How Vodafone improves energy efficiency within their Network Site Infrastructure

What is the ideal combination of energy generation, energy storage and air conditioning equipment to optimising energy efficiency at cell sites with different levels of grid availability? TowerXchange spoke to Barry Kingsland, Vodafone’s Group Head of Energy, and Solange Karwera, Vodafone’s Senior Category Manager for Network Site Infrastructure. Barry is a recognised leader in energy procurement, operations and management, with over 35 years experience working across the power and telecom sectors, providing thought leadership and strategic guidance direction across increasingly complex global energy markets. Solange has more than 13 years experience at Vodafone, and seven within the Procurement Company.

TowerXchange: How does Vodafone select the optimum equipment to maximise the energy efficiency of different cell sites?

Defining the optimal energy solution is a matter of balancing grid availability with the site configuration, particularly in terms of DC load.

In Europe we’re primarily dealing with cell sites with good grid availability where no or float charge batteries are sufficient to provide a few hours of backup power regardless of the load on the site.

If we consider an unreliable grid environment, with grid power available for 16-22 hours per day, a controller-only solution provides energy efficiency with the lowest TCO for most site configurations. On an unreliable grid site, it is usually sufficient to retain the existing battery bank until its end of life, but replace them with cycling batteries.

Power cubes (where the DG, battery bank, fuel tank and a controller are containerised for ease of transportation and installation) typically offer a competitive TCO for sites with less than 12 hours of grid availability per day. Most outdoor 2G sites need only a 1.5kW power cube, but if you add 3G or if it’s a hub site, you may need a 3kW power cube solution. If you introduce LTE or multiple tenants, driving the load over 3kW, then traditional deep cycle battery / DG hybrid energy solutions come back into play. However Vodafone are currently testing a 9KW power cube which may displace some DG battery hybrids at higher load sites, depending on the cost of diesel and its impact on TCO.

While they are capital intensive with high initial CAPEX, power cubes are an appealing proposition for tower companies because they are much more compact than typical hybrid generators. However, it is important not to underestimate the complexity of integrating all the components of a power cube, and the challenge of finding knowledgeable local maintenance partners hence the very good ROI.

Adding plug and play solar to a power cube installations improves your green credentials, opens up an opportunity to provide community power, and can increase power cube efficiency from 67% to 82% compared to standard DG.

There is also a role for pure solar sites, but we see those primarily for sites with up to 0.5kW loads, or what we call “Diet BTS”.

TowerXchange: Could you provide some similar guidance on the optimal energy storage solution for sites in different grid conditions?

Again choosing the right batteries depends on grid availability, with the other variable in this case being shelter temperature.

The shelter temperature at most cell sites in Europe is low enough that standard standby lead acid batteries, designed to provide one to four hours backup, are sufficient. You may need high temperature batteries (HTB) in countries of Southern Europe and Turkey, and also for most cell sites in MEA, particularly if you are implementing free cooling.

If the grid were unreliable but the shelter temperature remains below 25°C, you will need an increasing depth of discharge from your batteries to meet the corresponding level of autonomy, which means a hand-over between standard lead acid batteries (good for sites with around 21-24 hours of grid availability) to cyclic batteries which need to deliver 1,500-2,000 cycles to 50% depth of discharge as the grid deteriorates from 21 down to around nine hours’ availability. With less than 14 hours of grid, you should consider a power cube with integrated energy storage.

If yearly average temperature in the shelter exceeds 25°C, you may need high temperature batteries (HTB), even in a good grid environment. Because HTB are more expensive, we need to have confidence in their performance, so Vodafone have our own HTB certification programme, developed in partnership with China Mobile. While 12V HTB batteries are commonly used at good grid sites, using 2V HTBs may be an option both from a performance cycle and theft deterrent perspective, while they are generally a more efficient solution for unreliable and poor grid environments (10-22 hours of grid availability). However, using 2V rather than 12V does incur the downside of needing more space. Cyclic HTBs, offering at least 2,500 cycles at a 50% depth of discharge, combined with DG backup become an option if your grid availability is 0-12 hours, where the shelter temperature remains high.

While high priority sites may benefit from investment in premium batteries, you must take into account the operational realities: regardless of how they perform in analysis, is it worth investing in premium, longer lifetime batteries if you are facing theft challenges?

TowerXchange: What is your view on alternate energy storage chemistries such as lithium-ion or flow batteries?

Generally we have found lithium-ion batteries cost around three times the price of lead-acid but cycle three times higher. Lithium-ion batteries also readily operate in temperatures in excess of 40°C.

The space in tower companies’ shelters is often at a premium as the equipment of multiple tenants is added, which is where the space efficiency of lithium-ion can be attractive. For similar reasons, lithium-ion is often a compelling alternative for power cube designers.

Replacing lead-acid with lithium-ion batteries can also be a deterrent to battery theft as lithium-ion has more limited re-use scenarios.

Proponents claim that flow batteries, a newer energy storage technology, deliver a large number of cycles with very low maintenance. Flow batteries are expensive but are a much less attractive target for theft. We are currently testing a flow battery, so in six months from now we may have more findings.

TowerXchange: What has been the progress of modernising Vodafone cell sites to use free cooling, and what efficiencies have been achieved?

Free cooling uses outside fresh air to cool equipment and replace mechanical air conditioning.

We sort existing sites into three levels of priority and are working through those to retrofit free cooling solutions into legacy sites. We estimate around 70% of all operators shelters site should have free cooling, and that modernisation process is ongoing.

We have found that free cooling can save up to 2,000kWh depending on the climatic environment and deliver ROI in less than two years for a tower company; in our experience free cooling reduces cooling energy consumption by an average of 35%.

In Northern Europe you typically only need free cooling, whereas in temperate zones of Southern Europe and into MENA you generally need active and free cooling split systems. The efficiency of many split unit cooling systems can be improved by using inverter technology to avoid peaks, saving a total of up to 3,500kWh.

One step many MNOs and towercos can take is to increase their operating temperature to 35°C, reducing air conditioning runtime. This will probably necessitate switching to HTBs, as discussed earlier. We have found that in combination, free cooling, increased operating temperature and HTBs reach the maximum in level of energy efficiency.