World record solar cell with 44.7% efficiency

Concentrator cells make a number of tradeoffs in order to make their performance as high as possible (and keep from melting, etc.). I would guess around 22% efficient in one-sun AM1.0; that's about what other concentrator cells in this upper tier do.

If it's slightly cloudy, I could see efficiencies dropping to the single digits, as each of these cells is actually four different cells all wired in series, each sensitive to different wavelengths of light. If the blue drops out, the corresponding cell on the top of the stack acts as a resistor (and it can even burn out, being so thin).

Solar cell efficiency records (particularly for concentrator applications) are like discovering new transuranic elements- extremely useful and interesting at first, then significantly diminishing returns.

Imagine you have commissioned 100 different manufacturers to make you 100 different arbitrary Lego knockoffs; each manufacturer picks a color, thickness, and a peg pitch (spacing between the pegs). Each manufacturer only makes exactly one kind. Some manufacturers' legos will fit together, and some won't.

Some manufacturers make theirs very cheaply and in mass quantities, and some will take years to deliver a very small number at very high prices.

As a solar cell designer, you want to make a stack of these legos to form a rainbow. It has to go from blue on the top to red on the bottom, and it has to stack together without too much force.

Think of a brand-X terrestrial Home Depot crystalline solar cell as just yellow lego bricks. They aren't the whole rainbow (and green would actually be a closer match to sunlight if you could only pick one color) but they're cheap.

Gallium Arsenide legos are green, but they're really hard to make. Germanium legos are red, and it turns out that the green Gallium Arsenides fit on them really well. Yellow Silicon ones, on the other hand, don't fit well with either.

So that brings us to two. Indium Phosphide legos are blue and so are Gallium Phosphide legos. But neither of those fit well on the green Gallium Arsenide; one's lego pins are too dense, the other too sparse. It took a long time for a manufacturer to come up with the right blend, thickness, and color, but they were able to come up with a lego that is blue, made from a mix called Indium Gallium Phosphide, and stacks nicely on top of the green Gallium Arsenide. So that's 3.

The fourth layer might be Indium Gallium Arsenide Nitride (let's just call it orange), shoved between the existing layers; somehow making a mix of a good quality lego, but one that makes the right color, right thickness, and right pin pitch.

Now to translate to real physics: The pin pitch is the lattice parameter of each of these crystals, or the distance between individual atoms. If you attempt to epitaxially grow (grow on top of in the same fashion) a different compound than what already exists there, it tends to work ok if the lattice parameters are close. If they're radically different, you can get growth but it's highly disordered and ends up making a lousy layer and a lousy solar cell.

+1 for the Futurama reference

Regarding storage, I've read some interesting things about the potential of electric vehicles here. If every car were electric, that's a massive array of large efficient batteries connected to the grid. If utility companies charge varying amounts at different times, depending on supply, you could imagine a smart charger for your car whereby you buy electricity when it's cheap, store it in the battery, and sell it back for a profit when the price goes up (or just use the power in your home, reducing the amount you buy from the grid - the effect is the same). The utility company is effectively renting your electric car battery as short term storage.

And a 44% efficient process that quadruples its efficiency is now 86% efficient (ignoring whether 100% is achievable, etc).

You've been hanging out with marketing too long. ;)