An investigation into the potential of low head hydro ...

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An investigation into the potential of low head hydro power in Northern Ireland for the production of electricity a

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David Redpath & Michael J. Ward a

Centre for Sustainable Technologies, University of Ulster, Coleraine, UK Published online: 09 Jun 2015.

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International Journal of Sustainable Energy, 2015 http://dx.doi.org/10.1080/14786451.2015.1050395

An investigation into the potential of low head hydro power in Northern Ireland for the production of electricity David Redpath ∗ and Michael J. Ward


Centre for Sustainable Technologies, University of Ulster, Coleraine, UK (Received 11 December 2014; accepted 1 May 2015) The maximum exploitable potential for low head hydroelectric sites (gross head ≤ 10 m) in Northern Ireland (NI) was determined as 12.07 MW using a simple payback analysis for 304 potential sites investigated to derive a classification scheme in terms of economic viability. A techno-economic analysis with validated numerical models from previous research estimated the capital investment required for the development of a hydroelectric plant, using the low head Michell-Banki cross flow turbine, for the 304 sites investigated. The number of potentially viable sites in NI for low head hydro ranged from 198 to 286 with an estimated installed capacity ranging from 11.95 to 12.05 MW. Sites with a limited installed capacity were not economically viable unless increased government support in the form of longer term (25–50 years) low interest loans as well as the current (Renewables Obligations Certificates) Renewables Obligation Certificates scheme is provided and sustained. Keywords: low head hydro; net present value; benefit cost ratio; economic; electricity

1.

Introduction

Water power has been used as a source of energy in Northern Ireland (NI) for over a thousand years. The high level of innovation required to develop the numerous typologies of water wheels used throughout NI helped drive the high level of industrial development within NI, before the various conflicts that occurred in the twentieth century after partition of the island. The North Eastern region of Ireland had a higher level of industrial development compared to the more rural-based agrarian economy in the South of Ireland (Gribbon 1969). By 1950, 10 MW of hydropower was installed across NI (Gribbon 1969). With the development of the national grid a large number of these old hydroelectric sites became obsolete as the output they produced was small compared to an increasing demand. The electricity provided by the national grid had a lower cost, more reliable (most schemes had limited storage facilities) making private electricity generation using small run of river hydro power schemes unprofitable or more costly than gridsupplied power. Ireland’s current energy mix is 96% reliant on fossil fuels, the fourth largest fossil fuel dependency in the EU (DOENI 2010) the national grid in Ireland is shared between the two political jurisdictions. With abundant rainfall throughout the year, as shown in Figure 1, a mean height above sea level of 57 m and the climate of NI classed as mild maritime, low head hydro is ideally suited for *Corresponding author. Email: [email protected] © 2015 Taylor & Francis

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Figure 1.

D. Redpath and M.J. Ward

Annual rainfall NI, 1910–2013.

this region. The Meteorological Office (MO) provides data on Standard Annual Average Rainfall (SAAR) using measurements from 1910 which are shown in Figure 1 (Anon 2013). From Figure 1 the average annual rainfall that NI received over 103 years was 1111 mm yr−1 , the variance over this period was 112 mm ( ± 10.1%). The Department of Agriculture and Rural Development in NI classifies low head sites as those with a head below 10 m and a high head site as one with a head height greater than 20 m (D. o. A. a. R. Development 2012), similarly the British Hydropower Association (Britishhydropowerassociation 2012) deem low head sites as those less than or equal to 10 m. The approximate range of head, flow and power output applicable for different hydroelectric turbines are dependent on the design used (D. o. A. a. R. Development 2012) and is outlined in Figure 2. The potential for hydro generation from run of the river schemes is often underestimated since small-scale hydro power schemes (less than 10 MW) are often not included in hydrological assessments (Paish 2002). The NI assembly has aimed to reduce carbon emissions by 26% by 2025 compared to the levels emitted in 1990 (DOENI 2010). As part of the UK, NI is committed to the target of generating 30% of the electrical energy requirements by 2020 via renewable energy systems (DECC 2009). Low head hydroelectric schemes have almost zero CO2 or other greenhouse emissions and a high energy payback during operation. If an economically viable exploitable resource for low head hydro schemes existed in NI then this could contribute towards

Figure 2.

