Effects of clouds on your array? I'm considering SMA's Secure Power Supply inverters.

[Mike90250]

on a cloudy day, my KW of arrays produce 300-500 watts. It's a pretty drastic cut off when clouds come in, power drops to zilch.

[nomadh]

This off grid secure power seems to be a near zero cost feature on an already competitively priced inverter. Just a few bucks to mount an extra ac socket in the garage and a 100 ft extension cord it seems. At least I can keep the koi pond breathing for a few hours during the day or pumping water if a flood or the mini fridge or small ac unit if hot. Hell if its just an easy way to charge the cell phones and laptop it would be nice. If this feature is near the 97% efficiency of the main inverter most people should be able to get their 1500 watts during much of the daytime. How effiecient it is is a great question.

I was sold on enphase but ran across this feature on the sunnyboy. After talking to a solar sales company they are working up a quote with 1/2 enphase for the shaded part and half sunnyboy for this feature. He thinks they would be very compatible together and should be a pretty good price.

[home4]

A few tidbits are available from SMA in the comments of their product launch page. Greg Smith works for SMA.

Thanks a lot for that thread. There is a lot of good info there.

I heard back from SMA. They claim that although there is no buffer built into the inverter, the DC->AC conversion abilities match the normal grid-tied efficiency of the inverter, so for example a 500W load would require about 512W from the PV.

They also mention that a UPS could possibly aid in surge loads beyond the 1500W. That other thread mentions that someone had been successful in using this UPS, connected to the Secure Power Supply, to allow starting up a newer-model refrigerator.

[nomadh]

The secure power feature seems to be about as good as hoped first glance. It does seem to put out 1500 watt and gracefully shutsdown when overtaxed and can function is less than ideal conditions. Turns on around 800 watt dc and needs little headroom to be functional. Now to see how well their power pt tracking works.

some info from the sma thread quoted below



Testing on a rainy day, the total wattage of my panel system was about 670 watts on the inverter screen (grid-tied) and was slowly rising as the clouds were moving out. I shut off the grid disconnect and started the SPS at this wattage. The charger kicked in at about 700 watts registering on the “stand-alone ops” status – with a reading of 13 DC amps, quickly settling at 11 amps on the charger. The inverter continued to show 700 watts and started cutting back as the DC amps started coming down. When I shut down the SPS and reconnected the inverter to the grid, the wattage reading on the inverter screen was around 800 watts. This indicates to me that the SPS can start a golf cart type charger with little “surge” capacity required and can consistently charge the batteries with anything above 800 watts available from the PV panels. This would of course vary with the type of charger, but again appears that the computer controlled type charger of the typical club car will work very well with the Sunny Boy SPS. - See more at: http://www.smainverted.com/2013/05/1....3VR8Ql8K.dpuf


Follow-up on SPS testing;
Full sun testing – Cart charging 12 amps (48 volts) – 715 standalone watts
Added Low fan hair dryer – 795 watts
low fan, warm hair dryer – 964 watts
high fan, warm hair dryer – 1383 watts (9 amps on charger)
low fan, high hair dryer – SPS kicks off (this is a 1850 watt hair dryer)
Comments; Under cloud cover, the cart charger will lower it’s charging amps and corresponding “standalone Ops” watts to as low as 460 watts, then would come back up to 523 watts as the cloud cover lifted. Cannot explain this, but it consistently happens. Also, the charger will click off on occasion, but comes back on within a few seconds – not the 45 seconds or so when the SPS is overloaded.

Again, appears the SPS is very well suited to charge a rather large set of 4-12V deep cycle batteries in the Club Car Golf Cart using the charger designed for the cart. Due to continuing downward amperages as the batteries get more fully charged, it could take most of the day to fully recharge depleted batteries – especially if there is substantial cloud coverage.

- See more at: http://www.smainverted.com/2013/05/1....3VR8Ql8K.dpuf

[nomadh]

More info on optitrac

http://forums.whirlpool.net.au/forum-replies.cfm?t=1697128#r9

In summer, I have no shading, however now the sun is lower, I get shading until about 9:30am.

I initially had OptiTrac off, as I had no shading. However I turned it on and you can see the difference in the following graph.

http://pvoutput.org/comparelive.jsp?sid=1006&df=20110601&dt=20110602

Both days were sunny in the morning. Here is a direct comparison:
Without Optitrac @ 8:20am, 1/06/2011: 384W
With OptiTrac @ 8:20am, 02/06/2011: 971W


or:

I also noticed a small improvement, but I haven't quantified it.
My panels are shaded 2-3pm in winter. Before before enabling OptiTrack, the worst I got was about 10% of the unshaded output. After enabling OptiTrack it looks like it gives up on the shaded panels and the MPTT follows the unshaded string, giving closer to 50% of the unshaded output.

[inetdog]

More info on optitrac

http://forums.whirlpool.net.au/forum-replies.cfm?t=1697128#r9

In summer, I have no shading, however now the sun is lower, I get shading until about 9:30am.

