The current world’s energy consumption, which is estimated today to be 12 billion tons oil equivalent (TOE) could increase twofold or threefold by the start of the 22nd century. In parallel, the fossil reserves (oil, coal and natural gas) are being depleted, while the cost to extract and exploit them is increasing. According to recent scientific literacy works, about 78–80% of the world commercial energy comes from fossil fuels, such as, petroleum, coal and natural gas. Those high-carbon sources have negative effects in our environments, such as, effects on heath, land, air and rain. The threat and impact of Climate change forces us to seek energy sources that emit less GHGs. Therefore the trend is to use renewable energy that is abundant and ongoing like Sun, wind, waves, rivers, tides and the heat from radioactive decay in the earth’s mantle as well as biomass. Our ability to transition from fossil fuels to renewable sources of energy will likely determine the fate of the planet.
About five percent of total global energy usage is by electronics. That number is projected to grow to at least 40 percent by 2030 unless there are major advances made in the lowering of electricity consumption. The Natural Resources Defense Council (NRDC) predicted that by 2020, data center electricity consumption will increase to 140 billion kilowatt-hours annually, equivalent to the output of 50 U.S. power plants. Therefore there is push from Google, Apple, Face book, Amazon, CenturyLink and other to build green datacenters based on renewable energy like natural gas , hydro-electric power and wind power. Renewable energy is also required to meet the demands of large rapidly developing countries like India, China and Brazil, to run power plants, Modern agricultural sector, Water Utility Industry, Industrial and public wastewater treatment sector e.t.c.
Renewable energy is at the centre of the transition to a less carbon-intensive and more sustainable energy system. According to IRENA, 171GW of renewable energy was added to the global mix in 2018, marking an annual increase of 7.9 percent, and accounting for two-thirds of new power generation capacity altogether. Hydropower takes the largest share with 1,172GW worldwide, followed by wind at 564GW and solar with 480GW, although solar saw the largest growth in 2018. The International Renewable Energy Agency (IRENA) says that renewable energy now forms one-third of the world’s total energy capacity — its highest level ever — but at the same time, the International Energy Agency (IEA) reports that energy demand is growing at the fastest pace this decade, and fossil fuels are leading the charge.
Military equipment is becoming increasingly sophisticated delivering far greater capability such as network centric warfare and advance weapons and protection systems. The unavoidable side effect is the increasing demand for mobile electrical power on the battlefield. The demand to combine maximum adaptability with sustainable power is leading to the increasing use of renewable energy on the battlefield. Department of Defense (DoD) has embarked upon an ambitious program of expanded renewable energy generation on bases and in the field, with a goal of producing 25% of its energy from renewable sources by 2025.
“Photovoltaics, and other renewable technologies such as small wind turbines, mini-hydro, biomass or their hybridization can provide quality electricity to those who do not have access to reliable modern energy services. This helps to significantly improve lives in terms of comfort, communication, health, education and income generating activities. It also opens up new opportunities for businesses and services,” say Xavier Vallvé, Trama TecnoAmbiental S.L., Barcelona, Spain and Werner Weiss, AEE-Institue for Sustainable Technologies, Gleisdorf, Austria.
However, in comparison to conventional energy sources, renewable energy sources are less competitive due to their uncertainty, intermittency due to dependence on weather and location, and high initial cost. Solar power can be harnessed almost anywhere and operates silently and cleanly. Solar radiation is the most abundant source of energy that can be converted into electricity and heat. It is a widely distributed resource that can be harvested and consumed near to where the needs are. Solar thermal systems are able to meet not only the heat demand for all domestic needs like hot water and space heating, but it can also fulfill the heating needs of hotels, hospitals and industrial processes. But it is costly and requires a sizable footprint while producing a small amount of power for only 20-25% of the day.
Wind energy is almost everywhere around the world. But the wind speed strength varies depending on the particular area. Wind energy can be operates during the day and night times, unlike other renewable. Hydro produces much more power all day at a lower cost but requires enormous construction producing a sizable environmental impact.
To overcome the intermittency and uncertainty of renewable sources requires either reliable duplicate sources of electricity beyond the normal system reserve, or some means of large-scale electricity storage. Storage is relatively costly because the storage medium, batteries or hydrogen tanks, must be larger for each additional hour stored.
Because of this intermittent nature of renewable, single renewable energy source tends to be problematic in terms of energy yield and operational cost. Therefore to provide an economic, reliable, and sustained supply of electricity, Researchers are proposing a modified configuration that integrate these renewable energy sources and use them in a hybrid system mode to form a hybrid renewable energy system (HRES). Hybridization of different alternative energy sources can complement each other to some extent and achieve higher total energy efficiency than that could be obtained from a single renewable source. Future energy supply will be based on a smart mix of different technologies in order to cater to people’s needs.
