Considering a Cogeneration or 
Trigeneration (District Energy) Power Plant?   

Listed below are two formats for a feasibility study when considering cogeneration or trigeneration at your facility. 

First format

Developing and planning a cogeneration or trigeneration installation requires significant time, effort, and investment. So it's prudent to approach the task in a series of steps. The first step requires less work, typically only one to two days, and help you to determine whether further efforts are justified. The next step is a more detailed feasibility analysis, which, if positive, would be followed by a preliminary design. At that point, the cost projections should be sufficient to allow you to make an informed decision about whether a full cogeneration or trigeneration project design effort would make sense for your application.

1. Walk-through analysis -  Screen a potential site to decide whether a detailed analysis is appropriate:
   
   
   • Technical issues – Are thermal and electrical loads sufficient to support cogeneration or trigeneration? (Are they above a minimum size threshold, are the electric and thermal loads coincident, are thermal requirements compatible with cogeneration/trigeneration outputs?)
   • Site conditions – Can the facility infrastructure support a cogeneration/trigeneration system (available space, fuel availability, zoning limitations)?
   • Economics – Do the fuel and electric rates support cogeneration/trigeneration (average retail electric price, fuel costs, required return on investment, or payback)?
   • Environmental issues – Are there any environmental limitations that would preclude cogeneration/trigeneration?
   
   
2. Feasibility Analysis – If the Walk-through is positive, the next stop is a screening analysis that considers more specific details such as:
   
   
   • Bundled and unbundled electric tariffs (retail service rates, partial service rates, standby/back-up rates, transmission and distribution tariffs)
   • Fuel access and price
   • Capital budget
   • Operation and maintenance costs
   • Operating modes (baseload, thermal following, electric following)
   • Interconnection requirements and costs
   • Environmental permitting requirements and costs (including the cost of offsets)
   • Project structure and project development costs (insurance, administrative and management fees, financing)
   
   
3. Preliminary Design -  The preliminary detailed design phase is a more comprehensive evaluation than the screening analysis, including:
   
   
   • Analysis of hourly energy requirements and costs
   • System part load performance
   
   
4. Detailed Design - forms the basis for performance modeling and budget 
5. Data Collection - at the very minimum, the following data must be collected. reviewed and analyzed.

Electrical requirements

• Average demand during operating hours*
            kW
  
• Minimum demand during operating hours
            kW
  
• Peak demand during operating hours
            kW
  
• Annual electricity consumption
            kWh
  

Thermal requirements

• Form of thermal energy use*
             steam            hot water            other (specify)
• What is the primary application for thermal energy at the plant?*
                      
• Average demand during operating hours*
             lbs/hr, Btu/hr, Btu fuel/hr (circle correct units)
• Minimum demand during operating hours
             lbs/hr, Btu/hr, Btu fuel/hr
• Peak demand during operating hours
             lbs/hr, Btu/hr, Btu fuel/hr
• Required conditions*
             lbs/hr, Btu/hr, Btu fuel/hr

Operating conditions

• Nominal operating hours per year*
            
• Number of hours per year that electrical and thermal loads are simultaneously at or above average values*
            

Energy rates

• Average retail electric rate*
             cents/kWh
• Peak demand charge (if applicable)
             $/kW/month
• Fuel price*
             $/mmBtu, $/therm, $/gal (circle appropriate units)

Site Conditions

• Is there sufficient floorspace (inside or outside for a cogeneration/trigeneration installation?*
             Yes            No
• Is adequate fuel accessible/available for a cogeneration/trigeneration installation?*
             Yes            No
• Are there specific environmental or zoning restrictions that may preclude a cogeneration or trigeneration installation?*
             Yes            No

Format 2

Here is another format for your review when considering cogeneration at your facility:

Cogeneration feasibility project analysis is the same as any other commercial project requiring high investment, relatively longer period, and presenting certain financial risks. Therefore, the steps which 
should be followed in developing a cogeneration facility will be similar as those utilized for any investment project. 

Projects will obviously vary from one to another on the basis of factors such as who is the project developer, what is the size of the project, who is financing the project, etc. 

Prior to undertaking any economic analysis to assist the commercial benefit of a cogeneration project and the following technical parameters which need to be considered first: 

1.    Heat-to-power ratio; 
2.    Quality of thermal energy needed; 
3.    Electrical and thermal energy demand patterns; 
4.    Fuel availability; 
5.    Required system reliability; 
6.    Local environmental regulations; 
7.    Dependency on the local power grid; 
8.    Options for exporting excess electricity to the grid or a third party, etc. 

Typical steps for cogeneration project development:

A cogeneration system may be sized to meet either the electricity or the heat demand of the site. When the local power utility allows selling excess electricity generated at the site, one should make sure that the buy-back rate is attractive enough before over-sizing the cogeneration plant.

As the electrical and thermal loads of the site tend to vary with time, the cogeneration system may require that any shortfall in the electricity supply be met by the purchase of electricity from the grid. Likewise, any shortfall of thermal energy should be met by either post-combustion of exhaust gases in the case of gas turbines or reciprocating engines, or from an auxiliary source such as a stand-by boiler. These solutions will certainly have consequences on the annual average efficiency and the economics of the project. The ideal operation would thus consist of the use of the maximum electricity on site, while assuring continuous operation of the processes at nominal conditions and avoiding the generation of excess thermal energy.

If the thermal load is negligible or if it is required to produce only low-pressure steam or to heat a fluid at low temperature, gas engine may be preferred because of its higher efficiency. When opting for gas turbines in a cogeneration power plant, it is advisable to first verify gas supply pressure. If the pressure of gas in the pipeline is low, it will necessitate additional investment on the gas compression station. Moreover, some amount of electricity generated would be diverted for running the compressor, and the operation and maintenance costs will be higher. 

The availability of fuel, its price and guarantee of its long-term supply are the major factors determining the choice of the prime movers. As prime movers can operate with different types of fuels, the option for fuel switching should be taken into consideration.

Designing of the cogeneration facility at the initial stage should incorporate the possible evolution of future energy demand. This would help in the appropriate choice of equipment and in planning the schedule for expanding capacity according to the changes in need. 

Modern cogeneration plants are highly reliable and have a high load factor; one cannot however ignore the occurrence of stoppages for scheduled maintenance or unscheduled breakdown. There may be a need for back-up power to assure continuous operation of activities at the site. One solution would be to provide stand-by generation capacity at the site, which will increase the investment further. Alternatively, a stand-by contract may be signed with the power utility so that electricity can be tapped from the grid up to the maximum contracted demand whenever the cogeneration plant stops operating.

It is imperative this information is accurately collected by a competent party - preferably an engineering team with the requisite skills, qualifications and knowledge to then precisely assess and interpret the information and data they collected.  

Or, give us a call.  We can quickly determine your overall energy requirements and answer the questions of whether your company is a candidate for either  cogeneration, trigeneration or other on-site power option.