Kwh---Mwh---Gwh---?------Carl Schwab

These three abbreviation stand for Kilowatt-hour, Megawatt-hour and Gigawatt- hour.  They are measures of energy and are related to each by 1000 i.e. Megawatt is 1000 times a Kilowatt and a Gigawatt is 1000 times a Megawatt.

When we talk about the energy in say an EV or a home Kilowatt-hour is convenient. When we speak about peaking generators, the Megawatt-hour is convenient. When you start speaking about a state or a collection of states then the Gigawatt-hour is needed.

For example an EV such as the Nissan Leaf has a battery capacity of 23 Kwh and a range of 70 to 100 miles depending upon how you drive it. My home has a 200 amp service, hence can draw up to 200 x 240= 48,000 wh or 48 Kwh. Now that is a maxed out case but Kwh fits for comparison.

Near here on LI LIPA had under consideration a 12 Mw capacity gas fired peaking generation facility. Per hour it could deliver 12 Mwh. But let us now look at electric power generation at the town, city and state level. Best data indicates that at this level the number is approximately 80Gwh for the continental US level and of that 62% of the Gwh is by coal!

Now EPA with Obama’s backing seems bent on stopping the burning of coal. Now the basic facts are that so far as CO2 generation for each Gwh is concerned, coal puts our 2x what oil does and oil puts out 2x what NG or natural gas does. For anyone reading the newspapers knows that just now we have a huge surplus of NG and the price for NG just now is lower cost than coal! So why not just switch to NG? Part of the reason for this BLOG is to try to explain extenuating circumstances. So here goes---

10-TO-1 RULE: Under the 10-to-1 rule, the natural gas price is one-tenth the price of oil.  For example, a $50 price for a barrel of WTI crude oil would indicate that natural gas should trade at $5.00 per million BTU at Henry Hub (market for NG).  The 10-to-1 gas/oil relationship has been the most accurate rule of thumb over the past 10 years. Using these guides the cost to generate a Kwh will be the same for oil and NG---what about coal?    

ASSUMPTIONS: Power plant heat rate= 10,300 Btu/Kwh                                                             

Fuel heat contents: 1) Coal = 20,000,000 Btu per Short Ton (2,000 lbs) Note: heat contents of coal vary widely by types of coal. 2) Natural Gas = 1,027,000 Btu per 1,000 Cubic Feet                                       3) Residual Fuel Oil = 6,287,000 per Barrel (42 gallons).

Using the assumptions, coal comes in between $10—$40 per short ton. The large variance speaks to the actual variability experienced with coal and where it came from. So within this context using oil, NG or coal is nearly interchangeable.

ASIDE: While attending college in 1950 I visited a KP&L plant in Kansas City. The plant was located on the Missouri River so coal could be “barged in”. Also a 12” gas main from the Hugoton gas fields near Eldorado and Oil by rail car from Southeast US. This allowed a novel boiler firing chamber that could burn coal, NG and/or oil in any combination under the supervision of a COMBUSTION engineer. What was burned at any time depended on the fuel market pricing. Life was simple.

Nowadays NG is usually burned in a gas turbine coupled directly to an alternator/generator. The BIG gain here is that from start, the RPM can be achieved and synched in one minute. If shorter time is needed synched-RPM-hot-standby can be done at little cost. This is NOT possible with coal or oil. So NG is a natural for peaking generation.

Much as was outlined in ASIDE, NG can be burned to generate steam in lieu of using coal, but to be competitive requires NG at $2-$4 range i.e. below the $5 number. Alternatively the CO2 from coal needs to be about 75% sequestered (stored in some manner) and NOT released into the atmosphere. One use of sequestered CO2 is purging residual oil from depleted oil fields. This has been experimentally done but EPA is not pleased with the results and seems to oppose the technique. EPA seems to favor “forced” adoption of biofuel claiming that “economy of scale” will drive the biofuel price down from the current $40/ gallon the government now pays. That is right---$40/ gallon for biofuel! BTW the armed forces are being use as “guinea pigs” to use the mandated biofuel. Demonstration of capability is one thing------if it stops at that.

FWIW----stack scrubbing for pollutant removal and CO2 capture while burning coal is well understood and termed “clean coal” burning. Giving EPA the benefit of a doubt they may feel they have nothing to contribute. But they are spending a lot of money and just maybe the spending is misdirected.

INTERESTING----

Comments

[george storm]

"My home has a 200 amp service, hence can draw up to 200 x 240= 48,000 wh or 48 Kwh"
Careful! that's how much you can draw in one hour

[carl schwab]

Reply to George-----You are absolutely correct. Thanks for the comment. Carl Schwab

[Gas turbine]

They can be adapted to use almost any flammable gas or light distillate petroleum products such as gasoline, diesel and kerosene which happened to be available locally.