Hybrid energy systems
Hybrid energy system is the engineering design of hybridizing power supply components or pairing them, for example, arranging diverse energy resources to work in parallel (equivalent) is very common in power. So, hybridizing is defined as forming crossbreed of pairs of agent for working together to achieve a purpose. Thus, hybridizing is to manually or automatically synchronize two or more electric power generator resources or components to supply electric power to the grid, therefore forming hybrid energy system. Hybrid energy system is an infrastructural design that integrates diverse or multiple energy converters to energy storage, energy conditioners, energy management system. By and large hybrid renewable energy system (HRES) is an extension of HES that uses mix diverse resources as hybrid or all hybrid renewable energy resources to supply the electric power system.
A HERS can be applied in stand-alone or grid-connected modes. Stand-alone system must have a large storage to handle the load. While in a grid-connected mode, the storage can be small, and the deficient power can be acquired from the grid. It should be noted that, grid-connected mode must have a power electronic controllers for load sharing, voltage, harmonic, and frequency control. Thus HERS operating model is classified into Island mode where the generated electricity is consumed locally and grid connected mode where the renewable energy source is connected to the gri
The maximisation of energy production from offshore sites is critical, both in relation to keeping costs down and minimising environmental impact. This is especially important for the more exposed sites in Atlantic regions, which the wind industry will be moving into in the next decade. Hybrid energy platforms take advantage of synergies and compatible aspects of different energy types or even different technology types within the same industry.
An example of combining wind with wave energy is the Blackbird system . This consists of a Storage Base Anchored Uniaxial Hybrid VAWT with a Wave Energy Converter (WEC) supported on a fully submerged Tension Leg Buoy. This hybrid unit consists of a synergy between VAWT, WEC, horizontal sea level generator, submerged WEC system and a single mooring line with integrated cable, moored to the seafloor via a drilled anchor/suction caisson storage concept.
The European (EU) project MARINA examined more than 100 hybrid concepts, from which three were chosen for more detailed examination. These three concepts were the Spar-Torus-Combination (STC), the Semi-submersible Flap Combination (SFC), and a large Oscillating Water Column (OWC)-array floater. The STC and the SFC concepts add wave energy converters to an existing floating wind turbine, while the OWC array concept is an integration of a wind turbine with a very large V-shaped floating platform.
Another type of hybrid is the wind–wind system. The development of multi-converter platforms exploits conventional and airborne wind energy converters on the same platform. Multi-turbine floating platforms are already being developed, e.g. SCDnezzy, presenting a clearer path forward, whereas various types of airborne wind technologies are still in an early stage of development. Assessment of whether tethered airborne systems will work on floating platforms is needed. The design of a stable floating platform allowing efficient operation is critical. In some cases, the platform needs to be very large and, given the lower power generation of kites (at present 100 kW though this could be scaled), it impacts significantly on the cost of energy. Combining AWE with a platform for a conventional wind turbine, if technically feasible, could have beneficial impacts such as better exploitation of the wind resource.
The benefits of hybrid platforms lie in the synergies between the different forms of energy production. The combination of elementary technologies on a single platform may have the potential for higher overall production levels and to share infrastructure, e.g. platforms, cables, substations, etc. In addition, resource analyses for wave energy sites have generally shown that viable sites also have a high wind energy resource. Wave energy tends to be more predictable and less variable than wind energy with the peaks in wave energy production trailing the peaks in wind energy production. This will have the advantage of smoothing combined wind/wave production overall thus increasing energy market value. Hybrid platforms could operate efficiently at most wave energy sites, but floating platforms incorporating only a wind generator can be unstable. The use of the STC helps to stabilise the system, which constitutes a major advantage. Several projects, some of them being in pre-commercial stages, are in place and still have a higher levelised cost of energy than conventional fixed offshore wind, since for the latter the learning curve is based on more years of experience.
These hybrid devices present, compared to the single floating devices, an additional set of challenges and development needs due to greater complexity and reliability problems. The MARINA project has highlighted the challenges associated with the hybrid wind-wave platform design, by presenting a comparative numerical and experimental study for the STC and SFC concepts. It was found that for these concepts, wave energy technology contributed less than 10% of the total energy production of the hybrid platform. In addition, for some combinations, the inclusion of a wave energy converter tended to destabilise the platform, going against the fundamental principles of the platform. For instance, the spar is designed to be hydrodynamically transparent but this is no longer the case when a point absorber is added. The large OWC array had good energy balance but the large pitch motion of the floating platform gave rise to operational and survival problems.
