With the constantly increasing penetration of renewables—intermittent power generation—in their energy system, there is in many jurisdictions an equally increasing need for firm, base load capacity. A power capacity that can generate electricity at any time and enhance grid flexibility. One of the responses of the sector to this need is the deployment of battery-based energy storage. Battery energy storage systems (BESS) are in their early years and while utilities and project developers alike see significant business opportunities, system operators and regulators are looking for the most appropriate policies to integrate this nascent technology in a safe and sustainable way. California, the United Kingdom, Germany, Italy, Greece, Australia, to name a few, are introducing support policies to make the projects commercially viable by either bridging the revenue gap or providing offtake long-term visibility -or both- which are essential measures for a successful project finance scheme. For a ramp-up of BESS, lenders and investors must master the technology and what batteries are really capable of and developers must excel in the structuring of project finance with all its upsides and challenges. It is certainly also worthwhile to have some understanding of the principles of energy markets, to fully grasp these complex concepts.