From Stanford University
Stanford scientists calculate the energy required to store wind and solar power on the grid
Renewable energy holds the promise of reducing carbon dioxide emissions. But there are times when solar and wind farms generate more electricity than is needed by consumers. Storing that surplus energy in batteries for later use seems like an obvious solution, but a new study from Stanford University suggests that might not always be the case.
“We looked at batteries and other promising technologies for storing solar and wind energy on the electrical grid,” said Charles Barnhart, the lead author of the study and a postdoctoral scholar at Stanford’s Global Climate and Energy Project (GCEP).
“Our primary goal was to calculate their overall energetic cost – that is, the total amount of fuel and electricity required to build and operate these storage technologies. We found that when you factor in the energetic costs, grid-scale batteries make sense for storing surplus solar energy, but not for wind.”
The study, which is supported by GCEP, is published in the online edition of the journal Energy and Environmental Science.
Climate change and renewable energy
Most electricity in the United States is generated at power plants that run on coal and natural gas – fossil fuels that contribute significantly to global warming by emitting large amounts of carbon dioxide. Solar and wind power are emissions-free and renewable, but depend on sunlight or wind to operate.
“For the grid to function efficiently, power supply needs to match power demand at all times, but with renewables, that’s not always the case,” Barnhart said. “For example, wind farms sometimes produce too much electricity at night when demand is low. That excess energy has to be stored or used elsewhere. Otherwise it will be lost. However, the U.S. grid has very limited storage capacity.”
A wide variety of technologies are being developed to address the lack of grid-scale storage. The Stanford team looked at several emerging technologies, including five battery types – lead-acid, lithium-ion, sodium-sulfur, vanadium-redox and zinc-bromine.
In a previous study, Barnhart calculated the energetic cost of building and maintaining each of the five battery systems for grid-scale storage. Lead-acid batteries had the highest energetic cost, lithium-ion the lowest, he found.
“We calculated how much energy is used over the full lifecycle of the battery – from the mining of raw materials to the installation of the finished device,” Barnhart said. “Batteries with high energetic cost consume more fossil fuels and therefore release more carbon dioxide over their lifetime. If a battery’s energetic cost is too high, its overall contribution to global warming could negate the environmental benefits of the wind or solar farm it was supposed to support.”
For this study, he and his colleagues calculated the energetic cost of grid-scale photovoltaic solar cells and wind turbines.
“Both wind turbines and photovoltaics deliver more energy than it takes to build and maintain them,” said GCEP postdoctoral scholar Michael Dale, a co-author of the study. “However, our calculations showed that the overall energetic cost of wind turbines is much lower than conventional solar panels, which require lots of energy, primarily from fossil fuels, for processing silicon and fabricating other components.”
To store or curtail?
Next the scientists looked at the energetic cost of curtailment – the practice of shutting down solar panels and wind turbines to reduce the production of surplus electricity on the grid.
“Curtailment of renewable resources seems wasteful,” Barnhart said. “But grid operators routinely curtail wind turbines to avoid a sudden, unexpected surge of excess electricity that could overload transmission lines and cause blackouts. Curtailment rates in the U.S. will likely increase as renewable energy becomes more prevalent.”
Shutting down a clean source of electricity seems counterproductive, but is storing surplus energy in batteries a practical alternative?
To find out, the researchers compared the energetic cost of curtailing solar and wind power, versus the energetic cost of grid-scale storage. Their calculations were based on a formula known as “energy return on investment” – the amount of energy produced by a technology, divided by the amount of energy it takes to build and maintain it.
Using that formula, the researchers found that the amount of energy required to create a solar farm is comparable to the energy used to build each of the five battery technologies. “Using batteries to store solar power during periods of low demand would, therefore, be energetically favorable,” Dale said.
The results were quite different for wind farms. The scientists found that curtailing wind power reduces the energy return on investment by 10 percent. But storing surplus wind-generated electricity in batteries results in even greater reductions – from about 20 percent for lithium-ion batteries to more than 50 percent for lead-acid.
