The amount of money you can gain from renting out your equipment vs. the electrical cost is not worth the effort you will need to employ to make this work. Especially for these entry-level spec computers. The best way to monetize is to liquidate them into cash and churn that cash into something more profitable, which is not easy, but it works for those who are creative and passionate enough. Another method is to make them do tasks that frees up your time, or you can delegate tasks that will help you. Good luck on your monetization efforts