Hydroelectric Power Generation Engineering, Design, and Economic Analysis

 

For:  [-------------], Carate, Costa Rica

 

By:  Osa Water Works, S.A.

 

October 9, 2002

 

Introduction

 

            This document includes a feasibility analysis for the installation of an AC-Direct hydroelectric system for providing continuous electrical power to [-redacted-].  A system design and quote for procurement and installation follows.

 

Data Summary

 

            Previous field investigations by [-redacted-] identified the most viable approximate pipeline trajectory for the development of hydroelectric power generation from the one stream with sufficient year round flow to provide for continuous hydroelectric power generation.  The land surface profile of the trajectory is shown below.

  

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 


 

            At the time of the survey a stream flow of 120 gpm was approximated at the optimal site for deployment of the hydroelectric water intake.  As shown in the graph above, the vertical relief from the intake point to the optimal generation point is 640 feet.  At the 68% efficiency of the AC turbine contemplated for this installation, half the observed flow can be diverted for hydroelectric generation of 4.7 kW.  Although the survey was undertaken during the rainy season, conditions during and preceding the survey were unseasonably dry.  A water flow measurement made in the dry season (March 16, 2002) by [-redacted-] personnel revealed a flow rate of 62 gpm, which means that in the driest time of the year all of the flow would have to be diverted to achieve comparable power generation.  Verbal reports from [-redacted-] personnel suggest that the flow observed on the day of the survey (10/5/02) is either sustained or exceeded in all but one or two months (March and April) of the dry season.  Average flows are considerably larger during most of the year and capable of sustaining much greater power generation rates. 

 

            On the basis of the information collected and that provided by [-redacted-] personnel, an AC-direct mini-hydro system can be sustained year round on the basis of the measured flows and vertical relief.  A system design has been prepared that will enable the generation of power based on a range in flow from 40 gpm to 120 gpm, which corresponds to a theoretical hydroelectric power generation potential ranging from 3.1 kW/hour to 9.4 kW/hour.  It is expected that the average annual production will be in the range of 7 kW/hour on the basis of seasonal rainfall distribution and the actual power demands of the facility.

 

            A conceptual design of the system under proposal is presented below.

 

  

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 


 

            System components are described briefly below:

 

  1. Intake.  Water is to be captured by a proprietary water intake infiltration gallery developed by Osa Water Works.  The infiltration gallery and coffer dam provide for the collection of water in the stream sediments of the river being developed.  The infiltration gallery is guaranteed maintenance free and has a usable life expectancy, barring acts of God, measured in decades.

 

  1. Pipeline.  A three-inch diameter PVC pipeline is proposed in order to accommodate the flow required and to minimize the pipe friction losses expected over the approximate 4000 foot length of the pipeline.  Because the anticipated static pressure varies from 0 to 278 psi, OWW recommends the installation of PVC pipe of three different pressure ratings:  160 psi, 250 psi, and 350 psi (see diagram above). 

 

  1. Hydroelectric Plant.  An AC-Direct 3-10 Kw/hour mini-hydro power generator with adjustable nozzle diameter will provide for power generation throughout the flow regime from 60 gpm up to 200 gpm.  It is anticipated that during most of the year this nozzle will be set to provide for 7 kW/hour, thus exceeding the actual facility power demand under normal power usage conditions.  During dry months, when power generation potential is lower, it will be necessary to reduce the nozzle size accordingly.  Attentive facility management of power consumption patterns may also be required.  During high flow conditions, the nozzle can be opened if desired to boost power output up to a ceiling of around 10 kW/hour.

 

  1. Power Bodega.  A simple one-story concrete structure measuring 8 feet by 12 feet will house the hydroelectric generator.

 

  1. Transmission Cable.  The final component of the system is a run of 1,182 feet of electrical cable from the hydroelectric bodega to the lodge.   Whereas this cable can be either buried in conduit or run above surface, the quote that we have prepared is for the least expensive alternative, above surface power transmission.

 

Scope of Work.  The project will consist of the following job elements:

 

  1. Materials and Equipment Procurement. 
  2. Fabrication of infiltration gallery in Puerto Jimenez.
  3. Construction of power bodega
  4. Installation of infiltration gallery and coffer dam
  5. Installation of pipeline
  6. Installation of power transmission cables.
  7. Delivery and installation of hydroelectric power generator
  8. Commissioning, testing, and training.

 

Budget

 

            The table below details the materials required and a budget for turnkey system installation.

