The standard unit for discussing power is the watt, and the standard unit for discussing energy production is the kWh. I am using these here when discussing energy issues.
These units have the advantage of being used universally. They have the disadvantage of being hard to visualize.
In contrast, every one has an idea of what kind of power one horse could pull. The old unit of “horsepower” therefore is easier to understand for people who don’t spend a lot of time thinking about these questions.
The Wikipedia article about “horsepower” is rather long, but for my purpose here it is enough to note that one horsepower is 746 watts.
That means one kWh is equivalent to having a standard horse working for about eighty minutes. If you want to get that done, you need to buy a horse, buy some fodder, build a stable, employ someone to look after the horse (or do so yourself), and deal with the manure.
Good luck with getting all that for the wholesale price of a kWh of around 5 cents euro on the German market.
If later generations need to get back to animal power because they have run out of fossil fuel, they certainly will need to pay much more in today’s money for one kWh. And a difference of 1.6 cents euro (the increase in surcharges in the German feed-in tariff system next year) will seem trivial to them.
They would be right, in my opinion.
I recall that some of the stories in Paolo Bacigalupo’s “Pump Six” I reviewed on this blog explore such a world.
I also recall that Jared Diamond wrote in “Guns, Germs and Steel” that having the horse available was a large comparative advantage to humans in Europe compared to Africans, who were stuck with the zebra.
Standard rooftop solar power systems only have a couple of kilowatt capacity and are viewed as small. But if you get 5 kW of peak power, you have the equivalent of close to seven horses working on your roof. That’s not too bad.