Currently, i've been working on a side project for months now, but i remember it took me years to get started. The essence of how i did start was to take a weekend, bang out a basic proof of concept that had occurred to me, then over time add to it, even in small ways. fix a bug here, add a view there, model data this way, etc.
It's less about energy and more about motivation. Some people would say discipline, but if you're exhausted, you're exhausted, and to push harder would only damage your resolve (IMO). It's an emotional energy thing more than physical energy, so in combination with other suggestions on here (like do it in the morning not the evening), take some time (off or the weekend, etc) to get momentum on a hobby or project (dev env setup takes at minimum a day in many cases), and then put in tiny steps or amounts of energy over time.
You'll be surprised how far you can go once you're moving.