With a grid that is becoming increasingly dominated by intermittent renewables, gas engines are now being called upon to offer flexibility and reliability in the brave new world of distributed generation. As a result OEMs are pushing the limits of technology to maintain optimum efficiency over a wide range of operating modes, finds David Appleyard
A unit for every power demand
Credit: MAN Diesel & Turbo
In many respects distributed energy has become the new normal. The fundamental shift towards clean and green has had a profound impact on the structure of energy generating assets in many markets, both developing and developed.
Sustained growth in variable-output renewables has had a major impact, and the need to balance this renewable capacity with rapid-response thermal power – or electricity storage – assets has pushed gas-fuelled reciprocating engines up the investment priority list.
“Probably 10 years ago we were not really thinking of distributed generation having such a big impact in the energy and power industry. Driven by the strong drive for emission reduction and efficient power, distributed generation has come of age, and everybody is now talking about multiple power generation sources,” explains Pritil Gunjan, Senior Energy & Environment Industry Analyst at Frost & Sullivan.
|Credit: MTU Onsite Energy|
Gunjan continues: “Energy-efficient gas gensets would be one of the key ingredients of the entire distributed energy sector.”
Alongside renewables and the closure of many large baseload fossil- or nuclear-fuelled power stations, other factors such as low gas prices and the availability of LNG have allowed gas engines to gain market traction. Jussi Laitinen, spokesman for Wärtsilä Energy Solutions, says: “Gas is more widely available and with the shale gas reserve now being utilized more, gas is more available and an affordable price. And it’s now being transported more and more in liquid form.”
However, the changing market dynamics are also placing new demands on gas engine technology.
“The requirements for gas engines will not only be to act as backup power support, they need to be more flexible, agile, and need to comply with [emissions] regulations,” says Gunjan.
Certainly this view is reflected by Jürgen Winterholler, Vice President, Propulsion & Power Generation at MTU Onsite Energy, who emphasizes the key challenge as grid balancing – and achieving maximum efficiency whilst offering this service. Using gas engines to stabilize a distribution grid dominated by renewables suggests multiple start-stop cycles, rapid ramping in power output and the central requirement of maintaining high efficiency and clean burn low-emission combustion whilst operating in various modes.
“The global trend of renewables brings us to this demand response programme where you have to start maybe, two, 10, 20 times a day, maybe only for a few minutes, and you have to ramp up very fast. That means your application is changing.
“We see the next step, the next phase as demand response programmes. We have to work much more on flexibility on our gas engines and gas systems.”
The flexibility of gas engines is seeing them applied to develop cash flow from the energy market, selling power into the grid at peak times or when renewable output is low. The potential revenue streams available in certain jurisdictions is also prompting existing installations to change operating modes.
|Grid balancing is a key challenge says MTU Onsite Energy|
Nonetheless, as Winterholler explains: “It’s stress on the high-efficiency engine.”
The key to designing an appropriate system is a clear understanding of the application, and this is of crucial importance in the gas engine sector. Demands for either electrical efficiency or overall thermal efficiency can place competing constraints on engine designs, as well as for ancillary systems such as one or two turbo chargers, heat recovery units, steam turbines and the balance of system.
As Dr Tilman Tütken, Vice President and Head of Power Plant Sales for Europe at MAN Diesel & Turbo, explains: “If we look at efficiency in the gas engine market these days, we have to look at the desired application first, to determine which type of efficiency is needed. There is the pure electric efficiency, which is important if you are grid operated. But, especially for Europe, the CHP market is gaining importance and efficiency is more complex here. As a CHP plant not only has to provide good electric efficiency but, overall, good fuel usage, the total efficiency – i.e., heat efficiency and thermal efficiency – is really of the essence.
“For an OEM this is a trade-off we have to deal with. We can specify the engine to meet either the electric highest efficiency, or combined heat and power efficiency. Optimizing for CHP, you can go up to the range of 95 per cent fuel efficiency, which you would not reach when you just take a standard electrical optimized engine.
“Another application we need to consider is baseload mode. Here we can complement our gas engine with a steam turbine and roughly gain an extra 10 per cent of output. As efficiency in the engine market is getting more important also for baseload plants, we have been selling a number of combined-cycle engine plants in recent years.
“It’s all a complex optimization how to meet efficiency targets, how to meet emissions targets, and then what are the right operating modes to save money for the customer.”
However, it is not always possible to predict the ultimate requirements in a volatile and competitive energy market. Says Winterholler: “In some cases the customer is starting with one application, providing heat and power to industry and to a village or whatever, but then maybe some laws in the country change and immediately he sees the chance to make additional money.”
