How effec(ve is the Archimedes Screw as a source of hydropower?

This project will be analysing the effec5veness of the Archimedes Screw by considering the environmental, economic and social effects as well as its system efficiency compared to other types of hydropower. The Archimedes Screw is introduced with a brief descrip5on of its history and how it works. A case study of the Osney Lock Hydro is used to present the factors that effect the efficiency of the screw as well as the effects it has. Other types of hydro turbines are introduced and compared to the Archimedes Screw in order to come to a conclusion on how efficient the Archimedes Screw is compared to other sources of hydropower.

The Archimedes Screw design that is used today for energy produc5on wasn’t introduced un5l recently. Its main advantage over other sources of hydropower is the lack of effect on the flow of the river and fish. The screw turbine was patented by William Moerscher in 1916 but the idea of using it 1

as a source of hydropower was first suggested Claude Louis Marie Henri Navier in 1819. 2

It is one of the newest sources of hydropower, most installa5ons done in the past 10 years. 3

Hydropower is the most used and most efficient source of renewable energy. During 2015, 16.6% of all the energy produced and 70% of renewable energy worldwide was hydropower. Renewable 4

energy is becoming more and more important recently with problems like global warming and pollu5on, it is the only solu5on to protect the future of the environment. Addi5onally, with supplies of fossil fuels con5nuously decreasing renewable energy presents a sustainable source of energy for the future.

History

The Archimedes Screw was invented by Archimedes, a Greek scien5st, between 287 B.C. and 212 B.C. Yet he didn’t men5on the inven5on in his works at the 5me. Detailed informa5on of the screw was included in the De Architectura wri\en by Vitruvius between 30 B.C. and 15 B.C. which allowed the screw to be recognised and used in the future. The screw described was constructed from a tree trunk and other wooden pieces covered in liquid pitch to seal it. 5

It was originally used to transport water upwards as a manual pump, first turned by hand then later by use of a motor. It is used to irrigate fields, drain ships, mines and land as well as the design being used in many machines s5ll today including snow blowers, power drills and crop harvesters. 6

While being used as a pump the screw was set at a steeper angle, between 20° and 40°, compared to its set angle as an energy generator. The water is scooped from the bo\om into the troughs as the screw rotates. Due to fric5on the water follows the direc5on of screw rota5on but is stopped by gravity. Any water that escapes between the blades and centre are caught in the compartment

h\p://greenbugenergy.com/sp_faq/what-are-the-benefits-of-using-archimedes-screws-over-other-1

technologies [accessed 18:02 26/08/28]

h\ps://www.google.com/patents/US1434138 [accessed 18:05 26/08/17]2

h\p://www.renewablesfirst.co.uk/hydropower/hydropower-learning-centre/archimedean-screw-hydro-3

turbine/ [accessed 22:06 20/08/17]

Renewables 2016 Global Status Report pg 18,32 [accessed 22:13 30/08/17]4

The Turn of the Screw: Op5mal Design of an Archimedes Screw pg.725

h\p://www.sogschools.com/inven5ons/history/archimedes_screw_history/14/ [ accessed 14:04, 10/08/17] 6

bellow. The con5nuous turning of the screw eventually transports the water to the top and out of 7

the screw. The water level doesn’t affect the efficiency as long as the bo\om is par5ally submerged. 8

How it works

9

The Archimedes Screw turbine produces electricity based on the same principle as many other hydropower sources, water flows through the turbine causing it to rotate; the rota5on is then converted to electrical energy by a generator. The screw turbine is set in rivers at an angle, with a 10

sufficient height difference between top and bo\om, as the rota5on is produced by the velocity of the water as well as the pressure. Most of the weight of the water, which is the ver5cal component, acts on the cover around the screw, so it has a negligible effect on the rota5on. 11

A part the torque that turns the screw is produced by hydrosta5c force. Hydrosta5c force is created by the difference in height, therefore difference in pressure, of the buckets (compartments) in the screw. The force acts on both sides of the blade but the higher bucket has greater pressure, so there is more hydrosta5c force and the resultant force is downward. The velocity of the water from the river creates the remaining rota5on as it flow through the turbine. 12

Osney Lock Hydro

Osney Lock is an Archimedes Screw hydropower sta5on in Oxford on the Thames River. Its development started in 2002, but it wasn’t built un5l 2013 and energy produc5on started in May 2015. The project is the first community owned hydropower sta5on built on the Thames River. As

h\ps://www.historyanswers.co.uk/inven5ons/ba\ering-rams/ [accessed 15:00, 10/08/17]7

Manual for Archimedean Screw Pump pg.12-138

h\p://www.sciencedirect.com/science/ar5cle/pii/S0960148116302282 [accessed 17:38 07/05/17]9

h\ps://www.renewablesfirst.co.uk/hydropower/hydropower-learning-centre/archimedean-screw-hydro-10

turbine/ [accessed 17:28, 07/05/17]

