I'd like to offer my opinion as someone who LOATHES the SaaS model.
The first and only thing you need to consider is who you're selling to (power systems engineering businesses, as you said) and what they do.
They make power systems that need to be reliable and last for fifty years or more.
You probably know banks use 30 year old COBOL software to make the world tick. Why? Because it's reliable and rarely breaks. When it breaks, they have people there to fix it. Same goes for power and manufacturing industries, they have old control systems that rarely break, because failures are very expensive.
So now you come along trying to sell them software as a service. Can you GUARANTEE that your service will be available for the next ten years? Of course you can't, you can almost guarantee that is WON'T.
So now maybe you understand why they want to BUY the product and maintain ownership of it; because that means they can manage the risk, they don't have to trust you.
And this is why I never, ever buy SaaS, because I don't trust that whoever is providing me that service is going to be there next year, or even next month (the only exception is recreation, because if Netflix shuts down tomorrow, I don't lose any value). That's why I don't use an online album to store all my photos, why I don't use SkyDrive to store all my personal documents, because I can't TRUST them.
tl;dr: SAAS == No trust (in my opinion). Either you don't trust your client (like Adobe are doing with Creative Suite) and the client can't trust you, because despite your best intentions you just can't guarantee that you'll stay in business for the next fifty years.