[R] fitting a sinus curve

[maaariiianne]

Dear R community! 
I am new to R and would be very grateful for any kind of help. I am a PhD
student and need to fit a model to an electricity load profile of a
household (curve with two peaks). I was thinking of looking if a polynomial
of 4th order, a sinus/cosinus combination or a combination of 3 parabels
fits the data best. 
I have problems with the sinus/cosinus regression: 
Thanks a lot, 
Marianne 

time <-
c(0.15,0.30,0.45,1.00,1.15,1.30,1.45,2.00,2.15,2.30,2.45,3.00,3.15,3.30,3.45,4.00,4.15,4.30,4.45,5.00,5.15,5.30,5.45,6.00,6.15,6.30,6.45,7.00,7.15,7.30,7.45,8.00,8.15,8.30,8.45,9.00,9.15,9.30,9.45,10.00,10.15,10.30,10.45,11.00,11.15,11.30,11.45,12.00,12.15,12.30,12.45,13.00,13.15,13.30,13.45,14.00,14.15,14.30,14.45,15.00,15.15,15.30,15.45,16.00,16.15,16.30,16.45,17.00,17.15,17.30,17.45,18.00,18.15,18.30,18.45,19.00,19.15,19.30,19.45,20.00,20.15,20.30,20.45,21.00,21.15,21.30,21.45,22.00,22.15,22.30,22.45,23.00,23.15,23.30,23.45,0.00) 
watt <-
c(70.8,68.2,65.9,63.3,59.5,55,50.5,46.6,43.9,42.3,41.4,40.8,40.3,39.9,39.5,39.1,38.8,38.5,38.3,38.3,38.5,39.1,40.3,42.4,45.6,49.9,55.3,61.6,68.9,77.1,86.1,95.7,105.8,115.8,124.9,132.3,137.6,141.1,143.3,144.8,146,147.2,148.4,149.8,151.5,153.5,156,159,162.4,165.8,168.4,169.8,169.4,167.6,164.8,161.5,158.1,154.9,151.8,149,146.5,144.4,142.7,141.5,140.9,141.7,144.9,151.5,161.9,174.6,187.4,198.1,205.2,209.1,211.1,212.2,213.2,213,210.4,203.9,192.9,179,164.4,151.5,141.9,135.3,131,128.2,126.1,124.1,121.6,118.2,113.4,107.4,100.8,94.1) 
df<-data.frame(time, watt) 
lmfit <- lm(time ~ watt + cos(time) + sin(time), data = df)  



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