For 30 years c-Si PV module production has not incorporated many changes and developments from the R&D labs. The standard modules still consist of c-Si cell strings soldered and laminated in between EVA, white backsheet and front glass. The edges are sealed with silicone and framed with aluminum. On such modules product guarantees of 10 years and 80% power guarantees for 20 years are given. In our Photovoltaics International article (“Module technologies for high efficiency solar cells: The move away from powerful engines in old-fashioned car bodies”) we discussed the fact that these days, innovations like back contact, glass-glass and also bifacial modules are now slowly entering the PV the market.
Not only do standard modules look almost identical to ones from 30 years, they were also mostly all constructed and the components optimised for European conditions. Besides temperature cycling and damp heat testing, certification institutions also check how modules perform under conditions such as snow and hail, which are not typical for many regions, for example desert areas. The future of PV generation belongs to countries with high solar irradiance, which means mostly dry, hot and sandy or dusty conditions.
This blog describes the initiative of ISC Konstanz together with Chilean network of excellence, SERC, to develop a module designed for conditions in the Atacama Desert. Atacama has extremely PV-friendly conditions on the one hand, with the highest irradiation on earth, offering high UV and IR content combined with low temperatures at high elevations sometimes above 5000m. On the other hand drastic temperature changes and the dry, dusty and sandy ambient conditions create some challenges to making PV electricity generation in Atacama possible. However due to local content, R&D and green jobs creation in Chile the government is extremely interested not only to install systems in the Atacama desert but also to produce solar cells and modules locally and to create a technology “developed and made in Chile”.
For this reason the government in Chile is creating good conditions for PV applications and the energy ministry is investing lot of money in order to push PV R&D and to develop a module suited for Atacama conditions. Companies like Sun Edison, First Solar, EDF, Accioana Energia and MegaGroup are setting up large PV systems in the north of Chile and Mega Engineering even plans to set up solar cell and module production close to Santiago de Chile with the support of the government. The production is based on BiSoN technology already in production in Carmignano di Brenta with the use of local content, for example from the glass industry.
ISC Konstanz is adapting its BiSoN technology further in a publicly funded ‘Project SolarChilD’ (Solar Cooperation between Chile and Germany) with the goal to create a long lasting and extremely robust bifacial glass-glass module for Atacama Conditions (AtaMo). The first results from the project will be summarised in an oral presentation from Jorge Rabanal-Arabach, Enrique Cabrera et al. at the EUPVSEC in Hamburg on Friday in the 8:30 am module session (5EO.1.6.).
Long lasting module under harsh conditions
There are many deserts close to the equator – however many deserts show different conditions. When we compare the Atacama with the Sahara there are a few important differences for PV. The first one is that while systems in the Sahara must face south, do not make the mistake and install a PV system in the Atacama facing south, as you are in the southern hemisphere!
The Atacama is extremely dry as from the east the Andes are blocking the clouds and from the sea side the temperature inversion in the atmosphere is creating a “wall” so that the clouds are also blocked from the west direction. Therefore there are hardly any clouds. In combination with its very high altitude, the Atacama shows the best conditions for PV as it is cold and has extremely high UV and IR irradiation as there is very low absorption in the atmosphere. Not only are the conditions nearly perfect; a huge amount of electricity is also needed in the desert due to the mining activities in the North of Chile.
However, as already mentioned, besides these excellent conditions there are also challenges for PV generation in the Atacama Desert. Extremely high UV irradiation and soiling are the most prominent ones.
Therefore testing is done for UV stability in a UV chamber (accelerated UV testing) for different glass/encapsulant/cell compounds and under real conditions at a testing site in the Atacama Desert (PSDA: Plataforma Solar del Desierto Atacama) coordinated by the University of Antofagasta (see Figure 3). This site will be the centre of Chilean R&D activities similar to PSDA in Almeria in Spain. The testing in the SolarChilD project under real conditions also evaluates the influence of soiling and sand abrasion of the glass and the use of protective ARC on the surface.
With the outdoor testing experience, testing standards for the Atacama Desert must be created – for example the damp heat (DH) testing must be extended in order to create realistic desert conditions. Whereas DH testing is performed standardly for 1,000-2,000 hours, extended DH testing for 6,000 hours has to be done. In addition it has to be agreed on how long and with which intensity the accelerated UV test has to be performed to generate realistic conditions and how abrasion tests with sand from Atacama has to be adapted into standard testing.
Figure 4 presents some interesting results from damp heat testing for 6,000 hours for different modules with various glass thicknesses (1.5mm, 2mm and 3.2mm), back sheets (standard back sheet (SBS), transparent back sheet (SBS) and desert back sheet (DBS)) and encapsulants (EVA (E) and thermoplast (P)). The outcome is quite clearly visible in EL as well as in IV measurements. Modules with EVA experience large degradation after 3,000 hours of DH tests, whereas the modules with thermoplast are still performing well. In the future different silicone technologies will also be tested, as this encapsulant is a very good candidate for UV transmission as well as for stability. For standard modules it is currently not used because of its higher costs; however for desert modules this might change in the future.
Most powerful module for lowest LCOE
Longevity and stability are the not the only key attributes for successful module development; in order to reduce the levelised cost of electricity (LCOE), the modules also have to become more powerful. One possibility is single-axis tracking, something many PV installers are already using in the Atacama Desert – another is bifaciality and the most powerful is the combination of both.
About bifaciality and its advantages we have reported in detail in one of our earlier PV Tech blog posts (“Bifaciality: One small step for technology, one giant leap for kWh cost reduction”).
In order to make bifaciality more bankable, MegaEngineering together with Chilean local installer Imelsa is setting up bifacial fixed tilt and tracked systems in Chile. The bifacial 2.5MWp fixed tilt system in St. Felipe will be finalised in October 2015 and the 1.24MWp bifacial tracked one in Curico in November 2015. Both systems will in addition have a small 30kW system with standard fixed tilt mc-Si modules for reference. In order to increase the albedo, conditioning of the ground is also foreseen in these systems. At the EUPCSEC a presentation from Corrado Comparotto et al. will be shown from bifacial measurements in El Gouna, Egypt (5DO.11.1 scheduled for Thursday 17 September 15:15-16:45), which has the same elevation in the Northern hemisphere as the Atacama Desert. The outcome is that a bifacial gain of >26% is observed.
A solution for soiling minimisation and therefore lower costs for cleaning could be the installation of vertical bifacial systems. However also the wind load has to be considered as it is extremely windy in some parts on the desert.
Highly efficient module (UV and IR sensitiveness)
In our last blog post for PV Tech (“Limit for industrial c-Si solar cells reached in 2030: what next?”) we reported about the future of c-Si PV. The c-Si solar cells will reach their theoretical limit while improving the Voc implementing a better metallisation and collecting all the light which can be used by c-Si by anti-reflective coatings and light trapping films. In addition, especially in the case of the Atacama conditions of extremely high UV and IR irradiation due to high elevation and hardly any water in the atmosphere, additional layers on top of the c-Si will become interesting. Multi-junction, tandem solar cells or up-and-down converters will be extremely interesting for the collection of additional light, which will be tuned toward the c-Si absorption band.
In order to investigate all the discussed points above ISC Konstanz together with SERC Chile plan with the support of CORFO and CIFES to set up an AtaMo R&D centre (ARC) in Chile to speed up these developments.