Ah. "Loans precede deposits".
What this means is that when you go to the loan officer at the bank, and they decide whether or not to give you a mortgage (or business loan, or line of credit, or whatever), they *don't actually check whether they have the money*.
So, sometimes they find a lot of people walking through the door who they think are creditworthy. They give loans to all of them! So sometimes, at the end of the day, the accounting people say "Uh, you loaned out $20 million more than we actually had." They phone up the Federal Reserve and get a quick loan for $20 million immediately.
The next day, the bank tells its deposit department to start running ads and trying to chase up depositors, so that they can pay back the Federal reserve loan. If they're lucky, after a few weeks they manage to chase up those deposits. Possibly by *offering higher interest rates on CDs and savings accounts*, which costs them money in the future. This can drive them into a loss-making position. They prefer to fund the loans with longer-maturity stuff like CDs, to reduce the risk of bank runs.
If they're unlucky, they can't chase up the deposits, the Federal Reserve orders them to recapitalize, and they have to issue stock or long-term bonds or something similar.
So, SolarCity was running the same business model -- making leases (which are a lot like loans in this regard) willy-nilly, buying and installing the solar panels using very-short-term lines of credit (stuff payable in weeks or months) without really lining up the long-term financing first -- and then they tried to finance the installs afterwards. But they couldn't just get a loan from the Federal Reserve to cover the shortfall, because they weren't a bank!