Electrolysing water to make H2 and extracting CO2 from the environment, and then synthesizing hydrocarbons from them, is extremely energy inefficient.

Sure, theoretically, it can be done, and maybe one day it could even be done efficiently. But Tesla is making battery-electric cars that work today.

The military does not care about efficiency because they have nuclear reactors on their ships and their goal is to not to have to transport liquid fuel.

Tesla's cars are wildly price inefficient because they cost $100K. For 10K you can get a decent car that has 4 times the range. http://en.wikipedia.org/wiki/Tesla_Roadster

How many gallons of fuel can you get for 90K?

They are nice toys for rich people. Perhaps there is a market for that. Good luck to them.

But for mass transit unless you can get the price of the batteries to plummet it just does not work.

This doesn't eliminate the tail (we still have to deliver ammunition, lubricating oil, food etc. to the fleet) and it doesn't eliminate replenishment at sea (we still have to get that stuff from supply vehicles to ships), but it does lighten the supply load and create more military options.

Lots of people killed by IEDs on long supply lines in Afghanistan is an extreme example of the human and military costs. Some of those died to fuel A/C for uninsulated tents... madness.

1) uranium -> nuclear power -> expensive synthesis -> local transport -> fuel

2) uranium -> nuclear power -> transmission lines -> charging batteries

3) crude oil -> refinement -> transport -> fuel

EDIT: Found a reference from another comment: http://en.wikipedia.org/wiki/Fischer%E2%80%93Tropsch_process... It says that the input energy is 2-4 times the stored energy for synthesized hydrocarbon fuel.

Instead of the energy system, consider the cost of military supply lines. There's more than the financial cost of delivery; long supply lines are vulnerable to attack and disruption. You don't need to imagine an example: consider IEDs in Afghanistan. Many of those were trucks delivering food and fuel to bases. Efficiency (i.e. insulating tents so less fuel is needed for A/C) results in less deliveries and less deaths.

The same principle applies at sea. Oil ships are a vulnerability and another thing to plan, as well as a major cost that can be more important than the energy efficiency issues.

Telsa, like many startups, is pursuing a low-volume, price-insensitive market first. That helps pay for all sorts of startup and R&D costs, and lets them work out issues before they scale. Their long-term goal is, per Wikipedia, "eventually mass producing fully electric cars at a price affordable to the average consumer".

There are several fully electric vehicles in production that cost $35k.

http://en.wikipedia.org/wiki/List_of_production_battery_elec...

They have a substantially lower cost of operation than gas-powered vehicles, so they are plausibly cheaper to operate over the lifetime of the car:

http://en.wikipedia.org/wiki/Nissan_Leaf#Operating_costs

And over the long term, expecting batteries to get better is a pretty good bet. Everybody from Apple to Toyota is eager for battery improvements.

A mass-produced commuter could be much cheaper, but there's a huge risk. Tesla aims to reduce the risk by validating the market, solving technical problems, creating infrastructure (recharge stations) and solving social problems (convincing people that range doesn't always matter, and educating them on the strengths and weaknesses of electric cars).

A low total-cost (including fuel and maintenance) electric car can probably be produced, but it's not the Tesla's top model.

I agree that we will need carbon-based fuels for jet engines, but as for cars, the physics and economics are by no means as favorable as you represent.

That is incorrect. If the fusion source is compact, and can produce a lot of instantaneous electrical power, and is quick to throttle up and down, then a "Back to the Future"-style Mr. Fusion would be the best way to power cars.

Energy density isn't the only factor. There's also a question of infrastructure. Electrical distribution has few moving parts, while extracting C02 from the atmosphere to make fuel and distributing the fuel has many more mechanical parts. A fusion plant which could produce 50 kW, weighed 2 tons, and could be installed in the back yard of a home would mean that a house could be off the grid and still have power left over to charge the car, while using intermediate hydrocarbon storage would mean trips to fill the car, or heating oil, or cooking gas.

So while I completely agree that airplanes will not be powered by batteries, I don't think that energy density is the only factor to consider in the economics equation.

There's also safety to consider.

Regarding the comment of sophacles, power distribution is part of the economic factor. It may be that the central plant is much more reliable than a backyard plant, but the power grid - subject to thunderstorms, ice, tree falls, backhoes, curious squirrels, and so on - makes the overall power supply system less reliable than a backyard fusion plant.

There is still a grid. If my power source goes out, I want backup to come from other nearby sources - the timeline of power restoration from the current delivery system is on the order of minutes or hours for over 80% of outages, and on the order of a couple weeks for over 99% of the rest of outages. If my power plant breaks, I need restoration numbers that meet that. (additionally, I need plant repair bills to be lower than however much money having the backyard plant would save me. TCO considerations again).

Further, these two assumptions are built into your "better" assessment:

* It is cheaper to have a power plant in my back yard than buying it from the grid.

* The backyard source can be made safe.

Combining these two assumptions is a big deal. If both are true, I will agree that it is a good option (with the caveat listed above). However, there is a HUGE amount of R&D to get there, including a massive set of efficient production runs for parts to build all the systems to make it happen. The economics of this points to it not being likely that everyone has a backyard fusion plant.

