When used as a diesel hybrid application Vanadium Redox Energy Storage Systems can provide tremendous energy savings, particularly at larger off-grid and poor, unreliable grid sites. The diesel hybrid concept of storing spare load from a diesel generator is nothing new, however the charging and discharging properties of different battery technologies allow some battery technologies to deliver much greater efficiencies and therefore cost savings than others. In this interview, Tom Tipple of GILDEMEISTER Energy Solutions introduces the CellCube Vanadium Redox Energy Storage System and shares his perspective on how to maximise the efficiency of the diesel hybrid model.
TowerXchange: Please introduce yourself and GILDEMEISTER to our readers.
Tom Tipple, Head of Emerging Markets, GILDEMEISTER Energy Solutions:
I recently Joined GILDEMEISTER energy solutions as Head of Emerging Markets. The GILDEMEISTER Group is a leading German manufacturer of precision milling and machine tools, as well as software and energy solutions, all produced to exacting German engineering standards.
GILDEMEISTER made a strategic decision to diversify into renewable energy with the acquisition of a+f GmbH, manufacturers of sophisticated PV Tracking systems for industrial use, and Cellstrom, one the pioneers of developing commercial Vanadium Redox Flow Energy Storage Systems.
GILDEMEISTER Energy Solutions offers a full range of alternate energy solutions - PV, wind turbines and energy storage. Its PV tracking capability is a particular specialty. Any off grid site could be 100% green energy, however space is usually the limiting factor. We can also model sites to determine optimum alternative energy requirements, but this is such a large subject it is perhaps better to concentrate today on energy storage solutions.
One of the challenges has been that license requirements require operators to provide coverage in areas where the commercial returns on network infrastructure were at best marginal - low ARPU was compounded by the difficulty of installing, securing and fuelling sites in remote locations. With local currency depreciating against the dollar and fuel prices steadily rising, the payback time on remote installations increased, yet these network extensions remain a licensing commitment.
So there is an increasingly urgent requirement for telecom operators to reduce energy costs at remote sites, and diesel hybrid solutions provide a convenient first step in reducing operating costs by capturing and utilising the spare generator power available in most off grid sites. The problem has always been the cost of replacing batteries which are simply not designed to be deep cycled on a regular basis. Vanadium Redox energy storage solutions are specifically designed to offer unlimited cycle capability to any state of charge. It has the potential to be something of a disruptive technology and a potential game-changer.
TowerXchange: At which sites are vanadium redox batteries such a good potential energy storage solution?
Tom Tipple, Head of Emerging Markets, GILDEMEISTER Energy Solutions:
Vanadium redox energy storage systems work well in a number of applications, specifically diesel hybrid solutions for off grid sites that require unlimited deep cycle capability and poor grid sites suffering daily outages, where the system essentially works as a UPS providing back up power for long periods until grid power is restored.
Telecoms and tower operators are looking for efficient solutions to reduce energy OPEX - i.e. reduce diesel consumption. The optimum way of doing it is to install large PV arrays, wind turbines and energy storage, but this requires a large capital outlay, and a lot of space - neither of which are readily available.
For off grid sites, most diesel generators are sized three to four times above the average site load as they have been engineered to accommodate unusual load spikes and network expansion. However, this over-engineering is detrimental to a generator’s asset life and results in poor fuel efficiency. Running a generator at a sub optimal load leads to cylinder coking, which reduces the asset lifespan of a generator from around four years to around two and a half years. This is compounded not just by the cost of the extra fuel being burned, but also by the high cost of remote fuel deliveries.
To run generators at their maximum, most efficient load you would usually add a dummy load which removes the low load coking issue, but wastes around 60% of the available power from the generator. By harnessing this spare power in an energy storage device, you can reuse the wasted energy by simply cycling power to the site between the generator and the energy storage device.
