- Doris - A thought experiment in progress (1) - Description
- Doris - A thought experiment in progress (2) - Energy Delivery
- Doris - A thought experiment in progress (3) - Storage Sensitivity
- Doris - A thought experiment in progress (4) - You have to do both
- Doris - A thought experiment in progress (5) - Good and Bad Years
- Doris - A thought experiment in progress (6) - The Mix
- Doris - A thought experiment in progress (7) - Climate
- Doris - A thought experiment in progress (8) - The winter problem
It is important to remember that Doris is a computer simulation with some arbitrarily set parameters and rules, it exists only in the imagination and has no physical reality.
When I first started looking at wind as a resource, It became apparent that there is a considerable variation in the nature of wind, even within a small area. For example where I live on the south coast of England, there are at least five regimes (the average wind speeds are for comparative purposes only):
Offshore, the average wind speed rises to approx. 9 m/s, more importantly, the proportion of observations which are less than 5 m/s is much lower.
When I first started looking at wind as a resource, It became apparent that there is a considerable variation in the nature of wind, even within a small area. For example where I live on the south coast of England, there are at least five regimes (the average wind speeds are for comparative purposes only):
- The open spaces around an airfield, typically these are located in uncluttered areas away from hills and other natural obstruction to air flow. Airfields are the largest source of wind speed data, but it may not always be relevant to wind turbines, the average speed might be 5.0 m/s.
- Urban and wooded areas where the rough surface attenuates the wind speed and causes turbulence, mounting a turbine on a tall mast reduces the effect of these, but these may not be practical or desirable. In this situation, the average wind speed might be 1.0 - 3.0 m/s.
- Special locations, these include ridges and hills where the air flow is not obstructed by the surrounding terrain and may even be enhanced by it. An average speed might be 6.0 m/s, data on these locations is hard to come by, but looking at the location of corn grinding wind mills can be instructive.
- Offshore, relative to the land, the surface of the sea is smooth and losses to friction and turbulence are much lower, the average wind speed in an offshore location might be 7 - 9 m/s. Data sources are offshore platforms and moored buoys.
- Coastal areas. When the wind is blowing off the sea it can be smooth, but when it is blowing off the land, it becomes turbulent.
The graphs below are not strictly comparable and only serve to show the difference in the nature of offshore and offshore wind. Doris uses the latest available weather report, to form a distribution, it is preferable to have regular sampling, say, just use the reports that are on the hour. The height at which the observations was made was probably different. Height correction was not applied in the compilation of these graphs, although Doris does make some adjustment in estimating the energy that can be extracted from the wind.
For the onshore location, the mean wind speed is approximately 5 m/s and the distribution has a clearly defined mode at around 8 - 10 m/s.
The amount of energy that can be extracted from a stream of wind is proportional to the cube of it's velocity, the wind flowing at 7.5 m/s has the potential to provide more than 3 times the energy of one flowing at 5.0 m/s. This accentuates the difference between onshore and offshore wind.
Whilst the energy yield from offshore wind is potentially greater than onshore, so are the costs which might be two to four times higher. The higher costs come from two sources, the first is the high cost of working offshore which requires similar equipment to that used by the oil and gas industry for building platforms. Secondly, the installations need to have the resilience to withstand storm conditions and be tolerant of the corrosive effect of salt. The relationship between onshore and offshore locations involves some complex economics.
Running an offshore data set through Doris produced the following graph (some software changes are needed to make the solar component in each graph comparable, they will be updated when this is done, however, the nature of the graph is not expected to change much). To take account of the offshore data set, it was assumed that the access to wind generating capacity was reduced to 0.5 kw, it is 1.0 kw in the onshore base configuration.
The difference between the two plots is the lower draw down from conventional sources, this is in part due to the higher output and in part due to the smaller number of days when the yield from wind is low.
As with all the output from Doris, there are some gross oversimplifications, one of which may be the ability of wind farms to deliver energy at low levels, this needs to be understood and some allowance built into the model.
Author's Note
Due to some odd career advice, I left school at 15 and was for two year's England's most incompetent merchant seaman. The fact that I have spent most of my working life writing computer software suggests I was not cut out for a life on the ocean wave. At the time I did not know that what I saw on lookout duty on the monkey bridge could be described in terms of wind speed distributions or Fourier transforms of wave motion. In the context of this post, I appreciate the complexities of offshore operations and that offshore structures must be designed for extreme conditions, not average ones.
Whilst the energy yield from offshore wind is potentially greater than onshore, so are the costs which might be two to four times higher. The higher costs come from two sources, the first is the high cost of working offshore which requires similar equipment to that used by the oil and gas industry for building platforms. Secondly, the installations need to have the resilience to withstand storm conditions and be tolerant of the corrosive effect of salt. The relationship between onshore and offshore locations involves some complex economics.
Running an offshore data set through Doris produced the following graph (some software changes are needed to make the solar component in each graph comparable, they will be updated when this is done, however, the nature of the graph is not expected to change much). To take account of the offshore data set, it was assumed that the access to wind generating capacity was reduced to 0.5 kw, it is 1.0 kw in the onshore base configuration.
The difference between the two plots is the lower draw down from conventional sources, this is in part due to the higher output and in part due to the smaller number of days when the yield from wind is low.
As with all the output from Doris, there are some gross oversimplifications, one of which may be the ability of wind farms to deliver energy at low levels, this needs to be understood and some allowance built into the model.
Author's Note
Due to some odd career advice, I left school at 15 and was for two year's England's most incompetent merchant seaman. The fact that I have spent most of my working life writing computer software suggests I was not cut out for a life on the ocean wave. At the time I did not know that what I saw on lookout duty on the monkey bridge could be described in terms of wind speed distributions or Fourier transforms of wave motion. In the context of this post, I appreciate the complexities of offshore operations and that offshore structures must be designed for extreme conditions, not average ones.
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