We can find out the potential osmotic power of a region by estimating how much pure water reaches the sea, and multiplying by the osmotic energy per unit volume of sea water, which is about 0.8 kWh/m^3. This energy per unit volume is the same as the energy per unit volume of water falling through 280m [
]. So in principle, the osmotic power associated with every river meeting the sea is equivalent to a 280m high hydroelectric dam with the same flow of water.
That sounds quite a lot! Perhaps countries with big rivers should look into this. How would it add up for the UK? As in chapter ??, we chop Britain up into ‘England’ (represented by Bedford) and ‘Scotland’ (represented by Kinlochewe). The rainfall in Bedford is 584mm per year, and in Kinlochewe it’s 2278mm per year. Don’t forget that some of this rainfall ends up evaporating from the ground or out of plants. To allow for this water loss, let’s ignore England’s water altogether, and just count Scotland’s. The area of Scotland, shared out among all Brits, is 1300m^2 per person. So the osmotic power (per person) is rainfall volume per day (per person) × osmotic energy per unit volume = 2.3m × 1300m^2 × 0.8 kWh/m^3 / 365 d = 6 kWh/d, if every river had a perfectly efficient osmotic power station at its mouth.
The rest of the world
Let’s discuss big rivers. The Mississippi is the tenth biggest river in the world, discharging 16 200m^3/s. Rather than persisting with the ideal osmotic energy density of 0.8 kWh/m^3, let’s try to be realistic and assume that some yet-to-be-defined technology delivers one eighth of this: 0.1 kWh/m^3. Then the osmotic power from the Mississippi would be about 6GW. The Saint Lawrence discharges 10 000m^3/s of water, corresponding to a potential osmotic power of 3.6GW. The Congo is four times the Saint Lawrence. The Amazon is twenty times the Saint Lawrence.
http://www.withouthotair.com/
]. So in principle, the osmotic power associated with every river meeting the sea is equivalent to a 280m high hydroelectric dam with the same flow of water.That sounds quite a lot! Perhaps countries with big rivers should look into this. How would it add up for the UK? As in chapter ??, we chop Britain up into ‘England’ (represented by Bedford) and ‘Scotland’ (represented by Kinlochewe). The rainfall in Bedford is 584mm per year, and in Kinlochewe it’s 2278mm per year. Don’t forget that some of this rainfall ends up evaporating from the ground or out of plants. To allow for this water loss, let’s ignore England’s water altogether, and just count Scotland’s. The area of Scotland, shared out among all Brits, is 1300m^2 per person. So the osmotic power (per person) is rainfall volume per day (per person) × osmotic energy per unit volume = 2.3m × 1300m^2 × 0.8 kWh/m^3 / 365 d = 6 kWh/d, if every river had a perfectly efficient osmotic power station at its mouth.
The rest of the world
Let’s discuss big rivers. The Mississippi is the tenth biggest river in the world, discharging 16 200m^3/s. Rather than persisting with the ideal osmotic energy density of 0.8 kWh/m^3, let’s try to be realistic and assume that some yet-to-be-defined technology delivers one eighth of this: 0.1 kWh/m^3. Then the osmotic power from the Mississippi would be about 6GW. The Saint Lawrence discharges 10 000m^3/s of water, corresponding to a potential osmotic power of 3.6GW. The Congo is four times the Saint Lawrence. The Amazon is twenty times the Saint Lawrence.
http://www.withouthotair.com/
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