Renewable Energy Sources for the mCCHP-SE-RES Systems - Design for Micro-Combined Cooling, Heating and Power Systems - page 126

Table 3 The voltage variation of the solar cell in open circuit
Temperature [ ° C] 27 35 40 45 50 55 60

V OC [mV]

567.5 550 538.4 526.9 515.3 503.8 492.9

ʔ V OC / ʔ T [mV/ ° C]

− 2.18 − 2.3 − 2.3 − 2.31 − 2.31 − 2.18

Table 4 Main characteristics of the solar cells
Material Ef ciency (AM 1,5) Life cycle Costs (Euro/

(%) (years) W)

Amorphous silicon 5 - 10 <20

Polycrystalline silicon 10 - 15 25 - 30 5

Monocrystalline silicon 15 - 20 25 - 30 10

15 - 20

Gallium arsenure (monolayer)

Gallium arsenure (two layers)

20

Gallium arsenure (three 25 (30 % la AM0) >20 20 - 100

layers)

which leads to a low ef ciency. This is the reason why another parameter, P NOCT ,

which indicates the power at the normal operating cell temperature, should be taken
into consideration. For example, Table 3 presents the voltage given by the solar cell
in open circuit, as well as the voltage variation, depending on temperature, which
also implies a decrease of its ef

ciency.
Solar cells may supply an electric power on the surface unit of up to 300 W/m 2 .
Included in the module (photovoltaic system), it will be lower, since there is a
certain distance between the cells and the edge of the module. To calculate the
electric power, a radiance value of 1,000 W/m 2 , in optimum conditions of natural
illumination (clear sky, temperature between 25

C, total exposure to solar rays,
etc.) may be taken into consideration. The irradiance may decrease up to the value 0
during the night. Otherwise, intermediary values of 200, 400, 600, 800 W/m 2 ,
depending on conditions of illumination, exposure, etc. may be taken into con-
sideration. Table 4 presents the ef

- 40 °

ciency, life cycle, and the cost for different types

of solar cells.

7.2 Connection to Load

Photovoltaic systems are designed to fuel both the electric loads in continuous
current, and those in alternative current. In both cases, they may operate in insular
mode (operating as an independent generator) Figs. 22 and 23 , or connected

through the electric grid, injecting electric energy into it

—

Figs. 24 and 25 .
From Figs. 22 , 23 , 24 , and 25 what may be observed is the fact that the electric
accumulator appears in all the schemes, as an element with the role of taking up

—