24-Hour Uninterrupted Solar Power with Battery Storage is Real: Ember
Achieving 97% of full-year 24-hour coverage is possible, says report
June 27, 2025
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Battery-backed solar energy systems need just 17 kWh of storage to flatten a 5 kW solar generation profile into a steady 1 kWh of output across 24 hours, according to a new report by Ember.
For example, in a sunny city like Las Vegas, which has a solar capacity factor of around 20%, a 5 kW system generates an average of 1 kWh per hour or 24 kWh per day.
However, the city requires storage to redistribute excess generation since most of this energy is produced during daylight hours.
Of the total 24 kWh generated daily, approximately 9.6 kWh can be consumed directly during sunlit hours. The remaining 15 kWh must be stored for non-sunlight periods. Typically, a 90% usable capacity is required to ensure safe operation between 5% and 95% charge levels, and a 17 kWh battery is needed to reliably store the 15 kWh. This configuration enables approximately 14.4 kWh to be discharged later.
While achieving 24-hour solar power is straightforward in sunny locations, delivering this consistently across all 365 days remains a challenge due to seasonal and weather-related variability.
However, the Ember report said that modeling using hourly solar irradiance data from 12 cities worldwide shows that optimized solar and storage ratios make achieving approximately 97% of full-year 24-hour coverage possible. In high-insolation regions, this can be achieved at a competitive levelized cost of $104/MWh.
Impact of Solar Tracking
Battery requirements vary across days and regions, but the variation is not large in sunny locations. In Las Vegas, the daily battery requirement fluctuates between 15.8 kWh and 18.2 kWh throughout the year. Analysis shows that a 17 kWh battery remains close to optimal for most sunny areas.
The requirement for battery storage remains largely unchanged, even if solar panels use tracking systems rather than fixed mounts. Although tracking can increase output during early morning and late afternoon, any power above the 1 kW continuous demand would be used to charge the battery rather than being utilized.
Significant Savings
Solar energy paired with batteries can reduce the need for expensive grid expansion. In sunny regions, a single solar panel has an annual capacity factor of 20%. A fixed grid connection that would otherwise support only a limited solar installation can now support up to five times the solar capacity with the addition of batteries.
In 2024, over 3,000 GW of renewable projects worldwide were stuck in interconnection queues, compared to 585 GW of total new installations during the year. The report opines that batteries offer a practical and immediate solution for such situations.
Cost Declines
In 2024, battery prices dropped 40%, reaching a record low of $165/kWh for a fully integrated system (excluding engineering, construction, procurement, and grid connection costs). The downward trend continues into 2025, with auctions in Saudi Arabia achieving prices as low as $72/kWh.
This price drop is largely due to the widespread adoption of lithium-iron-phosphate (LFP) batteries, which comprised 80% of new grid-scale installations in 2023. LFP technology does not use nickel or cobalt, improves safety, and now comes with 20-year warranties from some manufacturers. These improvements significantly enhance the economics and reliability of battery investments.
Last December, BloombergNEF reported that lithium-ion battery pack prices dropped 20% from 2023 to a record low of $115/kWh, the most significant annual decline since 2017.
Battery enclosures have also witnessed technical improvements, enabling denser cell packing, improved insulation, and reduced maintenance, particularly in hot and arid regions. Simpler integration further reduces system installation costs.
The development of sodium-ion batteries could potentially eliminate the need for lithium entirely and further reduce costs. The first grid-scale sodium-ion system is already operational.
Despite these advances, battery deployment remains in its early stages of development. In 2024, only 169 GWh of grid-scale battery capacity was installed globally, despite 1,450 GWh of battery manufacturing capacity already being in place. This includes electric vehicle batteries and is more than enough to support the 585 GW of solar capacity added in 2024 at a ratio of over 2 kWh of battery per 1 kW of solar panel.
Global energy storage capacity additions are expected to grow by 35% in 2025 to 94 GW or 247 GWh, according to BloombergNEF’s latest outlook.
Shortfall Variation
A standard configuration of 6 GW of solar energy paired with 17 GWh of battery storage was tested across 12 cities worldwide to assess how close each location could get to delivering firm, round-the-clock solar electricity year-round. The analysis revealed that the sunniest cities can achieve over 90% of full 24/365 reliability, but seasonal and climatic variations still impact output, especially during extended periods of cloudy weather.
Even in high-irradiance cities like Las Vegas, which achieves 97% reliability, shortfalls occur in winter, when daylight drops to just over nine hours on the shortest day, nearly three hours below the average.
Across the hemisphere, in Hyderabad, India, another city with high irradiance, monsoon clouds rather than winter, caused dips in solar generation.
In Spain, Madrid experienced its worst gaps during November and December due to low sun angles and frequent overcast skies. Birmingham in the UK saw limited sunlight even in summer, managing just two months of consistent solar generation.
In China, Wuhan suffered from dense cloud cover throughout the year.
Muscat in Oman performed best overall, reaching 99% of the way to 24/365 solar generation. Other top performers included Mexico City, Mexico (96%); Johannesburg, South Africa (95%); Manila, Philippines; and Abuja, Nigeria (both 92%).
Four other cities surpassed the 80% mark: Hyderabad (89%), Madrid (88%), Buenos Aires, Argentina, and Washington, D.C. (both 81%). Only Wuhan (74%) and Birmingham (62%) fell short due to persistent cloudiness and lack of sunlight during the winter months.
Commercial and Industrial Consumers
Commercial and industrial users are also turning to behind-the-meter microgrids to reduce reliance on the grid and shield themselves from price volatility and outages.
Notable examples include the 100 MW Moro Hub data center in the United Arab Emirates, powered entirely by a co-located solar project. In West Virginia, U.S., a 106 MW solar microgrid with 261 MWh of storage can power titanium melting operations. Saudi Arabia’s tourism development now operates 16 resorts using a 400 MW solar project with 1.3 GWh of battery storage.
Regulatory and Financial Barriers
The Ember report identified entrenched regulatory and financial mindsets as the primary obstacles to delivering 24-hour solar power. While the systems are now mature, cost-effective, and capable of providing round-the-clock clean energy, power planners, regulators, and financiers remain either unaware of the potential or skeptical of its reliability.
Properly designed solar battery systems can meet or exceed these reliability standards, especially when supplemented by modest oversizing, grid electricity, or rarely-used backup generators. Unlike fossil fuels, solar systems benefit from increasingly accurate weather forecasting and lower maintenance requirements.
Reduction in Grid Costs
The report stated that integrating 24-hour solar with battery storage offers a strategic advantage at the national level by reducing the need for costly grid expansion. While not a standalone solution, solar-plus-storage plays a vital role in balancing the grid alongside other resources such as wind, hydro, geothermal, interconnectors, and flexible demand systems.