Understanding MW of electricity

Wattage is an electrical term but it is also a "mechanical" term in that it represents a unit of thermal energy (especially in SI)- the thermal energy contained in one watt of electrical power, NOT the thermal energy necessary to produce a watt of power.

In "English" terms, a watt is equal to 3.412 BTU. Since Watt measurements are usually done on an hourly basis- kWh = kilowatts per hour- a watt is typically BTUs per hour.

1000 MW = 1000 x 1000 kW, so a 1000 MW rated boiler is rated to PRODUCE 1,000,000 x 1000x3.412 BTUs or 3,412 million BTU per hour or 103,156 boiler horsepower.

By the way, using the typical 35% thermal to electricity ratio, this boiler could produce about 350,000 kW or 350 MW of power to the grid if connected to a generation system- which calculates into 35% times the boiler's thermal rating in MW.

Hello energygod

Not sure what you mean by "Since Watt measurements are usually done on an hourly basis- kWh = kilowatts per hour - a watt is typically BTUs per hour" but I think it will confuse the OP more! kWh = kilowatt*hour, not kilowatts per hour. Also did you mean "- a watt is typically 3.142 BTUs per hour" ?

I've never heard of horsepower being used for anything other than mechanical power. There's obviously no reason it couldn't be used for boiler rating, but if it's the usual horsepower I make 1000 MW more like 1.34*10⁶ hp.

Cheers...........Codey

Codemaster-

You have nicely pointed out one of the challenges of a world-wide engineering forum.

Here in the States, steam boilers are typically "sized" based on one of two factors-

Pounds Per Hour of steam production at a given pressure per hour - fairly easy to rate and/or convert

and

Boiler Horsepower - A BHP is the thermal output in BTUs (regardless of pressure or steam production) divided by 33,475 BTU per BHP. I have not looked into the background of this terminology, but it is VERY prevalent across the pond.

Since you brought it up- I decided to check Wikipedia-

Boiler horsepower

A boiler horsepower is used for boilers in various industrial applications, however it is considered an antiquated term and is not used in modern power plants. It is equal to a boiler thermal output of 33,475 BTU/h (9.8095 kW), which is the energy rate needed to evaporate 34.5 lb (15.65 kg) of water at 212 °F (100 °C) in one hour.

The term was originally developed at the Philadelphia Centennial Exhibition in 1876, where the best steam engines of that period were tested. The average steam consumption of those engines (per output horsepower) was determined to be the evaporation of 30 lb/h of water, based on feedwater at 100 °F (38 °C), and saturated steam generated at 70 psi (480 kPa) gauge pressure. This original definition is equivalent to a boiler heat output of 33,485 BTU/h. In 1884, the ASME re-defined the boiler horsepower as the thermal output equal to the evaporation of 34.5 lb/h of water "from and at" 212 °F. This considerably simplified boiler testing, and provided more accurate comparisons of the boilers at that time. This revised definition is equivalent to a boiler heat output of 33,469 BTU/hr. Present industrial practice is to define boiler horsepower as a boiler thermal output equal to 33,475 BTU/h, which is very close to the original and revised definitions.

The amount of power that can be obtained by a steam engine or steam turbine based on boiler horsepower varies so widely that use of the term is entirely obsolete for these purposes. The term makes no distinction as to the steam pressure or temperature which is produced (both of which significantly influence engine/turbine output), it merely defines a thermal output of a boiler. Smaller steam engines often require several boiler horsepower to make one horsepower, and modern steam turbines can make power with as little as about 0.15 hp (boiler) thermal output per actual horsepower developed.

I think you may be missing the point. This has little to do with differences in terminology around the world.

Your first post is largely wrong in its use of commonly understood engineering language and concepts.

For example:

the thermal energy contained in one watt of electrical power (wrong)

a watt is equal to 3.412 BTU (wrong)

kWh = kilowatts per hour (wrong)

a watt is typically BTUs per hour (this is merely misleading -- wattage can be converted to or expressed as BTU's per hour, but it is a stretch to say that it is typically BTU's per hour. It is more typically P=IE, I'd think)

You might find the link in PWSlack's post helpful.

My comments were totally based on mechanical versions of electrical terms.

Since you are apparently much more broadly educated than I, what is the THERMAL ENERGY contained in one watt of electrical power?

Correspondingly, how many BTUs are "contained" in a watt? I assume that it is OK to use the term BTU when discussing thermal energy, or is that another indiscretion of mine where I show the world how utterly ignorant I am?

