| Intermediate Technology Education | Energy and Power Technology | Design Stage 2 | Topic 6 | Optional Activity 4 |

Renewable Energy Storage

The purpose of this activity is to examine how solar and wind energy can be stored during peak activity time
  • Learn why solar and wind energy devices are not constant sources of electrical energy
  • Investigate the components needed for a useful storage system
  • Use rechargeable batteries to store the energy output from a photovoltaic solar cell array and a DC wind generator

Energy Storage

Solar and wind energy are variable sources. That is, they do not provide continuous power as do hydro, thermal, and nuclear sources.  It is obvious that winds are constantly changing in speed and direction and solar panels have zero output at night and reduced output on cloudy days. In addition, solar panels that are fixed only output their maximum energy at one time of the day when sun shines directly on them. As well, for part of the year, the sun's angle is such that the panel gets less radiant energy.

If devices need to be powered 24 hours a day, energy must be provided from other sources, or excess energy generated during peak hours needs to be stored.

Battery Storage

Consider the following block diagram

Figure. Block diagram of solar energy production and storage

For purposes of this activity, we will consider a solar array as the source of the DC energy. Let's look at each of the components from the image above:

  • Photovoltaic array outputs pure DC energy
  • Battery charge controller is an electronic circuit that makes sure the battery charges at an optimal rate and does not overcharge
  • Storage battery holds energy for off peak times and also helps to keep the voltage at a constant level
  • DC devices can use DC energy directly eg. 12 volt lights
  • DC-AC converter (also called a power inverter) changes DC current to 120 volt, 60 Hertz AC current
  • AC devices found around the home can use the AC energy provided the converter is powerful enough
  • Excess AC energy can be sent through a traditional energy meter which usually measures energy coming into the home. (This step would not occur in an isolated location where normal AC energy is not available.)
  • The AC power grid accepts the excess energy to be used elsewhere. It can also supply AC energy for the home

This process can be deployed on a small scale as illustrated by the next image. The heart of this system is a rechargeable sealed battery with a charging circuit and jacks for energy input and output. The cover of the unit has been removed to show the battery and control circuit.

Figure. Commercial 12 volt electrical storage unit

The image below shows the storage battery and the rest of the devices needed to complete the system—a photovoltaic solar panel and a power inverter. These components were purchased for less than $100. This configuration is useful for camping since it can power small DC and AC devices such as cell phone chargers, audio systems and laptop computers. Several solar panels can be connected together to lessen the charging time.

Figure. Complete solar charger and storage with 120v AC inverter

For More information

For more information on these topics, check out these web pages

When you are ready, go to Your Turn