Within any power protection system, the type of battery installed can critically impact on the overall performance of the uninterruptoble power supply. Aside from different battery brands, sizes, performance specifications and design lives, there are different technologies including valve regulated lead acid (VRLA) and lithium-ion. Whichever is selected, the battery installation must be reliable and cost-effective if it is to provide sufficient power to the UPS system when required and provide the best possible Total Cost of Ownership.
Firstly, let’s review the role of a UPS battery set. In an online datacentre UPS, the ‘front end’ is typically an IGBT-based rectifier, connected to the mains power supply, from which it receives a source of AC (alternating current) power. When mains power is not available, an alternative power source could be a generating set. The rectifier assembly converts the input power into two levels of DC; one to charge the battery set and the other to power the UPS inverter. The inverter takes the DC power input and inverts this into an AC waveform to power the load i.e. servers, storage and networking peripherals.
The purpose of the UPS battery is to provide a source of DC (direct current) power to the input of the inverter section, when the AC mains power supply fails or is momentarily interrupted. Without an alternative power source, the inverter would fail within milliseconds and the load drop. Millisecond hold-up is made possible through internal system capacitance but it is not long enough to cover the start-up of a local standby generator or the return of the mains power supply. UPS systems are available for specialist applications with additional capacitor banks; these can provide useful energy storage for transportation or manufacturing line protection.
Within the UPS industry, lead acid batteries have been the dominant battery for many decades. Wet cell lead acid were the most common type before the introduction of valve regulated lead acid (VRLA) maintenance free types. Lithium-ion batteries are widely available in consumer goods, communications and computer products including mobiles, laptops and tablets. Here the battery technology has replaced the more traditional NiCd (Nickel-Cadmium) battery which was banned due to the impact of cadmium on the environment. Lithium-ion battery usage has also grown alongside the renewables industry (solar PV and wind turbine) here it is used to store energy for local consumption or later export to the electricity grid. Only in recent years has lithium-ion been considered as an alternative to lead acid batteries in UPS installations. Here is a comparison checklist between the two UPS battery types: lead acid and lithium-ion:
The battery-choice related issues can be summarised as:
|Item||Concern||VRLA UPS Battery||Lithium-ion UPS|
|1||Cost||Lower due to widespread usage and scale economies||more expensive to manufacturer and requires a more complex and costly battery charger|
|2||Availability||typical float charge to 80% within 24 hours, 300-400 cycles||typical recharge to 80% within 40 minutes, unlimited cycles|
|3||Size||larger floor space and weight due to the lead plate component||physically smaller battery cells, higher power density|
|4||Maintenance||Visual inspection and handheld battery testing as part of an annual planned preventative maintenance visit||Visual inspection and continuous battery monitoring as part of the battery management system (BMS)|
|5||Replacement||5 year or 10-year design life||10-15-year design life|
|6||Safety||Established technology, little chance of leakage, design life degrades with temperature above 25degC||More concerns over flammability and thermal runaway, more suited to hot aisles as less temperature sensitive|
|7||Logistics||VRLA batteries are considered safe for air freighting||Legislative restrictions especially for air freight|
|8||Sustainability||More eco-friendly with up to 95% recyclable materials||Fewer recycling centres and harder to recover lithium and separate metals|
The table is not exhaustive and provides a general summary comparison. For more specific information on our UPS batteries please contact our projects team.
The UK electricity grid requires significant investment if the country is to discontinue new petrol, diesel and hybrid car sales by 2035. Each new vehicle will by then use either lithium-type batteries or hydrogen-powered fuel cells or some new energy medium that has yet to reach mainstream automotive manufacturers.
The UK grid is also becoming more complex as it incorporates more renewable power sources (e.g. solar, PV, tidal, compressed air and hydro) and large-scale energy storage. There is much anticipation of Ofgem’s next guidelines but these are expected to put a greater focus on how to provide electricity for a dramatic rise in electric vehicle usage and the replacement of gas-fired boilers, central heating and cookers.
There are several energy storage and saving initiatives underway under the National Grid’s Demand Side Response (DSR) program. One way global UPS manufacturers have adapted their uninterruptible power supplies to meet the challenges is to introduce bi-directional rectifiers and offer lithium-ion UPS battery options. Spare battery capacity can be used to generate income for an enterprise or colocation datacentre by supplying this to the grid or by disconnecting the building load from the grid supply for short periods of time i.e. running on battery power.
Lead acid has long been the de facto standard for UPS batteries whether in a computer, server room or datacentre. This is likely to be the case for the next 3-5 years until lithium-ion batteries and their battery management systems becomes less expensive to incorporate into future UPS designs and installations. For now server room and datacentre UPS installations will continue in the main to use VRLA-type batteries, with lithium-ion being adopted if there is more of an energy storage and/or demand side response type application.
The energy efficiency of your datacentre UPS is important for two critical reasons. The first is running costs and the second is related to the battery runtime available when the mains power supply fails. An undersized UPS is often immediately obvious as load is applied on start-up but may not always be so. Intermittent overloading can occur if there is marginal capacity for extra load. Oversizing can also be an issue, whilst providing what can prove to be a false sense of security.