Winterholler further notes some of the technical developments that are enabling these new modes of operation: “Clearly you have to do something on engine control, so the engine has to have some new control strategy. You have to do many things on the system control side, you have to be careful in mixing gas, you have to have really fast ramp on speed control and the load control, but also you have to control auxiliaries in a different way, and also you need a connection to the utility. You have to do, in some areas, changes on auxiliaries like the preheating system, pre-pump system, pre-lube systems.”
And, in 2015, Rolls-Royce’s MTU and energy services company EnerNOC began offering genset operators in German, Austrian and Swiss markets a way to market any available load-balancing energy. The system enables CHP plants and emergency backup generators to be connected to a virtual energy system via an interface box that allows the units so equipped to offer balancing services. For example, the system can reduce the amount of electricity it feeds into the grid with CHP plants, which can reduce their otherwise constant supply of electricity. Winterholler observes: “We see this trend now in the UK and other areas.”
He also points to the impact on system optimization in the face of changing technical requirements for gas engines: “With renewables, now the game is changing. In the past, power generation units had to completely disconnect immediately if something in the frequency, the voltage or the utility grid was happening. Now, it’s completely different. Where before it was the big power plants, now we have to do it with our small decentralized power plants, and we have to fulfil grid codes.”
Tütken also picks up on the trend towards sector coupling between power, heat and gas: “The electricity markets in Europe, especially the electricity price is very low, so if you can sometimes generate more heat, and you can sell it to your heat consumers, you might be better off economically.”
Taking this idea perhaps one step further, another area that is attracting growing interest is the development of hybrid systems. Gunjan explains: “Intermittency and integration are some challenges of renewable power generation, and to reduce those challenges we will see more hybrid power generation systems coming up, where renewables are combined with gas gensets or diesel gensets and act as a small micro-distributed energy system.”
This is an idea that is being actively pursued by Wärtsilä, for example, which in April 2016 announced that it was entering the solar energy business by offering utility-scale solar photovoltaic (PV) and gas engine hybrid systems. Aimed at PV plants of 10 MW and above, Wärtsilä’s first solar project will be built in Jordan. Standing next to a plant commissioned in 2014 and comprising 16 of its 50DF engines supplying up to 250 MW, a further 46 MW of solar modules, covering an area of 81 ha, is being installed. The solar unit will reduce the carbon footprint of the power plant by saving fuel during the daytime, says Laitinen: “This is automated and synchronized so that the engines automatically follow the output curve of the solar.”
Target customers for Wärtsilä’s solar offering are utilities, independent power producers (IPPs) and industrials, the company says.
Pushing emissions control
The push for clean and green energy generation is having other influences too. Udo Sander, Director Development Gas Engines at MTU, highlights the increasingly stringent emissions legislation found in the US, Europe and elsewhere. For example, in Europe emissions directives set out the maximum permitted exhaust emissions in relation to the power of an engine. Manufacturers must ensure that new engines comply with the limits set out in the Directive before placing their products on the market.
Sander says: “What we know very well from the diesel side, but now it’s coming more and more over to the gas engine side, is the emissions. In Germany, the new TA Luft is coming and everybody is thinking how to fulfil the 100 mg NOx. In Asia, engines are still running on 500 mg NOx conditions. In some areas, you have half TA Luft, which is 250 mg. So, it is not unique worldwide, and we have to have the right answer in each country, which makes our job more difficult.”
He continues: “At the moment, on the emission side, the gas engine can do everything without external after-treatment systems.” However, he adds: “We expect in the long term it’s not possible, it’s not the best way to do it, everything in the engine.”
Suggesting an expectation of future installations fitted with catalytic converters or SCR, he continues: “You can do it, but maybe it’s better to do something outside of the engine scope and then you are much more flexible and you can react much faster to applications.”
This is a point also noted by Tütken: “Exhaust gas cleaning is a key topic also in our development, that’s why I’m saying the engine is one thing, but more and more we have to look also to the plant to be compliant, and to meet the customer requirements.”
Improving the cost profile
Gas engines are relatively flexible and efficient, but further improvements in performance can potentially have cost implications, as Gunjan warns: “The agility of gas engines is increasing, but then obviously all these companies have to keep in mind that though they’re investing in new technological upgrades, new emission standards, increasing their fuel efficiency. They still need to keep them within an accessible cost level, and that is a challenge that probably is top priority right now.”
Certainly, the rapid cost reductions seen in electricity storage technology potentially represent a threat to the new buoyancy seen in the gas engine sector.