“Ideally, the energetic cost of curtailing a resource should at least equal the amount of energy it cost to store it,” Dale said. “That’s the case for photovoltaics, but for wind farms, the energetic cost of curtailment is much lower than it is for batteries. Therefore, it would actually be more energetically efficient to shut down a wind turbine than to store the surplus electricity it generates.”
He compared it to buying a safe. “You wouldn’t spend a $100 on a safe to store a $10 watch,” he said. “Likewise, it’s not sensible to build energetically expensive batteries for an energetically cheap resource like wind, but it does make sense for photovoltaic systems, which require lots of energy to produce.”
Increasing the cycle life of a battery would be the most effective way to improve its energetic performance, Barnhart added. Conventional lithium-ion batteries last about four years, or 6,000 charge-discharge cycles. Lead-acid batteries only last about 700 cycles. To efficiently store energy on the grid, batteries must endure 10,000 to 18,000 cycles, he said.
“Storing energy consumes energy, and curtailing energy wastes it,” Barnhart said. “In either case, the result is a reduction in the overall energy return on investment.”
Other options
In addition to batteries, the researchers considered other technologies for storing renewable energy, such as pumped hydroelectric storage, which uses surplus electricity to pump water to a reservoir behind a dam. Later, when demand for energy is high, the stored water is released through turbines in the dam to generate electricity.
“Pumped hydro is used in 99 percent of grid storage today, ” Barnhart said. “It works fantastically from an energetic perspective for both wind and solar. Its energy return on investment is 10 times better than conventional batteries. But there are geologic and environmental constraints on where pumped hydro can be deployed.”
Storage is not the only way to improve grid reliability. “Energy that would otherwise be lost during times of excess could be used to pump water for irrigation or to charge a fleet of electric vehicles, for example,” Dale said.
It’s important for society to be energy-smart about implementing new technologies, Barnhart added. “Policymakers and investors need to consider the energetic cost as well as the financial cost of new technologies,” he said. “If economics is the sole focus, then less expensive technologies that require significant amounts of energy for their manufacture, maintenance and replacement might win out – even if they ultimately increase greenhouse gas emissions and negate the long-term benefits of implementing wind and solar power.”
“Our goal is to understand what’s needed to build a scalable low-carbon energy system,” said co-author Sally Benson, the director of GCEP and a professor of energy resources engineering. “Energy return on investment is one of those metrics that sheds light on potential roadblocks. Hopefully this study will provide a performance target to guide future research on grid-scale energy storage.”
Adam Brandt, an assistant professor of energy resources engineering in Stanford’s School of Earth Sciences, also co-authored the study.
This article was written by Mark Shwartz of the Precourt Institute for Energy at Stanford University.
Absolutely ridiculous Gail. If a company sells an inferior product then another company will put them out of business. The reason manufacturers don’t powder coat the bottom of cars is
1) The powder will get scratched off anyway (road debris)
2) The customers of new vehicles don’t care so much if a car lasts 20 years since their needs will typically change in less time than that anyway.
3) The average vehicle age in the US is already 11 years meaning for every brand new 2013 on the road somewhere there is a 1991 Geo Metro still running. That is pretty impressive, and the average age is getting older.
@Gail Combs at 9:44 am
Corporations are not interested in the best engineering only in the engineering needed to sell the product and get repeat customers. And interlocking corporate directorships.
Gail, I share much of your cynicism about oligopolies, crony capitalism, and government cures worse than the disease. While there may be some truth in what you say above, I’m not convinced that’s the problem here. With all the money governments have been throwing at high mph cars and battery companies, there is every incentive for corporations to adopt bad engineering ideas, much less bury good engineering ideas in this area.
I’ll keep your comment running in “spinning reserve”. Meanwhile until I get more information, I’ll pursue the dual hypotheses that
1.) The public just doesn’t take to a car with a motor that runs at the same RPM whether you are going zero or 80. I believe it might be necessary to add sound effects that sound like a typical car to make it a constant RPM hybrid sell. On the other hand, the habits of Hybrids turning their motors off at stop lights would turn me off.
