Renewable generation sources still have not achieved economic validity in many countries including Korea, and require subsidies to support the transition to a low-carbon economy. An initial Feed-In Tariff (FIT) was adopted to support the deployment of renewable energy in Korea until 2011 and then was switched to the Renewable Portfolio Standard (RPS) to implement more market-oriented mechanisms. However, high volatilities in electricity prices and subsidies under the RPS scheme have weakened investment incentives. In this study we estimate how the multiple price volatilities under the RPS scheme affect the optimal investment decisions of energy storage projects, whose importance is increasing rapidly because they can mitigate the variability and uncertainty of solar and wind generation in the power system. We applied mathematical analysis based on real-option methods to estimate the optimal trigger price for investment in energy-storage projects with and without multiple price volatilities. We found that the optimal trigger price of subsidy called the Renewable Energy Certificate (REC) under multiple price volatilities is 10.5% higher than that under no price volatilities. If the volatility of the REC price gets doubled, the project requires a 26.6% higher optimal investment price to justify the investment against the increased risk. In the end, we propose an auction scheme that has the advantage of both RPS and FIT in order to minimize the financial burden of the subsidy program by eliminating subsidy volatility and find the minimum willingness-to-accept price for investors.

可再生能源在包括韩国在内的许多国家仍未达到经济有效性，因此需要补贴来支持向低碳经济的过渡。最初的上网电价（FIT）用于支持韩国可再生能源的使用，直到2011年，然后转换为可再生能源投资组合标准（RPS）以实施更多面向市场的机制。然而，RPS计划下电价和补贴的高波动性削弱了投资动机。在这项研究中，我们估计RPS计划下的多重价格波动如何影响储能项目的最佳投资决策，其重要性正在迅速提高，因为它们可以减轻电力系统中太阳能和风力发电的可变性和不确定性。我们基于实物期权方法进行了数学分析，以估算具有或不具有多重价格波动的储能项目投资的最佳触发价格。我们发现，在多种价格波动下，称为“可再生能源证书”（REC）的补贴的最佳触发价格比没有价格波动时的最优触发价格高出10.5％。如果REC价格的波动性增加了一倍，则该项目需要将最优投资价格提高26.6％，以使投资抵御风险的增加。最后，我们提出一种拍卖计划，该计划同时具有RPS和FIT的优势，以通过消除补贴的波动性来最小化补贴计划的财务负担，并为投资者找到最低的接受价格。