[Samuel1988 (OP)]

Evening all,

I have an allotment (in the UK an area used to grow food) and I am thinking of setting up an aquaponics system (which is where you grow vegetables in a media bed and raise fish for food in a closed loop system newbielink:http://en.wikipedia.org/wiki/Aquaponics [nonactive]) but the trouble is I have no access to electricity (to pump the water from the fish tank into the vegetable growing media bed). 

I stumbled across siphoning and was wondering if it would be possible to utilise this phenomenon to get around the need for a fish pump?
newbielink:http://en.wikipedia.org/wiki/Siphon [nonactive]

'While a simple siphon cannot output liquid at a level higher than the source reservoir, a more complicated device utilizing an airtight chamber at the crest and a system of automatic valves, may discharge liquid on an ongoing basis, at a level higher than the source reservoir, without outside pumping energy being added. It can accomplish this despite what initially appears to be a violation of conservation of energy because it can take advantage of the energy of a large volume of liquid dropping some distance, to raise and discharge a small volume of liquid above the source reservoir. Thus it might be said to "require" a large quantity of falling liquid to power the dispensing of a small quantity. Such a system typically operates in a cyclical or start/stop but ongoing and self-powered manner.'

Thank you for your help,

Samuel

[evan_au]

get around the need for a fish pump

Depending on the species of fish, you may need to pump air into the water to aerate it.

I think you will find that there are regulations about discharge of used water into streams, so you may need to use some biological filter beds to clean up the water before discharging it.

You should plan on keeping the system as closed-cycle as possible. You could use solar cells to provide input power to make up for losses in the system. If you have a nearby stream with a steady flow of water all year round, you can use a micro-hydro generator to produce some electricity.