RELIABILITY AND AVAILABILITY ASSESSMENT

Reliability and Availability Assessment

Introduction2

Energy Production Of Small Hydropower Stations3

Cost-Benefit Analysis Of A Small Hydro Power Station4

Application Results8

Calculation of Energy Production9

Cost-Benefit Analysis10

Parametrical Analysis Of The Financial Behaviour Of A Small Hydro Power Plant14

Capacity Factor14

Turnkey Cost15

Subsidization Impact15

Electricity Price Escalation Rate17

Maintenance and Operation Cost Inflation Rate17

Investment Residual Value18

Taxation Impact19

Weibull Analysis Of Water Plant20

Use of Censor Data in Reliability Analysis21

Conclusions and Recommedations25

Reliability and Availability Assessment

Introduction

Hydropower has by far been the most mature renewable energy resource used for electricity generation, providing almost 1/5 of our planet electricity consumption. In Greece, several -mostly large- hydroelectric plants are in operation, exceeding 3100MW of electrical power. Recently, the investors' interest was whipped up by the mass development of small hydro power stations, being in accordance with the E.U. target to increase small hydro capacity by 4500MW (50%) before the year 2010 (Tsang, 2006, pp. 96-105).

In this context, it is important to mention that small hydro power (SHP) plants are the most prosperous way for additional hydro power penetration in European electricity market, considering that most large-scale opportunities have either been already exploited or face serious contradictions by local societies as environmentally unacceptable. On the other hand, SHP units usually operate as "run-of-river" systems, thus any dam or barrage used is quite small, not really disturbing the water flow rate. Although to date there is no internationally agreed definition of SHP plants size, the officially size in the local electricity generation market is set equal to 10MW maximum (Andrews, 2002, pp.58).

The present work is concentrated on the systematic investigation of the techno-economic viability of SHP stations on the basis of the NPV (net present value) and IRR (internal rate of return) criteria. Accordingly, the impact of the governing techno-economic parameters on the financial behaviour of SHP plants is analysed. This study is concluded by a sensitivity analysis properly adapted for the local market financial situation, in order to enlighten the decision makers on the expected profitability of the capital to be invested.

Energy Production Of Small Hydropower Stations

Hydro-turbines transform the water potential (mainly high pressure) into mechanical shaft power, which is finally converted to electricity (Fig. 1). The electrical power "N" available of every turbine used is proportional to the product of total pressure head "H" and volume rate "Q" of penstock, thus one may write:

(1)

where "?" is the total efficiency of the turbine (including the electrical generator), see for example Fig.1, "?" is the water density and "g" is the gravity acceleration.

The energy production over a time period "T" (e.g. one year) of a hydro power station based on "z" hydro-turbines of rated power "No" (generator loss is included) is given as:

(2)

or equivalently as:

(3)

where "CF" is the corresponding capacity factor of the installation and "dE" describes the line transmission and transformer loss as well as any self-consumption of the power station on annual basis (Procaccia, 1995, pp. 187-197).

It is important to underline that the water flow-rate through the turbine is not exactly the river flow-rate "Qr", because a minimum flow-rate "Qe" should remain in the ...