The traditional approach to choosing the right UPS system is centred on achieving the greatest reliability. However, over the last few years, the focus has shifted and IT managers are now much more likely to want a standby power solution that offers a high efficiency. Why? Because they need to reduce costs and they want to adopt cleaner, greener IT solutions.

There are several factors that IT managers need to consider when specifying a standby power solution in order to achieve high efficiency levels from it. Because it is difficult to optimise a system for efficiency with a one-size-fits-all approach, it is common practice to customise each UPS installation in some way to meet the exact needs of the organisation.

Total cost of ownership

The efficiency of the UPS system has a major impact on the total cost of ownership. Using old, less efficient UPS technology, or specifying a system that is simply too big for the load can result in an inefficient system that is more expensive to run and maintain.

IT managers can look at a number of issues to reduce cost of ownership of their standby power environment. We are going to highlight three of them here: the topology of the UPS, use of advanced ‘eco-mode’ technology, and the choice of cooling system.


There are several ways that engineers can configure UPS systems to provide sufficient power to meet the standby power load. Different topologies come with different engineering tradeoffs. To help explain how to use topology to make a UPS system more efficient, we will look at an example involving a load of up to 80kVA?a typical load for many small-to-medium businesses.

Any of the following topologies could be used to support an 80kVA load:

  • Traditional approach: a single 100kVA unit
    • Parallel approach: two 50kVA units
    • Modular approach: nine 10kVA units

Traditional topology

Using the traditional approach can be the least efficient way to support the load. This is primarily because it is the least flexible configuration. An organisation’s standby power requirements often change over time, and if the standby power solution is not scalable then very often the UPS system that the company first installed will be oversized to allow for future business growth. The problem with this approach is that it may not allow the UPS to run at its most efficient operating point, which is approximately 75-80% of the load.

While modern UPS units have better operating efficiencies at low loads, older UPS units do not cope so well if there is a mismatch between their operating rating and the actual load. A UPS that is 10 years old is typically 8-10% less efficient than a modern one. For a UPS supporting an 80kVA load, a 10% improvement in efficiency can to amount to electricity savings of almost £10k per year at today’s prices.

Parallel topology

Operating two or more separate UPSs in parallel can increase the overall system efficiency because each UPS is more likely to be running at, or near, its optimum capacity. This solution is scalable: it is possible to add more units in parallel as the load increases. It is often the chosen method when there is the need to either increase capacity and increase the redundancy of the system.

Having physically separate units allows them to be located in different rooms, which minimises the chances of an accident taking out the entire UPS installation. This is probably the best configuration to maximise the redundancy of the standby power solution. A disadvantage is that the physical space requirements for the parallel topology will most likely be greater than the traditional topology.

The total cost of ownership of the parallel configuration?taking into account the initial purchase, installation, maintenance and running costs?can be similar to the cost of the traditional topology.

Modular topology

A modular UPS comprises several smaller UPS ‘modules’ that are housed in a single cabinet. Employing a modular approach to the UPS configuration is generally a more expensive option?at least initially. The capital cost can be as much as 50% higher than an equivalent traditional or parallel topology. However, if ‘going modular’ allows an organisation to exactly match the UPS output to the changing load, then the total cost of ownership can be less than the other options. A modular topology can be the most scalable way to provide standby power and it can offer the best operating efficiency across a broad range of loads.

This approach is scalable both ways?the organisation can more easily downsize its UPS provision as well as expanding it. For this reason it can be very attractive to organisations whose needs change frequently, particularly where they use the same type of system widely, because they can deploy the modules wherever they are needed. The current trend towards virtualisation, where organisations are looking to reduce their IT hardware investments by creating virtual hardware environments in software, can lead to a situation where the UPS is actually too big for the load. In such a case, if the business has invested in a modular topology it can improve the operating efficiency of its standby power by simply removing UPS modules.

UPS manufacturer APC calls this approach ‘pay as you grow’, because users only ever pay for their current UPS requirements, which substantially reduces the overall cost of ownership in a business where the load is frequently changing.


Manufacturers have introduced other efficiency improvements to their standby power products, which offer similar protection benefits to online UPS, but use much less energy.

