The duck curve refers to the anticipated shape of the electricity demand curve as more solar panels get installed. 

To understand this, let’s start by considering the electrical demand curve with negligible solar energy production. Currently, electrical demand changes throughout the day, but is generally very predicable.

• The demand rises in the morning as people are getting up.

• By noon the demand levels out.

• In the evening, the demand increases again when everyone gets home from work.

The graph below shows a typical electrical demand curve.

With traditional fossil fuel power plants, it is relatively easy to keep up with electricity demand since you can easily increase the production of your plants by burning more fuel.

The issue with solar power is that it cannot be scheduled like a power plant – since the sun follows its own schedule. When the sun is out and rooftop solar panels are producing electricity, there is less demand for power from the grid.

From the electricity grid operator’s point of view, all they see is a reduction in demand for their power during the middle of the day. As more solar power comes online, the electricity demand curve will start to look like a duck.

Why is a duck curve dangerous for the existing electricity grid?

• Sudden increase/decrease in demand: As you can see from the duck curve, the demand changes very quickly. This means that power providers will have to rapidly increase and decrease electricity production during the day. Sudden changes like this are very expensive as entire plants may have to be shutdown during the day, and brought back online a few hours later.

• Stability Issues: With large and sudden changes in demand, it is very difficult to balance supply and demand. This makes it hard to maintain the voltage and frequency integrity of the electricity grid.

So what can we do to combat the duck curve? Here are some ideas grid operators are investigating:

• Implement electrical energy storage to serve as a buffer.

• Share electricity resources between regions.

• Replace coal and nuclear plants with natural gas plants as gas plants can respond to changes more rapidly.

As solar energy becomes more common, we will no doubt see more implementation issues like this appear. The issues are not hard to overcome, but we must ensure that we plan for it.