Analysing the performance of the Archimedes screw turbine within 5dal range technologies, pg.5411

Analysing the performance of the Archimedes screw turbine within 5dal range technologies, pg.54,5512

well as providing green energy, thus reducing the carbon footprint of the area, the project aims to fund other environmental ventures in the community from its surplus income. 13

The 49kW hydropower scheme is built on a small island, one of only a few loca5ons in Oxford suitable for a hydropower sta5on. There are also solar panels on the roof of the building housing the screw to produce addi5onal energy. The project was set as an ‘Industrial and Provident Society for the Benefit of the Community’, now known as a registered society and works alongside West Oxford Community Renewables and Low Carbon West Oxford to help reduce the carbon emission in the area by 80% before 2050. 14

Water flow

This is one of the most important factors, without the correct water flow, whether it’s too high or low, the efficiency of the turbine is dras5cally reduced. The top of the screw is placed at a set level in the river based on the normal water level, so low water levels cause less water to enter the screw. Less water means there is a smaller force ac5ng on the screw so the rota5on speed decreases and less energy is produced. If it falls too low the screw stops altogether. Alterna5vely, when the water level is too high, water is let out of the side-track, which is required to be installed in screw turbines, due to the risk of flooding. This allows a majority of the water to bypass the screw, so the pressure on the screw reduces, overall having the same effect as a low water level. If the bo\om of the screw is submerged completely, the water in the lower-level area of the river could hinder the rota5on of the screw. 15

The velocity of the water generally changes with the water level. As the water level increases the resistance increases in propor5on to the surface area of water touching the banks. However the resistance to volume ra5o decreases because the contact area doesn’t increase as much as the water volume. The efficiency of the screw is be\er if the speed of the screw rota5on is comparable to the 16

velocity of the water flow. Some Archimedes Screws are now designed to have a variable speed that can increase or decrease rota5on to produce energy the most efficiently. The variable-speed 17

screw at Osney Lock increases the energy genera5on by 15-20% and could also decrease sound produced at the site which is already minimal due to soundproofing. Considering the efficiency of 18

energy genera5on is already high at around 70% and increase makes it a very efficient source of hydropower. Variable-speed turbines are also used with some other types of hydropower, a Francis 19

h\p://www.osneylockhydro.co.uk/about-us/ [accessed 9:58 27/08/17]13

Osney Lock Hydro Offer Document pg.614

Archimedes Screws For Microhydro Power Genera5on pg.515

h\ps://www.quora.com/Why-does-a-rivers-velocity-increase-at-higher-water-levels [accessed 13:22 16

27/08/17]

h\ps://www.renewablesfirst.co.uk/hydropower/hydropower-learning-centre/archimedean-screw-hydro-17

turbine/ [accessed 20:19, 15/08/17]

h\p://test.osneylockhydro.co.uk/now-onto-the-good-bit/ [accessed 18:21 28/08/17]18

h\p://www.renewablesfirst.co.uk/hydropower/hydropower-learning-centre/archimedean-screw-hydro-19

turbine/ [accessed 19:08 30/08/17]

turbine, which is a reac5on turbine like the Archimedes Screw, can have an efficiency increase of between 3%-22% depending on the head design. 20

The main cause in varying water levels is the weather. The effects of the weather can be forecasted and measured at gauging sta5ons along the river. In the case of Osney Lock, there is gauging sta5on just below the Archimedes Screw as well as further up the Thames River at Farmoor. However the 21

data from Farmoor can be inaccurate for use at Osney Lock as a result of the distance between the loca5ons.

The water level at Osney Lock gauging sta5on has varied between -0.312m and 0.188m in the last 15 years. There are nega5ve water levels because when the gauging sta5on is installed a default water level is set at 0 so the readings aren’t affected by river bed erosion. 22

Month Max (m) Min (m)

Jan 0.101 -0.051

Feb 0.226 -0.086

Mar 0.206 -0.092

Apr 0.177 -0.053

May 0.12 -0.056

Jun 0.12 -0.028

Jul 0.075 -0.107

Aug 0.079 -0.110

Sep 0.071 -0.074

Oct 0.094 -0.102

Nov 0.098 -0.051

h\ps://revistas.unal.edu.co/index.php/ingeinv/ar5cle/view/44995/52672 [ accessed 16:36 11/11/17]20

www.gaugemap.co.uk/#!Map [accessed 18:12 07/05/17]21

h\p://kumina.water.wa.gov.au/waterinforma5on/telem/explanatory.cfm [accessed 15:16 27/08/17]22

Wate

r Le

vel (m

)

-0.15

-0.075

0

0.075

0.15

0.225

0.3

Jan Mar May Jul Sep Nov

Max Min

http://www.gaugemap.co.uk/#!Detail/1012/1053/2016-11-28/2016-12-29

Maximum and minumum water levels at Osney Lock Hydro in 2016

In 2016 the level varied from -0.110m to 0.226m which is a range of 37.6cm. Since the river is rela5vely wide at this point even a slight rise or fall in water level would cause a large change in volume flowing through the screw causing a change in energy produc5on.

