6 MW (continuous) * 8760 hr/yr = 52600 MWh/hr

1500 vehicles * 15000 km/vehicle/yr = 22.5 million km/yr

Efficiency = 5.26e10 Wh/hr / 2.25e7 km/yr = 2300 Wh/mile.

A typical PHEV gets in the range of 200-300 Wh/mile.  2.3 kWh/mile is pathetic.

To engineer-poet, this is efficient and this is not pathetic at all. You cannot plug a big windmill to the grid as impedance is not even but with this process you can harness efficiently wind power with his inconstant electric impedance as you can always match the output of the windmill and also store the fuel and fill up the car in 5 minutes. All in all a way better method then recharging electric-car with wind energy as you imply. Don"t just trow in stupid numbers, this is not the picture. Storing wind energy with variable impedance and matching this impedance with a car on the road that also use variable impedance have been the long time goal reached by these engineers, and they have nail down a good method for ice cars and future hydrogen fuelcell cars and trucks.

E-P,

I looked at the previous article about this project, and looked at your comment about the amortized cost. I thinked the calculation slipped a decimal:

"•...produces an average 56 W(th) of methane.
•Multiplied by 8766 hr/yr this is a total of 49 kWh(th)/yr of methane."

Should be

"•...produces an average 56 W(th) of methane.
•Multiplied by 8766 hr/yr this is a total of 491 kWh(th)/yr of methane."

That makes the numbers look much better: about 6 cents per kWh before energy costs. Yes?

E-P,

How did you estimate $1,000 per kW?

Nick

E-P,

Thanks.

I wonder why the German approach is so focused on methanation? The simplest, cheapest approach (IMO) would be simple electrolysis to H2, with the H2 stored underground. Both electrolysis and underground storage are old and cheap, and you can generate power directly from H2 pretty much as easily and cheaply as from methane.

Methanation adds substantial costs and complexity, so I don't see it's appeal.

Nick

There's no question that "power to gas" is inefficient, but if the input power is very cheap (less than 2 cents per kWh), and the total kWs relative small (5% or less of total annual kWhs), then that becomes less important.

Conventional storage, like pumped storage and chemical batteries, has very high capital costs for seasonal grid backup (which is only used a few times per year, so capex has to be amortized over very few cycles). P2G, on the other hand, can be very cheap per kW (heck, you can use very cheap ICE peak generators). So, P2G seems like a sensible answer for low volume but large peak power grid backup.

Does that make sense?

Nick

Is wind etc. economic at 2¢/kWh?

No generator plant can pay the bills with 2¢/kWh, which is part of the reason that so many (including nuclear) are having so much trouble in many places right now.

But keep in mind, we're not talking about the majority of wind output: we're talking about off-hours: night time, and parts of the year when the output curve will rise above the production curve. At 25% efficiency, you only need overbuilding of 20% to get the 5% one needs for seasonal backup.

Also, at the moment power prices can go to zero, or even below. An energy sink like this would make both wind and nuclear much more economic.

All of this stuff has high capital costs

Not really. Remember, this is asymmetric: the equipment that captures surplus power can run 50% of the time, stockpiling output that will be used 5% of the time. The generation can be very cheap ICE. That means much less capital cost.

Which brings me back to H2 vs methane: electrolysis alone is much cheaper than methanation, so why go to methane?

No generator plant can pay the bills with 2¢/kWh

That's close to the O&M cost (including fuel) of the best-run nuclear plants, BTW.

we're not talking about the majority of wind output: we're talking about off-hours

When a very good wind site yields a capacity factor of 35%, I'm afraid that you ARE talking about the majority of output.  There are loads which lend themselves to price arbitrage by time-shifting (particularly A/C, since ice is so cheap to make and store), but stashing electricity at 70% efficiency would require nameplate capacity roughly 4x the average load for that same 35% capacity factor.  The price of the electricity that goes into the storage system is crucial, because that's going to be the bulk of sales.

at the moment power prices can go to zero, or even below.

This is only possible because of market-rigging by feed-in tariffs and per-unit tax credits.  If not for that, RE generators would curtail their output to keep prices above zero.

Remember, this is asymmetric: the equipment that captures surplus power can run 50% of the time, stockpiling output that will be used 5% of the time.

The equipment that captures the power has to operate when there are surpluses to capture.  If generators had a 90% or even 70% capacity factor, those surpluses would be relatively small and available much of the time... but they're not.  A really good wind site may reach 35%, and PV is closer to 20%.  While processes like methanation can go on around the clock, electrolysis has to be done when you have electricity.  That sets the size and thus the capital expense of the major part of your chemical energy-storage system.  The producers wouldn't get paid much; Fraunhofer writes this:

In future power grids, wind power is likely to be very economic and available at 0-2 EUR-cents kWhel-1 in times of high wind penetration and low residual load.

So it appears that the energy-storage wonks assume that the energy-generation wonks won't be making any money much of the time, or it'll come out of some third party's pocket as a feed-in tariff.  This has "failure" written all over it.

E-P,

2¢/kWh...That's close to the O&M cost (including fuel) of the best-run nuclear plants

Yes, the last I looked the US O&M average was 1.9 cents. OTOH, that doesn't include capital investments, depreciation, major repairs, profit, etc. Nuclear (and coal) plants are now shutting down because they can't afford major repairs.

stashing electricity at 70% efficiency would require nameplate capacity roughly 4x the average load for that same 35% capacity factor.

