The following is the article submitted by Len Visser of Lindsay Broadband.
(© 2022 Society of Cable Telecommunications Engineers, Inc. All rights reserved.)
HFC Network Powering Using Lithium Iron Phosphate Batteries
History, Science, Comparable Attributes and Use Cases
A Technical Paper prepared for SCTE by
Len Visser, Product Line Manager Power Solutions, Lindsay Broadband Inc., SCTE Member
2-2035 Fisher Drive
Peterborough, ON K9J6X6 Canada
[email protected]
(705) 742-1350 x241
Table of Contents (Title / Page Number)
Table of Contents 2
1. Introduction 4
2. Battery Background 4
3. LFP Technical Overview and Attributes 5
3.1. Reliability 5
3.1.1. Lifespan 5
3.1.2. Energy Density 6
3.1.3. Charge Time 7
3.1.4. Depth of Discharge 7
3.1.5. Discharge Rates 7
3.1.6. Maintenance 8
3.2. Green/Environmentally Friendly 8
3.2.1. Contaminant-free 8
3.2.2. Recyclable 8
3.2.3. Less Waste 9
3.2.4. No Fossil Fuel 9
3.3. Safety 9
3.3.1. No Outgassing 9
3.3.2. No Sulphuric Acid-Based Electrolyte 9
3.3.3. Non-Combustible 9
3.4. Efficiency 9
3.4.1. No Float Charging 9
3.4.2. Temperature Effects 10
3.4.3. Low Self-Discharge Rate 10
3.5. Social Responsibility 10
3.5.1. No Cobalt 10
4. Application Use Cases 10
4.1. Network Standby Power Supplies 10
4.2. Disaster Recovery Emergency Power Trailers 11
4.3. Portable AC Generators 11
5. Final Considerations 12
6. Abbreviations and Definitions 13
6.1. Abbreviations 13
7. Bibliography and References 13
List of Figures (Title / Page Number)
Figure 1 – Battery Lifespan: LFP, VRLA, NMC 5
Figure 2 – Energy Density 6
Figure 3 – Energy Density: LFP vs. VRLA (Run-Time, Weight, Size) 6
Figure 4 – Charge Time: LiFePO4 vs. VRLA 7
Figure 5 – Depth of Discharge: LFP vs. VRLA 7
Figure 6 – Discharge Test: LFP vs. VRLA 8
1. Introduction
Network powering is a complex imperative. In today’s evolving environment, powering solutions need to be clean, energy-efficient, safe, reliable, and sustainable. Deployment scenarios extend across hybrid fiber/coax (HFC) networks, small cells, and Wi-Fi access points, as well as long-duration utility power outages and disaster recovery using fixed and portable solutions.
Powering solutions also span a range of considerations and goals, including:
• Device and system efficiencies – to reduce energy consumption;
• Clean, environmentally-friendly devices – to reduce the carbon footprint;
• Reliable devices – to provide continuous service, minimize maintenance and extend lifespans;
• Renewable and sustainable energy sources – to reduce fossil fuel use;
• Safe devices – to remove hazards to personnel and surroundings; and
• Emergency and disaster-recovery suitability – to ensure portability, quick set-up, smooth operation, and long run-time
Broadband operators have typically used valve-regulated lead acid (VRLA) batteries to meet their power requirements. To help achieve today’s expanded objectives, they now have other options, including lithium iron phosphate (LiFePO4, or LFP). Based on a highly stable chemistry, LFP batteries offer premium performance while being environmentally friendly. They are safe, with no corrosive substances or fire and explosion hazards. They use fewer materials and contain no rare earth metals or groundwater-contaminating compounds, avoiding the drawbacks of VRLA and other leading lithium battery technologies, such as lithium nickel manganese cobalt oxide (NMC). They allow network operators to maximize run-time with minimal battery counts and minimal maintenance. In this paper, we will provide additional background on LFP batteries and chemistry, review their attributes, and discuss three use cases.