Manufacturers are therefore consistently targeting lifetime cost of energy (LCOE) issues, for example in extending service intervals. Gas engines are typically spark ignition, but as Sander explains, there are alternatives to spark plugs under consideration: “We are talking now in laser ignition systems, how many years, 20 years? But I see still a gas engine is a spark, with spark plugs.
“On the ignition side, one of the first obstacles was to improve the lifetime of the spark plug. Let’s say more than 5000, up to 8000, sometimes 10,000 hours with one set of spark plugs. More than 5000 hours is normal today, and compared to laser systems it is the cheapest way.”
Wärtsilä’s planned hybrid solar project
Another area of growing significance is data, and this also potentially could present obstacles to growth, as Gunjan explains: “Another key challenge would be to find new skills in the industry. Obviously, when you have technically intelligence equipment, you need that kind of people to service and operate it.
“From a technical aspect, monitoring and control of these engines has become critical. Remote monitoring, control, predictive analysis, even servicing of these units, the Internet of Things: these are becoming exciting concepts in the energy sector now.”
Gunjan continues: “These fuel-flexible engines have to be intelligent enough to do things like predictive analysis or proactive maintenance, where they send data to, say, cloud data centres. Integration with smart grids, integration with renewables, that will require intelligence and monitoring.
“We’re not really talking of energy companies like GE, Seimens and gas engines manufacturers, we’re talking of companies like IBM, and your technology providers who are tying up with the OEMs and bringing in that kind of intelligence into this equipment.
“You have multiple gensets which work together as a plant. So these are new concepts, these are disruptive business models.”
This is a point also noted by Winterholler: “Digitalization on our systems creates added value for the customer. What we are doing now is really collecting all the data of the engine, all the data of the plant systems, to optimize the operation mode.
“The main task is to reduce lifecycle cost for the customer. The target is to develop and get more information to produce long-term quality on engines and systems, and keep up the operation time going close to 100 per cent availability. This is the main goal.
“To have the data at the right time and with analytics in order to operate in a much better and efficient manner to save on lifecycle cost – fuel cost, and operation costs, are much lower.”
Laitinen also highlights the increasingly important role of digital technology: “We are consistently fine-tuning the engines to be faster and faster because this is needed in this application. We are already capable of going from zero to 100 per cent of output in less than two minutes, but now what is needed in the solar hybrid is more of a software optimization. Aiming to predict the variation in solar output as precisely as possible to prepare the engines a little bit in advance to ramp up when the clouds come and cover the sun.”
Tütken further emphasizes the advance of digital technology in gas engine genset systems: “What we see in the market is that the unmanned power station is a topic of today. Especially peaking plants. People want them as a resource in the grid, but they don’t want to have them permanently manned, so you have to be able to operate, start, stop the whole plant and equipment remotely – it has to be fully automated. Also, when you see these peaking markets you have to act very fast, so this has to be automatic. In reality there will be nobody locally.”
Gas engines are already being hooked up to remote monitoring and maintenance centres, which can give advice for operation and maintenance.
Flexibility through diversity
Another avenue of flexibility afforded to gas engine technology is the diverse range of units available. The major manufacturers all offer a comprehensive range of engines. For example: “Our smallest one is 7 MW,” says Tütken, noting that the company is set to offer a 21 MW unit. “There’s not an official launch, but now we are putting it into the field. We have now also factory tests for the 21 MW gas engine. So for every power demand we have a matching element. Secondly, we also have the option of single turbo-charged engines, and dual turbo-charged engines.”
As the energy sector becomes more diverse, with far greater penetration of distributed generation sources, the flexibility of gas-engine technology is expected to see it occupy a considerably larger role in maintaining grid stability, as Tütken says: “In Europe we see more and more renewables and ‘big’ centralized power stations of a few hundred megawatts. It might be less, more decentralized units on the 20, 50, 100 MW range.
“I think in the short term, I see the transition from the big, centralized peak power stations and gas turbines to smaller units. There will be, in my view, more engine-based power plants in the future.”
Given that this is true, the expectation of increased demands for flexibility and efficiency, lower emissions and lower costs is set to increase technical demands on gas engine technology. As Laitinen points out: “The very feature of fast starts and stops and the fast ramping of power up and down, that this is very capable without any additional cost, that seems to be more and more valuable for a few reasons.
“We need flexibility in the power system to integrate more renewable wind and solar, that’s number one. And also the demand of electricity is less stable than before. It’s getting more and more peaky. And to follow those peaks as precisely as possible, you need fast and flexible generation, and this is what the engines are capable of.”
David Appleyard is a freelance journalist