In this 4-hour engineering course, we break down how to determine if solar PV power is sustainable or not by answering these questions:

1. How can we ensure that our human activities do not surpass the planet's ability to sustain us?

2. How can we use Life Cycle Assessments to determine the environmental impacts of a technology?

3. How can we determine if the environmental impacts of a technology are low enough to allow us to exploit it without pushing the Earth beyond its limits?

4. How are solar modules manufactured?

5. How do the environmental impacts of solar PV compare with other electricity-producing technologies?

Here's a summary of some key points.

How can we ensure that our human activities do not surpass the planet's ability to sustain us?

In 2009, Johan Rockström led a group of 28 internationally renowned scientists to propose nine Planetary Boundaries. These are limits for Earth system processes within which humanity can continue to develop and thrive for generations to come. 

The 9 Planetary Boundaries

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How can we use Life Cycle Assessments to determine the environmental impacts of a technology?

LCA is a technique used to determine the environmental impacts associated with all stages of a product's life, starting from the raw materials extraction stage, continuing through the stages of materials processing, manufacturing, distribution, operation, repair, maintenance, and finally ending at the disposal, or the recycling stage.

This figure shows the life cycle stages included in the LCA method. The inputs refer to the materials and energy consumed during each life cycle stage, and the outputs represent emissions, such as greenhouse gases, heavy metals, SOx, NOx, etc.

The LCA Flowsheet

The LCA considers the material and energy inputs to all stages of solar modules production and the processes used to manufacture what is known as the balance of system components, also known as BoS.

BoS refers to all of the elements associated with the PV system, other than the solar modules themselves. The LCA then would also consider the energy and the raw materials used to produce these components, such as the copper used to make the cables.

This data is then used to calculate the values of the LCA indicators which ultimately determine how the technology influences Human Health, Ecosystems, Resources and Climate Change.

Relating the LCA to Impacts

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How can we determine if the environmental impacts of a technology are low enough to allow us to exploit it without pushing the Earth beyond its limits?

The LCA can be linked to 5 main sustainable development goals, commonly known as SDGs, namely:

SDG 3, Human Health and Well-being.

SDG 6, Clean Water and Sanitation.

SDG 13, Climate Action.

SDG 14, Life Below Water, and

SDG 15, Life on Land.

The LCA indicators can also be related to the Planetary Boundaries as shown below.

Relating the LCA indicators to the SDGs and Planetary Boundaries

If we are studying a technology that is to be implemented on a national level, such as a national electrical grid, for example, the Planetary Boundaries may be scaled to define the limits the country must respect in order to ensure that its strategy will remain within the safe operating zone of the Earth.

However, we cannot do this to access the impact of a specific smaller-scale process or product on the Earth. The LCA helps to calculate what the impacts are but does not provide guidance on whether or not these are too high or sufficiently low with respect to the "Earth System".

This is where a new approach called Planetary Accounting comes in. Once fully developed, Planetary Accounting will link the Planetary Boundaries to quotas we can act on. They will consist of ten global budgets, including those for carbon, nitrogen, water, and forest land, divided amongst the world's population in measurable units.

This way, nations, cities, businesses, and even individuals will be able to understand what their impact looks like.

Planetary Accounting

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How are solar modules manufactured?

In this course, we take a deep dive into the manufacturing processes of both crystalline silicon and thin-film solar modules.

The manufacturing process of crystalline silicon modules occurs in three stages: the Wafer Stage, the Cell Stage and the Module Stage.  This is true for both monocrystalline silicon and multicrystalline silicon solar PVs, however, as you can imagine, the crystallization step differs greatly for these two technologies. The figure below summarizes the overall manufacturing process. In the course, we discuss each step shown here in great detail. 

Crystalline Silicon Solar Module Manufacturing Process

The production of thin-film solar modules is very different. It is essentially comprised of alternating thin-film deposition and scribing steps. Scribing means separating the continuous semiconductor film that was deposited in a previous step into separate solar cells connected in series. In this course, we discuss the manufacturing processes of the two most popular thin-film PV technologies, namely, cadmium telluride (CdTe) and copper indium gallium selenide (CIGS) solar cells. The general process flow is shown below.

Thin-film Solar Module Manufacturing Process

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How do the environmental impacts of solar PV compare with other electricity-producing technologies?

The chart below shows the normalized LCA scores for various electricity generation technologies. The score for each LCA indicator is weighted according to the spread of its impact, its reversibility, and its effect on its respective planetary boundaries. In this way, lesser weight is given to eutrophication and toxicity effects, while more weight is attributed to climate change. The lower the score, the cleaner the technology.

Normalized and Weighted LCA Scores for Various Electricity Generating Technologies

We see that thin-film PV is the 4th cleanest technology, after efficient hydro, nuclear, and tower CSP.  We can also see that wind power falls just after thin films and is about two times cleaner than multi-crystalline PV. 

However, our analysis does not stop here. We realize that it isn't enough to determine which technologies have the so-called "best LCA scores."  Once an LCA allows us to identify the cleanest technologies, the question becomes, "Are their environmental impacts low enough to allow humanity to stay within the Earth's ability to sustain us?"

We must also realize that the energy resources needed to power the technologies shown in the chart are not evenly distributed across the Earth. Cost is also an issue that must be considered.

In this course, we explore these topics by answering the following questions.

• Does there exist a mix of power technologies that would allow us to remain within the planetary boundaries?
• How much would it cost?
• How big a role would solar PV play in this mix?

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