32 ReNew Issue 92 July-September 2005 email: ata@ata.org.au WWW: http://www.ata.org.au/

W hile there are not manyhydro turbine manufacturersin Australia, there is still an

excellent range of turbines available inthe under-20 kilowatt class, in both ACand DC output models.

Why buy a micro-hydro?The potential energy stored in watersituated above sea level is considerable.You just need to look at the deep poolsoften found below large waterfalls orhow the rocks in a creek are wornsmooth, to be awed by its power.

Harnessing the power of water is byno means a new concept. Waterwheelshave been used for centuries for mill-ing, grinding and other types of mechan-ical work. Turbines came in to play toreplace waterwheels and to power elec-tric generators in remote areas in themid 19th century.

Nowadays, water turbines are in-creasingly being used in developingcountries due to their relatively lowcost, comparatively simple mainte-nance, clean renewable nature and theabundance of suitable hydro sites. Withenvironmental awareness increasing,the push is away from big centralisedpower sources and back towards ener-gy systems that use local natural resourc-es.

All that aside, if you have a remoteproperty and need to supply reliablepower, then in some cases a micro-hydro turbine will be the best option.

Turbine types and sitingThe basic layout of most micro-hydrosystems involves a turbine, mounted atsome low point on the creek or river,being fed by pipes running from a much

higher point in the water source. Theweight of water in the pipes causes arelatively high water pressure at the tur-bine end of the pipe, thus providing ameans of driving the turbine. To get anidea of the forces involved, try aimingthe jet from an ordinary garden hose atyour hand. You will feel the force of thewater striking your hand and being de-flected. This is how many turbineswork, in a round-about way.

Flow rate (in litres per second ofwater flowing through the unit) andhead (the vertical height that the waterfalls) are the two major factors govern-ing the amount of power available froma site. Several different types of turbineshave been developed to cope with a va-riety of situations, such as a high headwith a low flow rate, or a low head witha high flow rate.

The turbines available generally fall

into one of two categories—impulseturbines or reaction turbines.

Impulse turbinesExamples of impulse turbines includePelton, Turgo and Banki Crossflow.The water is directed through one ormore nozzles and onto the ‘runner’ (tur-bine wheel). This rotates above the levelof the water source, and the water fallsbelow the turbine to the tail water, usu-ally flowing from there back into thecreek.

This turbine won’t function sub-merged in water, so it must be situatedabove the maximum flood level that thewater source may reach. This oftenleads to significant loss of head, whichis one reason why this sort of turbineisn’t used in low-head applications.

The Pelton wheel is probably the bestknown and most commonly used of the

Tap your onsite power resourcesThe last time we looked at the micro-hydro market was in ReNew 72, so wethought it was about time we looked at them again to see what’s new

The Platypus Power range is available in DC

battery charging and AC output designs. Here

you can see a DC output M1-125 unit, as well as

the stainless steel hybrid runner (right).

[Buyer’s guide]

WWW: http://www.ata.org.au/ email: ata@ata.org.au Issue 92 July-September 2005 ReNew 33

impulse turbines. The Turgo is verysimilar, but has a slightly higher effi-ciency. Both types run at relatively highspeeds, allowing them to be directlycoupled to a high-speed generator, butTurgos will spin at a greater rpm for thesame size jet diameter.

Turgo turbines can also be arrangedto spin at half speed, allowing efficientoperation at low heads.

The Crossflow turbine is somewhatdifferent. It uses a cylindrical type ro-tor through which the water passestwice. It can be used with virtually anyhead (1 to 200 metres). These systemsare good for water pumping, and thePlanetary Power machines are some-times used this way.

Reaction turbinesThis class of turbine includes the Fran-cis and Kaplan types. The blades onthese turbines are submerged in thewater itself. As the water flows overthem, lift forces are created, similar tothe way lift is generated by the wings ofan aircraft. These forces cause the tur-bine blades to rotate. The water exitingthe turbine is discharged via a draft tubewhich creates a negative pressure on thatside of the turbine. This means that thefall of water after the turbine can alsobe included in the net head, which isvery significant if there is not a lot ofhead to begin with. The Francis tur-bines are the most efficient of the reac-tion turbines but are generally moreexpensive.

A novel form of reaction turbine canbe seen on the next page—the Aquairgenerator is designed to be fully sub-merged in a water flow to generate elec-tricity.

Reaction turbines tend to be biggerand are more expensive than impulsetypes, so if you’re lucky enough to havea choice between a high head, low flowsite or a low head, high flow site it’sbest economically to opt for the former.

[Buyer’s guide]

Other things to consider if you’rethinking about installing a micro-hydro system are generators, load regu-lation, civil works and electrical work.

AC or DC?There are two common systems availa-ble—DC, or battery-charging turbines,and AC turbines.

The DC turbines are designed to feedtheir power into a battery bank for useat a later stage. These are well suited tosites that may not flow all of the time,but do have regular or seasonal flows.Some installations use micro-hydro tur-bines to provide power during the win-ter months, when water is mostabundant, and rely on other powersources, such as the sun, during the hot-ter, dry part of the year.

