Page 58 - Energize March 2022

TECHNICAL

deployment. A second augmentation If one or more of these conditions are limited interconnection capacity with
may be possible, but it depends on violated, or if the system is operated neighbouring grids.
system size and the number of original in a different manner than modelled, According to Julian Leslie, head of
batteries and central inverters. the system owner faces a reduction electricity network development at
The wrong way to design for in warranted usable energy. Many of National Grid, “At the moment we are
flexibility is to assume that battery the battery warranty conditions have a spending around £1 billion a year [on
rack-based augmentation will be direct correlation to battery usage and balancing services], ever-increasingly,
possible. The appeal of battery rack- system revenue, which leads to trade- and I think personally by the next five
based augmentation is that, in theory, it off decisions regarding how the system years or so that will be £2 billion a year.”
could be less costly. Battery rack-based is used. Is it better for a battery storage While there is certain to be future
augmentation would allow an ESS owner owner to operate the system aggressively need for balancing services beyond the
to add the minimum incremental storage and chase additional revenue, or operate short-term contract terms of EFR and
capacity necessary, conduct multiple it conservatively to maintain a higher dFFR, ESS investors have no certainty
augmentations, and eliminate the labour warranted usable energy over time? The regarding the structure of future
from moving previously installed racks at only way for system owners to make balancing service market products or
the time of augmentation. informed decisions is to track all values their future price levels.
However, battery rack-based using dashboards and analytics. These
augmentation renders a system unsafe are core functions of the GEMS platform. Market uncertainty
to operate. As batteries age and degrade, An incorrect approach to track ESS owners that win EFR or dFFR
their internal resistance increases. When battery warranties is to rely on the contracts face uncertainty in evaluating
new batteries are installed in parallel battery management system (BMS). what the market for balancing services in
with old batteries, the new batteries The BMS does not track all warranty the UK will look like, after the expiration
will operate at higher currents than the conditions, so if a warranty claim arises, of their contract terms. In addition, many
old batteries. These higher currents the BMS is not sufficient to ensure ESS projects that are providing EFR and
will exceed the current limitation of the warranty compliance. Without an energy dFFR are “value-stacking” by also bidding
conductors, over current protection management system to track all energy into the UK capacity market. Contract
devices, switches and contactors in the storage performance data, the system terms in the capacity market last up to
power path. Therefore, battery rack- owner is not protected in event of 15 years.
based augmentation is not a feasible failure. In addition, trade-off decisions As of this writing, capacity in the
approach to future-proofing energy regarding changes in battery operation UK required an energy duration of 30
storage. within the terms of the battery warranty minutes for ESS, but UK regulators have
An alternative is rack-based inverter are not possible. signalled an intention to lengthen the
design. In this scenario, racks are wired energy duration requirement. As in the
in parallel on the AC side of the inverter Case studies of future-proofing ESS case of PJM Reg D, an increase in energy
rather than the DC side. A rack-based Case Study 1: UK National Grid duration requirement of capacity would
inverter configuration allows for more Market overview have an adverse impact on system
design flexibility for future augmentation The United Kingdom is poised to revenue, so prospective owners need
but can be less cost effective. The become one of the largest ESS markets to plan for flexibility in their current
selection of the right approach is in the world. National Grid, the UK grid installations.
dependent on the degree of flexibility operator, has announced its intention to
desired by the system owner. procure ESS for grid balancing services Future-proofing approach
through its Enhanced Frequency For National Grid EFR and dFFR projects
Strategy 3: Track ongoing operations for Response (EFR) and dynamic Firm that are participating in the capacity
flexibility with warranty Frequency Response (dFFR) market market, Wärtsilä offers an ESS design
Li-ion battery warranties are complex. products. National Grid has awarded with spacing and cabling pre-planned
Warranty terms differ by battery vendor four-year EFR contracts for 201 MW of to modify battery storage duration at
and model. Typical terms include: ESS capacity, and dFFR contracts ranging a future date. Wärtsilä developed a 10
• Annual energy throughput from a period of months to two years for MW / 5 MWh system, with spacing and
• Peak DC charge/discharge rate more than 100 MW of ESS capacity. cabling pre-planned for conversion to
• Daily average DC charge/discharge rate The UK has a need for incremental 10 MW / 20 MWh in the future. Before
• Average daily temperature resources for balancing services due and after the conversion, the system will
• Maximum temperature deviation to multiple market drivers. These maintain a set of five 2 MW inverters.
across measurement points drivers include increased wind The change comes from adding three
• Common mode noise level (voltage) penetration, retirement of large storage containers with batteries to
• Common mode noise level (current) synchronous coal- fired generation and increase the energy rating. By increasing

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