Heliostats 101

单个模块热功率变为50MWt

eSolar此前的电站设计单个模块为2.5MW发电功率，其在加州Lancaster建设的5MW示范电站即由两个的2.5MW塔式热发电模块组成。新的设计改变了其集热功率，升至50MWt。

集热场设计重新调整

eSolar此前的镜场设计为长方形设计，两个长方形布置的镜场中间放置集热塔，单个发电模块的镜场面积约28000平方米。新的镜场设计采用了一种六边形的结构，四个子镜场围绕一个集热塔布置。反射镜尺寸也随之增加，此前的反射镜尺寸为1.136平方米，新的设计采用了2.2平方米的反射镜，单个集热模块共配装47000面定日镜，使得单个六边形镜场的集热面积大幅增加至103000平方米，集热塔高100米，比此前的55米的集热塔高度也有大幅增加。

增加储热系统

此前eSolar采用水工质方案，新的设计采用了熔盐传热储热的技术方案。使电站的容量因子由之前的25%获得大幅提升。以组建一个净发电功率100MW，配置13个小时储热的塔式电站计算，需要大约14个集热模块，容量因子可达75%（空冷）或78%（水冷）。如果配置6小时储热，则仅需要10个集热模块，容量因子约为50%。

通过管道联接将各个集热场的热量汇集至储热换热单元，以100MW配13小时储热的电站装机计算，预计冷熔盐的流通管道的长度在10500米，热熔盐的流通管道的长度在17400米，

为最大程度地降低熔盐对管道的腐蚀但不过多地增加成本，冷熔盐管道采用碳钢材质，热熔盐管道则采用不锈钢。所有管道均安装热追踪设备，采取多种保温措施，实现完全疏水。

以100MW装机的配置13小时储热的电站计算，需求的总储热能力在3500MWht左右，需要36500吨熔盐。据此设计的熔盐罐的尺寸为直径39米，高17.5米。

吸热器的变化

加州Lancaster的5MW示范电站采用了两家公司生产的不同的吸热器，分别为

Babcock&Wilcoxgs公司生产的外置式吸热器和VictoryEnergy公司生产的双向腔式吸热器。此次新的电站设计则由eSolar和B&W公司合作，将采用B&W为其新设计的熔盐吸热器，依然为外置式，外形结构与此前的设计基本相似。eSolar宣称，此款吸热器在工厂实现完全整装，减少了在项目现场的组装程序，更易实现快速安装。吸热器采用垂直管板和蛇型管线设计，具备30秒内的完全疏水能力，可实现快速启动。

Heliostats 101

The heliostat is the basic building block of the Solar Collector System (SCS). In our system, a heliostat consists of three main components: 

The drive – The drive houses two motors enabling our heliostat to move in two axes. The control software provides commands to the drive to use the motors to track the sun very accurately as it moves through the sky.  

The reflector module - The reflector module consists of the mirrored glass and metal frame that can be easily attached to the drive so it can be accurately controlled.

The structure – The structure provides a rigid, sturdy anchor for the heliostat to the ground.

Small Size, High Volume Approach

All of the heliostat components are designed to take advantage of high volume manufacturing techniques proven in industries such as automotive manufacturing. This enables both a cost effective design as well as rapid production and deployment of hardware. 

The drive is almost completely composed of aluminum die cast, sintered powdered metal, and injection molded plastic components. Final assembly is performed on a streamlined, dedicated line that includes an automated end of line test. 

The reflector module utilizes roll formed steel components, robotic welding, and a fully automated, robotic final assembly which ensures high quality and repeatability. Automated end of line tests evaluate the shape of the reflector using proprietary software based image analysis. 

The structure also takes advantage of roll formed steel components and robotic welding as well as progressive dies stamping. The optimized triangular truss structure offers a greater stiffness with less steel consumed.

History in the Making

From eSolar’s first heliostat in 2007, the design has come a long way! Quality and performance information from field testing and commercial plant installations has been leveraged to create a high value product. Additionally, advanced system modeling has led to optimization of heliostat size and packing density.

A comparison of eSolar’s last heliostat design to its current one shows improvements in manufacturability and cost, as well as some optimization to its size and shape.

Patented Calibration

A figure from one of our many patents in heliostat calibration and control

To direct sunlight (referred to as flux in the CSP industry) at a target hundreds of meters away, we have to know the position of the sun, the position of the tower and the position of the actuated mirror, or heliostat, to great precision.

There can be hundreds of thousands of heliostats at a single plant and accounting for each one is a significant challenge. Our competitors have avoided this challenge by deploying fewer, larger, and more expensive heliostats which are difficult to install and monitor. Our control software, Spectra, accepts the challenge head-on, massively parallelizing the problem, and using novel, patented algorithms to identify each heliostat as it is installed, and to prepare each heliostat for tracking by calibrating it to milliradian accuracy.

Precise Control

Using our control system to celebrate the 4th of July at Sierra.

That’s right: our control system points our heliostats with milliradian accuracy. For example, a 2m-wide beam of light is being directed to a point on a thermal receiver absorber panel 300m away. We need less than 1/10th of a degree of accuracy if we don’t want to spill our light off of the receiver. And we do it. With such fine individual heliostat control, we can create intricate flux distributions on our thermal receivers allowing for a wide variety of applications. We can control for superheat, salt temperature, peak flux or delivered power, our patented throttling algorithm gives us the unprecedented precision we need to respond to the necessary environmental and plant conditions.

Large-Scale Optimization

The techniques for our high performance in the field required many years worth of research, experimentation, and testing via large-scale simulation and optimization. We optimize everything: heliostat range of motion, thermal losses, receiver aim-point selection, control group selection, and which heliostats to use at every minute of every day in every plant around the world. Our models of instantaneous and annual performance have been validated time and time again, giving us the confidence (and the tools) to move forward with project bidding, winning, and construction.

Our SCS5 heliostat performing a pointing test.

eSolar’s Field Layout is Flexible

eSolar’s solar field includes the heliostats and all of the systems required to use them to deliver flux (heat from the sun) to a receiver. This flux can be used on a pre-qualified steam or molten salt receiver built by eSolar partner Babcock & Wilcox or a customer selected receiver. eSolar’s Applications Engineering team can also work with customers to deliver flux to receivers for other applications (such as EOR or desalination).

Dispatchable Power Reference Plants

eSolar won a grant from the United States Department of Energy to develop a reference design for a dispatchable baseload power plant. The result was an optimized molten salt power plant designed for rapid deployment and capable of producing power hours after the sun goes down. Because of the modular design of eSolar’s system, this reference design can be modified to fit customer needs.

eSolar has another reference design for an Integrated Solar Combined Cycle power plant. This design was created in concert with GE around their Flex Efficiency Turbines.

DOE Molten Salt Preliminary Design Specifications

     

Fourteen 50-MW thermal modules on 530 hectares total land area Central power block 13 hours thermal storage 275 MWt steam generator 115 MW (gross) turbine generator

Capacity factor: 75% (dry cooled (design basis)), 78% (wet-cooled)

 

Annual production: 655 GWh (dry cooled), 687 GWh (wet cooled) No fossil fuel hybridization required

Reference layout for the DOE Molten Salt Plant.