I learned a new term yesterday for something we have been doing for five years. The term is Daylight Drive, and it is used to describe an off-grid solar power system that doesn’t include batteries. When you are charging off of our solar panels at the field school, we recommend that you bring your own battery. When the sun is shining, you charge your battery. Then at night or when the weather is bad, you use your battery to charge your devices.
There’s an old farm saying that goes “Make hay while the sun shines.” The idea behind a daylight drive system is to store energy and do your heavy lifting while the sun shines. Why? Because batteries are usually an expensive weak link in an off-grid solar system. I came to use this system because I got tired of maintaining lead-acid batteries for other people who wouldn’t take care to not discharge them too much so as to prolong their life. This article from No Tech Magazine describes the system used at the Living Energy Farm in Virginia. They call it the Living Energy Farm DC Microgrid Energy System, and it is setup where they do all the heavy lifting using power directly from the solar array. They also maintain a much smaller battery bank that can keep lights on at night, but is not scaled to run machinery.
Our system where students maintain their own battery by charging it while the sun shines might not be technically a Daylight Drive system because there is a battery involved, but it operates with the same idea of make power while the sun shines.
If you are interested in different approaches to solving problems with solar power, it is worth a read. Here’s a pdf that Living Energy Farm puts out that describes their system titled DC Microgrids: Home Power With A Dramatically Reduced Financial and Environmental Pricetag.
This thread at Permies.com discusses the idea in some detail.