My ROI is up in smoke with that because the forecast was that I will even up over 5 years. We are a year short, plus added to that I needed to replace the batteries about 6 months ago.
The question then is Solar power sustainable....?
Lets look at the Maths... (using average values to simplify it)
System cost R 42 626.93 ( this includes the new batteries)
The average usage per day before solar was 20.24 units so annually its 7386.76 units and at the time to cost of a unit was R 1.55 so prior to solar a years worth or power cost me R 11449.48
The average usage per day after solar was 15.89 units, so the same calculation means its 5800.90 units for the year at R 1.87 per unit means a total cost of R 10 847.69.
Now that does not look too great at first glance but we need to consider that the cost of power is a moving target.
To simplify it lets assume I had two identical houses one on solar and one on Grid.
The table looks something like this...yes... year 3 power cost more than year 4, I have the slips to prove that, not quite sure how that worked, it might have had something to do with Free basic units..
| Units | Year 1 | Year 2 | Year 3 | Year 4 | Total | |
| Grid House | 7386 | 12985 | 13849 | 14240 | 13864 | 54937 |
| Solar House | 5800 | 10196 | 10875 | 11182 | 10887 | 43140 |
| Power cost | 1.76 | 1.88 | 1.93 | 1.88 |
So the grid house has a power bill of almost 55K while the solar house has a bill of about 43K.
Not a lot in that, in fact take into account the initial investment of almost 43K and the estimated savings of 11K per 4 year cycle and you would be better off investing 43K into a savings account at 8% which would yield 13K over the 4 year period. (simplified)
BUT, we are not taking everything into account, what we can't measure is the exponential growth in power use, we have added things to make our lives easier, we ran a small air conditioner on the Solar system on hot days, we added appliances, computers and smart devices, all these use power and all this power is supplemented by the solar system in the day. So our demand is higher than the pre solar days.
ADD to this the convenience that when load shedding happens our power stays on, we are all willing to pay for this convenience.
So just exactly how do we then view Solar power from an ROI perspective? The ROI charts don't have a column for "cost of convenience".
I guess someone with a lot more knowledge can spin the numbers a little better and break it down into components so you have the things that last 25 years and the things that only last 4 years, crunch all those and it probably looks a lot better.
To me, I would do it purely for the convenience without giving it a second thought..