 


Time Line

 

 

 

 

 

 

 

 

 

 

 

 

 

 

            The table below provides a time line for completion of key project elements.  Due to the relative danger of the work required for pipeline installation, OWW is not prepared to deploy its pipeline crew for this job during October and November owing to the potentially life-threatening interference of heavy rains with the highly difficult nature of pipeline installation along semi-vertical forest mountainsides.  Since the generator must be custom manufactured, there is an unknown lag time in delivery.  Preliminary pipeline, intake, and bodega construction could be undertaken as early as December.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Economic Analysis

 

            The cost of the proposed power system was used as the basis for an economic analysis of the proposed hydroelectric power generation system.  Economic comparisons of the hydroelectric alternative were made for two cases:  1) Diesel power generation that produces power output comparable to that of hydroelectric power generation;  and 2)  Actual patterns of diesel power generation at [-redacted-].  Parameters common to both that were used for the analysis included the following:

 

  1. Useful life of hydroelectric system:  20 years
  2. Diesel Generator Value:  $12,000
  3. Mean Diesel Value:  $2.00/gallon
  4. during useful life:  2 times
  5. Fuel Consumption for generator:  1 gallon per hour
  6. Dollar Inflation:  0 % per year
  7. Amortization:  Assume depreciation is constant across useful life of system.
  8. Backup Generator Replacement during useful life:  1 time.
  9. Diesel Generator Operation to supplement hydro:  5 % of operation without hydro.
  10. Hydroelectric Generator Replacement:  $6000
  11. Value of money:  For the sake of expediency and transparency of the analysis, the interest rates of a loan to offset capital outlay and the interest accrued by investing comparable capital in secure investments as an alternative were not factored into the economic analysis that follows.

 

The parameters specific to the two regimes of generator usage that are compared with the hydroelectric alternative are listed in the table below.

 

Economic Analysis Parameter

Comparable Power

Actual Usage Patterns

Diesel generator replacement

2

1

Time Generator Turned On / Day

24

10

Annual generator maintenance

1000

500

 

Calculations

 

  1. Comparable Power:  Total cost of full-time diesel power generation for 20 years.
    1. Generator replacement:  $24,000
    2. Generator maintenance:  $20,000
    3. Fuel Consumption:  $350,400
    4. Total Cost:  $394,000
    5. Annual Cost:  $19,720

 

  1. Actual Usage Patterns:  Total cost of diesel power generation assuming current usage patterns.
    1. Generator replacement:  $12,000
    2. Generator maintenance:  $10,000
    3. Fuel Consumption:  $146,000
    4. Total Cost:  $168,000
    5. Annual Cost:  $8,400

 

  1. Hydroelectric Alternative:  Total cost of hydroelectric alternative over useful life.
    1. Hydroelectric capital cost:  $45,640
    2. Hydroelectric maintenance:  $6,000
    3. Total Cost:  $51,640
    4. Annual Cost:  $2,582

 

  1. Investment Pay Off
    1. Comparable:  2.6 years
    2. Actual:  6.1 years

 

  1. Annual savings After Pay Off
    1. Comparable:  $17,138
    2. Actual:  $5,818

 

  1. Cost / Benefit Analysis.  The costs of hydroelectric and diesel power generation are outlined above.  However, the benefits include additional considerations that cannot easily be assigned monetary value.  These are detailed below.

 

    1. Renewable Resource Utilization.  Mini-hydro systems have been declared in the most recent global environmental summit in Johannesburg as a renewable resource.  Diesel, of course, is a fossil fuel and is a non-renewable resource.  Implementation of mini-hydroelectric power generation at [-redacted-] is, therefore, an exercise in responsible planetary stewardship.  In a more mercantilistic vein, since [-redacted-] is an “Eco-Lodge,” hydroelectric power generation represents a de facto marketing tool.

 

    1. Emissions.  Diesel fuel, beyond being a non-renewable energy resource, emits upon combustion carbon dioxide, carbon monoxide, and a variety of nitrogenous compounds, all of which are greenhouse gases.  Hydroelectric power generation has no emissions whatsoever, and has no effect on climate change.  In addition to exercising responsible planetary stewardship, a reduced greenhouse gas emissions operation is a strong marketing tool for an Eco-Lodge.

 

    1. Maintenance.  Maintenance requirements of hydroelectric power generation equipment is nominal.

 

    1. Noise.  Although the hydro turbine does make noise, it is considerably less noise than what is emitted by a power generator, and the location of the proposed power bodega is so isolated as to never impose upon lodge guests.

 

    1. Transport.  Beyond the cost of diesel, its transport to the lodge is a very real expense (which was not factored into the economic analysis presented above).  The savings in time and effort of filling drums at the gas station, transport, and unloading at [-redacted-] are appreciable, particularly over the useful life of the system.  The hydroelectric power generation system is self-supporting and requires no transport once the system is installed.

 

    1. Value Added.  A functional hydroelectric power generation system increases the value of both [-redacted-] and the property upon which it is located.

Conclusions

 

            On the basis of the economic analysis presented, it is apparent that the hydroelectric alternative is clearly favorable from both a mid- and long-term perspective.  Even in the short term of five years or less, the hydroelectric alternative carries such ancillary benefits (both aesthetic and practical) as to warrant serious consideration.  When the increase in the value of the facilities and property is factored into consideration, it is almost certain that the hydroelectric alternative is the economically favorable alternative.