Efficiency has improved somewhat, but also, the cost to manufacture PV is enormously lower than it was then, which means that it's using much less materials and energy to produce. Therefore the energy payback time should be much shorter.
How much shorter depends on the fraction of the energy cost in the first place then. Price is not even an upper bound for energy which is cheap in China, and also production is probably subsidised.
Intensive investigations of Chinese "subsidies" from the US Department of Commerce have come up with embarrassingly little.
The current €0.100/Wp price level (12¢/Wp) combined with the US$0.08/kWh given above does give us an upper bound of 1500 hours of full sun for the energy payback time. At a Californian 29% capacity factor, that's 7 months of operation.
But in fact not 100% of the cost of the solar module is the cost of energy; there are some labor and raw materials costs as well, as well as capital costs and, astoundingly, some profit. So 3 months is probably a better estimate.
Process energy will still be a lot cheaper than .08 US$/kWh in China. I doubt they process glass with electric ovens. OTOH that is primary energy then, which kind of supports your argument. Still other emissions in the silicon supply chain that cause global warming are also relevant. If I find the time, I‘ll look for recent LCA.
I'm delighted to see Fraunhofer's report! I'll read it carefully.
You are probably right about the glass. Processing glass in electric furnaces has been a well-established technology for many generations, but it is more expensive than fossil-fuel-fired furnaces, and is used for making more expensive kinds of glass. But the glass in solar panels is an especially cheap kind of glass.
Coal is probably the cheapest form of energy.
https://www.coal-price.com/ says that currently in China coal is on the order of US$100 per tonne. Coal has up to 33MJ/kg, so that works out to 0.3¢ per megajoule, or 1.1¢ per kilowatt hour, or more if the US$100/tonne coal isn't the best anthracite. You probably can't literally run a glassmaking furnace with a coal firebox, because of the contaminants from the coal, but you almost certainly can't run it on cheaper energy than that. If 100% of the cost of the solar panels were coal energy instead of electric, that would extend my upper bound out from 7 months to a bit over 4 years.
This seems to be in rough agreement with Fraunhofer's more informed estimate that you cite.
