Problem # 1:
Let’s say we have a river able to generate 100 kW. In a 24 hour period, it produces 100 * 24 = 2,400 kWh. Let’s also say that we have a total daily demand of 2,400 KWH, but it is not evenly spread out: for 16 of the 24 hours, it averages 50 KWh, and for the remaining 8 hours it averages 200 KWh.
If we just throttle the turbine back (typical control method) to 50% of its capacity during the off-peak 16 hour period, we will have just dumped 800 KWh, and will then have to have some other source of energy (solar? wind? diesel?) to make up the extra 100 KWh during the 8 hour peak period. If the river is the ‘fuel’, we will have wasted a full third of it. My first obvious thought was to add enough battery capacity to store the excess during off-peak. But then the questions of cost, comparison between different storage technologies, balance between storage and generation, etc. arise.
Problem # 2
The sun shines and the wind blows unevenly throughout the day and throughout the year. (See distribution pattern). The peaks and valleys do not coincide with the usage peaks and valleys. The challenge is to find the most cost effective, environmentally benign, sustainable and efficient way to store the energy when the supply exceeds the demand, for use when the demand exceeds the supply. This storage can take many forms, and addresses both problems.
General how-to information:
- Article in the oildrum about flywheel storage: http://www.theoildrum.com/node/8428
- Good article on how to calculate it all: Got Storage? How Hard Can It Be?
- http://en.wikipedia.org/wiki/Beacon_Power (bankrupt in 2011)
- Lead acid: Best price found is
- Flow batteries: Prudent energy VRB systems
A Costa Rican cooperative effort between Cummins Diesel, AASEA and Earth University: http://www.adastrarocket.com/aarc/AASEA