Gravity Compressed -Air- Hydraulic- Power-Tower Energy Storage Plants

Abstract

In the era of the increasing implementation of renewable energy sources in the electrical energy supply the demand for energy storage continues to grow. This is because the renewable energy sources, mainly in the form of wind and solar energy, are sustainable, but at the same time are subject to natural fluctuations. The wind does not always blow, and the sun does not always shine. Therefore, a stable and reliable power supply is more challenging than ever. It now must regulate fluctuating electricity demand and fluctuating electricity supply. At the same time decentralized energy supply systems based mainly also on PV and wind energy (e.g. as hybrid systems) storage requirement will become a key component of these local electrical energy supply networks especiallyy to balance the energy demand and supply. Among the many storage techniques an important example is the Hydro-Power-Tower an innovative hydraulic energy storage system based on pumped storage technology. Depending on the actual storage method that can be based on gravity (lifting / falling of weight in a vertical underground or above ground Tower), on air compression / decompression or on a combination of both techniques, can be distinguished the following Storage systems, Gravity Hydro Power Tower Storage (GHPTS), Compressed Air Hydro Power Tower Storage (CAHPTS) and Gravity Compressed Air Hydro Power Tower Storage (GCAHPTS).The GHPTS is the classic form of the Hydro Power Tower Storage and is widely discussed in the literature with scientific results and technical applications especially in the last decade. Besides the many advantages of (GHPTS) an important disadvantage is the very high weight and high cost of the tower piston (usually metal) which is the key component for potential energy storage. The storage based on Compressed Air is also widely applied in different storage systems but less so than Power Tower. Regarding the application of compressed air, in the PTS system, some own results are to mention, proposing a replacement possibility of the heavy overload piston of (GHPTES) using a part of the tower as a compressed air reservoir. The present study considers the combination of both storage techniques Gravity and Compressed Air integrated in a so-called Gravity-Compressed-Air-Hydro- Power- Tower - Storage (GCAHPTS). The combined influence of compressed air pressure and high of weight tower piston on the stored energy will be analysed. The obtained results allow the optimal design of such a combined power tower storage system. When the compressed air or high weight piston is missing on obtain GHPTS or CAPTS respectively.