I guess that the ASHRAE committee must have been a bunch of blithering idiots to have awarded me an international First Place for a project that I submitted (or maybe I just copied the information from someone else who was a lot smarter than I). And I am sure that the Assoc of Energy Engineers did not notice that I used a ringer to take my exam for the Certified Energy Manager ranking and that that "ringer" answered every question on the test although only about 45% were required to be answered.

Since the discussion was FOCUSED on thermal values, how is the comment on how a watt might be expressed in units of equivalent thermal energy misleading? IF we were discussing the ELECTRICAL VALUES, then P=IE makes perfect sense.

Maybe I got it all wrong- Maybe the original post was about an ELECTRIC BOILER that had an input of 1,000 MW. If that was the case, I guess that most of the posts in this thread were totally incorrect.

I look forward to your responses to my requests for clarification.

I stand corrected for improper usage of terms.

Sorry for the secondary rant- I'd had a bad day and reviewed these comments with a totally out-of-personality mindset and my responses indicated as much.

The big problem in this thread is that a bunch of fairly smart people are trying to help someone who is, apparently, a lot earlier in their career than most of the responders who has asked a not-well worded question and has not returned to see what is being said or to respond to the comments.

Maybe the best thing is to move on to other threads and let the OP try to figure it out.

"what is the THERMAL ENERGY contained in one watt of electrical power?" ZERO! The Watt is a rate of energy transfer (power). Unless a time is specified together with the power, there is no energy. One Watt-second (one Watt of power supplied for a duration of one second) is one Joule of energy. One thousand Watts of power supplied for a duration of one hour (or one Watt of power supplied for 1000 hours, etc) is one kWh, or 3,600,000 Joules (3,600 seconds per hour).

One kWh is equal to approximately 3,412 BTU. or one Watt-hour≈3.412 BTU. Since one Watt-hour =3,600 Watt-seconds, then 3,600 Watt-seconds=3.412 BTU, or 1 BTU=3,600/3.412=1055 Watt-seconds. Again, without the -seconds, there is no ENERGY associated with the POWER of one Watt.

You mention P=IE. That too is POWER, not ENERGY. P(Power in Watts)=I(Intensity, or current, in Amperes)*E(Electromotive Force, or Voltage, in Volts). If you want to calculate electric ENERGY, you must multiply by time in seconds to obtain energy in Watt-seconds, or Joules.

OK energygod

Thanks for the clarification. When I said I'd never heard of boiler hp, I wasn't implying it doesn't exist. There's plenty of things I've never heard of, but there's one less now!

Cheers.......Codey

A unit of power tells you how fast you can do work. A unit of energy tells you how much work you can do. So power is a rate, and energy is a quantity.

Two cars may have the same sized fuel tanks. Therefore they can each store the same amount of energy. One car, however may have an engine that can produce twice the power of the other. If the more powerful engine is operated at full power, then it will consume energy (fuel) about twice as quickly as the less powerful engine.

A 1000 MW powerplant has produces a power of 1000 MW. If this plant runs for one hour, it will have supplied 1000 MWh of energy.

Hyperphysics is a very good site for exploring such concepts. It has a graphic index that makes it pretty easy to navigate, and to explore topics in whatever depth you would like.

The starting question of this thread referred to a BOILER rated at 1000 MW, NOT a power plant.

Your statements are true, but not relevant to the question.

My response also referred to energy and power, but focused on the BOILER's output, then later on what it COULD do in a power plant.

I answered with the key thought being to address the poster's confusion with power and energy. He said "May be foolish question but want to clear the concept of power & energy."

Given that he wrote "...will supply 1000 MW power per sec to grid..." he clearly does not understand the concepts of energy and power. This take on the thread is supported by the thread title, I think: "Understanding MW of electricity".

While your post is correct in some respects (and completely wrong in others -- especially in regard to the original poster's apparent confusion, which you seem to share), I think it may fly over the head of the original poster.

Or not. Your guess is as good as mine.

http://www.evsource.com/articles/mind_your_units.php

I checked out your post, and MOST of it was correct.

However, the final line of the post was not fully correct. I understand that Mr. Ang was trying to say that you buy kWh from the utility- but virtually ALL utilities charge their commercial and industrial customers a "demand" charge that is totally based on the RATE of power usage because the utility had to have capacity (generating or distribution) to support that rate of usage, even for just 15 minutes. Those "demand" charges are usually in kW (occasionally in kVA).

