Solar tracker design choices
Considerations and objectives that inspired the realization of our low cost mobile solar tracker.
One of the guiding principles is surely the idea that it should be a simplified realization in order to contain the costs and to allow the construction DIY to anyone with a minimum of tools and craft skills.
The low cost for the type of small tracker like ours was an essential feature as it would not make sense to spend more than 100/110 € - 110/120 $ in materials to increase the performance of a single panel when with a slightly higher cost you can buy a second solar panel to be placed at an angle so as to better cover the path of the sun throughout the day.
The iron structure was therefore designed as simple as possible assembled with screws and bolts, it had to give up the vertical movement (tilt) giving a fixed inclination so you can use only one linear actuator with 150 mm stroke definitely suitable for the movement per pair and strength even of 300/350 Watt panels.
[ First steps design of mechanical structure ]
- Control electronics for commercial solar trackers, until not so long ago with high costs but now on the market there are very low cost Chinese production control units equipped with sensors, control unit with LCD display and programming keys, this type of control units have not been taken into consideration because even with an excellent price for a low cost project they have poor reliability for the economy of the materials and being "universal" they must be programmed with rather complex procedures, in addition in the event of failures or malfunctions there is no practical possibility of having assistance.
- Control electronics for solar trackers made on Arduino base with pre-assembled electronic boards, with management program made by amateur or even professional programmers who network the files for programming, in this case the pre-assembled electronic part turns out to be of good invoice and reliable but the difficulties may arise from the management program that if not well studied leads to malfunctions or blockages in case of particular weather conditions. In addition to these boards should be added 2 watertight containers being components sensitive to moisture this need brings up costs, for this reason , while being a good solution provided that a well-made program is supplied, it was chosen not to use them.
- Control electronics for solar trackers with analog electronic components; operational amplifiers, transistors, photodiode resistors. On the web there are some tables of these electronics some only theoretical, some realized, others incomplete, that is often missing after chasing the sun during the day the circuit part of the system that makes the panel return to the initial position so as to receive sunlight on the sensors the following morning. We also tried this type of circuit designed to work combined with the timer type CN101 building a prototype (described here - Photoresistor Circuit -) that presents some original part and that in short tests has proven to work properly, further tests have not been carried out as this also requires at least one watertight container with window for photodiodes.
- The solution we used and new, has as main difficulty the DIY construction of what can be defined linear cam, to be made of plastic material that must be shaped according to the measures described below, overcome this small obstacle the solution has many advantages.
In addition to the linear cam only need 2 switches, 3 relays mounted on simple printed circuit board and the timer, it is an electro-mechanical system that except for the timer does not use electronics, this makes it reliable and much less sensitive to moisture and extreme heat, if you shelter it from the rain you can also leave it without container.
[ All the "electronics" needed for controlling our solar tracker ]
The principle of operation is based on the rotation of the panel in steps set by timer, there is no sensor so no indecision on the placement, the cam attached to the linear actuator takes one step and then a rotation of a few degrees every time interval set in the timer,basically, each ON click switch stopping movement until the timer goes OFF ,this change of condition makes it move one step until the new click of the switch. This is repeated for 15 timer programming, the last of which triggers the second lower switch used to bring the solar panel back to the initial position waiting for the next morning to start with a new cycle.
[ VIDEO step-by-step rotation test with automatic return from bottom position to initial position ]
