Our autopilot uses a reversible pump that sends hydraulic fluid backwards and forwards through a rather stout cylinder. It has ample power to steer the boat, much more than I have certainly!
For those times when you do not want to steer by autopilot, or when it is off, a bypass is installed. Look at the photo on the right. The steering cylinder is at the very bottom of the picture. The black and black-and-orange hoses carry the hydraulic fluid from the pump (not depicted) to the cylinder. The bypass line is the shiny "inverse U" shaped pipe. At the rear you see a metal box with a plastic black blob attached to it with another smaller blob attached to it and a black cable sticking out. The metal box contains a hydraulic valve that is controlled by a solenoid (electromagnetic coil) in the bigger black box. Industry has, smartly, standardized the size of these solenoids and even the connectors.
The story of today is about replacing the smallest of the two black boxes. This is a replacement for the standard connector that attaches to the industry standard magnet. As you can see here it isn't much to look at. Instead of the normal connector which only contains a bit of plastic and some screws, this version contains a small electronic circuit that aims to reduce the power used by the magnet. The reasoning behind this product is that the current used by the solenoid to move the valve initially is much higher than the current required to keep the valve open. Since the standard coil is just a bit of wire it doesn't know how to do this. And that's where the Ecopilot comes in: it measures the current and reduces this to the point where the valve just stays open.
With my solenoid the power consumption went from 1.4 A @ 24 V to 0.3 A. That is a 1.1 A saving, and adds up to a 26,4 Ah savings per day (when sailing). So this € 110 device is a very worthwhile investment -- easily cheaper than adding another solar panel.
To find one on sale, search the internet for "ecopilot 2204028" for the 24V version and "ecopilot 2204027" for the 12V version. Note that most web stores selling this will be French. The one that I ordered from (www.tyboat.com) was very helpful but their online ordering process did not yet take into account any increase in shipping costs outside France... C'est la vie.