Head flow and power output ranges for hydroelectric turbines.


International Journal of Sustainable Energy

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meeting reduction targets for greenhouse gas emissions and additionally revive the sustainable green economy that at one stage powered a high proportion of homes and industry across NI (Gribbon 1969). Previous research undertaken on low head hydro schemes has demonstrated the usefulness and sustainability of such systems (Gribbon 1969; McCutcheon 1980; University of Salford 1989; Williams 1996; Müller and Kauppert 2002; Paish 2002; Montanari 2003; Shaw 2003; Bartle and Hallowes 2005; Kaldellis, Vlachou, and Korbakis 2005; Anagnostopoulos and Papantonis 2007; Tsoutsos, Maria, and Mathioudakis 2007; Alexandera and Giddens 2008; Ogayar and Vidal 2009; Aggidis et al. 2010; Gaiusobaseki 2010; Singal, Sain, and Raghuvanshi 2010; Abbasi and Abbasi 2011; Cyr, Landry, and Gagnon 2011; Dursun, Alboyaci, and Gokcol 2011; Padrón, Medina, and Rodríguez 2011; Tristán et al. 2011; Fishpal 2012; Margeta and Glasnovic 2012; Selvakumaran 2012 and Retscreen). The study undertaken by University of Salford (1989) is the most relevant to low head hydro in NI as it provided a comprehensive list of potential locations for installation of hydroelectric turbines. The study provided clear details of the numerous sites throughout NI with potential for generation of electrical energy using small-scale hydroelectric systems. This previous work rejected sites with a potential installed capacity of less than 25 kW as small-scale power generation was not previously supported through government interventions. Hydropower is a well-established technology with information readily available but it can be difficult to estimate the cost. The main reason for this is the extremely site-specific, construction costs. The dominant factor in determining the cost per unit output is the initial capital cost and major part of this is the civil engineering costs, which vary from site to site (Montanari 2003). Most low head systems last without any major refurbishment for 50 years or more. Existing or older hydro sites where the initial investment has been paid off are exceptionally competitive at power production as the only costs incurred are operation and maintenance. Economic analysis of hydropower projects is given insufficient credit for the exceptionally long lifetime and low running costs of small hydroelectric schemes, often due to the lack of foresight or desire for only short-term gain in the private sector (Müller and Kauppert 2002). In NI hydroelectric schemes are eligible for government support to help increase the development of potential sites. The Renewables Obligation Certificates (ROC) bandings and relevant payments available when this investigation was undertaken (2012) are summarised below. • • • •

Hydroelectric schemes ≤ 20 kW receive four ROCs per kWh generated. Hydroelectric schemes 21 kW to ≤ 250 kW receive three ROCs per kWh generated. Hydroelectric schemes 250 kW to ≤ 1 MW receive two ROCs per kWh generated. Above 1 MW receive one ROCs per kWh generated.

The aim of this investigation was to determine the potential low head hydro resource available within NI and the economic conditions required (discount rates, inflation and payback periods) for identified potential hydroelectric sites to be economically viable developments. In 2012 the installed capacity of the hydroelectric plant in NI was 3 MW with an estimated annual power generation of 15.4 GWh yr−1 (D. o. A. a. R. Development 2012). Due to the introduction of financial incentives in the form of government subsidies (ROCs), increased fossil fuel costs, and policy drivers such as international agreements on limiting greenhouse gas emissions, the economic viability of the sites investigated by University of Salford (1989) has altered, necessitating updated research on these. This research used standard economic indicators for determining viability such as Simple Payback Periods (SPP), Net Present Values (NPV) and Benefit Cost Ratios (B/C) for the sites investigated. Variables affecting the economic viability of hydroelectric schemes such as the discount rate, inflation rate and repayment period were varied and it was assumed that the sites would be subjected to typical patterns of precipitation. The maximum potential installed capacity

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for low head hydro schemes in NI was estimated initially using an SPP analysis for each site investigated and used to develop a classification scheme. Further economic analysis was undertaken using NPVs under different economic conditions to determine the B/C of each site. The results generated were used to determine the economic viability of each site to identify those with the highest potential returns indicating those which should be developed if possible.


