Principal energy officer Kipola So'otanga said the hospital had previously been powered by a generator which only gave it power for six hours each day.
King Tupou VI commissioned the new system for when he visited the island for its Agricultural Show last week.
Equipment such as electric fans, refrigerators, lights and others can operate through the system, Mr So'otanga said.
A team from the Energy Department was also replacing existing solar home lighting in 122 households in Niuafo'ou, with the new units having a lifespan of 10 years.