If you have a good flow of water allyear round, then an AC turbine may bethe best option. These produce powerat 240 volts AC, just like mains power,so you can draw power from the tur-bine directly, without the need for bat-teries, inverters and the like. Anexcellent example of this type of systemis the 13kW turbine at Stevensons Falls,near Marysville in Victoria. This tur-

bine supplies power directly to lightsused to illuminate the falls at night.

The disadvantage with this system isthat you are limited in the amount ofinstantaneous power you can draw fromthe turbine. For example, if you have a1.2kW system, then that is the mostpower you can draw from the turbine.Loads larger than this will need to bepowered from some other source. Youcan, of course, use an AC turbine tocharge a battery bank, just like a DCturbine.

Power controlLoad regulation of most turbines usu-ally occurs by ‘dumping’ the excess en-ergy into some form of load. This isoften a series of light globes or heatingelements, such as in a hot water system.Regulation is required to avoid largevoltage fluctuations, and to keep theturbine running at a near-constantspeed. There are several types of regu-lation systems, from simple on/offswitching to variable load dumping,where the load dump connected to theturbine varies inversely proportionateto the main load.

As an example, if you have a 1kW tur-

A new player in the micro-

hydro market, EcoInnovation

from New Zealand, makes

this turbine that uses a

Turgo runner to drive a

Fisher & Paykel washing

machine motor. Power output

is up to 1kW.

34 ReNew Issue 92 July-September 2005 email: ata@ata.org.au WWW: http://www.ata.org.au/

bine, and you are using 200 watts fromit, then the other 800 watts will be fedinto the load dump. If your load increas-es to 650 watts, then the excess 350 wattswill be dumped. This system can beachieved in several ways, but a com-monly used method is to switch in loaddump elements of varying sizes in theright combinations to form a load dumpof the correct size.

A novel approach to regulation hasbeen taken by Tamar. It has developed awater economiser that varies the waterflow through the turbine, depending onthe load. This reduces the power pro-duced by the turbine, reducing the pow-er dissipated by the dump loads. Thissystem suits sites where the flow is in-termittent or where water storage in aweir or dam is used.

Tamar has another device, ‘AutomaticStart’ which actually stops the turbineif the load falls below 40 watts. When aload of 40 watts or greater is applied themachine automatically starts in a fewseconds. It is designed to help the sys-tem cope with intermittent power re-quirements such as a refrigerator.

Civil worksThis refers to the other parts of the sys-tem, including head (penstock) and tail(draft) pipes, dams and other parts of

the water supply system. Civil worksmay involve as little as a couple of hun-dred metres of plastic piping with ascreen filter at the collection point,right through to construction of a largeweir or dam, along with the other asso-ciated parts. These include trash racks,which deflect solid material from en-tering the feed pipe, control valves, andeven flood control systems. Be sure notto underestimate the effect the civilworks will have on the cost of the sys-tem—it can become very expensive ifyou can’t do it yourself.

Some councils charge a fee for watertaken from a stream, even if it is returnedat a later stage. Check with your coun-cil before planning a system.

Buying a turbineThis can be a complex process, as youhave to determine head, flow rate at theselected site, ease of access, type andamount of power required from theturbine and possible environmentaldisruption to the area. Remember thatto minimise the effect you have on thelocal ecosystem, you must not divertall of the water from the source to runthrough your system. If you are unsure,set yourself a limit of, say, 50 per cent ofthe total flow at the lowest flow rateperiod, usually during summer or thedry season.

Once you have these details workedout, you can then start thinking aboutthe type of turbine you want. See thetable at the end of this article for theturbine most suitable for your require-ments. If more than one turbine seemsideal, then you will have to look at otherfactors, including price and mainte-nance requirements, though you shouldalso look at these initially. It all dependson your priorities.

Other turbinesWe have covered the most common

commercially available turbine types,but there are others you may want toconsider. These are mainly used in di-rect flow applications, such as water-wheels.

Waterwheels are usually undershot,where the lower paddles of the wheelare simply placed in the flow of a riveror stream, or an overshot wheel, wherewaterflow is directed from the sourceto the top of the wheel. The weight ofthe water in the wheel ‘buckets’ pullsthe wheel around.

Floods can be a problem for under-shot wheels, as they need to be placedin the water source directly, but over-shot wheels can be located in safer are-as and have water diverted to them.

While there are no commercial man-ufacturers of waterwheels that weknow of, they are quite a simple de-vice to make. There have been severaldesigns for waterwheels published inprevious issues of ReNew. If you are ofthe do-it-yourself persuasion and havea useful creek with good flow but lit-tle head (common on small proper-ties), then a waterwheel may be the bestoption—though for electricity gener-ation some form of gearing up is need-ed. ✲✲✲✲✲

[Buyer’s guide]

Rainbow Power Company’s 300 watt

Pelton turbine.

The Aquair UW is designed to be

submerged in a fast flowing river or

stream and will generate up to 100 watts.

WWW: http://www.ata.org.au/ email: ata@ata.org.au Issue 92 July-September 2005 ReNew 35

[Buyer’s guide]