Solar energy has become a major source of new electricity generation around the world. Solar photovoltaic (PV) systems can be deployed across a wide range of applications, from rooftop installations and commercial facilities to large utility-scale projects. In 2025, solar PV accounted for more than three-quarters of new renewable capacity added globally.
But generating more solar electricity comes with a practical challenge: solar power is not always available when electricity demand is highest. Production changes throughout the day and with weather conditions, while electricity demand follows its own pattern. As solar becomes a larger part of the electricity mix, managing this difference becomes increasingly important for grid flexibility.
Energy storage is one way to address that challenge. By storing electricity when solar generation is high and releasing it when demand increases or solar output falls, storage can help shift renewable electricity to when it is more useful.
In this guide, we’ll look at how solar energy works, its main benefits and challenges, how energy storage supports solar, and what to consider when choosing a solar-plus-storage system.
What Is Solar Energy and How Does It Work?
Solar energy is energy from the sun’s radiation that can be converted into electricity or heat. The two main technologies used to turn sunlight into useful energy are photovoltaics (PV) and concentrating solar-thermal power (CSP).
Photovoltaic (PV) Solar
PV is the technology most people associate with solar panels. When sunlight reaches a PV cell, the cell absorbs that energy and generates electrical charges, creating an electric current. A complete PV system includes more than the panels themselves, with other components used to convert, manage, and deliver the generated electricity.
PV systems can be deployed in different settings, including rooftops, commercial facilities, community solar projects, and utility-scale solar farms. Their output depends on the amount of sunlight available, which varies with location, time of day, season, weather, and other conditions.
Concentrating Solar-Thermal Power (CSP)
CSP operates in a different way. Instead of turning sunlight directly into electricity, mirrors focus the sunlight onto a receiver that produces heat. You can then use that thermal energy to generate electricity by a turbine or heat engine. Some CSP systems can also store the heat and use it later, allowing electricity production beyond the time of direct sunlight.
PV is the technology that most readers will be familiar with for discussion of increasing solar electricity generation, but CSP is still an important utility scale technology, with the advantage of thermal energy storage.
What Are the Main Benefits of Solar Energy?
Solar energy offers more than an alternative way to generate electricity. Its value comes from being a scalable renewable resource that can be deployed close to electricity users or at utility scale. As solar PV deployment continues to grow, it is becoming an increasingly important part of the global electricity mix. The IEA reports that solar PV accounted for more than three-quarters of new renewable capacity added worldwide in 2025.
Renewable Electricity Generation
Sunlight naturally replenishes, so solar PV can generate electricity without consuming finite fuels during operation. This makes solar PV an important option for expanding renewable electricity generation and reducing reliance on conventional power sources.
Scalable Deployment
Solar systems can be located in very different settings, from rooftop and commercial systems to community solar projects and utility-scale solar farms. That flexibility allows solar generation to be built to match the space available, the electricity demand, the grid conditions, and the project goals.
Potential Energy-Cost Benefits
Solar can offset grid electricity purchases when you use the electricity it generates on-site. However, the actual financial benefit depends on system costs, electricity prices, financing, incentives, solar output, and how much of the generated electricity you use. Therefore, no single savings figure applies to every project.
Greater Energy Independence
Generating electricity locally can reduce your reliance on electricity from the wider grid. When you combine solar with energy storage or a microgrid, the system can also support critical loads during certain grid disruptions, depending on its design and operating conditions.
Supporting a More Flexible Electricity System
Solar can also contribute to a more diverse electricity supply. As deployment grows, however, its variable output creates a greater need for flexibility across the wider power system. This is where resources such as energy storage, demand response, transmission, and other forms of grid flexibility become increasingly important.
What Are the Main Challenges of Solar Energy?
Solar energy offers a renewable way to generate electricity, but increasing its share of the power system creates additional technical and operational challenges. The main issue is not whether solar panels can produce electricity. It is when that electricity is produced, how much is available, and whether it can be used or delivered when it is needed.
1. Solar Output Is Variable
Solar PV generation depends on available sunlight. Production falls after sunset and can change during the day because of cloud cover, weather, seasonal conditions, and shading. These variations are a normal part of solar generation, but the wider electricity system still needs to respond as output changes.
