What happens to light after it enters an eye What happens to the light [energy] after it enters an eye and hits the rods and cones? I presume the energy becomes electrical, and it must be near 100% perfect, else our eyes would heat up? Or am I missing something? 
The motivation of this question is solar panel technology.
 A: There is some heating that takes place, but the amount is pretty trivial, because there just isn't that much light reaching the back of your eye. A back-of-the-envelope sort of estimate would be to say that the light of the Sun reaching the Earth's surface amounts to about a kilowatt of radiation per square meter. Your pupils have a radius of maybe a millimeter, probably much less in bright sunlight. So, if you're staring directly at the Sun (which, hopefully, you're not really doing), you're getting at most a few milliwatts delivered to the back of your eye. That's not going to tax the temperature regulation systems in your body, given that a living human generates about the same heat as a hundred-watt light bulb.
If you dramatically increase the amount of light delivered to your eye, say by accidentally catching a high-power pulsed laser in the eye, you can overwhelm the body's ability to carry away the heat, and do real damage. The pulsed-laser lab next to the office where I did my undergrad thesis research had a sign on the door explaining in gruesome detail what would happen if you were to catch a full YAG laser pulse in the eye, which involved the boiling retina basically blasting your eyeball out of your skull. Which is why you wear safety glasses in those labs, and knock before entering any optics lab.
A: Your reasoning is correct. Our eyes do heat up. The constant flow of blood is likely what carries away the heat.
Elaborate explanation: all biological processes are ultimately thermodynamical processes. Any "operation" - such as a single cycle of ATP production by ATP synthase, or the conversion of incident photons into metabolic energy (photosynthesis) or into neuronal impulses (vision) - can be thought of as an engine with a certain efficiency $e$. This is traditionally given by the ratio of the amount of useful work $W$ the engine performs in a single cycle to the total amount of energy $E$ fed into it:
$$ e = \frac{W}{E} $$
and since $E = W + Q$, where $Q$ is the waste heat released into the environment, we have:
$$ e = 1 - \frac{Q}{E} $$.
The second part of your question as I interpret it is: "What pressures of natural selection lead to the evolution of vision?". The simplest answer I can think of is the exposure of photo-reactive compounds to a constant bath of photons (from the Sun) over millions of years lead to the evolution of different mechanisms to exploit this energy, one of those mechanisms being that of vision. Of course, this is not really an answer. Maybe somebody with greater knowledge of evolutionary biology can shed more light on this aspect.
A: You are correct, that the light becomes an electrical charge from our eyes, and the resulting signal is processed by  a very complex system. The rest of it will heat up our eyes, but realize that the same thing is true of light hitting our body anywhere.
The signal generated from our eyes is minimal, I wouldn't use the word solar panel in the slightest to describe the affect at all.
A: "The second part of your question as I interpret it is: "What pressures of natural selection lead to the evolution of vision?"
algae grows at sunny spots. having a means to detect these sunny spots gives a greater
chance of having more food and thus more offspring.
A: In humans (and vertebrates) the retinal structure evolved basically inverted in that the photons have to pass through layers of neurons and blood vessels before they hit the rods and cones. Wolves and some other vertebrates have a reflective membrane(the tapetum lucidum)  behind the photoreceptors that reflect the photons back through the rods and cones and provide a double pass amplification (causing "eyeshine"). Humans lack this.
The retina has ten layers which process signals from the photoreceptors, whose surface membranes contain retinol, which is isomerised by the photon energy, which affects ion channels, and may result in an action potential (necessarily leaving out all sorts of steps) which is preprocessed by retinal ganglion cells and information compressed and conducted along the optic nerve axons to the visual processing areas of the brain.
Vision has been extensively studied and is immensely complicated. Much of the energy takes part in chemical reactions and in multiple action potentials (electrochemical) in the preprocessing in the 10 layer retina.  Francis Crick (physicist, of DNA fame) and Christof Koch have written much about it--Koch's book, The Quest for Consciousness is fairly technical neuroscience focussing on the visual system.
