Conclusions
Case Study 1 Conclusions & Future Areas for Research
For
this energy system to meet the demand of 2000 residents in the
Stornoway area, it was designed to provide uninterrupted power all year
round. To do this the system must have four 2.5MW turbines, one 4.5MW
fuel cell to match the peak demand of 4.4MW, one 7.5MW electrolyser,
one 7.5MW converter and 24Tonnes of Hydrogen storage tanks.
The
system must also deploy an energy dispatch strategy in its power
control system that tracks the load so as to output the maximum power
necessary to meet the demand.
To
exploit the surplus Hydrogen for transport, hydrogen loads had to be
simulated for both the electrolyser and a daily demand of 152kg. These
loads had to be guaranteed by designing the system with an appropriate
tank system size and hydrogen load dispatch schedule.
Case Study 1 Recommendations
This
system suffers from a low round trip efficiency of 29.2%. This is due
to the loop in the hydrogen buffering sub-system that recycles the
power generated by the fuel cell, so that buffer power is available to
the electrolyser when the wind power is unable to match the demand.
This
problem in the round trip efficiency can be remedied by installing a
battery array to store the excess and dispatch it when necessary to
power the electrolyser. This will allow the fuel cell to serve the
Stornoway consumers solely.
Also, the heat generated from
the fuel cell system was not harnessed. This could have been used to
explore the cogeneration potential i.e. CHP. The best candidate for
this would be the Solid Oxide Fuel Cell, which operates at temperatures
close to 1000 degrees Celsius.
The Stornoway wind hydrogen buffering system generates sufficient hydrogen to fuel two buses on the island for the year. Not only does this provide an additional income for the wind farm, but it has the added environmental advantage of reducing the island’s emissions from public transport.
Current fuel cell buses have fuel efficiencies that are comparable with that of diesel buses. Future improvements in component efficiency for the buffering system and fuel cell transport could lead to the same wind farm generating enough hydrogen to fuel more of the island’s public transport. This would reduce the dependence Lewis has on fossil fuels which they have to pay a premium for to import.
However, the use of hydrogen public transport on Lewis would depend on financial support from local authorities (or the European Commission for example) since the costs involved are significantly higher than that of diesel buses.
Case Study 2 Conclusions & Future Areas for Research
In the second case study three scenarios, in which firm power production was successfully achieved for varying periods of time, were analysed. Of these three case studies it is apparent that Scenario_3 was the most cost effective and most efficient system in terms of dumped electricity. The most desirable characteristic of this system is the reduced storage size in comparison to the other two scenarios, which would result in less required infrastructure. These advantages over the other two systems can be attributed to the schedule, which the fuel cell was set to follow. This schedule allowed for the buffering system to extract the maximum amount of energy from the wind after efficiency losses.
Following
on from this observation it would be sufficient to say that an
improvement in component efficiencies, in particular fuel cell and
electrolyser efficiencies, would go a long way to making a hydrogen
buffering system feasible.
Economic Conclusions & Future Areas for Research
It is apparent that both the off-grid and all of the strong grid scenarios are far from being economically viable and they all make a considerable loss at the end of the 25 year project lifespan. At best, case study 1 makes a loss in the region of £130 million and case study 2, scenario 3 makes a loss in the region of £180 million.
As expected, the wind turbine system alone, which produces an intermittent power output has proven to make a profit in all four scenarios and this is despite only being able to sell electricity at the lower system sell price (SSP). The economic success of such a system should probably be attributed to the much reduced component costs: which only include land rent and wind turbines, compared to the buffering system, which include these in addition to: fuel cells, electrolysers, compressors, and sometimes converters.
Currently, the difference in price that can be achieved between selling non-firm electricity at system sell price (SSP) and firm electricity at market index price (MIP) is not sufficient to enable a costs effective purchase of all of the components necessary to implement a buffering system. The extortionate capital cost and replacement cost of the components is far too great to be recouped by the current electricity, ROC and fuel sale prices.
Therefore, to ascertain if a buffering system could become economically viable in the future where different circumstances exist, a number of sensitivities were applied to the off grid case study.
The findings were as follows:
· A continued low interest rate would prove very favourable for the projects economic viability.
· If the technology was developed to extend component lifecycles and replacement costs were no longer necessary, the case study would conclude with 40% less debt.
· If future Department Of Energy component cost target reductions for fuel cells and electrolysers were to be achieved, the case study would conclude with 49% less debt.
· If an annual increase of 15% could be applied to the price of electricity, this would make a 143% improvement to case study 1 and bring the project into profit at the end of the 25 year lifespan. Although 15% per annum may seem very high, between the years of 2005 and 2008, electricity market index prices actually rose by 89% and therefore this could become reality in the future, particularly when the raw materials required for alternative forms of electricity generation become scare in supply.
Other areas that could potentially benefit the projects economic viability, that were not investigated and we would advise for future areas of research include:
· Improved component efficiencies.
· Continued subsidy or incentives for the uptake of renewable technologies, for example, the extension of the renewable obligation beyond 2027.