2) There is some fundamental electrical engineering control issue with simultaneous constant charge and highly variable discharge and charge through regen. But haven’t existing Hybrids ironed these problems out?
A third possibility is that batteries alone can’t provide the needed acceleration and needs direct drive assist. But Tesla Motors invalidates that hypothesis.
Richard, excellent study but needs updating. Example with geothermal, Hawaii could be totally energy independent, as could Japan, Indonesia, New Zealand to name but a few. Also water turbines are not beefed up fans, East River in New York found that out to their cost, idiots. Suggest turbine integrated with the generator. Much more viable.
Roger Sowell says:
September 10, 2013 at 10:18 am
@ur momisugly Gail Combs, re missing the point.
I fully understand the point of using more energy to manufacture a device than the device will produce. My point is, we do not care.
Economics is what matters.
>>>>>>>>>>>>>>>>>>>>>>>>
No it is energy returned on energy invested AS A WHOLE. Our entire civilization works because we use energy from fossil fuels and nuclear to replace the energy from slaves and animals.
To put it in simpler terms. If we build a sail boat we expend X amount of muscle power using hand tools. However that sail boat with care will return Y amount of energy via the wind moving product that we otherwise would move by rowing (muscle power = Z). We do this because the effort Z is greater than the effort X. The same goes with building an old fashioned mill for grinding grain. The effort in grinding by hand over the years is much greater than that of building a mill that will last a life time. Mankind has advanced by making these energy trade-offs.
Now back to wind turbines. If ALL your electric power is from Wind and “The manufacture, installation and operation of wind power facilities will consume more than 3 times the energy they will ever produce” Then ALL the energy produced by Wind gets reinvested into producing a smaller and smaller number of replacement turbines.
This means you can only run Wind turbines and Solar panels to make an ever decreasing number of Wind turbines and solar panels. There is no energy left over to light an electric lamp or keep a refrigerator cold.
To run a civilization you have to have an NET ENERGY GAIN form your activities or it is not worth the work invested.
At this point we can not use ‘Market Signals’ because they are badly distorted by government subsidies and by manufacture using coal, cheap labor and little to no pollution controls in China. The CAGW scammers are using this confusion in the market place to hide the fact that wind and probably solar don’t return a useful net energy and certainly not enough energy to run a modern civilization with.
Your insistence on looking at the economics only helps them hide how useless solar and wind are for major energy generation that much longer.
Thankyou, Richard Courtney
I read your .pdf and consider tidal coffer dams a neater solution as power output is continuous. Tidal barrages only provide varying power with zero output 4 times a day and present all sorts of environmental problems.
Grey Lensman:
Your post at September 10, 2013 at 11:03 am says in total
The paper dealt with the UK situation where nothing has changed except to get worse. Hence, I do not agree it needs updating.
As for application of geothermal, the only one of the places you list which I have studied is Hawaii (i.e. the Big Island). As you say, technically it could more than supply all its electricity needs from geothermal, and the power would be cheap. However, local culture would put obstacles in the way of taking power from what would be perceived as being the volcanoes. A good alternative for Hawaii (all the islands) would be OTEC for supply of cold water to operate air conditioning. This would be very cheap air conditioning and would provide its own electrical power.
Not being familiar with the situations of the other places in your list, I cannot comment on them.
Richard
paulinuk:
re your post at September 10, 2013 at 1:02 pm.
Glad to help. That is why we post on WUWT: we can learn from each other. It is a rare day when I don’t learn something from WUWT.
Richard
@ur momisugly Gail Combs, you are fixated on a very irrelevant issue, energy returned over energy invested. It is a useless measure, because energy has many different forms and prices.
I repeat myself: we simply do not care. We can, and often do, use huge amounts of cheap energy to produce more valuable but less energy. I gave the example of diesel-powered emergency generators. I also gave the example of a simple cycle gas turbine peaking power plant. How many more examples will it take to convince you? Here is another: small wind generators that recharge batteries on sailboats.
