Modeling life cycle greenhouse gas emissions from photovoltaic and wind power generation, with and without energy storage

Abstract

Several approximate findings are made on the carbon intensity of PV power. (1) Reversible temperature effects raise the carbon intensity of silicon PV power installed in warm regions, including by -10% in the southwestern US and ~13% in western India. (2) All temperature effects raise silicon PV carbon intensity by ~23% in southern India (from 35 to 43 gc/kWh). (3) Chinese manufacturing of multi-crystalline silicon (mc-Si) modules emits ~25% more GHGs than European manufacturing, due not only to higher carbon intensity of upstream electricity, as previously reported, but also to more energy input per module produced. (4) Relative to stationary mounting, tracking decreases the carbon intensity of mc-Si PV in most regions analyzed (by 0 to ~12%, or 0 to ~4 gc/kWh), and increases the carbon intensity of cadmium telluride PV in most regions analyzed (by 0 to ~12%, or 0 to ~4 gc/kWh).

This dependence on cell type is explained by the interaction of tracking energy gain, tracker production emissions, and module production emissions. (5) Inverter overloading slightly diminishes PV carbon intensity, by less than 2 gc/kWh. This thesis also presents a simple model for estimating emissions from integrated power generation and energy storage. The model applies to emissions of all pollutants, not only GHGs, and to all storage technologies, including pumped hydroelectric. Our case study applies the model to systems that couple PV and wind generation with lithium-ion batteries (LBs) and vanadium redox flow batteries (VFBs). We find that, even when coupled with large amounts of LBs or VFBs, PV and wind power remain much less carbon intensive than fossil-based generation.

The most carbon intensive renewable power analyzed (sc-Si PV produced in China, installed in Berlin, and coupled with sufficient VFBs to store 50% of generation) still emits only ~25% of the GHGs of the least carbon intensive mainstream fossil power (combined cycle gas turbine with no storage). Lastly, we find that the pathway to minimize GHG emissions of power from a coupled system depends upon the generator: given low-emission generation (<50 gc/kWh), the minimizing pathway is the storage technology with lowest production emissions (VFBs over LBs for our case study); given high-emission generation (>200 gc/kWh), the minimizing pathway is the storage technology with highest round-trip efficiency (LBs over VFBs). The latter case applies to a majority of the world's power generation today.