Dear Hussein,

Unfortunately there is no simple answer to this as it depends how you operate the PVT panel. Please see, for example, Fig. 9 in: http://www.sciencedirect.com/science/article/pii/S0306261914000907

Best,

Christos

Dear Christos: Thank you for the interested article. I went through it. I agree with you my question is a bit general and need to be more specific. What I am asking about is how much the range of improvement in temperature and efficiency of PV in PVT claimed by researchers in literature? Experimental results not simulation is the needed one. Back to your article and particularly Figure 16, which is a very good comparison, we can see the percentage of electrical (E) is non-significant for PV alone comparing with other five scenarios. So that, the improvement electrical production is low. May be because of the low temperature in London. But in hot regions the temperature is high and PVT expected to reduce the temperature more.

Dear Hussein,

Sorry for the delay. I thought I had already replied but my reply did not appear. So I am re-writing this.

Most such models are validated against experimental data, and so the results are going to be similar to experimentally obtained values (within some acceptable error). There should be very little disagreement on this between the two.

In that figure that you mention (Fig. 16), but also in Table 2 (the values are the same just shown in a different way), you see that the PVT system we recommend with a fully-covered panel and with a flow rate of 20 L/hr (P=1;Vp=20L/hr) is only slightly better than PV only (by 4.4% in terms of electrical demand). The reason why the increase appears low is because of the decision to run the PVT panel at low flow rates in order to promote higher temperatures that also support the generation of hot water (i.e. we also care about the PVT system's thermal output, not just the electricity produced). If you prioritise electricity only, you would use a PVT system with a fully-covered panel and with a significantly higher flow rate of 160 L/hr (P=1;Vp=160L/hr). This allows a higher electrical output by 9% compared to PV-only, which is double than before. The hotter the climate the larger this benefit will be because the more "cooling" the water flow can do to the panel. We've seen reported improvements up to 10-15% being reported in the literature.

I hope this answers your question.

Best,

Christos

Thank you Christos for the clarification. Frankly speaking, the improvement in the thermal part efficiency is higher than that in the PV efficiency. So that, the research and researchers focus more on the thermal side view. As you mentioned 10-15% is small with respect to that of thermal part.