As discussed in the previous article, the Upstream and Mining industries have been working to accommodate sources of Renewable Power generation for their facilities. Wind Power is the topic of this article. For every amount of power generation generated from Renewables, a remote facility saves fuel costs and reducing conventional power generation reduces the carbon footprint of the facility with less GHG emissions. Offshore Wind Power is attractive with generally more persistent winds. Onshore Wind is a well developed power component for many locations.
As offshore wind farms expand, a common development is shown below – it represents offshore Wind Turbines with a large 600 MW Substation / Transformer Platform. Subsea electric cables interconnect these facilities.
It is also possible to use this energy to support conventional offshore Upstream facilities like Equinor is developing offshore Norway. The Hywind Tampen Wind Farm will consist of 11 x 8 MW Wind Turbines for a total capacity of 88 MW which is ~35% of the annual power demand of the five platforms shown. More Wind Turbines could be installed physically, but it is also apparent that, with wind being an intermittent Renewable, there would need to be significant Energy Storage Systems (ESS) also provided. The cost for this development is NOK 5 billion ($486 million) which includes the floating Wind Turbines and the associated power cables and transformers. For 88 MW this is expensive ($/MW), but it is a step in the right direction.
Future developments could involve more Wind Turbines surrounding a conventional offshore Upstream development, combined with high capacity, long-duration ESS. A possible ESS could use the Wind Power for electrolysis to generate Green Hydrogen as the energy storage medium and then use fuel cells to produce power. If subsurface geology permits (e.g. depleted reservoirs), this Hydrogen could also be stored subsurface. Alternately a Compressed Air Energy Storage System (CAES) may also be possible with the right subsurface geology.
Analytical studies have been performed to see how an offshore Wind Power system (e.g. 4 x 5 MW) could interact with conventional offshore Upstream facilities (peak load 45 MW, supplemented by 40 MW conventional power generator) directly:
An offshore Wind Farm (133 x 1.5 MW) was studied connected to an Upstream facility (100 MW nominal load) and the Main Grid onshore:
Recent studies by Ideol SA and Kerogen Capital have investigated the benefits of using floating Wind Power to power offshore Upstream facilities. Significant progress has been made with floating Wind Turbines to increase the number of potential locations, especially where busy shipping channels may have been a consideration for nearshore locations.
Total is participating in another study to investigate powering offshore Upstream facilities with floating Wind and Wave Power. Electricity generated would be used for electrolysis to produce Hydrogen (P2G2P) for energy storage.
On a much smaller scale, Wind Turbines have been installed on unmanned offshore platforms to generate utility power for communications and instrumentation. These Wind Turbines have been sized from hundreds of watts up to 6 kW. First example is SD6 Wind Turbine from SD Wind Energy with a rated capacity of 6 kW with a 5.6m diameter rotor. Second example is the HALO-6.0 shrouded Wind Turbine from Halo Energy with a rated capacity of 6 kW with a 3.7m diameter. Third example is the Qr6 Vertical Axis Wind Turbine from Quiet Revolution with a rated capacity of 6 kW (at 10 m/sec wind speed) with a 3.13m diameter. There are a number of Vertical Axis Wind Turbines as shown.
Previous articles have shown numerous examples of Wind Power being used at onshore Upstream and Mining facilities. Something most had in common was that it was typical to have a significant amount of conventional power generation equipment (Heavy Fuel Oil or Diesel, engine or turbine driven) to cover the intermittency of Renewables. It was also increasingly common to have both Solar PV panels and Wind Turbines. The intermittency of each is not necessarily in sync which would help. As seen in the industry facility details, the amount of energy storage was often only to accommodate short duration grid stability issues. Usually Lithium-ion battery systems with a duration of 1-6 hours were used. This amount of ESS would not accommodate multiple days of bad weather or light winds, and would not allow continuous load to be supported through the nights. Significant conventional power generation with high fuel and maintenance costs (for rotating equipment) and GHG emissions was needed in these facilities.
