Mecc Alte: From AC to DC power, from indoor to outdoor solutions – an innovative solution to extract maximum value from standard DGs

African towercos have invested over US$4bn acquiring 41,000 distributed cell sites, and the associated distributed independent power network. The reality is that the standard DGs used at the majority of the off grid sites are not likely to be replaced until those DGs reach the end of their service life. With the increasing use of outdoor equipment, many sites don’t need oversized DGs to start air conditioning units any more, so how can you ensure those oversized DGs run more efficiently until the end of their lifespan? How can you implement a solution that does not need to be replaced when alternate energy solutions start being installed into your network? The answer may lie in the innovative Mercurio power converter from leading alternator manufacturers Mecc Alte.

TowerXchange: Why is there a trend toward DC power in emerging market telecoms?

Most telecom tower networks in emerging markets were rolled out under extreme time to market pressures, and rolled out before renewables were a realistic alternative. So as networks extended beyond the grid and required independent power solutions, tens of thousands of diesel gensets (DGs) were installed. Given the climate variations found in emerging markets, the energy storage, electronics and rectification equipment needed cooling, so air conditioning units were required, needing an AC generator and placing a parasitic load on the site.

Starting an air conditioning unit might require 15-20kW, whereas the site may need just 4kW once started, so the DG has to be oversized. And to maximise uptime, many sites needed redundancy, which means dual gensets. As a result of DGs running below capacity, engines build up carbon or smooth cylinder bores, and alternators die because they’re not getting hot, and can’t dissipate moisture (condensate) from their windings – it all adds up to increased maintenance costs and reduced lifecycles.

Technology has matured, with the next generation of antenna now able to function outdoors, so many sites no longer need air conditioning. Without needing to start the air conditioning motor, most equipment at a cell site is now DC powered. The DC unit provides power to the antenna and charge to the battery pack, it’s all one load, so you can refine the engine, alternator and other components to effectively and efficiently deliver the required energy load.

TowerXchange: If many sites no longer need air conditioning, are the DGs installed on these sites still the best solution?

With Mercurio, you can extend the lifespan of existing DGs.

I see a conflict between consultants who love to dream up new technologies, and who would advocate the replacement of perfectly good standard DGs with bespoke variable speed gensets with permanent magnet alternators to provide DC generation, or who would advocate leapfrogging directly to bespoke hybrid systems. What this fails to take into account is that MNOs and towercos don’t want to throw out perfectly good standard DGs that may have months if not years of service life left in them. What this also fails to take into account is that when you use a bespoke product it doesn’t work at every site, it doesn’t offer economies of scale, there may be no redundancy, no local support, and the average field maintenance engineer doesn’t know how to fix it.

In my opinion, variable speed permanent magnet generators are too expensive for today. They do the job – with little efficiency advantage. I’d advocate a more cost effective and practical approach. Our solution for the same problem is to retain existing equipment yet still deliver the fuel economy which energy efficiency programmes are targeting – with Mercurio we’ve been able to improve fuel economy by 35%-40%. With no air conditioning to start anymore, the engine size can be reduced. Instead of throwing out the oversized generator, we advocate installing a governor with distinct speed settings such that two speeds can be used. This is made possible because of the Mecc Alte digital AVR technology, and the hybrid on and off modality.

Mecc Alte’s Mercurio system provides power conditioning. It connects to the alternator (including other manufacturer’s alternators, not just ours!) It talks directly to the engine and batteries, and is able to accept feeds in from the alternator, grid and any renewables (wind or PV). It checks the charge state of the battery, and switches the genset on and off to deliver power as you need it. It can also drive the speed as well as a function of the real load, if this full variable speed control scheme is chosen. So sites where once the DG ran 24/7 can now run from the battery bank where possible. And if you add in renewables; Mercurio understands (with external switch) when to use PV resources too at no extra cost on power converter.

TowerXchange: What is the impact on battery life?

You can leverage Mercurio to charge any battery bank, whether lead acid, lithium-ion or any other alternate chemistry, and in the process to condition the lifecycle of batteries to make them last as long as possible, controlling the voltage and the temperature. It is supervising the number of cycles charge as well, and can insulate galvanically the output for the total safety of the site. It also has an emergency mode, where the batteries can be disconnected during maintenance but still powering the load, to keep the station operating.

