The scheme has been successful (about 118,000 m2 of SWH installed). Its main advantage lies in the fact that payment through the utility bill reduces risk of credit default (STEG can cut off supply in case of default) and lowers collection costs. The customer now legally carries the debt whereas in the earlier version of PROSOL the installer was the legal debtor. The programme was extended in 2007 to the tertiary sector. It is also beginning to emerge for residential customers. Under the TPPPA model, a third party designs, builds, owns, operates and maintains the solar systems and sells back solar-generated electricity to the end-user.