The data acquisition has begun since October 2003; the observations consent to determine:

—

: approximately 8,5 %

the efficiency of the PV system

— the efficiency of the

electrical generator set: 1 liter of gasoline produces

1,2 kWh electrical energy on average;

— the dispersed energy for

charge and discharge of the battery pack:

approximately 25 % of the total produced electrical energy.

On the basis of these experimental data and knowing the monthly average solar irradiation and the

monthly average electrical Monthly energy flows experimental data

loads, we can preview with

good confidence the electrical energy that has to be produced by electrical generator set and the fuel consumption month by month during the year.

Energy [kWh]

350 n 300 250 200 150 1001 50

jan

mar may jul

sep nov

0

These distribution diagram allows us to recalculate the optimum size of the photovoltaic field as a function also of the cost of the fuel. Maintaining constant the electrical load but

varying the power of the photovoltaic field, the annual energy the electrical generator have to produce has been calculated and, as a consequence, the annual cost of the fuel has been determined. The optimal size of the photovoltaic field is the one that determine the minimum total annual cost of the system, addition of annual fuel cost and annual PV field cost.

In the two following diagrams the annual total

Monthly energy flows calculated data cost of the system is

reported as a function of the photovoltaic field size

1800 2000 2200 2400 2600 Wp PV field

Euro/year 1600 1400 1200 1000 800 600 400 200 0

Annual cost

Annual cost of the hybrid PV-Fuel system gasoline feeded

Annual cost Euro/year 1400 1200 1000 800 600 400 200 0 1600 1800 2000 2200 2400 Wp PV field Annual costs of the hybrid PV-Fuel system LPG feeded

PV field gasoline total

using as a fuel, respectively, gasoline or Liquefied Petroleum Gas (LPG).

The annual PV field cost has been evaluated supposing an effective life of 25 years and a depreciation rate of 3%; moreover in this period three replacements of the battery pack have been considered. Fuel costs have been determined taking into account the cost of a liter of gasoline equal to 1,05€ and the cost of a liter of LPG equal to 0,55€; moreover with the use of the LPG a diminution of the electrical generator efficiency of approximately 15% has been considered. The optimal size of the photovoltaic field outcomes to be 2300 Wp utilising gasoline and 1900 Wp utilising LPG.

1. Conclusions

All costs of three kinds of PV system for domestic user in stand-alone are reported in the following table:

1. classic PV system

2. hybrid PV-Fuel system, gasoline feeded

3. hybrid PV-Fuel system, LPG feeded.

Using an hybrid PV-Fuel system, an investment cost reduction of approximately 28% is possible by supplying the electrical generator with gasoline, and of approximately 35% in the case of LPG supply. The corresponding cost

reductions of electrical kWh are, respectively of approximately 23%, with gasoline supply and of 28% with LPG supply, confirming in such a way the objective of this project.

Moreover using an electrical generator of back up an increase of the reliability and the continuity of electrical energy service has been obtained.

A second experimental activity will follow in which the Sunny Island will work as a normal inverter connected to the grid but able, in case of main voltage interruption, to behave as a back-up source, guaranteeing to the loads need it a high continuity of electrical energy service.

4. References

— Francesco P. Califano, Vittorio Silvestrini, Gianfranco Vitale. The planning of PV Systems, Publisher Liguori, Napoli 1988.

— Francesco Paolo Vivoli. Electric power from the sun, ISES Italy-ENEA, 1998

— G. Cramer, J. Reekers, M. Rother, M. Wollny. The future of village electrification — More than two years of experiences with AC-Coupled Hybrid Systems -, SMA Regelsysteme GmbH — Niestetal