The most developed technology at present would seem to be the hybrid platform with floating wind and wave energy, such as the P80, developed in the framework of the Poseidon project. The P80 project (from the company ‘Floating Power Plant’) is the upgraded version of the P37 device. P37 is a hybrid wind-wave floating scaled device that has been tested in North Sea conditions having 33 kW of installed wind power and 50 kW of installed wave power. The wave energy converters are heaving/pitching flaps that must always be aligned towards the incident waves in order to maximise production. The P80 was tested at 1/50 scale (TRL of 4, possibly 5). It aims at a single wind turbine of between 5 and 8 MW and a 2–3.6 MW wave energy converter. The actual power values are low, e.g. the floating power plant P37 has a nominal power lower than 100 kW.
Better together: batteries and fuel cells
Fuel cells are gaining traction as a potential solution for decarbonisation. Fuel cells do not store energy but convert it to electricity from an external fuel source (often hydrogen), as opposed to batteries which store and then discharge electricity. Investment in these technologies – and the number of projects aiming to deploy them in the marine arena – has advanced rapidly in the first few months of 2019.
A project by researchers at the École Polytechnique Fédérale de Lausanne (EPFL) has proposed a hybrid power system centred on solid oxide fuel cells (SOFC) running at a constant load. Batteries would store any excess electricity generated when electricity demand is lower than the SOFC output, while syngas produced by the cells would be processed to hydrogen that could fuel auxiliary proton exchange membrane (PEM) fuel cells at peak power demand.
SOFCs developed by EPFL have achieved 75% efficiency, compared to just over 50% for the most efficient engines, but can take 20 hours to reach full capacity. They can be used to produce a combination of electricity, hydrogen-rich synthesis gas, and high-temperature heat. This heat would be used in a purifying process – consisting of a two-stage water-gas shift reactor and a pressure swing absorption unit – to generate hydrogen. The only by-products would be CO2 and water.
EPFL researcher Francesco Baldi explains that the hybrid power system would suit cruise ships because of their diverse power demands, compared to the mainly propulsive power needed for merchant vessels. SOFCs can run on a wide variety of gas and liquid fuels, while PEMs use hydrogen fuel, which would require vast storage space onboard if used as the main power source.
While solid oxide fuel cells may be a more distant prospect, other projects are exploring the combination of ‘traditional’ PEM cells with batteries. One is being conducted by Norwegian shipyard Fiskestrand, which is exploring how hydrogen fuel cells and batteries can be used on a short ferry route from next year. The shipyard’s HYBRID ship project is considering the optimum engineroom layout for fuel cells as well as how they can be integrated with other systems. The aim is to ensure that propulsion (including fuel cells) is robust enough for repetitive, short-burst service.
The SINTEF Ocean laboratory in Trondheim and ABB will assess how fuel cells and batteries can best function together for short-distance ferry operations. The tests will simulate the conditions that a ferry is expected to encounter on a high-frequency, 10-km route. Fuel cells need batteries – or at least some form of energy storage – to be truly effective in helping to decarbonise shipping. And, surprisingly, there could be more barriers to uptake for relatively mature batteries than for the fledgling fuel-cell technology. Chief among them are cost and energy density.
On Hurtigruten’s battery-assisted cruise ships, Roald Amundsen and Fridtjof Nansen, the installed 1.35-MWh systems occupy just a fraction of the battery rooms designed to accommodate installations of up to 6.5 MWh. When those installations are complete they are expected to weigh around 80 tonnes. That is nearly half the total weight of the four Rolls-Royce B33:45 engines which cater for the majority of the vessels’ power needs.
It is not hard to see why big battery packs have yet to find applications on more weight-sensitive vessels. And technology advances that are expected to bring battery energy density to a new level are proving painfully slowly to emerge. According to research institute BloombergNEF, solid-state batteries – the next great hope in scaling down battery technology – are not expected to have a ‘meaningful impact’ on the electric vehicle market until the late 2020s. For the more conservative and challenging marine market, it could be much later.
Even more than batteries though, it is answers to the hydrogen challenge that will determine the success of fuel cells in shipping. The difficulty of storing hydrogen in large volumes is well known. Even in its most compact, liquefied form, hydrogen takes up twice the space of LNG. For vessels taking long voyages between bunkering, this is a key issue. Storage concerns could be overcome only with major changes to vessel design. Adapting bunkering schedules would not be a possibility unless the availability of commercial liquefaction plants, in Europe in particular, is dramatically improved.