You have been trapped into worrying about a non-issue. I hope you can see that, someday.
Excellent, and let’s have the owners of these solar and wind sources PAY for those batteries out of their own pockets and not pull the usual green scam of placing the costs created by green into someone else’s wallet.
@roger Sowell at 1:49 pm
We can, and often do, use huge amounts of cheap energy to produce more valuable but less energy
Name some cases.
The ones that are true are more like the Boy Scout Flashlight.
Apollo Fuel Cells.
Cassini Radioisotope Thermocouple Generators.
Backyard emergency generators
What is any thing big?
The Kern River Steam Flood Oil Field. Back in 1980’s they were burning 1 barrel of every three produced to generate the steam. The point is, if you left it in the ground, there were zero barrels. If you do steam flood, you may burn 1 in 3, but you net 2 you otherwise wouldn’t have.
Maybe, someday, we could use coal to make oil well drill and casing steel that would ultimately be net energy negative, but burning cheap coal to get valuable liquid hydrocarbons. Maybe… but we are not there yet and there is no guarantee we will.
Perhaps we can point to agriculture. We might use more energy in petroleum-diesel to farm and bring to market the energy content of the grain we grow. …. Drum Roll …. That’s Biofuels!. But we hardly do that without political subsidies to support that folly. A money loser as well as an energy loser
Here is another. Electrical heating. Natural Gas is a far better heat source… but it works only if you have a pipeline to your home. Without the pipeline, it is the next best choice.
Plastics? No. You are taking a cheap feedstock and adding value to turn it into something useful and in demand be thay trash bags or joint replacements.
What else? Oh! Wind Turbines and PV Solar Panels.
Roger Sowell says:
September 10, 2013 at 1:49 pm
@ur momisugly Gail Combs, you are fixated on a very irrelevant issue, energy returned over energy invested. It is a useless measure, because energy has many different forms and prices.
>>>>>>>>>>>>>>>>>>>>>…
Roger, you again missed the whole point. I do agree that things like solar powered fence energizers or diesel generators or flashlight batteries have NICHE markets where energy can have many different forms and prices and you match the usefulness to the price. However the emphasis is on NICHE and a FREE MARKET. President Obama and the EU are NOT TALKING NICHE markets, they are not talking free market. They are talking about drastically changing the major form of energy to fuel our civilization. They are talking and writing laws/regulations implementing lowering CO2 emissions by 80% by 2050 WITHOUT the use of nuclear (which you are against) without the use of coal, without the use of oil, or natural gas. That means your point about “energy has many different forms and prices” just got shot in the head. So you are down to hydro — OOPS, forget hydro the Wild & Scenic Rivers Act already shot that down. As a matter of fact the Greenies want to remove dams and have been meeting with quite a bit of success.
So without Fossil fuels, without Natural Gas, without Nuclear and without Hydro what the heck is left that actually returns a decent Net Energy, Unicorn Farts? It is definitely not wind, or solar and again geothermal only works in some areas.
You may not understand what I am trying to say but it seems some are finally getting the message.
Gail, Let’s see them take down the dams without the use of fossil fuels.
@ur momisugly Gail Combs, now you change the subject. From energy returns to EU policy on curbing CO2 emissions.
Again, economics will win. If a society can remain competitive with a carbon tax and carbon capture on power plants, then I’d like to see it. If they cannot remain competitive with their Carbon Curbs, then the election process will turn out the greenies and bring back some rational policies. We see this now in Australia.
My husband just came up with the solution. Get the Chinese to hide a mini thorium nuclear reactor in the base of every wind turbine they ship to us and DON”T TELL THE GREENIES (or Roger Sowell)
Stephen Rasey says:
September 10, 2013 at 3:16 pm
Gail, Let’s see them take down the dams without the use of fossil fuels.
>>>>>>>>>>>>>>>
Can I hand them the pick axes and sledges?? PLEASE? PLEASE?
They would probably just get Earth First to place b*mbs.
Roger Sowell and Gail Combs:
With respect, I think you are talking past each other. And you are both right in specifics you are addressing.
