These look like pre-paid power-minutes or something similar. So you pay for 500 minutes of power, and when you've used it all the power stops. When the solar

These look like pre-paid power-minutes or something similar. So you pay for 500 minutes of power, and when you've used it all the power stops. When the solar panel knows when you've paid for however many minutes are required to "own" the device you stop having to buy minutes for it. So they could run the risk of people just not paying for the device anymore because they can't afford or don't want it anymore, or tamper with it to try and get it working without paying it off. They'd still have the 10% initial fee plus any minutes they paid for already.