Different types of motors :
DC motors : a voltage is provided once (which in fact means speed) and the motor will run until we send a stop signal. You have to use speed reducing gears because otherwise they are running too fast and have a low torque. Their characteristics (especially amperes) depend on the weight of the solar module(s). In this case you also need a dual H-Bridge motor driver like the L298 board. It can work between 6 and 46 v and up to 2A. This board will be connected to the Arduino so that the software can drive the two motors.
Stepper motors : a number of steps is provided to move forward / backward, after that the motor stops automatically.
: it is a rotary actuator
that allows for precise control of angular position, velocity and acceleration. It consists of a suitable motor coupled to a sensor for position feedback. It also requires a relatively sophisticated controller, often a dedicated module designed specifically for use with servomotors.
Evaluating production / consumption costs of electricity
Here is an interesting document evaluating the consumption of a 4 persons family during the year (2007 in France).
It turns out that a four family person consumes 6800 kWh in one year. So for ten people (size of a typical unMonastery project) it would be about 17000 kWh per year.
If you want to produce 25% of electricity using solar panels, you'll have to make 4250 kWh per year. Then to know which quantity of solar panels to install it will depend on :
So for Matera with a 2.4 kW installation (eight 300W solar panels) you should produce 4690 kWh per year using solar trackers (see this document that estimates PV production for a 1kW installation in Matera). To estimate the PV production you can use this site.
Of course this is an average value for a year. During the the winter it will be significantly less so you'll have to adjust it according to the season.
To evaluate the costs of such an installation you'll have to consider other things :