I just posted a new video. The main difference with the lab manual is that instead of using a DC wattmeter I use two multimeters: One is set up to measure amps and the other is set up to measure volts. Most high schools and colleges already have multimeters (used is physics) so this can save you money. This is the same way I measured electricity generated from a cordless drill. In this new video I also incorporated a slightly more simplified equation for calculating the cost-effectiveness of solar panels. Unfortunately I did not think of this when I wrote the second edition of the lab manual, but those who have this edition can easily make the modifications in your book.