How to create a formula ?

[Externet]

Hello all.

Am on first steps to make a solar thermal water pump for drip irrigation purposes.    Assume 60% efficiency of solar thermal irradiation (600W/m².     Assume average daylight temperature 25C.  Assume average night temperature 15C.

Or, make those parameters real, entered in the formula.  Area of sun exposure as parameter, say =1 m² (Tank lid)  Capacity of reservoir as parameter, say = 1 m³    Volume of air, =Va.  Volume of water =Vw.

For a desired pumping height,  what would be the flow in 24 hours ? [Plus whatever am missing] 

In the hermetic reservoir, the solar heat expands the air pushing the water up during the day, and suctioning water below from cooled air contraction during the night to refill the reservoir.   How to arrive to such a formula, how is it done ?

Ordered the parts to build the contraption.  Should get in 2weeks.