PV array parameters to match with inverter

[highway7]

Hi there,

I am looking at purchasing a solar system. Ive gotten a quote for a 5 kW grid-tie-system. It will come with a 5kW SolarEdge inverter and twenty 250 W astronenergy PV modules (see attached data sheets).

I have been reviewing the data sheets and I had a question that I thought I would ask some folks with more experience than I.

As seen from the data sheets the max input voltage of the SolarEdge inverter is 500 Vdc and the maximum input current in 16 A.
Then based on the data sheets for the 250 W PV modules you can see the max open circuit voltage (STC) is 38.19 V and the max short circuit current (STC) is 8.69 A.

Based on these values I know that I can not have only one string because I will exceed the max voltage however, with two strings thats means the max amperage will be exceeded.

I know that these values are not nominal operating conditions but they are still possible and I have been told that you must also account for the worst case scenarios possible when sizing an inverter.

So my questions are:
-Is my thinking correct?
-Will the system be okay or not okay?
-Should I ask for the 6.5kW inverter instead which would then ensure the max current would not be reached.
-The datasheets for the PV modules also talk about a safety factor of 1.25. Taking that into consideration the max current could definitely be exceeded.

Any help would be appreciated.

Regards,

Mod note - I removed the company name as it is a competitor to our sponsor - it wasn't needed to get the input you need.

[bonaire]

Can you post your location of city/state?

It's rare you would oversize an inverter by that much. You also have other options like different inverter vendors. Check PowerOne, SMA, Fronius to start.

[highway7]

Can you post your location of city/state?

It's rare you would oversize an inverter by that much. You also have other options like different inverter vendors. Check PowerOne, SMA, Fronius to start.

I am located in Newfoundland, Canada. I feel like im one of the first few installing solar here in Newfoundland because I can not find very much information with regards to regulations.

I didnt think oversizing the inverter by that much was a good idea either. I am wondering though am I right when saying that the inverter should not only be sized to the power from the panels but also sized so the maximum open circuit voltage and short circuit currents do not exceed limits on the inverter? or is it sufficient to say under nominal operating conditions voltage and current are within limits, and the 8 A fuses in each of my strings will protect my inverter in the case of a short circuit for example?

[bonaire]

The lack of solar in your province may indicate the lack of value of doing it. In Ontario, they had a high-value Feed in Tarrif that the government there setup. It attracted a variety of high-priced installers and money-hungry buyers to put up Solar to "suck on the teet" of the government incentive. Maybe Newfoundland isn't considering that.

Anyway - what is your per-kWh price there? If it is below .10/kWh (in Quebec, it is about .06 or .07 CDN per kWh) then it probably isn't worth doing. Also, not worth doing it as much if you have a lot of high cloudy days. Low electric prices mean that Solar power prices for products and installations must be subsidized in order to be valuable to the buyer - unless the buyer deems it more of a hobby and doesn't care about the return on investment.

[Yousef]

You are definitely right!

having two strings will not work with this inverter. the company that's selling you the system they should know that. if they don't, then get it from somewhere else because this is ridiculous.

here's my calculations:

sc current : 2x8.69x1.25 = 21.75 vs. 16A max. No good!

make sure your pv array dc power is approximately close to the inverter output power for better efficiency.

btw i would recommend sma over solaredge, and don't let them raise the price for the exchange.

[highway7]

You are definitely right!

having two strings will not work with this inverter. the company that's selling you the system they should know that. if they don't, then get it from somewhere else because this is ridiculous.

here's my calculations:

sc current : 2x8.69x1.25 = 21.75 vs. 16A max. No good!

make sure your pv array dc power is approximately close to the inverter output power for better efficiency.

btw i would recommend sma over solaredge, and don't let them raise the price for the exchange.

Thanks Yousef for your input. That is the exact calculation I did which alerted me to the problem. I will first ask them if they can find an inverter that will fit the solar panel arrays or switch out the panels so they work with the inverter. However, this is just one issue of a few that have occurred now with the company I am dealing with so I am most likely going to look somewhere else.

[highway7]

The lack of solar in your province may indicate the lack of value of doing it. In Ontario, they had a high-value Feed in Tarrif that the government there setup. It attracted a variety of high-priced installers and money-hungry buyers to put up Solar to "suck on the teet" of the government incentive. Maybe Newfoundland isn't considering that.

