Hacker News Reader

Comment by londons_explore | Hacker News Reader

Electrolyzer reactions tend to be reversible...

If they could do the reverse (water+propane to CO2+hydrogen+electricity) at the efficiency claimed (91%), they can replace all gas turbine generators (who typically have efficiencies of only 60% at best)

View on HN

Gas turbines scale much better than fuel cells, and can achieve great power density, are durable, can be produced without too much exotic materials needed, are a proven technology. If you can solve the storage of intermittent renewable production as conversion to propane, you already won!

At a current density of 395mA/cm² @0.8V, these already won on the power density and scalability front.

500 stacked 0.5mm layers of this would make 400 volts for an ev battery or stationary AC generator. It would have a power density of 6.3 kilowatts per litre, far exceeding both lithium batteries and gas turbines.

Propane fuel cells already exist, and are in use for remote power. The problem with using them for cars is that they operate at high temperature, so you spend a lot of battery warming the cell for steady state, but most trips are short so you would be there before it got to temp. Might make sense as a phev sort of thing where you punch in a trip and it decides to warm it up or not. You'd always leave enough battery to warm the cell while driving so you never get stuck.

Several tesla superchargers near where I live have fuel cell setups, presumably to shave peak loads for the rare cases that the charging stations are all in use and all charging at peak rates.

I suspect they have batteries rather than fuel cells?

Tesla is known to colocate them for exactly the reasons you say - also to shift load to cheaper hours of the day and to get paid by the grid for balancing services.

I think the current ones don't use generators, but that one time they used a gas generator to charge Teslas, called it a "battery swap station", and got a bunch of money from California that was supposed to go to zero-emissions car projects. I doubt they'll ever live that down.

sorry for the late reply -- definitely fuel cell setups.

Orleans MA and Hyannis MA supercharger stations. The one in Hyannis is right next to the superchargers, the other is 2 minutes walk away.

I believe one or both have "bloom energy" branding.

I can't find a good picture on the internet.

Live what down? California paid for a research and demonstration project. Tesla did that but decide for a whole number of reasons that it wasn't worth doing.

High temperature isn't a problem for cars. It's simple enough to have a small fuel cell which can be heated up quickly, which in turn can provide the energy required to heat up a larger cell if needed. A small battery can drive you a few miles while that process is happening. The small fuel cell could then recharge the battery while parked if most journeys are only a couple of miles, avoiding the energy cost of heating the large cell except for extended journeys.

Not sure why no one has done it? Not carbon neutral I guess, but paired with this and solar power it would be. Batteries are already so good is probably part of it too. But adding about 25% travel time on long drives is annoying.

Up until this point I'd imagine there was no significant advantage to creating propane vehicles unless they could be made significantly more efficient than petrol or diesel (which I'm guessing is not known to be the case)

by comparison, this discovery could make it a green-vs-brown fuel debate, at which point it would be much more valuable to invest in for vehicles

Propane combustion vehicles are common, and I'd guess a fuel cell would extract roughly 30% extra energy from the same fuel. They typically have battery efficiencies.

This is massively more complex then you make it sound. And if it doesnt work at least as well as current ICE its not going be used. There is a reason this simply isnt done.

If you want to use that fuel, just burn it.

Did they? Are they capable to be scaled to 100 MW scales with MTBF of years already?

I wonder if you can have the same plant act as both a propane producer at times of extra power available on the grid, but also generate electricity when there is a shortage. Then the power density and exotic materials are irrelevant as the plant already exists.

You'd use the plant mainly to make propane, just run it backwards when electricity prices were the highest.

Reversed electrolyzer would be called a fuel cell then? What are their typical efficiencies?

Yep. Fuel cell efficiency varies widely, but the efficiency of the reverse process is a good guide - typically efficiency is fairly symmetrical.

Shouldn’t the chemical reaction be: 4 H2O + 3 CO2 <=> C3H8 + 5 O2

The reaction described in the paper doesn't have spare oxygen on either side, presumably because oxygen has a habit of destroying catalysts and being explosive when mixed with hydrocarbons. Instead hydrogen is required.

(Not having access to the paper)

So are you saying the reaction is

10 H2 + 3 CO2 <=> C3H8 + 6 H2O

Of course, neither this nor the reaction mentioned in the parent comment matches up with the diagram in the linked article which says "water + CO2 => propane + water", which well, doesn't make sense..

So you would need to have two separate electrolyzing processes, one that isolates H2 and one that runs this operation? How much energy would have to go into the first one?

I’m asking because a lot of the demand for hydrocarbon that I see mentioned is for processes that have more efficient, non-hydrocarbon equivalents.

Reply on news.ycombinator.com