What is the ideal temperature and pressure to crack water?

Using sun mirrors and solar cells for electricity. What temperature, pressure and voltage ideal for cracking water. 


[![enter image description here](https://i.stack.imgur.com/rgSO3.jpg)](https://www.npr.org/sections/alltechconsidered/2016/04/05/470810118/solar-and-wind-energy-may-be-nice-but-how-can-we-store-it)  

Source: [NPR](https://www.npr.org/sections/alltechconsidered/2016/04/05/470810118/solar-and-wind-energy-may-be-nice-but-how-can-we-store-it)  



[![enter image description here](https://i.stack.imgur.com/ZVUgK.jpg)](https://thefraserdomain.typepad.com/energy/2006/03/huge_concentrat.html)  

[Source](https://thefraserdomain.typepad.com/energy/2006/03/huge_concentrat.html)  



Would it take more or less electricity to crack water under pressure or in a liquid or vapor state?


