The SRTM download functionality in SolarFarmer (and WindFarmer Analyst if you use that) has been problematic over the last couple of days. The API web service that SolarFarmer uses was completely down on Wednesday and no downloads available yesterday. It seems to be back up and running ok today.
The website for the API that we use (https://m2m.cr.usgs.gov/) had a status message when it was down, so check there if it doesn’t appear to be working. Also, sometimes downloading them manually still works even when the API we use doesn’t, so check out the instructions on downloading tiles manually in our online documentation in that case.
I’ll keep an eye on it over the next few days, but hopefully it’s stable again. Sorry for any inconvenience!