Capacity factor is a bit misleading here. The thing that matters is average output. For instance, wind output would have to average about 220GW in the US to achieve 50% market share. If we were to overbuild wind to an average output of 275GW in order to reduce periods of low output in an optimal fashion (e.g., it might be cheaper than additional storage) then we would have an average surplus of 55GW.

The price of the electricity that goes into the storage system is crucial, because that's going to be the bulk of sales.

Ideally, most output would be used directly, thus eliminating conversion inefficiency. For instance, EV/PHEVs could automatically charge when prices were lowest (and nuclear/renewable output was highest relative to demand).

More importantly, P2G isn't a primary storage solution for daily time shifting. It's for that one week in January when there's no sun or wind. Realistically, it would be needed for only 5% of overall kWhs.

RE generators would curtail their output to keep prices above zero.

Sure - and that curtailed power is the "surplus" power we're talking about.

electrolysis has to be done when you have electricity.

Exactly. And, if you have an excess average output, that will be quite often. Remember, even with the skewed distribution of wind power over time, wind output is above average 45% of the time (half of all kids are below average!).

So, if we have sized the wind output at 20% over the average needed, then there will be surplus very roughly 75% of the time.

it appears that the energy-storage wonks assume that the energy-generation wonks won't be making any money much of the time

They assume that prices will be low much of the time, and proportionately higher at other times: this will incentivize market responses, including DSM, timeshifting, etc, etc, etc.

Kit,

power prices can go to zero, or even below....Just how many hours a year do think this happens?

Right now, not often. But, P2G is a long-term plan for a time when renewables have much higher market share - eventually, of course, fossil fuels will have zero.

Nick

E-P,

I think we agree that: 1) either wind and nuclear would work alone, if absolutely necessary; 2 supply diversity is a good idea, and that a single source isn't likely to be anywhere close to optimal or lowest cost. Even without nuclear, you probably wouldn't want any single source to provide more than 50% of overall kWhs.

I agree that wind & sun have more variance than nuclear, and that that difference carries a cost, but I think you're overstimating how important that is. 1st, variance is smaller than that, and 2nd, there are a lot of relatively low cost solutions.

Okay, into details:

The lower the capacity factor, the higher the peaks and the bigger (and more expensive) the storage system must be.

A single turbine will often have zero or maximum output. A reasonably large windfarm will almost never have 100% output, and it will rarely go above 90%. Zero output will be rather less common. The Law of Large numbers tells us that every time we double the number of non-correlated wind farms, the ratio of variance to mean output will go down by very roughly 30%. US continental wind production would only rarely exceed 75% of the theoretical peak output. And, periods of very low output would be rare and not that long.

And, of course, in the real world we'd never rely on wind alone: we'd use sun, and geothermal, and wave, and biomass, etc. Many of those would be countercyclical, or consistent, or dispatchable.

overbuild to 800 GW to meet just half the demand on a grid with an average load of 450 GW, you are going to have many regular events where most of the output cannot be used directly.

It will certainly happen (maximum output during minimum demand), but the large majority of overall output will be used directly. See below re PHEVs.

The small batteries of PHEVs require them to charge almost every day (preferably, before every trip).

1st, The average mileage of 30 per day is an average. Many people will drive less than that. 2nd, even if charging every day is important, dynamic charging allows moving demand around by up to 8 hours - that helps a lot.

3rd, and most important, a world where wind & sun provided as much as 50% of the kWs would be a world in which almost all vehicles would be PHEvs or EVs, and the average battery would be much larger. 230M vehicles with 25kWh each gives 6 TWhrs of storage. That's enough to capture 250GW of excess production for up to 24 hours, and it would allow deferral of charging for a day or two for many drivers (incentivized by pricing, of course).

P2G isn't a primary storage solution for daily time shifting. - I don't see what else you're going to use.

There's quite a lot of demand that can be shifted around: industrial demand (steel smelting happens at night right now because of primitive DSM), I/C/residential HVAC, freezer and fridges, hot water heating, washing & drying all can be shifted to a greater or lesser degree. Heck, lighting could dim by 20% at periods of maximum stress without people noticing much.

And, of course, pumped storage, CAES, chemical batteries etc., all become feasible for daily load shifting.

Nick

Well, keep in mind the timeframes involved: major storage isn't needed yet, and won't be for a while. Also, there are a variety of solutions available, including DSM and V2G. Heck, major centralized utility storage may be viable as a solution, yet never become the lowest cost choice.

Things are unpredictable: who would have expected that day vs night arbitrage would become *less* important in some areas because of aboundant PV, and that pumped storage would start to be needed less than before??

When unreliable power forced onto the grid under "must-take" laws and feed-in tariffs is forcing wholesale prices to zero and below, it's a sign that the system is broken.

Low prices aren't really a problem. And, It's no different than we saw with nuclear, and we'd see much more if nuclear were to expand. Nuclear caused night time power to be very low, and they'd go much lower if nuclear expanded to 50% or more market share.

it looks like the economics of pumped storage were hit by the anti-market cost structure imposed by law.

They were hit by the expansion of solar, which reduced peak period prices. That's the same thing that would happen under a good stiff carbon tax. I'd prefer a free-market solution like a carbon tax (blocked by the fossil fuel industry), but the end result is pretty similar.

The fact is that we don't need much storage right now - the German grid is more reliable than ever. Plans for expanded storage are a matter of planning ahead in case of future need. And, of course, it may not be needed for quite a while - DSM, V2G, long distance transmission, supply diversity - all these are very powerful.