When the billing is in kW, there is also USUALLY a third charge that might pop up regarding power factor. Most utilities have a minimum acceptable power factor- often 0.8 or 0.85. If the customer has a kVA load (true power) that is higher than the acceptable value for the kW (apparent power) that was read, the utility will "adjust" the kW up to where it would have been to match the minimum power factor, or they will bill for the kVA used in excess of what would have occurred with the kW and an acceptable power factor.

Boilers as far as I know and we are manufacturers of this size of boilers are not rated in MWs that is the portion of TG (there also the G is in MVA)

Boilers are rated in TPH and other parameters

First thing: a watt is NOT an electrical term ... it's the measure of instantaneous POWER being delivered. One watt = one joule/sec, that's it, that's all.

A boiler that generates 100 MW of power (or whatever) generates 100 MW of HEAT CONTENT. That is, it generates a flow of steam, with the steam containing a quantity of heat energy per unit. Steam flow generated x heat content per unit of steam = power generated.

The Heat Content is NOT how much energy can be generated by passing the steam through a turbine, by the way. It's the TOTAL heat in the, including sensible heat, vapourization heat, and superheat (so basically all of the heat energy to get the steam up to the working temperature at the working pressure and volume).

Cheers! DZ

1000 MW is the power of the boiler and when thermal conversion and other efficiencies are taken into account indicate the power output of the turbine (or whatever) the boiler is connected to.

Energy (or work) exactly equals power multiplied by time - so for example 1000MW for 10 secs would give 10000MW sec of energy.

So whereas in imperial units for power and energy you can talk about HP and HP hr with 1 HP = 550 ft lbf per sec, In SI units its Watts and Watt Hr with 1 Watt = 1 Joule/sec. And of course in electrical units 1 Watt is 1Amp x 1 Volt.

All these units are exactly mathematically related and you can convert from one to the other at will at a given point in a system. If you compare points through a system you need to recognise physical conversion efficiencies.

Interesting discussion on practical aspects of energy and power. I would like to quickly review the theoretical aspects of these terms to clear the basic concepts to the question posted .In daily life when we consume energy by mental or physical exertion it is said that we are doing work but in physics work is said to be done only when a force is applied and it produces motion or displacement. Therefore work is measured by the product of force and component of the displacement in the direction of the force. N-m or Joule is the unit of work. As Joule is small unit many times we use KJ. Energy is defined as the capacity for producing an effect. It is mathematically defined as capacity for doing work and measured by product of amount of work done and time for which it is done.Unit of energy is the same as for work. The rate of energy transfer or storage is called power.Unit of power is watt,kW or MW.1 W = 1J/S=Nm/S. Heat is defined as the form of energy that is transferred across a boundary by virtue of a temperature difference.The temperature difference is the potential or force and heat transfer is the flux.Heat transfer and work transfer are the energy interactions. To understand these terms clearly one has to understand the laws of thermodynamics

Soheb,

No question is foolish unless it is left unanswered. Boilermakers rate commercial boilers in horsepower, HP (think rate of doing work). Since they want to advertise their products in the best light, they do not include downstream conversion losses. A HP is equivalent to 746 Watts or 550 ft-lb of work per second. Energy is a term of total work and may be expressed as HP-hours or Watt-hours. A boiler usually burns hydrocarbon fuels to heat and maybe boil water to heat something or drive a turbine-generator set etc. Each process wastes energy and each one must be taken into account, but 3.412 BTUs of heat are equivalent to a Joule, AKA a Watt-second of energy.

Regards,

Luther M

Yours is good question, which needs to be known to many. Being a non electrical person, I needed some information on MW rating on capacity of power plants. I happened to ask the basics to many professional engineers, who were confused about,whether the rating is with reference to seconds, minutes. hours or day.

Some body finally clarified the matter.

Mega watt rating of a power generation system [ whether HYDRO, THERMAL or DIESEL based] refers to the maximum designed capacity of the power generation system on power generation output per second.

As per your question on assumption that the combined boiler and generator is at it's maximum efficiency, will supply 1000MW per second to the grid.

I think not.

1000MW is 1000Mjoule/sec because 1W = 1 Joule/sec

- and the argument here is not about the choice of time unit.

Putting it another way, since 1 Watt = 1VoltAmp

You can't say that "a boiler" delivers the equivalent of 1VoltAmp/sec

You would say it can deliver, or has the capacity to deliver 1VoltAmp, and that in the course of 1 hour it will provide 3600 VoltAmp of energy.

