The effects of cyclotron proton beam accelerator radiation on single-crystalline and polycrystalline silicon cells have been investigated. The maximum allowable output powers of exposed single-crystalline and polycrystalline silicon solar cells were decreased by 35% and 30%, respectively, as compared with non-exposed solar cells. The effects of proton energies of 10.7 MeV and 20.3 MeV and fluences of 2.28 x 10(11)/cm(2) and 3.24 x 10(11)/cm(2) at the solar cells are also included and discussed.