The castaways' electricity came from two renewable sources: wind and
hydro turbines. Energy was stored in a battery, and then converted
to 230 volts mains power by two inverters - one for normal use, and one
for backup. These are Trace
SW series inverters, with many sophisticated software functions built
in - including the ability to automatically start a generator (not used
on Taransay, where the generator was hand started if necessary).
The backup inverter was also used to feed surplus power to heaters and
prevent the battery from overcharging. There is a changeover switch
to allow easy transfer of the load between inverters and also (in the worst
case) to a backup generator. This switch was never needed.
The inverters synchronised with the generator automatically (when it was
started up), and use it to charge the battery when necessary.
The wind turbine is a 2.5kW 'Proven' with 48 volt output, on a 6.5 metre free standing tower (see bottom of page for detailed pics of tower). The tower comes complete with a Tirfor rope hoist for easy erection. There is a kit of spares for the turbine, including blades and springs. Heavy armoured cable takes the power down to the battery room. Adjacent to the battery room is a plant room, with the 'controller' for the wind turbine. This converts the 3 phase AC power form the wind turbine to DC, and monitors the battery voltage. If voltage indicates that the battery has reached its maximum optimum charging rate, then surplus current is diverted to a special (multiple element) immersion heater.
The battery comprises 8 quantity, 12 volt units, each with 230 amphour capacity (at the 20 hour rate), giving a total of 460 amphours at 48 volts nominal. This represents about 15-20kh units of usable electricity storage. Battery charge level is displayed as a % on an amphour meter panel, for easy interpretation by the castaways.
The hydro turbine is a 'stream engine'
from Energy Systems and Design
<http://www.microhydropower.com/> It has two nozzles which can be used to control water usage.
At present it has 440m of 5 inch pipe (MDPE which could be re-used with new fittings) and a mile of high voltage cable (6mm 3-core steel wire armoured). There is a 3-phase transformer at the battery, to step the voltage down to 48 volts for battery charging. The existing site has 30m head (drop from intake to outlet). It functions with between 1 and 8 litres of water per second, as available.
This turbine would supply all the electrical needs of a typical home, from a stream one mile away, producing up to 1kW charge rate into a 48 volt battery, (depending on the available water),
wind turbine tower details: