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I'm skeptical of most bioenergy projects that involve growing things in a field. The best by far I've seen is seen is Brazilian sugarcane to ethanol. Sugarcan

I'm skeptical of most bioenergy projects that involve growing things in a field. The best by far I've seen is seen is Brazilian sugarcane to ethanol. Sugarcane is around 8% efficient at converting light into biomass, for comparison corn which the US uses for ethanol is 1-2%. Of course you then have to process those into something else to allow us humans to make use of that energy, so real efficiency is lower. Compare that to PV solar which is around 18% in a form that humans can use. Of course electricity is more difficult to store than ethanol and hydrogen but there's a big efficiency advantage that has to be made up. Much better would be to use organic waste. People have to pay to get rid of that stuff so if you can make it your fuel there's money to be made. Hydrothermal gasification or liquification both seem promising for that.

driverdan 8y ago
You're ignoring the energy and materials costs for building solar panels. Land is not the problem so the difference between 8% and 18% is negligible.
- thinkcontext 8y ago
  This is a good point, I debated whether to express things as EROI instead of efficiency. Brazilian ethanol is estimated to be about 8:1, corn ethanol is less than 2:1. According to a Wikipedia a 2015 metastudy for solar PV found between 8:1 and 40:1. https://en.wikipedia.org/wiki/Energy_returned_on_energy_invested https://en.wikipedia.org/wiki/Energy_returned_on_energy_inve...
chimere 8y ago
(Co-founder at Charm) Fair points. I'm not going to defend corn ethanol - our process yields 10x more saleable energy per acre than corn ethanol. The energy crop we're currently field trialing is similar to sugarcane, with extremely high yields (and our process uses the entire plant, unlike ethanol). Of course, energy crops are only required at large scale. At small scale, there's plenty of agricultural waste available for cheap, as you mentioned. PV certainly wins on efficiency compared to crops, but it's also relatively expensive (an acre of PV vs an acre of perennial crops). Also PV is quite unremarkable at removing CO2 from the atmosphere :]
- iso1337 8y ago
  Looks like Miscanthus grass. Although shouldn't it not matter? Why not partner with a corn grower and use corn stalk or chopped corn cobs? Or gasify cardboard.
- mirimir 8y ago
  Also, crops have built-in storage. Good work! Grasses are the best energy crops, but a serious pain to gasify (or burn, for that matter). Silica plus alkali metals => glass.

driverdan 8y ago

You're ignoring the energy and materials costs for building solar panels. Land is not the problem so the difference between 8% and 18% is negligible.

thinkcontext 8y ago
This is a good point, I debated whether to express things as EROI instead of efficiency. Brazilian ethanol is estimated to be about 8:1, corn ethanol is less than 2:1. According to a Wikipedia a 2015 metastudy for solar PV found between 8:1 and 40:1. https://en.wikipedia.org/wiki/Energy_returned_on_energy_invested https://en.wikipedia.org/wiki/Energy_returned_on_energy_inve...

chimere 8y ago

(Co-founder at Charm) Fair points. I'm not going to defend corn ethanol - our process yields 10x more saleable energy per acre than corn ethanol. The energy crop we're currently field trialing is similar to sugarcane, with extremely high yields (and our process uses the entire plant, unlike ethanol). Of course, energy crops are only required at large scale. At small scale, there's plenty of agricultural waste available for cheap, as you mentioned. PV certainly wins on efficiency compared to crops, but it's also relatively expensive (an acre of PV vs an acre of perennial crops). Also PV is quite unremarkable at removing CO2 from the atmosphere :]

iso1337 8y ago
Looks like Miscanthus grass. Although shouldn't it not matter? Why not partner with a corn grower and use corn stalk or chopped corn cobs? Or gasify cardboard.
mirimir 8y ago
Also, crops have built-in storage. Good work! Grasses are the best energy crops, but a serious pain to gasify (or burn, for that matter). Silica plus alkali metals => glass.