Energy demand (D)
Investigate the following possibilities:
- shorter use of gas-fueled appliances, e.g. burning time of lamps,
- omitting certain appliances, e.g. radiant heater, second lamp,
- reduction to a partial-supply level that would probably make operation of the biogas plant
more worthwhile.
The aim of such considerations is to reduce the energy demand, but only to such an extent that it
does not diminish the degree of motivation for using biogas technology.
Energy supply - biogas production (P)
Examine/calculate the following options/ factors:
- the extent to which the useful biomass volume can be increased (better collecting methods,
use of dung from other livestock inventories, including more agricultural waste, night soil,
etc.), though any form of biomass that would unduly increase the necessary labor input
should be avoided;
- the extent to which prolonged retention times, i.e. a larger digester volume, would increase
the gas yield, e.g. the gas yield from cattle manure can be increased from roughly 200 1/kg
VS for an RT of 40 days to as much as 320 1/kg VS for an RT of 80-100 days;
- the extent to which the digesting temperature could be increased by modifying the
structure.
The aim of such measures is to determine the maximum biogas-production level that can be
achieved for a reasonable amount of work and an acceptable cost of investment.
If the gas production is still smaller than the gas demand (P < D), no biogas plant should be
installed.
If, however, the above measures succeed in fairly well matching up the production to the demand,
the plant must be resized according to subsection 4.3.
4.5 Sample calculations
Energy demand (D)
Basic data
8-person family, 2 meals per day. Present rate of energy consumption: 1.8 1 kerosene per day for
cooking and fueling 1 lamp (0.6 1 kerosene = 1 m³ biogas).
Desired degree of coverage with biogas
Cooking: all
Lighting: 2 lamps, 3 hours each
Cooling: 60 I refrigerator
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