At lower levels of solar deployment, existing grid resources may be able to manage these changes relatively easily. As solar provides a larger share of generation, however, greater flexibility is needed to keep electricity supply and demand in balance.
2. Solar Generation Does Not Always Match Demand
Solar production is often strongest during daylight hours, while electricity demand can remain high later in the afternoon or evening.
For example, a commercial facility may generate more electricity from its solar system around midday than it needs at that moment. A few hours later, its electricity demand may increase just as solar output begins to decline.
This creates a timing difference:
- High solar production: more electricity may be available than the site or grid can use immediately.
- Higher later demand: more electricity may be needed after solar generation has fallen.
When available solar electricity cannot be consumed, exported, or moved through the network, some generation may be curtailed. The IEA identifies high renewable output, transmission constraints, and system conditions as factors that can contribute to curtailment.
3. Integrating More Solar Requires Grid Flexibility
Adding more solar generation also increases the importance of the systems that manage and move electricity. Depending on the local grid, higher solar penetration may require stronger transmission and distribution networks, better forecasting, flexible generation, demand response, improved grid operations, or energy storage.
There is no single solution for every electricity system. The right combination depends on factors such as solar penetration, demand patterns, network capacity, existing generation, and local market conditions.
4. Solar Projects Have Practical and Lifecycle Considerations
Solar development involves more than selecting panels and calculating expected generation. Available land or rooftop space, grid interconnection, permitting, maintenance, equipment replacement, and end-of-life management can all affect project planning and economics.
These considerations do not reduce the value of solar energy. They show why solar projects need to be evaluated as part of a wider energy system rather than by panel output alone.
As solar deployment grows, managing these differences between generation and demand becomes increasingly important. This is where energy storage can provide additional flexibility by allowing some solar-generated electricity to be used at a different time from when it was produced.
How Does Energy Storage Help Solar Power?
Energy storage helps solar power by separating when electricity is generated from when it is used. Solar panels can produce substantial electricity during the day, while demand may remain high later when solar output is falling. Storage can capture part of that daytime generation and make it available when it is more useful.
A Battery Energy Storage System (BESS) paired with solar can follow a simple cycle:
Solar generation rises → excess electricity charges the battery → solar output falls → stored electricity is discharged later.
For a commercial facility, this could mean charging the battery around midday when solar production is high, then using the stored electricity during a later period when the facility’s demand increases.
That can give solar-plus-storage systems several practical uses:
- Shift solar electricity: Move some daytime generation into later periods when it is more useful.
- Reduce some curtailment: Store surplus electricity that may otherwise be difficult for the site or grid to use immediately.
- Support peak demand: Discharge stored energy during higher-demand periods.
- Manage short-term variability: Respond to temporary changes in solar output, such as fluctuations caused by cloud cover.
- Support resilience: A system specifically designed for backup operation can help maintain critical loads during an outage.
The amount of storage required depends on what the system is supposed to do. A project designed to manage short-term fluctuations has different requirements from one designed to shift midday solar production into the evening. Power capacity, energy capacity, discharge duration, cycling profile, and the site’s solar and load patterns all influence the design.
This is also where storage duration becomes important. A few hours of storage may be sufficient for some intra-day applications, while longer periods of energy shifting require more energy capacity. DOE defines long-duration energy storage as systems capable of delivering electricity for 10 hours or more, with separate categories for inter-day, multi-day, and seasonal applications.
For a solar project, the goal is therefore not simply to add a battery. It is to match the storage system to when solar electricity is produced, when it is needed, and what the system is expected to achieve.
What Type of Energy Storage Works With Solar?
There is no single storage technology that works best for every solar project. The right choice depends on how much electricity you need to store, how long you need to deliver it, how often you expect the system to cycle, and what you want the project to achieve.
Lithium-Ion Batteries
Solar applications make extensive use of lithium-ion batteries because of their rapid response, high energy density and flexible system configurations. They are especially good for applications such as daily solar shifting, peak-demand management, and other short-duration needs.