Roger is right when he says at September 10, 2013 at 1:49 pm
The easiest way to see this is to consider a thermal power station. It loses most of the energy from its fuel and the remaining energy is electricity. Clearly, energy returned is much less than energy invested. But the obtained electricity is worth it. The important thing is the value of the electricity.
However, Gail is right when she discusses niche markets for e.g. wind. It can be very beneficial to use wind to pump irrigation water distant from a power supply.
At present, the most important issue is – as Gail says – allowing the market to decide what is wanted where. Mandates for energy sources prevent that.
Richard
Roger Sowell says:
September 10, 2013 at 3:19 pm
@ur momisugly Gail Combs, now you change the subject. From energy returns to EU policy on curbing CO2 emissions…..
>>>>>>>>>>>>>>>>>>>>
No Roger that has been what I have been saying all along and WHY I was saying it. See my comment HERE.
Without the politicians involved it is may the best technology win and I am all for it. That is what I meant by free market. But that is not the situation as it exist right now. Not with Obama/EPA determined to shut down coal via regulation. See: President Obama’s war on coal is real, industry supporters say
Why ever did you think I was talking about anything else than the current idiotic political situation?
richardscourtney says: @ur momisugly September 10, 2013 at 3:29 pm
…The easiest way to see this is to consider a thermal power station. It loses most of the energy from its fuel and the remaining energy is electricity. Clearly, energy returned is much less than energy invested…..
>>>>>>>>>>>>>>>>
That is not quite it.
Yes you loose a lot of energy via heat but the total amount of energy invested is still less than the energy gained with coal, oil and natural gas. (Adding up energy cost of mining, transport, fabrication and construction.) This is not true for wind power. Again from Charles S. Opalek, PE, “Wind turbines have an embarrassingly low Energy Returned On Energy Invested [EROI] value of 0.29. The manufacture, installation and operation of wind power facilities will consume more than 3 times the energy they will ever produce.”
Their graph shows EROI of ~4 to 10.5 for oil fired electricity and ~ 12 to 24 for coal-fired electricity. Since the report is fluffing up Solar the numbers are probably good. (Solar was in the same ball park as oil in this report but as they admit it is real easy to play games with the numbers.)
I never realized this point was so difficult to get across. Maybe it is because I deal with horses that I find it so clear. If I want to farm with horses I need ~ 5 ac per horse. I also need to add grain to make up for the energy I ‘Steal’ when I have those animals work for me for several hours instead of grazing (The five ac is 2 ac for grazing, the rest for hay and grain.) The more I work the animals the more I have to change the hay/grazing to grain ratio. If I mess up and feed too much grain the animals get too fat and I waste grain. If I do not feed enough grain while working them they become too thin and lose muscle. If I feed them nothing they die.
@ur momisugly Gail Combs, again, you are fixated on an irrelevant issue. Energy returned is of interest only to academics. No amount of quoting sources or making the same argument will change that.
And yes, your passing comment about nuclear power was noticed. Nuclear power is just about the MOST expensive, and therefore UNeconomic means of producing electricity that has ever been devised. See Figure 14, from http://www.energy.ca.gov/2009publications/CEC-200-2009-017/CEC-200-2009-017-SD.PDF This is a Comparative Costs of California Central Station Electricity Generation performed by the California Energy Commission, August, 2009. With the sole exception of simple-cycle gas turbines, nuclear power is the most expensive way to generate electricity. The study compared 21 different types of electricity generation, from natural gas, advanced coal, nuclear, wind onshore, wind offshore, geothermal, solar thermal, solar PV, hydroelectric, ocean waves, and biomass. The biggest loser, excepting solo gas turbines, is nuclear at 34 cents per kWh. There are other studies that reached the same conclusion: nuclear power is far too costly.
So, pardon me if I’m against nuclear power. (insert a large dose of sarcasm on that “pardon me!”) I don’t like to see poor people’s electric bills skyrocket because some fools think it is “cool” to build nuclear power plants. I’ve been poor and unable to pay my electric bill. I do all I can now to stop this nuclear madness. It may not be much, but it’s a worthy goal for which I strive.
