In this article we will discuss about:- 1. Introduction to New Energy Sources 2. Requirements of New Energy Source 3. Design Requirements 4. Exergy Analysis 5. Economic Evaluation 6. Internal Rate of Return for Investment.
Contents:
- Introduction to New Energy Sources
- Requirements of New Energy Source
- Design Requirements for a New Energy System
- Exergy Analysis of Energy Systems
- Economic Evaluation of Energy Systems
- Internal Rate of Return for Investment in New Energy System
1. Introduction to New Energy Sources:
Modern societies require increasing amounts of energy for domestic, industrial, commercial, agricultural and transport uses. These energy needs are being met by a combination of short-term, depletable fossil fuel supplies and long-run, renewable energy sources. Economic growth will require massive infusions of energy in the foreseeable future. Urbanization and industrialization are both energy intensive.
ADVERTISEMENTS:
Even rural development and agricultural productivity and production depend on larger and larger amounts of power. There is an urgent need for the development of new and more efficient energy sources.
2. Requirements of New Energy Source:
Heavy demand for energy poses the problem of developing new, efficient methods of energy production based on latest achievements in science and technology. At the present time, the existing methods of converting different forms of energy into electricity are limited because these are mostly based on depleting chemical fuel reserves.
The conversion technologies are inefficient based on large material consumption. Large amounts of heat and by-products are released heating the nearby water sources and contaminating the environment with release of harmful waste matter into the atmosphere. This may be regarded as one of the most important social problems.
ADVERTISEMENTS:
Research of new energy sources and development of efficient conversion technologies have to meet the following requirements:
i. The energy source and conversion technology to usable form should be harmonious to the five bodies of nature, i.e., the earth, the water, the wind, the fire and the sky. These natural sources should be used as minimum as possible and the harmful waste should not be rejected to these bodies by the energy system.
ii. The source of energy should be an indigenous resource. It should be available in considerable quantities.
iii. The local source of energy should be used to conserve foreign exchange and generate local employment.
ADVERTISEMENTS:
iv. The conversion technologies should be based on available scientific and technological knowledge. It should be possible to design, manufacture, assemble, install, operate and maintain the energy system by local people using local skills and materials.
v. The conversion technology should be flexible and modular and rapidly deployed.
vi. There should be ease in adding new capacity, less risk in investment, lower interest on borrowed capital because of shorter lead times and reduced transmission and distribution costs.
vii. It should be financially and economically competitive with current systems.
ADVERTISEMENTS:
viii. There should be no technical and economic uncertainties in the new energy systems.
ix. It should have high energy efficiency and low economic and financial costs.
x. The new energy source should have flexible applications for lighting, heating, cooling, mechanical work.
3. Design Requirements for a New Energy System:
ADVERTISEMENTS:
The design and analysis of a new energy system have to be approached from a system analysis view point combining technical design with economic analysis. There is no single solution to a given task in energy utilization, and each problem has to be analysed separately from fundamental principles.
It is necessary to match the available energy source to the task at hand and there is no general solution. Proper design and optimization of new energy systems may require a high level of engineering analysis. The system engineer has to decide on the basis of the task at hand, the system available to achieve a technical solution and economies involved.
1. Collection System:
Energy delivery of a collector depends on its physical configuration, its operating temperature, and the climatic parameters of the solar radiation level, ambient temperatures and wind speed. Collector performance is also determined by secondary variables, including fluid flow rates, collector orientation, geographic location and system control strategy. Table 18.1 provides a collector- task classification showing the best combination of collectors and tasks.
The detailed design of a collector will depend upon the selection of the type of collector, type of focussing and concentration ratio and also type of selective coating for the absorber. All these are functions of fluid temperature required as shown in Fig. 18.1.
2. Solar System Model:
The rational design of a solar-thermal system requires the knowledge of the dynamic interaction of all system components for solar collection, thermal storage, fluid circulation and energy distribution, control and non-solar auxiliary energy source.
Computers are generally required for calculation of numerical solar models because many component models are non-linear and a closed-form simultaneous solution of the equations describing a system is not possible in all but the simplest cases. In addition, most solar systems operate in a continuously changing, transient manner subject to short-time scale changes in all forcing functions.
Since meaningful modeling results require delivery totals for fairly large periods (months or years), and since solar systems respond on fairly short time scale (minutes or hours), a great many calculations are required. For these reasons computerised models are the method of choice for analysis of most solar-thermal systems.
A simple block diagram of the computer model of a solar system using hourly weather data shown in Fig. 18.2.
