JIE_hybrid_PVT_model

Presenter: Sameer Simms
Supervisor: J.F. Dorville
University of the West Indies, Mona Campus
JIE Conference, Knutsford Court Hotel, Kingston, Jamaica
September 24, 2014
Dynamic Numerical Model of a
2D Hybrid PVT Panel

The purpose of this presentation
• To give a comprehensive report on the work
done to simulate the performance of a 2D
hybrid photovoltaic thermal collector (as well
as a PV panel) using a dynamic numerical
model.
Dynamic Numerical Model of a 2D Hybrid PVT Panel, Sameer Simms

Outline
• Introduction
• Description of the Model
• Results and Analysis
• Conclusion and Future Work

Introduction
.

• More than half of the sunlight incident upon
photovoltaic cells does not contribute to useful
energy production. (Annis and Baur, 2011).
• In Jamaica PV cells can operate at
temperatures in excess of 55°C
according to Field (2011).
• Crystalline silicon PV cells have a negative
temperature coefficient of about -0.45%/°C
(Du, 2013).
• Efficiency is reduced for high temperatures.
So what is the problem?

Temperature of PV panels during
operation in Jamaica
Field, D. A. (2011). The
performance characteristics of
commerically available
photovoltaic technologies under
Jamaica's climatic conditions.
MPhil thesis (112 pages),
University of the West Indies,
Mona Campus, Jamaica, WI.

Solution to the problem of high
operating temperatures.
Solar Thermal
Collector
Photovoltaic
Panel
Lower Operating
Temperatures

So what about the current status of PVT systems?
• Amrutkar et al. (2010) stated that the feasibility of
solar energy as a new source will improve when
better efficiencies are obtained and equipment costs
are reduced.
• Current systems on the market feature relatively low
thermal efficiency. (on average 30%-50%)
• There has been a relatively low implementation
of PVT systems due to high initial costs.

Optimizing the thermal and electrical
efficiencies through design
Recall that a PVT collector is a hybrid system made from the
combination of PV cells and a solar thermal collector.
• Higher thermal efficiency may be realized from higher
operating temperatures and larger heat extraction rates.
• Higher electrical efficiency may be realized from lower
operating temperatures and larger heat extraction rates.
• Do you see the dilemma faced by researchers?
• THERMAL COUPLING IS A BIG PROBLEM

Current PVT system
Photo of TESZEUS® PV-T Photovoltaic-
Thermal Hybrid Solar Collector
http://www.tessolarwater.com/index_
en.html?zeuspv-t.html&2

Methodology
• A dynamic 2D numerical model was created using
Scilab (version 5.4.1).
• The model was used to simulate the performance of a
PV panel and hybrid PVT collector in controlled
conditions.
• Various meteorological variables collected at the UWI
Mona campus were fed into the model to produce
simulated data for both PV and PVT technologies.
• The performances of both were compared.

Description of the
Model
.

Assumptions
• Heat losses through side insulation is negligible
• All energy not converted to electricity by PV cells is
converted to heat
• Each layer is isothermal
• All material properties are independent of
temperature
• The difference in the temperatures of the PV cells
and metal absorber is negligible

Electrical Component
• 𝜂 𝑒𝑙=𝜂 𝑟𝑒𝑓[1−𝛽(𝑇 𝑝𝑣−𝑇 𝑟𝑒𝑓)]
Determines the efficiency at an instant in time
based on the temperature of a particular PV cell.
• 𝐼 𝑝𝑣=𝜏 𝑔 𝜏 𝑒𝑣𝑎 𝐼
Determines the net flux incident on a particular
PV cell after sunlight passes through the glass
and EVA layers.
• 𝑄 𝑒𝑙=𝜂 𝑒𝑙 𝐼 𝑝𝑣 𝐴 𝑝𝑣
Determines the electrical output of a particular
PV cell based on the previous calculations of 𝜂 𝑒𝑙 ,
𝐼 𝑝𝑣, and cell area.

Thermal Component 1
Temperature of primary layers
• 𝑇 𝑝𝑎(𝑖+1)=𝑋0 𝑇 𝑤(𝑖)+𝑋1 𝑇 𝑔𝑒+𝑋2 𝑄 𝑝ℎ(𝑖+1)+𝑋3 𝑇 𝑝𝑎(𝑖)
• 𝑇 𝑤(𝑖+1)=𝑇 𝑤(𝑖)+𝑌0 𝛥𝑡
• 𝑇 𝑔𝑒(𝑖+1)=𝑇 𝑔𝑒(𝑖)+𝑌1 𝛥𝑡
Where,
𝑋0=(𝑈 𝑝𝑤 𝐴 𝑝𝑣 𝛥𝑡)/𝑚 𝑝 𝑐 𝑝
𝑋1=(𝑈 𝑝𝑎 𝐴 𝑝𝑣 𝛥𝑡)/𝑚 𝑝 𝑐 𝑝
𝑋2=(1−𝑋0−𝑋1)
𝑋3=𝑋2(𝛥𝑡/(𝑚𝑐) 𝑝𝑎)
𝑌0=𝑄 𝑝𝑤(𝑖+1)/𝑚 𝑤 𝑐 𝑤
𝑌1=𝑄 𝑝𝑔𝑒(𝑖+1)/(𝑚𝑐) 𝑔𝑒