2.

Methodology

To ascertain the economic viability of investigated sites; SPP, NPV and B/C were used. This paper re-evaluated the sites for hydroelectric power generation listed in University of Salford (1989). Six different scenarios with different discount rates, inflation and repayment periods were used to estimate the potential economic viability of the low head hydro sites investigated as well as highlighting potential risks to investors should any economic parameters change (Paish 2002). The study used the following procedure to determine the potential low head hydro resource; (1) Identification of the most appropriate type of hydroelectric turbine for low head sites using the information shown in Figure 2. (2) Identification of the location of low head sites in NI from the information presented in University of Salford (1989). (3) Initially calculating the SPP of each site, then the NPVs and B/C ratios under different economic conditions. (4) Validation of the estimated economic results using RETScreen software. First all potential hydroelectric sites with a gross head height greater than 10 m identified by University of Salford (1989) were eliminated. The total number of sites accepted by University of Salford (1989) with a gross head height of ≤ 10 m was 50. A further 410 sites were deemed unviable by University of Salford (1989), and assigned a classification code outlining the reason for their rejection and are discussed below. To identify potentially economically viable low head hydroelectric sites in NI from the 410 sites rejected previously, those with classification codes N (Reasonable potential but not practical for development), OP (Operating scheme), AR (Access for development restricted), (PR) Prior use of water (fish farm, etc.), NP (No potential), (NC) (Head less than 3 m, no existing civils) and W (Weir removed or breached) were eliminated due to any potential cost and environmental constraints. An economic analysis of sites assigned with codes (H2) head less than 2 m, (P25) power less than 25 kW, (P50) (power less than 50 kW no on site demand) and do it yourself (installed capacity less than 25 kW but suitable for small development) was then undertaken assessing the viability of low head hydroelectric system installations for each site. Ordnance survey (OS) maps with scales of 1:50,000 and 1:25,000 were used to estimate gross head and catchment areas. Of the 410 sites rejected by University of Salford (1989), 135 were rejected again based on the classification codes described, a further 21 sites were removed as these had gross heads greater than 10 m as calculated from the contours shown on the OS maps leaving 304 sites to be investigated. The estimated generating capacity of each potential site within NI was then calculated using available statistics on rainfall (see Figure 1), the catchment area of each site and the procedure are outlined below. The MO classifies actual evaporation as equal to potential evaporation for SAARs greater than 850 mm. All the sites considered had a SAAR greater than 850 mm. The study by McCutcheon (1980) provided further information on the potential evaporation of ‘accepted sites’. Using this information, values for the potential evaporation for rejected sites were then calculated. The head height (m), catchment area (km2 ) and historic data on SAAR, and the actual evaporation precipitation levels of the sites were used


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to calculate the mean flow (Qm ) using Equation (1), (University of Salford 1989). Where Qm was the annual mean flow (m3 s−1 ), SAAR the Standard Annual Average Rainfall for the catchment (mm), Ea the actual evapotranspiration (mm) and A the catchment area (km2 ) Qm =

(SAAR − Ea ) × A × 103 . 8760 × 3660

(1)

From Equation (1), the mean flow rate at each location under investigation was calculated allowing the installed flow (Q) to be determined from Equation (2). The compensation flow (Q95 ), was assumed as 12% of the mean flow as reported by previous investigations (University of Salford 1989).


Q = Qm − Q95 .

(2)

The installed flow and the calculated head for each site were used to estimate the installed capacity (P) using Equation (3), the acceleration due to gravity (g) was assumed as 9.81 m s−2 and a crossflow turbine was installed at each site with an assumed efficiency of 70%. The cross flow turbine was chosen as it maintains its efficiency across a wide range of flows rates and head heights as shown in Figure 2 which is an appropriate choice as the majority of rivers in NI are Spate Rivers (Fishpal 2012). P = ηρQgH.