The graph shows the way the water level of the river varied throughout the year in 2016. The data is from the Osney Lock gauging sta5on. It shows lower water levels during the summer months as expected due to the rainfall generally being less in the summer which is shows in rainfall data of 2016 in Oxford.

The water level generally follows the same trend as the rainfall throughout the year. Some anomalies in the data could be caused by rainfall further up the Thames river, it has a large catchment area so the rainfall in Oxford doesn’t account for all the water entering the river. Also not all of the rainfall reaches the river some5mes caused by evapora5on in the summer or absorbed by plants in a vegetated area. In addi5on the type of rainfall makes a difference, periods of moderate rainfall results in more energy genera5on than very heavy bursts of rain.

Although all sources of hydropower depend on rainfall and river flow to a degree, impoundment and pumped storage are more effec5ve in areas where the rainfall varies a lot. They both use dams to store water and release it through a turbine when required. This allows them to store water in 23 24

5mes of high rainfall which can be used at other 5mes. The disadvantage of the Archimedes Screw is that it can only produce energy when the rainfall and river flow is high enough so energy can’t be

Dec 0.11 -0.048

2016 Oxford Rainfall

Month Rainfall (mm)

Jan 83.9

Feb 47.6

Mar 74.2

Apr 53.1

May 86.1

Jun 95.7

Jul 3.4

Aug 41.2

Sep 44.6

Oct 26.5

Nov 76.1

Dec 25.8

h\p://www.metoffice.gov.uk/pub/ data/weather/uk/climate/sta5ondata/ oxforddata.txt

h\p://greenthefuture.com/HYDROELECTRIC_HOWITWORKS_IMPOUNDMENT.html [accessed 22:45 23

29/08/17]

h\ps://energy.gov/eere/water/types-hydropower-plants [accessed 23:02 29/08/17]24

produced on demand. The Archimedes Screw wouldn’t be a effec5ve source of hydropower in an area with rainfall that varies a lot.

The rainfall – energy produc5on graph, using quarterly energy produc5on and monthly rainfall data, show a pa\ern, both peak in the second quarter and dip in the third quarter. Although there are inconsistencies in some months, this can be explained by the energy produc5on being grouped into quarters which could hide fluctua5ons similar to the rainfall data. The similari5es show that the amount of energy generated is highly dependent on the weather and season.

Even though weather can’t be controlled it can be forecasted and ogen follows the same pa\erns throughout the year. This allows for rainfall and thus energy produc5on to be predicted. Also by analysing the weather pa\erns as well as the water source it can help determine where would be a viable site to install the hydropower sta5on.

Set angle

Changing the flow of the river is difficult and may damage the environment in the area, so the angle of the screw is limited to the shape of the river at the loca5on it is placed. The angle can be slightly modified by changing the length of the screw, as the length increases the angle of inclina5on decreases. 25

As the angle increases the efficiency increases up to a certain point, because there is more of a height difference so the pressure difference increases crea5ng more hydrosta5c force. At the point when the ver5cal component of the weight is more than the horizontal component, the efficiency starts to decrease because the rota5on of the screw is driven by the horizontal component as well as ver5cal. The op5mum angle is generally 22°. 26

Analysing the performance of the Archimedes screw turbine within 5dal range technologies, pg.6525

h\ps://www.renewablesfirst.co.uk/hydropower/hydropower-learning-centre/archimedean-screw-hydro-26

turbine/ [ accessed 21:04, 15/08/17]

Rainfall and energy production at Osney Lock Hydro in 2016

En

erg

y p

rod

uct

ion

(kW

h)

0

22,500

45,000

67,500

90,000

Rain

fall (

mm

)

0

25

50

75

100

Months

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

RainfallEnergy Produced

http://www.metoffice.gov.uk/pub/ data/weather/uk/climate/stationdata/ oxforddata.txt

At Osney Lock the length of the screw is only 4.35m, which is set at the ideal angle of 22°. This allows the head height to be at 1.7m which is rela5vely low, having less effect on the river and any fish need to travel from downstream to upstream of the screw. 27

The Osney Loch screw was installed at a pre-exis5ng weir, so there wasn’t need for many altera5ons in the flow of the river. However hydropower sources that require a large dam to collect and store water cause a big disrup5on to the river flow. The dams on the Elwha River in America were removed because they stopped fish travelling along the river as well as not producing enough energy. It was also found that the dam cause a change in the habitat for water wildlife, including a large difference in water temperature between the surface and depths and material build-up using oxygen while decomposing resul5ng in the area being unable to sustain any wildlife. 28

Size of Screw

The screw turbine can be built in many sizes, there is no ideal or minimum size but the energy produc5on at any par5cular size should be enough for the installa5on to be viable. The size requirements of the screw depend on the water flow at the loca5on. A higher flow rate allows for a smaller diameter screw head to produce the same amount of energy. 29

h\p://www.hallidayshydropower.com/qa/

The graph shows the parameters for water flow and screw head diameter that Hallidays Hydropower Company uses to assess the viability of installing a screw.

