Solar panel performance Vietnam
Solar energy system at Suntiki office in District 3, Ho Chi Minh City.
This post is updated each year. Latest update: 2019.03.30
What is the system power?
What is the optimal string strategy to mitigate the shadows:
Structural mount: should you hire local construction company instead of full package with solar energy company?
It depends on how involved you want to be in the construction and how familiar you are with construction standards. Remember, this installation need to outlast 25 years wear and tear going through major storms rated as natural disasters, typhoons, extensive flooding and more. And the electrical part require an experienced solar engineer to make sure it is installed safe from personal danger as well as making sure the equipment installed correctly.
Suntiki Tips for DYI enthusiasts:
1. Nr.1 offender, we call this the “welder’s spree”. We notice some local construction guys think the solar panel is an indestructable metal piece and will weld right next to it either in front or from behind! For obvious reasons, this will destroy pv output and invalidate your warranty!
2. Some guys will suggest welding your solar panels right into the structure. This will destroy solar panels! Mechanically fasten your solar panels is the only sensible way.
3. Be careful handling connected electrical cables under direct sunlight. It will carry live current if negative and positive touch each other.
4. Need to consider watertight construction:
* Cement the ground plate that interface the penetrated roofparts.
* Use Sikaflex Construction to seal the edges of the cement ground for extra protection against rooftop flooding. This material they call “xúc xích” in Vietnam construction lingo.
5. Some people think the equipment in the house connect into solar panels. This is not correct and will not work. The solar panels connects into inverter that connects into the house electrical system.
Are you using the correct circuit breakers?
Easy9 vs. C60H-DC
In accordance with American electrical standards (NEC standards), we apply double pole circuit breakers in the following locations:
* between solar panels and inverter. One CB for each string.
* 1 AC circuit breaker between inverter and the house electrical system.
So, in total 3 double pole CBs. That way we can cut electricity from both sides of the inverter for maintenance. Furthermore, a good design have these 2 in consideration:
1. Use Schneider C60H-DC breakers for DC connections (between solar panel and breaker.) These are properly rated for direct current connections. Some shops in HCMC sell this. However, they costs significantly more, 700,000 VND, compared to the Schneider Easy9 breakers that cost 150,000 VND but only good for AC electricity.
2. What amp rating should the CB be? For example, is 20 amp too high?
* Let us apply NEC rule that OCPD minimum size should be maximum circuit current = Isc x 1.56
* In this case, 9.66 x 1.56 = 15.0696 amp
* Therefore, theC60H-DC of 16 amp is sufficient in accordance with NEC.
* Too high amp rating is dangerous because the CB does not break when it needs to! Too low amp rating will trigger CB all the time!
Where to place the inverter?
We have SMA 1 phase Sunny Boy 3.0 with 3,000 Watt AC. Strategy for inverter location:
* Enough space to meet minimum inverter clearing room requirements
* In cool shaded environment, definitely not exposed to sun.
* Close to solar panels to minimize wire length. Also close to house electrical connection at the floor CB.
* NEC require connecting inverter at the far end of the main distribution panel (MDB). And there are further rules depending on MDB amp rating and solar energy system power. However, in Vietnam, the typical house does not have a centralized MDB. If there is a centralized MDB, it consists of a number of separate circuit breakers as opposed to a central sub panel with many connected circuit breakers. In this case, we recommend deviation from NEC requirement by locating inverter to the nearest floor circuit breaker and make the connection there. This minimize the electrical wire from top floor to bottom but where the connection would still be the same.
* The major startup issue is the ground fault when the inverter is not grounded. If any issue, I recommend to contact a solar engineer rather than your local electrician because it probably an inverter software setting fault rather than electricity fault. But, unless you are electrical engineer with excellent knowledge of inverter, I don’t recommend DYI approach because handling equipment with live electricity is dangerous.
How many kwh do you get for 4,000 Watt?
The benefit of flat rooftop is that we can set ideal tilt, which is 15 degree in Ho Chi Minh City. This gives us a maximum possible of 5,785 kwh first year according to PVGis. This is represented by the blue line in graph. However, the real production in year 2018 is 4,847 kwh which is about 15% less than the maximum possible. This is due to following:
* We switched off pv systems for some days for testing.
* The shadow effect of the tank in the mornings.
From the graph we see that for 4,000 watt DC system we have average month production of 400 kwh. This is with shading effect. On ideal with no shadows, we should get 450 kwh.
The reasons the system is producing less solar energy than the model are:
1/ is due to the water tank shadows. It affects one string in the morning from 7 to 10 am.
2/ we have disconnected the system from time to time to test our battery system.
Did you get the correct EVN 2-way meter?
The system began production on 25 September 2017 and were the first solar energy system in District 3 to have EVN meter. However, this meter malfunctioned and we had to replace by 18 January 2018. So unfortunately, our EVN meter is counting from this day, 4 months after our system is installed.
From the below table we see that during period of 18 January 2018 to 02 April 2019 we have:
The office has 2x 1hp aircon. At least one aircon is used at all times. The office pays EVN residential progressive rates, and with an electric bill of at least 500,000 vnd/ month, the solar energy offset the highest rates of 2,701 VND/ kwh.
How much money do you save? Now we can answer the question you have been eyeing for!
The quick answer: 450 kwh x 2,086 vnd = 938,700 vnd/ month… but this is not correct.
The real answer:
But, wait, it gets better, the above was for 2017. Recently, government came with new incentives for us:
1. 2,086 vnd/ kwh increased for 2018 period.
2. EVN rates just increased electricity prices by 8%. So…, redoing the calculation again with new rates:
The cost of solar energy system varies from 18,000,000 to 30,000,000 VND/ kW.
So, for 4,000 watt we have: 72 – 120,000,000 VND.
So, on these number, the low cost solar energy will break even at 5 years and at high cost it will break even in 8 years.
Thank you for reading.
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