ENERGY BALANCE

The measured data have been processed according to the guidelines of the Joint Research Centre of the European Communities (1988). The used abbreviations have the following meanings:

TEBI: total energy input to battery

TEBO: total energy output from battery

ТЕ 11: total energy input to inverter

TISA: total incident solar energy (array plane)

ETAsa: potential maximum average array efficiency

SIA: specific solar input

SAY: specific array yield

Figures 1 to 3 show monthly means of daily sums. By comparing figs. 1 and 2 it can be seen, that the energy input to the inverter exceeds the battery output. The difference was provided by the solar generator directly to the inverter. The maximum energy capability of the generator (TISA * ETAsa) is considerably higher than the energy used for propulsion (inverter input). So the surplus of energy indicates that the operation mode of the boat was not adapted to the energy supplied. In fact, the boat was used in different operation modes for certain periods. (The PV system of the "Korona" being a research vessel has not been designed for a special operation mode.) Consequently the specific solar input

and the specific array yield (fig. 3) show the same behaviour.

In fig. 4 the PV generator output is plotted versus the irradiance. As only a few values indicate operation at the maximum power point, it is evident that the generator was directly coupled to the battery (no MPP tracking over the period covered by the presented data). Since the battery often was fully charged as

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3.89 5.89 7.89 9.89 11.89 1.90 3.90 5.90 7.90 9.90

4.89 6.89 8.89 10.89 12.89 2.90 4.90 6.90 8.90 10.90

I Eat. input (TEBI) Month H Bat. output (TEBO)

 

Fig. 1. Energy balance of the battery

 

kWh

 

In

 

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image490

consequence of the energy surplus, many output values lie within the lower part of the diagram.

 

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Fig. 3. Specific solar input (SIA) and specific array yield (SAY)

 

900

W

800

 

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100 300 500 700 900 1100

W/m’2

Fig. 4. Plot of generator output power versus solar irradiance

 

Table 1 Indices of Performance

Подпись:Specific energy output: Array efficiency (mean): Array efficiency (maximum): Array utilisation factor:

(covered period: March 1989 – October 199o)

The fact that not all possible energy was used, which is expressed in the value of AUF (proportion of the array’s maximum energy capability that is actually used), leads consequently to rather low values of the overall efficiency ETA and the overall system performance SEO (table 1).

Updated: August 20, 2015 — 2:46 pm