Is 85% the highest efficiency we can achieve with PV technology?

[Integral]

80 MWhr in 2 years, means 40 MWhr in 1 year means average power 40 MWhr / 8760 hrs = 4.6 KW.

Did I do that right ? We're talking about 4.6 KW average ?

Ya, got to start somewhere!

 

[mheslep]

... Right now, increased power demand is increasing coal electricity and increasing emissions. That's a fact.

Perhaps you mean historically, but electrical demand clearly declined recently, and substantially.
http://online.wsj.com/article/SB125003563550224269.html

...On Friday, the nation's largest wholesale power market serving parts of 13 states east of the Rockies is expected to report that electricity demand fell 4.4% in the first half of the year...
Wholesale electricity -- power furnished to utilities and other big energy users -- cost an average of $40 a megawatt hour in the region, down from $66.40 a year earlier. The price declines in this market, which extends from Delaware to Michigan, come on top of a 2.7% drop in energy use in 2008 over 2007.

Part of that is no doubt due to the recession, but there's also apparently been some large investments in efficiency given the spiking oil prices last year and now the threat of pending carbon taxes.

Adding electric transportation only makes that situation worse, unless we make a change in how we make power.

It could if its done with no planning, but as you probably know some 10% of US electrical generation (~100GW) is idle overnight. Edit: That's enough to charge 200 million sedans w/ a 110 mile (25kWh) capacity ( 5 hours charge @ 5 kw)

 

[mheslep]

Scalability becomes less of an issue when photovoltaics are integrated into buildings and roads of urban areas and thermochemical or photochemical methods are used in non-rural areas.

No, it doesn't. Making smaller and more distributed generation with poor availability makes scaleability worse, not better. Instead of providing back-up power at the grid level, with distributed production of photovoltaics, you need full conventional redundancy. And that's in addition to the main meaning of "scaleability": economies of scale. ...

I'd say you both have a point here, depending on use. If PV's are deployed on roof tops to provide for only peak load, say for grocery store air conditioning in the middle of a sunny day, then Topher is correct, as they lessen the demands on the grid. To the degree PV's are deployed to handle base load without their own long term storage mechanism, then Russ is correct, as then the grid has to be there to match every PV deployment in the event of a four day blizzard.

 

[Ivan Seeking]

Yes, but in the end, you DID bring that CO2 in the atmosphere (when you use the fuel), although you used it twice, and so you divided the emissions per KWhr by about two.

Then we replace the coal with algae biomass: Loop closed.

 

[mheslep]

... A coal plant is worse than a car in emissions.

http://www.epa.gov/otaq/climate/420f05001.htm": 2.095 lbs CO2 from coal/ kWh (year 2000 plants)
http://www.eia.doe.gov/cneaf/electricity/page/co2_report/co2emiss.pdf" : 19.4 lbs CO2 / gallon gasoline

CO2 per mile (28 miles):
EV (4 miles/kWh - battery to wheel): 14.7 lbs. Including charging losses, 16.3 lbs.
ICE vehicle (28mpg): 19.4 lbs

The coal CO2 figures are net over all the old coal plants in the US. I understand the new supercritical coal plants do much better.

 

[mheslep]

Ok, I guess - I've just never heard someone claim that trading oil for coal was a good thing!

Not for the long term, and not all of the oil would replaced with coal of course. Replace just half of the oil with coal, the rest is natural gas, nuke, etc.

The efficiency gains are probably more on the order of 1.3:1. A gas car is about 30% efficient and a power plant is about 45% efficient. The electrical transportation, storage, and usage is altogether about 85% efficient. Multiply that out and you get 30:38 or 1.3 A

Ok, I was talking tank-to-wheel, your figure is the more inclusive well-to-wheel which I agree is the one we want at the moment. However these advocates (Tesla) still show well-to-wheel efficiency of EV's at least 2x or 3x better than even small ICE cars.
http://www.teslamotors.com/efficiency/well_to_wheel.php
They rightly include petroleum well-to-station distribution losses, and using a natural gas 52.5% electric source.

 

[mheslep]

..In fact, if you have access to large amounts of direct sunlight such as in hot deserts, CSP is much cheaper and much more efficient than PV, and this will always be so, because mirror will always be cheaper than PV. ...

