What Hydropower

8/13/2019 What Hydropower

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DIFFERGROUP.COM | 29 May 2013

Takeaways

Small hydro projects must be standardised. As large scale hydropower projectsare custom-made with lots o engineering capacity going into them, small hydroprojects up to 2kW require standardised solutions in order to keep investmentcosts down and to become protable.

Low-head Kaplan and Cross ow technologies are preferable. For a majorroll-out o hydropower solutions, we believe we should aim or a lower-headsolution, and it is difficult to look past small versions o the classic designs, orexample kaplan and cross-ow. Kaplan design is very versatile, relatively cheaptechnology thanks to Chinese mass production, and as long as there is a lo-cal repair shop, it is difficult to beat such a setup. Moreover, cross-ow designseems versatile and good at small sites. This design is ound in several versions,and can sometimes close down parts o the turbine at low ow to increase e -ciency.

These designs eliminate much o the technology risk; they have some trackrecord even or kW-sized operations, have predictable maintenance require-ments and available spare parts. Empirical evidence even supports that localmaintenance is possible.

Competitive to solar home systems? In a rural electrication context, it is pos-

sible to get a very decent price per kWh or a hydropower system i there islimited civil works and small distance to end users/limited wiring. However, inproviding basic lighting and mobile charging or a scattered rural population andplaces without in rastructure, it is becoming increasingly difficult to competewith solar PV. Solar home systems (SHS) requires no civil works and barely anywiring, and given the LED revolution, these systems can provide a good servicelevel at below 10W/SHS, which is smaller than the smallest turbines.

Contents Takeaways 1

Introduction 2

Factors determining versatile technology 2

Available low-head technologies 4

What would we roll out? 5Appendix: Low-head technologies 8

Against the stream in developing coun-tries: Selecting versatile hydropowertechnology or rural roll-out


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2Against the stream in developing countries I N T R

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Introduction

Sustainable Energy or All has become a vision and aslogan or the UN-driven ambition o providing accessto reliable, clean electricity or those 1.3bn people glob-ally that do not have electricity today. Although many othe main barriers or achieving this are not on the tech-nology side, but rather on nance, structures, local andnational regulations and policies in general, nding theappropriate technology is still a critical step or makingrenewable energy available or the population.

Differs business idea is to develop projects that areindividually small, but that aggregated could be large ireplicated several times. As argued in some o our previ-ous analyses, the advantage o small-scale projects isthat they are relatively easy to implement compared tothe large scale projects; the investments are smaller, thegrid-connection costs are ar lower (and zero in case ooff-grid), the construction phase is much shorter and theplant is producing electricity much aster.

Our main geographic ocus areas are developing coun-tries in A rica and Asia. For some villages, solar homesystems might be the best solution, while or others located close to a river hydropower could be pre erable.What to choose depends on a variety o actors including

investment & operating costs, environmental conditions,reliability & stability o the technology, durability, user-

riendliness, sa ety etc.

This analysis ocuses on very small-scale hydropowertechnology, in the area 0-2 kW. Traditionally, hydropowerhas been developed in large scale, typically 10+ MWwhere each project has been engineered and tailored..This is not possible or small-scale projects as the engi-neering costs would have made the project too expen-sive. The technology going into small projects shouldthere ore be standardised to t various kinds o condi-tions in order to make replication in developing countriespossible.

The question is there ore how to choose and deploy aexible hydropower technology that would work in manydifferent local environments and river ow conditions,and suitable or a larger roll-out o very small systems.Are there any technologies that are more likely to suc-ceed than others? And are these competitive to otherrenewable alternatives, or instance solar home systems?

Factors determining versatile tech-

nologyWhich actors can determine whether a hydropowertechnology is stable, robust, affordable and reliableand is ultimately benecial or end users under varioustopographical and river-related conditions? We haveidentied 5 actors that we nd critical when deciding onhydropower technology in developing countries:

SizingRural electrication is about giving access to basic unc-tions or households during daily li e. A single non-elec-tried rural household relying on kerosene today wouldbe improved signicantly with only 2-3 LED lamps anda mobile charger. With new LED technology, this wouldimply a net demand or around 10W o power during 3-4peak hours in the evening. Adding a TV would take thedemand up to around 30W or simple DCTVs, while ACTVs could use anything rom 50 to 200W.

