FUTURE WORK
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Vision H2 has made progress in the research of hydrogen as a storage medium in combination with a renewable and stochastic energy source. What Vision H2 created is an intelligent and iterative H2ool that can be made adaptable to contribute to future research. We believe whilst this system is unfeasible for now, the future will see a greater hydrogen economy emerging which will further support the increase in efficiency and reduction in cost of this system, most notably in that of the key components: the electrolyser and fuel cell. Below details key areas in which Vision H2 believes this system and hence H2ool could be developed:
Current System
As the current system stands, putting all solar energy harnessed through the electrolyser, it is just 33% efficient whereby it takes the PV array delivering approximately 3 kWh energy to the electrolyser for every 1 kWh actual demand required. As a round-trip efficiency for the system, this is very poor hence this section looks at future work that may increase this value of efficiency.
Hybrid: Control (Excess to Electrolyser)
A key step could be making use of the available solar energy straight to the demand throughout the day, and only utilising the storage in the case of no or insufficient solar irradiance such as evening time.This 24hr profile above shows the behaviour of the system whereby the solar energy harnessed throughout the day flows directly to the demand, shown by the grey shading. The key component this design would reduce is the size of the electrolyser required to meet the peak demand - you can see the approximately 50% reduction indicated by the yellow circles.
Control System
It’s understood that PV power is inherently stochastic. Our current tool is designed to deal with this by varying the PV array size and storage size in order to produce enough hydrogen prior to its required usage so there is no period whereby the demand cannot be satisfied. However other approaches could be taken, such as implementing a control system to deal with this intermittency and fluctuation in solar irradiation to ensure a reliable supply of energy.
By design of a dynamic control system, the solar-hydrogen system can be adapted to only send excess power to the electrolyser during the day in the case the supply is greater than demand from the PV panels to the load. Research has been carried out investigating in particular the use of an integrated maximum power point tracker (MPPT) and load splitter in order to design a dynamic system that can allow the electrolyser to receive diverted power in the case of surplus (Dou and Andrews, 2012).
Figure 1: 24 Hour Profile
Hybrid: Batteries
Looking at further hybrid opportunities, batteries could be implemented as seen in this diagram in order to support periods of peak demand, reduce losses due to standby operation and so increase the efficiency of the system. Batteries don’t share the long term storage capability of hydrogen however it’s likely that they can both be utilised in a hybrid system to compliment the other and become more cost effective. Research carried out in 2008 to estimate the energy cost of various solar-hydrogen configurations concluded that it was more feasible by implementation of a battery according to economic constraints (Lagorse et al., 2008). The electrolyser hence would not have to be sized in order to meet the PV maximum power output but instead a smaller size, reducing costs. The fuel cell could be similarly reduced in size however in respect to the peak demand by the load.
Figure 2: Hybrid with Batteries
Further Considerations
Selling Excess Hydrogen
As the market for hydrogen increases, driven largely by EVs, in the case of excess, the system could become profitable in selling hydrogen. This could be further supported by a modular design.
Modular Design
By modular design, mainly of the electrolyser and fuel cell, depending on the demand, the system could be more adaptable to fluctuations both daily and seasonly.
Grid Connection
By connection to the grid, excess electricity could potentially be sold back; his option could be assessed economically in the future in comparison with the selling of hydrogen. Whilst the system would be assumed to be sized to ensure it is a reliable source, by connection to the grid, reliability could be heightened in the case of system failure or breakdown. However as the grid is generally associated with the production of greenhouse gas emissions, its most desirably to be avoided.
Integrated Heat Recovery
Integrated heat recovery could allow for heating of buildings or purposes directly surrounding the system, increasing its attractiveness in respect to sustainability and cost.
Recycling Oxygen
Oxygen produced in the electrolyser could have potential in being recycled later on in the system for the fuel cell, reducing costs and the requirement to transport resources to the system.
Standby Operation
In particular, standby operation of the electrolyser can drain the system of a considerable amount of energy during hours whereby the renewable energy source isn't available. This area of research could be a key factor in respect to reducing the components cost along with its start up and shut down operation.
Compression
By compressing the hydrogen to a higher pressure, the land use required by the system as a whole would be reduced. If the location was in a packed city with minimal land area this would be useful however can be very costly so the suitability would have to be assessed. Also, by integration of compression into the electrolyser, costs could potentially be minimised by not having a separate compressor; a PEM electrolyser has reportedly used in experiments at 200bar (Barbir, 2005).
Other Renewable Energy Sources
The group would aim to investigate the suitability of other renewable energy sources in place of the solar energy implemented in the H2ool. For example, harnessing wind energy is more prevalent in a multitude of areas whereby harnessing solar energy is not as appropriate hence this would be a beneficial aspect to have further integrated into the model.
References:
Dou, X. and Andrews, J. (2012). Design of a Dynamic Control System for Standalone Solar-Hydrogen Power Generation. Procedia Engineering, 49, pp.107-115.
Lagorse, J., Simões, M., Miraoui, A. and Costerg, P. (2008). Energy cost analysis of a solar-hydrogen hybrid energy system for stand-alone applications. International Journal of Hydrogen Energy, 33(12), pp.2871-2879.
Barbir, F. (2005). PEM electrolysis for production of hydrogen from renewable energy sources. Solar Energy, 78(5), pp.661-669.