A Novice’s Guide To EV Charging With Solar

My Solar Charged Electric Vehicle Experience

After watching enough movies about our inconvenient truth (just watch the sequel and it is worth checking out) it has been playing on my mind that I should be thinking more about my how much carbon I am putting into the atmosphere.

Roof Solar

In my view, if we are going to tackle the climate crisis, we need to fix 3 core things – coal powered electricity plants, transport that burns fuel, and cattle that produces methane.

So I have decided to try to tackle the first two and invest in an electric vehicle (EV) and bought Tesla model S. Now while EVs can be great for the environment, if charging from the grid in Australia it does little to help the climate given that a large part of our power comes from coal. Hence I decided to invest in solar as well.

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Through my journey I found that very few of the solar providers I spoke to understand how solar would work with an EV. Luckily a mate of mine works in this part of the energy sector (http://www.wattblock.com/) and I spoke to many people and did some research. Here is what I learnt and some decisions I made:

  • Battery or no battery: Initially I was considering investing in a battery. After seeing the costs of this project mount up (I started ar what I thought would be $5K), a friend convinced me to spend more on the solar system and feed the excess back into the grid. The logic was that if my aim was to reduce my carbon footprint then feeding power into the grid is offsetting overall power, so a battery isn’t going to help achieve that goal. Doing some quick maths I realised a battery would have a long payback period – so my view is get a battery if 1) you have power issues 2) You are staying in the same place for a long period of time 3) you just want to get off the grid altogether. you may quickly realize that 2-3 Tesla batteries is what you need as that is what my math conclusion pointed me to.

 

  • Power Supply: Firstly a tesla can charge off house power with a normal power plug, but it is very slow! You might get a 20% charge in a night. I have only used it once when on a road trip. The best bet is to install the charging device that comes with the Tesla. This will allow fast charging off the grid. Now one conversation that came up was single phase Vs 3 phase. My power to the house was old and blew, so I took the opportunity to get 3 phase installed by the electricity company. I believe I spent about $2-3K (from memory) more than a single phas connection. Its nice to have as it means I can get a fast charge if I really need to. In hind sight I probably didn’t need it given I almst always slow charge… see below.

 

  • Solar panels: As I went through multiple quotes and sizing, I realised there were many cheap and more expensive options. I went the more expensive options for a couple of reasons:
    • I chose new LG panels (launched in 2019 in Australia) that generate 330 Watts each because I have limited space on the roof. These panels have a high amount of energy per panel compared to most panels, meaning more use of the space.
    • Enphase inverter system – one thing I learned on the journey is that you can either have one single big inverter for all panels, or an inverter per panel. The first option is cheaper, but what I learned was that with a single inverter, if one panel reduces power or stops working, all panels do the same! I have trees and other obstacles around the roof, which means at certain time of day my entire system could stop even when only some panels have shade.

What about sizing? Based on the estimates I was advised to deploy 15 panels, giving me a maximum output of 5KWs at any time. This decision was more driven by available space, but in hindsight I wish I had pushed for a few more panels. Another 2 panels I would have gotten more closer to the carbon neutral goal.

The enphase system is great. For a while I found myself logging in to the app daily and seeing how the production was going. This really helped tweak a few things to optimize solar power usage (e.g. when do I run our spa filtration system).

I spent about $12K (AUD) on the panels and enphase system. I am betting I will save about $1K per year on my power bill, so payback is probably 12 years. I need to do more work to see if I am really saving that much.

I had an electrician install the charging device near my power box. Make sure you have enough amps to cover it! The device itself does come with a fairly long cable and handle, so you can have a bit of distance from the car to the charging device. Its about 6 meters (https://forums.tesla.com/en_AU/forum/forums/standard-charging-cable-length)

Does the system fully power the charging of the Tesla? No. Based on the few first few charges I let the system run at maximum charge (I believe that it is 24 amps). The charging consumed far more power than the solar was producing.

So now I set my Tesla to charge at the slowest speed possible. In the Tesla dashboard I bumped the power down to 5 amps maximum, which slowed the charging. It still consumes more power per hour than I am producing even on the sunniest days, but at least I am maximizing power from the sun and reducing the strain on the grid. I can only remember ever raising the amps back up once in the last 9 months to do a fast charge.

In general I charge my car every 2-3 days, and where possible during the day when the sun is out. I typically charge it when the car drops to 60-70% and it defaults to stop the charge at 90% to protect the battery. Occasionally I charge to 95-100% if doing a long trip.

Side by side comparisons from the enphase app of 2 different days. The 1st day is cloudy (low power production) and I charged my car. The second day is fairly sunny and I did not charge my car.

It takes a couple of hours to get from 60-90%, but that is rarely an issue. I know I could charge much faster if needed. I don’t believe I have ever gone below 40% charge (range anxiety!) and only once went below 50% on a road trip. A bigger battery would be great, but the one I have works. I know I could do 400KMs with it, but you never know how far a charge is away if driving away from the city where there are no chargers.

One issue I had during the installation was that we had some of our panels raised at an angle, and after install realised how much they towered over our neighbours dining room. We felt terrible and got the installers back (for a cost of $500) to move those panels two meters.

One thing that surprises me about the panels is you will notice how much the power drops off outside of the middle of the day. The angles are all fixed which means they lose direct sunlight fairly quickly. Someone should develop some low cost brackets that swivel the panels to track the sunlight. It would really help maximise power.

Overall the project has been successful. I love the Tesla and the power system works great. It takes a few seconds to connect my power each time I charge, and never having to visiting a petrol (gas) station is a dream!

So far this year, I have generated 4 MWhs of power from the sun, and used 7. The system was installed Feb 2019, and it is now Oct 2019. It will be interesting to see how this changes over the next 3 months with summer coming.

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