photovoltaic curves

how to make E =ΔP/ΔV=P(n)-P(n-1)/v(n)-v(n-1) from curve of p&v of pv in simscape for fixed load coz every time i do it it produce error that ΔV=0 then it divided by zero when i put switch to detect zero i producer error at some Resistance

plz anyone can help