I we set demand to 50W per household and 5 hoursper day to reect some increased usage, there will be aneed or around 100kWh/household/year. This is verysmall or a hydropower turbine, and creates a possibiityto combine several households to purchase a system.

Given that the installation o hydropower will requirecivil works regardless o size, it is practical to scale thesystem somewhat more than to the minimum powerrequirements. Hence, we would expect to look at systemssized in the low kW range or a normal small village. Withdemand rom 10W to 100W per household, we wouldassume that a hydropower turbine with a net capacity o500-2000W could power up to 200 households.

Efficiency on variable owsRelevant developing countries are characterised byhaving tropical or sub-tropical weather with varying

precipitation over the year. The best technology shouldthere ore be efficient at various and less predictableows.

All larger hydropower turbines are custom-made toextract every bit o efficiency gain possible. Smallerturbines will have lower efficiencies per se, but as engi-neering expertise is expensive or smaller systems; minorcustomisation in a small rural context will have to bedone on the spot, i at all.

In a varying ow context, maximum efficiency, efficiencyduration (efficiency curve or lower ows) and cut-offows are all important eatures, and the pre erred solu-


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3Against the stream in developing countriestion should likely provide acceptable efficiency also orows below 50% o the design specication require-

ments.

LocationThere are several arguments why small hydropowertechnology should be installed close to the end-user.First, it is important to reduce the transmission distanceto minimise the cost o equipment and labour, and tolimit transmission losses. Lowering the amount o equip-ment also lowers transport cost and limits the number oparts that can break.

Second, large-scale hydropower equipment is ofen

heavy and rmly mounted, and is difficult to remove.However, as we move down to kW- and W-scale, itbecomes increasingly simple to carry away essentialequipment. We there ore assume that the best option isto ocus on hydropower equipment that can be installedcloser to the village at the expense o hydraulic per ec-tion. A power plant close to the village will ease main-tenance, decrease likelihood o thef and reduce cost oauxiliary equipment to electri y the village. It can alsoeven be turned off and locked in at night.

Villages are not likely to have a large-head hydropowersite close. It would also be impractical to install a largeturbine where there is bustling marine activity. Hence,there could be terrain constraints making low-drop andlow-ow equipment more attractive. A pre erable small-scale hydropower technology should there ore be smallenough to be installed close to the village.

Investment costs and on-site engineeringOne hurdle or installing hydropower technology indeveloping countries is the up ront investment costs.Although nancial support rom developed countriesand/or its local or national authorities could contribute,low up- ront cost is a key requirement in rural electri-cation. Whereas a community might have satis actoryliquidity over time, there is usually limited capacity withinlocal banking system to allow or investments even withaggressive payback schemes.

In Kenya, Differ ound evidence that people consistentlypre erred slightly cheaper petrol- over diesel generatorsets (gensets) because the main barrier was the invest-ment, not the capacity o the system. At the same time,they were ully aware that petrol would be more expen-sive than diesel throughout the system li etime. Thisshows a pre erence to swap high returns or low invest-

ment cost.

In a report recently issued by Lahimer et al. lookingat kW-scale hydro in a developing context, one o the

ndings was that the suggested high-quality PVC pipingwas ofen replaced by worse-quality HDPE or pure pricereasons. Hence, not only will rural societies look more atinvestment cost than quality, but that they are probablywilling to sacrice reliability or cost, and rather repairwhen damaged. This could be expensive in the long run,but would still be pre erred i the investment is reduced.

Paish et al. investigated Vietnamese markets or small-scale hydropower, and ound that the largest marketcomprised low-quality illegally imported small Chinesesets (propeller systems). These were supplied at cost o20-30 USD or a 100W system, but would also require40-60 USD worth o cables, tubing and ancillary equip-ment to work. Locals are able to replace broken bearingsin local workshops, and could seemingly live with theuncertainty.

The system should there ore be possible to install quicklyat a new location. This carries on-site and engineeringcost. Such know-how is expensive, imported knowledgenot ound in rural environments. Anything installed interrain will require some adaption to local conditions. Itis there ore important that construction o in rastructuresuch as diversion and a simple power house can be done

largely by locals.

Differ recognises that it is essential to keep investmentcost down. We there ore try to provide nancial solutions

or end-users by taking a majority o the investment cost,leaving the monthly expenses or the end-users at thelevel as prior to the electrication.

