Solar plants don't need us.

Beam-down optics for making glass in a solar furnace using an array of telescopic heliostats.

A common assumption is that the purpose of a solar plant is to produce electricity. That is incorrect. The purpose of a solar plant is to reproduce itself. Electricity is just the reward we symbionts get for helping reproduction along.

The easiest way to make a solar plant that can reproduce itself is to form it out of glass. The raw materials of glass are very cheap, except for one—high-temperature heat—and that is precisely the resource a solar furnace produces in abundance.

Overall view of a glass-making solar furnace employing an array of telescopic heliostats.

An order-of-magnitude calculation of the reproductive rate of an all-glass, solar glass-making plant can be attempted.

Direct normal insolation in Tucson averages just over 7 kw-hr/m2 per day. Assume one-fifth of this flux is collected by the glass-making plant per horizontal square-meter of its total land area, or about 1.4 kw-hr/m2 per day. Assume the total glass used in building such a plant is equivalent to a 2-cm thick layer of glass covering the land area of the plant, or about 50 kg/m2. Assume the thermal energy used in making glass this way is similar to the energy intensity of industrial glass-melting and refining, which is 6.5 MMBtu/ton, or about 2 kw-hr/kg of glass. Thus each square meter of land area needs to produce 2 kw-hr/kg x 50 kg = 100 kw-hr in the time it takes for a plant to make a copy of itself. Under these assumptions, the time required is 100 kw-hr/(1.4 kw-hr/day) = 71 days.

If glass-making is indeed the limiting factor, a single glass solar furnace can spawn a thousand glass solar furnaces in ten reproductive cycles, or about two years. If we don't need such a high rate of growth, we can parasitize the plants with radiant boilers and make some electricity on the side.