But there is a more fundamental issue than storage. Fuel cells can only cut greenhouse gas emissions from well-to-wake if they use clean fuel. There are technologies emerging which could supply renewable hydrogen. Large scale electrolysis plants have been designed for onshore use which would deliver many hundreds of tonnes per day. Hydrogen could also be produced cleanly by combining natural gas steam reforming with carbon capture and storage. And a recent breakthrough by Stanford University researchers could make seawater electrolysis effective at greater volumes.
Hybridization of hydropower with floating solar
Solar power is widely seen as one of the most promising ways of satisfying the world’s growing demand for renewable electric power. Combining solar and hydropower in a hybrid power plant can smooth out generation fluctuations over the course of days and seasons.
“The cost of solar power equipment has fallen dramatically in recent years. As a result, solar power is now one of the world’s cheapest energy sources, capable of competing with conventional technology like coal and gas in many places. Hydropower has the potential to act as a battery for solar power. A good control system incorporating accurate short-term forecasts for solar power generation is the key to optimising the power plant’s operations”, says Stanislas Merlet.
Having the solar power plant floating on the reservoir avoids potential land use conflicts and makes it possible to use the hydropower plant’s grid connection and thus reduce the project development costs. Solar power requires daylight to produce electricity and hydropower requires precipitations. There is generally little sun during wet periods and there is little water during droughts. This means that the two energy sources can complement one another and optimise electricity generation over the course of days and seasons.
Floating solar power on a hydroelectric reservoir can provide a reliable supply of electricity and may become an important energy source worldwide. Stanislas Merlet is starting a Ph.D. focusing on how the two energy sources can work together to optimise renewable electricity generation.
BOURNE’s Hybrid solar and hydro
Bourne Energy, an energy and water tech startup, has found a way to harnesses two different energy sources drawn from the exact same footprint thus producing several times more power than a similar size solar panel. Bourne’s Fusion Watermaker Panel, a floating watermaking panel, combines the best of solar and hydro power while bypassing their major limitations.
Placing solar and water power systems together in one unit creates many benefits. This hybrid configuration actually improves the output of the solar side of the system. The surrounding water is used to cool the PV panel increasing output up to 30%. Water is used to spray dust and dirt from the surface of the PV panels which can rob power up to 30%. Furthermore the float eliminates the need for foundations and supports that make up an average 40% of total land based PV costs.
The Fusion Watermaker Panel is composed of approximately 2,500 square feet of solar panels covering the surface of a 60 foot diameter round floating panel. Total solar power output is estimated to be approximately 42kW/hr and 250kW/day. Twenty micro-hydrokinetic generators are attached underwater around the perimeter of the panel to harness hydropower from the passing current. The streamlined panels are designed to be moored in rivers, canals, tidal flows and aqueducts. Together they silently produce power without being interrupted by clouds, rain or even nightfall
Each generator utilizes proprietary technology to drive a DC generator producing 600W/hr per unit and totaling and estimated 12kW/hr and 280kW/hr every day. Total output per panel, estimated to be more than half a megawatt a day, powers four internally mounted state-of-the-art RO systems capable of producing freshwater from either brown water or seawater.
It is particularly valuable for: baseline power for utilities; backup power for data centers and nuclear plants; baseline and backup power for IoT; as well as remote power charging stations for EVs and ROVs
WindStream Technologies’ Hybrid rooftop wind and solar generator
WindStream Technologies’ have developed a hybrid rooftop energy system, which combines solar panels and vertical axis wind turbines in a single modular unit.
The 1.2 kW SolarMill SM1-3P, with three 300W solar panels and three Savonius wind turbines, measures 10′ wide by 10′ deep by 7′ high (3m x 3m x 2.1m) and weighs in at 375 lbs.(170 kg), and is designed to be mounted on a roof, where it is claimed to be capable of producing up to 135 kWh per month under optimal conditions.
According to WindStream, the SolarMill unit offers “very high” renewable energy density, and because it incorporates both wind turbines and solar panels, can continue to produce clean electricity after the sun goes down, with power generation at wind speeds as low as 4.5mph (2m/s).
Florida Power & Light’s (FPL) Martin Next Generation Solar Energy Center (MNGSEC) began operation in 2010 as a first-of-its-kind hybrid solar facility. The site spans more than 500 acres of land, a subset of the larger 11,300-acre Martin Plant that contains it. At peak operation, the 75-MW facility is expected to produce 155,000 MWh per year.
The CSP solar field operates as a true hybrid facility, integrating with the 4-on-1 combined-cycle Unit 8 that pre-existed it at the plant. Infrastructure at the site is comprised of 190,000 parabolic trough mirrors, arranged in 284 rows that stretch 51 linear miles. The plant circulates 800,000 gallons of a heat-transfer fluid called Dowtherm through the focal point of these mirrors, where it is heated by the sun to about 740F. From here, it combines forces with the combined-cycle asset to create electricity via a shared steam turbine. The roughly $400 million project does not result in increased production output from Unit 8. Rather, the CSP resources are intended to reduce the use of natural gas at the plant.
