The Study On Solar Energy Utilization Of Low Ground Coverage Multi-tower Heliostat Field Near The User Side

This context establishes a low-ground coverage multi-tower heliostat field that can be used in urban and rural areas to achieve the comprehensive utilization of solar energy.The heliostat field is composed of multiple identical basic modules of two towers.The average annual cosine efficiency of the field is improved by the way of time-focusing.But the tower cost of this kind of heliostat field may be higher than that of a single tower heliostat field.In order to study the use of this kind of heliostat field,this context establishes a heliostat field model,taking the twin tower module heliostat field as an example,optimizes the heliostat field boundary,analyzes the characteristics of the heliostat field efficiency distribution,distribution hour of incident angle,tower height and other characteristics,and by analyzing the shadow distribution of the heliostat field on the ground to provide a basis for the combination of the heliostat field with crops or fish ponds.The main research contents and conclusions of this context are as follows:(1)Establish a heliostat field model,and explain and verify the heliostat field parameters,light-gathering methods,sun tracking,etc.involved in the calculation of the heliostat field performance.It also explains why the sparse heliostat field can be arranged: due to the limitation of the land and the use of the heliostat field,the dense heliostat field cannot be arranged,and the heliostat field is only used for heating,and a small-scale sparse heliostat field can meet the heliostat field heat collector power.In the calculation of the optical efficiency of the sparse heliostat field,it is found that the optical efficiency of the heliostat field can be higher than that of the single tower heliostat field while keeping the ground coverage of the heliostat field low.(2)To optimize the boundary of the multi-tower heliostat field at different latitudes with the annual average cosine efficiency not lower than the single-tower system and the tower cost per unit area not higher than the single-tower system as a constraint.The results show that there are multiple combinations of heliostat field boundaries between 11 ° N-51 ° N,which makes the maximum annual average cosine efficiency of the multi-tower heliostat field higher than that of the single-tower heliostat field.The higher the latitude,the more obvious the improvement of the cosine efficiency of the multi-tower heliostat field.Among them,the annual average cosine efficiency of 11 ° N-51 ° N is 9.5%-13.9% higher than that of the single tower scheme using PS10,respectively.(3)Compareing the tower cost of single tower and multi-tower,it’s found that within the scope of calculation,the cosing efficiency is higher,the unit heiostat tower cost of the multi-tower scheme can be reduced to 18% of the single-tower scheme.As a result,the tower cost per unit area of multi-tower heliostat field is not higher than that of a single tower,which can allow much lower ground coverge of the heliostat field,thus avoiding various obstacles in the field ang being flexibly application to complex sites condition.(4)By analyzing the angle of incidence,the reason why the average annual cosine efficiency of the multi-tower heliostat field is higher than that of the single-tower heliostat field is investigated.The increase in the annual average cosine efficiency of the heliostat field is mainly due to the increase in the distribution time of the small incident angle of the heliostat field.At mid and high latitudes,the multi-tower heliostat field has an incident angle of no more than 40 ° for more than 96% of the operating time,and even in an unfavorable low-latitude area,the incident angle does not exceed 50 ° for more than 97% of the operating time,that is,the multi-tower scheme has lower incidence angle fluctuations(5)The ray tracing method is used to trace the shadow coordinates of the incident point of the sun rays on the heliostat surface on the ground.It can be drawn that from the spring equinox day to the summer solstice,the shadow distribution of the twin tower module’s heliostat field to the ground,the shadow area on the east side of the heliostat field has a long shadow time and a small shadow area;the west side of the heliostat field has a short shadow time and a large shadow area.