Here's some math for you.
Those solar panels will provide 40 kilowatts of energy to the ships crew, .2 per cent of the total ships energy consumption.
$2,400,000 for .2%.
Assuming you had the space, it would only cost $12 billion dollars to build a fully solar powered freighter.
Or you could spend $700k or so on a Sky Sail and save 20% of your fuel costs, a couple of thousand dollars per day of operation.
Green for the sake of green can be really dumb sometimes.