The Stillwater Triple Hybrid Power Plant: Integrating Geothermal, Solar Photovoltaic and Solar Thermal Power Generation
The Stillwater Hybrid Power Plant, owned and operated by Enel Green Power North America, a subsidiary of the Italian Enel Group, is the first hybrid plant of its kind in the world, and the first triple hybrid power plant to be constructed anywhere. The facility near Fallon, Nevada combines a geothermal plant with both PV and CSP forms of solar generation to provide offtakers NV Energy with carbon-neutral energy. The first phase of the project began in 2009 with commissioning of geothermal plant, 33-MW, and four-turbine geothermal plant provides continuous generation capacity via a medium-enthalpy geothermal binary cycle.
A desire to increase output led EGP to add 26 MW of solar photovoltaic (PV) power to the project in 2012. The PV array combines 89,000 polycrystalline silicon panels on 240 acres to generate about 40 million kWh of clean energy per year. The solar PV project size was tailored to complement the geothermal plant output degradation during hot summer temperatures. In 2013, design began on an additional solar project using Concentrated Solar Power (CSP) thermal technology. The augmentation project relies on linear parabolic trough mirrors to add energy to the incoming geothermal fluid, which allows the binary plant to increase output. The CSP array at the site generates about 17 MWt, bumping up overall plant output by about 2 MW.
The project consists of collectors, a heat exchanger, a circulating pump and a control system integrated with the geothermal plant. The solar field adds about 17 megawatts of thermal energy, and is estimated to add an equivalent of up to 2 megawatts of boost in power generation to the geothermal power plant.
Virginia City Hybrid Energy Center
The Virginia City Hybrid Energy Center entered commercial operations on July 10, 2012. The 600-megawatt station, which produces enough electricity to power about 150,000 homes, is one of the cleanest coal-fired power stations in the country. The $1.8 billion facility utilizes two Foster Wheeler circulating fluidized bed (CFB) boilers to burn 2.85 million tons of coal per year. The circulating fluidized bed unit uses coal and up to 20 percent biomass (up to 537,000 tons/year) for its fuel, providing 117 megawatts.
Advanced circulating fluidized bed technology is proven clean-coal technology that also enables the using of run-of-mine coal, waste coal and renewable energy sources, such as wood waste. CFB technology combined with modern post-combustion controls has low emissions of sulfur dioxide, nitrogen oxide, particulate matter and mercury. This technology is compatible with the need to be able to use a wide variety of fuels available in the region and compatible with the requirement to construct and operate a facility in an environmentally responsible manner that minimizes overall impact to air, water and land resources.
Germany’s Combined Power Plant
A far more extensive hybrid system, called the “Combined Power Plant, exists in Germany. Operated by Schmack Biogas AG, SolarWorld AG, and Enercon, this system relies on an integrated network of wind, solar, biomass, and hydropower installations spread across Germany. Wind and solar units generate electricity when those resources are available; and a collection of biomass and biogas plants, and a pumped hydro facility make up the difference when they are not.
The eleven wind energy plants, four combined heat and power (CHP) units based on biogas, twenty photovoltaic plants as well as a pumped storage power plant are linked to one another through a central control unit. The Combined Renewable Energy Power Plant adjusts itself to the nearest minute to meet daily needs. It covers peak loads, such as at midday, and stores electricity that is not needed during quiet periods.The forecast of the electricity requiremenst, the “load profile”, is communicated to the central control unit. This is also where the forecasts for the wind and solar power installations arrive. The German Weather Service (DWD) provides the forecasts for wind strength and hours of sun. In the central control unit this data is then evaluated. Wind and solar energy cannot precisely meet the electricity demand since the amount of wind and solar radiation fluctuates. This creates oversupplies and shortages, which have to be balanced out in order to ensure security of supply and grid stability.
The system can immediately adapt to a shortfall in any one resource by drawing on the others. As of early 2009, the 23.2 MW Combined Power Plant consisted of 11 wind turbines at three separate wind farms, four combined heat and power biogas units, 23 distributed solar systems, and a pumped hydro storage plant linked via central control. In 2008, the facility produced 41.1 GWh of electricity without a single interruption of supp. If the amount of electricity produced by wind and solar power installations exceeds demand, the surplus of energy is used for filling up the pumped storage reservoirs. The electricity can also be exported or used for driving electrical cars.