## 3 Results
### Comparison with Actual Data
#### 3.3.3 Comparison with Power Output  
The scalar difference and trend of HHWS and REWS compared to SCADA actual wind speed by time of day were compared. At the same time, the predicted generation using HHWS and REWS was also compared to the actual generation. Figure 12 shows the trend of daily wind speed and power generation for each turbine. The gray solid line and bar indicate the wind speed and power generation of SCADA, respectively. Red and blue represent HHWS and REWS, respectively. In the time-series analysis, the difference between the wind speed at the turbine location input to SCADA and the wind speed simulated by WindSim was significant. Clearly, the diurnal trend seems to coincide without any major problem, but the absolute value difference is up to 0.47 m/s. The actual wind speed of the turbines A02 and A03 was similar to that of the REWS, but unfortunately, the wind turbines A01, B01, and C01 located in a straight line showed a large error in relation to the simulated wind speed. It is necessary to sufficiently check whether the WindSim software does not simulate the wind speed at each wind turbine location well, or whether special weather phenomena at the site where the wind speed is amplified are overlapped. When only looking at the average wind speed and daily change, REWS showed a consistently higher value compared to HHWS. This eventually seems to imply that REWS is closer to SCADA wind speed, but REWS generation accuracy was not dominant at all time-points. The daily change graph shows the error rate of the expected generation of HHWS and REWS, compared to the actual generation. The data of the five wind turbines to be analyzed were averaged, and the error rate was calculated by subtracting each simulated power from the actual power generation, and dividing by the actual power generation (Figure 13). Through this formula, a positive error rate means that the simulated power generation is smaller than the actual power generation, and a negative number indicates that the simulated power generation is greater. As Table 8 clearly shows, it seems that there are times when the REWS-based generation forecast is more accurate, and there are times when the HHWS-based generation amount is rather more accurate. In more than half of the day, the REWS-based simulated power generation showed a higher value than the actual power generation. In particular, it showed a pattern of simulating a value that was consistently higher than the actual power  
Figure 11: Wind speed difference distribution of REWS and HHWS within the research domain including the Anholt offshore wind farm. The closer to red, the greater the wind speed difference. generation from 14:00 until sunrise. On the other hand, HHWS simulated a relatively small amount of power generation, compared to the actual power generation. A slightly higher power generation was simulated 2-3 h before and after sunset, but lower values than the actual power generation were simulated in other sections. To find out whether such a result is overestimated or underestimated compared to the actual power generation, the absolute value difference with the actual power generation was calculated. Among REWS and HHWS simulated power generation, the section with a smaller error with actual power generation is indicated in yellow in Table 4. From midnight to 14:00, most of the REWS simulated power generation was close to the actual power generation. On the other hand, from 15:00 to 21:00, the HHWS simulated power generation was closer to the actual power generation. The maximum release time of heat flux from the land surface with low specific heat is 14 h, whereas the time for heat flux emission from the ocean with high specific heat is delayed. This is because the ocean can retain more heat, and do so longer. The time when the REWS-based simulated power generation and the actual power generation error increases is from 15:00 to 21:00, which is generally the time when the heat flux from the ocean is released.