, with a new subpanel to dedicate some circuits for use when the power would go out.  Because I usually need to charge one of the cars at night, I realized one battery would not be enough.  By adding a second battery, I am able to meet most of my charging needs, and I was able to eliminate the electric subpanel, which paid for half of the second battery.  (Two batteries provide enough current to power the whole house – except for the A/C unit.)  I discovered the backup batteries were working one day when my next-door neighbor asked if my power was also out.  Power outages are much less stressful now.

Visiting Carmel-by-the-Sea

 I love to visit Carmel-by-the-Sea.  The weather is never hot, there is world-class food all around you, art galleries, wine-tasting rooms, distinctive clothing, imaginative toys, and charming architecture all around.  The beach is a short walk from the center of town.  And the best bet is to park in the city lot just south of the main street where they have installed a handful of level-2 EV charging stations.  From there, it’s a short walk to the various attractions in town.

The level-2 chargers are important to the journey.  Carmel-by-the-Sea is 75 miles from my home, making for a 150-mile round-trip.  Under the best of conditions, my BMW i3 can travel 150 miles without spending much time on the freeway and staying on level land.  But I don’t like to drive anywhere without a safety margin of 20 miles of extra range.  So, a visit to Carmel necessitates a charging stop.  (Most newer cars can drive there and back on a single charge because of their larger battery packs.)  When I get to Carmel, I can plug in, enjoy the town for two or three hours, then come back to my car charged up with an additional 45 to 75 miles of range and enjoy a comfortable return home (free of anxiety).

The level-2 chargers are a short walk to downtown attractions.

For this trip, the level-2 chargers are preferable to DC-fast-chargers.  With the level-2 chargers, I plug in and take my time taking in Carmel.  I want to spend more than two hours there and charging for that long satisfies my charging needs.  I could also have used a DC-fast-charger on my way home, but that would have meant a 15- to 25-minute stop in a place where I had little interest in dwelling.  Plus, I would have had to stay within a short walk of the car while it charged, limiting my ability to explore or dine.  Level-2 chargers have a real need in places like Carmel, where you are likely to enjoy spending a few hours in one spot.  (DC-fast-chargers make the most sense along busy travel corridors like along the interstate freeways.)  Now, if we could only get a few level-2 chargers installed near hiking locations like in our national parks.

Picking a Charging App (or Two)

 If you never drive beyond your car’s winter battery range, and always charge at home (or work), then you will likely never need to use a public charging station and won’t need a charging network’s app for your smartphone.  Even if you do decide to venture beyond once or twice, you can likely get by with Google Maps and a credit card.  Google Maps can help you locate most charging stations and can help you plan your route to include them.  And many chargers now have credit card (tap) readers for payment, just like a gas pump.  But, using the charging network’s app can improve the charging experience by providing station availability, station notes left by prior users, monitoring the charging progress, and even start and stop the charging session and arranging the payment.

In the early days of EV adoption, there weren’t many public chargers around.  Individuals with home chargers were willing to provide access to their charger to other EV drivers in order to promote EV adoption.  A smartphone app emerged to allow individuals to advertise their home charger and collect payment for its use, called PlugShare.  PlugShare is ideal for travelers passing through regions with low EV adoption and limited public EV charging infrastructure because it connects drivers with these generous hosts.  It also includes the public charging stations and helps with route planning.  Because I live in a high-adoption area, I have not used PlugShare personally, but I have read good things about it.

Instead, I have made use of the following EV charging networks and apps:  ChargePoint, EVGo, and Electrify America.  These are the most relevant networks for California, though other charging networks are available.  EVGo and Electrify America provide detailed information and status for their own charging equipment.  They manage payments and can start and stop charging sessions.  They also report the amount of power flowing into the car, which can help to anticipate when charging will complete.  And they notify you once charging has completed so you can disconnect (and move) your car before parking charges are applied.  ChargePoint does all the same for its own network chargers, and it also includes information about chargers on other networks, but does not control those off-network chargers.  ChargePoint also installed a number of destination (level-2) chargers, while EVGo and Electrify America are almost exclusively DC-fast-charging focused.  ChargePoint has become my go-to charging app.

