Would it be worth it to equip an ebike with a small portable solar panel on the stem to recharge while sitting idle outdoors? I commute and can only lock my bike outdoors. If I were to get an e-bike, I wonder if I could forget to charge it overnight.

I guess it depends on a lot of things, but the amount of electricity you get from a small, stem sized solar panel for ?? minutes is unlikely to equal the amount of electricity it takes to move you and your bike.

How many weeks do you plan on leaving the bike out between rides?

Under ideal conditions, solar panels generate approx 15 watts per square foot or .1 watt per square inch. Determine how many watt capacity your battery pack is and google will assist you with the math from there.

Now I am sure my calculations are way off but first run-through for a 1 Sq/Ft panel, you would need to have 127 peak sun hours to charge a Specialized Creo e-bike. Hopefully, there are some smart engineering types who point out how wrong I am but its a start.

All day between morning and evening. Depending on the length of my commute it would be 1-2 miles a day.

When I worked downtown in my community, I had to walk half a mile from my rented parking place to get to work.

If the one way distance for your commute to work is a distance of a half mile to one mile, reverse that at the end of the work day, do you really need an e-bike for that commute?

Yes if I wake up late.

No. Simply not big enough. It would be worth it to put one (or many) on your house.

A second alarm clock costs less than an e-bike.

it would be closer to “worth it” if you put it on or where a rear fender/rack goes. you could probably get one square foot without a massive drag penalty. maybe you can make something that unfolds to two square feet. at that point, you’re talking about 30-40 watts, which over 6-8 hours is about half of a smallish eBike battery if you had a reliable and efficient way to do DC to DC charging. unfortunately that’s not easy. there’s lots of info out there on this, but most people choose a much larger array, an inverter, and standard AC chargers. not something you want for your commute rig.

That depends if your house has clear sky around, and the house is in the sunbelt, otherwise no, it's not worth it on a house.

If you have a secure location to park your bike, which I assume you don't since you have to lock it up, but the only way you could charge the bike is to get a 4 panel portable solar charger, cost about $70 on Amazon, you could put some charge into the bike, problem is, if your bike is like my wife's, they don't make the battery compatible to be plugged into a USB port to charge it with, instead there is a large round plug that plugs into a charger, then the charger has a standard wall outlet style plug, portable solar chargers only use USB style plugs.