You guys are probably all pros and know these tips already, but here are a couple ways to cut down on energy use while canning.
Steam canning is now an officially approved method. You need a steam canner or a big pot with a vent on the lid so you can monitor the steam. there are a few differences obviously, but for the most part, you just follow the rules for water bath canning. At this point, they tell you not to steam can anything that requires processing for more than 45 minutes, but that's only because some steam canners only hold enough water for 45 minutes and they don't publish guidelines for individual models. There are models that hold enough water for longer processing times.
Also, you do not need to sterilize jars if you're going to be processing them for at least 10 minutes (or the 10-minute equivalent for higher than 1000' elevations). You still want them hot when you pour the hot food in so you don't shock the glass, but don't waste time and energy boiling them.
I canned 26 litres of salsa with it Friday evening and was very happy. It heats up quickly and maintains canning temperature with the burner turned down quite low. I noticed that the lid on mine didn't seal around the lip of the pot very well, so maybe it was losing more steam than it should and I should have been able to turn the burner down even more and maintain temp. Maybe. I've never used one before so have nothing to compare it to. To keep a big waterbath canner boiling, I have to have the burner turned near to max, though.
This one has a gauge on it to tell you when the temperature is high enough to start timing. I like that because it can be hard to see the steam coming out of the hole in the lid (which is the other way to judge if your temperature is high enough) when the light isn't right or your lid doesn't seal so there's steam everywhere or whatever.
Bonus - it's stainless steel, so I actually used it to make the salsa in two batches, rather than the four batches it would have taken in my regular-sized stockpot.
The thing I am confused about is that steam ought ot be much much hotter than 212 degrees anyway, I'd assumed that steam sterilizing would be much more sterile, no?
Something either is or isn't sterile, so the temperature shouldn't matter in that sense. And steam is actually the same temp as boiling water. Steam feels hotter than boiling water cause it holds more heat energy for its mass than water. If you stick your hand in the steam, it releases all that heat energy when it condenses on your skin. Anyone with better physics knowledge than me is welcome to chime in and explain it properly.
And then the temperature of the steam (or boiling water) is going to change according to pressure, which is why you have to keep your jars in the canner longer as you go up in altitude.