2.1. Power Dispatch Data for California
2.1.1. Electricity Generation Data per Technology (Hourly Resolution)
2.1.2. Electricity Imports Data (Hourly Resolution)
2.1.3. Electricity Demand Data (Hourly Resolution)
2.1.4. Power Curtailment Data for Wind and Solar Generation (Hourly Resolution)
2.2. Current and Future Electricity Generation and Storage Technologies in California
2.2.2. Gas-Fired Electricity
2.2.8. Concentrating Solar Power (CSP)
2.2.9. Photovoltaic (PV) Solar
2.2.10. Energy Storage
2.3. California Grid Mix Composition in 2018
3.1. Definition of the Future Grid Mix Scenario in 2030
- It is assumed that in 2030 the total hourly electricity demand profile will remain the same as in 2018. This future extrapolation is based on the analysis of the demand profiles from 2001 to 2019, which shows that the cumulative yearly electricity demand remained nearly constant during the past 19 years, with minimal oscillations around a centre value of approximately 200 TWh/year. This result appears to be “due to a combination of energy efficiency measures and less electricity-intensive industry that counterbalances increased population and economy” . Other potential variations in electricity demand (both its hourly profile and total year-end cumulative value), for instance due to a possible large-scale deployment of electric vehicles (EVs) and the associated requirement for battery charging, are outside the scope of this study.
- CAISO will rely single-handedly on solar PV as the technology of choice to increase the penetration of renewable energy in the grid. This is a bold assumption, but it was deemed reasonable in view of the abundance of solar irradiation in California, and it also appears to be supported by a simple linear extrapolation of recent past trends, which indicate that wind installations in California have plateaued, whereas PV installations have been sharply and consistently rising (see Figure 3). The final value of installed PV power in 2030 was determined iteratively, so as to match a target of 80% total net domestic renewable electricity generation, after duly taking into account all PV storage and curtailment losses (as explained below). Hence, the PV installed capacity in 2030 is 43,710 MW, as shown in Figure 3. The hourly “potential” (i.e., pre-curtailment and pre-storage) PV output profile was calculated by scaling up the corresponding 2018 “potential” PV electricity generation, proportionally to the respective 2030 vs. 2018 installed power levels.
- Lithium-ion batteries (LIBs) will be deployed as the storage technology of choice (as discussed in Section 2.2.10). The amount of assumed installed LIB power (P) and the maximum consecutive hours of storage duration at such maximum power (t) were set after performing a parametric investigation of the resulting % of VRE curtailment ensuing from a range of P and t values (following the grid balancing algorithm described at points 7 and 8 below). The results of this parametric analysis are illustrated in Figure 4; in order to make a realistically conservative assumption on the amount of storage, for the purposes of this study the choice was therefore made to set P = 60% of the installed PV power (a value consistent with previous literature [63,64]) and t = 6 h. When taken together, such values of P and t lead to the total installed storage capacity E = P × t. As reported in Table 1, this resulted in 2.8% of the overall “potential” VRE generation being curtailed.
- Nuclear generation will be zero, consistently with the planned decommissioning of all remaining reactors in California (as explained in Section 2.2.1).
- “Other renewables” (i.e., hydro, biogas, biomass and geothermal), wind and CSP generation profiles will remain exactly the same as in 2018.
- Single-cycle gas turbines (SCGT) will be completely phased out.
- Combined cycle gas turbine (NGCC) output and electricity imports will be used, together with LIB energy storage, to balance overall supply and demand, following a strict order of merit, as follows:
- On an hourly basis, the increased PV output in 2030 with respect to 2018 (more precisely: the difference between the “potential” PV output in 2030, calculated as per point 2 above, and the net PV output in 2018) will first be compensated for by reducing NGCC output. This is deemed the preferred strategy since gas-fired electricity is the most carbon-intensive technology in the California grid mix, and it is also more carbon-intensive than the average mix of technologies used to generate the electricity imported by California .
- Then, if/when no residual NGCC power is left, the second intervention will be to curb imported electricity.
- Then, if/when the hourly imported electricity value has been reduced to zero too, and the “potential” PV output is actually in excess of the total demand profile value, such excess PV output will be preferentially routed into storage, as long as neither total storage capacity (E) nor maximum storage power (P) are exceeded.
- Finally, if, after taking steps (a–c) above, either the maximum E or maximum P condition is met, then the residual excess PV output (i.e., the share thereof that cannot be sent to storage) is curtailed.
- After each PV “peak”, i.e., as soon as the “potential” PV profile curve has returned below the total demand profile curve, the electricity stored in LIBs will start being dispatched back to the grid (at a maximum rate limited by P), and will thus curb NGCC output (in the first instance) and imported electricity (if/after NGCC output has already been reduced to zero) with respect to their respective 2018 hourly values.
3.2. Life Cycle Assessment (LCA)
3.3. Net Energy Analysis (NEA)
4. Results and Discussion
Conflicts of Interest
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|Share of total California demand supplied by domestic generators 1||73%||165||88%||199|
|Share of net renewable energy (RE 2) in domestic generation mix||50%||82||80%||159|
|Share of net variable renewable energy (VRE 3) in domestic generation mix||27%||44||61%||121|
|Share of net PV generation in domestic generation mix||16%||27||52%||104|
|Share of gross VRE generation that is routed into storage||0%||0||25%||32|
|Share of gross VRE generation that is curtailed||1%||0.4||2.8%||3.6|
|Technology||2018 EROIel||2018 EROIPE-eq|
(ηG = 0.48)
|2030 EROIel||2030 EROIPE-eq|
(ηG = 0.69)
|Nuclear (pressure water reactor)||20||42||N/A||N/A|
|Natural gas (single-cycle gas turbines)||5||11||N/A||N/A|
|Natural gas (combined cycles)||8||17||8||12|
|Biomass (co-generation) (a)||6||14||6||9|
|Biogas (co-generation) (a)||4||7||4||5|
|Photovoltaic||13||28||15 (b)||22 (b)|
|Concentrating solar power||8||18||8||12|
|Grid Mix Results||2030|
(“Conservative” PV Assumptions) (a)
(“Optimistic” PV Assumptions) (b)
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