2. Battery Background
As in most areas of science and industry, the technology of batteries has developed more rapidly in the past forty 40 years than in the pastprior 1620 . Invented in the mid 19th century, the lead-acid battery remained largely unchanged for about 100 years. The first type of VRLA battery (gel cell) emerged in 1957 and the second (absorbent glass mat or AGM) was patented 15 years later. Then in the late 1970s, scientists began developing what would become the lithium-ion battery.
Several other technologies also appeared on during this timeline. Wet-cell nickel-cadmium (NiCd) batteries, invented at the end of the 19th century, later became widely used in portable power tools and other electronic devices, until being supplanted by nickel-metal hydride (NiMH) batteries, which emerged commercially in the 1990s. The VRLA and the lithium-ion families, however, remain the dominant segments. As the global scientists driving lithium-ion technology continued to experiment (eventually winning the Nobel Prize for their discoveries) [1], they focused on the chemical makeup of the battery’s positive terminal, or cathode. Two major technologies that emerged were NMC and LFP.
Looking forward, some analysts expect LFP batteries to overtake NMC as early as 2028.[2] Two leading markets are transportation and utility-scale stationary energy storage. Demand comes from manufacturers of low-speed vehicles (LSVs), automated guided vehicles (AGVs) and now, with Tesla’s decision in 2021, high-speed electric vehicles (EVs).[3] The renewable energy sector is also leaning on LFPs to capture energy during periods of excess production. Communications and broadband service providers represent additional demand for LFPs, but before looking at these use cases, let’s examine the underlying technology and assess its comparative advantages.
3. LFP Technical Overview and Attributes
Like other lithium-ion batteries, LFPs discharge and recharge energy through lithium ions that move from a negative electrode (anode) through an electrolyte to a positive electrode (cathode) and back again. Lithium-ion cells typically use a graphitic carbon compound at the anode and an intercalated lithium compound on the cathode.
Why does LFP work so well? Experts point to its thermal and structural stability, its aversion to water molecules, and its exceptional performance. Largely responsible for that performance is LFP’s crystalline lattice, or olivine-like structure, which features an “extremely flat charge/discharge profile.” [4] The application of LFP olivine material was the fruit of a decade of intensive research and development, leading to commercialization and widespread use of these batteries beginning around 2012.[5] The upshot is they are today among the longest-lived batteries ever developed. Manufacturers typically rate LFP batteries for 5,000-plus Test data in the laboratory show up to 5000 charge/discharge cycles, due again, to because iron phosphate’s robust crystalline structure, which does not break down under repeated packing and unpacking of the lithium ions.
Supplementing the chemistry is a battery management system (BMS), which constantly monitors key operational parameters during charging and discharging using outputs from sensors, which and gives the actual status of voltages, currents, and temperatures within the battery as well as the state of charge (SoC). A microcontroller manages information from the sensing circuitry and makes decisions with the received information using application-specific algorithms that are digitally encoded into the microcontroller. For more details on LFP and how it compares to VRLA and NMC chemistries, see Ssection 3 and its subsectionthe following discussions of its reliable, green, safe, efficient, and socially responsible attributes.:
3.1. Reliability
3.1.1. Lifespan
LFP (LiFePO4) batteries live ten times longer than VRLA and three times longer than NMC. (See Figure 1.) This means a higher reliability over a longer period. A longer lifespan also increases reliability, reducing labor and replacement costs. (For the relevance of longer lifespans to mandated network reliability, see section below on use cases.)
Figure 1 – Battery Lifespan: LFP, VRLA, NMC
3.1.2. Energy Density
LFP batteries have a higher energy density (≈140 Wh/kg) compared to ≈ 45 Wh/kg for VRLA. (See Figure 2.) The lead-acid battery is an aqueous system. The single cell voltage is nominally 2V during discharge. Lead is a heavy metal; its specific capacity is only 44Ah/kg. In comparison, the LFP cell is a non-aqueous system, having 3.2V as its nominal voltage during discharge. Its specific capacity is more than 145Ah/kg. Therefore, the gravimetric energy density of an LFP battery is three times higher than that of VRLA. An additional bonus is that because the that because LFP is a non-aqueous battery, there are no spill hazards, and the battery can be installed on its side, upside down or standing up.
