The integrated system might be more convenient than the two separated ones. But at the moment such level of integration has not been joined yet.

The main reasons are that at the moment the two technologies do not match very well.

If the efficiency of the PV module increases, the gain of efficiency of the collector is very low. With the crystalline Si cells, since the efficiency is decreasing as the temperature rises it is convenient to operate at the lowest possible temperature. That requires very efficient collectors operating at low temperatures.

Usually for the Domestic Water House application water is needed at about 50 ° Celsius, so the absorber will be at a temperature around the NOCT.

The amorphous Si technology since it is less affected by the temperature could be applied in a more efficient way in the hybrid application.

During test:

1) The tests on the component show that it is possible to reach good levels of electrical and thermal efficiency.

2) When mounted on buildings not always the thermal gain is warranted due to the seasonal mismatch, high insolation in summertime or in hours when the needs of thermal load are less, the difficulty to find efficient thermal seasonal storage or considering the storage in the project.

3) On public buildings with large glazed walls the thermal load is not high even in the low insolation months.

Experiments

To better understand better the possibility and the limits of the hybrid technology, the Photovoltaic PVT hybrid Dunasolar modules have been chosen for the experiments. They are tandem type amorphous Si and present a water thermal collector behind the module. The main electrical characteristics are reported in table 1.

Type	Isc (A)	Voc (V)	Pp (W)
Dunasolar 40	1.115	62.2	40

Table. 1 Electrical characteristics for the Dunasolar 40 module.

The modules have been tested at outdoor conditions by means of the Solar Tracker FT4000from Ecovide s. r.l. The main features are:

1. two axes

2. turnable platform sized 2×2 m2,

3. tilting from 0° to 99°,

4. azimuth from -180°, east direction, to 327 °.

5. spinning of the module plane from -35° to 35°.

The outdoor measurements were aimed to observe the behavior of the hybrid modules and to estimate the advantages when the module is being cooled with water.

In that way several experimental campaigns have been undertaken on the Dunasolar modules in real operating conditions other from STC.

At first the module was measured without any cooling. The metoclimatic conditions are reported in table2.

	Module Temp.	Radiator Temp.	Tube Temp.	Air Temp.	Humidity	horizontal global radiation	horizontal diffused radiation	Module Rad	Wind speed	Wind direction
Average	52.9	46.3	45	21.1	63.7	810	103	1024	3.9	257
Max	53.3	46.5	45.2	21.6	67.0	823	106	1035	5.0	294
Min	52.2	46.2	44.8	20.8	61.3	800	101	1018	3.0	160

Table 2. Meteoclimatic conditions with standstill water

The measurements have been repeated forcing water trough the collector. The meteorological and climatic conditions are reported in table 3.

	Module Temp.	Radiator Temp.	Tube Temp.	Air Temp.	Humidity	horizontal global radiation	horizontal diffused radiation	Module Rad	Wind speed	Wind direction
Average	44.0	24.9	26.5	20.7	62.3	829	86.4	1037	3.8	250
Max	44.1	25.1	25.1	21.1	64.9	834	87.3	1040	4.7	286
Min	43.3	24.7	26.2	20.3	58.55	821	82.4	1032	2.5	182

Table 3. Meteoclimatic conditions with forced water

The Figures 3 and 4 show the I-V and P-V characteristics of the module for both the cases.

VOLTAGE (V)

Figure 3. I-V characteristics for the Dunasolar module with and without cooling.

Figure 4. P-V characteristics for the Dunasolar module with and without cooling.

By comparing the graphs it is clearly seen how the open voltage surely decreases by cooling effect while the peak power gets just a bit higher.

The results seem to confirm the difficulty to take real advantage of the potential benefits, the breakthrough of the increased efficiency versus the more complicated and costly solution is not yet optimized.

Conclusions

The PV/T technology presents Interesting potential to gain advantages respect the two separated technologies. From one side the thermal collector could exploit the more highest standards for the reliability and the highest high tech consideration of the PV module, while the photovoltaics could take advantages of the wider marketing channels of the thermal collectors. The building Integration applications can be the bridge for allowing a good penetration in the market. At the end of the day instead to compete each other for the needed surface for their application, on the roofs for instance, the hybrid device could be efficiently installed providing both electricity and heating. Israel has reached a very Interesting position on that field. Nevertheless some important technical problems related to the proper materials choice like the absorption for the heating collector and the thin film technology, especially related to the amorphous Si option, although promising at the moment, will require more research and development and at the same time economical issues and market preparedness will call for more attention.

REFERENCES

DRAFT ROAD MAP ON PV/T SYSTEMS November 2000 Status Report of task 7 of the IEA PV Power Systems Program

Hybrid Photovoltaic Building Fagades: the challenges for an Integrated overall performance evaluation

PASLINK EEIG, Violestraat 21-23, 1000 Brussels European Economic Interest grouping of Outdoor Test Centres

PV-HYBRID Development of Procedure for Overall Performance Evaluation of Hybrid Photovoltaic Building Components, JOULE Project coordinates by PASLINK EEIG "Building Integrated multi PVT Solar System Roof Tile". Ami Elazari, 3rd ISE-Europe Solar Congress, Copenhagen, Denmark, 2000, june 19-22