Why is Energy Storage the Ultimate Destination for Photovoltaics?

Introduction: Starting from a Case of Power Grid Congestion

Imagine you are a power grid dispatcher. One noon, under bright sunshine, hundreds of millions of PV panels across the country are generating electricity at full capacity, with the power output reaching an astonishing figure—even exceeding the national electricity demand at that moment.

Would you be overjoyed? No, you would break out in a cold sweat.

This is because electricity has a fatal characteristic: it can hardly be stored on a large scale. The electricity generated must be consumed instantly, and the power generation and consumption of the entire grid must maintain a precise balance at all times. Otherwise, frequency and voltage fluctuations will occur. In mild cases, equipment may be damaged; in severe cases, large-scale power outages or even grid collapse could result.

As a result, you are faced with a dilemma:

– Option 1: Disconnect some PV power plants from the grid and force them to stop generating electricity (referred to in the industry as “curtailment of wind and PV power”). This directly wastes valuable clean energy and huge investments.

– Option 2: Instruct thermal power plants and hydropower plants to reduce their power generation to make way for PV power. However, thermal power units (especially coal-fired and nuclear power units) are not like light switches that can be turned on or off at will. Frequent startup/shutdown and load reduction not only cause equipment wear but may even increase carbon emissions.

This hypothetical “power grid congestion” is precisely the most real and core pain point in the current global energy transition. And the key to solving this dilemma lies in energy storage.

Energy storage has become a core link in the energy transition, essentially to address the mismatch between energy supply and demand in terms of time, space, and stability. As the fastest-growing renewable energy source today, PV inherently has the characteristics of intermittency and volatility, making energy storage an essential supporting facility for its large-scale and high-proportion grid connection. The combination of the two is a key support for promoting the transformation of the energy system from traditional fossil energy to clean energy.

I.Why is Energy Storage So Important?

Traditional energy systems (such as thermal power and hydropower) have the advantage of strong adjustability. Thermal power can increase or decrease output according to demand, and hydropower can adjust the power generation rhythm through reservoirs, enabling them to stably match users’ electricity demand (e.g., generating more power during peak daytime consumption and less during off-peak nighttime hours). However, with the increasing proportion of new energy sources like wind power and PV, the problem of “supply-demand mismatch” in the energy system has been amplified, and energy storage is exactly the core tool to resolve these contradictions.

1. Smoothing the Intermittent Volatility of New Energy to Ensure Grid Stability

The power output of wind power, which depends on the wind,and PV power, which depends on the weather, is entirely determined by natural conditions: on cloudy days or in the evening, PV output drops sharply; at night or when there is no wind, wind power and PV output are almost zero. This fluctuating output characteristic can deal a heavy blow to the power grid. For example, when PV output surges at noon, the grid may experience abnormal frequency due to excessive electricity that cannot be consumed; in the evening, when the peak electricity demand coincides with a sharp drop in PV output, a power supply gap may occur due to insufficient electricity.

Energy storage acts like an energy buffer. When new energy output is excessive (e.g., when PV generates a large amount of power at noon), energy storage stores the surplus electricity (charging process). When new energy output is insufficient (e.g., in the evening) or peak electricity demand arrives, energy storage releases the stored electricity (discharging process), preventing grid frequency fluctuations and ensuring stable power supply.

2. Replacing Part of the Backup Power Supply to Improve Power Supply Reliability

Traditional power grids rely on thermal power and hydropower as backup power sources to cope with sudden failures (such as line tripping and power source shutdown) or extreme weather (such as cold waves causing coal shortages for thermal power and blizzards reducing PV output). However, backup power sources have low utilization rates and high costs in normal times. The rapid response capability of energy storage (millisecond to second-level discharge) can replace part of the backup power supply: when the grid suddenly faces a power shortage, energy storage can instantly release electricity to fill the gap between power source switches and avoid power outages. For instance, in 2021, when many areas in southern China faced tight power supply due to extreme weather, energy storage power stations served as emergency power sources, ensuring basic electricity consumption for residents and key industries.

3. Supporting Distributed Energy and Microgrids to Achieve Local Consumption

With the popularization of distributed PV (such as rooftop PV for households and factories), more and more users have transformed from electricity consumers to electricity producers + consumers. However, the output of distributed PV is unstable. If the surplus electricity is directly connected to the grid, it may affect the safety of the distribution network. Energy storage, however, can realize local consumption: the PV electricity generated by households during the day is prioritized for self-use, and the surplus is stored in energy storage batteries; at night or on cloudy days, households can directly use the electricity stored in energy storage, reducing reliance on the grid. Even when the grid fails, PV-storage integration can form a microgrid to realize independent power supply for households or communities.

II.The Relationship Between Energy Storage and PV: A Perfect Match and the Best Pair

1. Inherent Complementarity: Resolving the Core Time-Space Mismatch

This is the most fundamental reason for the combination of the two. There is a natural and significant phase difference between the PV power generation curve and the social electricity consumption curve.

PV Power Generation Curve: A “single-peak curve” that peaks at noon and is low in the morning and evening. The peak usually occurs between 11 a.m. and 1 p.m.

Social Electricity Consumption Curve: A typical “double-peak curve.” There is a huge demand for electricity during the morning peak (9-11 a.m.) and evening peak (6-10 p.m.), while there is a small trough at noon (when many people take lunch breaks and some factories suspend operations).