Figure 2 – Energy Density: Lead Acid (VRLA), NiCad, NiMH, LiFePO4 (LFP) (Wh/Kg) LFP batteries also provide more power for the same battery weight, resulting in a longer run-time. More energy storage in the same physical space equates to three-times longer run-time in terms of energy density alone. Also, LFP batteries are one-third the weight and one-third the size of VRLA in terms of energy density. (See Figure 3.). This means, there is a much higher capacity-battery in the same physical form-factor, allowing greater configuration flexibility in the same enclosure.
Figure 3 – Energy Density: LFP vs. VRLA (Run-Time, Weight, Size)
3.1.3. Charge Time
Due to its very low internal resistance, LFP has a charge rate four times faster than VRLA. (See Figure 4.) This would means that during multiple successive outages, LFP batteries used in network standby power supplies come up to full charge faster, resulting in longer run-times and greater plant reliability when applied, for instance, in an HFC network. During recurring utility power outages, LFP batteries can often fully recharge before the next outage.
Figure 4 – Charge Time: LiFePO4 vs. VRLA
3.1.4. Depth of Discharge
LFP provides longer run-time for emergency use. Depth of discharge (DoD) refers to the percentage of a battery that has been discharged relative to its capacity. For LFP, 80 percent of its capacity is usable energy vs. only 40–50 percent for the typical VRLA. (See Figure 5.).
Figure 5 – Depth of Discharge: LFP vs. VRLA
3.1.5. Discharge Rates
High discharge rates have minimal effect on LFP battery lifespans, whereas it greatly reduces VRLA lifespans. LFP battery capacity is independent of the discharge rate, whereas a VRLA battery is reduced to only 60 percent of its rated capacity (equaling less run-time) and its lifespan is significantly shortened.
LFP battery discharge voltage is almost constant, thereby keeping the discharge current constant, e.g., for the same amount of battery power delivery to a standby power supply inverter. WhereasIn contrast, , VRLA battery discharge voltage decays as run-time progresses, resulting in increasing discharge current to maintain the same battery power delivery to the power supply inverter. (See Figure 6.). Consider a flashlight that dims over time because battery voltage is decreasing as the battery discharges. If the battery was LFP, the bulb would be bright from beginning to end. Once discharged, the battery would simply not turn the light on.
Figure 6 – Discharge Test: LFP vs. VRLA
3.1.6. Maintenance
Due to lack of corrosion concerns, periodic battery interconnect cable changes are not required in LFP batteries. This results in a lower OpEx for maintenance and higher reliability in normal and emergency use. When used in AC generators, LFPs eliminate start-up mechanical problems, such as carburetor and sparkplug fouling, stale fuel, etc. (For more on generators, see discussion of use cases below.)
3.2. Green/Environmentally Friendly
3.2.1. Contaminant-free
LFPs have no lead, mercury, cadmium, cobalt, or rare-earth metals to pollute and enter ground water.
3.2.2. Recyclable
LFPs are 100 percent recyclable, compared to only 60 percent recyclable materials in VRLA.
3.2.3. Less Waste
Fewer raw materials (from fewer batteries required) for the same energy density reduces waste. A longer lifespan also equates to fewer batteries used over time, translating to more reductions in waste.
3.2.4. No Fossil Fuel
When used in AC generator applications, LFPs replace fossil fuel-powered generators:, which also conform to anti-idling regulations. this enables conformity to anti-idling regulations.
3.3. Safety
3.3.1. No Outgassing
Based on a safe chemistry, LFPs are the most stable lithium-type battery on the market. They LFPs eliminate do not suffer from the outgasing of harmful acidic gases and explosive hydrogen that are is present with lead-acid during charging. Unlike lead acid, they produce no out-gassing of harmful acidic gases or explosive hydrogen during charging.