3. Optimum Task to Energy Level Match:
Solar energy is the only major source where entropy level of the form in which it is collected can be manipulated to provide an optimum task-to-entropy- level match. This match can be accomplished by varying degrees of concentration of solar energy or by improved receiver design, for example, with an evacuated cover.
For high-entropy uses such as space heating, water heating and crop drying, low temperature, high-entropy solar energy collected by flat-plate collectors provides the best match between the energy source and task. The operation of a solar-thermal generating station requires low-entropy (high- temperature) thermal energy to match the task of producing low-entropy shaft work.
4. Exergy Analysis of Energy Systems:
The exergy analysis of air energy system enables us to identify the sources of irreversibilities and inefficiencies with the aim of reducing the losses and achieving the maximum resource and capital savings. This can be achieved by a careful selection of the technology and optimization of design of the system and components. Exergy analysis involves the determination of exergy efficiency or second-low efficiency.
1. Exergy Efficiency:
The analysis of energy systems based on second law of thermodynamics calculates the changes in the quality of energy or entropy. The exergy of a system decreases as a process loses its quality.
An exergy balance of an energy system gives:
Where,
Ein = Eu + Ed [kW]
Ein = Rate of exergy input [kW]
Eu = Rate of useful product exergy [kW]
Ed = Rate of destruction or loss of exergy [kW]
Exergy efficiency, e of an energy conversion system is the ratio of actual performance of system and ideal performance of the system.
2. Exergy Efficiency of Solar Collectors:
The exergy efficiency of solar collectors can be given as:
where,
ṁSC = mass flow rate of collector fluid [kg/s]
Δe = exergy increase of collector [kJ/kg-K]
Δh = enthalpy increase of collector [kJ/kg-K]
E = Incident solar radiation [kW]
ESR = exergy flow rate of solar radiation [kW]
Ƞsc = efficiency of solar collector
The efficiency of solar collector:
where,
T0 = Ambient temperature [K]
T1 = Inlet temperature of collector fluid [K]
T2 = Outlet temperature of collector fluid [K]
ΔTSC = Temperature increase in collector [K]
The exergy efficiency of a solar collector will increase with the increase of solar collector efficiency, ƞsc.
The exergy efficiency of flat plate solar collector is low, because this type of solar collector transforms low-entropy (high-temperature) solar radiations into high-entropy (low-temperature) energy of air or water.
The exergy efficiency of a concentrating type solar collector is high as it produces low-entropy (high-temperature) fluid at 700 to 1400 K.
Example:
A flat plate collector heats water from 305K to 335K. Calculate the exergy efficiency of the collector if its efficiency is 48% and ambient temperature is 293K.
Solution:
5. Economic Evaluation of Energy Systems:
The following methods may be used for economics evaluation of energy systems:
1. Life cycle costing method,
2. Net benefit (cost saving) method, and
3. Net benefit/cost ratio method.
1. Life Cycle Costing Method:
The total present values of total annual value of the alternative energy systems are calculated. The system with the lowest cost is the best economic alternative.
The present value of a system:
where,
I = Capital cost or investment cost.
RV = Residual value at nth year
n = no. of years of economic evaluation
i = interest rate
OMj = Annual cost of operation, maintenance, repair and replacement in the year j.
pcon = initial price of conventional energy
Qcon = energy requirement (conventional)
e = escalation rate of energy cost
2. Net Cost Savings Method:
The present value of cost savings:
3. Net Benefit/Cost Ratio Method:
6. Internal Rate of Return for Investment in New Energy System:
A variety of technical, economic and financial factors determine the financial feasibility and economic attractiveness of investments in new technologies. Investment decisions are made by comparing the cost of a project for new energy system, which depends upon the price of capital with expected returns (yearly cash flow). The price of capital is either the interest rate of loans or the rate of return on equity or investment in the new system. The degree of risk associated with a new system affects the price of capital; high risk ventures cost more.
Figures that are widely used to evaluate the financial and economic aspects of new projects are the internal rate of return (IRR), the gross payback period (GPB) and net present value (NPV), all of which are related.
The internal rate of return (IRR), which measures how profitable a project is, is basically the discount rate (r) at which NPV is zero.
For a project with an expected equipment life of N years and expected net cash flow of Qt in year t, the IRR(r) is defined by:
Where the net cash flow (Qt) is given by
Qt = (1 – Tt) (St – Omt – ALPt)
Where for the year t,
St = saving on fuel,
OMt = operation and maintenance cost
ALPt = annual loan payment
Tt = corporate income tax
Given the capital cost, equipment lifetime and cash flow sequence; it is possible to calculate the IRR as shown in Fig. 18.3. The IRR should be great in the cost of capital.
