Comparison of CNG & Diesel - for Generators

CNG has only about 25% of the energy density of diesel. So diesel does about 4 times as much work.

Now, let's look at this:

"Therefore CNG is cheaper than Diesel by 80%."

"CNG has only about 25% of the energy density of diesel"

Looking strictly at cost to operate what do you get, assuming the above quotes are correct?

Thank you Steven & Lyn.

Does this mean that I need to factor in the energy density factor of CNG & Diesel into that equation??

I assumed that the "Kilowatt hours" generated by a litre of Diesel & a kilowatt hour generated by 1 SCM of CNG would reflect the differences in energy density etc.

I would greatly appreciate if you can tell me how to calculate how many kilowatt hours are there in a litre of Diesel & in a scm of CNG. I tried to "google" this but the numbers with different units of measures are simply mindboggling.

Warm Regards

Baiju

IF your figures about the price to generate 3 kWh are correct - referring to quantity and price, it doesn't matter what diesel does compared to CNG. According your figures, CNG is way cheaper. A kWh is a kWh, however it is generated.

Thank you.

The cost figures (per Litre of Diesel & per scm of CNG) are absolutely correct.

My concern is how many kWh does a litre of Diesel & a SCM of CNG actually have respectively in order to arrive at the cost difference. The 3 kWh figure was just an assumption that I made to illustrate the logic of my equation.

CNG has variable calorific values depending where it is found. I have seen you posted in 2009 that Nigeria will supply.

What you need is to go to a calculator - unit converter and type in from MJ to kWh.

try units conversion.

The rest is easy.

You should be thinking in terms of the volume of fuel required to generate your 3 kW-hr of energy, especially considering your remote location. Diesel is sold in liters or gallons, while CNG is sold in cubic meters or cubic feet, or weight. The actual energy content of the natural gas volume will depend on hw compressed it is. A question you should not ignore is how big a storage facility you will need to meet your power demand. This is going to have a major impact on your operating costs...

The best way to determine what is best for your application and location is to determine what your ultimate power requirements are and get your local suppliers of diesel and CNG to cost out their products and state their case for total cost, reliability , flexibility, security, and ease of use compared to each others products. Probably limiting yourself to one of these two choices is a mistake since you are building from scratch other green energy sources such as solar, wind, and geothermal could also be incorporated with government aid and financial incentives. If you use my recommendation you owe me an espresso and biscotti!

Hi Trueheart,

Here's sending you an espresso & bicsotti....thanks a lot!!!

We are talking about West Africa and hence exploring other options like geo-thermal ,wind ,solar etc is just out of question....no technology & no expertise availbale.

As we are a manufacturing company we would like to follow a tried path but would at the same time look at the most efficient & economic option for our energy.

CNG being cheaper than Diesel, we are looking the numbers right now......the only challenge with CNG however is that it is not piped and would be delivered at site by trucks.

Warm Regards

Baiju

Do not be a naysayer so quick. Yes I am a green world idealist, Sierra Club, Audubon Society, Green Peace , etc. The solar, wind energy, heat pump, etc. packages have become much more user friendly and efficient than in the past . They can be installed by ordinary construction tradesmen, are cost effective, excellent advertising for your business, and once installed can be easily expanded or upgraded. Unlike natural gas or diesel they only have to be transported to the site once and provide subsistence emergency energy backup for communications etc. You now owe me 2 expressos and biscottis.

Hi Trueheart,

I hate to be a naysayer but then the harsh realities of life in West Africa makes you look at things through a different type of lens altogether.

However I shall surely explore the suggestions given by you as alternatives. Perhaps I jumped into saying "NO" cos I had not done much research on alternative energy to the extent that I did for Diesel & CNG.

Thats 2 espresso & biscotti credited in your account.

The new solar cells and wind turbines are virtually maintenance free and aesthetically appealing. About 4 kilometers from where I live they installed a massive rooftop PV system as shown on the link below.

http://www.conestogasolar.com/cambridge-rooftop.html

Wind generators can be made so they can be repaired with indigenous materials such as wood or fiberglass blades. The only downside to wind generators is they kill unwary birds. A plate of bruschetta is required for this advice.

I agree with your statement. The modern way is to get diesel generators, that are eventually also easy to convert to CNG. MAN is strong is this field. Yes, I am talking about gensets with diesel engines. No thermal - turbine setups. A GA from me.

Hi DVM,

Thanks for this hint.

I guess it might make sense to look at this option (perhaps even a bi-fuelled generator that can alternate between CNG & Diesel) so that of CNG supply is disrupted at any point in time, there is diesel back up.

The question however is how to arrive at the "operating costs savings" numbers. I am still wondering if my logic with the equation is correct technically or not.

