Great to hear from you. 1000mT sounds like quite a lot indeed. To give you an impression, it's anywhere between 5 and 10 million potatoes. Having said this, it's not that big either. Industrial storages can be at least 20 times as large.
We've chosen 1000mT is it corresponds with the amount of potatoes that are harvested in and around a typical farmer village in Northern Bangladesh (at least within a radius of 5km). Actually, given the right training, farmers will be able to harvest much more potatoes (in The Netherlands the yield per acre is about eight times bigger).
Getting back to your question, yes we have been looking at cooling and solar. Fully powering the storage on solar year round is practically impossible as we would need a whole lot of battery power to store the solar energy. We're currently exploring a hybrid option that combines power from the grid (or a diesel generator) with solar. Send me a direct message if you're interested in the exact figures for cooling and power supply.
Great that you mention evaporative cooling, as we were part of a pilot a year ago to set up a storage that runs without electricity. The results were mediocre though, in order to properly store potatoes we need to really cool down the air (and control humidity and CO2-levels). We may want to use it for pre-cooling, which takes about one to two weeks and happens after pre-processing and before the potatoes go into the cold storage. During pre-cooling we bring the temperature down so that the potatoes can adjust to a colder climate and our cooling equipment has less of a temperature drop to take care of.