Following higher than expected adoption of rooftop solar PV, there is a growing trend of installing battery energy storage system (BESS) to complement solar PV, termed Advance Behind the Meter Energy Systems (BTMES).
This trend is likely to grow with declining BESS costs, increased BESS life and performance and government incentives. Theoretically will translate into greater penetration of advance BTMES, that provide partial grid independence to consumers. How does it impact the traditional grid power industry, as move towards grid liberalization gains pace partially due to rising power costs and partially due to decarbonization commitments. We attempted to answer this through numbers, using advanced modelling.
We used the following methodology;
1. Considered an LV distribution feeder with mixed customer demand.
2. Estimated its current demand independent of embedded solar PV generation, as 30 min interval values for one whole year.
3. Estimated maximum solar PV hosting capacity of the feeder1
4. With rooftop solar PV capacity (RTS) equal to maximum hosting capacity, estimated the amount of energy that does not pass through meter (BTM grid independent energy)
5. Estimated capacity of Advance BTMES (Solar PV + RESS) that would maintain the overall impact on the feeder identical to as hosting capacity of the feeder.
6. Estimated the resulting BTM energy consumption (BTM grid independent energy)
7. Estimated net reduction in grid energy under each scenario, to conclude impact on power/grid industry.
The results are presented below.
Scenario 1: No RTS or BESS Installed
• Total annual demand = 2,500 MWh
• Maximum demand on grid = 0.562 MW
• % demand supplied by grid = 100%
• % reduction in energy supplied by grid = 0%
• RTS hosting capacity of feeder = 0.287 MW
• RTS capacity installed = 0 MW
• % demand supplied by RTS = 0%
While the supply and demand profiles would be different each day, the average day profiles are shown in Figure 1. The whole year 30 min interval demand profile is shown in Figure 2. 100% of demand is met by grid supply, on an annual basis.
Scenario 2: RTS = Hosting Capacity of Feeder, No BESS
• Total annual demand = 2,500 MWh
• Maximum demand on grid = 0.52 MW
• % demand supplied by grid = 85%
• % reduction in energy supplied by grid = 15%
• RTS hosting capacity of feeder = 0.287 MW
• RTS capacity installed = 0.287 MW
• % demand supplied by RTS = 15%
The average day profiles are shown in Figure 3. The whole year 30 min interval supply and demand profiles are shown in Figure 4. While the majority (85%) of demand is met by grid supply, some (15%) is supplied by RTS, on an annual basis. Please note that these results apply to this specific feeder with given demand and solar PV generation profiles. Results may change for a different feeder with different demand and solar PV generation profiles.
Scenario 3: Advance BTMES (RTS + BESS) = Hosting Capacity of Feeder
• Total annual demand = 2,500 MWh
• Maximum demand on grid = 0.50 MW
• % demand supplied by grid = 47.9%
• % reduction in energy supplied by grid = 52.1%
• RTS hosting capacity of feeder = 0.287 MW
• RTS capacity installed = 0.989 MW
• BESS capacity installed = 0.52 MW x 8h = 4.16 MWh
• % demand supplied by RTS + BESS = 52.1%
The average day profiles are shown in Figure 5. The whole year 30 min interval supply and demand profiles are shown in Figure 6. The majority (52.1%) demand is now met by advance BTMES, only (47.9%) is supplied by the grid, on an annual basis. Please note that these results apply to this specific feeder with given demand and solar PV generation profiles. Results may change for a different feeder with different demand and solar PV generation profiles.
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Figure 6: 30 min interval supply and demand profile – Scenario 3
CONCLUSIONS
1. With maximum hosting capacity limits applied, customer owned rooftop solar PV can result in up to 15% reduction in grid supplied energy.
2. With maximum hosting capacity limits applied, a customer owned advance BTMES can result in up to 52.1% reduction in grid supplied energy.
3. In both cases the reduction in maximum load on the grid is marginal i.e. from 0.562MW with no RTS or BESS to 0.52 MW with only RTS and to 0.50 MW with advance BTMES.
In summary, the impact of customer owned simple RTS is limited to 15% reduction in grid supplied energy, mainly due to limitations imposed by hosting capacity of LV feeders. However, advance BTMES can increase the hosting capacities of LV feeders several times. This can result in a reduction in the share of grid supplied energy by more than 50% of the actual demand. These results are specific to the feeder analyzed. Other sections of network sections can have higher hosting capacities, and thus exposed to greater reduction in demand for grid supplied energy, potentially in the order of 60%+.
Can this be start of a death spiral for grid system? As less energy passes through the grid, the per unit cost of grid services will increase. Thereby incentivizing more consumers to adopt technology that helps them grid independence. As demand increases, more economically feasible technological solutions become available e.g. rapidly dropping prices of long duration storage solutions. Shall the demise of the conventional grid be allowed this way?
DNSPs cannot hide behind “hosting capacity” of network for too long to resist greater penetration of advanced BTMES. Mitigating options are available to offer equally beneficial solutions for all stakeholders. However, requires consideration for long-term wholistic evidence based thinking and action.
