mena661 wrote:
HiTech wrote:
You get more energy from the solar panels into the load by sending it directly, rather than by charging a battery, then discharging it into the load. Batteries let you time phase your usage, but at a cost of wasting some of your amp hours from the solar PVs.
Jim
Must be just above my head. Sorry I just don't see that.
Anytime you convert energy from one form (electrical to chemical, then chemical back to electrical), there is loss. All things being equal, it is better to convert it fewer times. That's what solar driving the load directly does. Plus the extra resistive loss of high current traveling in through the battery wires then back out the wires again at high amperage. Plus the loss at the extra connectors for the battery terminals. ...etc. Look up the different types of charge efficiency for lead acid batteries if you are really bored.
The mechanical equivalent is rolling a rock up a hill, to roll it down a hill, to use its rolling energy. Because of friction, it's less energy to just roll it in the first place, than have the extra loss of rolling it up the hill, to let it roll down later.
From a systems point of view, batteries are loss we accept in the system to be able to accumulate more charge than we could get instantaneously from the charging source, or for time phasing. But if you can skip the battery all together, it is inherently more efficient to have fewer loss points and energy form conversions between the source and the load.
It varies with a lot of variables including charge rate, but
This paper shows that their efficiency of charging a particular Trojan 12v jar at a fairly low current from 79% SoC to 84% is only 55% efficient, for example.
Jim
