The design team analyzed three scenarios for the EcoBlock Integrated Energy System, and each scenario includes the five DERs described above, as well as a central utility plant, which is a single location in the microgrid where shared assets, such as the energy storage system and microgrid controller, are located. The scenarios vary primarily in how the power is distributed around the block, where power conversions take place, and where in the system the connection to the utility grid is made. The three scenarios are as follows:
Scenario 1e. AC Solar/Storage Microgrid with Energy Efficiency Retrofits and Existing AC Houses
The design strategy in Scenario 1e is to outfit each home with an individual photovoltaic (PV) array and to build an AC distribution circuit around the block, which would connect to each home’s PV system through an inverter. The AC microgrid would receive power from the PV arrays, store it in a centralized energy storage system, and distribute it back to the homes.
Existing Pacific Gas and Electric (PG&E) high-voltage cables would be reused to connect the block’s transformers to the new central utility plant. Existing 240 volt (V) cables from the PG&E transformers, existing AC load centers, and existing power meters would all be maintained.
Figures 3-1 and 3-2 show the configuration of this scenario at the individual home and block level. The advantages of this scenario include: reducing the cost of PV by purchasing in bulk, reducing the cost of materials by reusing existing high-voltage cables, reducing the cost of storage by using a block-scale approach, and allowing the existing AC circuits in the homes to remain unchanged.
Figure 3-1: Scenario 1e: AC Solar/Storage Microgrid – House Diagram
AC Solar/Storage, Microgrid with Energy Efficiency Retrofits and Existing AC Houses.
Source: Skidmore, Owings & Merrill, LLP
Figure 3-2: Scenario 1e: AC Solar/Storage Microgrid – Block Diagram
AC Solar/Storage, Microgrid with Energy Efficiency Retrofits and Existing AC Houses.
Source: Skidmore, Owings & Merrill, LLP
Scenario 2e. DC Solar/Storage/EV Microgrid with Energy Efficiency Retrofits and Existing AC Houses, at Block Scale
The design strategy in Scenario 2e is to outfit each home with an individual PV array and to build a DC distribution circuit around the block to form the backbone of the microgrid, which would connect to each home. The DC microgrid would receive power from the PV arrays, store it in a centralized flywheel system, and distribute the power back to the homes. Each home would also be outfitted with an inverter, and a new AC load center, in order to feed their loads with reliable power from the DC microgrid. Figures 3-3 and 3-4 show the configuration of this scenario at the individual home and block level. The advantages of this scenario include:
reducing the cost of PV by purchasing in bulk, reducing the cost of storage by using a block-scale approach, the ability to underground the DC distribution circuit for improved reliability, and allowing the existing AC circuits in the homes to remain unchanged.
Figure 3-3: Scenario 2e: DC Solar/Storage/EV Microgrid – House Diagram
DC Solar/Storage/Electric Vehicle Microgrid with Energy Efficiency Retrofits and AC/DC Houses.
Source: Skidmore, Owings & Merrill, LLP
Figure 3-4: Scenario 2e: DC Solar/Storage/EV Microgrid – Block Diagram
DC Solar/Storage/Electric Vehicle Microgrid with Energy Efficiency Retrofits and AC/DC Houses.
Source: Skidmore, Owings & Merrill, LLP
Scenario 3 e. DC Solar/Storage/EV Microgrid with Energy Efficiency Retrofits and AC/DC Houses, at Block Scale (Preferred)
The design strategy in Scenario 3 is to outfit each home with an individual PV array, new energy-efficient DC appliances, and a new DC load center to serve the new appliances. A new DC microgrid would be built around the block and connected to each home. The DC microgrid would receive power from the PV arrays, store it in a centralized flywheel system, and
distribute the power back to the homes. A new, central interconnection would tie the DC microgrid to the AC utility, so that the extra power produced during summer hours could be sold to the utility. The existing utility connection and AC load center in each home would be maintained, however most loads would be moved from the AC load center to the new DC load center. Figures 3-5 and 3-6 show the configuration of this scenario at the individual home and block level. The advantages of this scenario include: reducing the cost of PV by purchasing in bulk, reducing the cost of storage by using a block-scale approach, the ability to underground the DC distribution circuit for improved reliability, eliminating the need for inverters in each home, improving efficiency of home loads by powering them with DC while allowing some hard-to-convert existing AC circuits in the homes to remain unchanged, and fully utilizing excess power generated by selling it back to the utility. The team analyzed two different options for Scenario 3 e: a maximum size microgrid and an economically sized microgrid.
1. Maximum Size Microgrid
Option A is to size all of the block-scale equipment (such as the flywheel, DC microgrid conductors, DC/DC converters, and grid interconnection) to accommodate the
maximum PV output for every home on the block. This approach would allow
homeowners who initially do not opt-in to the EcoBlock to buy in and participate at a later date. The extra capacity could also be used to make the EcoBlock a net energy exporter in ~30 years as the PV arrays are replaced with newer, presumably higher efficiency PV.
2. Economically Sized Microgrid (Preferred)
Option B is to size all of the block-scale equipment to accommodate only the owners who opt-in initially, with incremental expansion of the energy system as additional homes undergo energy retrofits and connect to the microgrid. This expansion would logically happen in one or two “waves” to achieve economies of scale. This incremental approach would reduce the initial cost of the total system using smaller storage and distribution equipment.
Figure 3-5: Scenario 3 e: DC Solar/Storage/EV Microgrid – House Diagram
DC Solar/Storage/Electric Vehicle Microgrid with Energy Efficiency Retrofits and AC/DC Houses.
Source: Skidmore, Owings & Merrill, LLP
Figure 3-6: Scenario 3 e: DC Solar/Storage/EV Microgrid – Block Diagram
DC Solar/Storage/Electric Vehicle Microgrid w. Energy Efficiency Retrofits and AC/DC Houses.
Source: Skidmore, Owings & Merrill, LLP