Sorry to hear about your losses, I know just how you all feel, hopefully my 'problem' has been dealt with.
My call ducks would normally be around waiting to go in, I fed them inside at nights, they spent the day foraging so maybe only got a few layers pellets if they came up to the water trough.
I don't see why solar power wouldn't work? during summer there should be enough light, winter they are shut in earlier anyway so it would be easier to remember?
I'm sure I've seen how to make a homemade one somewhere - Youtube?