I have done something similar to you with respect to the hydro project as well. New Zealand has lots of its hydro producers listed, meaning you can get a very good estimate of Market Cap per MW installed on generic hydroelectricity schemes in New Zealand.
Easiest thing to do though is follow your model again for the hydro project, but then assume that they only receive an arbitrage on the total sales price of 0.01c (lets assume 0.001c or 10% arbitrage).
450MW could be produced per hour, but only for 6 hours (off the top of my head - I think I read this in the research note).
As you said;
1 million w = 1 MW
So 450 million x 0.001c = $450,000 an hour
x 6 hours a day = $2,700,000 a day
Now lets assume that this opportunity is only around for 20% of the year
x 365 day's x 20% = $197.1 mill a year
Lets say up keep etc cut into this revenue so the bottom line only sees 20%;
197M x 0.2 x PE of 10 = $400 million market cap + solar addition.
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