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the purpose of doing solar PV is to reduce and eliminate fossil fuels that are causing an increase in carbon dioxide in our atmosphere. A review of the materials that are used in the solar PV installations would help to understand the carbon footprint from these materials. Solar installation materials consist of solar panels, inverters, racking and balance of system components.
While each of these components have numerous sub-components, in this blog we will restrict our study to the racking materials. A lot of engineering goes into racking since it is site specific. Materials used in the racking are:
We will address the carbon footprint for each of these materials used in solar PV installations.
Rails are either made from aluminum or steel, both materials are highly recycled. However, steel is recycled more than aluminum. Aluminum or steel can be infinitely recycled and its properties retained. Unlike plastic, cement (or concrete) or wood, steel and aluminum properties are unchanged when it is recycled.
Steel and aluminum use a lot of energy to be melted into ingots or finished products for recycling. As the grid electricity is used for these melting processes, the more renewable energy used in the grid the lower the carbon footprint for the recycling process.
According to Energy Information Administration of the US Government, steel consumes anywhere between 1×106 to 14×106 BTU per ton of steel of energy to produce. This is about 4000 kWh per ton or 2 kWh per lbs.
Brackets and splices are also typically made from aluminum or steel and have the same recyclability as discussed for rails.
Most flashing are made from aluminum.
Conventional rooftop solar racking manufacturers use architectural aluminum as the rail and flashing. Hence use stainless steel bolts, nuts, and washers for rooftop racking material.
For ground-mounted racking galvanized steel hardware along with galvanized steel rails, brackets and beams are used. On ground-mounted solar racking, all materials are made from mild steel coated with zinc to ensure there are no dissimilar materials. Dissimilar materials increase galvanic corrosion potential. To avoid this potential difference, mild steel with zinc coating is used on all component parts.
Z RackTM and Z LiteTM use all steel components with zinc coating like the ground-mounted solar racking.
Caulking compounds are routinely used in sealing the penetrations. Duralink is one of the commonly used sealants in the solar industry and is available in most home improvement supply stores. Duralink brochure indicates it uses “unique polyether chemistry at work: moisture actually speeds up curing, unlike typical urethanes, which bubble on damp concrete, DURALINK is ideal for damp surfaces.”
Typical polyether is made from fossil fuels. Synthetic polyether is available using new carbon. New carbon is derived from plant-based biomaterials such as sugarcane. However, the vast majority of polyether is made from crude oil as the base. While switching to new carbon is possible, the sealants used by installers use crude oil as the base material.
All sealants are used in penetrated attachments to seal the edges, gaps, and perimeter of flashing so water does not seep into the penetration. Sealants are rated to weather the conditions however, they have a finite life. It is not known what that life is.
Per the application notes for most sealants, they have to be kept at room temperature all the time. It helps in gunning the sealant and also makes a good continuous bead during gunning. They also do not recommend the application of the sealant when the ambient temperature is below 32F (0C).
Z RackTM does not use any penetrations or attachments. Hence there is no use for sealants.
Ballasts are placed on flat roof racking to help provide wind resistance to the array during high wind and storm conditions. Ballasts are made mostly from concrete. The concrete comes as a block and is placed over a tray as in the figure below.
Concrete although recycled, it is used as an aggregate at end of life hence has a lower property than its original starting point.
Also Concrete uses a lot of energy for its manufacturing. Energy in cement manufacturing is used in:
According to the Columbia Climate School, it takes 4.7×106 BTU per ton of energy to manufacture cement. And if you add another 1×106 for the manufacture of aggregate the energy required to manufacture concrete is about 5.7×106 BTU per ton. This amounts to about half that of steel. Since the cement is a one-time manufacturing material and more mining must take place to ensure more concrete can be made.
Concrete has a very high heat capacity. Which means it can retain heat for a very long time. Hence on a hot day, the concrete block gets hot and retains the heat. The heat is then transferred to the underlying roof requiring the building to use more energy to cool the building.
Z-LiteTM solves these problems by eliminating 90% of the typical ballasted structure by strategically placing the ballasts directly underneath the solar panels. This means the ballasts have minimal sun exposure while also only weighing 5.5 lbs per square foot which is 45% less than most ballasted systems. Unlike traditional systems which lie directly on the roof, SolarPod’s Z-Lite system is elevated off the roof to improve airflow and circulation while greatly decreasing heat retention, keeping the building cooler without sacrificing the structural integrity of the panel installation.
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