Typical power transmitted over lines? 1

[vdonovan]

Friends have raised the idea of using hydrogen generation coupled with fuel cells as a buffering mechanism on major transmission lines. When a line fails, the supply side would store electricity by generating hydrogen while the load side would continue to generate power using hydrogen previously stored. Seems like even a few minutes of this kind of buffering would help manage huge outages like the one we just saw and make the grid less vulnerable to local outages.

My question is does this make order-of-magnitude sense? (forget about cost for the moment). I know that power lines are rated by their voltage, but how much power (in megawatts/hr or kilowatts/hr or whatever) do the various rated lines transmit? Large fuel cells with 200kw capacity are already commercially available. Is that enough to buffer the transmission lines of the national grid?

 

[scottf]

I am not sure I follow you about the hydrogen storage as a means to buffer the system.

However, I can answer than most large transmission lines would have the capacity to carry between 3000-5000A, depending on the conductor configuration. Some lines are of course larger and some smaller. Also, for a given transmission line path (i.e. between 2 substations)there may be multiple sets of lines.

 

[rbulsara]

An average house with a 100A service in the USA is worth 30kW. Considering diversity say 200kW may feed 10 or 12 houses.

A commercial office uses 8W/sf.

Make you own calculations!!

1000kW = 1 MW
A national grid carries power in several hundred megawatts (MW).

 

[3winding]

Lance Arsmtrong has a reaches 300W output during his training - maybe we should hook him to the grid

 

[SidiropoulosM]

Here are some typical transmission line capacities:

69 kv --> 50-150 MW
115 kv --> 150-250 MW
230 kv --> 300-600 MW

500 kv lines are usually not thermally but stability limited. A typical 500 kv line can transfer 1500 MW.

Note that a transmission path consisting of a mix of lines of various voltages can have transfer capacities of several thousand MW.

 

[cuky2000]

Vdonovan,

I would like to encourage you and others to explore alternatives to be energy independent. The moment than the regular citizen became self-sufficient or live in a society capable to deliver energy at low cost; the world must change dramatically in benefit of the human kind. I believe that there are sufficient technologies available today that could lead to successful adventure in this area.

Few of those available technologies are:

Distributed power generation (micro turbine, fuel cell, wind mills, etc)

http://www.distributed-generation.com/dpca/publications/linden/linden.pdf

http://www.bchp.org/status-2-public.html

Ocean thermal power plant

http://www.poemsinc.org/FAQOTEC.html

Power Electronic: used to actively controlling power flow and wide-area power quality such as Flexible AC Transmission Systems (FACTS), Static Synchronous Series Compensator (SSSC), STATCOM, HVDC, Static Var Compensator (SVC)/ Synchronous Condenser (old technology), etc.

http://grouper.ieee.org/groups/1409/s14_16.pdf

http://www.nypa.gov/services/newtechtransmission.htm

Distributed Temperature Sensor (DTS) and other could provide transmission system with tools for dynamic rating using real time parameters to optimize the power delivery transmission system.

http://www.epri.com/corporate/products_services/project_opps/pwrdel/1007780.pdf

 

[vdonovan]

Regarding hydrogen generation as storage: Let's say there's a transmission line between power plant and a load (a bunch of houses) and that line fails. In that case the plant's power must be immediately either shunted to other lines (possibly overloading them and leading to more failures) or the plant must shut down. If the power plant could automatically use the surplus electricity to extract hydrogen from water and store it in tanks (like some power plants do by pumping water), system operators would have more time to repairthe failed transmission line or to otherwise balance the system. The stored hydrogen could then be used to generate power later via a fuel cell at a time of peak demand.

 

[vdonovan]

THANK YOU everyone, by the way. This is just the kind of back-of-the-envelope information that I was looking for.

 

[jbartos]

Suggestion: It appears that it is better to build redundant transmission lines. It is good for transmission line failure and maintenance.

 

[SidiropoulosM]

Jbartos is right. The scheme, if at all workable, is a very expensive way to provide standby power.

 

[jghrist]

OK, hydrogen has a combustion constant of 123,100 BTU/lb, a density of 0.00531 lb/cu ft. So, to store enough energy to allow for an 8 hour outage of a 1500MW 500 kV line, you would need 62,640,000 cu ft of hydrogen, assuming 100% conversion efficiency. A 490 ft diameter spherical balloon should do it if you can hold it down. You could liquify the hydrogen, but that would take energy.

 

[peebee]

Comment #1:

What you're really talking about is not that much different from having a battery charger and a battery and an inverter.

Those systems are commonly called UPS's (uninterruptible power supplies).

The only difference between your concept and a standard UPS is that you're using a fuel cell and inverter instead of a battery to store energy. Another potential storage device is a flywheel (flywheels are in common usage too for larger UPS systems).

-------------------------
Comment #2:

Why a fuel cell? Why not a generator instead?

You could still do exactly what you're talking about with the hydrogen, but use a generator instead of a fuel cell.

-------------------------
Comment #3:

You'd really want to generate your hydrogen at the load, rather than at the source. If you generate it at the source, you need to transport it or pipe it to wherever your load is. If you generate it and store it at the load, well, then it's already there.

 

[vdonovan]

What I'm thinking of are buffering nodes at strategic points on the grid. Each node would contain both an electrical source (a large fuel cell with hydrogen tank) and a sink (a small plant that generates and stores hydrogen from electricity). The node would be able to react to short-term fluctuations in the grid by temporarily absorbing power surges (by using the excess electricty to generate and store hydrogen) or drawing from the stored hydrogen to compensate for supply gaps. Since electricy flows back and forth through the grid, any buffer node has to be able to handle both. Think of it as a self-fueling UPS.

