The agreement says the power station will guarantee up to 20 MVA, that's enough for the first 2 furnaces.
And according to this research note
http://gulfmanganese.com/wp-content...t-cap-42m-PRICE-TARGET-BUY-PT-0.028-share.pdf
A price of 0.11 USD/kWh is a fair assumption.
0.11 USD/kWh is currently 1540 Rp/kWh, which is higher than the price that Low Voltage (LV) connections (households essentially) currently pay in Indonesia. Medium Voltage (MV) connections (which is what GMC will have) pay 1114 Rp/kWh, or 0.079 USD/kWh.
So, do we think they're undisclosed agreement (which is commercially sensitive by the way) is ~38% higher than the going rate for MV connections? If so then its close to what the research note has assumed and GMC still make a healthy profit. It's more likely to be closer to 0.079 USD/kWh than 0.11 though.
Yes they need to pay for at least 40 hours a month (USD 61k/month), this is nothing, and not the concern, the concern will be why the furnaces are down...
And PT PLN is state-owned, it's not going anywhere