How efficient can a solar system be?

As you may well know a solar system has a number of parts, each with there own efficiency ratings.

This article is made to show you the differences between good and bad solar installations. And why it is so important to get it right the first time.

The items below have the potential of losing power through their operation.

  • Solar panels
  • Solar Cable
  • Solar Charge Controllers
  • DC Cable
  • Solar Batteries
  • Solar Inverters

Solar panels have a typical efficiency of 15%-18%. This is ranges from the most common solar panels today.

Solar cable has a typical efficiency of 97%-86%. This is based on various Voltages, Amps, diameters and lengths.

Solar charge controllers have a typical efficiency of 80%-99%. This is between PWM and MPPT's.

DC cable has an efficiency of 96%-99.5%. There is not a huge amount of losses involved in short distance DC cable routes. This, however, can get worst in cases where long distance is involved.

Solar batteries have an efficiency of 60%-99%. Battery technology is still under huge RnD. Each technology has its own pros and cons but is getting better every day.

Solar inverters have a typical efficiency of 70%-96%. Solar inverters are designed around efficiency for the most part. Other inverters are designed with other factors in mind, such as higher reliability, stability and convenience.

 

Best to worst-case scenario examples

If we take the best-case scenario and the worst-case scenario we can determine the range of efficiency a solar system can produce power.

Sunlight at the upper atmosphere has a Solar Irradiance of 1,360W/m2. Depending on a number of factors this figure decreases before meeting the surface. The highest amount I could find was 1066W/m2 at surface level.

To do the math I will need to choose a starting point for this example. I will start the Solar Irradiance at 400W/m2, this is the mid to lower levels of solar irradiance that South Africa has to offer.

 Solar irradiance (sunlight)Solar Panel EfficiencyUV Cable Volt DropSolar Controller EfficiencyDC Cable Volt DropBattery EfficiencyDC Cable Volt DropInverter Efficiency=Total Efficiency
The Good Solar System (Highest Efficiency System)   18% 97% 99% N/A 99% 99.5% 96% = 16%

400W/m2 of sunlight

72W

(-328W)

70W

(-2W)

69W

(-1W)

69W

(-0W)

68W

(-1W)

68W

(-0W)

65W

(-3W)

=

400W - 65W

=335W Lost to Efficiency

The Bad Solar System (Lowest Efficiency System)   15% 86% 80% 96% 60% 96% 70% = 4%

400W/m2 of sunlight

60W

(-340W)

52W

(-8W)

41W

(-10W)

40W

(-2W)

24W

(-16W)

23W

(-1W)

16W

(-7W)

=

400W-16W

=384W Lost to Efficiency

 

Below is an illustration of the efficiency curve as the power flows through a solar system.

Efficiency Curve With Panels

The conclusion is that at the end of the day a good solar system can be 4x more productive than a badly designed solar system.

 

Most of the losses originate from the solar panels.

This technology is improving every year. but for now, let us negate the panel losses and only look at the losses after the solar panels.

 Solar Panels RatingUV Cable Volt DropSolar Controller EfficiencyDC Cable Volt DropBattery EfficiencyDC Cable Volt DropInverter Efficiency=

Total Efficiency

The Good Solar System (Highest Efficiency System)   97% 99% N/A 99% 99.5% 96% = 16%
300W Solar Panel

291W

(-9W)

288W

(-3W)

288W

(-0W)

285W

(-3W)

284W

(-1W)

272W

(-11W)

=

300W - 272W

= 28W Lost in Efficiency

The Bad Solar System (Lowest Efficiency System)   86% 80% 96% 60% 96% 70% = 4%
300W Solar Panel

258W

(-42W)

206W

(-52W)

198W

(-8W)

119W

(-79W)

114W

(-5W)

80W

(-34W)

=

300W - 80W

= 220W Lost in Efficiency

 

Below is an illustration of the efficiency curve as the power flows through a solar system.

Efficiency Curve Without Panels

Looking at the above results shows that there is a substantial difference between good and bad solar systems. Most of the differences in efficiency are based within the rest of the solar system (After the solar panels). The good system is 3.4x more efficient than the bad designed solar system.

 

Please be aware that certain estimations had to be made in order to acquire the above figures.

The efficiencies of these items can be more or less efficient than represented here.

If you see any errors please contact us.

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