Four ways to make the sunlight last all day

21.09.2023

Toni Darwish, Director of Development, Region Americas, Ørsted

1,625 hours. 

That’s the average amount of sunshine Berlin gets annually. Compared to cities like Rome, Dubai, and Sydney – which average 2,500-2,800 hours of sunshine per year – that isn’t much. Yet despite its long winters, Germany has one of the best developed solar power industries on earth.

In fact, many of the first movers in solar were countries with moderate climates. They developed the technologies and economies of scale that make solar energy what it is today: the world’s cheapest, fastest-growing source of electricity. This foundational work has enabled many countries to rapidly scale up solar power without requiring generous subsidies.

However, having inexpensive, reliable technology available is just one part of the solar puzzle. To accelerate solar power’s deployment, American developers need to make solar energy last – even when the sun goes down.

Making the sunlight last all day

When we talk about “making the sunlight last”, it’s a way of discussing two related issues with American solar power: intermittency and value.

Solar energy is an intermittent power source – that is, it comes and goes. Because the sun sets each night, solar farms can’t generate energy at all hours. This means that solar projects can’t always provide energy when consumers demand it.

To be clear, when the sun is shining, solar is a great energy source. When photovoltaic (PV) panels are first added to a region and start supplying energy to the electrical grid, their power can easily meet daytime demand. That’s the lights in your office, or your home air conditioning, for example.

The challenge comes as solar power floods the electrical grid during the day. This influx of power can reduce the daytime value of solar energy to $0. When solar power is offline at night, demand spikes can require expensive backup power to supply. If developers can’t get decent power prices during the day and don’t have the storage to meet evening peaks, they may not build the next solar plant.

So how can we overcome solar’s intermittency and the loss of value it creates?

Developing flexible energy systems

A ‘flexible energy system’ is an energy ecosystem that can dynamically harness intermittent energy sources. There are many technical, operational, and economic changes that could help develop a flexible energy system for U.S. solar, including:  

• Better grid infrastructure: Adding long-distance transmission lines and upgrading energy distribution grids would vastly improve solar’s flexibility. This infrastructure could connect solar-generating areas with solar-consuming areas across time zones – imagine the sunny Southwest powering major cities countrywide. Grids covering larger regions can lower mismatches between supply and demand on average, limiting drops in solar’s value as solar energy reaches more of the grid.


• More energy storage: Storing excess solar energy for later use would help with evening demand. Today, lithium-ion batteries with a maximum 4-hour energy capacity are the most common storage systems. While no cost-competitive, long-duration battery system yet exists, promising innovations are emerging. Once scaled, these technologies could economically store solar energy for more than 100 hours.


• Demand-side measures: Dynamically stimulating demand when solar reaches its daytime peak could maximize the value of solar generation. For example, people could be incentivized to charge their electric vehicles (EV) when excess solar energy is available. These EV could then work as mobile batteries, discharging energy to support the grid when renewable energy is scarce – as some automakers have already discovered.


• Complementary clean energy sources: When solar can’t meet evening demand, other clean energy sources could step in. These could be intermittent energy sources like wind, or predictable, dispatchable power, like geothermal. Electrical grids using both can reliably meet customer demand while eliminating emissions.

The added value of digitalization

First, digitalization could make the electrical grid smarter – meaning, more able to dynamically respond to different scenarios.

Think of the grid like an orchestra, where the grid operating system is the conductor. Distributed solar power is the woodwinds. Demand from homes, vehicles, and businesses are the brass. Distributed energy resources, such as industrial machinery or home water heaters, are the strings. With digitalization, Maestro Operating System could optimize his performance, choosing when to distribute or store energy, when to stimulate demand, and how to best use available solar energy.

Second, Artificial Intelligence (AI) will increase efficiency, and therefore the value, of solar energy. For manufacturers, AI could optimize panel production, delivering more PV panels with fewer defects and a longer operational life. AI-supported drones could help optimally design and monitor solar farm construction. Operations also stand to benefit, with AI using electrical signals from solar arrays and thermal imagery from drones to detect anomalies and identify repair needs.

What American solar stands to gain

Solving the problem of sundown will require improved infrastructure, greater storage capabilities, increased digitalization, and the development of more renewable energy of all kinds. While this won’t happen overnight, supporting these developments will serve America in the long-term, enabling the country to generate 50% of its energy from solar power.