data <- read.table(file="data.txt", header=TRUE, sep="t")
Power <- as.ts(data$y)
Temp <- as.ts(data$temp_MA)
linearfit <- lm(Power~Temp)

x <- seq(from = -19, to = 25, by = 2) #breakpoints
require(segmented)
fit <- segmented(linearfit,seg.Z= ~Temp, psi=list(Temp=x))
summary(fit)
plot.segmented(fit)