Thin Film Silicon Bankability

Thin Film Silicon Bankability

A curious thing happened in the solar market in 2010. Relatively expensive modules from well-established manufacturers sold well, while less expensive modules from startup firms did not sell as well. Why did developers pay more? Modules from the established firms had demonstrated excellent, predictable energy production over many years. In contrast, startups had not built this data set for their modules. Established firms have the financial strength to replace the modules if they failed. Startups had not yet established this strength. Developers paid more to reduce the risk to their investors -- Banks.

Applied foresaw this "bankability" issue for our thin film silicon customers. We started an effort at the beginning of 2009 to collect the performance and reliability data demanded by developers and their banks.

Our first step was establishing test sites around the world. A variety of regions were selected to show the module performance in different climates. The sites monitored are in Neustadt bei Coburg, Germany (cold/hazy climate), Singapore (hot/hazy), Phoenix, Arizona (hot/clear), and Santa Clara, California (moderate). For comparison, crystalline silicon modules were also installed in Singapore and Phoenix. The sites included single junction amorphous silicon and tandem junction amorphous silicon/microcrystalline silicon modules.

The most remarkable result was the comparison between thin film silicon modules and crystalline silicon modules. In both of the hot locations, Phoenix and Singapore, the thin film silicon panels produced >8 % more kWh per rated kWp than c-Si modules. Two notable trends explain the energy harvest advantage:

  1. Less negative temperature coefficient which gives thin film silicon modules a performance advantage over c-Si modules at increasingly high irradiance and cell temperatures.
  2. At low irradiance, the thin film silicon panels out-perform c-Si, due to a combination of spectral and angle-of-incidence effects.

The performance data allowed us to establish predictability. We produced PVsyst models which predict the output of thin film silicon module arrays. The model predictions were compared to the actual performance of the four sites. The actual performance exceeded the predicted performance by ~5 %, which gives banks confidence that they can calculate the financial output of an investment in an array of our customer’s modules.

There is no fast way to establish 20-years of reliability data, but we can run accelerated tests to show that the module design is sound. The reliability test lab in Xi`an, China has subjected thin film silicon modules to two and even three times the environmental stress than the standard tests require, and the modules have maintained performance within the limits set in these internationally recognized standards. This gives banks confidence that there will be no unexpected long-term degradation of the modules.

This data also allowed our customer to address the issue of financial strength. Our customers are using the data to attract insurance to cover their modules in the event of major failure. Banks know that there is someone standing behind the module manufacturer.

This data allows us to answer the big question: How does the cost of a kWh produced by our customer's thin film silicon panels compare to other sources of electricity? How close are we to "grid parity?" Electricity production has a complicated pricing structure which depends on, among many things, location. The most expensive source of conventional electricity is natural gas peak production plants, which meet demand during hot summer days. Riyadh, Kingdom of Saudi Arabia as a good location for thin film silicon due to the advantageous temperature coefficient, so we have compared thin film silicon modules to peaker plants in Riyadh.

To compare difference sources of electricity production, we have built a Levelized Cost Of Energy (LCOE) model which calculates the cost per kWh of a source of electricity over the entire life of that source. The model predicts that thin film silicon modules have an ~1 ¢/kWh lower LCOE than a comparable c-Si installation at an equivalent system cost in Riyadh. Our present megawatt reference design, which we have made available to customers, has a Balance-of-System (BOS) cost of 1.35 $/Wp (AC) for 9% thin film silicon modules. With thin film silicon module manufacturers continuing to drive to $1/Wp module cost, we should see systems with total costs <$3/Wp (AC) in 2011. This cost corresponds to an LCOE of ~13 ¢/kWh, which is comparable to natural gas peak-production power plants in Saudi Arabia. Our customer's thin film silicon panels are at price parity for the peak production in this location.

We have established the bankability of our modules by demonstrating the performance, predictability, and reliability of thin film silicon modules. As a result, larger numbers of our customer’s installations are getting backing from banks. To reduce construction risk, we developed mounting structures, 1000V electrical systems, and shipping racks for thin film silicon modules. We demonstrated these designs at our campus in Santa Clara, California. For more information on the study which we presented at EUPVSEC or our system designs, please feel free to contact me via this blog.

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