Solar energy generation along highways. Refer to the International Journal of Energy and Environmental Engineering (Dec. 2013) study of solar energy generation along highways, Exercise 9.47

(p. 491). Recall that the researchers compared the mean monthly amount of solar energy generated by east-west and north-south oriented solar panels using a matched-pairs experiment. However, a small sample of only five months was used for the analysis.

How many more months would need to be selected in order to estimate the difference in means to within 25 kilowatt hours with a 90% confidence interval? Use the information provided in the SOLAR file to find an estimate of the standard error required to carry out the calculation.