There are different energy storage options: lead-acid, lithium, sodium sulfate and vanadium redox batteries. The key performance criteria of the different battery technologies are defined by; the round trip efficiency of the system, the charge / discharge ratio of the battery (i.e. charge the battery as fast as possible by using ALL the available power from the generator), the usable capacity of the battery, the ability to charge to different states of charge and the number of deep cycles (i.e. expected lifespan).
TowerXchange: Talk us through a comparison of those different energy storage options.
Tom Tipple, Head of Emerging Markets, GILDEMEISTER Energy Solutions:
First you need to consider which technology offers the best opex saving, then work out the total cost of ownership (TCO) which would include the capital cost, annual operation and maintenance cost, replacement cost, generator asset life extension and miscellaneous cost saving such as temperature control.
Realistically, TCO or return on investment should be taken over a minimum of 5 years, as this would tie in with ESCO service contracts. So which energy storage technology can deliver the best performance?
Lead-acid batteries are relatively cheap, proven, and readily available. The problem is that their chemistry is simply not designed for deep cycling, so even though a manufacturer may claim a lifespan of 10-15 years, the reality is that replacement is typically required every 2 years. You cannot use the full capacity of the battery to cycle without damaging the battery, usually only to the top 50% of its charge level, so you need to dimension the battery capacity at least two times your actual capacity requirement. You also need to the charge the battery according to the manufacturer’s guidelines, to its full capacity which is a slow process, and does NOT use the full power available from the generator. This is the biggest performance handicap for lead-acid batteries - you have to charge to full capacity or you damage them, and as a result, you are not running the generator at its maximum load.
Vanadium redox batteries are good for over 20,000 cycles without damage or degradation - they’re designed for a 20-year life expectancy
The key to energy storage efficiency is to use as much of that excess power in the generator as possible, and to charge your energy storage system as fast as possible. As soon as charging begins to slow down (as you approach the top of charge), you want to be able to switch over from generator power to battery power. So whenever the generator is on, it should be working at its maximum and most efficient load. Vanadium Redox batteries allow you to do that; you can be very flexible with both charge and discharge criteria. As mentioned earlier, other energy storage solutions need a full 100% charge otherwise you’ll get performance issues and damage the battery - you don’t have to do that with vanadium redox. You can charge or discharge to any state of charge with absolutely no degradation to performance. So you can run your generator at full load to charge the vanadium redox battery and power the site, then as soon as the charging starts to slow down (usually at around 85% state of charge), you turn off the generator. This means the generator is working at full load when it is on. It is working at its most efficient optimised state.
Vanadium redox batteries are good for over 20,000 cycles without damage or degradation - they’re designed for a 20-year life expectancy.
TowerXchange: Go easy on the chemistry Tom, but how does it work?
Tom Tipple, Head of Emerging Markets, GILDEMEISTER Energy Solutions:
It’s a classic flow battery principle. The vanadium redox battery is a type of rechargeable flow battery that employs vanadium ions in different oxidation states to store chemical potential energy. The vanadium redox battery exploits the ability of vanadium to exist in solution in four different oxidation states, and uses this property to make a battery that has just one electro-active element instead of two, so if the electrolytes are accidentally mixed the battery suffers no permanent damage.
A vanadium redox battery consists of an assembly of power cells in which the two electrolytes are separated by a proton exchange membrane. Both electrolytes are vanadium based, the electrolyte in the positive half-cells contains VO2+ and VO2+ ions, the electrolyte in the negative half-cells, V3+ and V2+ ions.
When the vanadium battery is charged, the VO2+ ions in the positive half-cell are converted to VO2+ ions when electrons are removed from the positive terminal of the battery. Similarly in the negative half-cell, electrons are introduced converting the V3+ ions into V2+. During discharge this process is reversed and results in a typical open-circuit voltage of 1.41 V.
Vanadium redox technology has been around for a long time but it’s only been commercially available for the last ten years. It may have taken a while to get it right, but there are proven installations worldwide now - we know it works, and it makes economic sense on certain sites.
TowerXchange: What is your installed base in emerging markets?
