Business cases for wind battery storage

Many government policies have been implemented worldwide aiming at accelerating the development of renewable energy systems and therefore, reducing carbon emissions. This has led to increased wind energy penetration. However, the uncontrollable and inflexible nature of wind power sources causes various problems regarding the operation of power systems, such as frequency problems and increased balancing costs to back up the volatile wind power production. The revenue of wind farms is also affected by (high) imbalance costs in case of direct participation in electricity markets. Battery storage units, and especially lithium-based batteries, can mitigate some of these problems by stabilising the wind power output. However, lithium-based batteries have high capital costs and lifetime problems associated with the way they are operated. In this thesis, we examine how to optimally dispatch wind battery storage units to manage the imbalance costs of the wind farm and increase its revenue while also extending the lifetime of the battery. We begin by proposing and testing with empirical data a stochastic wind speed model that captures both the stochastic short-term variations and the daily cycle that wind speed follows. Given the daily cycle and the stochastic parameters of wind speed, the expected wind power output is computed for the whole day and it follows the trend of the empirical wind power output. This is important since it provides valuable information to those making investment and operational decisions linked to wind farms combined with storage units regarding the availability of the wind farm and the time of the day at which lower and higher wind power generation occurs. Then, compared to previous literature that considered time-shifting of wind supply to higher price periods and managing the imbalance costs of the wind farm in isolation, we examine these two services combined for a battery storage unit co-located with a Spanish wind farm. It is shown that under the presence of the battery storage unit the revenue of the wind farm is increased. Then, when the capacity of the battery storage unit is restricted, the revenue of the wind farm is reduced on daily and annual basis but the lifetime of the battery is extended. However, for the investment in wind battery storage to become profitable overall, the capital costs of the battery need to decrease significantly and further revenue streams need to be stacked. Lastly, we examine a bigger wind farm located in the UK. In this case, two different business cases are examined for the wind operator along with subsidised Contracts for Difference. It is proven that with the current capital costs of the wind farms and of the battery storage units, it is more profitable for the wind operator to hold a Power Purchase Agreement with another party than owning a battery storage unit and trading wind power directly in the intraday market. Then, for both business cases examined, the capital cost of the wind farm and the strike price of the Contracts for Difference are the most critical factors affecting the profitability of the investment and also, if subsidies are totally removed from both business cases, they prove not to be economically justifiable. Lastly, we prove that considering only the calendar life of the battery (and not the cycle life) leads to significant overestimation of the investment.