The screw at Osney Lock has a blade width of 3m which allows a flow of over 0.2m3/s for it to be viable. The closest gauging sta5ons that measures flow rate is further up the river at Farmoor and downriver at Su\on Courtenay, both of which are around 10 miles away from Osney Lock. The flow rate of the Thames at Farmoor varied from 0.7 m3/s to 64 m3/s, with the flow staying between 1 m3/s and 20 m3/s most of the year. The flow rate at Su\on Courtenay had a minimum of 0.6 m3/s and maximum of 89 m3/s, 30

but it also mostly stayed in the range of 1 m3/s to 20 m3/s in the past year. The flow at Osney Lock 31

is likely to be in the same range because there isn’t much change in terrain and al5tude along the river in the area. According to the data from Halidays Hydropower the Osney Hydro project is very feasible with a head size of. 3m and flow over 0,5m/s.

Osney Lock Hydro – Harnessing the power of our river pg.127

h\ps://www.scien5ficamerican.com/ar5cle/how-do-dams-hurt-rivers/ [accessed 17:40 11/11/17]28

h\p://www.hallidayshydropower.com/qa/ [accessed 10:59 26/08/17]29

h\p://www.gaugemap.co.uk/#!Detail/1001/1037 [accessed 19:18 28/08/17]30

h\p://www.gaugemap.co.uk/#!Detail/1043/1094/2016-08-01/2017-08-31 [accessed 19:32 28/08/17]31

The size and speed of the blades of the screw turbine allow for fish to pass through safely, unlike impulse turbines which requires fast moving water which strikes each blade causing rota5on. The Archimedes screw is a reac5on turbine which is placed in the river and uses the pressure of the water to turn. Reac5on turbines use lower velocity and high flow which makes it a lot easier and safer for wildlife to pass through. 32

Construc5on and maintenance

Cofferdams were built upstream and downstream of the building area. Cofferdams are structures that contain water, so they can be placed in a river and water is pumped out so building can be done on the river bed. While the cofferdams were in place there was protocol in place for 5mes of high 33

rainfall to avoid flooding, by removing the upper cofferdam and levng water through exis5ng weir gates. An alterna5ve piling technique was found to build parts of the cofferdams allowing for less 34

noise to be produced in the process. The construc5on started mid-2013 and energy produc5on was 35

planned to start in the beginning of 2014 but there was a lot of rainfall which delayed the building. There were subsequent delays in comple5ng legal work and all the work necessary to start genera5ng, including the fish pass required by the Environment Agency, the building housing the screw, and the commissioning of the screw meant opera5ons started in May 2015. 36

The hydro is run by volunteers and regular maintenance needs to be carried out. The majority of the maintenance is clearing the trash-screen gra5ng stopping debris entering the screw and gardening the surroundings. One of the advantages of the Archimedes Screw is that it requires minimum 37

maintenance, the size and speed of the screw allows for larger debris to travel through without harm. The gra5ng doesn’t have to be as fine so there is less build up at the mouth of the screw. The 38

screw itself doesn’t need regular a\en5on, there are maintenance checks on the machinery and equipment twice a year, it automa5cally runs and stops depending on the flow of the river, and has a life5me of 25-40 years. 39

The Archimedes Screw turbine requires minimal building work and simplified founda5ons compared to some sources of hydropower. Crossflow or Kaplan turbines need a drag tube to decrease the velocity of the water leaving the turbine so loss of kine5c energy decreases, but this requires addi5onal building downstream and increase the cost. 40

h\ps://energy.gov/eere/water/types-hydropower-turbines [accessed 23:27 29/08/17]32

h\p://www.deepexcava5on.com/en/Cofferdam-cellular-cofferdams [accessed 16:49 29/08/17]33

h\p://test.osneylockhydro.co.uk/construc5on-work-begins-at-osney-lock/ [accessed 18:22 29/08/17]34

h\p://test.osneylockhydro.co.uk/building-work-starts/ [accessed 18:25 29/08/17]35

h\p://www.osneylockhydro.co.uk/construc5on/ [accessed 18:45 29/08/17]36

Osney Lock Hydro Offer Document pg.1437

h\p://www.renewablesfirst.co.uk/hydropower/hydropower-learning-centre/archimedean-screw-hydro-38

turbine/ [accessed 18:50 29/08/17]

h\p://www.osneylockhydro.co.uk/technical-details/ [accessed 18:59 29/08/17]39

h\p://nptel.ac.in/courses/Webcourse-contents/IIT-KANPUR/machine/chapter_7/7_7.html [accessed 19:29 40

11/11/17]

It is also much cheaper and easier compared to building a dam. A screw turbine can run with a low head so it can be built into the river and doesn’t require a dam. Some turbines require a dam for high output hydropower sta5ons or to produce energy on demand.

