This parking meter is a shadow of its former self in terms of watts. Although I don't know number, I could measure the panel by using a digital multimeter then multiplying amps by volts to get watts.
Panels are damaged by impacts, extreme weather and temperature, and regular degradation. My friends at the Solar Energy Industries Association claim that solar panels decrease in efficiency by 0.5% per year.
However, damaged and old panels can be reused. There are a lot of DIY videos on re-purposing solar cells: this and this for example. You can purchase old panels online for cheap.
As for the parking meter, DDOT claims that there are about "550 multi-space meters in the District, managing approximately 4,200 parking spaces". That's 5,500 watts of solar power--about 92 of your standard 60-watt light bulbs.
Finally, I've already posted about solar and parking twice before: Pesky Solar Parking Meters (11/19) and Giant Solar Parking Lot at FedEx Field (12/31). Obviously, there's a big intersection between parking and solar.