Firstly, I think it’s important to not “miss the wood for the trees” on this issue. The relative percentage increase of an indicator is not a good representation of the net environmental gain or loss. For example, 10% improvement in one indicator and 10% performance loss in another would rarely “cancel each other out” due to the following factors:
- The “business as usual” or “reference case” design may have far more significant levels of one indicator verse the other. For example, it may be that the design has very minor levels of indicator A but much higher levels of indicator B in which case a small percentage drop in indicator B would be more significant than the same change in indicator A. In LCA this problem is addressed with normalisation (expressing each impact as a % of a typical person’s impacts giving a relative magnitude compared to “normal” levels). From ISO 14044: “The aim of the normalization is to understand better the relative magnitude for each indicator result of the product system under study.” It is not possible (or at least very difficult) to understand the relative magnitude of indicators without normalisation.
- The actual relative damage of each environmental impact may be quite difference, for example small amounts of one indicator may be far more damaging than larger amounts of another indicator. This is normally addressed with weighting. From ISO 14044: “Weighting is the process of converting indicator results of different impact categories by using numerical factors based on value-choices. It may include aggregation of the weighted indicator results.”
The GBCA calculation technique for assigning credits to the LCA outputs ignores normalisation and weighting and hence should not be used for making design decisions. The GBCA method aggregates results before any normalisation or weighting is conducted which is almost certain to result in adverse design decisions if used to assess the relative merits of design options particularly where there are trade-offs. eTool have expressed this concern and provide real life examples of flaws in its application in previous public submissions to the GBCA, for example see the section titled “Lack of Normalisation and Weighting in the Green Star LCA calculations” in this submission which summarises our feedback to the GBCA during the public consultation for the V1.2 credit. We encourage the eToolLCD community to lobby the GBCA to tackle this issue.
Notwithstanding this flaw in applying the GBCA calculation method to making design decisions, the high levels of Abiotic Resource Depletion associated with solar 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.
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).