Energy efficiency for fish farming

The world in which we live is becoming increasingly power hungry and power has become more expensive, forcing fish farmers to become more efficient.  Cages don't use power directly and earth ponds only use power to intensify their grow out systems. However, both require hatcheries and if those hatcheries are recirculating aquaculture systems (RAS), these are dependent of power, and growout RAS and aquaponics systems are also completely dependent on electricity. For this electricity to be suitable for the operation of a commercial fish farm it needs to be reliable, stable and cost effective.
 
Grid power as supplied by national governments is normally the least expensive form of electricity that is available to businesses. Unfortunately, across Africa grid power is typically unstable and unreliable. This necessitates the use of alternative sources of power, either as the primary power and/or as the backup supply. Generators are typically used as the backup source of electricity and machines that incorporate an automatic transmission system (ATS) are ideal as there is minimal downtime between the grid power failing and the backup power initiating.  Within a hatchery or growout system for sensitive species, the delay between grid power failing and the generator starting, which is usually 20 seconds or so, may be unacceptable, in which case we typically run the power through a battery system before it gets to the critical equipment, thereby ensuring stable power supply to these vital components during the time between grid power failure and the ATS generator starting to supply power.
 
Solar generated power is becoming widespread across Africa with battery backup for nighttime power supply.  Such systems are stable, reliable and cost effective, but they do require a high installation cost.  When fish farmers use energy efficient systems there is a consequent saving both in the capital that is required to erect a solar system or in the usage cost of a grid based power supply. Lower power needs through increased efficiencies also requires a smaller backup generator, again saving the investor money.
 
What utilises energy within a RAS and what causes this to be high?
For now let's exclude potential heating costs as these are a subject on their own which may or may not be required and may or may not be supplied via electricity.
Within a RAS it is necessary to move water between the various components, including the fish tanks, mechanical filters and biological filters.  Water is heavy and it requires energy to lift it from the lowest point to the highest.  Also, water is dense, so it does not compress when travelling down pipes, quickly resulting in friction against the pipe walls if the pipe diameter is restricted relative to the velocity at which the water flows within the pump.
The other major power requirement is to stir the biofilter, replace oxygen and remove carbon dioxide from the system water, all of which is achieved by aeration provided from a blower.  Air compresses well so relatively narrow diameter pipes can be used for this purpose, but submerging the air to the desired release depth requires water to be displaced, and water is heavy.  This can therefore only be achieved by using the correct air supply system that simultaneously meets the aeration volume and delivery depth requirements, and such systems are driven by electricity.
 
So how then do we make our aquaculture systems more efficient? Economy of scale is certainly our friend in this regard and large systems give us choice from a wider selection of equipment that we can work with, enabling us to select optimal blowers and pumps that are highly efficient in terms of work done per unit power consumed. This is especially so when combined with low head designs, i.e. the pump only needs to lift the water a short vertical distance, and there is minimal friction between the suction point and the delivery point of the water pump. For example, the designs that Aquaculture Solutions currently works with have a vertical head of about 50 centimetres. We also ensure that the diameter of the pipes is wide enough and that pumping distances are as short as possible to minimise friction. Furthermore, we also understand the ranges of equipment that we use, so that we can select for the unit that offers the greatest efficiency in each situation. Sometimes this sweet spot requires water depth to be adapted in a particular design according to the energy consumption performance of the piece of equipment that has been selected.  This has enabled us to get the efficiency on large catfish systems down to around 2 700kg p.m. / kW of power demand, assuming that heating is either not required or provided by an alternative fuel type.  Surely, not many forms of agriculture are this energy efficient!
 
Being energy efficient as fish farmers is not only good for the planet that is also good for business.