In the pa per, in a long-term test pro ce dure, monocrystalline sil i con cells were sub jected to exam i na tion. Cells were tested in well-con trolled lab o ra tory con di tions and real con di tions. In lab o ra tory con di tions, white light of the ar ti fi cial sun and mono chro matic bright ness of yellow so dium lamps were used. The test ing was aimed at achiev ing the same ag ing re gime in the lab o ra tory con di tions as in real con di tions. This would al low for the lab o ra tory ag ing al gorithm of so lar cells as in real con di tions, to be de fined, hence their work ing life of com mer cial ex ploi ta tion in ur ban ar eas to be de ter mined. By com plex math e mat i cal meth ods, i. e. us ing the the ory of time du ra tion, it was found that lab o ra tory ex pos ing so lar cells to ther mal neutrons causes their ag ing with the same mech a nism as in real con di tions Key words: so lar cell, ag ing, gamma ra di a tion, ra di a tion by fast and ther mal neu trons