Tom Tipple, Head of Emerging Markets, GILDEMEISTER Energy Solutions:
There have been over 150 installations of Vanadium Redox Battery systems between 10kW and 30kW, many in hostile environments (from deserts in Oman, to Saudi Arabia and India). The company is fairly new to the telecoms market, so we are actively appointing partners in key markets.
TowerXchange: What’s the ‘sweet spot’ for CellCube deployments?
Tom Tipple, Head of Emerging Markets, GILDEMEISTER Energy Solutions: The CellCube 48 Series comes in 10kW, 20kW and 30kW options. Most telecom sites need less than 5kW. So our current product is particularly suited to high-powered sites, multi tenant sites and small data centers. A 10kW system can be easily upgraded to a 20 kW or 30kW option by simply plugging in more power stacks, so this is a very interesting model for the towercos as they add more tenants and their site power budget increases.
In terms of capacity, our smallest system is 40 kWh, then 70kWh, 100kWh and 130kWh. As it’s simply a case of adding more electrolytes into tanks, you can start with a capacity of 40 kWh and expand easily up to 130kWh with exactly the same site footprint.
TowerXchange: Tell us about the potential use of vanadium redox batteries at sites with unreliable grid connections.
Tom Tipple, Head of Emerging Markets, GILDEMEISTER Energy Solutions:
Take Nigeria as an example where the grid is particularly unpredictable and outages are a daily occurrence. A Vanadium Redox energy storage system is an obvious solution for sites that need long autonomy during a power outage. A 130kWh system will provide 24 hours back up power for a 5kW site and can be fully charged in under 6 hours. So a CellCube system can be used as the first backup - when the grid goes off, the battery takes over, so it’s acting as a UPS (Uninterrupted Power Supply). With any other type of battery, you must charge the battery back to its full capacity to get the maximum lifespan, so if the grid goes off again when charging the battery and its only 80% charged, you will permanently damage the battery. Only vanadium redox batteries’ performance is unaffected by partial charge and discharge. I would personally keep the generator as a second back-up in case the grid is off an extended time, but in some cases, the generator can be removed completely.
TowerXchange: Is there any prospect of developing a smaller vanadium redox battery for the average BTS sites?
Tom Tipple, Head of Emerging Markets, GILDEMEISTER Energy Solutions:
Our design engineers are looking to develop a smaller 5kW power solution, but this is a little bit of a red herring as you need to match the energy storage solution to the spare power available to get the best commercial return.
TowerXchange: How should tower operators determine the right energy storage solution to meet their needs?
Tom Tipple, Head of Emerging Markets, GILDEMEISTER Energy Solutions:
I got it wrong for years trying to dimension battery size and capacity to site load. It is more important to look at the spare power available from the generator rather than the site load, and design a system capable of capturing as much of that spare capacity as possible in the most efficient manner. For instance, if I have a 25KVA generator providing power to a 5kW site, I theoretically have 20kW of spare, available power, so I should size my storage system to capture as much of that spare power as possible (i.e. run the generator at full load); in this case a 20kW storage system would provide the best cost saving and TCO return. For off grid sites, the storage power rating is more important than its energy capacity, it just means you have more cycles per day for smaller capacities. Each site is different, you decide which power / capacity system best suits that particular site.
Where autonomy is important, such as on a poor grid site, you want the largest capacity possible to provide UPS back up. You don’t know how long the grid outage will be.
TowerXchange: What kind of DG runtime savings can vanadium redox batteries deliver?
Tom Tipple, Head of Emerging Markets, GILDEMEISTER Energy Solutions:
We have recently evaluated energy solutions for a number of different site scenarios ranging from 1-20kW load and different generator combinations. In some instances we can deliver up to 85% generator runtime saving. Of course this depends on the power difference between the generator and the site load.
In practice, the lowest generator run time saving we’ve had is 50% and the best is 88%. RoI is dependent on the amount of spare generator capacity - over-engineered sites with big generators and relatively low load yield a very quick break even. The beauty of Vanadium redox storage solutions is that they transform the OPEX inefficiencies of over-engineered sites into real energy savings.
