When designing the ESS used in the Tesla Roadster, developers were faced with an inherent problem of lithium ion batteries. Lithium is an unstable metal, especially during charging, and has the potential to harm users by catching on fire. Eventually, Tesla designed a suitable battery but then faced the challenge of producing them on a large scale, economically and reliably.
After seven different designs, developers came up with what they thought to be a good, safe and reliable design. Word quickly spread, and now there are a number of manufacturers asking about the technology including several major auto companies.
The Tesla Energy Group has now been formed and will be working to provide ESS technology to other companies and at the same time reducing the cost of the technology by driving up the volume of cells used in cars more quickly, eventually shifting demand towards electric vehicles.