Reduction of Carbon Dioxide Emissions by Using Photovoltaic Modules in Remote Areas

By Richard Komp

How much reduction in carbon dioxide emissions can be accomplished by using photovoltaic systems? I have just made some calculations of just how many tons of CO2 emissions could be mitigated by using photovoltaic systems instead of fossil fuels to either generate electricity or replace kerosene lamps.

Photovoltaics compared to small Diesel Generators
For the first calculation I looked up some performance specs on web sites for small gas and diesel generators. Picking a Yanmar L90AE 9 hp. Unit, I found that the generator would produce 5 kW continuously using up about 1/2 gallon of diesel fuel per hour. (This is at full output, at part throttle, the engine is probably less efficient but would last considerably longer between overhauls.)

Diesel fuel has a density of about 0.78 Kg/liter. (I converted all the numbers to metric units for ease of calculation but will give the final answer also in old fashioned "English" units.) Diesel fuel is a mixture of hydrocarbons with an average weight ratio of 12 parts carbon to 2 parts hydrogen with small amounts of other elements like sulfur (which is supposed to be taken out in the next few years anyway). Therefore 1 liter of diesel fuel has 0.67 Kg of carbon and will produce 2.45 Kg of CO2. The Yanmar generator will produce about 2.5 kWh. per liter of fuel used, which works roughly out to the easy to remember number of 1 Kg of CO2 produced for each Kilowatt-hour of electricity produced. (2.2 pounds/kWh.)

Home PV system in Maine: A typical off-grid home system in Maine might have a 1000 watt (1 kW) pv system to give an approximation of a middle class life style. (My home system is 400 watts but I have given up on trying to be middle class.) Given average weather conditions, such a system would produce about 1000 kilowatt-hours of electricity per year in Downeast Maine. This system would mitigate 1 Tonne of CO2. per year. (Those are metric Tonnes of 1000 Kg, or 1.1 English short tons.) Over the 25 year lifetime of the system (somewhat arbitrary, since pv modules come with 25 year guarantees nowadays), that adds up to 25 Tonnes (or over 27 Tons) of CO2.

Home PV system in Nicaragua: The Grupo Fenix I have been working with in Nicaragua has been installing 25 watt pv systems on remote homes for Nicaraguan campesinos (No pretense of middle class here at all). Based on the weather and solar insolation data furnished to us by Padre Julio Lopez de la Fuente (a Jesuit priest at the University of Central America who had been measuring the sunlight intensity for more than the past 30 years), this system would furnish about 120 watt-hours per day or about 44 kWh per year. Over the 25 year "lifetime" of the system, this adds up to 1.1 Tonnes (1.2 Tons) of CO2. Photovoltaics compared to Kerosene Lamps.

The second calculation is a bit more difficult to quantify since the amount and quality of light from a photovoltaic powered fluorescent lamp is quite different from poor quality, yellow illumination from the typical kerosene lamp. Therefore I will use another example from Nicaragua and assume the pv array with two 20 watt fluorescent lamps in the campesino's home simply replaces two kerosene lamps, one per room, without attempting to match illumination (The rooms are very much brighter after the pv system is installed.) I am also assuming that the campesino would have been using about 250 ml (one US pint) of kerosene per day before the changeover.

Kerosene has a density of 0.82 Kg/liter, slightly higher than diesel fuel but the same type of calculation applies, giving 2.6 Kg of carbon dioxide for each liter of kerosene burned. This adds up to 240 Kg/year for the 91 liters of kerosene eliminated by installing the 25 watt pv system. Over the 25 year "lifetime" this is 6 Tonnes (6.6 tons) of CO2 mitigated for the $400 photovoltaic system.

Implications for Carbon Emission Trading
Recently there has been a good deal of interest in the concept of "buying the right" to emit carbon dioxide. There is even an International Carbon Bank and Exchange; and the price of CO2 emission mitigations is expected to soon be about $20 per Tonne ($18 per ton). Using the example above, a large multinational corporation may be willing to pay at least $120 of the cost of the Nicaraguan campesino's system if they got some sort of certificate giving them the "right" to pollute the 6 Tonnes of CO2 saved by the system.

The philosophical implications of this line of reasoning can be far reaching but I will leave those for another article. I will, however, point out that a common Conservative argument for doing nothing to cut the wasteful use of energy in the US and subsequent release of CO2; is that the Third World Nations are unwilling to commit themselves to drastic reductions of their small (per capita) CO2 emissions. Billions of people in the world live by the meager light of kerosene lamps and each of the thousands of small pv systems now being installed for these people, in addition to markedly improving the quality of their life, will cut the carbon dioxide emission by about 6 Tonnes per systems over their lifetime.

Richard J. Komp, President Maine Solar Energy Association (MESEA) RR 2 Box 7751 Jonesport ME 04649 207-497-2204, e-mail: sunwatt@juno.com

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