Feature

Distributed power generation – Is it right for your datacentre energy strategy?

As datacentre complexity and size grows, enterprises are looking for greener, more energy efficient ways to power these energy-guzzling facilities. One option is using distributed generation strategy, but will this cost and energy-efficient strategy work for datacentres of all sizes and types? 

Most datacentres are powered directly from the grid. Power generation is still carried out by utility companies, and the datacentre operator taps into the supply through relatively standard means of distribution via high-voltage lines stepping up and down through various transformer stages until the datacentre gets a supply that is fit for its own use. 

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These various transformer stages, along with the distances involved in power distribution, can lead to massive efficiency losses in the overall utilisation of the power. To fully understand this, we first need to have a little physics lesson.

The amount of power dissipated (P) is equal to the square of the current (I) times the resistance of the transmission media (R).

In high-voltage lines, the current is minimised through Ohm’s law (Current (I) = Voltage (V) divided by Resistance (R)).  For example, transmitting at a national grid level of 11,000V compared to a local distribution level of 415V will involve one 26th of the current.

So, using high voltages for national grids means that this consequently smaller current leads to less power dissipation over long distances.

OK – enough of the physics lesson.  On to the other problems of datacentre power generation and distribution. In the first place, burning fossil fuels is not particularly efficient for electricity generation. Coal is on average only 36.2% efficient, combined cycle gas is 46.8% and even nuclear is only 37.9%. The rest of the energy is lost as heat. Those massive cooling towers you see at power stations do not have smoke coming out of them. What you see is steam produced in the cooling process. This is all wasted energy.

Datacentre energy lost in transmission

According to the Electrical Engineering Portal, technical losses on transmission and distribution run at around 22.5%.  Therefore, that 36.2% of electrical energy created at the coal-fired generator is already down to 28%, before you then do anything within the datacentre itself.

Maybe rather than looking at how to save a few percentages of power used by the datacentre itself, is it time to investigate how to effectively and efficiently power the datacentre overall?

If you are a major datacentre user, then you could be looking at building your datacentres close to a major form of generation

This then leads into discussions around distributed power generation. Instead of using power stations that are a distance away from the datacentre, a smaller generation unit is used that is close to the datacentre. This unit can be dedicated to the datacentre or can share its output between the datacentre and other surrounding properties. In a lot of cases, the best way to look at this is that the datacentre uses the electricity generated – business and domestic properties can use the heat.

Distributed power generation strategy

It is likely that your organisation already has a basic electricity generating unit, or two as part of your datacentre in the diesel auxiliary generator, which takes over electricity provision should the grid fail. The problem is that it is far too costly to run as the main electrical generator.

What other options are available?  If you are a major datacentre user, then you could be looking at building your datacentres close to a major form of generation, such as Google’s Dallas datacentre in Oregon using hydro from a local dam or Thor in Iceland using geothermal energy. But this is just changing the way that a grid is used to minimise distances involved or to minimise costs. 

What is really needed is a means of powering average-sized datacentre cost effectively without having to build the datacentre in a specific place to suit the generation type.

Bloom Energy's servers are 200kW solid oxide systems using natural gas or bio-methane as fuel

Solar and wind energy to power IT  are options, but are too inconsistent to be seen as being prime energy sources without energy storage being put in place at the same time. Using batteries for this storage is possible, but the initial capital outlay and on-going replacement costs make it an unlikely means of powering the datacentre.

Companies such as Microsoft are using alternative systems, such as fuel cell technology.  Here, a fuel source (generally hydrogen, but can be methane or even heavy oil) reacts with oxygen to create electricity, heat and water. 

With hydrogen, that’s it – no other emissions, so no negative hit on carbon footprint, no toxic gases such as the various nitrogen oxides or carbon monoxide. With alkanes such as methane or oils such as diesel, there will be other emissions, but on the whole, these can be captured and dealt with to avoid major carbon or other chemical pollutants.

One such supplier of fuel cells is Bloom Energy. Its energy servers are 200kW solid oxide systems using natural gas or bio-methane as fuel. These units have a direct electrical efficiency of greater than 60% – over twice the fuel efficiency of the grid. There are virtually no transmission or distribution losses, and if the right output voltages are tapped from the unit, the datacentre can make more efficient use of the available power with fewer inefficiencies with internal datacentre distribution.

Syracuse University designed and built a datacentre using combined heat and power using gas microturbine units supplied by Capstone as the electrical generation systems. The heat of generation is captured through Thermax chiller units and the heat is used both to provide environmental heating to classrooms as well as hot water to the University. 

At a basic cost-per-kilowatt level, it is unlikely that distributed generation will save your organisation money

Phoenix Media in Nanjing, China, has a similar approach to its datacentre. It was originally going to use diesel power generation with heat capture, but switched to a mix of diesel and Cummins natural gas units, making cost savings of over $2.4m and cutting NOx emissions by over 50%.

Will it work for your datacentre?

At a basic cost-per-kilowatt level, it is unlikely that distributed generation will save your organisation money unless you are a very large datacentre facility operator and can sell the captured heat to surrounding businesses and homes to offset the electricity costs.

However, if your organisation wants to tout truly green credentials, distributed generation will offer far more kudos than you can get from signing up to a utility that claims only to use renewables. Bypassing transmission and distribution losses and gaining overall fuel efficiencies of 80% or greater will always beat the national grid.

However, one word of caution: national grids are nominally fault tolerant in that they have multiple routes for transmission. Distributed generation will tend to be a single point of failure. It is recommended that you maintain your standard diesel auxiliary units and also have a fall back to the grid, just in case your local units should fail for any reason.


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This was first published in May 2014

 

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