Solar Energy is rather new and emergent in Asia and in many countries consumers and companies do not know exactly what it is or what it means and some myths have paved their way into the market place. Here are the top ten:
1. Radiation, irradiation, irradiance
This is the one of the classical ones. It is common to hear all of the three names used as if they were the same. Radiation is a general term in Physics to describe a phenomenon where energy is transmitted through a medium.
Irradiation on the other hand is the energy transmitted and is measured in Watt-hour being Watt = Joule per second which means a power, measured in Watt. Irradiance is power, exactly what was mentioned before. The Sun is seen as a “machine” with a power rating of one 1 KW and so the energy delivered to earth is measured in KWh. Usually what people are mentioning is solar irradiation and in some specific cases solar irradiance.
2. KW and KWh
This is a global problem and everyone seems to be unaware of the difference between energy and power. We consume at our homes electricity, which is energy and the source that generated that energy is rated in power. So we do not consume “KWs”, but KWh and a PV module does not generate 220 W, but is rated with 220 Watt peak and generates that power times the number of working hours at a peak rate (or equivalent).
3. GHI, DNI and diffuse
Solar irradiation is actually made of three components while people think that there is only one component: “solar radiation”. Those three components are named Global Horizontal Irradiation (GHI), Direct Normal Irradiation (DNI) and Diffuse irradiation (or irradiance in all cases, if you want to use power).
GHI is measured, as the name clearly mentions, horizontally, which means on the ground and globally, which means without any device/shadow on top of it. GHI measures all irradiation that arrives to the horizontal surface. This energy can be calculated to any tilted surface based on simple geometry and that is the total available irradiation on the surface. DNI on the other hand is just the normal or perpendicular component of the irradiation and so the surface has to be always perpendicular or normal to the sun, requiring tracking.
Diffuse irradiation is meant to be all the irradiation that comes onto the surface indirectly, that means that the measuring device shades the direct irradiation from the sun and only captures the diffuse irradiation. GHI is the “solar fuel” for PV applications while DNI is the “solar fuel” for tracking and concentrating technologies.
4. Tracking is much better than non-tracking
Tracking as mentioned above is based on DNI, since the system is tracking the sun totally – 2 axis - or partially – 1 axis. Clearly sites must be evaluated in order to understand the GHI available, convert it to the tilted surface that yields the maximum throughout the year and compare it with the DNI available to understand which potential is greater. On the tracking case there is also the need to power the tracker which subtracts to the energy generated. Just some places in the world display DNI higher than GHI.
5. What is good for PV is even better for CPV
This is a common mistake and often mentioned when PV is compared to CPV. As mentioned above DNI is the “fuel” for CPV while GHI is the “fuel” for PV. So to compare CPV with PV require at least the same “fuel”. Clearly high GHI sites as Singapore, Hong Kong, Macao or South Korea do not have god DNI values so CPV will not produce much when compared to PV. Though CPV is more efficient than PV it is far from the claimed efficiency of the CPV cells (triple junction cells).
6. The Sun is always in the south
That is actually not true and only true if you are “above” 23º latitude north. The opposite – the sun is always on the north – is also only valid for latitudes “below” 23º latitude south. Within the +23 degrees and -23 degrees latitude the sun is in both sides and the more you are near to the Equator it will be actually half of the year on South and half of the year on the North. BIPV (Building Integrated PV) benefit from this and clearly horizontal mountings favour such locations and not latitude mountings.
7. CSP is cheaper than PV
This is also not true and it is something that was left from the past. The potential of being cheaper is indeed there, but currently PV is cheaper than CSP in every sense of the word: equipment and financing. CSP has on the other hand clear advantages: can be stored and so become dispatchable and integration with existing thermal power plants. The current market sizes of PV and CSP are also completely different, with PV installations being more than 20 times the size of CSP, so clearly CSP may still become cheaper than PV in the long run and bring the mentioned advantages.
8. Solar energy is expensive
This is another global myth that Fit (Feed-in-Tariffs) have helped strengthen. Renewable Energies, namely solar and wind are driven by strong initial investments but carry what no other power generation equipment carries: energy. Energy is built-in, it will not be paid for as in conventional fuels. There is nothing similar in our lives: we are used to buy equipment and pay additionally to run them. Solar modules do work on their own if correctly positioned and will yield electricity without further cost. The cost of the generated electricity by these systems can be calculated and is called Levelized Cost of Electricity (LCOE). Such cost can then be compared with other sources of power generation. Solar energy costs less than grid price, but requires a higher price to be financially viable and to generate an Internal Rate of Return (IRR) that makes the investment interesting. It is important to understand the difference between price and cost.
9. Solar Energy will never be cost competitive
This sentence usually heard throughout the power markets and some high level government officials is all but accurate. Conventional power is still cheaper due to the more than 100 years of history of that industry with subsidies from all governments for its development and deployment. Clearly the current market players were not born this decade or the previous, but have many decades of existence.
Solar Energy as well as other Renewable Energies are infants compared to these mature technologies. It is clear that Renewable Energies have to be incorporated in the energy mix of each country and it is up to each country to actually determine the potential of each one and benefit from it. The future will be Renewable and not fossil and it is time for everyone to start putting their efforts and join the revolution. Solar Energy is already cheaper than diesel based generation and in some cases already regarding the grid costs.
10. “I have a 1 KW installed system at my home so I need 1 KW of solar power”
Although it comes as number 10 this is a myth that should have been “upgraded” in the scale. This is usually a more technical question: it is common to see people using power ratings of equipments as the source of sizing PV systems, comparing the cost of conventional systems with PV modules and other Renewable Energy products.
As mentioned above electricity/energy is built-in on all Renewable Energy equipments (and those that do not have such clear built-in features require some deeper analysis) and so the initial cost contains the electricity to be generated throughout the life time of the product/system while a conventional power system does not yield any power unless fuel is purchased.
Secondly the driver for sizing equipments is the electricity required and not the power rate of the equipment. For off-grid applications the time of consumption is also of crucial nature for an adequate sizing. So focus on the electricity required per day on an hourly basis, if possible, and throughout the year, look at the resource available and determine the right size based on consumption and cost. It may turn out to be more than the power rating of your existing equipment, but it may also be less than that.
Solar deserves a chance to make it to the mainstream and follow on the footsteps of Wind Energy. Myths are sometimes harmful and spread bad concepts.
The views expressed in this column are the author's own and do not necessarily reflect this publication's view, and this article is not edited by Asian Power. The author was not remunerated for this article.
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Agostinho Miguel Garcia is the Chief of Development and Engineering at Sun Business Development Lda.