For what little it is worth, I had a little something to do with the South Texas Nuclear Project expansion being mothballed – due to economics. The project was to install an additional two reactors at 1100 MW each, and was cancelled when the reactor designer/vendor reluctantly conceded that the installed cost would be somewhat higher than $17 billion. How much higher, they would not or could not say.
My views on nuclear power for commercial power generation are on record here:
http://sowellslawblog.blogspot.com/2011/10/on-nuclear-power-plants.html
Roger Sowell says:
September 10, 2013 at 5:06 pm
@ur momisugly Gail Combs, again, you are fixated on an irrelevant issue. Energy returned is of interest only to academics.
>>>>>>>>>>>>>>>>>>>>
No Roger it is THE MOST IMPORTANT ISSUE.
Energy invested vs energy gained is the driving force for everything living things do.
If I am on a South Seas Island and can live off the sea and land every day without much effort there is zero reason to farm or to move. If I live in North America at latitude 43 N I had better invest the energy during the summer/fall to stockpile food to last the winter or invest the energy in following the herds south. Life is all about investing some amount of energy in hunting, gathering plants/fire wood, farming or work for a greater return in the future (food/warmth/shelter/clothing) Modern energy is just an extension of these basics. If you have fire you do not have to burn as many calories to stay warm. Therefore it is worth the calories expended to gather firewood for the winter so you burn less calories later.
Again in a free market this all gets sorted out. However as soon as politicians get involved and add laws and regulations to the mix Energy Invested vs Energy Gained gets skewed badly. That by the way is what you see in nuclear in California.
I would also suggest you read The Broken-Window Fallacy since killing off coal and fossil fuels is akin to breaking a perfectly good window.
BTW Energy invested vs energy gained is the killer for most ‘Green Energy’ if you would just bother to try and grasp the concept.
@ur momisugly Gail Combs, what you fail to grasp is that I am perfectly familiar with the concept of Energy Returned over Energy Input. That is why I assure you that it is irrelevant. I’m also very familiar with the Broken Windows concept, but I’m puzzled why you raise that issue. Nobody is breaking windows, just to replace them with more windows. If you want to argue that renewable energy is like Broken Windows, I’m afraid that argument has no merit. Renewable energy is an adjunct to the existing power plant infrastructure. It is like adding a smaller window to a house that already has windows.
Your example of Stockpiling wood for the winter is not in either category. That is simply harvesting energy (wood) now for later use (in cold winter). Where some academics get all excited at EROEI is when evaluating, for example, oil reserves as they gleefully predict Peak Oil. They observe that some oil fields have declining production rates, (note that some have increasing production rates, it depends where one is on the production curve), and that more and more energy is required to keep producing oil. Being impractical academics, they extrapolate where they ought not to, and conclude that eventually, it will require more energy to extract the oil than is obtained from the wells. They then conclude that the EROEI is less than 1 so we should stop using oil at that point. That is completely wrong. Oil has a high value, as lubricants, petrochemical feeds, paving and roofing asphalt, and transportation fuels. It is entirely economic to use a great amount of a low-value energy source such as coal to provide the energy necessary to extract oil. This will be increasingly true as, if and when, oil ever becomes sufficiently scarce that the price increases. To date, oil price on the world market has not risen at all in inflation-adjusted terms since OPEC set the price at $32 in 1980. Again, the energy returned for an investment is useless. Economics is all that matters.
We can go on and on, arguing the same points, if you like. I do grow weary of this, and it is clear to me that you have a cherished ideal and will not let it go. So, I will conclude my end of the argument and wish you well. One last point: engineers and our investors have spent trillions of dollars over many decades in almost every country on the basis of EROEI being irrelevant. We know, and have always known, that economics is what matters. I suggest you drive past the industrial parks or complexes in any country, and look at all that was built and is still running, probably at a profit, because engineers laugh at EROEI.
I do hope you reconsider your stance.