The Energy Transition challenge is to have 100% Renewable Energy and this is possible with a hybrid system incorporating Wind Power, Solar Power, and long-duration ESS. South Korea’s EPC LS Electric’s Yeongam 133 MW Power Generation Project facility has a 40 MW Wind Farm, a 93 MW Solar PV Farm, and 242 MWh (PCS 78 MW) Battery ESS. This example could be applicable for a remote Mining Facility.
Components of Wind Turbine Systems
Horizontal Axis Wind Turbines (HAWT) are the most common type of large scale units. Upwind designs have the rotor facing the wind. These units have a number of mechanical and electrical components which need careful operation and maintenance. Yaw and pitch systems help keep the turbine aligned with the wind direction and adjusts the wind’s angle of attack by turning the blades to enable control of the rotational speed and generated power (including stopping the rotation at cut-in or cut-out speeds). The wind turns the blades around the rotor which is connected through a low-speed shaft to a gearbox to a high-speed shaft to a generator to produce AC electricity. Step up transformers (at ground level) boost the generator output voltage from 690 V to the collection system’s medium voltage distribution level of 34.5 kV. If long collection distances within the wind farm are present, there may be a further step up to high voltage overhead lines 115 kV. Onward connections to users (and sometimes a main national grid) could be even higher voltages in some cases.
The various transformers have severe duty requirements – “variable loading, harmonics and non-sinusoidal loads, transformer sizing and voltage variation, low voltage (LV) fault ride through, as well as protection and fire behaviour, step-up duty, switching surges and transient over-voltages, loss evaluation and gassing”. Frequent daily thermal cycling can cause insulation and electrical connection integrity issues.
Digital transformation provides useful technologies and tools to monitor the operations, performance, and integrity of all these components. All components would have IoT sensors to capture data which would be Edge processed in some instances, then transferred through communications systems to control centres. One supplier has over 300 sensors transmitting ~200 GB of day per day from each of their Wind Turbines. Data would need to be stored in a Cloud Data Platform to allow access for data analytics to help predict any integrity degradation issues.
Sizes of Wind Turbines
Wind Turbine sizes and power ratings have increased dramatically over the past 30 years:
One of the largest offshore Wind Turbines currently available is the Siemens Gamesa SG 11.0-200DD which is rated at 11 MW with rotor diameter of 200m and IEC Wind Class I. Each blade is 97m long. Vattenfall plans to install 140# of these units for the Hollandse Kust Zuid (HKZ) wind farm, offshore Holland for a total capacity of ~1.5 GW. Only specialist offshore installation equipment is able to transport and install this size of a Wind Turbine. An even larger turbine is in development (SG 14-222 DD) with capacity up to 15 MW.
Wind Turbines are characterised by IEC 61400 Wind Class and there is a range of normalised Power Curves as shown below. Generally IEC Class 1 curves are to the right side and IEC Class III are to the left side of the family of curves. Offshore Wind Turbines experience generally higher wind speeds with greater persistency, so fewer but larger Wind Turbines may be installed to support offshore Upstream facilities (e.g. Equinor’s Hywind Tampen Wind Farm example discussed earlier in this article). “Low wind” Wind Turbines have also been developed to increase the potential locations, especially onshore in calmer wind locations to facilitate “cut-in” at lower wind velocities.
Whilst large Wind Turbines are becoming more common offshore, the average size of onshore Wind Turbines is considerably smaller due to physical land transportation and installation issues. The average onshore Wind Turbine manufactured today is IEC Class III with power rating 2.5-3 MW – designed to function in lower wind speed locations typical for more onshore locations. It just means that a larger number of Wind Turbines may be required for a high power demand Upstream or Mining facility (e.g. similar sizes to the Turkana-Kenya Wind Farm below which has Vestas V52 variable-speed pitch-regulated upwind Wind Turbines with power rating of 850kW and 52m rotor diameter and 44m hub height – sized for easier transportation and installation in remote onshore locations).
