# New Tendencies in Wind Energy Operation and Maintenance
## 4 Discussion
### LCOE Wind Energy vs. Research on Wind Farm Maintenance
Between 2007 and 2019, the LCOE of wind projects declined from USD 0.082/kWh to USD 0.053/kWh [129]. In 2010, the LOCE was USD 0.075/kWh. For the O&M costs (Figure 6), between 2007 and 2019, the O&M costs of wind projects fell 30%, from USD 57/kW year to USD 44/kW year. In reference countries for wind energy, such as Germany, Ireland, Sweden and the United States, in 2008, the O&M costs of onshore wind projects ranged from USD 40/kW year (in the case of Ireland) to USD 78/kW year (in the case of Sweden). In 2018, O&M costs of onshore wind projects were around USD 40/kW year. In the case of offshore projects, between 2015 and 2018, the O&M costs declined from USD 118/kW year to USD 67/kW year [129,130]. Comparing the evolution of the LCOE and O&M with the evolution of research into the maintenance of wind farms, it can be seen that over the period 2007 to 2019, the LCOE maintained a downward trend. This downward trend is due, as mentioned above, to the fact that both annual production and total annual costs influence the determination of the LCOE. Thus, annual production has increased year by year since 2008 (Table 1). In the case of O&M costs, the evaluation is different depending on the stage considered. For example, in the first stage (growth) of research into the maintenance of wind  
Figure 5: Wind energy O&M research evolution. Figure 6: LCOE and O&M wind projects vs. maintenance of wind farm research. farms (2007-2014) there has been a clear decrease. In the second stage (stagnation) of the investigation, during the period 2014 to 2016, a stagnation of O&M costs is observed, while due to the influence of the technology's capacity to generate (Table 1), the LCOE continues to decrease. Finally, in the third stage (growth), from 2016 to the present, there is an increase in scientific production and stagnation in the decrease in O&M costs. Bearing in mind that it is likely that the results obtained in the latest research have not been reflected in the reality of the operation and maintenance of wind farms, it is possible to predict that, in the coming years, there will be a decrease in both the LCOE, which is also influenced by the progressive increase in the annual production of the technology (Table 1), and the O&M costs, in a similar way to the trends observed in the first stage (growth). In conclusion, the evolution of the investigation of the maintenance of wind farms has influenced, in an inversely proportional way, the O&M cost. In other words, in the periods in which scientific research in this field has increased, it has led to a reduction in this very important factor in the LCOE. However, the increase in electricity production from the technology (Table 1) has led to a constant decrease in the LCOE between 2007 and 2019, without taking into account the evolution of research into wind farm maintenance. Therefore, it is possible to predict that the increase in electricity production capacity of wind technology over the next few years will lead to a progressive decrease in the LCOE, regardless of the evolution of research on this technology. However, this positive evolution in the research on the maintenance of this renewable technology will continue to influence the decrease in the O&M cost.