Operation & maintenanceOnce the hydropower plant is operational, it should beoperated by a (trained) local. This is good or cost andgood or community development. It is probably also

the best and most reasonable protection against thef,because i local people onsite have incomes dependingon the system, it will be guarded well. Also, other localswill be more reluctant to steal rom their own.

Most likely, rural villages and households can acceptthat the efficiency o the hydropower plant is reducedperhaps as much as 10-20% as long as there is somepower and ordinary maintenance can be done using locallabour. The power plant could even be turned off both atnight and during idle hours during the day to allow theriver to be utilised differently. The system li etime is still

important, but not at the expense o increased invest-ment cost. This avours compact, moveable structures,

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4Against the stream in developing countriesand dis avours large constructs, complex technology andequipment that is difficult to replace.

It is important that the system will work, and that it canbe made to work i not. Maintenance requirements are a

unction o breakage, debris and normal wear. The classicturbine types are virtually maintenance ree, particularlyi the thrash rack has been designed cleverly. In the casethere is maintenance, this could be bearing changes,penstock breakage, damage to concrete structures and amultitude o small incidents.

Environmental impactsWhen developing hydropower in rural areas, it is

important to bear in mind that the state o the localin rastructure and challenging terrain make rivers themain channel or transportation. It also provides water

or irrigation. Moreover, animals live in and around riv-ers. In the Western world, particularly in the North, largeanimals do not live in rivers. Damming up rivers will leadto other challenges that need to be solved, and smaller,non-permanent solutions might be pre erred.

Because water has been utilized in rural communities orthousands o years, it is not uncommon to nd existingirrigation and man-made river diversions in many ruralsettings. These could divert water or agriculture andmills, provide transport or simply lead water closer to thevillages. Small lower-head technology could ofen be t-ted somewhere along these diversions.

Available low-head technologies

The main capacity or hydropower today is dominatedby mid- and high head installations. On the turbineside, Pelton (impulse) and Francis (reaction) turbinesconstitute somewhere between 70% and 80% o theworld market, counted as installed capacity, and willundoubtedly continue to have a prominent position inthe hydropower markets also in the uture. The technol-ogy is tailored to the site to become efficient, reliable andvirtually maintenance ree.

The gross energy P (Watt) rom a conventional turbinecan be expressed as a relationship mainly between thehead (H, meter) and ow (Q, m3/second), efficiency ( ), liquid density ( , kg/m3) and gravity (g, 9.81 m/s 2).Following this relationship, 100 litres/second at a head o5m give the same energy as 5 litres at 100 meter head.Hence, low-head turbines will have to capture morewater than high-head.

Q H g P =

Figure 1 shows an overview o the number o opera-tional hydropower turbines and installed MW across theglobe. The plants have been grouped roughly accordingto resemblance to technology, specically the classical

Kaplan/propeller, Pelton and Francis (KPF) turbines. The most obvious trend is the importance o Kaplan,Pelton and Francis turbines or MW-scale technologies,with Francis-style turbines as main contributor. Notethat Kaplan turbines are low-head turbines, commonly

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5Against the stream in developing countriesused in rivers. Traditionally, these turbines have beengreater in size, but being a very mature technology, this

is typically a market where Chinese equipment can bepurchased or low prices.

Large-scale, high-head hydropower is one o the mostefficient orms o electricity generation available, withover 90% o energy converted. This very high efficiencypresumes that the water ows through the turbine atdesigned ow at the correct angle. When size decreasesand customisation disappears, the efficiency drops. It isdifficult to generalise, but it should be relatively commonto see efficiencies around 50% or very small turbines.

The market or other turbines, is around 1% o thelarge-scale market, but seemingly comprises around30% o the market or small turbines (


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6Against the stream in developing countries WH A T W

O U L D WE R

O L L

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7Against the stream in developing countriesturbine, generator and draf. The better design, the lessmaintenance there will be on the electrical and mechani-

cal equipment.

Whereas we have just briey assessed small high-headsolutions, we realise that these are to be pre erred inmost situations where the necessary head is avail-able. There are also good, reasonably priced Peltric sets(Pelton turbine with electric generator) available on themarket. Simply put, doubling the head halves the waterow or the same amount o power. Hence, moving rom10 to 100 meters o head will lead to efficient generationat low equipment cost where the distance to end userspermits it.

