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Natural Science Forum / Chemistry / General Chemistry / July 2008Ethanol vs Photovoltaic
As I understand it photosynthesis is ~6% efficient and then conversion to ethanol is ~65%. Thus ignoring all the costs of growing, fertilizing, transporting… less than 4% of the energy from the sun is captured in ethanol. Some analysis I’ve seen say that a total energy accounting results in a efficiency of <0. OTOH photovoltaic cells are 10 to 20% efficient. My son, the electrical engineer, tells me that some approach 50%. But that they are expensive. Am I missing something here? Steve > As I understand it photosynthesis is ~6% efficient and then conversion > to ethanol is ~65%. Thus ignoring all the costs of growing, [quoted text clipped - 9 lines] > > Steve You are missing how VERY expensive solar cells are. Think about covering you roof with Pentium processors. Main cost component in processor IC is silicon, and so it is in solar cells - because they are made of solid ultra-pure silicon mono-crystal slices!. To get the cost of present 20% efficient solar cells back, you need to power your house for 10-20 years (and at that time they will degrade and you have to trash them). Basically it is not economical at this point, except for the areas where there is no grid - for example on Mars or on remote outpost in Arizona desert. To make it economical at present electricity prices, solar cells W/$ has to improve 2-3 times (developments in this direction include polysilicone cells and thin film cells, that trade efficiency for price). Increase of electricity prices 2-3 times will also make them economical... Regards, Yevgen > To make it economical at present electricity prices, solar cells W/$ > has [quoted text clipped - 3 lines] > Increase of electricity prices 2-3 times will also > make them economical... That wouldn't overcome solar's unreliability. You can't have more than about 20% solar in the energy mix powering the grid, because the operating reserve needed to back up the solar would be too expensive. This is because you can't control the clouds, and you need to have generators running in hot standby mode ready to take over when clouds move over your solar array. A similar problem exists for wind power. Dear Mark Thorson: > > To make it economical at present electricity prices, > > solar cells W/$ has to improve 2-3 times [quoted text clipped - 4 lines] > > That wouldn't overcome solar's unreliability. ... in most locales where people choose to live ... > You can't have more than about 20% solar in the > energy mix powering the grid, because the [quoted text clipped - 4 lines] > to take over when clouds move over your solar > array. A rare occurence here in the desert. However an increasing amount of atmosphere and then the Earth itself gets in the way once a day... for several hours. ;>) > A similar problem exists for wind power. I was servicing an ozone generator once when the clouds came over. A significant amount of static charge followed them. 125 each 80pF cells charged to more than 1000 volts... I wonder if that could not be harvested too? David A. Smith > > I was servicing an ozone generator once when the clouds came over. A > significant amount of static charge followed them. 125 each 80pF > cells charged to more than 1000 volts... I wonder if that could not be > harvested too? Solar needs a large operating reserve because it is unreliable, as compared to hydro, nuclear, or any kind of fossil fuel. Electrostatic would be unreliable squared. > > > I was servicing an ozone generator once when the clouds came over. A > > significant amount of static charge followed them. 125 each 80pF [quoted text clipped - 5 lines] > > Electrostatic would be unreliable squared. I will say solar and wind works better with grids containing a large hydro component as the water saved serves a battery in a manner of speaking. Dear trigonometry1972: <trigonometry1972@gmail.com> wrote in message news:f877999b-0019-40aa-82bb-adbed719dd1f@c65g2000hsa.googlegroups.com... On Jul 3, 1:38 pm, Mark Thorson <nos...@sonic.net> wrote: > dlzc wrote: > [quoted text clipped - 9 lines] > > > Electrostatic would be unreliable squared. > I will say solar and wind works better with grids > containing a large hydro component as the > water saved serves a battery in a manner of > speaking. Hydro should not be part of a permanent plan, IMHO. Rivers (and hence dams and their resulting reservoirs) end up on fault lines, and the last thing I want to press down on on an egg, are fault lines. Each such installation has been observed to decrease the surrounding elevation. ... as much as I like boating. David A. Smith On Jul 5, 9:08 am, "N:dlzc D:aol T:com \(dlzc\)" <dl...@cox.net> wrote: > Dear trigonometry1972: > [quoted text clipped - 32 lines] > > David A. Smith Nothing is permanent. If nothing else the reservoirs fill with sediment. Nor is this to mention the problems the dams cause for the various fish runs and the related issue of tribal rights. That bring to mind a nightmare scenario in which an earthquake ruptures the Grand Coolee Dam which in turn takes out every dam on the Columbia below it and WPPSS number 2 nuclear power plant, its spent rods, and perhaps some of buried nuclear waste out in the Hanford nuclear reservation. I shudder to utter this scenario.......Trig Dear trigonometry1972: On Jul 6, 3:46 am, "trigonometry1...@gmail.com |" <trigonometry1...@gmail.com> wrote: > On Jul 5, 9:08 am, "N:dlzcD:aol T:com \(dlzc\)" <dl...@cox.net> > wrote: ... > > Hydro should not be part of a permanent plan, > > IMHO. Rivers (and hence dams and their [quoted text clipped - 9 lines] > Nothing is permanent. If nothing else the > reservoirs fill with sediment. Sediment weighs more than water. > Nor is this to mention the problems the dams > cause for the various fish runs and the related [quoted text clipped - 9 lines] > > I shudder to utter this scenario....... That is how Nature does it. River deltas are unusally high in background radiation. The heavy metals that get picked up by the river, gets settled out as soon as the stream velocity drops. Of course, it is not spent fuel rods... insurance will fix it all though, right? ;>( I sure wish such were considered a harvestable resource. Seems like it is such a hazard being "ignored", when it could yield a good deal of salable material... material we also spent good deal of political capital in obtaining intially. David A. Smith > I will say solar and wind works better with grids containing > a large hydro component as the water saved serves a battery > in a manner of speaking. You need natural gas peaker plants that are spinning and synchronized to the grid to handle sudden drops in solar array output. Those generators can be throttled up faster than any other source of power. Hydro takes several minutes to throttle up, during which time the cloud over your solar array may have moved on. > > To make it economical at present electricity prices, solar cells W/$ > > has [quoted text clipped - 13 lines] > to take over when clouds move over your solar > array. A similar problem exists for wind power. That is correct, but there are some favorable correlations between peak demand on solar peak - during the day. Also air-conditioning usage increase at the same time where solar is most effective. Grid is already has massive generator overcapacity to deal with just a few hours of high demand. Solar might actually reduce the needed overcapacity because it is active during this times. Regards, Yevgen |
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