Engineers know that there are all kinds of machine efficiency; Thermal efficiency, volumetric efficiency, mechanical efficiency etc. They're all different but efficiency is always the ratio of what comes out to what goes in. If the efficiency talked about isn't defined or at least described, the efficiency debate is a waste of time.
Four efficiencies come to mind relative to any wind machine, or any other type of so called renewable energy generator for that matter and there may be others:
- Energy efficiency i.e.the quantity of energy generated over its life divided by the sum quantity of energy required to make, transport, erect, maintain, dismantle, remove and recycle it.
- Financial efficiency i.e. the quantity of money earned during its life divided by the sum cost of manufacture, maintenance and decommissioning including all the subsidies that government throws at it and the discounted cashflow effect.
- Availability efficiency i.e. If the wind blows only half of the time, the availability efficiency is 50%. We need energy in the right quantities when we need it, not just when nature says we can have some.
- The one that isn't quantifiable, call it 'wellbeing' efficiency if you like i.e. the net good that results from having it, divided by the net downsides of amenity loss, adverse health effects, shipping hazards, unsightliness including the extra pylons and power lines and the effect on weather downwind.
There's another type of efficiency that has reared its head recently: Personal earnings efficiency i.e. where one's earnings are divided by the sum cost of education, employment, training etc. On that basis it seems that bankers are the most efficient with engineers well down the league table, although that may change if one takes into account the effects on industry, commerce and ordinary taxpayers.
John Halstead, Cranage, Cheshire