Warm Regards

Baiju

Transportation costs, especially to remote areas make CNG expensive to ship. LPG, Propane, Butane, or mixtures have much more energy density if tanked in. This would also be a possible backup fuel for a CNG unit.

You are absolutely right.

The quoted cost of CNG for delivery at our site (no piped CNG network there) is about 3 times higher than that of piped CNG.

But the operating cost still works out cheaper than Diesel.

I agree with your concern.

However the trucked CNG is provided from a location just about 150Kms from our site plus the fact that our site is on the expressway making logistics that much more easier (provided of course the CNG provider has enough trucks to be delivering CNG in time).

Diesel is much more expensive compared to CNG and this is what I am looking to fix,in the sense ,an estimate of savings that CNG could provide.

if you dont have electrical grid, dont think that you have gas one. storage of the gas is very expensive and dangerous matter. also delivering will cost you a lot. gas gensets are more effective while you have gas pipeline (ofcourse with the permission to join to it).

xpecial tanks, which can withstand pressure, gas receiver, safety, approvals issues. diesel storage more simple and safe. and ofcourse cheaper.

Hi,

I think you understand the fuel cost issue correctly, so I won't try and contribute to that - basically the suppliers have to be cost competitive or their product would not sell, so you will probably find that (excepting government taxes etc which can easily distort the situation) the fuels will be pretty close on cost per kWhr of electricity produced. Local conditions can however change these numbers quickly and by large factors, so today's answer may not be tomorrow's!

Given this the other considerations are probably more important ie:

cost of fuel delivery (by whatever means)

cost of infrastructure (fuel handling & storage, exhaust system, safety equiment etc)

cost of maintenance (for engine but also for any infrastructure issues)

However there will also be other considerations that may make significant difference:

diesel engines have much better efficiency at part load, so if your gen set is likely to run at part load much of the time (highly likely) then you will probably have lower real-world operating costs using diesel.

Can you recover waste engine heat for process heating? This can just about double the cost effectiveness of running your own generator. If process heat is required, heat can be extracted from (in order of ease of access / capital cost of extraction)

engine cooling circuit (temp approx 90 deg C, output energy approx 80% of generator output),

turbocharger intercooler (temp only approx 50 deg C, output energy approx 20% of generator output),

exhaust heat boiler (temp approx 120 deg C, output energy approx 80% of generator output)

Hope this sparks off some useful thoughts / debate ..... DP

Thank you Phil.

Your point of heat recovery is well taken....we have the need to use steam for our process and will have boilers for the same. Hence heat recovery will play an important part in the scheme of things.

I'm not sure that this post will be helpful or not, but some diesel engines can run on a tiny amount of diesel for ignition at each stroke and a larger volume of CNG or similar to actually supply the varying load.

To repeat, a small amount of diesel is used only as an igniter. But a really tiny amount...

I don't know the proper name for such engines and they are probably a more expensive investment.......but this can mean that diesel fuel can be used for power generation as well if no CNG available...

I believe buses in many metropolitan areas around the world use this as a method of saving money and getting cleaner exhaust!!

Just a thought!!

Thank you Andy,

I guess they call it bi-fuel generator and we are exploring this option too. It is just that there are not many real-world examples of people who are actually using this type of generators here in Nigeria and hence I am unable to get concrete user feedback on the efficiencies, costs etc.

Talk to engine makers like Mercedes, Volvo and other big bus and stationary engine builders/manufacturers...

Maybe someone here can give you a better indication....

Have you checked out the LNG Generators made by Capstone Corporation ?

Check out running these Generators on BOTH fuels I believe all that is needed is a simple valve or metering device to change over.

Then you can use the fuel is most affordable at the time. That seems the most effective way to plan because locking yourself into one one fuel source is limiting your own ability to resond to market condition.

Thank you dadw,

I just responded to Andy's thread which was along the same lines as yours.

We are looking at this option too and I appreciate your input.

Hi

Your equation is valid. " Just go for CNG whenever available" . It is cheaper. Rest fuel types can be thought of as backup.

Just to add to your equation. A normal CNG engine 1000cc do about 20KM for 1 kg of gas, while diesel engine do about 14KM for 1Liter. So saving is there on CNG.

However true saving can be published from your side here on this website CR4 after you have used the adopted system (CNG or Diesel) for about a month.

On this link there are some conversion formula given.

http://forum.onlineconversion.com/showthread.php?t=12734

Have fun.

Thank you Wahaj,

I shall surely share the numbers with all of you here as we gather realtime numbers after usage of the systems for a while.

If you can get to the USA or use Bidspotter or other agent an auction of the equipment you are looking for will take place in 4 days. Buy your equipment for a fraction of the cost.

Check out the link below.

http://ca.mg202.mail.yahoo.com/neo/launch?.partner=rogers-acs&.rand=3imqcsuo0mjqh