Renewable energy ....pitfalls and falsehoods

[Bruce Clark]

Considering solar and or wind power installations at home....there are a huge load of pitfalls that the industry does NOT generally make consumers aware of upfront. Many of these are easy to overcome once the consumer is made aware and allowed to apply his mind with the foundation of good information and realistic data at his disposal.

Major falsehoods / perceptions / pitfalls

1. A solar panel is just as effective at 30 degrees off the sun as it is facing it.
   
   This is extremely misleading and the biggest pitfall. A PV panel will generally convert the suns energy to electrical energy just as efficiently between the sun being at right angles (straight on) to the panel and all the way through up to approx 40/45 degrees off the sun, depending on the panel. So this portion is correct HOWEVER....the AREA of the panel EXPOSED to the sun is the big variable! A panel at right angles to the sun will provide 100% of the expected power (so a 2m2 panel will show 2m2 to the suns rays.) If however the panel is tilted at 45 degrees from the sun then only 70% of that panel is exposed = .7 x 2m2 = 1.4m2. SOoooo 30% is lost already. The lower the angle to the sun gets the worse this becomes...ie. the sun sees an ever diminishing cross section of the panel having a diminishing power capability equivalent of the sine of the angle of incidence of the sun.
   
   Considering a flat panel on a flat roof in the winter in JHB....the sun rises and sees nil of the panel.....at around 12h25, the sun is at its peak around 50 degrees above the horison.....the panel is then at 50 degrees from the sun....sin(90-50) = 0.64 x 2m2 = 1.28m2...THE BEST IT WILL BE! In summer this improves quite a bit as the sun peaks almost vertically above resulting in the panel being at almost 90 deg. to the sun at 12h20....This however is the best situation for the whole day....starts off with NIL and ends with NIL and sees everything in between as the sun rises and sets. A max. of 75% can be expected as the average over 7 hours of a summer day.
   
   So if your panels are flat allow at least 40% of additional panels. If they are fixed and face the sun direction at 12h20 (~N in JHB), and tilted at 23.2 degrees above the horizontal (average between winter and summer best angles), then an overall year power expectancy of around 65% is possible
   
   
2. If a house consumes 100Kw.hrs of power a day then a system that theoretically provides 100Kw.hr per day (100/7hrs = 14Kw of PV panels and a 100/24hrs = 5Kw inverter with 5Kw.hr battery) will be all they need.
   
   The 100Kw.hrs is the average. Possibly you use 80Kw.hr during the day alone..= 80/8 = ~10Kw/hr whilst the sun is shining. At the peak of usage during the day you may need power at the rate of 15Kw/hr however to cover all your appliances that may switch in at the same time. Depending how you use your power this number can be massaged considerably however the inverter size limits the max. you can use at any given moment EVEN if still connected to the grid.
   
   The panels you will need will need will be the 14KW mentioned above, plus an efficiency for the MPPT, transfer and inverter losses (10 - 20%), plus the panel orientation losses (see 1. above), plus an additional capacity allowance to charge the batteries which is not included in the average daily consumption. So as much as these are just random illustrative figures, these used would require a 15Kw inverter. and double the number of panels!
3. A system needs to be designed based on your maximum instantaneous power consumption measured over one or 2 weeks whilst on grid.
   
   From points 1 and 2 above this is moot and far more consideration needs to be given.
4. Simply adding a few panels will ensure the system can handle peak demand periods..
   
   Also mooted by 1 and 2 above.
   
   There are many more, however, they do all for the most part have workarounds but if the system is not designed properly you will end up paying a lot more for a heartache than is otherwise possible.
   
   I am willing to provide anyone interested with help and guidance towards the design of their system to fit their requirements and avoid the pitfalls, circumvent the constraints and get what they pay for...FREE of charge!

 

[Bruce Clark]

Who has any of the following problems / conditions...or any other not mentioned here, that pertain to their renewable energy installation?

You are off grid and experiencing "fatal" overload trips of the inverter (ie. inverter does not reset automatically).

You are grid tied and experiencing regular inverter "fatal" trips.

Your system is not producing the expected power

Inclement weather drains battery on non important appliances during inclement or cloudy weather.....especially when you are at work and you get home to a cold geyser etc.

If you are grid tied, you are not saving close to what you expected...this is very common with easy explanation

Your inverter is much larger than one that would be required to maintain a consistent power delivery for your normal daily consumption. ie. Your average is perhaps only 5KW/hr during the daylight hours, however your inverter and panels are provided to deliver 10Kw/hr. SOOooo.....somewhere along the line you are throwing a lot of your available power away, simply to accommodate peaks.​

These problems proliferate throughout all renewable installations and VERY FEW are really even close to being optimised. I would like to initiate discussion on any of the issues mentioned and have any others added to the list for consideration as well please. I have a multitude of possible solutions to share but also know that there are so many more valuable ones out there that I would love to learn of.

Pile in ...lets try and add as much value as possible PLEASE.