Why is it Important to Model the Performance and Reliability of Photovoltaics Under Qatar's Climate?
Authors: Barth Nicolas , Ennaoui Ahmed , Ahzi Saïd 
Published: July 2019

Photovoltaics (PVs) are the solar harvesting devices currently envisioned to anchor the will of increasing Renewable Energy in Qatar. These devices are planned to be deployed within the next few years to achieve the GW scale. Less oil and gas dependence is important on the very long timescale, as per the perspective of the energy security grand challenge of the state of Qatar. Within Qatar Environment and Energy Research Institute (QEERI), HBKU, Qatar Foundation, we are developing modeling and numerical simulation tools that aim at predicting the behavior and performance of photovoltaic panels. Based on scientific grounds, this work also aims to show how such a predictive tool is important for the energy transition of Qatar.

Manufactured PV panels are opto-electronic devices having as a core the solar cells, sandwiched within electrical collectors, generally connected together in modules that are finally encapsulated and mounted as the panel. For silicon-based solar cells, the mainstream technologies feature different laminated materials such as a front glass layer, encapsulating polymers and a metal-based back-sheet. Our initial modeling and related results are based on a two-dimensional design of the PV panel, with interest in the through-thickness physical state inside the panel.

Our current modeling is developed following a multi-physics approach capable of simulating the performance as function of the thermal behavior under any atmospheric conditions – and for any mounting conditions. We particularly consider the harsh conditions of Qatar's hot and humid desert climate. The modeling scheme of this initial work is illustrated in the support Figure that should be attached to this abstract. The computational code consists in three sub-models for this initial multi-physics modeling:

(1) the solar irradiance modeling which places the PV panel under mounting conditions within an environment having direct Sun light, diffuse light irradiance from the sky, and ground-reflected irradiance (albedo);

(2) the thermal modeling, allowing to compute the through-thickness temperature of the PV panel;

and (3) the electrical modeling, assuming a perfect yield of the current–potential “I–V” curves of the PV device (which is to say that the PV module is assumed stationary on the grid at its maximum power point, whatever the irradiance and temperature conditions).

The through-thickness temperature is then obtained within the PV device throughout the undertaken computational experiments. This temperature field is resulting from heat dissipation effects at the boundaries of the PV panel due to convection and radiation in the thermal environment, where ambient temperature and wind speed of the air may vary. Moreover, the solar irradiance data from Qatar is also used as input for the PV device at the front interface of the solar cell in the PV panel. Following this input from the solar radiation, and at any simulated time, the electrical yield of the PV device is also taken into account in the thermal balance. This can be done since the solar radiation not converted into electrical energy should end up as a thermal energy source (the device is not in open-circuit conditions).

Following this approach, we established numerical methods with application to long-term service (>1 year) conditions simulations, relevant to the Gulf region of silicon-based PV modules. Thermal variations are obtained due to the alternation between daylight and nights in Qatar, as well as seasons.

It can be noted that the PV performance simulations are used as first approximations to estimate long-term performances of the PV devices in Qatar. Later, in future works, the models will be coupled to the reliability and failure mechanisms relevant to the warranty period and consensus lifespans of the PV technologies. In future works, it is also relevant to account for soiling effects due to dust in Qatar, and estimate the nominal performance of PV panels/arrays/plants with mitigation solutions (cleaning etc.).