Data centre managers consider and explore different approaches to cut down on energy costs as part of their data centre strategy. In a previous tip, we looked at the energy generation process and using local CCHP
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In this tip, we explore the issues with using renewable and sustainable energy sources as primary energy sources for data centres and more importantly how to successfully use them.
For many, the question is where do renewable and sustainable energy sources fit in and how can they be used in data centres. Unfortunately, there are many issues around the use of renewable and sustainable energy sources -- such as wind, solar and tidal energy -- which make them unsuitable as primary energy sources for data centres.
The generation capability of wind and solar is intermittent due to lack of wind or sunlight. With tidal power, where the renewable source is completely predictable, the energy produced is cyclical and cannot be counted on as a primary data centre energy source.
Other renewables such as wood or (to a lesser extent) garbage as fuel sources for more standard generation plants may be more useful, but there are problems here too. Those sources remain outside the direct control of a majority of data centre owners, primarily because of their enormous capital expense and regulatory impact. Large power generating companies are more inclined to choose those methods because they provide a mix of generating technologies across their own commercial utility portfolio.
Their use for power generation is only something that makes economic sense for an electricity generator -- there would be no economic case for a small-scale system.
Then there is hydroelectric generation from lakes or river water controlled with a dam. This could be a viable option if the water source is constant and does not dry up or run too sluggishly during dry periods. But few organisations or data centres are built next to a suitable river, so this approach is restricted to a small minority of IT pros looking to improve data centre energy efficiency.
Smoothing the wrinkles in renewable energy availability
Data centre managers that wish to use standard renewables/sustainables in their data centres have to find a viable solution to this quagmire of availability.
The majority of countries now offer feed-in tariffs, where energy generated “off-grid” can be fed back into the grid which will reimburse the local energy producer, usually at a generous rate.
One potential solution is to store the energy in batteries to smooth out supply. However, battery technology is expensive and batteries need to be replaced on a regular basis, making the option for many cost prohibitive. Another alternative is to pump water from a low point to a higher one, and then use hydroelectric generation to fill the gaps in output from the primary source.
For a pump-driven hydroelectric solution to work, there has to be sufficient energy to spare when some of the primary source is diverted to pump the water and, as such, the primary source has to be engineered to be larger than the base need -- again, impacting the costs of such a system. Also, unless there is a suitable terrain around for a contained lake and hydroelectric system to be put in place, the cost of creating such a system will be too expensive for all but major generating companies.
Data centre strategy – role of renewable energy sources
So, can renewables be worth considering at all when looking at optimising data centre energy efficiency?
Certainly. One way is to choose an energy supplier that can demonstrate a good mix of renewables in its portfolio. If you’re looking for a more sustainable energy policy with greater control over the points of generation themselves, then you should see renewables (wind or solar especially) as a secondary rather than a primary source. In other words, since they are not a predictable energy source, they can’t be the main source of energy. But they can be a secondary source, and that provides a means of minimising the amount of primary energy sources used.
So, data centre operators can have their own energy generation capability based on renewables, but unless they are going for a nonrenewable approach (eg, CCHP), then the grid will have to remain their main energy source.
Another strategy is to figure a base load for the data centre and rely upon the commercial utility grid for that essential supply, but then turn to renewable/sustainable alternative energy sources to address additional energy demands.
How to use sustainable/renewable energy sources?
Let’s assume that the data centre requires 2 MW of energy overall. And, let’s assume that with cyclical workloads and the capability to turn off some parts of the IT estate during certain times, there is a minimum energy need of 1.6 MW, with the 400 kW remaining being used by the more cyclical workloads, therefore only needing power on an intermittent basis.
The organisation concerned negotiates an agreement with a central generator for 1.6 MW of “base” power on a continuous basis on preferential rates (as there will be no variability in the load taken, many generators will offer better rates because it helps them in their energy-generation planning). The additional 400 kW required is then theoretically provided via renewables.
Still, the problem with renewables is that they are not a guaranteed source. Ideally, the energy from the renewables would be available just as the cyclical workloads needed it. In practice, this will not happen. Some of the time, the renewable energy will be available when the workloads aren’t running; other times, the workloads will need to run when the renewable energy is not available.
But this can be ironed out. The majority of countries now offer feed-in tariffs, where energy generated “off-grid” (ie, locally to an energy user) can be fed back into the grid which will reimburse the local energy producer, usually at a generous rate. Therefore, any renewable energy produced at times when the data centre (or the rest of the organisation’s estate) cannot use it can be sold to the grid.
Where the energy generated by the renewables and the data centre workloads coincide, wonderful! The energy, then, is used in the data centre and everything works as per theory and helps you execute your planned data centre strategy.
However, when the workload requirements and the renewables energy generation are out of sync, other approaches have to be brought to bear Because of the financial risk involved.
Large users of energy will have special deals with energy providers, based on tiered usage. So, if a 10 MW data centre says it will buy 10 MW from a supplier, it will get a better per-KW deal than one that buys just 1 MW.
But if a data centre owner wishes to use renewables for just 50% of the energy and agrees a deal based on 5 MW of energy, then anything that is used above that 5 MW will be charged at a higher price per-KW rate.
At that juncture, if the user agrees on a 6 MW deal to get a lower price still and allows for a bit of overrun, but uses only 5 MW, the energy provider will have the rights to put in place some charge-back mechanism that would undoubtedly be in the supplier’s favour.
So, does the data centre owner agree to a tier price that only just meets his need and pay anything over and beyond? Or does he agree to a price for an oversupply and use it come what may, putting more of the renewables energy back into the grid to maximise energy income?
The risks can be pretty big for data centre owners who get their math wrong.
Spot pricing and aggressive negotiation
The best approach is to buy energy from the grid based on spot pricing, rather than on long-term agreements. In many cases, spot pricing may be more expensive than long-term agreements, and, as such, the aim is to minimise energy usage. However, in other cases, good prices can be found for using energy at certain times from certain sources.
For example, a standard fossil-fuel-based generating plant is not good at flexing to follow changing energy usage. Therefore, a degree of energy is generally purposefully lost through shunting the steam required for driving the generators through to cooling towers. The fossil fuel is still burnt, but no useful energy is created from it. Therefore, if a possible customer comes along who is willing to pay for some of the energy that would otherwise be shunted away as lost steam, then a good price may well be negotiable, as anything is better than nothing to the generating company.
The key is to engineer the system so that there is a good balance of how renewables feed into the data centre, how feed-in tariffs provide revenue, and how these tariffs offset the costs of spot energy usage when extra external energy is required.
From my point of view, renewables on their own cannot meet a data centre’s energy needs outside of centres that have the wherewithal to be able to build next to massive hydroelectric generating systems or similar, but renewable energy sources can be used as part of an overall approach to cut down on overall energy use from the grid.
This creates a less carbon-heavy, more sustainable energy plan and helps you succeed in your data centre energy efficiency strategy.
Clive Longbottom is a service director at UK analyst Quocirca Ltd. and a contributor toSearchVirtualDataCentre.co.UK.
This was first published in November 2011