(3)

Each site was assigned an ROC value in relation to its installed capacity. To determine the revenue earned by generation of electricity, the likely annual power output was estimated. The annual amount of electrical energy generated from each site investigated was estimated using a capacity factor of 0.5 (University of Salford 1989) as shown in Equation (4). Annual power generation (kWh yr−1 ) = P(kW) × 0.5 × 24 h × 365 days.

(4)

For accepted sites the annual power output was already determined (University of Salford 1989) and the previously determined value was used for subsequent economic assessment. The annual revenue earned under government support via ROCs was calculated using Equation (5) Revenue (£) = annual power output (kWh) ∗ ROC unit Price (p/kWh).

(5)

Electricity exported to the grid also contributes revenue to a scheme, at a rate of 0.056£/kWh and revenue earned from exporting electricity to the grid calculated from Equation (6). Revenue (£) = annual power output exported to grid (kWh) ∗ 0.056.

(6)

The total annual revenue earned from a low head hydro scheme was estimated using Equation (7) Total revenue (£) = (5) + (6).

(7)

Previous research by Aggidis et al. (2010) presented a costing formula (Equation (8)) for the cost of developing small-scale hydro projects to within ± 25%. Cost = 25000 x(kW/H0.35 )0.65 .

(8)

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3.


Results

The SPP for each site was calculated using Equation (9) and used to develop a classification scheme for the 304 potential hydroelectric sites comprising four categories based on the time taken to repay the initial capital cost and the installed capacity (kW) indicating their economic worth for development. Payback period (yrs.) =

total cost for small hydro installation (Equation (8)) . total revune (Equation (7))

(9)


Potential hydroelectric site classifications derived were denoted as good, fair, marginal and poor: • Sites classified as good (G) had a payback period less than six years with an average installed capacity of 190 kW. • Sites classified as fair (F) had a payback period ranging from 6 to 10 years with an average installed capacity of 14.7 kW. • Sites classified as marginal (M) had a payback period ranging from 10 to 20 years with an average installed capacity of 3.8 kW. • Sites classified as poor (P) had a payback period greater than 20 years with an average installed capacity of 0.6 kW. This classification scheme was applied to all the 304 sites investigated and used within each county in NI (see Figure 3) (Anon 2015) to estimate the number of potential low head hydroelectric generation sites given the new level of government support under the ROC scheme described in Section 1. Table 1 lists all the total potential hydroelectric sites identified per county, their installed capacity, annual power generation and the CO2 savings that would result from their development. Table 1 indicates a possible 304 sites, with a low head hydroelectric development potential before more complex economic factors such as discount rates, inflation and capital repayment periods are considered. The classification of these is shown in Table 2.

Figure 3.

Counties of NI, adapted from Anon (2015).


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Table 1. Total number of sites investigated and their characteristics. County

No of sites

Antrim Armagh Down Fermanagh Derry Tyrone Total

Table 2.

104 3 55 34 50 58 304

Installed capacity (MW)

4116 215 3153 353 1565 2670 12,072

4.1 0.2 3.2 0.4 1.6 2.7 12.07

Annual power output (kWh)

CO2 emissions saved per year tonnes

18,225,246 9,84,511 13,750,065 1,672,159 7,147,373 11,566,772 53,346,126

11,081 599 8360 1017 4346 7033 32,434

Total number of sites according to classification rating before economic analysis.

Category


Installed capacity (kW)

G

Number of hydroelectric sites Installed capacity (kW) Annual energy output (kWh)

