How many batteries?

Matthew's story - episode four: Why Solar? 


Design considerations when building an off grid solar power system.

In designing the off grid solar power system for Matthew and his family it was important that life remained as close to what it was when they were living on the national power grid.  Whilst the odd compromise was necessary, today's technology allowed for a reliable and robust solar power system to built.

The design of the solar power system is crucial.  The two major parts of the system are the solar panels themselves and the battery storage system that stores the excess power created by the panels allowing Matthew and his family to live on the battery system for up to 2 days without sunlight.

Batteries are the most expensive part of an off grid solar power system and so it is important that this is designed properly based on the requirements established during the energy audit.  The batteries for an off the grid system like Mathews have a 10-15 year design Llife however it is important to note that the “design life” of the batteries is actually dependant on the “Cycles” of the batteries charge.

A cycle in battery terms is one charge and one discharge.  When designing the battery backup Pranay says that the system should only ever reduce the battery charge to approximately 50%


“When we design an off grid system we try to design the Batteries so that they do not drain significantly. It drains up to 50% and you have an autonomy of up to 2 days, so it will cover you for at least two days without sunlight”.


For the panels there are two options for mounting.  One is on the house itself and the other is to ground mount the panels.  Matthews house was oriented for the views and not the sunlight and his roof pitch was not at the optimum angle for the winter sun so the decision was made early on to ground mount the panels.  Ground mounting enables the panels to be set at the right angle to the sun, especially for the winter months and also to face the right direction to enable sun to fall on the panels for as long as possible during the day.  This also means that less panels need to be used to generate the same amount of power.

For off the grid solar systems ground mounted panels are the preferred method for the very simple reason that it means the greatest efficiencies can be achieved both in terms of using fewer panels and also to maximise exposure to the sun.


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When talking about living in an off grid home compared to living connected to the grid. 

"The added value of course, is that you don't get any power bills every month!"

Matthew Hardy - Off Grid Home Owner.