As a result, when PV generates the most electricity, the electricity demand is not at its peak, leading to a large amount of green electricity having no place to go. Conversely, when people return home from work in the evening, turn on air conditioners, TVs, and washing machines, and the electricity demand reaches its peak, PV has already “finished work” and cannot generate electricity anymore. The power grid has no choice but to start more coal-fired and gas-fired power generation to meet the evening peak demand.

The integration of energy storage perfectly solves this problem:

Noon: The energy storage system starts charging, “absorbing” the surplus PV electricity.

Evening to Night: The energy storage system starts discharging, “releasing” electricity to meet the evening peak demand.

In this way, the intermittent PV electricity that was originally difficult to consume is transformed into a stable and dispatchable high-quality power source. Energy storage has installed a “time controller” for PV.

    2.With Energy Storage, PV Can Upgrade from a “Supplementary Energy Source” to a “Main Energy Source”

In the traditional energy system, thermal power and hydropower are main power sources because they can generate electricity on demand. Without energy storage, PV can only serve as a supplementary energy source and rely on other power sources for support. However, when combined with energy storage, a PV-storage power station can realize dispatchable power generation—the grid can obtain a stable output of electricity from the PV-storage station through the combination of PV power generation + energy storage discharge according to its demand. This is equivalent to transforming uncontrollable PV into a controllable power source.

For example, in China’s West-to-East Power Transmission project, large-scale PV-storage power stations in Qinghai can stably transmit PV electricity to load centers in eastern China (such as Shanghai and Jiangsu) through energy storage regulation, becoming one of the main power sources for the eastern power grid instead of an unstable supplement.

3. Technical and Market Perspectives: PV-Storage Integration Has Become an Industry Standard, with Synergistic Cost Reduction

From a technical perspective, PV inverters (equipment that converts PV DC power to AC power) and energy storage converters (equipment that controls the charging and discharging of energy storage) have achieved integration. A single set of equipment can manage both PV and energy storage, reducing system complexity and costs. From a market perspective, policies in various countries have clearly stipulated PV-storage bundling requirements—for example, China requires newly built large-scale PV bases to be equipped with energy storage accounting for 20%-30% of their capacity (e.g., a 1GW PV power station needs to be matched with 200-300MW energy storage), and the EU also mandates that distributed PV systems must be equipped with energy storage.

At the same time, the costs of PV and energy storage have shown a trend of “synergistic reduction”: over the past 10 years, the cost of PV modules has dropped by more than 80%, and the cost of lithium-ion battery energy storage has fallen by more than 70%. The cost of the “PV-storage integration” system, which combines the two, is now lower than that of some thermal power, giving it economic competitiveness.

III. The Spectrum of Energy Storage Technologies: Beyond Lithium-Ion Batteries

When talking about energy storage, many people first think of lithium-ion batteries. However, energy storage technologies are highly diverse, each with its own advantages and disadvantages, and suitable for different scenarios.

1. Pumped Hydro Storage – The Former Undisputed Leader

The principle of this technology is to use electricity to pump water to an upper reservoir when there is surplus power; when electricity is needed, the water is released to generate power. Pumped hydro storage has mature technology, large capacity, long service life, and low cost. However, it is extremely dependent on geographical conditions, has a long construction period (5-10 years), and requires huge initial investment. Currently, it is still the absolute main component of the global energy storage installed capacity, but its future growth space is limited.

2. Electrochemical Energy Storage – The Current Star

It realizes charging and discharging based on chemical reactions of batteries. Among them, lithium-ion battery energy storage has the advantages of high energy density, fast response, and high efficiency, making it the current mainstream choice. However, it faces issues of safety (risk of thermal runaway) and cost fluctuations. It is currently the fastest-growing and most widely used type of energy storage, and a core force in addressing the volatility of new energy.

3. Other Technical Routes – Explorations for the Future

Compressed Air Energy Storage: Converts electrical energy into the energy of compressed air and stores it in underground salt caverns or abandoned mines. When needed, the compressed air is released to drive turbines for power generation. It is suitable for ultra-large-scale and long-duration energy storage.

Flywheel Energy Storage: Uses a high-speed rotating flywheel to store kinetic energy; when electricity is needed, the energy is released through a generator. It has high power, fast response, and a long service life, but low energy density, making it suitable for short-term and high-frequency frequency regulation scenarios.

Hydrogen Energy Storage: Uses surplus electricity to electrolyze water to produce “green hydrogen.” Hydrogen can be stored for a long time and transported over long distances. When needed, it can generate electricity through fuel cells or be directly burned. It is one of the ultimate solutions for cross-seasonal and ultra-long-duration energy storage, but currently has low efficiency and high costs.

No single technology can be applied to all scenarios. The future will definitely be a pattern of “coexistence of multiple technical routes.”

Conclusion: Moving Towards an Energy Future of PV-Storage Integration

The wave of the energy revolution is irreversible. We are moving from a civilization that mines the earth’s heritage (fossil fuels) to one that utilizes real-time income (solar energy).

In this historic transformation, PV is our collecting hand, responsible for harvesting endless energy from the sun; while energy storage is our storage warehouse, responsible for organizing, preserving, and distributing this energy. It ensures that regardless of day or night, sunshine or rain, the energy pulse of civilization can beat stably and powerfully.

They are not just a simple combination, but an organic whole with in-depth coupling and mutual dependence. Understanding and vigorously developing PV + energy storage is not only a technical or commercial issue, but also a strategic one that determines whether we can smoothly move towards a clean, safe, and inclusive energy future.