It's not just sand. It's sand with the oxygen removed. The oxygen (especially every last atom) doesn't want to leave.
Silicon has to be purified to 99.9999% at the very least to make a crappy solar cell. Add four more 9's to get to making decent microprocessors. Getting certain impurities out (that behave exactly like silicon in a chemical sense) is really difficult.
Silicon wafers (cheap ones) cost about $150/kg.
Polysilicon (good luck making a wafer out of it) costs about $30/kg (market has crashed).
Copper costs about $7.50/kg.
It's not terribly energy intensive. You want to see energy intensive, pick up a beer can. Aluminum is electricity in solid form.
Silicon is capital equipment intensive. It is processed in batches. While each batch is being processed, it ties up an expensive processing station for a long time.
I'm sure you didn't mean it as such, but that's actually kinda funny; no, Silicon Valley did not get its name from the manufacture of Silicon from sand. Most of the sand that is sourced to make your microchips and solar cells comes from quartz mines and sand pits in Appalachia; Alabama, SE Ohio, and West Virginia are probably the top producers. Silicon Valley imports wafers and has historically had very little to do with how those wafers got made.
In fact, according to the foreman at one of said plants I talked to, they use pieces of quartzite that are more like pebbles than sand; no point in crushing it further I guess.
The function of the carbon is not just to create the heat but also to give the oxygen some way to remove itself. In fact, I believe the oxygen would still rather bond to silicon than carbon but the carbon is able to pull enough physically away as gas to make the reaction work. The resultant gas is mostly CO, carbon monoxide, which somehow becomes CO2 after the plant's done with it.
"Although the newest smelters can be closer to 12,500 kWh per ton let’s say most smelters are consuming electricity at 14,500-15,000 kWh/ton of ingot produced."
"In making MG-Si, approximately 12 kilowatt-hours of electrical energy are consumed per kilogram of silicon produced."
That already is in the same ballpark, for MG = metallurgical grade silicon. Getting from there at the purity needed for chip production is energy intensive. From the same text: "Energy consumption for the Siemens process is ~200 kilowatt hours/kilogram of silicon produced"
Even correcting for a potential bias of the author (who has his own patented process that he claims to be more efficient and, I guess, that he wants to sell), I conclude that, per kg, production of silicon-grade silicon is way more energy expensive than production of aluminum.
Yes, silicon panels are not the only solution. Although not as efficient as silicon other techniques have other qualities that make it commercially viable (price, scaling, maintainability) as explained in this video by nano solar http://www.nanosolar.com/nanosolar-technology-overview
My guess is that the copper oxide would be much cheaper to work into much thinner sheets than silicon, which is also expensive to purify, so although the raw material may be more expensive, the processing costs and volume used might be where the savings are made.
Also, the abstract on the referenced paper seems to indicate that the efficiency of this design is reasonable. I didn't go beyond the paywall to find out more though.
Photovoltaics (PV) are a promising source of clean renewable energy, but current technologies face a cost-to-efficiency trade-off that has slowed widespread implementation.(1, 2) We have developed a PV architecture—screening-engineered field-effect photovoltaics (SFPV)—that in principle enables fabrication of low-cost, high efficiency PV from virtually any semiconductor, including the promising but hard-to-dope metal oxides, sulfides, and phosphides.(3) Prototype SFPV devices have been constructed and are found to operate successfully in accord with model predictions.
You can deposit thin films of silicon on to, say, ordinary glass. Usually, this is done with CVD, although I think epitaxial growth is also a popular technique.
The problem is that this tends to produce amorphous silicon, which is not especially efficient. There is a good deal of work to get to the point where monocrystalline silicon thin film cells are viable outside of the lab, though.
* Copper oxide panels are not new.
* They are much less efficient than silicon panels.
* Cu2O is much more expensive than silicon.