Anyway - what is your per-kWh price there? If it is below .10/kWh (in Quebec, it is about .06 or .07 CDN per kWh) then it probably isn't worth doing. Also, not worth doing it as much if you have a lot of high cloudy days. Low electric prices mean that Solar power prices for products and installations must be subsidized in order to be valuable to the buyer - unless the buyer deems it more of a hobby and doesn't care about the return on investment.

Hi there.

We purchase electricity from NL Power at 11.171 cents/kWh. Based on the solar models that I have run for my location using the last 10 years of historical weather and solar data I have found that the PV system I am looking at installing will be paid off in less than 10 years. When I include the solar thermal air heating system I am going to install, the overall pay back period for both the PV panels and solar thermal panels will be within 5-6 years and my home will be near-net-zero. Sounds like value to me.

Just because a location doesn't have as great solar resource such as Ontario or even SW US for that matter, doesn't mean solar cant be economical. Take Germany for example: Their solar resource is approximately the same as the solar resource here in NL and their solar developments and the largest in the world.

I believe the days of solar being limited to areas with the best solar resources and the most government incentives is over. Solar energy will be the majority of energy produced in 20 years and that will mean solar installations will be all over the world.

[russ]

Just because a location doesn't have as great solar resource such as Ontario or even SW US for that matter, doesn't mean solar cant be economical. Take Germany for example: Their solar resource is approximately the same as the solar resource here in NL and their solar developments and the largest in the world.Germany only managed a very small fraction of their power by using massive subsidies and very generous FIT's - The program was to pacify the green party there but never made any sense.

I believe the days of solar being limited to areas with the best solar resources and the most government incentives is over. Solar energy will be the majority of energy produced in 20 years and that will mean solar installations will be all over the world.

You must have a special calculator to do your economic calculations - a rather optimistic one! The

For a place in your province - data from PV Watts - the insolation in July is horrible.
"Station Identification"
"City:","Battle"
"State:","NF"
"Lat (deg N):", 52.25
"Long (deg W):", 55.60
"Elev (m): ", 9
"Weather Data:","CWEC"

"PV System Specifications"
"DC Rating:"," 1.0 kW"
"DC to AC Derate Factor:"," 0.840"
"AC Rating:"," 0.8 kW"
"Array Type: Fixed Tilt"
"Array Tilt:"," 52.2"
"Array Azimuth:","180.0"

"Energy Specifications"
"Cost of Electricity:"," 0.1 dollars/kWh"

"Results"
"Month", "Solar Radiation (kWh/m^2/day)", "AC Energy (kWh)", "Energy Value (dollars)"
1, 2.69, 78, 0.09
2, 3.89, 99, 0.11
3, 4.24, 116, 0.13
4, 4.39, 112, 0.12
5, 4.54, 116, 0.13
6, 3.97, 97, 0.11
7, 4.15, 103, 0.11
8, 3.89, 97, 0.11
9, 4.03, 99, 0.11
10, 2.79, 73, 0.08
11, 2.08, 53, 0.06
12, 2.18, 61, 0.07
"Year", 3.57, 1103, 1.21

The link to PV Watts
http://gisatnrel.nrel.gov/PVWatts_Viewer/index.html

[highway7]

You must have a special calculator to do your economic calculations - a rather optimistic one! The

For a place in your province - data from PV Watts - the insolation in July is horrible.
"Station Identification"
"City:","Battle"
"State:","NF"
"Lat (deg N):", 52.25
"Long (deg W):", 55.60
"Elev (m): ", 9
"Weather Data:","CWEC"

"PV System Specifications"
"DC Rating:"," 1.0 kW"
"DC to AC Derate Factor:"," 0.840"
"AC Rating:"," 0.8 kW"
"Array Type: Fixed Tilt"
"Array Tilt:"," 52.2"
"Array Azimuth:","180.0"

"Energy Specifications"
"Cost of Electricity:"," 0.1 dollars/kWh"

