Independent micro-net is the development direction of renewable energy

Faced with relatively low power demand and relatively large abandonment rate of abandoned wind, sustainable development of the renewable energy industry will be challenged. With the rapid development of renewable energy, the abandonment of abandoned winds still exists. The wind curtailment rate in 2015 may reach 20%, and some regions may reach 40% or even 60%. The national abandonment rate from January to September this year is about 10%. Abandoned light mainly occurs in Gansu and Xinjiang regions, among which, the desertion rate in Gansu Province is 28%, and the desertion rate in Xinjiang is 20%. This is mainly a question of market demand, but there are also technical issues. This year's power demand growth is weak, and the number of thermal power utilization hours has dropped significantly. Although new energy is protected by policies, it is also affected by market demand. China's northwest and north China have large-scale new energy sources. The phenomenon of abandoning winds and abandoning light is also particularly prominent. The reason is that although new energy sources are large, the local market is small and can't be delivered.

To solve this dilemma, it is necessary to solve the problem of transportation and consumption through government coordination; besides, the government needs to better coordinate the pace of new energy development and rational distribution in the new energy strategic planning, so that the construction of new energy sources and power grids can be completed. May be synchronized. In addition, it is necessary to adopt technology innovation and change the renewable energy development model so as to truly solve the problem of abandoning wind and discarding light at the lowest cost.

In the past, the comparison between renewable energy and traditional energy mainly focused on its own cost of power generation, while ignoring grid cost and technical feasibility. Without energy storage technology, due to cost and technical problems, it is difficult for the power grid to absorb renewable energy on a large scale. That is to say, there is no cooperation with energy storage technology and it will not be far from renewable energy alone. Therefore, the establishment of an independent microgrid (distributed) model of “energy storage + renewable energy” is the future direction of human energy development.

With regard to the "energy storage + renewable energy + power grid" model, it is difficult to make profit at present. There are two main factors that affect the return on energy storage investment: one is how much economic value each energy storage and discharge cycle can bring, and the other is the number of charging and discharging of energy storage systems. Among them, the number of charge and discharge is limited by the performance of the battery and generally does not change much. Therefore, the key to influencing the benefits of energy storage investment lies in the difference between the cost of charging and the benefit of discharge during each cycle. If the calculation is based on the cost of the Tesla battery, at a discount rate of 6%, taking into account the charge and discharge power loss and battery capacity attenuation, only when the charge-discharge spread is around 1 yuan per kilowatt-hour, the battery investment can be recovered. cost.

The resident's subsidy policy for distributed photovoltaic power generation is 0.42 yuan per kilowatt hour for electricity subsidies. Assume that the distributed photovoltaic power generation costs about 1 yuan per kilowatt-hour, the post-subsidy cost is equivalent to 0.58 yuan per kilowatt hour, and the peak electricity price in Jiangsu province is only 1.46 yuan per kilowatt-hour for the peak electricity price, charging and discharging. The spread is only 0.88 yuan per kilowatt, which is lower than the break-even point. Moreover, the subsidy of photovoltaic power generation will likely decrease in the future year by year, which makes it difficult to obtain economic benefits for household energy storage investment combined with photovoltaic power generation.

For renewable energy power generation companies, it is also very difficult to rely on energy storage for profits. At present, the on-grid tariff of wind power is approximately 0.51-0.61 yuan per kWh, and the on-grid tariff of photovoltaic power generation is 0.8-1.1 yuan per kWh. Due to the limited capacity of the power grid, a large area of ​​abandoned wind has been abandoned in many areas. There are plans to use energy storage systems to store excess power. Although this part of the electricity of abandoned wind and abandoned light is stored, its marginal charging cost is close to zero. However, since the cost of using the energy storage system requires 1 yuan per kilowatt-hour, in the case of the existing on-grid tariff, we want to achieve Earnings are indeed quite difficult.

