Since the batteries are a sizeable investment in any autonomous power arrangement, they need to be protected from overcharging which will shorten their lifespan. A dumpload is a secondary place to put power when the batteries are fully charged. Simply put, the dumpload takes the power when the charge controller senses that the batteries are full, to protect them. Once the power has been diverted, the dumpload uses the power for something productive rather than lose it directly into the ground.
What constitues a typical dumpload?
A secondary heating element added to a hot water heater.
Extra power is used to augment gas or propane usage keeping the water warm.
A backup water pump for livestock. Since you know the cows are going to drink some water today, you can simply pump some water there when convenient. Whatever the backup pump doesn't cover, you do manually when you feed the cows. By using the main pump less, you save power through the batteries, elongating the life of the systems.
A light bulb in a conspicuous place is a great alarm. Every time the light turns on, you know you should run some power, or you are going to lose it. The light bulb is now your clue that it is the "Optimal Time" for laundry, cooking, or something that involves power. If you have nothing productive to do, it would be the time to turn up the stereo without guilt, you have to use the power or your going to lose it.
