A renewable energy technology could be ideal for pumping water where there is no mains electricity available, as a grid connection may be expensive and a diesel generator noisy and polluting.
Sizing a pump
The two main factors to consider when seeking a suitable pump are the flow rate – the amount of water that the pump will deliver, and the head – the height through which it will raise the water. These are related, as increasing the head will decrease the delivered flow. It’s important to minimise bends and other friction losses in pipework, as navigating these will require greater pressure, and as pressure and head are directly related, this effectively means a greater head.
Manufacturers’ technical data sheets will give the performance range of each pump, with graphs showing optimum combinations of flow and head. A pump sized properly to your needs will operate most efficiently. Suction pumps are limited to a depth of a few metres, so to draw water from a well or borehole, you’ll almost certainly need to lower in a submersible pump. Pumping wastewater or sewage necessitates one designed to handle drainage or effluent.
Small electric pumps for circulating water could cost tens of pounds, whilst those for drawing water from a well or borehole supply are likely to be a few hundred pounds. The main cost will be providing power to the pump, particularly when off-grid. Therefore, do first take all appropriate water-saving measures (such as spray-head fittings, mulches on plants to minimise water loss, etc) as these easily pay for themselves in the energy saved by reduced demand.
Off-grid electric pumps
Meeting a year-round water demand with a renewably-powered pump may require a combination of
PV panels and a
wind turbine, as this will balance energy production over the year. Sunshine and wind are naturally intermittent, so you may need some form of storage. Pumping water up to a tank (with demand then fed by gravity) during sunny or windy periods is more efficient than transferring the energy to batteries. If storing lots of water, you’ll need to balance the costs of a large tank (and supporting structure) against the costs of batteries (and their environmental impact and toxicity). An inexpensive control system can pump when needed, and otherwise divert power to batteries, giving extra backup facility.
The price of a small-scale renewable energy system will depend on the power and the maximum capacity needed. A very rough estimate is around £5 to £10 per installed watt. Siting generating equipment close to the pump minimises the cost and power loss incurred by cabling. As small turbines and PV panels usually produce power at 12 or 24 volts, a low-voltage pump would enable you to do without a costly inverter (for stepping up to 240 volts).
Mechanical pumps
For larger-scale pumping applications, you can avoid the losses in electrical systems by using mechanical power directly. See for example the question on our
wind power page about wind pumps, or the question on our
hydro power page about hydraulic ram pumps.