"If one now could replace the electrodes; say a piece of coal from renewable source and a compatible renewable partner for it, that might work in terms of making energy available for human use."
=^.^= that sounds a lot like the 'albanian style' microbial fuel cell..
sorry i haven't been working on this, there is just not enough time.
Why Copper Garden Tools?
Copper gardening tools enrich the soils with coppertrace elements and thereby provide plants with essential nutrients
They are hardwearing and will last for years
Stay free of rust – but age with a graceful bronze patina, perfect for the coastal gardener
They have sharp edges
They have an incomparably longer lifespan than devices from iron
Viktor Schauberger came to the assessment that cultivating the soil with copper implements would be more beneficial to the Earth and lead to healthier plants. In his writings, he listed several reasons for this.
Minute amounts of copper create the conditions for beneficial micro-organisms
Penetrate the soil easily -low coefficient of friction- less tendency for clay to cling to the tool
Copper is not magnetic - so does not disrupt the electrical fields in the soil
Can be kept sharp with a whetstone, file or by peening (hammering the edge against a steel anvil)
Production experience since 20 years. Quality confirmed by enthusiastic gardeners.
https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/copper-for-the-garden.htm