Flow Batteries
Flow batteries have liquid electrolytes that are stored in tanks outside the battery. Their architecture provides more freedom to scale power and energy capacity independently. They are worth considering for applications that require longer discharge periods and frequent cycling.
Other Storage Options
Solar can also be paired with technologies such as pumped-storage hydropower, compressed-air energy storage, thermal storage, and hydrogen. These options can serve different applications depending on project scale, location, operating requirements, and economics.
| Storage need | What matters most |
| Daily solar shifting | Duration, efficiency, cycling and cost |
| Frequent cycling | Cycle life and degradation |
| Extended energy delivery | Energy capacity and discharge duration |
| Backup power | Power capacity, energy capacity and system configuration |
Ultimately, the best storage technology is the one that matches the solar generation profile, electricity demand, operating pattern, site conditions, and project economics.
What Should You Consider When Pairing Solar With Energy Storage?
Sizing and selecting storage for a solar project is a project-specific exercise. A few factors consistently shape the decision:
- Solar generation profile. How much surplus does the system typically produce, and when?
- Electricity or load profile. When does demand peak relative to solar output, and how consistent is that pattern day to day?
- Required discharge duration. Is the goal to shift a few hours of midday surplus, or to cover longer gaps in generation?
- Power and energy capacity needs. How much instantaneous power is needed versus how much total energy needs to be stored?
- Cycling frequency. Will the system charge and discharge daily, or less predictably?
- Grid connection and interconnection requirements. Local utility rules and interconnection capacity affect what’s feasible and how quickly a project can move forward.
- Curtailment exposure. In regions or systems with higher curtailment rates, storage may deliver more value by capturing generation that would otherwise go unused.
- Site and safety requirements. Space constraints, fire codes, and equipment placement all factor into technology selection and system design.
- Lifecycle economics. Upfront cost, expected lifespan, degradation rate, and maintenance needs all affect the long-term value of a given storage choice.
- Future operating needs. Anticipated changes in load, additional solar capacity, or evolving grid requirements can affect how a system should be sized today.
Working through these factors rather than defaulting to a single storage technology or duration — is what separates a well-matched solar-plus-storage system from one that’s oversized, undersized, or misaligned with how the site actually operates.
Conclusion
Solar energy offers a scalable way to expand renewable electricity generation, from rooftop systems to large utility-scale projects. But as solar becomes a larger part of the electricity mix, when electricity is generated becomes just as important as how much is generated.
Solar output does not always match electricity demand, which can create challenges around variability, curtailment, and grid flexibility. Energy storage can help address this mismatch by storing electricity when solar generation is high and making it available when it is more useful.
The right approach is not simply to add storage to every solar project. Storage duration, power and energy capacity, cycling requirements, site conditions, load profile, grid requirements, and lifecycle economics all need to be considered.
Ultimately, the value of solar-plus-storage comes from matching the technology and system design to the job it needs to perform.
Frequently Asked Questions About Solar Energy
Does solar energy always need battery storage?
No. Many solar installations operate effectively without storage, particularly where the local grid can absorb variable solar output and demand patterns align reasonably well with generation. Storage becomes more valuable as solar penetration increases or when specific goals like backup power or peak-demand reduction are part of the project.
What is solar curtailment, and why does it happen?
Curtailment is when grid operators intentionally reduce solar output because supply exceeds what the grid can use or deliver at that moment. It happens most often during periods of high solar generation and comparatively low demand, such as spring and fall.
How long can a battery store solar energy?
It will depend on the technology and system design. Lithium-ion systems are typically designed for a few hours of discharge, while long duration storage technologies, which include some flow batteries, are sized for 10 or more hours.
What’s the difference between short-duration and long-duration storage?
Short-duration storage typically covers a few hours enough to shift midday solar surplus into the evening. Long-duration storage, generally defined as ten or more hours of discharge, addresses longer gaps, such as multi-day low-generation periods.
Can solar-plus-storage work during a power outage?
Only if the system is specifically designed for backup power. A standard grid-tied solar system without that design typically shuts down during outages for safety reasons.
How is storage duration chosen for a specific solar project?
It’s based on the site’s generation and load profiles, curtailment exposure, and operating goals there’s no universal duration that fits every project.
