Is solar-thermal power generation reliable?

Speaking of solar power generation, we must be no stranger to small street lights equipped with solar panels on the roadside, large to large solar power stations, there are solar power generation figures. However, most of these solar power projects are photovoltaic power generation, in addition to solar photovoltaic, there is a way to use solar energy into electricity - solar thermal power generation.

(A) What is solar thermal power generation?

Solar thermal power generation is a technology that converts relatively concentrated solar light energy into heat energy through the transmission medium, and then converts it into electric energy. General solar thermal power generation system can be divided into four parts: heat collection system, heat transmission system, heat storage and heat exchange system, power generation system.

The heat collecting system, as the name suggests, is to gather solar energy and convert solar energy into heat energy, in short, to use the sun to heat the working medium (editor's note: the working medium is to achieve the mutual conversion of thermal energy and mechanical energy). Heat transmission system, is through the pump and other equipment to transport the working medium to the heat storage system or heat exchange system, the transmission process is a word: "fast", so as to avoid the working medium "cool" down. The heat storage and heat exchange system is equivalent to a "big battery" and a "burning furnace".

The heat storage system stores the incoming heat, and the heat exchange system "boils" the working medium (usually water) into steam, which drives the turbine to spin. The power generation system is similar to the conventional thermal power generation system, the steam drives the turbine, and then drives the generator to generate electricity.

Therefore, solar solar thermal power generation has undergone a four-step energy conversion process: light energy - heat energy (stored or generated) - mechanical energy (turbine rotation) - electrical energy.

Four major systems of solar thermal power generation

Photothermal power generation is divided into high temperature power generation and low temperature power generation according to the temperature of the heating medium. High temperature solar thermal power generation is the use of water vapor as the medium of Rankine cycle. Low temperature solar power generation is a Rankine cycle with low boiling point organic matter as the working medium

Rankine cycle

At present, the mainstream form of solar thermal power generation in the world is high temperature solar thermal power generation, which can be divided into tower type, trough type, dish type and other types according to different forms of heat collection.

The tower system uses multiple flat mirrors (called fixators) to reflect sunlight to a receiver at the top of the central tower (the luminous part in the lower left image) and convert it into heat to transmit to the working medium.

The condenser of the trough system is a trough paraboloid, which is generally used in series, and the thin tubular collector is fixed on the focus line of the condenser, and the working medium is heated in the collector tube. At present, in the international solar thermal power stations that have been put into operation or under construction, there are many trough solar thermal power generation systems.

Dish photothermal power generation is a power generation method that uses rotating parabolic condenser to gather sunlight on the collector, and the working medium in the collector is heated to drive the generator to do work and generate electricity, which is the highest power generation efficiency at present, up to 30%.

Tower, trough, dish type photothermal power generation

(2) Tower type, trough type, dish type, three kinds of technical routes big PK

The three main forms of solar thermal power generation have been mentioned above - tower, trough and dish systems. Let's find out.

1, tower type photothermal power generation system

The concentrator of the tower system is generally a heliostat group (editor's note: heliostat is an optical device that reflects the light of the sun or other celestial bodies in a fixed direction), which concentrates the sunlight to a receiver fixed on the top of the receiving tower, and the heat absorber on the receiver absorbs the high heat flux radiant energy reflected by the heliostat system.

At present, most heliostats used at home and abroad are flat concave mirrors with small radian surfaces. Different from the other two, the tower system can store heat through molten salt, with high concentrating ratio, high working temperature, short heat transfer distance, less heat loss, and high comprehensive efficiency of the system, which can achieve high precision, large capacity, continuous power generation, suitable for large-scale grid-connected power generation.

2, trough type photothermal power generation system

Trough system Because the condenser is a trough paraboloid, the sunlight will be focused on a straight line, that is, the focal line. Tubular solar collectors are installed on this focus line to absorb the focused solar radiation energy.