# Can AC/DC conversion losses from solar panels be avoided with a Tesla Powerwall?

(background: I'm just playing with numbers, trying to estimate how many solar panels would be needed to fully supply the energy for a home and 2 Tesla cars)

I've been reading up on solar panels and on Tesla car charging. That page mentions that the conversion efficiency from DC (solar panel) to AC (what home appliances need) is 75-80%.

On some Tesla forum somewhere I read that the charging efficiency from the wall plug to the car is around 85% (can anyone confirm this?). Can I conclude from this info that a Tesla car is actually a DC device?

So, if I understand all of this correctly, I lose ~25% to convert solar panel energy from DC to AC (selling to the utility company) and then again ~15% to charge the car battery from the wall plug (buying from the utility company).

Is it possible to avoid both of these conversion steps by charging a Tesla Powerwall from the solar panels during the day, and then charge the car from the Powerwall during the night? (avoiding the energy grid completely, no net metering considerations)

• An AC car wouldn't have batteries because losses. All (consumer-grade) cars have batteries. Commented Jul 19, 2015 at 17:37
• You won't have 0% loss as you still will need some form of power conversion - for peak efficiency, the output voltage and current of a solar panel should track the maximum power point (so a one part of the day, you might get low voltage high current from the cell, and another you might get the opposite). The question is then how efficiently can you convert the output of the solar panel to a stable DC voltage. Commented Jul 19, 2015 at 17:50
• I would make the following (somewhat optimistic) assumptions. 10% loss on DC-DC conversion between Solar panels and Powerwall. 10% loss on DC-DC conversion between Powerwall and car. This is based on typical-optimistic losses in DC-DC converters. This may or may not stand up to further scrutiny; we shall see. Commented Jul 19, 2015 at 17:59
• Here's an AC car ... en.wikipedia.org/wiki/AC_Cobra
– user16324
Commented Jul 19, 2015 at 18:18
• For getting energy in: Powerwall is just a battery and AC charger. Bring your own DC-DC convertor for charging from solar, or DC-DC for providing mains power. Without a MPPT convertor you're throwing away some 20% of the solar cells anyway, so you might as well have one. Commented Jul 19, 2015 at 18:42