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PlanMyPower Deep Cycle Solar Batteries

Solar System Battery Sizing Calculations And Suggestions

The Choice of and design of Deep cycle batteries for Solar Panel Systems and solutions is much more complicated than the design of same for a power backup system, why?


Off Grid Solar systems can be categorized into 2 groups


A)    An Off grid- Hybrid system, these systems have an alternative energy source as backup, such as Eskom , it is thus a hybrid (combined system), between Solar Panel solution and Eskom (or generator)


B)    True Off-Grid, these systems, do not have a Eskom backup- typically a Farm, a remote location etc



Deep Cycle batteries are an essential very critical components of any Solar panel solutions system, the under design, over use and under charge of the deep cycle battery cause battery failures, a problem which will keep on repeating itself over in over in the same scenario.


Deep Cycle Batteries are designed according to certain specifications, they have limitations and should be used in accordance to these specifications.


We will herewith present to you considerations to choose the correct deep cycle battery and also the rating of the minimum requirement of deep cycle batteries for your specific solar solutions system application, in order to get the most effective prolonged lifetime out of the deep cycle batteries for any system.


We discuss battery types under a different page and so the rating and quality of battery chargers, the focus here is merely on the design of the deep cycle battery pack. I will do so with the help of a few real examples.


  1. A 5 kWh per day Small Off grid hybrid Solar system - typical user inside town who have Eskom to support, but use a solar system to become independent
  2. A 16 kW.h per day Medium size Off grid hybrid Solar system - typical user inside town who have Eskom to support, but use a solar system to become independent
  3. A 30 kW.h per day Big size Off grid hybrid Solar system - typical user inside town who have Eskom to support, but use a solar system to become independent
  4. A 16 kW.h per day Medium size FULL  Off grid  Solar system - typical user a farm owner
  5.  A 30 kW.h per day Medium size FULL  Off grid  Solar system - typical user a farm owner

 

It is very important to understand that in a solar panel system, deep cycle batteries could actually cycle more than once per day. A system should always be designed in such a way that it could not, but in reality the nature of the deep cycle  batteries (which is chemically slow in reaction) and the type of unpredictable load,

This, has the affect that the load is variable and unpredictable .  We actually do not know how deep cycle batteries really react on this notion over a long time, so we can only try and limit this cycling of deep cycle batteries and the design accordingly.

Deep Cycle battery data curves is always based on STC (Standard testing conditions) , ie tested at a fixed temperature, tested with fixed constant load etc.

Solar Panel solution - Deep Cycle Battery Design Examples

Example 1 - A 5 kWh per day Small Off grid hybrid Solar system - typical user inside town who have Eskom to support, but use a solar system to become independent


Example 2 - A 16 kW.h per day Medium size Off grid hybrid Solar system - typical user inside town who have Eskom to support, but use a solar system to become independent



Example 3 - A 30 kW.h per day Big size Off grid hybrid Solar system - typical user inside town who have Eskom to support, but use a solar system to become independent



Example 4- A 16 kW.h per day Medium size FULL  Off grid  Solar system - typical user a farm owner



Example 5 - A 30 kW.h per day Medium size FULL  Off grid  Solar system - typical user a farm owner



Conclusion

In Reality the true requirements and design of a Deep Cycle Battery bank for a true off-grid Photovoltaic Solar Panel solution is very high. In reality due to “budget” restrictions, a very competitive market and suppliers which under quote on such system, cause long term problems which will only start showing its head in 3-4 years time from round 2017. At least the option and the explanation of the differences should be presented to the potential clients to consider for himself- for your own system, you have the questions here to ask, the proof is within the specification documents of the various deep cycle batteries, consider your options.


Please feel free to contact us, for any enquiries or advice [email protected]  


Copyright : Dr Gawie van der Merwe ; PlanMyPower (PTY) Ltd