This was pretty nice! There's a lot of gameplay going on, and the graphics/music are nice too.
I wish there was a tutorial on the sun mechanic and shopping menu. The first time I played I hadn't read the page description, so I just ran out of ammo and died, lol! I'm not gonna knock points off for that, it's on me for not reading first. Just something to think about adding if you take it further.
After the player upgrades enough, the snowmen all get 1 shotted and the game just goes forever. I'd love to see this expanded on with some kind of meta/final boss/increase in difficulty for when we get too powerful.
Maybe some clouds could cover the sun and we have to make sure to upgrade our battery to survive the random weather change. Just tossing ideas here.
There's a lot here that is fun, and I still wanted to play more when I finally lost. You did great!