To prepare for a road trip up the California and Oregon coast (in 2024), I installed two other charging apps.  The first was EVCS, which serves the west coast well (but nowhere else).  Along my trip, I used EVCS stations a number of times and found the app helpful.  The other app was by Shell.  The one time I tried to use the app I was unable to start my charging session.  Fortunately, the credit card reader was working, and I was able to charge, but the experience was frustrating.  But overall, the trip went well.

My First Overnight Road Trip

 As the COVID-19 pandemic started to wane, all sorts of folks were itching to travel again.  A road trip, especially a run down the California coast, seemed a natural outing with minimal public interaction.  I wanted to return to Cambria, which is an artists’ colony that I have enjoyed visiting.  I had three days (and two nights) to plan.  And I wanted to visit a winery on the trip home while passing through Paso Robles.  (The winery where I work gets some grapes from Adelaida Vineyards in Paso robles and I wanted to try their wines.)

First, I needed to plan the trip for charging, so I turned to Google Maps.  The distance from San Jose to Cambria is about 170 miles running down Highway 1 on the coast.  My car can drive 140 miles reliably at the slower speeds along the coast, so I needed to charge somewhere midway.  South of Monterey there are no DC fast chargers along the route.  The town of Seaside lies about 65 miles along the route and is the last DC fast charger.  So, I planned a lunch stop in Seaside to charge.  In Cambria, I booked accommodations at a hotel with a level-2 charger, so I was able to charge there twice (once each night).  The winery offers a complimentary charger to visitors, which gave me enough of a boost to get to Soledad for the last charge stop (and dinner), before the final leg home.

The first leg of the journey with a charging stop near Seaside.

The remainder of the first leg of the journey to Cambria.

The return trip from Cambria by way of a winery.

The drive down the coast at the end of January was spectacular.  The weather was sunny the entire trip.  I saw sea lions crowding the rocky beaches.  I found the i3 was comfortable, quiet, and spirited for quickly passing the occasional RV.  Once in Cambria, I was a little disappointed to learn that my favorite blown-glass gallery had closed with no other gallery to replace it.  On the plus side, I discovered The Red Moose Cookie Company and their brown-butter chocolate chip cookies.  I also visited the town of Harmony, which prides itself on being the ideal spot to begin a marriage (and get a scoop of ice cream).  I also discovered that the wines made by Adelaida Vineyards were quite pleasing.  And I spent a total of 70 minutes fast-charging, during which time I ate on both occasions.  Overall, the trip went as planned and was relaxing.

What to Expect from DC Fast-Charging

 When I bought my purple Mitsubishi iMiEV, with its tiny 16KWh battery, I skipped the DC-fast charging port option because it really didn’t extend my range by much.  (110 miles is not much further from home than 60 miles, so I kept my gas car for longer trips.)  When I bought the 2017 BMW i3, the fast-charging port was standard.  That coupled with the larger battery and new DC fast-chargers meant that I could get to and from Napa Valley (or Carmel-by-the-Sea) with just a single, quick recharge.

Why is it called “DC fast-charging”?  If I plug in my BMW i3 to a standard wall socket (called “level-1”), I face a 27-hour charge time from empty to full.  (Nobody does this regularly.)  That is because the BMW’s 32KWh battery is being fed electricity at 120v and 1.2KW.  The math (32KWh ÷ 1.2KW = 27h) is straight-forward.  You can decrease the time by increasing the power (kilowatts, or KW).  Switching to a 240v socket and a more powerful charger (called “level-2”), I can charge at 240v and generate 7.2KW feeding into the battery.  The math (32KWh ÷ 7.2KW = 5h) shows how much faster this is.  Still, it takes hours but can be done easily at night or at work.  Both level-1 and level-2 use A/C voltage, which the car converts to D/C voltage for storage into the battery.  A DC fast-charger converts the energy from the electric utility into high-power D/C voltage and sends the D/C energy directly to the car’s battery, allowing greater power transfer rates.  This is called “level-3” charging.

