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Rate Calculations

The Utility Rate Calculation page is an interface to a customizable economic analysis for DG/CHP sites. Information about the prompts and reports are detailed below.

Utility Rate Calculation Prompt

The choices allow a user to specify the facility they would like to analyze, a base and CHP electric rate, a time period and the costs of generator gas, maintenance and heat recovery value.

Date Range

The starting date of a utility rate calculation is midnight on the first day of the month in the drop down.  The ending date is 11:00pm on the last day of the month listed in the drop down.  For a utility rate calculation, the period of analysis is limited to a calendar year beginning on the starting.  A selection for starting date of "4/2003" and ending date of "5/2005" will return a utility rate analysis for the period of 4/1/2003-3/31/2004.

Utility Rates

There are five large electric utility companies in New York state: Consolidated Edison (ConEd), Long Island Power Authority (LIPA), Niagara Mohawk (NIMO), New York State Electric & Gas (NYSEG) and Orange & Rockland Utility.  Each has a wide variety of electric tariffs, only one or a few of which a particular facility can accept service under.

The Base utility rate applies to the facility as if it did not have a DG/CHP System installed.  The CHP rate is the tariff that applies to the facility with the DG/CHP System.  For some utilities they may be the same rate, but for others the facility is billed for service under a standby or cogeneration rate.

Details for the available utility rates can be found here.

Generator Gas Cost

This is the cost in dollars per million Btu (MMBtu) consumed by the DG/CHP Generator.  If a default value is entered for the facility in the database, that value will be displayed in the prompt, otherwise it will be left blank.

Millions of Btu is used as the reference for cost because of the many available fuel sources for generators.  Other billing units may be in cubic feet of gas consumed or therms.  A therm is 100,000 Btu, ten therms is equal to 1 MMBtu of energy.

For cubic feet, the actual energy value must be calculated using the Higher Heating Value of the fuel.

Generator Maintenance Cost

The maintenance cost for a generator is generally small when compared to the power produced.  This field accounts for the cost of labor and parts necessary to keep the generator running per kilowatt-hour produced by the generator.

Heat Recovery Value

The Heat Recovery Value is the dollar amount per million BTUs of savings realized by utilizing heat recovery to perform a function that would otherwise cost the facility money from a utility.  This may be the cost of eliminating gas use or electric use for previous equipment.  This value may also need converting similar to Generator Gas Cost.

Utility Rate Calculation Report

The Utility Rate Calculation Report consists of two tables: "Monthly Electric Costs and Savings" and "Total Economic Analysis".

Monthly Electric Costs and Savings Table

This table presents a simple analysis of the electric bills with and without the Generator for the selected time frame.  The Base Facility uses the Total Facility Demand values from the database on an hourly time step with a data quality level of "Passes relational checks".  The CHP Facility uses the Total Facility Purchased Demand values.

These hourly values are used to calculate monthly electric bills.  For the CHP Facility, if the "Export Electricity to Grid" checkbox is marked under the facility details, the facility is allowed to export electricity to the grid.  In the case of exported electricity, the commodity value exported is credited to the monthly bill.  If the box is not checked, negative values for Total Facility Purchased Demand are set to 0.

Total Economic Analysis Table

This table shows a simple economic analysis of the full benefits of the CHP System based on the Monitoring Unit data.  The generator output and electric cost savings from the first table are included.  The generator gas use is charged based on the LHV entered on the Facility details page and is converted to HHV using the formula: HHV = LHV * 1.1.  The maintenance cost, heat recovery savings and generator gas costs use the values from the database and the user entered options from the Prompts page.  The values entered on the prompts page are show on footer of the table.

Values that are negative are displayed on the table in red and in parentheses.