Correction to my own answer

Last line should read 3600 VoltAmpSec not 3600 VoltAmp

As far as the little i know.wattage has to do with unit of power and energy with joules.

Boiler will generate heat in joules for use in drying or other purpose.It is not meant to generate electricty.However,it uses electricity to generate heat energy.

I would say the Boiler is manufactured to generate such unit of heat

Patrickwhowha

Energy is the capacity to do work.

Power is the rate at which energy is consumed or handled.

Once this much is very clear, other informations/calculations can be easily managed.

Rajan

Well put.

Hi Soheb,

The rating of modern boiler plant is usually stated in terms of MW output, whatever the heated medium may be. Given that your application is for power generation it is most likely to be in the form of superheated steam. Its what happens next that matters in terms of electricity to the grid. The turbine and all the ancilliary plant needed to convert the steam into the final energy output will have an overall efficiency dependant upon the steam conditions (pressure, temperature, No of reheat passes etc).

You may therefore end up with say 350MWe at the 'power station wall' available for sale at unity power factor. But if you then consider that the thermal efficiency of the boiler has not been mentioned so far then the fuel input rate to achieve the 1000MWth could well require 1250MW input.

You will readily appreciate the benfits of the common unit throughout this process as being maintained as the MW as this refers to an energy flow rate irrespective of the stage or medium to which it refers.

Good luck,

Massey.

I think the next step is to agree to disagree.

Energy = power x time; power = energy ÷ time.

There is no such meaningful thing as watts per second, because the term "watts" already includes "per second" (or other time unit) in its definition.

Energy units: ergs, joules, calories, Btu's, ft-lb, et. al., including various prefixes.

Power units: watts, hp, TR (tons of refrigeration), etc.

Thanks to all Dear friends,

All i can say is that it is simple but confusing terms being daily used in Power industry.

I am really thankful to all for there time and guiding for better understanding. I will really appreciate Mr Blink for his understanding and reading between the lines to understand to simple question and not just going by the words entering complexity and jugglery of units.

Thanks to all.

Soheb

Thank you also, Soheb, for the kind words.

Information below is extracted from website:

http://www.engineeringtoolbox.com/boiler-capacity-d_1115.html

Quote

Boiler Horsepower - BHP

The Boiler Horsepower (BHP) is the amount of energy required to produce 34.5 pounds of steam per hour at a pressure and temperature of 0 Psig and 212 ?F, with feedwater at 0 Psig and 212^oF.

An BHP is equivalent to 33,475 BTU/Hr or 8430 Kcal/Hr and it should be noted that a boiler horsepower is 13.1547 times a normal horsepower.

Horsepower (hp) can be converted into lbs of steam by multiplying hp with 34.5.

Example

200 hp x 34.5 = 6900 lbs of steam per hour

Lbs of steam can be converted to hp by dividing lbs steam per hour by 34.5

Example

5000 lbs of steam / 34.5 = 145 hp boiler

Unquote

Therefore, based on the above definition, then the term boiler power (in MW) is the equivalent term (but not the same) of boiler hp in SI unit.

So by using similar definition then we can say that 1 MW of boiler power is the energy required to produce 1,595.108 kgs of steam per hour at a pressure and temperature of 1 atmA and 100^oC, with feedwater at 1 atmA and 100^oC.

So, by definition, 1000MW of boiler power is not the electrical power generated, but is is the energy required to produce 1000 x 1595.108 kg of steam per hour at pressure and temperature of 1 atm and 100C.

Please note that power is energy per unit time. For example 1 MW is the same as 1MJ per second.

1 kW-h is the unit of electrical energy that is equivalent to 3600 kJ.

In my opinion this is what you will get:

1000 MW is the rated OUTPUT. Your power consumtion will be more than that. You may get the power of that unit by taking the declared efficiency and divide the rated output by the efficiency.

Now regarding the Joules and Watts. Remember that Watts are units of power. In other words, watts describes a rate of energy usage. Joules are units of energy equivalent to kWh. So if the boiler has a rated output of 1000 MW, and it runs for 1 hour you will have 1000 MWh of energy (someone else has written the convertion from Wh to Joules, you can figure it out)

Then what you look into is what is the type of boiler you have, continuos duty, emergency, prime source etc. That will tell you the number of hours per day that unit is meant to operate for.

I hope this helps.

Please comment.