Electronics
A small (micro ATX) motherboard can be used as the collectors control centre. The board should be equipped with a BIOS that is able to start up from an USB device. This way the use of a hard drive can be avoided. In stead the OS and programs are stored on a memory stick connected to a USB port.
The board should be reliable but does not have to be very fast. A processor speed between 500mhz and 1ghz is enough to accommodate the necessary functions. Processors in this speed range do not have to be equipped with a cooling fan, which will add to the durability of the system. 256Mb of installed memory should be enough to accommodate the whole system.
The operating system will be a special small distribution off Linux, with just enough functionality to support the connected peripherals. Supported must be:
- A screen driver
- A keyboard driver
- A mouse driver
- USB drivers
The control program can be written in any language, however a compact size language (like C) is preferable to realize a small footprint of memory use. The control program must have the following functionality:
- Positioning of the dish (azimuth and altitude). The program should calculate a theoretical position based on location and date/time. After which this position can be corrected by the two solar sensors. This way the dish will stay (more or less) in place when there is no direct sunshine for a while. At night and in rainy conditions the dish must be put in a stall position.
- Control of the salt pump. The molten salt pump is controlled using the input from a temperature sensor in the receiver and the temperature in the lower part of the Thermocline tank. If the temperature in the tank is too low (the salt is solid), the burner must be engaged until the right temperature is reached. During this time the dish should be set out of focus to prevent overheating.
- Control of the burner. If temperatures in the salt tank are getting too low, the burner is used until the minimum working temperature is reached.
- Control of the hot nitrogen fan. The hot nitrogen (in the area above the molten salt) is directed to the hot air engine (Stirling). The flow of the nitrogen is regulated by the fan in accordance with the energy demand from the engine.
- The application must react to the leakage sensors that are placed in critical locations to detect molten salt leaking. When this happens, the dish will be placed out of focus and the salt pump will stop.
- An interactive part of the application will handle user input from keyboard and mouse, that overrule the normal procedures.
- Temperature (receiver, tank lower and upper part), power output, failures, etc must be shown on the systems display and logged to a file on the memory stick.
All sensors, valves and other electronics will be connected to the board by an USB interface. If the board has limited place to accommodate the USB devices a USB hub must be installed. Care must be taken that the devices do not draw too much power from the USB ports.
Optionally a GSM device can be connected to report failures to a central service point. Service can be admitted in this way while the system falls back to it’s backup system.