Solar energy for hydrogen production : experience and application in South Africa

Hydrogen is expected to be a key role player in the future energy market for stationary, mobile and electrical grid balancing applications if produced from renewable energy sources. Hydrogen energy technologies include direct power from fuel cell, storage for intermittent renewable energy, and power-to-gas (P2G) applications. In the last year P2G has been identified as having a large potential with several possibilities in itself: (1) Hydrogen is produced from excess renewable energy and injected directly into natural gas networks. (2) Hydrogen along with a CO2 emitting source employing the Sabatier process produces synthetic natural gas (SNG). (3) Hydrogen in a bioreactor employing a biocatalyst increases the biogas energy content by reducing CO2 content. At HySA Infrastructure research focus is on hydrogen production from renewable energy as the central technology for the enhancement of the different hydrogen energy prospects. This paper will focus on presenting results from the recently upgraded solar-to-hydrogen system at the HySA Infrastructure center at North-West University. The previous small-scale solar-to-hydrogen system is upgraded to South Africa’s first commercial scale renewable hydrogen production plant. The main purpose of the upgrade is to increase the hydrogen production capacity and improve system performance. System performance includes the increase of overall system efficiency and to reduce the cost of hydrogen. The paper includes prospects of renewable hydrogen in South Africa, and how solar-to-hydrogen research falls into the bigger picture of hydrogen in South Africa. INTRODUCTION The transition towards a cleaner and more sustainable energy system requires large scale employment of renewable energy sources. Renewable energy sources have low life cycle carbon emissions but also have intermittent characteristics. To benefit from the low carbon emitting power production capable with renewable energy sources, the problem of electricity demand not being in line with production is a major stumbling block [1]. The purpose of renewables for future energy systems is low carbon emissions but also a sustainable supply. The energy source should be available at all times without restrictions [2]. Due to its intermittency renewable energy requires a larger net generation capacity for a higher penetration of renewable energy [3]. This larger net generation capacity allows access energy to be produced during times of surplus and can then be used during times when there is a shortfall. Thus, in order to be more reliable intermittent renewable energy sources require a form of energy storage. A review of energy storage technologies for electric power applications [4], looked at several storage technologies including: flywheel, super capacitor, hydrogen, pumped storage, liquid piston pneumatic, and compressed air pneumatic, with the conclusion being that hydrogen energy storage is not yet viable mainly due to cost. A more recent review on redox flow batteries (RFB) compared the same storage technologies with RFB [5]. The conclusion is that RFB is a promising storage technology. It however is still in a research phase with much promise. A comparison of available energy storage technologies are provided in Figure 1 [6]. Flywheel energy storage, double layer (super) capacitor, and superconductor magnetic energy storage have only seconds to minutes of storage. All the battery technologies (LA, Li-ion, RFB, NaS) have storage duration of hours to days in limited capacity. Pumped hydro and compressed air energy storage have large capacity possibilities and durations of a couple of days but require sites which are limited in South Africa. Hydrogen and SNG have large capacity potential capable of long term storage and seasonable balancing of intermittent renewable energy sources [2]. Hydrogen storage in [6] refers to the P2G applications which is the term given to the conversion of electrical power from excess renewable energy into the