It is far more likely to see big fusion plants in greater number scattered around the power grid to provide higher reliability in the cases of line loss etc. Further, with energy now being much, much cheaper to produce, you'll likely start seeing more reliable distribution channels for electrical power. Overhead lines would be reasonable to replace with underground ones, which are less efficient, but are also more reliable as they are less likely to be damaged in weather events. You'll also probably see a reduction in star-topology distribution - more redundancy in distribution paths, at the cost of some efficiency, because the complex equipment will be cheaper to manufacture (you know, because energy to do so will not factor into costs anymore).

My hypothetical was to show that there could be cases where it does not make sense to use a Mr. Fusion type device to produce hydrocarbon fuel which is then used as the energy source. Everything I said takes place in the original fantasy world. Under the original premise -- "some grad student gets fusion going at a very low price" -- then it must be using some principle we haven't yet thought of. And with that premise in place, almost anything goes.

Once I put realism into place, then the original hypothetical is not sustainable. The long term solutions for real life are decreased energy use, fission, hypothetical fusion, and renewable. None of the last three can exist without a grid, at least for most people. The only way to be without a grid is greatly reduced power use, a less concentrated population, and switch to local renewable resources. That isn't going to happen.

(Although if we had that technology in cheap enough form, some of the major loads in your house may switch to DC to avoid conversion losses to AC, since solar panels and batteries are both inherently DC technologies, and that might make the inverter less important.)

I don't think most will be willing to take that capital investment.

It would be interesting to see how distributed solar compares to grid-based distribution in the face of large disasters like a hurricane or ice storm. Especially if the power lines were underground. I assume that those with damaged panels would quickly look for replacements, causing an instant demand and price spike. While the large electricity companies would have stockpiled reserves and have agreements already in place to handle the short-term demand. I don't know how this would affect the overall long-term costs.

In 1992, would you have told me today's smartphones would be impossible?

If you only lose a few solar panels in a storm, and most of the panels on your roof survive, you may just use a bit less electricity for a while.

I built a little mixed DC (lighting) + AC (1kW inverter) system out in the garden (far enough from the flat that running a cable would be a nightmare of planning permissions & digging trenches).

Since it's for intermittent use the panel is tiny (50W Kyocera) compared to the battery (110 Ah 'leisure') & inverter (1kW true sine), and it works just fine even here at 53 deg latitude. It would scale up for the entire house quite well, were it not for the fact that it's a four-in-a-block with a communal roof, and 1/2 loft space unusable due to loft conversion.

If we figure an average American has a lead acid car battery and maybe a laptop battery pack, we currently have more lead acid batteries than lithium ion, certainly by weight, but probably also by total watt hours.

Tesla and Nissan might end up inverting that ratio in a market where they merely have to get the battery to beat the cost of gas; and if we get to the point where every American has an 85 kwH battery pack in their car, that's multiple days of average US electrical consumption (I believe average per capita electrical consumption is about 1.5 kw, and average per capita total energy consumption around 6 kw in the US).

Meanwhile, there's no path to pushing up volumes of lead acid battery production significantly. Maybe there will be a few old lead acid car batteries getting recycled after Tesla conquers the world, but if that's all we're relying on, those recycled batteries won't power very much in the grand scheme of things.

EDIT: Edison did not invent NiFe batteries, but he developed and championed them.

Cars, on the other hand, experience a combination of aerodynamic and powertrain drag and rolling resistance, of which only (mostly?) the rolling resistance depends on mass. The typical coefficient of rolling resistance is about 10x better than the typical L/D ratio for aircraft (if I believe Wikipedia). Hence, road vehicles are 10x less sensitive to energy density than aircraft.

So a statement that electric vehicles won't work is nonsense, without considering how sensitive the different vehicles are to fuel mass.

(*) Technically fossilised solar energy of course.

It is also effectively win-win. If such a thing becomes possible the costs in much of production will cut very drastically and the potential of things now open would be just incredible. So much of expense is due to energy constraints.

Electric engines run at 92% efficiency. Car engines run at ~15%. So energy density need not reach equivalence.

That physicist is wrong too (Nobel prizes don't mean you aren't wrong - it just means people listen to you more) - jet engines on planes require oxygen to work - hence capped at ~10 km altitude with massive drag causing ineffecient travel.

10 years till battery tech reaches complete parity for lowest denominator cars, and 7 years before we start to see hyper sonic electric passenger jets being tested way up in the upper atmosphere (no oxygen needed, go as high and fast as you want - London - LA in a few hours - space views - cheap power).

Gasoline has an energy density of 132 MJ/US gal, or say 1500 MJ on a full small tank. Modern engines hit 30% thermal efficiency, but then there are drive train losses etc, so I'll give you the 15% as an absolute worst case, AND give you a 100% efficient electric motor / drive train. Therefore your car needs to provide 225 MJ of stored energy for parity.

The best commercially-available Li-ion battery has an energy density of around 245 Wh/kg, or ~ 880 kJ/kg. Therefore you need at least 255kg of conventional batteries for motive energy parity (ie. not counting heat/AC/light etc.). The equivalent in gasoline (0.77 kg/l), weighs 35 kg.

You are asking for nearly a ten-fold increase in usable energy density in battery technology in ten years, at price-parity with gasoline, and with the charging infrastructure to support it. I don't think it's going to happen - assuming lithium-air batteries ARE commercialised on that time scale, the cost of charging that kind of energy in reasonable time, safely, is going to be the real problem here. Every gas station is going to need its own nuclear power plant!

If they aren't viable - I'm calling time of death on the world.

If none of them work, advanced fission designs like LFTR or IFR could be almost as good, with better safety and a hundred times less nuclear waste than conventional reactors.