51 9683 44,893,442

F 107 1897 2,522,154

M

P

138 522 2,317,867

8 5 20,290

Total 304 12107 49,753,753

The values shown in Table 2 do not take into account the discount rate, inflation and repayment of capital required to develop a low head hydroelectric site. The calculation of the B/C ratio and NPV ratio was then undertaken at the various discount rates, capital repayment periods and inflation rates for the six different economic scenarios are shown in Table 3. Sites accepted from the study undertaken by University of Salford (1989) already had details of their hydrology, installed capacity and projected annual power output. Fifty of these sites were classified as low head hydro ( < 10 m). The economic analysis was broken down into county level after the parameters presented in Table 3 were applied. All the hydroelectric sites investigated were subjected to an economic analysis using the values shown in Table 3 and the obtained values compared to those predicted using the RETScreen software program. Previous research found that the two most important factors determining the financial viability for any particular hydroelectric development are: • The capacity factor (assumed as 0.5 for this study University of Salford 1989). • The cost of energy per unit (kWh) generated (Harvey et al. 2002). Table 4 shows the total number of sites viable within NI for a discount rate of 5%, an inflation rate of 2% and a project lifespan of 25 years (most stringent economic conditions assumed). Table 4 shows a total potential installed capacity of 11.2 MW. Compared with Table 1, the number of sites has decreased, from 304 to 198 (34.9%) and the installed capacity by 7.44% from 12.1 to 11.2 MW. The sites eliminated using the described economic analysis have a small Table 3. Discount rates, inflation and capital repayment values used for economic analysis of hydroelectric site viability. Discount (interest rate) (%) 5 5 3 3 3 3

Inflation rate (%)

Capital repayment period for development of hydroelectric sites

2 2 2 2 5 5

25 50 25 50 25 50

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D. Redpath and M.J. Ward Table 4. Total number of sites assuming a discount rate of 5%, inflation of 2% and a capital repayment period of 25 years. County

Sites

Antrim Armagh Down Fermanagh Derry Tyrone Total

81 2 32 25 28 30 198

Installed capacity (MW)

Annual energy output (kWh)

4.1 0.2 3.3 0.6 0.4 2.6 11.20

CO2 emissions saved (tonnes)

17,954,645 9,83,000 14,941,744 2,663,200 4,420,367 11,231,274 52,194,230

10,916 598 9085 1619 2688 6829 31,735


Table 5. Total number of sites by county classification after cost/benefit analysis applied. Overall summary County Antrim Armagh Derry Down Fermanagh Tyrone Total Total

Good

Fair

Marginal

Poor

20 2 10 7 2 10 51 198

45 0 17 14 16 15 107

16 0 5 4 10 5 40

0 0 0 0 0 0 0

potential installed capacity (on average 0.1 kW) with a limited and costly impact in producing electricity. Table 5 indicates the total number of sites by each classification group by county using the same economic parameters as given in Table 4. Sites were rejected when the calculated B/C ratio was lower than 1, from Table 5 it is observed that the number of hydroelectric sites classified as poor is reduced to zero indicating that these sites are not economically viable for development. Figure 4 shows the total number of sites, by county and overall which are viable assuming a discount rate of 3%, an inflation rate of 2% and compares project lifespans of 25 and 50 years.

Figure 4. Comparison of viable low head hydroelectric sites in NI sites for a discount rate of 3%, inflation 2% and repayment periods of 25 or 50 years.


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From Figure 4 the total number of low head hydroelectric sites in NI calculated using the described economic conditions was 286, for project pay back periods of 50 years. This was reduced by 15.7%, to 241 sites for 25-year capital repayment periods, indicating most sites could still be developed at shorter payback periods under more favourable economic conditions than used to generate the values shown in Table 4. This indicates that the sites deemed non-viable under 50-year repayment periods contribute a minimal proportion to the potentially viable installed capacity. Under the 25-year payback scenario, an installed capacity of 11.95 MW, an annual generation of 52,992 GWh and the saving of 32,219 tonnes of CO2 per annum are possible. Under a 50-year capital repayment period; • • • • •

Installed capacity increases to 12.05 MW. Annual electrical power generation increases to 5,33,330 GWhe A saving of 32,219 tonnes of CO2 per annum. The total number of sites classified as good was 51 under both repayment scenarios. The total number of sites classified as marginal was 127 for a 50-year repayment period decreasing by 83 (reduction of 34.6%) when the capital costs were repaid over 25 years.

