Pilot project
Pilot project technical specs
INTRODUCTION
This paper examines the feasibility and environmental benefits of a gravity-based electrical energy storage system (GES) integrated with solar power generation. The system uses surplus solar energy to lift heavy concrete blocks, which store gravitational potential energy. When needed, this energy is released as the blocks are lowered, converting potential energy back into electrical energy. This approach offers a reliable, long-term, and environmentally sustainable alternative to chemical batteries, addressing the challenges of renewable energy intermittency.
Gravity-Based Energy Storage Principle
Gravity-based energy storage (GES) operates by converting excess solar energy into gravitational potential energy. This is achieved by using electric motors to lift heavy concrete blocks. When energy is required, the blocks are lowered, driving a generator that converts the gravitational potential energy into electricity. The amount of energy stored can be calculated using E=mgh, where m is the mass (in kilograms), g is the gravitational constant (9.81 m/s²), and h is the height (in meters). GES systems offer an efficient, durable, and low-maintenance solution compared to traditional battery storage.
Environmental Benefits of Gravity-Based Energy Storage
Sustainable Materials: The system relies on recyclable materials such as concrete and steel. In contrast, chemical batteries use rare metals like lithium, cobalt, and nickel, which have a significant environmental footprint due to mining and refining.
Minimal Degradation: Unlike batteries, which degrade over time and require replacement, gravity storage systems have minimal wear and can operate for decades without significant degradation. This reduces material waste and environmental impact.
No Chemical Waste: GES systems do not produce hazardous waste or require disposal of toxic materials, unlike batteries. This reduces the environmental risks associated with battery recycling and disposal.
Compact Footprint: The vertical stacking of blocks requires minimal land, making it adaptable for various locations, including industrial and urban environments.
Cost Comparison: Gravity-Based Storage vs. Battery Storage Systems
While gravity-based energy storage systems have higher upfront costs for infrastructure, they offer lower long-term operational costs. Over a 50 years time period, GES systems do not degrade, unlike lithium-ion batteries, which require replacement every 7-10 years, making GES more cost-effective for long-term use.
Here is a comparison of lifetime costs (over 20 years) for gravity-based storage and lithium-ion batteries:
Gravity-Based (GES)
$50 - $100
20-30
Low
None
Lithium-Ion Battery
$200 - $400
7-10
Moderate
High (battery replacement)
Graph: Lifetime Cost Comparison
This graph shows that while lithium-ion batteries have a lower initial cost for short-term storage needs, GES systems provide significant long-term savings due to the lack of replacement and minimal maintenance costs.
Efficiency Comparison: Gravity-Based Storage vs. Pumped Hydro and Chemical Batteries
Gravity-based energy storage offers an efficiency of 70-85%, slightly lower than pumped hydro systems (80-90%) and lithium-ion batteries (85-95%). However, GES systems do not suffer from efficiency loss over time, making them more reliable for long-term energy storage. Additionally, GES systems can be installed in various locations without the geographical limitations of pumped hydro storage.
Technical Paper: Design of a Pilot Electrical Energy Gravity Storage Installation and Its Energy Output Comparison
System Components
Solar Panel Array: The solar array is designed to generate 100 kW of power during peak sunlight.
Number of Panels: A typical solar panel produces approximately 300 W. To achieve 100 kW, the system will require approximately:
100,000 W divided by 300 W per panel ≈ 333 panels
Surface Area: Each panel covers approximately 1.6 square meters, so the total surface area needed is:
Total area = 333 panels × 1.6 m² per panel = 532.8 m² = 0.053 hectares
Therefore, the solar panel array requires 0.053 hectares (530 square meters), making it compact enough for various deployment scenarios.
Concrete Blocks: Each block weighs 10 tons (10,000 kg) with a base area of 2 x 2 meters and a height of 1.04 meters.
In the pilot system, the blocks are stacked 10 units high in each of five vertical lanes. The total stack height is 10 meters, with each block traveling 20 meters vertically within a 30-meter tall structure. This compact, vertical design minimizes land use while providing substantial energy storage capacity.
Lifting Mechanism: The system consists of electric motors, pulleys, and cables capable of hoisting the blocks.
Motors: High-efficiency three-phase induction motors are used, each rated at 20 kW, sufficient to lift a 10-ton block. Five motors, one for each vertical lane, will operate simultaneously. The total power requirement to lift all 50 blocks (5 lanes with 10 blocks each) is 100 kW, matching the peak solar panel output.
Pulleys and Cables: The pulley system uses high-strength steel cables attached to a drum winch. Each pulley system can handle 10 tons of force, ensuring the safe and stable lifting of blocks. The pulleys are made of hardened steel to withstand frequent lifting cycles without degradation.
Control System: A computerized system synchronizes the lifting and lowering of blocks, ensuring motors operate only when excess solar energy is available. The system maximizes efficiency by lifting blocks during periods of surplus solar energy.
Energy Conversion System: The energy recovered when the blocks are lowered is converted into electrical energy.
Discharge Mechanism: When the blocks are lowered, the motors switch to regenerative braking mode, acting as generators to convert potential energy into electrical energy. This process uses the kinetic energy of the descending blocks to generate electricity, which is either fed into the grid or used locally.
Generators: The motors act as synchronous generators during the discharge phase, with an efficiency of around 85%. A voltage regulation system ensures a stable power output even with varying descent speeds.
Energy Control: The control system manages the speed of the block's descent to optimize energy generation. During periods of low demand, blocks are lowered slowly to provide continuous power. In times of peak demand, blocks are lowered faster to generate more energy over a shorter period.
Energy Storage Capacity and Household Comparison
Energy Storage Capacity
The energy stored by lifting one 10-ton block to a height of 20 meters is calculated using the formula:
E = mgh
Where:
m=10,000kg,
g=9.81m/s2,
h=20m.
E = 10,000 × 9.81 × 20 = 1,962,000 J = 0.545 kWh
For the 50 blocks in the system (5 lanes with 10 blocks each):
Etotal = 50 × 0.545 kWh = 27.25 kWh
Comparison to Household Energy Consumption
The average U.S. household consumes approximately 30 kWh per day. The total storage capacity of the pilot system is 27.25 kWh, meaning it could power a single household for nearly 22 hours:
27.25 kWh
--------------- = 0.91 days (≈ 22 hours)
30 kWh/day
Alternatively, the system can distribute energy across multiple households during shorter peak demand periods, making it adaptable to different energy needs.
Conclusion
The gravity-based energy storage system offers a sustainable and efficient alternative to chemical batteries, particularly when integrated with solar power. By using readily available materials, requiring minimal land, and providing long-term reliability with low maintenance, GES systems are an environmentally and economically viable solution to energy storage challenges. As the demand for renewable energy storage increases, gravity-based systems could play a critical role in ensuring a stable and resilient energy grid.
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