Facility Requirements for Example Upstream and Mining Facilities
Wind Power has a different type of intermittency compared to Solar Power. Solar Power varies over the course of a day and is impacted by weather conditions like clouds, precipitation, and night-time. Wind Power is much more complicated and it varies according to atmospheric weather patterns (with extended lulls possible). The graph below shows Daily Wind Power Output Profile at one random onshore Wind Farm. Wind can be totally out of sync with Solar Radiation, so they might complement each other, but they might also both be intermittent at the same time. Wind often blows more at night, so this could help balance the lack of Solar Power at night. Wind is also varies seasonally. Wind intermittency is usually assumed to be between 7-30% efficient. This means it is similar (and maybe less efficient) than Solar intermittency. Cost differences in Wind and Solar Power systems and costs of Energy Storage Systems means that a strategy should be adopted to select a hybrid solution with a mixture of technologies, sized as appropriate for the particular location and resultant economic analyses.
Hybrid Renewable Power facilities for example purposes only could be a mixture of Wind (~1/3) and Solar (~2/3):
The geographical location of a particular Upstream or Mining Facility could change these assumptions significantly:
- For coastal Upstream Facilities, it may be possible to have the Wind Farm be located nearshore with much larger sized Wind Turbines, running efficiently with the more persistent winds, and effectively doubling the assumed Wind Power output efficiency from 20% up to 40% (as seen in European offshore Wind Farms). And in this case, the Solar Farm size could be significantly reduced (or eliminated);
- Certain regions might have more precipitation, especially seasonally, which may mean that Solar radiation would be inefficient without significant Solar Farm panel increases to capture the limited periods of sunshine – but a significant increase in the number of Wind Turbines may also be possible – either way more ESS would be required;
- Remote mountainous Mining Facilities might have logistical access difficulties that meant smaller Wind Turbines were required to facilitate installation of the blades and tower sections – so increased numbers of turbines would be needed;
- Latitude matters with respect to the length and intensity of daylight, and the row spacing of Solar PV panels would need to be adjusted to avoid shadows (higher spacings at higher latitudes);
- Global warming is also affecting wind circulation in some locations which can reduce the location’s available wind energy and require additional numbers of Wind Turbines for the required power output.
Intermittent Renewables may be combined into hybrid microgrid solutions (Wind Farm + Solar Farm) with large capacity, long-duration Energy Storage Systems (ESS) for Upstream and Mining Facilities. More details on a hybrid microgrid will be given in an upcoming article, but a typical daily generation / energy storage graph for an Upstream or Mining Facility could be represented as shown below. Wind (in dark blue) has whatever intermittency normal to the location, but it is often more persistent in the night. Solar (in orange) has the typical daily production curve shown (assuming minimal weather interruption). In this microgrid example the primary ESS medium could be hydrogen, so hydrogen storage (produced from excess Renewables electricity) is shown in light blue, and hydrogen generation (produced from fuel cells) is shown in grey. In order to improve efficiency of the fuel cells (and avoid unnecessary waste of hydrogen) it is recommended that a smaller Battery Energy Storage System (BESS) like Lithium-ion batteries would be included to provide microgrid “inertia” and stability for rapid supply or demand changes until the hydrogen fuel cells are able to react to fill any more material supply gaps. Additional Renewables could be used to increase hydrogen production and therefore provide longer duration ESS in locations where intermittency is more challenging.
It is possible to have 100% RE solutions, but potential higher initial CAPEX may need to be considered and traded off against much lower OPEX (no fuel costs and no rotating equipment maintenance costs). The ability to reduce GHG emissions, avoid high Carbon taxes, and attract ESG finance will be key drivers also. The Energy Transition path is clear for the Upstream and Mining industries with technical Clean Energy solutions available to be considered.
https://www.researchgate.net/publication/257712271_Voltage_and_Frequency_Control_in_Offshore_Wind_Turbines_Connected_to_Isolated_Oil_Platform_Power_Systems and https://www.researchgate.net/publication/281750082_Challenges_with_integration_and_operation_of_offshore_oil_gas_platforms_connected_to_an_offshore_wind_power_plant