@ur momisugly Gail Combs says:
September 10, 2013 at 7:32 am
***********************************************
OK, let’s not hyperventilate over the dangers of hydrogen. I worked for Matheson Gas Products for a number of years and the storage, transport, and use of hydrogen wasn’t high on the worry list, even at pressures to 6,000 psig. For the last 40 years or so, GE has produced steam turbines whose bearings are cooled using H2 as the cooling medium, so clearly the handling issues are not intractable. Consideration of electrolysis as a means of storing excess energy is strictly a matter of economics and engineeing (which also in the end comes down to economics).
“”””””…….Stephen Rasey says:
September 10, 2013 at 10:52 am
@Gail Combs at 9:44 am
Corporations are not interested in the best engineering only in the engineering needed to sell the product and get repeat customers. And interlocking corporate directorships.
………………………….
2) There is some fundamental electrical engineering control issue with simultaneous constant charge and highly variable discharge and charge through regen. But haven’t existing Hybrids ironed these problems out?
A third possibility is that batteries alone can’t provide the needed acceleration and needs direct drive assist. But Tesla Motors invalidates that hypothesis…….””””””””””””
Well your third possibility, is not a fundamental limitation; as you point out Tesla Motors demonstrates.
But they have a 416 horsepower engine, along with the accompanying torque to get their thrilling acceleration.
I would suggest that the Toyota Pius is a better design point, if one is designing practical transportation.
But having said that, the Tesla Model S, as silly an idea as an electric car is, is a marvelous piece of engineering design. I would have done some things differently; but perhaps if I had a chat with Elon Musk, he might show me why his chosen architecture is better.
The model S Tesla (and the other model) has a single three phase electric motor. So it has a semi normal rear end with a differential for driving both rear wheels. Not exactly like a regular Detroitosaurus Maximus rear end, but functionally the same.
I would have put in a pair of three phase electric motors, one for each rear wheel, and used solid state electronics, to generate the three phase AC drive, instead of a rotary DC to three phase AC inverter. Then the differential goes bye bye.
An advantage of a three phase electric motor, is that it is perfectly happy running with the rotor stalled. That produces the maximum torque; enough to climb trees in the case of the Tesla Model S.
On potential weakness in the model S is the liquid cooled battery system. Now because of high battery efficiency (low internal resistance) the heat generated is not too severe, so the cooling fluid radiator is quite modest in size.
But it is positioned in a highly vulnerable location for collision immunity. I’m sure they can fix that, and tuck it away where it is less vulnerable.
As I said, I think it is an excellent piece of engineering and manufacture; but I still think a can of gasoline, is a much smarter way to store a lot of energy.
Down the road, if Tesla survives, they probably will have cars with less than 416 horsepower; this one seems to be a proof of concept demonstration. Good luck to them anyway. I’m always happy, when somebody figures out how to take money away from people who have more of it, that common sense.. But if you can get a Tesla model S for the price of a fancy Porsche or BMW; then why not, if you only need a 90 mile driving radius.
Incidently did you know, that Ferdinand Porsche designed the German Tiger Tank, of WW-II.
He also designed a rear engine Italian race car called the Cisitalia, sort of a souped up VW beetle. It had a horizontally opposed flat 16 twin overhead camshaft engine; I think it was 1.5 litres supercharged; but don’t quote me on that. Very cool design.
Well down at the far end of the internet, it says the Cisitalia, was a flat 12; well so I made a [mistake]. I think I did that once before; something about CO2 snow. Well never mind; Ferdinand Porsche was some sort of mechanical genius.
[Most often, misteaks come from cows. Mod]
Richard, I think you forgot the recent M.O.U. between Iceland and the U.K. to import geothermal energy. I believe Belkin will supply the “extension cable” ( TIC)
As an aside, I worked on the MIDAS scheme in South Wales connected to the building of the Severn Barrage. That was back in 1976. Not much moved along it seems. I agree no need for a barrage but well designed independent turbines, linked by bridge would be very useful. Note double the height of a dam and you double the power but double the speed of flowing water and you quadruple the power.