Terra Purna is located in an area of the planet with excellent direct solar radiation and is situated in a fairly wide solar horizon, so we use for the initial phase as a starting point for the production of electric energy a photovoltaic system ( PV).


We follow an off-grid strategy (no plug to the public grid) because currently within the project the interest is to live in conditions of self-sufficiency.


The components of the power system are: two 270 Watt SolarWord monocrystalline modules each at 24 volts, four 550Ah / 100h 6V Rolls batteries, one Victron BlueSolar MPPT 75/50 solar charge controller and one 1200 VA Victron inverter.




PV modules, connected in parallel, are plugged directly into the MPPT load controller which in turn carries the energy produced to the batteries. The inverter is connected directly to the batteries.


The production / storage system was set up at a 24 volt base voltage to reduce the problem of losses in energy transport between the production and storage systems. Currently the PV production system is quite close to the battery bank, however, in the future we will integrate systems based on other forces, wind and mini-hydro, which will necessarily be further away.






The accumulation of 24 volt power is made by connecting the four batteries in series. The distribution with the main points of consumption, at 40 and 80 meters of distance, is already realized in alternating current to 230 volts / 60 Hz from the exit of the inverter.


It is necessary to mention that, from our experience, the MTTP load controller was an optimum acquisition given that the difference in the management of PV module efficiencies is noticeable enough, especially in the days when there are some clouds. This is due to the maximum power point tracking algorithm of the PV modules that these controllers use.


With this small system (540 watts of PV installed and 550 Ah of batteries) we were able to power a refrigerator with freezing, lighting, two laptops, small appliances like the blender, a radio, a mobile phone, a 80 watt SHURflo water pump and, except on cloudy days, a washing machine that gets to do two or three washes in one day.


We installed the two photovoltaic modules in the tower of an obsolete parabolic antenna that had 3m. diameter. It has the possibility of daily monitoring of the two (which gives great freedom). This structure was installed on top of a cliff to reduce possible occlusions by the treetops.

The solar tracking system is based on a control system with an Arduino UNO micro-controller, two phototransistors and the parabolic bikes with linear motion transmission. This forms an intelligent tracking control system for the modules that enables a significant increase in their instantaneous power production output. The control system uses the two phototransistors, located on each side of the modules, to detect the moment when the sun is born, moments after which it controls based on an internal state. That is, using its internal timers gives the command to the motor to provide a movement of the modules by 15 ° per hour. Phototransistors are also used during the movement to correct possible deviations of the algorithms from the internal state and at the end of the day know when to return to the initial position.



With the simple spreadsheet below, you can analyze the energy needs of your home and calculate the main parameters of a photovoltaic system.


PV calculator


Geographic information system PV online:


Sistema de informação geográfica e simulação PV