The energy use of a family

The energy use in different activities of a standard family

Often, energy efficiency is seen as the change into new types of equipment.
However, in the energy use by the equipments of a normal family (e.g. the house and the car), the energy use are far smaller than the energy use in the food system needed to support the family.

The grey parts of the bars are what could be considered possible to decrease by increased efficiency.

Sparpotential = Capacity for energy efficiency increase
Hus = House
Bil = Car
Mat = Food

Or, to put it simply: A neighbour farmer is far more worth than half a metre extra insulation on the house


Calculation background:

The calculations above could cast some light upon the energy use of a general family in the western Europe and USA societies. I pick an example with Swedish figures. 

House 

In Sweden, a normal new-built house for a family of four is assumed to have a yearly energy use of about 17 000 kWh (Svensk Byggnorm 1980). However, by applying energy conservation this figure is possible to diminish to below 10 000 kWh. The potential for increasing energy efficiency in the building is thus about 8 000 kWh/year for a family of four. 

Car 

A second large energy user of this four person family is the car. Assuming an average use of the car of 15 000 km/year, using 0.6 - 1 litre of gasoline per 10 km, the difference in energy use in the two types of cars is about 6 000 kWh/year. (The more energy-efficient car uses about 9 000 kWh of gasoline/year, the other about 15 000 kWh. Assuming the same indirect energy use, the difference is about 6 000 kWh/ year.). Thus, the potential for increasing energy efficiency in the car is about 6 000 kWh/year for a family of four. 

Food 

One effect of urbanisation is that food for the population cannot be produced where people live. It has to be imported from a larger, supporting area of agricultural land, about 25 times larger than the area of the town (Forsberg and Rengefors 1992). The area needed per person is estimated at about 2 000 m² / p (Günther 1989, 1993a). As an effect of the global trade system, a large part of this support area is situated in very remote places. E. g., the accumulated transport distance of the raw material of an ordinary breakfast could very well approach the circumference of the earth (Günther 1993a.). 

Thus, the energy used for transportation and handling of food is a high but to a large extent unrecognised part of the total per capita uses of energy. In Sweden the use of direct energy for transport and handling of food is conservatively estimated at about 10 % of total annual energy use (Olsson 1978). Nils Tiberg (LuTH, pers. comm. ) estimates the figure for Sweden at about 60 TWh, or 13 % of total energy use. In GB this figure is estimated at16-21 % in 1976, the higher number including energy use in home and agriculture (Leach 1976). In the US, the energy used in food distribution and handling is at the same time estimated at at least 16. 5 % of the total energy use. (Booz 1976) 

From these figures, the "efficiency" in food handling can be estimated. The per capita use of direct energy in food transport and handling are in the Swedish estimates between 5 625 and 7 500 kWh. Calculated on an average of 90 W, the annual biological energy uses for growth and maintenance of a human is about 900 kWh. From these figures, the efficiency of energy delivery in conventionally handled food in Sweden could be computed to about 7 : 1. In GB and the USA, this figure would be about 11 : 1. Hall & al. (1986) estimates this figure in an average western society to be about 9.5 : 1. 

In a report prepared for Carrying Capacity Network in September 1994, Mario Giampetro maintains: ". . the 3,500 kcal of food energy consumed per U.S. citizen cost the U.S. food system about 35,000 kcal per capita of commercial (exosomatic) energy. " These figures are per day, but the ratio is 1:10. 

In these figures, the energy use in agriculture is not included. Assuming the average use of energy in producing the food by ordinary western methods is about the same as the energy content of the food (Hall, op. cit.), the total energy delivery efficiency would be about 1:8 in the lower Swedish estimates. Correspondingly, the other estimates will also be one unit higher. From an estimate for US agriculture from 1976 (7,0 billion joules used for production per capita and 28. 5 after production for the delivery of 5 BJ of food, (FAO 1977)) the total energy delivery efficiency, including the fuels used for production could be calculated to 1:7,1. Since the mid-seventies, the energy intensity in food production and handling chain has increased, why these figures seem consistent with the former. 

Uhlin (1996) estimates figures for the total food production system in Sweden. Although he may be criticised for using conservative figures, the ratio that can be calculated from his figures is 1:11,5-14,1. 

The food energy need for one person is about 1 000 kWh. Industrial energy input used to produce this amount of food energy in American agriculture is between 3-400 kWh (cereals, vegetables) and 2000 kWh (rangeland beef, sheep) (Folke and Kautsky 1992). In Sweden, the efficiency of the agricultural system is about 1:1.04 , which can be calculated from the figures given by Hoffman (1995).

Assuming a local production of a diet where 30% of the energy comes from animal products and 70% from vegetables, the energy input needed for this will be about 900 kWh to deliver food for one person. Assuming a total energy cost of 1 000 kWh/pers for food, this leaves 1 100 kWh for local distribution and handling, which seems reasonable. 

An increased energy efficiency in the food chain by local food production could then decrease the need for fossil energy input by about 32 000 kWh in the family. This is by far the largest area available for increased energy efficiency.

 

References: 

Booz, A. (1976): Energy use in the food system Federal Energy Administration Washington DC 041-018-00109-3 

FAO (1977): The State of Food and Agriculture 1976 

Folke C. and Kautsky N. (1992): Aquaculture with its environment; prospects for sustainability, Ocean and Coastal Management 17 pp. 5-24 

Forsberg, C. and K. Rengefors (1992): Anrikning av fosfor i stadsregionen - en fosforbudget för Stockholm 1990, (Enrichment of Phosphorus in the Urban Area - a Phosphorus Budget for Stockholm 1990) Report. Department of Limnology, University of Uppsala 1992. 

Giampetro, M. and D. Pimentel (1994): Food, Land, Population and the U. S. Economy. A report prepared for Carrying Capacity Network. September 1994. 

Günther, F. (1989): Ekobyar, ekologiskt anpassad och resurssnål bebyggelse. Lund 

Günther, F. (1993a): Phosphorus flux and Societal Structure In Proceedings form the Stockholm Water Symposium Aug. 11-14, 1992. Stockholm Water Co. ISBN 91-971929-4-5, ISSN 1103-0127 

Hall, C. A. S., C. J. Cleveland & R. Kaufmann (1992): Energy and Resource Quality Wiley Interscience

Heady, E.O., 1976. Sci. Amer. 235 (3) p.118 

Hirst, Eric (1974): Food-related Energy Requirements, Science 184:134-38 

Hoffman, R. 1995 Jordbrukets energibalans - En analys av energiflöden i Svenskt jordbruk 1993 och jämförelse med åren 1956 och 1972. KSLA Tidskrift nr 6: Lantbrukets energibalans - Energiflöden i Jord- och Skogsbruk. Sammanfattning från seminariunm 19/4 1995, Stockholm.

Leach,G. (1976): Energy and food production IPC Scientific and Technical Press, GB 

Olsson, P. (1976): Energianvändning i livsmedelsproduktionen SIK rapport 425 / STU rapport 69:1978 

Skogsberg, J. 1997. An Estimate of the Energy Used to Produce the Food Consumed in Sweden. Examensarbete 1994:4, Institutionen för Systemekologi, Stockholms Universitet

Svejgaard, M. & U. Kamne, 1997. Handbok Mat och Energi. Naturskyddsföreningen i samarbete med Studiefrämjandet.

Uhlin, H-E, (1996): Energiflöden i livsmedelskedjan. SNV report 4732 

Tiberg, Nils Prof, End-product management, Technical University of Luleå, pers. comm. Nils Tiberg about this  

 

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2013-01-06