Effects of the Archimedes Screw – Environmental, Economic and Social

Biodiversity

A survey was done in the area before building was started to check the extent of wildlife in the area. The results showed that there was a lack of animals in the area and the limited amount that wouldn’t be affected by the hydro. Part of the building plan is to landscape around the building for the screw, including plan5ng more plants. In theory this could improve the biodiversity in the area due a larger variety of plants a\rac5ng more animals. Although it wouldn’t affect the already existent water species, the ar5ficial structures surrounding the screw wouldn’t improve biodiversity in the water. 41

Most hydropower sta5ons are fish friendly with a fish pass or alternate route for fish to travel past safely, but the Archimedes screw is safe enough for fish to pass through the actual turbine. Although a fish pass is s5ll used, it has enough spacing between the blades and low speed that allows any wildlife to pass through safely if any were to get in. However, as stated earlier any turbine that requires a dam could have a big impact on the habitat of any wildlife in the water, causing some to perish and for the area to become inhabitable.

Fish migra5on

The biodiversity study done on the area also evaluated the effect of the Archimedes screw on fish in the river. Before the building of the Archimedes screw the sec5on of the river was impassable for fish, because of the presence of the weir. Therefore the measure put in place to ensure fish can safely pass by the screw have made it more likely for fish to be able to travel that sec5on of the river. At Osney Lock there is nevng across the mouth of the screw to stop fish entering the screw and a fish pass alongside the screw for the fish to travel through. This also allows fish to travel upstream as well as down, which allows the upstream migra5on of salmon. There are fake reed beds in the river around the top of the screw for the fish to rest in without being washed downstream by the current, ager they travel up the fish pass. 42

However even if the fish enter the screw, Archimedes screws are generally safe for fish to pass through, they turn slowly and the troughs are large enough for the fish to fit comfortably. Studies and experiments have been done on Archimedes screws that show that they don't effects fish. One of the studies Osney Lock looked at, as well as an independent study, while considering fish safety was tes5ng done by Fishtek. The report provided the highest rpm values for fish to pass through safely. For the specifica5ons of the screw at Osney Lock, 4 bladed screw, the maximum safe speed is 32rpm but it’s highest is only 23rpm so if any fish were to enter the screw instead of fish pass they would travel through safely. 43

Osney weir ecological impact assessment pg.22-2341

h\p://www.osneylockhydro.co.uk/osney-lock-hydro-and-fish/ [accessed 18:49 14/06/17]42

Archimedean Screw risk assessment: strike and delay probabili5es pg.3343

The Archimedes Screw is efficient with a low head so it doesn’t cause a major height difference in the flow of the river allowing for fish to travel upstream easily, especially with the fish pass installed. Many high head turbines like the pelton wheel require a large drop for a high water velocity which requires a dam if a large enough height difference doesn’t occur naturally. Some dams include fish 44

ladders which allow fish to travel upstream by swimming against the water flow from pool to pool, this makes upstream much more difficult and in some cases impossible depending on the height to the dam. 45

Noise

A noise assessment report was done by Sound Solu5ons to assess if the noise created by the screw or generator would affect the surrounding area and if any measures would need to be taken to lessen the effect.

They measured the noise levels of different parts of the Archimedes screw including the water entering and leaving the screw, the generator and the water flow in the fish pass. The results show that the most noise is produced by the generator.

Ager tes5ng the sound levels at different points in the area, including within a meter of the nearest residen5al building, they concluded that at the normal river flow, the noise levels were unlikely to disturb the residents depending on the type of building the screw is in. The building housing the screw, had soundproof walls built on the side facing the nearby residen5al area which sa5sfies sound reduc5on index outlined by the report. 46

The main noise concern with many hydropower sta5ons is the generator, but if it is housed in the correct way, like at Osney Loch, with soundproof walls it isn’t a problem. The sound produced by the turbine itself wouldn’t differ much from the sound of normal river flow for reac5on turbines, impulse turbines may cause more noise due to the velocity of the water hivng the blades.