The increase of the repayment period from 25 to 50 years has resulted in the highest number of economically viable sites mainly due to marginal sites becoming economically viable. Low head hydro systems typically last longer than 25 years with many sites around the world already having lifespans in excess of 100 years (DOENI 2010). Borrowing the required capital investment to develop a hydroelectric site over 50 years may be difficult to obtain from private investors and indicates another potential area for government support for such schemes. Figure 5 presents the total number of sites viable per county in NI for a discount rate of 3%, an inflation rate of 5% comparing project lifespans of 25 years and 50 years. The rate of inflation increasing by 3% did not have a noticeable effect on the total number of viable sites which were reduced by only one for project life spans greater than 50 years, as the value of electricity exported and government support for hydroelectric projects would also increase at this rate. It did have an impact at the county level as seen in Figure 5. Figure 6 illustrates s the impact of an increased rate of inflation on the classification of the sites investigated. From Figure 6 the number of sites classified as good and fair remained the same using the lower inflation rate as those shown in Figure 4 have no significant effect on the development

Figure 5. Number of viable sites per county using a discount rate of 3%, an inflation rate of 5% and a project life time of 25 or 50 years.


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Figure 6. Classification of all sites investigated using a discount rate of 3%, an inflation rate of 5% and a project life time of 25 or 50 years.

Figure 7. Number of low head hydroelectric sites economically viable for a discount rate of 5%, an inflation rate of 2% and a repayment period of 25 or 50 years.

potential of low head hydroelectric sites. Figure 7 shows the number of low head hydroelectric sites economically viable assuming a discount rate of 5%, an inflation rate of 2% and a repayment period of 25 or 50 years From Figure 7 the increase in discount rate from 3% to 5% significantly reduced the total number of viable low head hydroelectric sites within NI by 21.16% and 13.29% over a 50year repayment period and a 25-year repayment period, respectively, compared to the number of viable sites shown in Figure 4.

4.

Analysis

The results show a currently unexploited, economically viable potential for the development of low head hydroelectric sites within NI. The predicted installed capacity ranged from 11.1 to 12.1 MW dependent on the economic conditions. Compared with the current economic rate of inflation and discount rates (interest) being offered by banks (Table 5), the longer the project



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life span, the more sites that become viable to exploit. The increase in discount rate from 3% to 5% resulted in uneconomic sites being eliminated allowing a more accurate estimation of the low head hydroelectric potential of NI to be identified. From Table 1 a maximum potential of 12.07 MW was identified, which was reduced when further economic parameters were taken into account, ranging from 12.05 to 11.2 MW (11.2% range). The potential 304 hydroelectric sites in Table 1 were reduced to 190–285 depending on the discount rate used and the capital repayment period. The allocation of the ROC unit price attributed to each site was based on the installed capacity of each site. Thus, the values attained to each site would have an important role on the predicted benefits of each scheme thus determining whether a site is economically viable or not. The results obtained are comparable to those of Shaw (2003) who reported that the capacity factor, annual escalation rate of local market electricity price and installation cost are the factors most likely to affect the viability of any small hydro scheme. The cost per kilowatt has a significant effect on the viability of any low head hydroelectric plant as smaller sites will always incur higher costs thus their economic viability requires a closer scrutiny if development is considered. This is consistent with the findings reported by Müller and Kauppert (2002), Shaw (2003), Kaldellis, Vlachou, and Korbakis (2005), Cyr, Landry, and Gagnon (2011) and Abbasi and Abbasi (2011). The formula used for estimating the total capital cost of a scheme (Equation (10)) was accurate to within ± 25%. The RETScreen analysis classified more sites as Good, 112, compared to the 51 estimated with the B/C ratio economic assessment, less sites as Fair, 84–107, and similarly less sites classed as marginal, 60 compared to 138. The RETScreen analysis does indicate more sites as having a poor payback period compared with the B/C ratio assessment (48–8) (greater than 20 years). Similar to the method to determine the payback period in Equation (9), simple payback does not consider the influence of inflation on the value of money nor the impact of inflation of costs. The results obtained from RETScreen software used similar economic and technical parameters as those described in the methodology. The most significant barrier to the development of low head hydro in NI and in Europe is the water framework directive 2000/60/EC. The potential development of hydro power in NI will also have to deal with other environmental concerns such as land ownership, land drainage and Areas of Special Scientific Interest (ASSI’s). It makes sense to develop a site based on economics, but this must consider environmental and societal impacts. This may prevent some

Figure 8.