Always is a very long time. I think both CSP and PV will win out in combination. You're right of course about the cost of mirrors, but consider:
1. PV's are http://thefraserdomain.typepad.com/energy/solarconcentrating_pv/" , making the use of high efficiency PV's affordable
2. Other work's being done to essentially 'waveguide' bandshifted http://www.technologyreview.com/energy/21066/"
3. Projects like the space based solar power plan for mirrors focused on PVs.
4. The upper limit on PV efficiency is apparently http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6V51-3VTFJVJ-16&_user=3938616&_rdoc=1&_fmt=&_orig=search&_sort=d&_docanchor=&view=c&_searchStrId=980826264&_rerunOrigin=google&_acct=C000061828&_version=1&_urlVersion=0&_userid=3938616&md5=2a2c22990ac5eae6adc6c2c8a4a98501", far beyond what any thermal heat cycle can do.

The advantage you mention of overnight heat storage in thermal CSP will hold off PV for awhile, but not forever I suspect.

 

[gloo]

Your point in the OP is absolutely correct and it is what I've said in other places in this thread: cars are going to be powered primarily by gas for the forseeable future, whether people like it or not. Efficiency legislation and stop-gap technologies like plug-in hybrids will help, but they don't change that reality. While we should promote reseach, we should put the bulk of our efforts into solving now the problems that can be solved now. And that means... That hypothetical world is not a pipe dream, it is a reality in France today, a nuclear fueled country. Nuclear does satisfy their needs cheaply and cleanly and can satisfy ours if we choose to do it. Sadly, this is only going to happen when the economics overcome the politics for nuclear power here.

Wait Russ, so you are saying that part of the equation to get off of gas for cars will be the use of Nuclear to create electricity for cars? Did you mean to create electric power to feed into cars at plug in stations? I am pretty sure you don't mean making hydrogen off some kind of electrolysis (not efficient). You think nuclear is abundant enough to significantly replace coal and nat gas? Not challenging you (you are way more of an expert) - just trying to clarify.

 

[Ivan Seeking]

Your point in the OP is absolutely correct and it is what I've said in other places in this thread: cars are going to be powered primarily by gas for the forseeable future, whether people like it or not. Efficiency legislation and stop-gap technologies like plug-in hybrids will help, but they don't change that reality. While we should promote reseach, we should put the bulk of our efforts into solving now the problems that can be solved now. And that means... That hypothetical world is not a pipe dream, it is a reality in France today, a nuclear fueled country. Nuclear does satisfy their needs cheaply and cleanly and can satisfy ours if we choose to do it. Sadly, this is only going to happen when the economics overcome the politics for nuclear power here.

But we'll have better options before that happens.

 

[Ivan Seeking]

I wasn't sure if this was linked or not.
http://www.exxonmobil.com/corporate/files/news_pub_algae_factsheet.pdf

What is described as an exhaustive two-year review of all alternative fuel options landed Exxon on Algae, which I have been pushing for three years now, btw.

 

[mheslep]

Your point in the OP is absolutely correct and it is what I've said in other places in this thread: cars are going to be powered primarily by gas for the forseeable future, whether people like it or not. Efficiency legislation and stop-gap technologies like plug-in hybrids will help, but they don't change that reality. While we should promote reseach, we should put the bulk of our efforts into solving now the problems that can be solved now. And that means... That hypothetical world is not a pipe dream, it is a reality in France today, a nuclear fueled country. Nuclear does satisfy their needs cheaply and cleanly and can satisfy ours if we choose to do it. Sadly, this is only going to happen when the economics overcome the politics for nuclear power here.

Going to all nuclear electrical power in the US would do little by itself to remedy the oil dependency and import problem. Oil primarily goes to transportation in the US.

 

[mheslep]

Following up on CO2 emissions from EVs vs conventional vehicles in https://www.physicsforums.com/showpost.php?p=2309271&postcount=75", page 8.

 

[mheslep]

...
4. The upper limit on PV efficiency is apparently 85%, far beyond what any thermal heat cycle can do...

Working link:
http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6V51-3VTFJVJ-16&_user=3938616&_rdoc=1&_fmt=&_orig=search&_sort=d&_docanchor=&view=c&_searchStrId=1046943350&_rerunOrigin=google&_acct=C000061828&_version=1&_urlVersion=0&_userid=3938616&md5=a8c43418a43c3d5ccadc277290468c9e