Thermal Component 2
Energy balance of primary layers
• (𝑚𝑐) 𝑝𝑎(𝛥𝑇 𝑝𝑎)=(𝐼 𝑝v 𝐴 𝑝−𝑄 𝑝𝑔−𝑄 𝑝𝑤)𝛥𝑡
• 𝑚 𝑤 𝑐 𝑤(𝛥𝑇 𝑤)=(𝑄 𝑝𝑤−𝑄𝑖𝑛𝑠)𝛥𝑡
• (𝑚𝑐) 𝑔𝑒(𝛥𝑇 𝑔𝑒)=(𝑄 𝑝𝑔−𝑄 𝑎)𝛥𝑡

Thermal Component 3
Thermal power produced by primary layers
• 𝑄 𝑝ℎ=(𝑄 𝑒𝑙/𝜂 𝑒𝑙)(1−𝜂 𝑒𝑙)
• 𝑄 𝑝𝑔=𝑈 𝑝𝑔 𝐴(𝑇 𝑝𝑎−𝑇 𝑔e)
• 𝑄 𝑝𝑤 =𝑈 𝑝𝑤 𝐴(𝑇 𝑝𝑎−𝑇 𝑤)
• 𝑄𝑖𝑛𝑠=𝑈𝑖𝑛𝑠 𝐴(𝑇 𝑤−𝑇 𝑎)
• 𝑄 𝑐𝑤=ṁ𝑐 𝑤 𝛥𝑇 𝑤
• 𝑄a=UaA(𝑇ge-𝑇a)

Results and Analysis
.

PV vs PVT performance (under controlled conditions)
The PV panel was significantly hotter and so
suffered more losses in electricity generation
The PVT collector was much cooler and had a
higher average electricity power output.

Thermal performance of PVT (under controlled conditions)
• As the absorber got warmer,
the thermal power output
decreased.
• This effect is a direct result
of the reduction in the
temperature gradient
• The temperature gradient
reduced with time due to
several factors, chief of
which is the small volume of
water in the system allows
the water temperature to
rise almost as quickly as that
of the absorber.Dynamic Numerical Model of a 2D Hybrid PVT Panel, Sameer Simms

Comparison of temperature variations (under real conditions)
• The PV-T collector peaked
at 51.7oC while the PV panel
was considerable hotter at
89.5oC.
• It is also evident, that the
PVT panel is much more
stable to changes in incident
irradiances (a high thermal
inertia is responsible for
this).

Comparison of electricity generation (under real conditions)
• The total electrical output
from the PV panel was 0.37
kWh while that from the
hybrid collector was 0.42
kWh, a difference of 13.5%.
• The average efficiencies of
the panel and collector were
8.9% and 10.1% respectively.
• The peak power for the PV
panel and hybrid collector
were 107.1 W and 110.0 W
respectively.

Thermal power generation (under real conditions)
• The peak power was 158.6 W
which is about 44.2% larger
than the peak electrical
output.
• The net thermal output was
0.14 kWh which is drastically
smaller than that of the
electrical energy output.
• The low thermal energy
output is a direct
consequence of heat energy
losses during periods of low
incident irradiance.

Conclusion and Future Work
• A dynamic model was created to simulate the performance of a
2D water-below-absorber hybrid PV-T collector.
• The results of the simulation indicated that the hybrid panel
operated at lower temperatures than the PV panel.
• This lower operating temperature resulted in an increase of
13.5% in the electrical energy output of the PV cells.
• The total energy output (14 kWh) was significantly lower than
expected.
• This poor thermal performance was a consequence of heat
losses during periods of low incident irradiance. A solution to
this problem, stopping the circulation of the thermal fluid
during said periods, was applied. The result was a 142.9%
increase in the thermal energy output (now 34 kWh).

Conclusion and Future Work continued
• The model provided realistic results
• The results were detailed and seemingly accurate
• The time taken for the model to produce results needs
to be reduced
• Work needs to be done to upgrade the model into a 3D
dynamic one
• The model needs to be validated

Questions?
THANK YOU FOR LISTENING

JIE_hybrid_PVT_model

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