Number of viable sites according to economic conditions prevalent.


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Figure 9.

Installed capacity and annual power generation according to economic conditions prevalent.

of the investigated sites from installing a low head hydro scheme no matter how sound their economic viability. Figures 8 and 9 provide an overall summary of the techno-economic results obtained. Limits of the analysis presented in this study are dependent on an accurate estimate of the total capital costs predicted for each site (reported as ± 25%) (Aggidis et al. 2010) which are dependent on the available head and installed capacity of the site. Thus, an accurate assessment of the economic viability of each site can be difficult to achieve agreeing with research presented by Müller and Kauppert (2002), Shaw (2003), Kaldellis, Vlachou, and Korbakis (2005), Cyr, Landry, and Gagnon (2011) and Abbasi and Abbasi (2011); important factors such as the annual output power predicted for each site and the unit energy cost generated for the electricity should be highlighted. The annual power output calculated for each site assumes that average annual precipitation levels will occur over the lifetime of the system. A greater annual output power would improve the revenue stream for the site, increasing the B/C ratio with a smaller than predicted output would result in less sites becoming financally viable. Before a site is developed, detailed measurements should be taken to determine if costs will be appreciably higher.

5.

Conclusions

A techno-economic assessment of the viability of the potential low head hydroelectric ( ≤ 10 m) resource in NI was first estimated using Equations (1)–(9) calculating the annual power output and SPP for 304 sites; then classifying these as either, Good, Fair, Marginal or Poor. Further economic analysis found that 168–286 hydroelectric sites previously rejected by an earlier investigation (McCutcheon 1980) had a potential exploitable viability, which was dependent on the economic conditions. The results obtained using the economic parameters outlined in Table 3 were numerically verified using the software program RETScreen for both previously accepted and rejected sites. From Figures 8 and 9, a minimum of 198 sites were classed as economically viable, whereas 286 sites are viable if lower interest rates are available. From the results presented, an increase in the project lifespan and a decrease in the discount rate increase the number of sites becoming economically viable. Sites investigated with lower capacities were more likely



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to be unviable and had a minimal effect on the predicted installed capacity for low head hydroelectric sites in NI due to the size of their potential installed capacity. From the results obtained it was evident that the annual power output, the predicted unit energy price for electricity and the cost per kW of installed capacity have a significant effect on the viability of low head hydroelectric plants. Sites with a rating of Good and Fair had higher B/C ratios and economically viable for all the conditions applied. The RETscreen analysis provided a more conservative estimation of sites payback periods. Sites that were rated as Fair were more likely to be rated as Good, whereas sites that were classified as marginal would more likely to be classed as Poor, thus less economically attractive. Once the potential economically viable resource was determined, further problems for the low head hydroelectric potential of NI to be fully exploited to its maximum potential are administrative issues, lack of foresight, granting of licences, environmental constraints, and conflict with fishery interests and social factors. The results presented should be used with caution as they provide a first-order estimation of total potential of low hydro head in NI that is potentially economically viable with an accuracy in capital costs from Equation (9) of ± 25% indicating the error associated with the cost estimates presented in this paper over project life spans of 25–50 years assuming no other issues such as plant failure arise. The figures presented are based on the investigated sites experiencing typical or average meteorological conditions. Hydroelectricity power production requires water, higher levels of rainfall will result in greater power production and vice versa. Annual rainfall levels for NI are shown in Figure 1 from 1911 to 2013 (Anon 2013), variation in rainfall is unlikely to influence site viability as this has differed annually by ± 10.1% over 102 years (Anon 2013). Future research should be guided towards possible integration of low head hydro with water and wastewater systems and other intermittent forms of renewable energy to avoid conflict with other users of the aquatic resources of NI. Acknowledgements The authors would to like express a sincere appreciation to, Clark Shields of the Upperlands community group and Robbie T Maguire (Sr. and jnr.) of Newmills Hydro.

Disclosure statement No potential conflict of interest was reported by the authors.

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