The objective is to make the grid more reliable and less vulnerable to human error and terrorist attack. The recent outage on the east coast was the result of a chain of events taking place over 9 seconds! If the grid could have buffered itself for an hour or so, perhaps engineers would have handled the situation more gracefully and so many plants would not have had to shut down. Maybe only thousands of customers would have been affected instead of millions.

A secondary aspect of this idea is to jump start the "hydrogen economy". Putting these buffer nodes throughout the grid would create demand for fuel cells and hydrogen storage technologies, lowering the cost for both. On the wacky end of the idea: these buffer nodes could even become local sources of hydrogen fuel, i.e. hydrogen gas stations, another revenue stream for the power companies.

The current administration has expressed support for both the "hydrogen economy" and anti-terrorism infrastructure. I think that using Homeland Security money to apply new technology to the power grid would not only make us safer against terrorist attack but also invest in our economic future, just like the space program did in the 70s and the DARPA programs did in the 80s.

 

[lengould]

What you're really suggesting is something I've considered for some time. My discussions with Stuart Energy indicate a utility could purchase sufficient PEM H2 electrolyser generators to load a 4 unit 880 MWe reactor set (might serve 1 milliom population) for about US$.9 billion. 1 MVDC transmission for the same output could be built ?1000 KM?/620 miles at US$.8 billion. Dedicated H2 pipelines would need to parallel the transmission lines if H2 generation separate from loads, ? 1/2 of transmission plus higher "line losses" ? Fuel cell generators at load end approx. = electrolysers.

All these numbers are not too significant compared to the US$5.8 billion to build the nuclear gen station. However you have the problem of only 90% eff. in H2 generation and 60% efficiency in fuel cells, all aux's netted. Plus huge losses in H2 pipeline (H2 expensive to compress). Possible solid polymer fuel cell / electrolysers could serve dual use without H2 transmission but Stemple wont be giving those away.

Better to investigate Vanadium Redox Batteries. (To clarify, I have no percentage in them or any other technologies discussed). Battery is similar to fuel cell but acts like a battery. Difference from battery is electrolyte contains all elements required to work (e.g. no solid metal anodes/cathodes to get used up), so battery output time limited only by electrolyte storage capacity. Cell will recharge electrolyte when excess power available. See WRB Power Inc. in Burnaby, or a couple of Japanese installations. Still new, but several large units now working, e.g. Moab Utah.

http://www.vrbpower.com/

They seem to be having some financial issues. My guess is management not technology. (System can also power vehicles, fast exchange of spent electrolyte for charged at service stations)

Better yet would be pumped water storage/re-generation. Long proven, quite efficient. I know, needs particular geography, not available at most load points.

Numbers above are large, but US needs to start some discussions before Washington goes off and sinks US$100 billion into "grid" only.

Cheers.

 

[peebee]

You've gotta ask yourself how many customers would be willing to pay the extra rate for the increased reliability. People already balk at the existing rates. To increase the reliability, which is currently not all THAT bad (despite the recent blackout), would increase the power bills for ALL users, not just those that require the utmost in reliability.

Currently, power users that demand the utmost in reliability install their own generators and/or UPS systems. That way, the cost of reliability is borne only by those that demand it. In addition, resources are allocated only where they are required -- high-reliability capacity is provided only where it is most needed, not to all customers.

There's certainly a valid argument that the existing system reliability could be improved for all users. But theres a whole lot of ground between "better reliability for all users" and "UPS power for all users."

It seems to me that a moderate upgrade to the existing system is justified, but UPS power for all is probably not.

 

[vdonovan]

Thus the whole government angle. New standards and maybe even a new regulatory body is going to come out of the current Senate investigation. Utilities are going to have to raise rates to meet the new requirements but in the current security environment they should be able to make the case for government funding to develop and deploy this kind of technology. Since the government seems intent on spending money like it's water (or hydrogen) we may as well get some technology development out of it.

 

[lengould]

Vdonovan: Most interesting thing about your suggestion of stored H2 is potential to substitute for new peak load generation. Used in this way, numbers become much more reasonable. e.g. install bi-directional H2 electrolysers at only 1/10th the capacity of the reactor set (320 Mwe, US$90 million) and run them only "off peak". Then use the stored H2 during peak periods as generation to shave off only worst peaks, i.e. 200 Mwe 4 hrs/day 5 days/wk, assists existing peak gen plants.

Advantages:
a) Expands system capacity/stability with no new transmission required.
b) Reduce stress on distribution by distributing electrolysers near heavy loads.
c) Overgenerates H2, which can be sold at very near retail natural gas prices by mixing into natural gas distribution to make Hythane or to transportation consumers if that market ever develops.
d) Generation immediately dispatchable, very fast startup.

Disadvantages:
??


In USA, population 300 million, there should be at least 300 such installations. Investment 300 x 90 million + 10% +- = 30 billion. (I could be plus minus 100% here but still). Ditto Canada at one tenth. And points a path to long term heating fuel security when natural gas runs out, which it will, sooner than most of us think. And eliminates chicken/egg problem of H2 as transport fuel.


We should investigate requiring every generation operator to finance 10% +- of their MWe capacity in electrolysers used this way, starting immediately. Or at least make such installations a condition of accessing the grid with new generators for the purpose of selling power. I'd far rather this than ratepayers or taxpayers (having to pay the tab for) sinking another US$100 billion into transmission, essentially a dead end, just adding complexity to an already over-complex transmission system where uncontrolled block trading just benefits a minority at the expense of reliability for the majority who paid for the system.