Welcome to classroom #E8:
Introduction to Hybrid Energy Systems 

Decentralisation of the energy generation and increase of intermittent renewable resources have been new drivers for Hybrid Energy Systems (HESs), which can form the bases for local micro grids - an independent energy generation and consumption "islands", which can work on off-grid (from the main grid) as well be connected with the larger grid to form the network to share the supply and demand. 
​We will look more into HES further down in this class.  

Key Points

  • HES can increase the amount of dispatchable renewable energy generation as well as the reliability energy access in rural areas.
  • HES bring together different generation, storage and consumption technologies in a single system, improving the overall benefits compared to a system that depends on a single energy source.
  • HES is operating like a micro grid, providing basic grid services and electric energy quality: controlled voltage, frequency stability and demand/supply balancing, including the system blackstart possibility.

HES explained

HES combines multiple types of energy generation and/or storage or uses two or more kinds of fuel to power a generator. In the past HES have been deployed primarily on islands, which are not connected to the mainland general electric grid. In last few years HES is a valuable method in the transition away from fossil fuel based electric energy and move to distributed renewable solutions. Particularly in the northern countries, where renewable energy sources like sun and wind may be limited in some time periods, backing these up with thermal electric production (Combined Heat and Power, CHP) using local residual biomass, can actually help to expand the use of other renewable energy sources and establish hybrid solution based local micro grid suitable for in rural areas.
​Some examples of HES types:
  • Photovoltaic + Wind + Biomass (CHP)
  • ​Photovoltaic + Wind + Hydro (+storage)
  • Renewable sources + FuelCell (electrolyser and generation) + Hydrogen storage
  • Renewable sources + Storage (Batteries)
  • Diesel generator (soon unwanted) + renewables

Small HES is presented on the drawing below:

 An important issue in renewable energy development has been the inability to rely on intermittent renewable sources, such as wind and solar, for base load power. Small, agile HES is one way to allow energy production into the local micro grid more reliably. Generally, at least one source of the fuel used to power a CHP generator is renewable. Such a system is designed to increase the reliability and thus usability of renewable energy sources (increase to more than 50%) by providing redundant energy production from conventional sources or, more efficiently, by providing storage for electricity produced by intermittent renewable sources.


In smarter HES the computer applications automatically increase or reduce conventional generation or battery usage as needed to respond to fluctuations in production from the renewable resources to maximize the amount of renewable energy in the system. In case the larger consumption loads are also controlled, then the HES would form a smart grid.


To respond accordingly to peaks and dips in renewable energy production, hybrid systems are best implemented on a small scale because small CHP generators are more flexible. These agile systems can, when possible, be interconnected into the central grid system and function as small power plants.


Implementing HES can create also market opportunities for the deployment of energy technologies that are not yet mature. If a particular technology, such as a new type of fuel cell, is not yet efficient or reliable enough to produce electricity in a stand-alone system, it may fit well as an additional component to a hybrid system in which other components can cover possible bumps in the production process.


The other option is use of hydrogen as the mean to store the energy for longer periods. As we know the process of electrolysis can produce hydrogen by breaking water into hydrogen and oxygen, it can be stored. In summer period the solar energy available is at its peak, so if the demand and supply is properly checked and calculated the excess energy can be used in the production of hydrogen and can be stored. In sunny and windy days the supply is maximum, and this excess power can be consumed for the manufacturing hydrogen. In winter, the power consumption is high, but the supply is low, and the stored hydrogen can be used in fuelcell to provide the required extra supply.


Challenges to using a HES
Technical
  • There is no single optimal HES configuration. Rather, optimizing is based on the availability of renewable resources, on site-specific energy infrastructure, production costs and incentive policies. Planning a HES thus necessitates an adequate study period for each proposed site location micro grid area to be covered. 
    Because many HES rely on the flexibility of small conventional power production facilities that can be dispatched as needed and/or on small storage devices to deal with intermittent renewable energy sources, these systems have limited scalability with the currently available technologies.
  • Not all energy production and storage technologies that are potential HES components are fully developed. It is risky to invest in long-term, expensive infrastructure that may improve significantly in the medium term.
Financial
  • Multiple components required to form a HES generally make them more expensive to build.
Institutional
  • Transmission and electric utilities interests may rely on political clout or financial assets to try to limit the expansion of local HES development because they encourage more decentralized energy production in rural areas and reduce the energy supply and economic control by the grid operators.
Environmental
  • Any form of burning (combustion) used for thermal energy generation produces the dangerous, unhealthy and environment polluting gases and particles (smoke). So, whenever possible, the combustion should be avoided or only the most efficient and clean burning methods should be used, like the example solutions presented on this website: Rocket heater and Woodgas generator. 
    Another option is a new combustion based microCHP technology created by Dutch company Microgen-Engine,
    described here below.
​

MicroCHP with stirling engine in fluidised bed 
The electric energy generating engine's (stirling) head is mounted into the hot fluidised sand, instead of turbulent gases in the conventional burning process. A fluid conducts much better the heat into the stirling head that a gaseous medium. In additions the solution provides many advancements for cleaner burning process and efficiency.
  • No ash build up, tar formation and or clinker forming
  • No corrosion due to elimination of sulphur and potassium effects
  • Superior heat transfer: very good efficiency
  • Fuel flexible: woodlogs, pellets, woodchips, etc.
  • Superior emissions in terms of lower fine dust, CO and NOx 

Latvian scientists from Riga Technical University have concluded a tests and study based on above mentioned  microCHP and PV in HES. The results are presented in the research paper available here. 
​



In the training video the experts explain the HES opportunities in off-grid markets, to reduce fossil fuel with cutting edge microgrid systems that hybridise diesel generators with solar and battery energy storage. Highlights how to plan and design the HES to optimize the energy mix and to bring clean, affordable power to underserved rural areas around the world is presented.
latvia_rtu_research_study_in_microchp_and_pv_integration.pdf
File Size: 605 kb
File Type: pdf
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Class continues..

More content in Classroom #E8 is to come..