3.3.2. No Sulphuric Acid-Based Electrolyte
The absence of sulphuric, acid-based electrolytes eliminates corrosion on connectors and cables. LFPs eliminate the need for rubber gloves, aprons, and personal protective equipment (PPE) to prevent chemical burns. They eliminate the need for corrosion-inhibiting grease on battery terminals, as well as corrosion itself, along with technician exposure to corrosive substances when replacing cables and connectors.
3.3.3. Non-Combustible
As indicated in lab tests, news stories and user-generated videos, some lithium battery chemistries, including NMC, can be very volatile and flammable. Newer LFP chemistry is inherently non-combustible and non-explosive. It is chemically and structurally stable with no chance of thermal runaway. It is safe to transport. Charged and discharged states of LFP are physically similar and robust, which allowsallowing ions to remain stable during oxygen-fluctuating charge cycles, which again prevents thermal runaway. If mishandled during charging or discharging, or if subjected to collisions or short circuiting, the battery won’t explode or catch fire. Internal decomposition occurs when the battery temperature reaches the 900°F to 1100°F range (500°C to 600°C). This absence of flammability hazards reduces the need for special personnel training.
3.4. Efficiency
3.4.1. No Float Charging
LFP chemistry does not require a floating charge or de-sulphation pulses applied to the battery to maintain its capacity at or near the full charge. Its absence during charging and maintenance cycles reduces operational energy use.
3.4.2. Temperature Effects
All batteries suffer from the effects of extreme temperatures; however, LFP suffers less from extreme temperatures. Its operating temperatures for charge are 32°F to 113°F (0°C to +45°C), and discharge from -4°F to 140°F (-20°C to +60°C). At 0°F (18°C), it can be discharged to 70 percent of rated capacity, whereas VRLA can only be discharged to 45 percent of rated capacity. The BMS monitors performance of the LFP cells and limits degradation from its optimal operating temperature of 68°F (20°C).
For extremely cold environments, optional internal BMS-controlled cell strip heaters maintain the cells between 60°F to 75°F (16°C to +24°C) and allow operation at lower ambient temperatures. Charging is then possible down to -13°F (-25°C). Lead acid batteries can be discharged and charged at a lower temperature limit, but in a less than fully charged battery, the electrolyte becomes more like water, which is more likely to freeze than when it is fully charged, resulting in permanent battery damage. LFPs operates better than VRLAs at hot temperatures due to the higher lithium ionic conductivity and can be discharged up to 140°F (+60°C); VRLA can only be discharged efficiently up to 113°F (+45°C).
3.4.3. Low Self-Discharge Rate
Very low internal resistance prevents wasted energy required to “top up” batteries.
3.5. Social Responsibility
3.5.1. No Cobalt
Over 70 percent of the world’s supply of cobalt comes from the Democratic Republic of Congo, where cobalt mining often involves human rights violations. Unlike NMC batteries, LFP uses no cobalt.
4. Application Use Cases
The long life, low maintenance, high efficiency, and unparalleled safety of LFP batteries make them applicable in a wide range of use cases. In addition to their roles in transportation and utility-scale stationary energy storage, they can lend vital support to communications networks. Power loss or continual sags in voltage (rolling brownouts), whether caused by fires, floods, hurricanes, terrorism, or other disruptive forces, require immediate remediation. LFP battery-based solutions are well-suited to fill that gap through standby power solutions, emergency power trailers, and portable AC generators.
4.1. Network Standby Power Supplies
Operators are looking for ways to increase standby run-times. One driver is regulation. Along with adopting several resiliency strategies for wireless and wireline service providers, the California Public Utilities Commission (CPUC), which has tremendous influence on utility regulation in the U.S., has prioritized backup power duration of at least 72 hours.[6] To achieve this level throughout the life of a battery, operators need to assess risks given realistic run-times for various battery chemistries.
