Environmental Footprint

The implementation of renewable energy technologies primarily aims to reduce the harmful environmental footprint of the power sector. Hence, the next step of this study was to estimate and compare the potential environmental footprint of the power systems in the two scenarios. Since the composition of the baseload in both scenarios is unknown, we compare the footprint of the flexible generation (gas power plants) and renewable technologies (solar PV and wind plants).

The environmental footprint of the two power systems was investigated from the perspective of: (i) CO<sup>2</sup> emissions (both direct and lifecycle) and (ii) the direct water footprint (water consumption). In this context, direct emissions refer to the emissions that appeared during the power-generation process (e.g., from burning fuel), whereas lifecycle emissions encompass the emissions from the foreground process (the power-generation process) and all background processes (extraction, processing, and transportation of fuels; construction of the power plant; etc.).

While environmental studies typically consider only CO<sup>2</sup> emissions, the water footprint of power-generation facilities is often overlooked [48]. For instance, thermal power generation consumes water for cooling purposes, and solar PV generation requires water for the occasional cleaning of PV modules. During the process of power generation, this water is withdrawn from the immediate water environment, which may lead to the depletion of water resources, especially in regions already characterized by high water stress [49]. According to the Water Resource Institute, two-thirds of California face high or extremely high baseline water stress [50]. Hence, an assessment of the water footprint for California's power sector is crucial.

The results of this analysis are shown in Table 5. The values were calculated for each generation type using the following formula

$$\begin{array}{c} \text{generation type using an incoming column} \\ \text{Life cycle or direct emissions} \left[ \text{gCO}\_2\text{eq} \right] = \text{Annual generation} \left[ \text{kWh} \right] \times \text{emission factor} \left[ \frac{\text{g}}{\text{kWh}} \right] \end{array} \tag{3}$$

for the annual lifecycle and direct emissions and

$$\text{Direct water} \left[ \text{of} \,\text{m}^3 \right] = \text{Annual generation} \left[ \text{MWh} \right] \times \text{water consumption factor} \left[ \frac{\text{m}^3}{\text{MWh}} \right] \tag{4}$$

for the annual water footprint.

The values presented in the table are the median estimates that were calculated using: (i) the lifecycle and direct emission factors obtained from IPCC [51]; and (ii) the water consumption factors for renewable and non-renewable technologies reported by Macknick et al. [52].

As shown in the table, the replacement of the gas capacities by solar and wind technologies in the GREEN scenario resulted in a considerable reduction in both the lifecycle and direct CO2-eq emissions and in the direct water footprint compared with the YELLOW scenario. Assuming the same base load in both scenarios, the YELLOW scenario is associated with additional direct emissions of about 22.7 mln. tons of CO2-eq annually

compared with the GREEN scenario. To put this value into perspective, it is larger than the combined annual total CO<sup>2</sup> emissions of Latvia and Lithuania in 2019 [53]. The results also demonstrate that the GREEN scenario allows us to "save" approximately 30.4 mln. cubic meters of water annually. This is equivalent to 12'160 Olympic-size swimming pools. This "saved" water in the GREEN scenario can be conserved or reallocated for other purposes, for instance, food production.

**Table 5.** The environmental footprint of the power systems in the two scenarios.


The intention of this simple calculation was to demonstrate the potential environmental benefits of the GREEN scenario, which aims to minimize the role of flexible (commonly fossil-based) generation in the power generation mix.