Run time
TowerXchange: High quality German engineering and bleeding edge energy storage innovations don’t often come cheap, so tell us about the Total Cost of Ownership of your solutions.
Tom Tipple, Head of Emerging Markets, GILDEMEISTER Energy Solutions:
For our largest 48 series system which would be 30kW / 130kWh, you would be looking at a capital outlay of around €170k. This would be suitable for a multi tenant site with an average site load of around 25kW. The generator would probably be around 75KVA. For comparison, an equivalent lead acid battery would need to be at least 5400 Ah capacity rated at C5 and be able to supply 30kW of continuous power for 4 hours.
The TCO for the CellCube overtakes lead acid batteries after three years. For smaller systems (10kW) the payback is closer to five years. And that’s compared to lead-acid batteries - the payback cycle versus diesel is faster.
Diesel Hybrid Opex and TCO Savings
Tom Tipple, Head of Emerging Markets, GILDEMEISTER Energy Solutions:
Towercos are empowered to take a longer-term view of opex savings, but we’ve seen forward thinking operators such as MTN and Vodafone embracing efficient energy saving technology.
Another potential target would be the ESCOs, but making the ESCO business model work is tough on a site by site basis. Every site has different characteristics - pricing per kWh across 100 different sites means you’re going to win some and lose some. On a smaller scale site by site basis the energy service model might work, but no tower operator is going to accept the complexity of pricing for individual sites - you have to offer a generic tariff for a basket of sites, which means you have to agree a price that works for both the ESCO and the operator. Eltek are pioneering much of the ESCO debate, but the operators and towercos have to take longer term view on investment in more efficient technology.
Alternatively you could install a self-contained microgrid, using a PV array and energy storage solution. If you can feed 15-20 cell sites, you have a very attractive business model, but you still have to transmit the power from the microgrid to the sites, so microgrids only work when everything is in close proximity, which is harder in Africa because of the distances involved.
TowerXchange: Tell us about the maintenance and security implications of using vanadium redox batteries.
Tom Tipple, Head of Emerging Markets, GILDEMEISTER Energy Solutions:
There’s nothing to do! You don’t have to backwash vanadium redox batteries, or clean filters, they keep on running 24/7. And you can switch them off. Sodium Sulfate batteries must be kept at on all the time to maintain their high operating temperatures, otherwise their molten salts solidify which can be an expensive mistake. There are no safety issues with Vanadium redox, the charging and discharging criteria are very robust, there is no chance of thermal runaway or explosion in the event of overcharging or short circuit as you have with certain Lithium batteries. It is recommended to replace the cell membranes every 10 years, which is a low cost service and in the unlikely event that a membrane fails, there are 10 cubes in each system providing redundancy so the battery will keep working.
Maintenance requirements are limited to an inspection - literally, opening the cabinet to check it’s still there. In-built remote monitoring sensors pick up and report performance status of the system. As for security, everything is in a locked steel container, and the ground wiring comes up from underneath the container, so nothing is exposed.
You’re looking for an energy storage system that charges as fast as possible using all available power from the generator; that’s the key to reducing generator run time and making the site as energy efficient as possible
TowerXchange: Thanks Tom. To sum up, how would you differentiate GILDEMEISTER’s CellCube vanadium redox flow technology batteries from other CDC batteries?
Tom Tipple, Head of Emerging Markets, GILDEMEISTER Energy Solutions:
Fast and flexible charging performance is key when it comes to optimising energy efficiency in diesel hybrid solutions. You’re looking for an energy storage system that charges as fast as possible using all available power from the generator; that’s the key to reducing generator run time and making the site as energy efficient as possible. TCO models differ, but it all comes down to DG runtime saving and the round trip efficiency of the storage system.
CellCube has the most flexible charge characteristics on any storage system specifically developed for the telecoms industry, and is ideally suited to larger power off grid sites, or poor grid sites.
The life expectancy of a CellCube system is 20 years. It has unlimited cycle capability to any state of charge. No other storage technology can do that.
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