One consideration is the number of battery strings vs. an acceptable depth of discharge (DoD). VLRA has a very mediocre DoD but can be pushed higher, which would allow for fewer battery strings, but the negative impact of a higher DoD on reliability over time can be significant. Temperature is another factor. Cold temperatures reduce any battery’s ability to function properly, although LFP can handle cold better, if fitted with internal cell heaters, than VLRA batteries. As noted above, LFP operates better than VRLA at hot temperatures and can be discharged up to 140°F (+60°C), considerably higher than the efficient discharge limit for VRLA.
Compared to traditional VLRA batteries, LFP batteries offer many advantages in standby scenarios. They are safer, higher performance, compact, and energy-dense, with 80-90 percent DoD and a very long lifespan to maximize run-time with minimal battery counts and minimal maintenance. By contrast, network operators must perform quarterly maintenance on VRLA batteries or suffer critical reductions in network readiness. As a result, LFP can provide reliable and long-lasting network standby run-times during power outages. The reduction in the battery footprint required also directly relates to a reduction in pad and cabinet size, which minimizes visual “pollution.” The contrast with standard VRLA is striking: An LFP standby system can achieve 72-hour run-times with 12VDC high-capacity LFP batteries using four times fewer batteries. In a modest plant leg scenario (with an 8 Amp PF=0.85 current draw), an operator would need 28 36VDC 100Ah VRLA battery strings (84 batteries) at a DoD of 60 percent, vs. 6 36VDC 344Ah LFP battery strings (18 batteries) at 80 percent DoD.
In addition to the dramatic reduction of batteries required, an LFP standby solution has the added benefits of a ten10x-times longer lifespan; significantly faster recovery/recharge time, which is critical to remaining operational during multiple outages; and an environmentally friendly battery chemistry that eliminates required maintenance. The elimination of any float charging requirement for LFP battery strings also reduces the operational use of energy.
4.2. Disaster Recovery Emergency Power Trailers
During natural disasters and rolling brownouts, rapidly deployable, portable, high energy-density backup power systems are also needed to power communications equipment in the field during recovery periods. Combined with high-efficiency inverters, LFP batteries can be combined to create sustainable, all-inclusive backup power trailers. Portable small-footprint trailers offer long run-time AC and DC power outputs and are capable of powering critical equipment, such as:
• 4G and 5G small cells
• Wi-Fi access points
• MDU communications equipment
• DAS networks
• HFC networks
• Fiber aggregation sites with active powering
Both 120 and 240VAC 60Hz AC sine wave power as well as 12, 24 and 48VDC power can be provided using 4-8 high-capacity 14kWh LFP batteries. This yields 56 to 112kWh of energy storage with 90 percent of that stored energy available as usable energy. Multiple 15A, 20A and 30A, 120/240VAC receptacles can provide vast amounts of power from the highly efficient inverters. They can be recharged via solar panels or flexible solar ground mats, or individually in warehouse settings via external charging stations. Run-time examples using an 84kWh trailer include a typical HFC leg (1080W), 2.2 days; 5G small cell (420W), 4.9 days; and Wi-Fi AP (64W), 32 days.
4.3. Portable AC Generators
Another application that pairs LFP batteries with high-efficiency inverters are smaller AC generators, which can be used at critical locations during power outages or at job sites in any conditions when field technicians need portable power. This LFP-inverter combination provides a green alternative to portable fossil fuel-powered AC generators, without compromising power or performance.
Anti-idling compliant and safe for indoor use, LFP-based AC generators feature large amounts of energy storage. They deliver high-quality, clean, regulated 120VAC, 60Hz sine wave power, free from the typical stepped sine wave and electrical noise (hash) that fossil fuel generators produce. This provides “normal” stabilized AC power that load devices are designed to use, increasing their efficiency, and reducing possible device malfunction or damage. This results in an electrically clean, operationally silent, low-carbon footprint AC supply without deadly undesired CO or CO2 greenhouse gas emissions.