For a major roll-out o hydropower solutions, we believewe should aim or a lower-head solution. Here, it is di -cult to look past small versions o the classic designs, orexample kaplan and cross-ow. These eliminate mucho the technology risk; they have some track record even

or kW-sized operations, have predictable maintenancerequirements and available spare parts. Empirical evi-dence even supports that local maintenance is possible.

It is difficult to set up the total budget due to the largedifferences in civil and auxiliary work. Generally speak-ing, small systems are cheaper than large, and easier to

transport. Higher drop will reduce size o turbine, andutilising existing in rastructure can lower cost substan-

tially. Finally, mass production lowers price. We are airlycondent that in most cases, the small Kaplans and

Crosstric systems will imply a sensible investment.

It is difficult to directly compare price o hydropower toother renewable technologies on a general basis. How-ever, in a rural electrication context, it is possible to geta very decent price per kWh or a hydropower system ithere is limited civil works and small distance to end us-ers/limited wiring. Hence, or a village close to a river, hy-dropower should be relatively competitive. It also offersadvantages i there is a demand to power larger machin-ery, as it is easily scaleable (limited by the river ow).

We lack deep insights into wind power, but judging romthe prices we have seen, small mass-produced hydro-power systems should so ar have an edge on smallwindmills, which is still a relatively new technology. It alsoprovides a much more predictable source o power.

However, in providing basic lighting and mobile chargingor a scattered rural population and places without in ra-

structure, it is becoming increasingly difficult to competewith solar PV. Solar home systems (SHS) requires no civilworks and barely any wiring, and given the LED revolu-tion, these systems can provide a good service levelat below 10W/SHS, which is smaller than the smallest

turbines.

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8Against the stream in developing countries

The section below comprises several low-head hydro-power solutions. The list is not exhaustive in any way, butserves as an illustration o the many different ideas thatcan produce power rom moving water. We are ocusingon turbines, but most, i not all, these systems will requirea gearbox and a generator to produce electricity.

Low-head turbinesIn terms o traditional low-headdesigns, small Kaplan generatorsare commonly seen in low-headkW-sized hydropower generation.The design consists o an axialpropeller inside a tube, and canrotate vertically or horizontally.Vertical turbines are most

common, particularly or kW-scale. Classic Kaplan designwould require the construction o intake, thrash rack andtail race. The Kaplan turbine can deliver at high efficien-cies even at low head, and work well at 2-5m head,meaning that the diversion is usually minimal. Propellerturbines are simplied Kaplan turbines without the abilityto adjust the blades.

Chinese manu acturers deliver small Kaplan kits withgenerator allowing or relatively simple solutions orkW-sized hydro, but ofen at poor quality. Also interest-ing, Nepal Hydro Electric has developed a small 1200Wpropeller turbine that works on around 3m o head.

Several designs o cross-ow turbines are applicableunder low-head conditions. A classic cross-ow turbine

uses gravity to rotate on ahorizontal axis. Water owsthrough the rotating cylinderwheel, generating 2/3 o the

power on entry and the remainderon exit. Cross-ow turbines areslightly less efficient than classichigher-head turbines, but

maintain satis actory generation efficiency as ow lowers.A cross-ow turbine will require a diversion and a thrashrack to work efficiently. The equipment in itsel is relative-ly comprehensible in size.

Cross-ow turbines have been around or many yearsand exist in several designs. In more recent inventions, USbased Natel offers a derivative o the cross-ow designcalled the hydroEngine, working with a head o 3-5m, thatso ar caters mostly or the mini-power segment around50-500kW. This turbine has blades mounted on a belt

instead o the classic cylinder design. On a low-kW scale,Kathmandu Metal Industry has developed a Crosstric Set a small version o the cross-ow turbine, or generationbetween 100 and 5000W.

The classic Archimedes screw turbine is a classic turbine that isonly used under low-headconditions. It consists o arelatively large helical structureinside a tube. Water ows throughparts o the helix and requires a

ew metres o drop and a smalldiversion to work. This has been known technology or along time, and can also be used as a pump i reversed.The large structure makes it less vulnerable to debris andthe low pressure and open design also makes it relatively

riendly even or larger sh. I the turbine is protected bya proper thrash rack, it can also be installed in lightweightplastic versions easing installation. It would require somecivil works. The screw structure is relatively large, but canbe built in light materials so that transport is mainly aquestion o volume, the weight is comprehensible.

