The California state in USA has been on the fore front of power sector transformation. In 2015, California lawmakers had passed a climate-change bill making it mandatory that the Golden State should get 33% of its electricity from renewable sources by 2020 and increase the production to 50% by the year 2030. The aim was to increase use of solar photovoltaic cells significantly especially in the residential area. The plan seems to be largely working. They seem to be well on track to meet their 2020 target and have already achieved 27% of their electricity in the form of renewable energy. But there is a hitch. According to a report by GE, California’s famous sunshine helps produce lots of solar electricity, but only during the day—when the demand is typically low. The report states that power demand peaks in the morning as people get ready for work or school. This usage drops while they are away during the day, that’s when maximum power is generated. Later, in the evening when they return home, the demands peak again as ACs, TVs etc are switched back on typically between 7 to 9 p.m.
To explain why it is called the “Duck Curve”, let us simplify this with the help of a graph given below. The blue line represents a typical electricity load pattern. The Grey line represents solar production on an average day. The difference between the two is the net load (represented by the orange line) that needs to be met by conventional sources. As solar production is increasing the net load curve is taking the shape of a duck’s belly).When the sun goes down, the demand for power from conventional power plants needs to quickly ramp up. In a span of 3 hrs in the evening the conventional sources need to ramp up production by almost 10 GW.In fact the California grid operator expects this problem to continue to worsen over next few years. See the graph below that shows how the ramp is becoming steeper year over year.
This is a practical problem as renewables become more widespread and their intermittency creates new challenges for effective management of the grid. India has set itself an admiral target of 175 GW of Renewable energy by 2022. The target will principally comprise of 40 GW Rooftop and 60 GW through Large and Medium Scale Grid Connected Solar Power Projects. With this ambitious target, India will become one of the largest Green Energy producers in the world, surpassing several developed countries. As is clear, generation output from solar before sunrise and after sunset is 0 MW.The power system works by doing real time balancing of supply and demand. The intermittency in renewable power generation creates a huge need for flexibility in the grid. The change in the net load needs be nullified by increasing output of other power plants, discharging energy stored in batteries or other storages etc. The “duck chart” suggests that flexible, non-solar energy resources will increasingly be called upon to compensate for the sudden drop in solar power when the sun goes down. An expected all India duck curve is provided below, extrapolated with just 20 GW of Solar generation connected to the grid.Today, most of the electricity is produced from coal based power plants in India.
They have a low ramp-up / ramp-down rate. This means that the Indian Grid will need to adapt to meet this flexibility challenge. It will need to look at a number of alternates to handle this challenge. On the supply side the biggest change needs to be recognition of ramp-up / flexible / ancillary resources as special and to have a separate pricing model for them. Hydro resources can very quickly ramp-up production and will need to be used more judiciously. Gas based power plants can also act as great peaking or ramp-up resources and will need to be priced and deployed appropriately. More supercritical coal thermal power plants will need to be built which can better handle lower base capacity and sustain higher number of starts/ stops and ramp rates. Grids will need to deploy more automate generator control units to be able to quickly respond to changes in an automated fashion. Also grid storage solutions like pumped hydro and newer means like battery storage etc. will need to be researched and invested in.
On the demand side, time of use pricing should help flatten the peaks to some extent and provide price signals for some of these peaking resources. This should be accompanied by products like Demand response where customers are incented to move their demand to times of day when power is cheaper helping reduce peak demand and therefore the ramp rate needed. This will also mean more detailed planning for generation, demand and transmission and to keep sufficient contingency for unexpected variations. All of this will require state of art grid management with increased real time supply demand balancing, monitoring and ability to control and react to changes. Our clients in North America are actively looking at solutions to handle this better and are reaching out to us to help evolve their market processes and systems to better prepare them for the future.