"Results"
"Month", "Solar Radiation (kWh/m^2/day)", "AC Energy (kWh)", "Energy Value (dollars)"
1, 2.69, 78, 0.09
2, 3.89, 99, 0.11
3, 4.24, 116, 0.13
4, 4.39, 112, 0.12
5, 4.54, 116, 0.13
6, 3.97, 97, 0.11
7, 4.15, 103, 0.11
8, 3.89, 97, 0.11
9, 4.03, 99, 0.11
10, 2.79, 73, 0.08
11, 2.08, 53, 0.06
12, 2.18, 61, 0.07
"Year", 3.57, 1103, 1.21

The link to PV Watts
http://gisatnrel.nrel.gov/PVWatts_Viewer/index.html

You have selected Battle Harbour, NL which is nowhere near St. John's, NL.

When I run the same calculator you used for Gander which is closer in St. John's but still 300 km away and put in more some more realistic values for my system you can see the results below. Still a little bit lower than my solar model but still good enough to make it economical.

"Station Identification"
"City:","Gander"
"State:","NF"
"Lat (deg N):", 48.95
"Long (deg W):", 54.57
"Elev (m): ", 151
"Weather Data:","CWEC"

"PV System Specifications"
"DC Rating:"," 5.0 kW"
"DC to AC Derate Factor:"," 0.807"
"AC Rating:"," 4.0 kW"
"Array Type: Fixed Tilt"
"Array Tilt:"," 30.0"
"Array Azimuth:","180.0"

"Energy Specifications"
"Cost of Electricity:"," 0.1 dollars/kWh"

"Results"
"Month", "Solar Radiation (kWh/m^2/day)", "AC Energy (kWh)", "Energy Value (dollars)"
1, 2.21, 289, 0.29
2, 3.11, 375, 0.38
3, 3.79, 489, 0.49
4, 4.21, 510, 0.51
5, 4.65, 555, 0.56
6, 4.82, 544, 0.54
7, 4.96, 572, 0.57
8, 4.36, 502, 0.50
9, 3.67, 420, 0.42
10, 2.75, 333, 0.33
11, 1.47, 166, 0.17
12, 1.48, 182, 0.18
"Year", 3.46, 4938, 4.94

[russ]

When I run the same calculator you used for Gander which is closer in St. John's but still 300 km away and put in more some more realistic values for my system you can see the results below. Still a little bit lower than my solar model but still good enough to make it economical.


"Year", 3.46, 4938, 4.94

Right! 3.46 annual average insolation on your location and and adjustments whereas I had 3.57 - you corrected things and it went down.

Nowhere and no when you will ever get payback with a 12 cent per kWh cost and that insolation - unless the government is shoveling money off the back of a truck in your direction.

If you want solar PV it is perfectly fine but be honest with yourself - you are doing it for fun - not because of any pay back. Your model is hopelessly broken I believe.

[highway7]

Right! 3.46 annual average insolation on your location and and adjustments whereas I had 3.57 - you corrected things and it went down.

Nowhere and no when you will ever get payback with a 12 cent per kWh cost and that insolation - unless the government is shoveling money off the back of a truck in your direction.

If you want solar PV it is perfectly fine but be honest with yourself - you are doing it for fun - not because of any pay back. Your model is hopelessly broken I believe.

I still disagree.

If we go with the estimated annual kWh production of 4938 and multiply by 12 cents per kWh thats $592.56/year.
The solar system the I already have a quote for is roughly $10,000. I plan to install my self.
So a simple pay back would be 17 years. (Simple because it doesn't even include the rising cost of electricity where I am located.)

I also believe the PV Watts calculator is conservative in its estimates and it also doesn't let me select St.John's only Gander which is 300 km away. My solar data and weather data says St. John's has slightly better insolation values than Gander.

When you take those into account and the rise in electricity cost over the next 15 years a pay back period of 13-14 years is a reasonable estimate. Which is only 3 years more than I first estimated. I therefore disagree with your statement saying my model is "hopelessly broken".

What you do have correct is that I AM doing it for fun! But also because it makes economic sense!

[russ]

I therefore disagree with your statement saying my model is "hopelessly broken".

What you do have correct is that I AM doing it for fun! But also because it makes economic sense!

Doing it for fun - 592 Canadian dollars per year ain't much. Using your calculations I have a bridge for sale - heck of a deal.

However = good luck and it will be fun.