Small hand-carried units (1kWh) are an ideal source of power for test instruments, fiber optic splicers, and other tools. Larger units (6.2kWh) are easily transported in a technician’s vehicle and can be used to power network power supplies, small-cell radios, Wi-Fi APs, etc. These AC generators are a sustainable form of energy with multiple charging methods, including AC mains rapid charger; efficient mMaximum pPower pPoint tTransferracking (MPPT) solar charge controller with conventional or flexible solar panel arrays; and simultaneous AC plus solar charging for very fast re-charging.
5. Final Considerations
Energy storage continues to evolve. While lithium iron phosphate (LiFePO4, or LFP) is one of latest commercially available technologies, this is an active area of research and development. New approaches will emerge, some of which may not even fall within the traditional battery category.[8] The push away from carbon-based energy and toward renewable sources is one driver. How well these products perform specific functions within an HFC network has been a key focus of this discussion.
The evidence is strong. In addition to the green and socially responsible attributes of LFP batteries, they outperform the alternatives in terms of reliability, safety, and efficiency. Of course, no technology does it all. While LFP has three times as much energy density as VRLA, as noted above, other lithium batteries, including NMC, surpass LFP in this metric. That in part explains why NMC batteries do well in the global motive power market, as forklifts and other heavy machinery look for all the power they can get. Some LFP strengths could also appear as drawbacks to some. Just as a boat owner may hesitate to purchase an LFP battery with a ten-year lifespan, the owner of an HFC network looking to sell within a few years may be less motivated to invest in LFP.
Any mention of investment raises financial questions. While economics is beyond the scope of this paper, a few points are in order. On the one hand, LFP requires no precious metals, such as nickel or cobalt, which is a cost advantage in comparison to other lithium batteries. Yet LFP’s long lifespan, among other benefits, creates a price premium, especially over VRLA. Operators should conduct their own analysis, including total cost of ownership (TCO). The key takeaway here is that LFP is a powerful technology, well-suited for operators looking to migrate away from a legacy base while addressing their persistent — and in many cases growing — need for standby power, disaster recovery and portable generators.
6. Abbreviations and Definitions
6.1. Abbreviations
AC alternating current
AGM absorbent glass mat
AGV automated guided vehicle
Ah amp hour
AP access point
BMS battery management system
CO carbon monoxide
CO2 carbon dioxide
CPUC California Public Utilities Commission
DC direct current
DoD depth of discharge
EV electric vehicle
HFC hybrid fiber/coax
kg kilogram
LiFePO4 lithium iron phosphate
LFP lithium iron phosphate
LSV low-speed vehicles
MPPT maximum power point transfer
NiCd nickel cadmium
NiMH nickel-metal hydride
NMC lithium nickel manganese cobalt oxide
OpEx operating expenditure
PF power factor
PPE personal protection equipment
RMS root mean square
SCTE Society of Cable Telecommunications Engineers
SoC state of charge
TCO total cost of ownership
V voltage
VRLA valve-regulated lead acid
Wh watt hour
7. Bibliography and References
[1] “The Nobel Prize in Chemistry 2019 was awarded jointly to John B. Goodenough, M. Stanley Whittingham and Akira Yoshino “for the development of lithium-ion batteries.” The Nobel Prize in Chemistry 2019. NobelPrize.org.
[2] “Global lithium-ion battery capacity to rise five-fold by 2030,” 22 March, 2022. Wood Mackenzie. Woodmac.com/press-releases
[3] “Tesla will change the type of battery cells it uses in all its standard-range cars,” 20 Oct. 2021. Cnbc.com.
[4] “Lithium Iron Phosphate: Olivine Material for High Power Li-Ion Batteries,” Christian Julien, et al., Research & Development in Material Science, December 2017.
[5] “Overview of olivines in lithium batteries for green transportation and energy storage,” K. Zaghib, et al., Journal of Solid State Electrochemistry, vol. 16, 2012.
[6] Communications Network Resiliency, California Public Utilities Commission. Cpuc.ca.gov.
[7] “Flywheel Energy Storage Replacement For Lead-Acid Batteries in CATV Network Stand-By Power Supplies,” William D. Bauer, Journal of Energy Management, vol. 5, no. 1, March 2020