TowerXchange: How do you ensure cell sites’ independent power systems designed for today are still optimised for tomorrow?

With Mercurio you can retain the conventional engines and alternators that are on cell sites todays. Keeping everything conventional is easier as the field engineers will still understand the equipment they are servicing. And when the existing DG has run it’s lifecycle and a new package of power systems optimised for the site is ready, Mercurio can be adapted to manage the new systems too.

Self contained/packaged hybrid power systems work, but are generally expensive, and the cost of replacing conventional equipment with remaining service life – the depreciation costs – means an intermediate solution is needed.  Mercurio provides an intermediate step between existing DGs and hybrid energy; Mercurio works with any renewables so you can retain it beyond the lifecycle of your conventional engines and alternators.

Reconditioned standard gensets can be sold on to the village to provide community power, whereas if you replace the standard DG with a custom made, self contained hybrid variable speed genset, you can’t resell it as it won’t work anywhere else.

TowerXchange: What does Mercurio cost?

The costs for Mercurio, inclusive of our alternator, come in at around €2,000 for the 5kW device, €3,000 for the 10kW, and €5,000 for the 15kW. In comparison, a conventional 5kW alternator costs around €600, €800 for the 10kW, and €1,000 for 15kW -  but it is the payback on opex costs which is  the real driver.

TowerXchange: Please put this in context and explain where Mecc Alte fit in the telecoms infrastructure ecosystem?

Mecc Alte is an indirect component supplier to the telecom industries around the world. We are the largest independent alternator manufacturer in the world, with solutions ranging from 1-3000 KVA.

For the AC fixed speed power generation, many of the most well known genset OEM’s use Mecc Alte alternators which have low sub-transient reactance (x”d) properties, suitable for rectifier loads, and also a competitively high efficiency for improved fuel consumption.

TowerXchange: Forgive the simplistic question, but for the benefit of our non-engineer readers, what role does the alternator play in optimising the efficiency of cell sites?

That’s not a simple question, and the answer has to be quite detailed. For the AC alternators, the x”d must be low to have better responses to the rectifier loads. It is proportional to the load applied, so oversizing is an option if the x”d is too high. If you start low then no oversizing is necessary. The higher nominal efficiency also helps. The peak efficiency of the Mecc Alte alternators is at around 80% load, so the modest oversizing most consultants build in help to keep this at peak.

The market is moving to further efficiency savings in both capital cost and running costs. The generation of DC at the machine eliminates the need for the BTS rectifier, which is quite an expensive item to acquire, maintain and replace. The Mecc Alte Mercurio ‘system’ comprises a standard copper wound alternator (not permanent magnet), with special AVR software to allow fixed speed, two speed or full variable speed operation. The latter two options help to maximise efficiency for the complete generation system and to lengthen the life of the engines. Part load operation of engines is typical in BTS applications, and engine life expectancy is relatively short. We were told once that in some countries, it costs three litres of diesel to deliver one litre of diesel to site! Of course the longer the interval between times to ‘fill up’, the better it is.

The Mercurio also controls the speed function of the engine so the costs of the engine/genset controller can be minimised. I have mentioned that we promote the use of copper wound standard alternators with the Mercurio. There are others who promote the use of permanent magnet alternators with their DC charging systems. The permanent magnet machine using rare earth magnets maybe 2-2.5 times the cost of the copper wound standard machine, and the not easy to obtain in large numbers. Many telecom projects talk of large volumes required either for new tower builds or planned re-powering. Using the existing plant, Mecc Alte has the ability to satisfy the large demand from existing production lines producing over 350 machines each day. Mecc Alte does offer permanent magnet alternator solutions as well although the financials are clear that the use of conventional alternators makes more sense in the real world.

TowerXchange: The first question our readers usually want to know is “how proven is the solution in the field?”

