There are many forms of energy, including electromagnetic energy, mechanical energy, chemical energy, light energy, heat, etc., so energy storage methods are also diverse. At present, mature energy storage technologies include pumped water storage, compressed air energy storage, and flywheel storage. energy, electrochemical energy storage, and heat and hydrogen storage technologies. All energy storage technologies can be roughly divided into two categories: power type and energy type. Power-type energy storage technologies include electrochemical energy storage and flywheel energy storage, which are characterized by high efficiency, high cost, and fast response speeds up to milliseconds, and can be used in occasions requiring fast response such as primary frequency modulation; energy-type energy storage technologies include pumped storage energy, compressed air energy storage, heat storage and hydrogen storage technologies, which are characterized by large volume, low cost, and reaction speed generally within a few minutes to ten minutes, suitable for large-scale energy storage, low cost requirements, and real-time requirements Not high items.
Electrochemical Energy Storage Technology
Electrochemical energy storage mainly includes lead-acid batteries, lithium-ion batteries, sodium-sulfur batteries, vanadium flow batteries, zinc-air batteries, nickel-hydrogen batteries, fuel cells and supercapacitors, of which lead-acid batteries, lithium-ion batteries, sodium-sulfur batteries and Flow batteries are the hotspot and focus of research. Electrochemical energy storage is a new driving force for the growth of the energy storage market. With the continuous improvement of electrochemical energy storage technology, the manufacturing cost and maintenance cost of electrochemical energy storage systems continue to decrease, and the capacity and life of energy storage equipment continue to increase. Energy storage will be applied on a large scale and become a new development trend of China's energy storage industry. The electrochemical energy storage market is dominated by lithium-ion battery energy storage, lead battery energy storage is an important component, and other electrochemical energy storage methods such as flow batteries, super capacitors, and sodium-sulfur batteries are also developing rapidly.
At present, lead-acid batteries are mostly used in small and medium-sized photovoltaic off-grid power stations, because the price is cheap and the initial investment is small, and the proportion in photovoltaic energy storage power stations is about 30%; More lithium batteries are used, accounting for about 65% of photovoltaic energy storage power stations, while other electrochemical energy storage methods such as liquid flow batteries, super capacitors, and sodium-sulfur batteries account for only 5% in total.
pumped storage technology
Also known as pumped hydropower generation, it is currently the most widely used large-scale, large-capacity energy storage technology in the world. In the global installed capacity, pumped hydropower storage accounts for more than 94%, occupying an absolute dominant position. The pumped storage system consists of three parts: the lower reservoir, the pump (hydraulic generator), and the upper reservoir. It uses the electric energy to pump water to the upper reservoir when the power load is low, and releases water to the lower reservoir to generate electricity during the peak power load period. It can transform the excess electric energy when the grid load is low into high-value electric energy during the peak period of the grid.
At present, there are very few cases of using pumped storage in photovoltaic power plants, but pumped storage and photovoltaic power generation are highly complementary, and they are both clean and renewable energy sources. In places with rich sunlight resources, water resources and terrain differences, the combination of photovoltaics and pumped energy storage can promote the sustainable development of photovoltaics. The pumped storage power station has the advantages of flexible start-up, fast climbing speed and other advantages of conventional hydropower stations and the characteristics of energy storage in low valleys, which can well alleviate the adverse effects of photovoltaics on the power system.
Photovoltaic water pumping system is also a way of pumped water storage. Water is pumped from low places to high water towers through pumping inverters and water pumps. When water is needed, water is taken from the water towers. This water storage method replaces batteries. , low cost and convenient.
heat storage technology
Heat storage technology uses heat storage materials as the medium to store heat energy such as solar heat, geothermal heat, industrial waste heat, and low-grade waste heat, and release it when needed, trying to solve the gap between heat energy supply and demand due to time, space, or intensity. It is a technology gradually developed to maximize the energy utilization rate of the entire system in order to solve the problems caused by matching. At present, there are mainly three heat storage methods, including sensible heat storage, latent heat storage (also known as phase change heat storage), and thermochemical reaction heat storage. Among the three heat storage technology forms, the cost of sensible heat storage is the lowest. Sensible heat storage technology is currently mainly used in industrial kilns and electric heating, residential heating, and photothermal power generation. Latent heat storage technology is mainly used for clean heating, power peak regulation, waste heat utilization, and low-temperature solar thermal utilization. field. In recent years, with the needs of clean heating and power system peak regulation, more and more latent heat storage technologies have begun to be applied on the power generation side and the user end. Thermochemical heat storage technology is still in the stage of small-scale research and practical application There are still many technical problems in the project, so there are few project cases.
Hydrogen storage technology
Hydrogen is currently the energy source with the highest content and high efficiency that we can obtain in nature. As a clean energy source, hydrogen energy has great potential for development. The products generated after the hydrogen combustion reaction are mainly water, hydrogen Compared with traditional energy sources such as oil, natural gas, and methanol, energy has wider access to energy, and is light in weight, high in energy density, clean and environmentally friendly, and has a variety of storage methods.
The storage methods of hydrogen energy mainly include low-temperature liquid hydrogen storage, high-pressure gaseous hydrogen storage, metal hydride hydrogen storage and organic liquid hydrogen storage, etc. These hydrogen storage methods have their own advantages and disadvantages. Hydrogen application technologies mainly include: fuel cells, gas turbine power generation, internal combustion engines and rocket engines.
In recent years, the continuous and rapid development of new energy has far exceeded the carrying capacity of the power grid, and the contradiction of new energy consumption is very prominent. Abandoned wind and water power are increasing year by year. In the long run, photovoltaic and wind power are the main sources of low-cost electricity for water electrolysis hydrogen production enterprises.
The working principle of the photovoltaic hydrogen production system: when the light is sufficient, the photovoltaic power generation system independently supplies power to the load, and the excess power generated at the same time is supplied to the electrolyzer to electrolyze water to produce hydrogen, and the hydrogen is stored in the hydrogen storage device through the compressor; when the photovoltaic power generation system supplies power When it is insufficient, the fuel cell uses the stored hydrogen energy to supplement power generation.
The continuous innovation of photovoltaic technology has led to a rapid decline in the cost of photovoltaic power generation around the world. Many countries and regions with abundant sunlight resources have achieved 10 cents per kilowatt-hour of electricity, and it has become the cheapest and cleanest power resource. At present, the combination of photovoltaics and electrochemical energy storage is developing well. In the future, photovoltaics will be combined with pumped storage and hydrogen storage technologies, and the development will be even better.