Water Loss

Water loss in the river is a very minor issue for the Archimedes screw as the water enters the top and in theory it all of it flows out the bo\om back into the river. The only source of water loss is evapora5on. Due to the large surface area of the screw, water leg on the surface of the blades is likely to evaporate, not rejoin the river. This however is a minuscule frac5on of water and compared to the amount in the river the loss is immeasurable. The annual water loss is reported to the Environment Agency, the Osney Lock hydro has a maximum allowance annually according to its Abstrac5on Licence.

There is no significant water loss with any source of hydropower because water flows through the turbine and back into the water source.

Funding and costs

h\p://www.renewablesfirst.co.uk/hydropower/hydropower-learning-centre/pelton-and-turgo-turbines/ 44

[accessed 20:03 30/08/17]

h\ps://oceanservice.noaa.gov/facts/fish-ladder.html [accessed 22:16 11/11/17]45

Hydropower Archimedean Screw - Noise Impact Assessment by Sound Solu5ons pg. 9-10 ,1746

The total funding needed to complete the project is £700,000 including the fish pass needed as part of the safety precau5ons for the fish and for fish to be able to travel upstream. £650,000 was raised 47

by selling shares, 40% of which were bought by people living within a mile, and the project is community run with volunteers for upkeep of the screw. The organisa5on also took out a loan of £150,00 from Resonance (Community Land & Finance CIC ).. 48

The shares were sold at £1 each with a minimum of £500 and legal maximum of £20,000. The SEIS and EIS investment schemes were used which allowed the investors to have 50% tax relief on the first £150k worth of shares sold, and 30% on the rest. This allowed the fundraising process to be a lot more effec5ve. However, the scheme is no longer available which will have a nega5ve effect on any similar projects, like the Osney Lock Hydro, during their fundraising. The interest rate offered on the shares is expected to be 4% (subject to a decision by the Board of Directors) with the original equity capital paid back within 20 years. 49

Income

The feed in tariff, which applies for the first 20 years, is the payment of all the energy generated by the hydropower sta5on. The rate was 20.21p/kWh at the beginning of the scheme but it increases every year. During 2016 it was around 21p/kWh. The same system is used for the electricity generated by the solar panels on the roof with a rate of 13.99p/kWh. (41)

Electricity is sold directly to the Environment Agency which pays the same rates as it does for energy from its na5onal supplier. The export tariff is the energy not used by the Osney Lock Hydro or the Environmental Agency which is sold to an energy company, through the Power Purchase Agreement. (41)

The scheme was forecasted to produce 159,000kWh and £50,000 annually. Both these goals were surpassed as shown in the data from 2016 above. 50

Energy Generated and Income at Osney Lock Hydro for 2016

Income (£)

PeriodHydro Genera(on

(kWh)Feed-in

TariffExport Tariff

Sale of Electricity

1 Jan – 31 Mar 54,303 11,452 1,041 2,405

1 Apr – 30 Jun 81,620 17,418 2,885 2,527

1 Jul – 30 Sep 14,410 3,075 405 603

1 Oct – 31 Dec 38,158 8,143 1,057 1,442

Totals 188,491 52,458

Osney Lock Hydro - Genera5on and Income from commissioning to 30 June 2017

h\p://www.osneylockhydro.co.uk/construc5on/ [accessed 20:42 29/08/17]47

Osney Lock Hydro Offer Document pg.848

Osney Lock Hydro Offer Document pg.4,549

Osney Lock Hydro Offer Document pg.7,850

The income and costs of any hydropower sta5on depend on the size of the build. Larger or mul5ple turbines cost more but also generate more energy. The change in cost and energy produc5on is generally propor5onal above a certain size. Small turbines are not economically viable because the same base rate for all turbines applies but the income is too low due to low energy produc5on. 51

However a hydropower turbine with a lower energy produc5on has a higher feed-in tariff, which is an important part of its income. 52

This table shows how the feed in tariff varies with power output, the export price remains constant for any hydropower sta5on. The total income per kWh is lower for a larger hydropower system but the higher power output means the total income is generally higher.

Hydro SystemMax. Power Output

Feed-in Tariff Export Price Total Value

< 100 kW 7.65 p/kWh 5 p/kWh 12.65 p/kWh

100 to 500 kW 6.12 p/kWh 5 p/kWh 11.12 p/kWh

500 kW to 2 MW 6.12 p/kWh 5 p/kWh 11.12 p/kWh

> 2 MW 4.43 p/kWh 5 p/kWh 9.43 p/kWh

h\p://www.renewablesfirst.co.uk/hydropower/hydropower-learning-centre/how-much-income-would-my-hydro-system-provide/