Theoretically, as long as the cost of the microgrid can be lower than the terminal price, it should be economically feasible. According to the "Renewable Energy Generation Costs in 2014" issued by the International Renewable Energy Agency, the minimum cost for independent wind power projects is only 0.32 yuan per kWh, and the minimum cost for utility-scale photovoltaics is about 0.52 yuan per kWh, according to the current The cost of energy storage is 1 yuan per kWh. According to the cost reduction rate of renewable energy and energy storage technology in recent years, it seems that the microgrid is not far away from the realization of the cost. Of course, the reality will not be so ideal. For example, the distribution of wind and light is uneven throughout the year, and there are seasonal differences, making the microgrid need to invest in certain redundancy, which will increase part of the cost. Therefore, there may be a certain distance from the implementation of the microgrid, but it is not remote.

In terms of energy storage technology options, lithium batteries are currently the most promising. Pumped energy storage and compressed air energy storage are limited by geographical conditions and cannot be applied to independent microgrids. Moreover, the energy conversion efficiency of these two energy storage technologies is not high, and there is a high power loss during use. The storage capacity of the flywheel energy storage is limited and it cannot achieve long-term output. Battery storage has great flexibility in terms of scale and usage environment, and has application advantages. Among several types of battery energy storage technologies, lithium batteries benefit from high energy conversion efficiency and have the lowest negative externalities during use. Energy densities and conversion efficiencies of other types of batteries are difficult to exceed that of lithium batteries. Therefore, in the path of energy storage technology, lithium batteries have obvious advantages.

The key to restricting the development of lithium batteries in the future lies in the scarcity of lithium ore. From the perspective of the cost structure of lithium batteries, the cost of the lithium-containing positive electrode and electrolyte accounts for more than 55% of the cost of the battery. The price of lithium ore is an important factor affecting the battery price. Scarcity The gross profit rate of lithium ore enterprises can also be seen. Currently, the smelting cost of lithium ore is about 2000-2500 US dollars per ton, while the market price is between 4000-7000 US dollars per ton, and the gross profit rate is relatively high. According to the 2015 data from the US Geological Survey, the global lithium reserves are only 13.5 million tons. In 2013, the global output of lithium ore was 34,000 tons, of which about 10,500 tons was used to produce rechargeable batteries. According to Tesla's data, the world's annual production of lithium batteries is only enough for 500,000 electric vehicles. Therefore, it is very difficult for lithium resource reserves to meet the development of electric vehicles, let alone to support large-scale distributed and micro-grid energy storage. Therefore, the status of lithium resources in the future may be equivalent to today's oil, while countries rich in lithium resources, such as Chile, Bolivia, China, and Australia, will be able to grasp the lifeblood of global energy.

Recently, it has been reported that Cobre Montana in Australia uses hydrometallurgical methods to utilize low-quality lithium ore, such as lithium oxide extracted from mica, and its smelting costs are even lower than the smelting costs of the original high-quality ores. This new smelting method may greatly expand the range of lithium resources that can be developed globally. Taking mica stone alone as an example, it has a wide distribution on a global scale and the acquisition cost is quite low. According to CobreMontana, only about 10 million tons of lithium raw materials are expected to be obtained in the Czechoincino mining area. Therefore, if there is significant progress in low-quality lithium mining technology, its long-term significance may be much higher than the hydraulic fracturing technology for shale oil extraction.

Environmental protection and recycling are involved in battery production and use. For environmental protection issues, lithium batteries may bring major hazards. The cathode material contains heavy metals such as cobalt and nickel, and fluorine contained in the electrolyte. However, these substances are encapsulated in the battery, and normal use will not bring environmental impact. Even if breakage or leakage occurs, the electrolyte will only flow out and will not cause heavy metal pollution. At present, there are mature processes that can use non-toxic lithium iron phosphate electrodes. For battery recycling, the lithium battery casing is metal or plastic, the electrode contains lithium, heavy metals and graphite, the battery also has copper, aluminum and other materials, these have a high recovery value. Previously, due to the low output of lithium batteries, and the use of dispersion, so it is not very important for its recovery, there are not many related cases. However, the large-scale energy storage system must use a large number of batteries in a centralized manner, which will make it possible for recycling to have economies of scale. Jay Whitacre and his team have reported recently that they have developed environmentally friendly brine batteries that are safe and environmentally friendly. It is said that founder Whitacre had eaten a battery electrode.