Paradox Engine combo question

[michaeldckmn]

I just bought a couple of Paradox Engine cards and want to include it into my green/blue energy deck.  If I have a card like Consulate Turret, does this combo give me infinite energy?

The question I feel like I have is "what defines a spell"?  is it something that cost mana?  is it something the player could block?  I have tried looking a solid definition on the internet, but I still feel confused.

Please help.

[Kaba]

A spell is only a card you cast from your hand. (excepting lands)

To cast "free" spells, you can give a look to greenbelt rampager with servant of the conduit.
You pay 1 erngy to generate a green mana, then cast greenbelt rampager, which will activate paradox engine et returns back into your hand so that you can cast it again.

[Firegriff]

Greenbelt Rampager states if you can't pay, return to hand.  If you can, I think you have to pay.

[Kaba]

That is why you need to pay 1E with the servant of the conduit so that you have only 1E left and greenbelt rampager bounces back.

[Firegriff]

Not infinite energy then.  But could be useful for when you have a tap ability on other creatures or artifacts like Endbringer or cultivator's caravan.