Water mills or water wheels areofen installed near ows to grindgrain, and can easily be convertedto small hydropower with a dropo 3-5m, produce kW-rangepower where grinding require-ments are served in other ways. Ithe wheel is in place, there is only

need or a gearbox and a generator, making this optionvery cheap i available. I not, efficiency and cost couldmake other solutions more attractive. Zagoni (2009)investigates improved water wheels or small hydropowergeneration.

A quick look at high-drop turbinesFrancis turbines are high-efficient,high-head turbines. They arereaction turbines; the waterpressure changes as the water ispressed through the turbine. Theturbine is encased so that allwater is pressed through thesnail-like shape o the turbine.

The Francis turbine is used or head rom 20 to 700m,and is a very popular design due to its efficiency o above

90%. However, the turbine efficiency rapidly drops orow under the designed level.

Appendix: Low-head technologies


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9Against the stream in developing countriesPelton turbines are also high-efficient, high-head turbines. They

are impulse turbines, extractingenergy rom moving water hittingturbine. The turbine is open, anddesigned to capture the water jetsas efficiently as possible. Peltonwheels are installed with heads

rom 15 to 1800m, and are also very popular and highlyefficient (around 90% or large-scale versions). Peltonwheels remain very efficient or lower ows.

No-drop kinetic turbinesIn rivers and tidal streams where there is signicantmovement o water, but no drop, hydrokinetic equip-ment can be utilised. Power rom hydrokinetic turbines isgenerally expressed as a unction o swept area (A, m 2),velocity o medium (v 3, m/s), efficiency ( ) and liquiddensity ( , kg/m3). This is the same relationship as used

or wind turbines.3

21)( = AW P

Several ideas or hydrokineticcross-ow turbines or cross-axisturbines exist, but many o theseturbines are still under prototyp-

ing or in early production. Theseturbines have been developedwith an eye on the Darrieus designwind turbines, and consist o a set

o blades on a vertically rotating cylinder construction.The turbine is submerged and rotates slowly at speeds1-2x the speed o water, meaning sh can sa ely passthrough them. Whereas the turbine rotation speed makesblocking less likely, large pieces o debris like a log couldeasily jam the system. The turbine must also be protected

rom rotating into the riverbed in the dry seasons.

Most designs are attached to a oatation device or ashore mounted rod. Hydrokinetic turbines see efficiencies

rom 20 to 60%, and the most efficient versions are duct-ed. There is theoretically limited civil engineering beyondthe oater, mount or anchor, as there is no diversion andno penstock. The picture shows the Gorlov helical turbine.

Hydrokinetic axial turbines arevariations o horizontally rotatingpropellers that can be submergedin water. These can be mountedon the riverbed, on oaters, oron a shore mounted rod. Mount-ing can be either square or atan angle. These propellers have

empirically measured system efficiencies rom 12% to50%. The most efficient versions are ducted models, the

least efficient are the open solutions that can withstandthe most thrash. Rotation is slow, and turbines havebeen known to be covered in seaweed, leading to still-inconclusive research on banana-shaped blades. Severalon-turbine thrash protection devices have been tried out.Freely moving propellers in rivers must be installed sothat it does not harm wildli e.

This list is ar rom conclusive. There are many newinventions including uttervanes, hydroplane blades,cycloidic turbines and fan/doughnut shaped turbines .However, many o these are still in a reasonably earlystage o development.

Figure 2: Efficiencies for traditional hydropower

The gure shows theoretical efficiencies plotted againstow. In a small hydro context, using small waterways andlimited dams, it is likely that ow will vary signicantlyover the year. It would there ore be important to have aturbine that would work satis actory also or lower ow,illustrated here by the curves towards the lef o thegure. Whereas these plots can vary signicantly, it showsthat whereas a Francis turbine is one o the most efficientdesigns there is, this only remains true i it is alwaysrunning at design ow. We have also included simplepropellers, which are simple Kaplan turbines without the

ability to change the pitch o the blades, showing howsimpler versions o this turbine might underper orm.

Pelton runners, proper Kaplan turbines, Archimedes andcross-ow turbines are relatively efficient at mid ows.For small cross-ow turbines, it is also possible to designthe turbine to close parts o the roller to increase e -ciency or lower ows.

We have been unable to nd good data or hydrokineticturbines, but see that quoted efficiencies range rom 10%to 60%.


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