Monday, March 11, 2019

A Solar-powered Car (+ Day #2 off-grid)

You could have a really nice solar-powered electric car.  
If you had solar power.  And an electric car. 

Electricity production accounts for 28.5% of America’s greenhouse gas production.  Transportation accounts for another 28%.  With solar-powered buildings and electric vehicles (EVs)  we could reduce our climate-killing air pollution by 56%.  I'm there. 

Ranking slightly behind saving the planet, is fun.  Modern EVs are way more fun to drive than the 20th Century gas-guzzlers we grew up with.  EV’s can accelerate a lot faster than gas cars, scary-fast in the case of Teslas.  EV’s are almost silent, so your music sounds better and conversation is easier.  No exhaust pipe, no exhaust -- I have driven back from the Home Depot with long objects sticking out the back hatch without sucking fumes into the car.  Maintenance is checking the tires, adding windshield washer fluid, and replacing wiper blades.

If you have a charger at home, you don’t have to contend with lines at the pump before a hurricane.  And, as I’m discovering, with home batteries, you can charge your EV when the grid is down.

An EV's range depends on the size of the battery and how you drive the car.  The power used in one mile of highway driving might cover 2 miles on surface roads.  Drive gently and that can become 3 miles.  If you’re taking a long road trip, today’s EV’s will plan the route with restaurant stops adjacent to fast-chargers.

EV chargers come in 3 flavors: slow, fast, and superfast.

A “Level 1” charger typically comes with the car and plugs into a 120 volt AC outlet.  Level 1 is also called a trickle-charger.  That’s what we’re using during our off-grid test. Yesterday’s trickle-charge took a bit over 5 hours.  Most people just plug-in when they get home and forget about it.

A “Level 2” charger runs on 240 volts AC, like an electric clothes dryer.  Level 2 charging is 8X faster than Level 1, and is 5-10% more efficient in its use of power.

The newest EVs can accept a Level 3 charger.  Cars made by Tesla can use their network of Superchargers.

Here's a visual comparison of my Level 2 charging (on-grid), and Level 1 charging (off-grid):

Our setup

We had an electrician wire two 40 amp circuits into our carport ($800).  One of these powers a Level 2 charger with a 25’ cord (Clippercreek HCS-40, $650 retail or $500 eBay).  The long cord is convenient.  It takes 45 minutes to re-charges the Nissan Leaf after my 17-mile FIU commute.  If we run the battery to near empty, charging takes 2 hours. 

When we’re on-grid, the car is programmed to charge at 1 am (as shown above).  This avoids drawing utility power in the early evening generated by the less-efficient “peaker” generators that service the peak demand time.  It reduces our carbon footprint by allowing us to push solar power onto the grid during peak demand time, while we draw back the most efficiently-produced “base load” grid power as Miami sleeps.  

We also set the car to charge to 80% capacity, which prolongs battery life and is likewise more efficient to charge.  We top off the battery for convenience prior to longer runs.  I’ve only needed to charge away from home once after someone (possibly me) forgot to plug in the car the night before.

Our second car is a 2010 Prius hybrid, which averages 50 mpg.  It’s a fine car, but burning gasoline feels so 20th Century.  We will never buy another gasoline-powered car.  

Report from day 2 off-grid.

Everybody always asks if the solar+batteries can run the A/C.  Yes.  You can see in the graph below that the A/C happily turned on 11 times yesterday (sharp spikes in the blue graph). We have a 3 ton A/C that covers the indoor space just fine.  Tesla's battery installers wired a "soft start" device into the A/C that eases the surge when the A/C turns on.  It does the job.  

The Powerwall controller had a temporary disagreement with my solar inverters at 1:35 pm, though I did not lose power.  Tesla’s technical staff just emailed me saying they are downloading a software modification to my Powerwalls that should resolve the issue. 

Other than that, everything worked as well as the day before.

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