Depending upon when your electric car was designed, your car will have charging capabilities of 50KW to 350KW and more.  Usually, the larger the car’s battery is, the faster it will need to charge.  My BMW’s electronics were designed for 2014 and modest battery sizes, so my car’s fastest charging speed is 50KW.  The fastest charging speed is not always used, though.  I can safely plug my BMW i3 into a 350KW charger because the car and the charger negotiate the best charging rate.  My car says any power level up to 50KW, the charger says any power request up to 350KW.  (I have seen an instance where the electric utility limited the power delivery rate to lower than the charger’s capability and my car was charging at only 25KW.)

Charging rate of various years of BMW i3.

When I connect my car to the charger and start charging, I watch the power level start out low and climb over the course of a minute or two to the highest the car can accept.  As the power flows into the car, the battery will warm up.  The car may direct the charger to reduce power (to protect the battery from excess heat) or increase power (because the warmer battery can now accept more power).  I have seen that my car will maintain the highest charging rate until the battery reaches roughly 85% capacity, at which time it starts to accept less and less power as the battery approaches full.  The last 5% of the charge trickles in no faster than it would using my home charger. 

Charging rate graphs of the Lucid and Porsche electric sedans.

My modest battery behaves differently than most of the newest car batteries.  I have seen the power graphs made by technical folks curious about how fast their cars charge.  In vehicles that charge faster than 100KW, the maximum charging rate is typically achieved between 15% full and 50% full.  After that, the rate usually drops substantially to avoid the battery overheating.  It then finishes out the charge cycle at around half of its maximum power until the last 10% of charging, at which point the power level drops dramatically (just as my car does).  This slow rate of charge at the end can take longer than the fastest rate at the start and only provides 10% of the charge (compared to 40% at the start).  Because of this, it is a courtesy to disconnect from the DC fast-charger when your car has reached 85% full to allow those waiting to charge a chance to get on their way sooner.

Locked-Down Chargers at Work

 

When I started working at a new job in 2016, I noticed the site was equipped with several level-2 charging stations that were made by ChargePoint.  So, I decided to take a closer look one day and discovered that the chargers were available only to employees of the main tenant at the site.  (My tiny company was not that tenant.)  It seems that discounted charging was one of the perks at that place.  After a year, the main tenant moved to a new site where they consolidated multiple office buildings into one, leaving behind the dedicated chargers.  After the tenant was gone, I would visit the chargers periodically to see if they had become open to the public (they hadn’t).

A level-2 EV charger like the ones by my office.

By this time, I was not the only plug-in car at my office, and I could see other EVs in the surrounding parking lots.  We could all benefit from these chargers being made available to everyone, so I started asking questions.  First, I reached out to ChargePoint to find out how to get these chargers made accessible to the public.  They pointed me to the company who had them locked down.  Next, I convinced our own office manager to reach out to the former tenant about making the chargers public.  They responded that the chargers were never their responsibility and to reach out to the property manager for the office buildings.  So, I directed our office manager to reach out to our property manager, who was very unresponsive.

I pestered our office manager to continue asking about the chargers and we finally were able to get in touch with someone who would talk with us about it.  The property manager agreed to unlock the chargers and make them publicly available.  After a few months, the chargers were on the ChargePoint network and available to everyone.  Of course, we were now paying full price for electricity to charge, but we had access.  By the time the chargers came online, there were at least eight plug-in cars from our office that often made use of the level-2 chargers.  I used them a handful of times when I would forget about a late-afternoon commitment and my charge level wasn’t quite enough to make it (comfortably).  It was worth the effort to bring this equipment back online.