We've got a finite amount of battery power in the 12AH, 12V leisure batteries and a finite amount of solar energy from the sun during a day, so we need to know when its coming and when its going if we are going to win in our challenge to run off-grid - even during mid winter when everything works against us. The main unit logs key parameters every 15 seconds that we can analyse the data and draw some graphs for future analysis, hence we need to gather this information first. Additionally, the user-interface on the main unit allows us to see instantaneous values.

The unit above is the power module. On the left is the sensor board which measures the Voltage and the Current in both a positive and negative direction up to +/-32A using a Hobbytronics Current Sensor module, this uses a hall effect transducer to measure current at ranges far above what we actually need.  We use them to measure the battery with a positive current indicating charge and negative indicating discharge. We use A second one for the solar panel but this should only ever show power being produced as a positive value. The right hand module is a Kemo M149 solar charge controller, which is rated at a theoretical 12V, 10A charging capability. Its important to control charge in lead acid batteries as over charging either leads to premature failure of the battery, or potentially explosive results that could cover me, or the chickens in boiling sulphuric acid. This now joins the increasing list of things we definitely don't want to happen in the design.

The solar panel is an 80W, 12V panel we obtained from SunStore, it has a no-load voltage of 21V and can produce 6.6 amps of solar power, which is huge!. The panel is 670mm by 900mm in size, so its fairly large and it comes mounted on a sturdy Aluminium frame. The plan is that this is to be fixed fixed on its pole mounting bracket and strapped to a sturdy tree in a high hedge, hence putting it above most of the trees where it can have a clear view and obtain the maximum solar energy, plus its well out of the way of people.

Given we know where North is, the plan is to fix it in an appropriate place and let it harvest the energy as the sun passes over the panel during the day.