For Green Star projects, increases in Ozone Depletion or Abiotic Resource Depletion Potential is a cause for concern as there is only a 10% allowance for such increases. This could mean losing your whole LCA credit for the project. Most notably, large PV systems are getting penalised in this way. You can read more about that in this post.
The high levels of ADP/ODP associated with PV systems are the result of Tantalum (an unusually rare mineral) in the inverter capacitors. It is likely a combination of the following:
- Incomplete inventory for other electronics in the building (meaning the benchmark isn’t complete, hence the increase associated with the inverters looks like a big increase, but it wouldn’t be if we had all the electronics in the building. Not easy to fix this one but we do have some templates that can fill some of the gaps.
- Incorrect / out of date LCI inventory data. I did some research on this previously and I think Tantalum capacitors have been largely replaced by polymer capacitors now in inverters. So potentially this is not an issue, it’s really hard to clarify this with suppliers though. Fronious was one manufacturer that did confirm that they don’t use Tantalum capacitors in their inverters though.
- Incorrect assumption about the mass of inverters (particularly for large systems). I think we assume 10kg of inverter mass per kW of solar system. This is probably a bit low for a 1kW solar system (even small inverters are usually 15kg I believe) but way too high for large systems (you can get 20kW inverters that are <50kg so 2.5kg / kW). This is something you can easily check. Micro inverters adds another dimension of complexity here.
Besides adjustments to the inverters, the following are some other measures that you can take:
- In case high efficiency panels is used, a % of the embodied impacts related to the panels can also be reduced.
- Another option is to increase inverter product life from default value referencing supplier documentation and product warranty period.
We have also noticed that where eToolLCD has detailed grid impacts for “Importing” and “Exporting” power, this can also have a large effect on the Net Abiotic Resource Depletion of elements for some grids. The reason for this is:
- To supply electricity Abiotic Resources (Minerals) are depleted along the electricity supply chain, in the extraction energy, the power plant, the transmission and distribution.
- In Particular, the transmission and distribution can have high Abiotic Resource depletion due to the rare minerals used in these assets (in some cases probably similar to PV inverters).
- The “Export” grids assume that the transmission and distribution impacts are not offset by the exported power, where as the import grids do offset this (by reducing load on the grid you are reducing the required transmission and distribution infrastructure, but by feeding in, you’re not necessarily reducing this infrastructure).
Note, that if you ran the same scenario assuming no power was fed in (and batteries were used to store energy on site) the abiotic resource depletion would probably be even higher than the grid connected scenario. The best way of using PV energy on a grid that is not yet renewables saturated is:
- Use the energy on site to power existing loads
- Export the power, so others (hopefully nearby) can use the power
- Store and use or export at another time
Below is a flow chart of the measures you can take to help reduce the Indicator increase to avoid losing Green Star credits.
If consideration of the above (and subsequent adjustment to your models) doesn’t rectify the problem in terms of your Green Star submission please reach out to eTool and we can provide some assistance normalising and weighting your results which may support a Credit Interpretation Request to the GBCA (this has been a successful avenue for some other users historically).
