What Is The Best Kind Of Generator For My Condominium Building?

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If we decide that a cost effective way to reduce our electricity bill is to generate our own electricity, then the next step is to decide what kind of generator is best. If we agree that natural gas is the cleanest, most economical fuel, then we have two choices.

The two choices are micro turbines that use a small gas turbine to drive the generator, a picture of a 60kW micro turbine generator set is shown on the right, or reciprocating natural gas engines that use a natural gas engine to drive the generator.

If we start our evaluation by comparing efficiency we will find that micro turbines are 20% to 30% efficient in converting natural gas to electricity while reciprocating engines are 25% to 40% efficient in converting gas to electricity. We can see that reciprocating engines are more efficient, but we also observe that neither type of engine is anywhere near 100% efficient at turning natural gas into electricity.

If we used a natural gas powered generator to generate electricity only, we probably wouldn’t save very much on our energy bill, because most of the energy from the natural gas we burn is being wasted in the form of heat.

So, how can we improve the efficiency of the natural gas generator in order to make it a cost effective option? The answer is relatively simple. Use the waste heat from the generator for space heating or hot water heating in the building. We then get heat and electricity from the gas we burn in the generator. Using the combined heat and power (CHP) approach the efficiency of both types of generators is boosted into the 70 to 90% range.

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Natural Gas Generator – Electricity and Heat Production

 

 

Natural Gas Generator – Electricity and Heat Production

The diagram above shows how the electricity and heat are produced in a natural gas CHP generator set. Since the CHP approach improves efficiency so dramatically, we will make our comparison between the two types of generators based on using both the heat and electricity that the generator produces.

So let’s take a look at the pros and cons of the two types of power sources. A summary table comparing the two options is shown below.

Summary Table of Typical CHP Cost and Performance Characteristics
Technology Reciprocating Engine Micro Turbine
Overall CHP Efficiency 70-90% 70-80%
CHP Installed Cost $/kW $1,500-2,200 $2,400-3,000
Noise High Moderate
O&M Cost $/kWHr 0.009 -0.022 0.012 – 0.025
Start-up time 10 sec 60 sec
Space requirement 100kW ≈ 3m² ≈ 3m²

 

From the table above you can see that the reciprocating engine is noisier than the gas turbine generator. But, we can also see that the reciprocating uses the natural gas fuel more efficiently and is less costly to buy, install and maintain. A picture of a 140kW gas engine CHP generator set is shown on the right.

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60 kW Natural Gas Micro Turbine Generator

 

 

So, there is a way to significantly reduce your building’s energy bill, and a natural gas engine CHP generator is the most cost effective option. A natural gas engine CHP generator can cut your electricity costs, as well as your natural gas heating costs, and provide back-up power so that residents aren’t stuck in the elevator when there is a power failure.

 

 

 

If you are interested in investigating the benefits of a natural gas generator further, contact us at 416 410-3815 or info@rikos.com. Let’s talk…

 


Dr. Glenn Allen PhD, P.Eng
Project Director,
Energy and Sustainability
Rikos Engineering Limited

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