A follow up article on our earlier post SolarMax principle

One example to make a difference between LoadMax and SolarMax amply clear is to take an example of Street Lights.

Let’s take a standard model – Sharp Street Light.

Lets take the model: SSLL 1018

The basic light there is a 18W light.

Load per day:  Let’s say the 18W light runs for 12 hours – Dusk to Dawn

18W x 12 Hours = 216 WHr is what is needed per day.

Let us look at what thay have designed it with:

Solar capacity:  80 W.

216 WHr / 80 W = Less than 3 hours.

So, the solar street light is designed to produce enough energy within 3 hours of sunshine. Sounds great and logical – when you evaluate from a general LoadMax principle.  But, imagine this – more than 300 days a year, sunshine will be for more than 5 hours.  So, Every single day on 300 days a year, 80W x 2 = 160 Whr is wasted.  And, we pay for that generation upfront.

Lets take batteries:  12 V, 75 AH.  Not to be a purist in battery design for ease of calculations – I will consider VxAH as a proxy for WHr.

12 V x 75 AH = 900 VAH or approximately 900 WHr.

We observed above that the requisite WHr per day is only 216 Whr.  So, this is designed with 4 times the requisite capacity.

I am not taking accurate figures.  For an application like solar street light where Hybridization with existing conventional sources of power is difficult, and where the focus is on automated reliable operations, I have no arguments against this design philosophy.  And, battery design is more to do with Depth of Discharge and life-time of batteries.

But, I am taking this as an illustration of LoadMax principle.

If there were backup conventional sources available – I would build this with a 50W module and 50 Ah battery – which is far more economical.  That will be “SolarMax”.

One word of caution though: SolarMax immediately means that it needs to be hybrid – to take care of low generation periods of solar energy.  Wherever hybrids are not possible or feasible or desirable – we need to go back to LoadMax.