That should already be priced into the present value of the property. On the other hand, if you can see the land value going up, that'll have an effect on expected property tax rates; but that should be a relatively minor line item. And not all cities are expanding in that way; if you pulled this right now in the States, in fact, there's a good chance that the cheap land you're picking up would once have been intended for a subdivision before the bottom fell out of the housing market.

Meanwhile, the barge full of solar panels will probably have needed hull repairs at least once in those fifteen years, and its batteries (assuming lead-acid, which give the best energy-to-price ratio with current technology, and assuming a cycle per day) will have been replaced two or three times.