# BMW looking at solar charging systems

While there has been talk of solar panel charging systems for many years now, its seems as though BMW has finally wiped the dust off this project:-

BMW

Regards,

Mark

Let’s do the math on this nice-looking solar car-port, ok?

Vehicle being charged: BMW i3 ‘City Car’ with 22 kWh battery

Solar charging station with grid-tied “storage”: In order to fully recharge a completely depleted 22 kWh battery with solar-generated power you would need to make at least 22 kWh and feed it back to the grid during the day to make the i3 ‘free’ to drive for its maximum range. Let’s figure the average American north-east city gets between 4 and 5 hours average insolation (the measure of available solar energy per day).

Using solar panels of 15% efficiency, you’d need to generate 22 kWh over a period of 4.5 hours. That equates to generating a peak power of 22/4.5 or 4.88 kW of solar panels. The typical panels available are about 180 Watts each so you’d need 4888/180 or 28 panels.

Typical installed price of any reasonably sized grid-tied solar system is between 10 and 20 cents per watt. So 28 180 Watt panels, the inverter and support structure would cost you somewhere around \$28,000 to \$56,000 installed.

If your utility power costs 14 cents/kWh it would cost you \$3.08 to fully charge the 22 kWh battery in the BMW i3 using grid-power. If you drive it every work-day and occasionally on weekends you’d recharge it once a day 6-days a week on average. That makes 312 full charges at \$3.08 each time or a total of \$961 per year.

Compare that to your “free” solar power system which costs you a minimum of \$28,000 to install and you can see that your payoff time would be approximately 29 YEARS!!!

So - as good as it looks; it’s just not feasible at this time in my educated opinion.

Now; if we can get the cost per Watt down to a penny or less, it begins to make more sense. I wouldn’t hold my breath though…

Thanks Bob

That puts it in perspective.

Mark