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How HOMER Calculates Emissions

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HOMER calculates the emissions of the following six pollutants.

Pollutant

Description

Carbon Dioxide (CO2)

Nontoxic greenhouse gas.

Carbon Monoxide (CO)

Poisonous gas produced by incomplete burning of carbon in fuels. It prevents delivery of oxygen to the body's organs and tissues, causing headaches, dizziness, and impairment of visual perception, manual dexterity, and learning ability.

Unburned Hydrocarbons (UHC)

Products of incomplete combustion of hydrocarbon fuel, including formaldehyde and alkenes. They lead to atmospheric reactions causing photochemical smog.

Particulate Matter (PM)

A mixture of smoke, soot, and liquid droplets that can cause respiratory problems and form atmospheric haze.

Sulfur Dioxide (SO2)

A corrosive gas released by the burning of fuels containing sulfur (like coal, oil, and diesel fuel). It causes respiratory problems, acid rain, and atmospheric haze.

Nitrogen Oxides (NOX)

Various nitrogen compounds like nitrogen dioxide (NO2) and nitric oxide (NO) formed when any fuel is burned at high temperature. These compounds lead to respiratory problems, smog, and acid rain.

Emissions of these pollutants result from the:

Production of electricity by generators.

Production of thermal energy by a boiler.

Consumption of grid electricity.

HOMER models the emissions of the generators and the boiler in a similar way because both consume fuel of known properties. It models the grid slightly differently. The following sections describe how HOMER calculates the emissions of the generators and boiler, then how it calculates the emissions from the grid.

Generators, Boiler, and Reformer

Before simulating the power system, HOMER determines the emissions factor (kg of pollutant emitted per unit of fuel consumed) for each pollutant. After the simulation, it calculates the annual emissions of that pollutant by multiplying the emissions factor by the total annual fuel consumption.

You directly specify the emissions factors for four of the six pollutants: carbon monoxide, unburned hydrocarbons, particulate matter, and nitrogen oxides. Using these values and the carbon and sulfur content of the fuel, HOMER does some calculations to find the emissions factors for the two remaining pollutants: carbon dioxide and sulfur dioxide. In doing so, HOMER uses three principal assumptions:

1.Any carbon in the fuel that is not emitted as carbon monoxide or unburned hydrocarbons is emitted as carbon dioxide.

2.The carbon fraction of the unburned hydrocarbon emissions is the same as that of the fuel.

3.Any sulfur in the burned fuel that is not emitted as particulate matter is emitted as sulfur dioxide.

Grid

In simulating a grid-connected system, HOMER calculates the net grid purchases, equal to the total grid purchases minus the total grid sales. To calculate the emissions of each pollutant associated with these net grid purchases, HOMER multiplies the net grid purchases (in kWh) by the emission factor (in g/kWh) for each pollutant. If the system sells more power to the grid than it buys from the grid over the year, the net grid purchases are negative and so are the grid-related emissions of each pollutant.