Category SOLAR

Collector Storage Walls

The thermal analysis of collector storage walls is presented in Section 6.2.1, Chapter 6, where a diagram of the wall and the thermal gains and losses are given. The unutilizability concept, developed by Monsen et al. (1982), can also be applied in this case to determine the auxiliary energy required to cover the energy supplied by the solar energy system. Again here, two limiting cases are investigated: zero and infinite capacitance buildings. For the infinite thermal capacitance case, all net monthly heat gain from the storage wall, Qg, given by

Life cycle analysis is performed annually and the following are evaluated according to Eq. (12.10) to find the solar savings:

• Fuel savings.

• Extra mortgage payment.

• Extra maintenance cost.

• Extra insurance cost.

• Extra parasitic co...

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UNCERTAiNTiES iN ECONOMiC ANALYSiS

Due to the nature of the economic analysis, i. e., predicting the way various costs will occur during the life of a solar energy system, a number of uncertainties are involved in the method. The person responsible for the economic analysis of a solar energy system must consider a number of economic parameters and how these will develop in the years to come. A usual technique is to find how these parameters were modified during the previous years and expect that the same behavior will be reflected in the future years. These two periods are usually equal to the expected life of the system. Additionally, the prediction of future energy costs is difficult because international oil prices change according to the quantity supplied by the oil-producing countries...

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Optimization Using P1t P2 Method

As we have already seen in solar energy system design, the collector area is considered as the primary parameter for a given load and system configuration. The collector area is also the optimization parameter, i. e., the designer seeks to find the collector area that gives the highest life cycle savings. A method for the economic optimization was given in Section 12.2.3, in which life cycle savings

image298

FiGURE 12.3 Optimum collector area determination from the slope of the Fversus Ac curve.

are plotted against the collector area, Ac, to find the area that maximizes sav­ings. The optimization procedure can be simplified if life cycle savings (LCS) can be expressed mathematically in terms of the collector area. Therefore, the optimum is obtained when

Подпись: (12.35)Подпись:d(LCS) = 0

dAc

or, by using Eq. (12...

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THE P1t P2 METHOD

Another way of viewing the calculations of Example 12.7 is to obtain the pres­ent worth of each column and sum them to obtain the present worth of solar savings, using appropriate signs for each column. Therefore, the life cycle sav­ings (LCS) of a solar energy system over a conventional system is expressed as the difference between a reduction in the fuel costs and an increase in expenses incurred as a result of the additional investment required for the solar energy system, given by

Подпись:LCS = PjCF1FL – P2Cs

where

Pi = ratio of life cycle fuel cost savings to first-year fuel savings.

P2 = ratio of life cycle expenditure incurred from the additional investment to the initial investment.

The economic parameter P1 is given by

P1 = (1 – Cte) PWF(ne, iF, d) (12.32)

where

te = effective income ta...

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Hot Water System Optimization Example

When a solar energy system is designed, the engineer seeks to find a solution that gives the maximum life cycle savings of the installation. Such savings rep­resent the money that the user/owner will save because of the use of a solar energy system instead of buying fuel. To find the optimum size system that gives the maximum life cycle savings, various sizes are analyzed economically. When the present values of all future costs are estimated for each of the alter­native systems under consideration, including solar and non-solar options, the system that yields the lowest life cycle cost or the maximum life cycle savings is the most cost effective.

As an example, a graph of life cycle savings against the collector area is shown in Figure 12.1...

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Hot Water System Example

The example in this section considers a complete solar water heating system. Although different solar energy systems have different details, the way of han­dling the problems is the same.

Example 12.7

A combined solar and auxiliary energy system is used to meet the same load as in Example 12.5. The total cost of the system to cover 65% of the load (solar fraction) is $20,000. The owner will pay a down payment of 20% and the rest will be paid over a 20-year period at an interest rate of 7%. Fuel costs are expected to rise at 9% per year. The life of the system is considered to be 20 years, and at the end of this period, the system will be sold for 30% of its origi­nal value...

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Fuel Cost of Non-Solar Energy System Examples

The first example is about the fuel cost of a non-solar or conventional energy system. It examines the time value of an inflating fuel cost.

Example 12.5

Calculate the cost of fuel of a conventional (non-solar) energy system for 15 years if the total annual load is 114.9 GJ and the fuel rate is $17.2/GJ, the mar­ket discount rate is 7%, and the fuel inflation rate is 4% per year.

Solution

The first-year fuel cost is obtained from Eq. (12.4) as

t

CL = CFL JLdt = 17.2 X 114.9 = $1,976.30

0

(because the total annual load is given, the integral is equal to 114.9 GJ).

The fuel costs in various years are shown in Table 12.4. Each year’s cost is estimated with Eq. (12.13) or from the previous year’s cost multiplied by

Table 12.4 Fuel Costs in Various Years for Example 12.5

Year

Fuel ...

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DESCRiPTiON OF THE LiFE CYCLE ANALYSiS METHoD

In life cycle cost analysis, all anticipated costs are discounted to their present worth and the life cycle cost is the addition of all present worth values. The cash flow for each year can be calculated, and the life cycle cost can be found by discounting each annual cash flow to its present value and finding the sum of these discounted cash flows. Life cycle costing requires that all costs are projected into the future and the results obtained from such an analysis depend extensively on the predictions of these future costs.

Подпись: PW„ Подпись: C (1 + i)n~l (1 + d)n Подпись: (12.14)

In general, the present worth (or discounted cost) of an investment or cost (C) at the end of year (n) at a discount rate of (d) and interest rate of (i) is obtained by combining Eqs. (12.11) and (12.13):

Equation (12...

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