Pizza is fun and every one likes food, that will interest them

I agree with everyone else. I never tried power type seminairs but have done little things like computer stuff. Most people don't want to learn how to do anything they just want it to work 
Hands on stuff is good. If you can't build something on site, maybe you can have various parts, small working model to spin and light lights or something. To demonstrate building a working daul rotor type maybe, have a coil winder, a wound coil, some wire, couple loose magnets etc.. for people to look at and play with. Mags should not hurt people, maybe lower powered ones to play with, one strong one stuck to steel they can try to get off to see how tough they can be. Most people think of toys when you say magnet! They don't think break fingers!!
It depends on alot of variables what you really want to do. As someone suggested building a machine on site. That is great if you can, but probably not going to be able to if this is a quick 2-4hr thing.
Again seeing is beleaving, so if you have a 300 watt mill turning to power a 150 watt inverter running a 100watt bulb and a 15watt CFL they will see it all work, and when they touch the bulbs they will understand what you meant about lighting and heat and power use also for conserving energy or wasting it.
Kinda like someone I am re-building one of my used Pcs to sell to. They only wanted their modem working in the old system they have when they first called me. They got internet service, computer can't find the modem when they try to dial out.
So what's this got to do with seminiars?
It shows people are not interested in how to do something, they just want to do it.
This person should have been able to install new drivers for the modem, but didn't want to bother trying. I was going to waste my time free over the phone to help them, they didn't want to try.
So now they are buying a system! Was to far for me to drive just to find out maybe they wouldn't have a needed disk or something when I got there and they don't know what modem they have etc.. so I won't try to fix it either.
In doing a seminar How to make DVD's, no one wanted to learn to make a DVD! I had a class set up and planned several hours of basic and advanced stuff. REALLY, "How to MAKE DVDs", but all they want to do is steal somebody elses. Turned out to be a 1hr class. Install ripping software, shrink, burn. Duhhh, really learned something didn't they 
So much for my capture settings, authoring, editing, chapters, menus, ect... plans.
Every one had fun, I made money, we had pizzas, everyone was happy, we left early :<
That was back before the set top DVD recorders were out and no-one thought Dual layer DVD R would ever exist.