Maximum Power Output Es(mated Project Cost £ / kW installed

25 kW £169k £6.8k

50 kW £300k £6.0k

100 kW £529k £5.3k

250 kW £963k £3.8k

500 kW £1.6M £3.2k

h\p://www.renewablesfirst.co.uk/hydropower/hydropower-learning-centre/how-much-do-hydropower-systems-cost-to-build/

h\p://www.renewablesfirst.co.uk/hydropower/hydropower-learning-centre/how-much-does-a-hydropower-51

system-cost-to-operate/ [accessed 20:39 25/10/17]

h\p://www.renewablesfirst.co.uk/hydropower/hydropower-learning-centre/how-much-income-would-my-52

hydro-system-provide/ [accessed 19:27 12/11/17]

The table above presents the costs of lower output hydropower sta5ons, the data shows that as the power output increases the price per kWh decreases even as the installa5on price increases. The price es5mates are for an average build, some hydropower sta5ons require more building work than others. Kaplan and Crossflow turbines both require drag tubes which makes the project more 53

expensive. The Pelton wheel needs a pipe and nozzle to fire the water at the turbine with the 54

correct velocity, otherwise a large amount of piping is used to transfer the water from a height to the turbine for it to gain the kine5c energy the same kine5c energy required to run. 55

The general equa5on for power genera5on of a hydropower sta5on is, P = m x g x H(0.9) x η. g is a constant (9.81m/s2), m is the mass flow rate which is the same as flow rate (litres/s), H is the head height which is mul5plied by 0.9 to account for head loss and η is the overall efficiency. 56

The data calculated using the equa5on shows that the Pelton wheel has the highest capacity for the highest output power but that is highly dependent on using a high head which can be complicated to set up without effec5ng the surroundings with piping to transport the water or a dam.

The Archimedes has the lowest maximum output but also requires less building work than the Crossflow or Kaplan, both requiring addi5onal downstream construc5on for the drag tube. This makes both op5ons more expensive to build.

Other Archimedes Screw Projects

Sandford Hydro – The project is similar to Osney Lock using Archimedes screws with a fish pass and a community funding. However it is on a much larger scale with 3 screws instead of 1 and es5mated to produce 1,600MWh and save 730tonnes of CO2 annually, it was completed in the summer of 2017.

Turbine Head(m) Flow(litres.k/s ) Efficiency Min. output(W) Max.output(W)

Archimedes Screw 1.5-5 1-20 0.7 9,270 618,030

Crossflow 2-40 0.1-5 0.82 1,448 1,447,956

Kaplan 1.5-20 3-30 0.9 35,757 4,767,660

Pelton wheel >25 0.01-0.5 0.95 2,097 >104,844

h\p://www.renewablesfirst.co.uk/hydropower/hydropower-learning-centre/

h\p://www.renewablesfirst.co.uk/hydropower/hydropower-learning-centre/how-much-do-hydropower-53

systems-cost-to-build/ [accessed 19:46 12/11/17]

h\p://nptel.ac.in/courses/Webcourse-contents/IIT-KANPUR/machine/chapter_7/7_7.html [accessed 19:29 54

11/11/17]

h\p://www.renewablesfirst.co.uk/project-blog/high-head-hydro-pelton-turbine/ [accessed 20:05 12/11/17]55

h\p://www.renewablesfirst.co.uk/hydropower/hydropower-learning-centre/how-much-power-could-i-56

generate-from-a-hydro-turbine/ [accessed 19:36 12/11/17]

Although both are situated on the same river, it’s larger and wider at Sandford which allowed the bigger build. 57

Totnes Hydro – The screw is privately owned by a secondary school in order to power a eco-classroom and sell and excess to the Na5onal Grid. It produces around 1,231MWh and saves 530tonnes of CO2 annually which is close to the produc5on of Sandford Hydro. In addi5on, it offers 58

an opportunity to educate people about the renewable energy and its importance.

Dauntsey Park – This is an example of the Archimedes Screw turbine on a small scale, with a maximum output of 12.5kW. It is used to provide energy for a private home with excess going to the Na5onal Grid. 59

Efficiency

Hydropower is the most efficient source of energy, figures can vary depending on the turbine but some are as high as 90% efficient while the most efficient fossil fuel plant has a maximum of 50% efficiency. Wind turbines are slightly less efficient with a 45% efficiency normally and 50% at 60

peak. Solar panels have one of the lowest efficiencies varying between 15% - 22%. 61 62

An example of a high efficiency hydropower turbine is the Pelton wheel which can have efficiencies of up to 95% and even 90% on a micro-scale. It is an impulse turbine so it works off high velocity and needs a head (water drop) of 20m to a few hundred meters. Cross sec5on turbines are another 63

type of impulse turbines, also with a high efficiency with a maximum of 82%. These both have a 64

higher efficiency than the Archimedes Screw but aren’t suitable for the Osney Loch site due to the low head and high flow.

