HomeMy WebLinkAboutKotzebue Electric AEA REF R13 130018 Questions Oct 21 2020Subject: Renewable Energy Fun Grant Application Reviewer Questions #130018 Kotzebue Community -
Scale Energy Storage System
The review team would like to ask the following questions. Please reply to this email at
your earliest convenience as the team is on a schedule to finish Stage 2 review of your
application.
Questions for the applicant:
1. What is the minimum and maximum state of charge limits on the existing system?
The existing BESS is used for grid frequency response and is maintained at 75% SOC +/- 5% until it is
needed to support the grid. If the battery is needed to support the grid, we will discharge down to 20%
if we need to. Discharge to 20% only occurs 1-2 times per year. Normally the battery responds at high
power for short periods of time (30sec to 2 mins) due to loss of wind power, reducing SOC to ~50-60%.
2. What are the O&M costs to maintain the existing BESS system over the last three years.
BESS operational costs consist mostly of the station service power to keep the BESS ready to operate.
KEA is using approximately 8,000 kWh per month to keep battery charged, inverter powered up and
HVAC on. This translates to about $1,500 per month of diesel burned (575 gals at $2.50/ gal).
BESS maintenance costs are approximately $2,500/yr related to fire suppression system testing and
vendor (ABB, SAFT, EPS) remote support over the internet for troubleshooting, etc.
3. Please provide data for both planned vs. unplanned outage of the existing BESS after the system
was considered commercial.
Two months after commissioning of the BESS (December 2015), the BESS suffered a lithium-ion battery
module failure due to accidental over-charging of the BESS by KEA. The BESS was still under warranty
and SAFT was able to repair the BESS promptly. The BESS was down for approximately 1 month.
Settings were changed in the BMS such that overcharging was no longer capable.
Shorter, partial outages of the BESS have occurred over the 5 years KEA has been operating the unit.
The SAFT battery consists of 17 strings of Li-ion battery modules. The ABB PCS100 inverter consists of
14 sub-inverters. KEA has had problems with individual strings and sub-inverters that have mostly been
software related. When a string or sub-inverter is tripped, the BESS will operate at a reduced power or
energy capacity.
KEA does not have any specific data related to these BESS problems
4. What is the estimated life of the existing BESS and does KEA intend to replace the bank?
KEA is at 5 years on the BESS and the unit is still performing well. The expected life of the batteries is 10
years but could be longer based on the way KEA is operating the BESS (limited high power, deep depth
discharges). The inverter has a 30+ year expected life. Remaining life of the batteries is measured by
performing a capacity test periodically (biennially). It is KEA's intention to repopulate the SAFT energy
storage container with new Li-ion modules once the existing battery modules have reached end of life.
The new Li-ion modules would be shipped in on pallets and installed into the existing energy storage
container.
5. How is KEA planning on heating the powerhouse during diesels-off operation in winter months.
KEA will use two heat sources for diesel-off operation. A 1,000,000 Btu/hr oil-fired boiler is currently in
place and DEC permitted to burn a blend #2ULSD and used oil (KEA generates approximately 3,000
gallons per year of used 40W engine crankcase oil). An electric boiler that will utilize excess renewable
power will be designed and added in the future. The electric boiler will be utilized first and the oil boiler
brought online to maintain system temperature as needed.
6. What is the monthly performance over the past three years of diesel, wind, solar, battery?
Please see attached PDF "Kotzebue Monthly Performance Sept 2017-2020".
7. What is the measured average roundtrip efficiency of the current BESS?
Round trip of the entire BESS is extremely low based on the energy measurement point at the bus
connection. Round trip efficiency of the storage lithium-ion modules individually is significantly higher
(approx 75%). On a monthly basis we are putting in approximately 8000kWh and getting out about
500kWh. Due the way KEA is using the BESS, on an energy basis the complete BESS (inverter, controls,
battery modules and HVAC) is about 6% efficient. However, it should be noted that the ~500kWh per
month received from the BESS are critical kWh and if they weren't available, grid outages would occur.
8. Section 6.1.1 indicates the current fuel cost is $11.13/gallon. Is this correct?
That is not correct. KEA power generation fuel (bulk purchase #2ULSD) is approximately $2.50 per
gallon. Community #1 heating fuel is approximately $6/gallon.
9. What is the anticipated cycle life of the BESS at planned depth of discharge rates?
The final design and permitting process accomplished with AEA REF Round 13 funds will produce the
power and energy capacity specifications for a community-scale BESS with a 10 year cycle life. At 10
years (and based on battery capacity testing), a replacement of the battery modules would be planned
and executed (inverters have a 30+ year life). To achieve a 10-year cycle life, the energy storage
modules will need to be sized sufficiently to allow for regular deep discharges and also high frequency
charging and discharging (mini/micro cycles). The chemistry of the battery (power or energy
chemistry) will also be selected based on the anticipated implementation of the community-scale BESS.
Please let me know if there is any follow up info needed.
Sincerely,
Matt Bergan, PE
Engineer
Kotzebue Electric Association
907-412-1591