NAESB REQ.21 Energy Services Provider Interface (ESPI)
The NAESB REQ.21 ESPI Model Business Practices define the data exchange protocol for transferring retail energy usage information from a utility (Data Custodian) to a Third Party with the Retail Customer's authorization. ESPI is the industry-consensus standard that is the basis of every Green Button implementation in North America and is the standard endorsed by the Green Button Alliance. NAESB publishes the standard; it does not operate an ESPI endpoint — each Data Custodian utility hosts its own, so there is no NAESB base URL. The Atom/XML payload schemas (NAESBespiSchema.xsd and retailcustomer.xsd, v3.3 and v4.0) are released under the Apache License 2.0 as a one-time exception to the NAESB Copyright Policy and are harvested here verbatim. The narrative Model Business Practices themselves are copyright-protected and must be purchased or obtained through NAESB membership. The v4.0 schema encodes an OAuth 2.0 authorization model directly — ApplicationInformation carries authorizationServerAuthorizationEndpoint, authorizationServerTokenEndpoint, authorizationServerRegistrationEndpoint, GrantType, TokenEndPointMethod, scope and OAuthError.