The Kaplan is reac5on turbine like the Archimedes Screw and has a maximum efficiency of 90% depending on the design, adjustable or fixed. However it requires a larger and more complicated build with the generator within a bulb placed in the main flow of the river, and access large enough for a person to get to the generator. 65

Variable-speed Archimedes Screws have an efficiency of around 70% when the flow rate is at its maximum; the mechanical efficiency is 85% but 15% is lost while conver5ng the energy to

h\p://www.lowcarbonhub.org/projects/sandford-hydro [accessed 23:43 29/08/17]57

h\p://www.mannpower-hydro.co.uk/project/totnes/ [accessed 23:56 29/08/17]58

h\p://www.mannpower-hydro.co.uk/project/dauntsey-park/ [accessed 21:18 30/08/17]59

h\p://www.wvic.com/Content/Facts_About_Hydropower.cfm [accessed 18:47 30/08/17]60

The wind energy fact sheet pg.361

h\ps://www.greenmatch.co.uk/blog/2014/11/how-efficient-are-solar-panels [accessed 18:59 30/08/17]62

h\p://www.renewablesfirst.co.uk/hydropower/hydropower-learning-centre/pelton-and-turgo-turbines/ 63

[accessed 20:11 30/08/17]

h\p://www.renewablesfirst.co.uk/hydropower/hydropower-learning-centre/crossflow-turbines/ [accessed 64

20:28 30/08/17]

h\p://www.renewablesfirst.co.uk/hydropower/hydropower-learning-centre/kaplan-turbines/ [accessed 65

20:51 30/08/17]

electricity. The maximum efficiency of the Archimedes screw is calculated by comparing the 66

poten5al energy of the water available and the actual energy produced. Poten5al energy is calculated by mul5plying mass, accelera5on due to gravity (9.81m/s2) and height difference.

Efficiency of Osney Lock Hydro - The capacity of the Osney Lock screw is 4000l/s, its height drop is 1.7m and the max output power is 47.8kW. 67

Mass of 1l of water = 1kg Mass of water through screw = 4000kg/s Poten5al Energy = 4000 * 1.7 * 9.81 = 66708 J/s = 66708 W = 66.708 kW Efficiency = (47.8/66.708) * 100 = 71.7%

The efficiency of the Osney Lock screw (71.7%) is similar to the average of 70%. As well as energy lost in the generator while transferring the mechanical energy to electricity, the remaining 15% is lost through sound and heat energy created by the fric5on between the water and the screw surface.

Conclusion

Taking into account its efficiency as well as the environmental, economic and social effects, the Archimedes Screw is an effec5ve source of hydropower. It is currently not very widely used, mainly privately owned, but its popularity is increasing with the demand for renewable energy. The success of the case study, Osney Lock Hydro, and other projects show that it is a viable source of energy.

The Archimedes Screw turbine is one of the most fish-friendly hydropower designs, unlike other turbines it has the right design and rota5on speed for fish to pass through safely. The fish pass is used to ensure fish safety and for fish to be able to travel upstream. It can also benefit the fish, before the Archimedes Screw was installed with the fish pass at Osney Lock fish weren’t able to travel upstream.

One of the main disadvantages of the screw turbine is the energy produc5on is highly dependent on the river flow and weather so energy can’t always be produced on demand. It could be used with a dam storing and releasing water when required but some loca5ons can’t accommodate a dam and it effects the flow of the river and its habitats.

The screw also has minimal social effects, aside from the original construc5on the screw produces low levels of sound. The building containing the Osney Lock has soundproofing in the walls due to its proximity to the residen5al area, which is a precau5on that can be added to any screw in a similar situa5on. In addi5on, the screw produces green energy, reducing the electricity bill and carbon footprint of the owner in the case of a privately owned screw, or raises money for environmental schemes for community run projects.

In comparison to other sources of hydropower the effec5veness of the Archimedes Screw turbine depends mostly on the situa5on. Hydropower sta5ons have very li\le environmental effects in excep5on to the building of dams for large hydropower sta5ons or to allow the sta5on produce energy on demand. The only social effect is noise which is mainly produced by the generator and can be masked using soundproof walling. The efficiency and energy genera5on of different turbines vary

h\p://www.renewablesfirst.co.uk/hydropower/hydropower-learning-centre/archimedean-screw-hydro-66

turbine/ [accessed 19:08 30/08/17]

Osney Lock Hydro – Harnessing the power of our river pg.167

as well as the requirements to run them. There is no way to decide which source of hydropower is the most effec5ve in general but for specific cases different turbines are most suitable depending on the water velocity, head height and size of the river.

The Archimedes Screw is economically viable to run at different scales from providing to a private home at Dautsey Park to the triple screw community project at Sandford Hydro producing 1.6GWh annually. Although there are some hydropower turbines more efficient, the specifica5ons needed to run them vary and the screw is ogen the most appropriate for the given site. The Osney Lock project has shown that by choosing a suitable site, viable energy produc5on and income figures can be forecasted, and successfully met.

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