•1992:
start of development by Henk Oldenkamp
•
•1994:
announcement / first papers on international conferences
•
•1995:
introduction (small series) by OKE-Services
•
•1996:
start of cooperation between OKE and NKF
•
•1997-2003:
production and distribution by NKF, more than 80 000 inverters
were sold (about 8 MWp)
•
•2001-2003:
problems occur with installed OK4’s, due to production
failures
•
•2003: NKF
suddenly stops production and distribution and ends cooperation
with OKE-Services
•