Here is a toy scenario, suppose we have 1000 people and they are capable and willing to build a new solar electric system. The problem is, nobody has any money

Here is a toy scenario, suppose we have 1000 people and they are capable and willing to build a new solar electric system. The problem is, nobody has any money. The 1000 people could form an institution, let's call it a bank, that would hand out IOUs to anyone who wants to build and install the solar panels. Some of the 1000 people agree and start building out the electric system. Once the system is in place, people start paying the organization for electricity and then all the IOU holders can get payed for their work. The payments to the organization might come in the form of goats, chickens, timber, or even IOUs! If the organization had used the debt to make a bunker instead of an electric system. The citizens may not be so interested in hanging out and using (paying) for the bunker, so all the IOU holders would be out of luck. In other words, if the IOUs to the contractors aren't eventually repaid. People won't accept IOUs from the organization (bank) anymore.