In this short report we analyse the effect of PV power penetration and tolerance margins on curtailment based on day-ahead forecasts of PV power generation. The analysis used data of Kyushu region, simulating 3 PV power penetration scenarios and 4 tolerance margins used to characterize when curtailment happens. The results show that tolerance margins are particularly effective in scenarios of low and medium PV power penetration. In this case, curtailment hours were reduced by 31.6%. On the other hand, PV power penetration had a strong effect on both curtailment detection and curtailment error when they are based on forecasts of PV power.