Originally Posted by boat_alexandra
It's actually very slightly more efficient than using a controller because the controller consumes power.
The PWM controllers have very low self consumption
. Good MPPT
controllers often have much higher self consumption
, but make up for this by using voltage conversion to extract more power from the panel than is possible from direct connection.
The real test for efficiency is how much power you can squeeze into the battery
during the short daylight hours. Here any controller is much more efficient than direct connection during the absorption and float stages. The controller allows the battery
voltage to be kept at the maximum that can be accepted without overcharging.
Direct connection only allows for a very crude voltage control even if you monitor
things carefully. Thus with direct connection the voltage at times will be too low, leaving the battery at a lower SOC, or too high. Neither is optimum. A controller will maintain the battery voltage at the highest level it can reasonably accept and will adjust this continuously.
The drawback of not using a controller is inconvenience and shortened battery life. For most people the cost of the controller will be more than re-paid in savings on battery costs. If your battery costs are zero I can understand that using a controller makes far less sense, but this situation does not apply to most people.