There are many of the Mercurio ‘systems’ with OEM’s for their development and promotion to the transmitter operators. Large numbers in projects are discussed widely although as yet I do not believe anyone has pressed the green button to go ahead. There are exhaustive tests which focus on the genset operation rather than the Mercurio itself. The fine tuning of the engine speed/power curve to the load profile to maximise the system efficiency, for each site characteristic is necessary and these will vary. The data we have from the OEM’s are very encouraging and will have real world benefits to the operators.

The Mercurio’s power electronics are housed within a totally enclosed IP65 box which can be wall mounted or built onto the genset, but in any case are in close proximity to the batteries. Components are rated to +55°C, and use established durable components to ensure longevity.

TowerXchange: How do Mecc Alte products integrate and optimise power from sources other than the DG, such as grid and renewables?

The Mercurio will accept AC input, either 3ph genset or grid, or 1ph grid (with power derate). It will also accept AC input with frequencies up to 400Hz so multi-pole wind turbine alternators can input power. When the batteries are fully charged and the AC input (genset) is stopped, the Mercurio in standby, there can be PV connected to two of the AC input terminals. An external switch (not supplied by Mecc Alte but controlled by the Mercurio) would disconnect the AC and connect the PV, making the MPPT and the impedance matching between the solar panel and the load. The same switch would close a relay within the Mercurio so it knows that PV DC power is coming through. There is an internal MPPT to accept the PV’s DC input and this will act to trickle charge the batteries to lengthen the period between charge cycles, without further costs to the PV array.

TowerXchange: How do your products save fuel, and can you share some examples of what savings can be achieved?

We have explained why the Mercurio ‘system’ has savings both in capital cost and operation. Extending the speed of operation upwards, with a range of say 1000rpm to 1800rpm, the engine size can also potentially be reduced. The fuel consumption in hybrid mode depends heavily on settings (VDC level to start and Amps drawn to stop) and battery condition/temperature, along with the direct transmitter loads applied.

With a 600W transmitter load and 650A battery pack, in light, rather than deep cycle charging (likely light charging at say 60% battery capacity, will be the most common with deep cycle on monthly basis), and 1000-1500rpm speed range, two speed operation, we have a 4.8 hour charge period at an average of 0.67 litres per hour. Taken across the full hybrid period this of course reduces.

Compared to fixed speed AC power generation, the fuel cost savings maybe up to 35-40% depending on engine and load characteristics.

It’s also important to note that the Mercurio power converter can be fitted to existing tower supplies with minor modifications to the engine and alternator

TowerXchange: How do you bring Mecc Alte products to market - who is your target customer?

We have our AC genset OEM partners who know the general intent of the market to move to DC power generation and we are working closely with them. There are also the more specialised companies drawn to the market by the move in technology and bringing with them fresh ideas. We are working with all of these but also helping to market the concept with the tower operators.

As a component supplier, it’s been difficult for us to get across our message and change the way people think. Having sold alternators to the OEMs who put together the genset packages subsequently sold to MNOs, towercos or their maintenance partners, we were several steps removed from the site designers and equipment specifiers. So we have started to talk to battery people, MNOs and towercos. Everyone is seeking to reduce fuel consumption and maintenance costs, but no-one knows exactly how to achieve the best results with what they’ve got.

TowerXchange: Tell us about your after sales service

Unlike the companies entering the market with new technology, Mecc Alte has been working with the AC OEM’s and operators for many years. Mecc Alte is the third largest in production of alternators and is one of the global leaders in its field.

Our service and support infrastructure is in place now with subsidiaries and regional agents/distributors approved/trained in the support of the products. Mecc Alte are strongest in Europe, Africa and the Middle East, where customers should not have any concerns over our support, both at consulting stage, during supply, commissioning and aftersales.

Our standard warranty is two years, exceeding most other manufacturers of similar equipment.

TowerXchange: Finally, please sum up how you would differentiate Mecc Alte from competitive alternator manufacturers.

We’re independent – we have no division competing with our alternator customers. We are dedicated to high performing competitive products, produced for a global market from Italy, UK, China and India. We’re focused on the simplicity of products and ease of maintenance. We are one of few manufacturers able to satisfy volume demands with solid, reliable products.