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.