Hybrid energy storage devices in off-grid PV energy systems

12/08/2019

Summary

Hybrid energy storage devices in off-grid PV energy systems - in the proposed hybrid energy storage concept, the supercapacitor as "dynamic" energy storage device supports the dynamic part of the load, while the battery only covers the mean value of the load power demand. Consequently, the battery operates in optimal conditions at all times.

Technology Description

Off-grid power systems have recently become an increasingly useful alternative for powering consumers and facilities that do not have access to the power grid. A key contribution is therefore the development of wind power plants technology, photovoltaic arrays and storage batteries. The rechargeable battery has the function of storing energy to supply electricity to consumers at a time when the primary energy source is inactive, e.g. without wind or when there is no sunlight. Although some modern systems still use lead acid gel batteries (lower cost systems), but the current state of the art is the use of lithium batteries. Two types of Li-ion batteries are used for different purposes: the "high-energy" type and the "high-power" type. The "high-energy" type has the capacity to absorb more energy, but their weakness is the relatively high internal impedance and the inability of high peak loads at dynamic loads.

Therefore, the electric battery is still the weak point of the whole system. In the proposed hybrid energy storage concept, the supercapacitor as "dynamic" energy storage device supports the dynamic part of the load, while the battery only covers the mean value of the load power demand. Consequently, the battery operates in optimal conditions at all times. Each energy storage unit within the system is connected to the DC bus directly or through its own bi‐directional power converter. An advanced management concept of energy flow between the different voltage levels of both energy reservoirs on one side and a common DC bus on the other hand, is used, based on control of amount of DC bus energy.

Main advantages

The main advantageous features of using high performance hybrid energy storage in PV energy systems are:

• better dynamic response at load changes,

• higher achievable amount of stored energy with fully charged energy storage unit,

• better overall efficiency of whole power plant,

• longer expected lifetime of the battery.

Stage of development

The technology is in the TRL 4- Technology validated in lab.

The hybrid energy storage as a part of PV energy system was designed for the needs of high-performance applications, which requires both high dynamic performance and good utilization of stored energy in the battery. The utilized analytical design method, which is based on a mathematical model, exposes some of the properties of chemical batteries, particularly the change of parameters in various stages of charge and non-linear dependence of the conversion of stored energy. A systematic examination of different hybrid storage unit configurations was performed, in order justify the decision for the proposed active hybrid storage unit. The proposed configuration combines a supercapacitor and a battery connected to a common DC bus.

The proposed concept was verified by long-term comparative tests, in which the hybrid storage unit was compared to a conventional battery storage unit. The long-term experimental test results have confirmed the advantages of the proposed hybrid storage unit system over a conventional battery.

Challenge and needs

Potential applications for PV energy systems with hybrid energy storage devices:

▪ Photovoltaic (PV) charging stations for e-bikes,

▪ PV off-grid energy systems for private homes,

▪ PV off-grid energy systems for holiday houses,

▪ PV off-grid energy systems for campers,

▪ PV off-grid energy systems for illuminated advertising boards,

▪ PV off-grid energy systems for telecommunication objects and weather stations,

▪ PV supply systems for water pumps supplying,

▪ PV supply systems for emergency and rescue vehicles,

▪ PV supply systems for communication devices in cable cars.

Intellectual property

The technology is not yet protected by a patent.

Potential markets and targets

According to Verified Market Research, The Global Off-Grid Energy Storage Systems Market was valued at USD 31.10 Billion in 2018 and is projected to reach USD 58.47 Billion by 2026, growing at a CAGR of 7.5% from 2019 to 2026. The North American Market is expected to participate heavily in the Off-Grid Energy Storage Systems. This position can be attributed to the increasing number of grid reliability issues in parts of the country, state-level storage mandates, and renewable support programs in the region. North America is therefore considered as the largest player in the market. Other regions such as the Asia Pacific are likely to expand in the coming years due to growth in electricity demand, supply security concerns and more. This broad market represents an opportunity for the presetned technology.

Potential partners

Potential partners who would be interested in participating in the development of a PV power plant with a built-in hybrid energy storage. The development of a prototype batch production product of this type is also expected in the future.

Partners who wish to invest in setting up PV energy systems in the field for users are also welcome (eg charging stations for smaller electric vehicles: for e-bikes, e-scooters and other electrical devices).

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