Means to store

and transport

solar energy

Figure 77 General concept of solar-driven thermochemical cycle

Some examples of solar thermochemical processes are as follows:

Methane reforming:

(a) CH 4 + H 2 O → 3H 2 + CO

(b) CH 4 + CO 2 → 2H 2 + 2CO

Reaction (a) can be used as fuel enrichment, while (b) can be reversed (i.e., run in a closed loop
as shown in Figure 77).

Metal oxide reductions:

(a) MxOy → xM + y/2O 2

(b) MxOy + yC → xM + yCO

(c) MxOy + yCH 4 → xM + y(2H 2 + CO)

Here M represents a given metal such as zinc, iron, magnesium, or boron. When direct
dissociation [reaction (c)] is impractical, the use of carbon or methane can often facilitate the
reaction [reactions (d) and (e)].

Water dissociation:

(a) H 2 O → H 2 + 1/2O 2