Varistors or Surge Arrestors

Surge arrestors and surge suppresors both incorporate MOV's - Metal Oxide Varistors.
Each particular application weather for line voltage or lightning surges, 120vac, 12vdc, etc., etc. decides the type and rating of MOV to be used.
http://www.rbs2.com/fire.htm
Dont let the bit about fire hazards get to you. Those probably happened because they didnt change there power strips after repeated surges.
The same could be true of a lightning surge arrestor used on a PV array but a brand name such as Delta bulges out after it has been hit and usually can take several hits before it has to be replaced.
MOV's dont last forever.
There is more about MOV's under that fire hazard stuff.