Smarter eco-mode systems constantly monitor the incoming power quality and switch to ‘eco-mode’ at the slightest suggestion of power disturbances. Whilst high-quality power is being provided, the inverter is in standby, reducing power consumption.

Another way to implement eco-mode is to monitor the input supply in real time. The UPS operates in offline mode when the input power conditions meet preset conditions. When the UPS detects a variation in the supply that exceeds the preset limits, it switches the inverter back on to run in double-conversion mode, which protects the system and guards it from the effects of voltage sags, surges, spikes, electrical noise, brownouts and blackout. This kind of eco-mode is sometimes called ‘hybrid technology’, or ‘double conversion on demand’.

High-capacity UPS

As loads increase, UPS operating efficiencies become even more critical. A new high-capacity offline UPS that can protect loads of between 313kVA and 20MVA is now available.

When compared to an equivalent online double conversion UPS, this new UPS offers power consumption savings of at least 7.5%?possibly far more. For a 1MVA load, the annual saving would be would be about £80k, or approximately £400k over five years. Furthermore, the saving on CO2 emissions would equal 300 metric tonnes each year (equal to approximately 70 acres of preserved forest).

Fuel cells

All of the standby power solutions considered above require a separate power source to ensure business continuity when mains power fails. Typically, the UPS will work in conjunction with a bank of batteries and a diesel generator.

Fuel cells are a new technology that can offer a clean energy alternative to traditional UPS power generation. They have the ability to offer both prime and standby power for portable and stationary applications.

In many ways fuel cells provide the perfect standby power solution for IT equipment and other applications:

  • For small and medium loads the IT manager can house the fuel cell in the same rack as the UPS unit, minimising the physical footprint of the entire standby power solution.
    • Fuel cells are virtually silent and produce minimal vibration during operation. They produce no emissions other than heat and water, which enables an organisation to put the entire installation in the computer room next to the equipment it protects.
    • Renewable energy sources can be used to generate hydrogen (a common fuel for fuel cells used for standby power) by electrolysis or by other sustainable means such as anaerobic digester gas (ADG), which means a source of standby power that is truly green.
    • It is possible to configure a fuel cell to operate continuously by replenishing its fuel supply, which means long standby power times are achievable.

Although fuel cells have higher capital costs than other equivalent sources of power, they are relatively inexpensive to maintain, which means that over a number of years the total cost of ownership can be comparable to traditional standby power solutions.

In a data centre environment, for every watt of power that the computers use, it takes at least another watt of energy to remove the waste heat. The way that an organisation chooses to cool its computing environment has a significant impact on both installation costs and running costs. Installers have a number of things to think about when optimising the cooling infrastructure.

As well as considering the relative efficiencies of cold-aisle and hot-aisle cooling configurations, there are other environmentally friendly cooling technologies that installers can call upon. Combined heat and power units work by reusing heat from operational processes to actually cool the systems, which reduces the need for mains power to conventional air conditioning units.

Another innovation is the concept of ‘free cooling’. An automated control system monitors the ambient temperature and when it is below a set limit uses outside air to cool the systems. When the temperature rises, conventional air conditioning kicks in again. The savings obviously depend on average temperature patterns, but some vendors estimate that in the UK it might be possible to switch off the aircon and use fresh air instead for up to 75% of the year.


Businesses are demanding more energy-efficient IT solutions across the board. Standby power is one area where UPS manufacturers are responding to current business demand by introducing more power-efficient technology.

These are just some of the alternatives that organisations should consider to ensure their standby power solution offers the right level of protection for their businesses. Ideally, the chosen solution should be scalable to meet the organisation’s changing needs. The financial payback for the investment in UPS technology can be relatively quick?such is the improvement in efficiency for new UPS technologies

Energy-efficient IT solutions are better for the environment, but some technologies do better than others in the green IT stakes. It is possible to use completely renewable energy to generate standby power using a fuel cell rather than a diesel generator, and free-cooling solutions can drastically cut energy bills.

Manufacturers are constantly looking for new ways to save energy with UPS, so it’s important to consider the state of the art products across a number of vendors to determine what best suits the organisation’s needs.

Finally, if possible, the installation should be considered as a whole. There are energy efficiency gains to be had from every single component and by looking at the system as a whole?including power generation, cabling and cooling?the best energy savings can be achieved whilst ensuring the right levels of standby power protection for the organisation.