When we compare the efficiency of a labourer, we see that he has an
efficiency of about 1%-5.5% (depending on whether he uses arms, or a
combination of arms and legs). Internal combustion engines mostly have an
efficiency of about 20%, although large diesel engines, such as those used
to power ships, may have efficiencies of nearly 50%. Industrial electric
motors have efficiencies up to the low 90% range, before correcting for the
conversion efficiency of fuel to electricity of about 35%.
When we compare the costs of using
an internal combustion engine to a worker to perform work, we notice that an
engine can perform more work at a comparative cost. 1 liter of fossil fuel
burnt with an IC engine equals about 50 hands of workers operating for 24
hours or 275 arms and legs for 24 hours.
In addition, the combined work
capability of a human is also much lower than that of a machine. An average
human worker can provide work good for around 0,9 hp (2.3 MJ per hour) while
a machine (depending on the type and size) can provide for far greater
amounts of work. For example it takes more than one and a half hour of hard
labour to deliver only one kWh - which a small engine could deliver in less
than one hour while burning less than one litre of petroleum fuel. This
implies that a gang of 20 to 40 men will require a financial compensation
for their work at least equal to the required expended food calories (which
is at least 4 to 20 times higher). In most situations, the worker will also
want compensation for the lost time, which is easily 96 times greater per
day. Even if we assume the real wage cost for the human labour to be at US
$1.00/day, an energy cost is generated of about $4.00/kWh. Despite this
being a low wage for hard labour, even in some of the countries with the
lowest wages, it represents an energy cost that is significantly more
expensive than even exotic power sources such as solar photovoltaic panels
(and thus even more expensive when compared to wind energy harvesters or
luminescent solar concentrators). |