What you need is a solar powered cryo cooler.
I've been wanting to build one of these setups for a long time just to generate large amounts of solar energy without the expense and space the panels require.
Basically, it uses a parabolic mirror to direct sunlight onto a Stirling engine. The Stirling engine moves a linear alternator to make lots of power (megawatts vs solar panels). Here's a video of the best system NASA and DOD use: Infinia Stirling Solar
If you just wanted to cool something though a Stirling engine in reverse is a cryo cooler - the same thing used to keep liquid nitrogen cool in labs. You could make a very, very small mod of the solar stirling and use it to drive a cryo cooler. From there you could cool a water reservoir, send super cooled liquid through pipes in / around your plants and in front of a fan, etc. You wouldn't need the big parabolic mirror, you could use a small Fresnel lens instead and actually get better performance.
I really need to build a couple of these and start selling them.....
i want one plz. very very cool.