I initially had OptiTrac off, as I had no shading. However I turned it on and you can see the difference in the following graph.

http://pvoutput.org/comparelive.jsp?sid=1006&df=20110601&dt=20110602

Both days were sunny in the morning. Here is a direct comparison:
Without Optitrac @ 8:20am, 1/06/2011: 384W
With OptiTrac @ 8:20am, 02/06/2011: 971W


or:

I also noticed a small improvement, but I haven't quantified it.
My panels are shaded 2-3pm in winter. Before before enabling OptiTrack, the worst I got was about 10% of the unshaded output. After enabling OptiTrack it looks like it gives up on the shaded panels and the MPTT follows the unshaded string, giving closer to 50% of the unshaded output.

Thanks for the experimental results nomadh.

One thing that readers should be aware of is that there are a great number of ways to implement MPPT, and some of them (e.g. full width scan) do what optitrac does as part of their basic operation and do not need any additional code.
The basic MPPT algorithm used by SMA is subject to capture by a local maximum on the high voltage/low current end of the curve, so for them Optitrac (TM) does add a significant benefit. It does not necessarily translate into a competitive advantage over anything but their own older inverters.

[nomadh]

Don't know how real any of the info is but it seems plausible. So you are saying the optitrac is pretty much what most of the other string inverters are already doing? It seems sunnyboy is claiming the technology gets them into the ballpark of power op modules or even microinverters. The info I'm looking for now is a head to head of sunnyboy optitrac vs microinverter vs solar edge.

[inetdog]

Don't know how real any of the info is but it seems plausible. So you are saying the optitrac is pretty much what most of the other string inverters are already doing? It seems sunnyboy is claiming the technology gets them into the ballpark of power op modules or even microinverters. The info I'm looking for now is a head to head of sunnyboy optitrac vs microinverter vs solar edge.

No, let me make this more explicit.
I have no idea what algorithms any other string inverter manufacturers use. Any of them might be using an algorithm that handles shaded panels fine but only scans at 5 minute intervals (not so good for intermittent shade) or might be doing just as well as Optitrac, or might be behaving even worse than SMA without Optitrac.

What I am trying to say is that without that information (which does not seem to be easy to get), you cannot use the existence of Optitrac alone as a competitive feature against all other string inverters.

As for doing as well as micros or optimizers, that is very hard to do in practice because those two will be able to actually capture power from partially shaded panels, while Optitrac can at best find the mixed string MPPT with no output at all coming from the shaded panel sections or panels.
If you have more than one string with unequal shading between them, then the combination of Optitrac with two or more independent MPPT inputs is what you will need.
PS: Which is exactly the combination that SMA is providing in its newer inverter models.

[sensij]

Don't know how real any of the info is but it seems plausible. So you are saying the optitrac is pretty much what most of the other string inverters are already doing? It seems sunnyboy is claiming the technology gets them into the ballpark of power op modules or even microinverters. The info I'm looking for now is a head to head of sunnyboy optitrac vs microinverter vs solar edge.

Under what assumptions? Perfectly sunny? Predictable AM clouds? Partial shade? Perfectly south panel orientation at latitude tilt? The level of granularity you are looking for will be very installation specific. You could spend some time setting up your conditions in SAM and see if you get different results with different inverters.

Here is one study, using older equipment in 2011. The technology for both kinds of inverters has improved since then.

[nomadh]

Under what assumptions? Perfectly sunny? Predictable AM clouds? Partial shade? Perfectly south panel orientation at latitude tilt? The level of granularity you are looking for will be very installation specific. You could spend some time setting up your conditions in SAM and see if you get different results with different inverters.

Here is one study, using older equipment in 2011. The technology for both kinds of inverters has improved since then.

Hopefully all of those real world conditions. I looked at the report you mention and it looks like a report designed to put string inverters out of biz. The microinverters trounced the older style in shaded and unshaded tests. Hopefully newer string inverters have upped their game. Have any of the more long time experienced installers seen the line inverter companies bring their power production per panel up at least 20% on unshaded installs over the last few years let alone shaded? And even then the newest microinverters have also upped their game.

[russ]

Hopefully all of those real world conditions. I looked at the report you mention and it looks like a report designed to put string inverters out of biz. The microinverters trounced the older style in shaded and unshaded tests. Hopefully newer string inverters have upped their game. Have any of the more long time experienced installers seen the line inverter companies bring their power production per panel up at least 20% on unshaded installs over the last few years let alone shaded? And even then the newest microinverters have also upped their game.

Pardon? Upped the advertising maybe - the game though - how?

[nomadh]

Pardon? Upped the advertising maybe - the game though - how?

I believe that the efficiency of both micro and string inverters have gotten at least a bit more efficient the last few years. That older report mentioned earlier made it look like string inverters would need to get about 20% more efficient and have not heard that. For instance has anyone seen a 20%+ efficiency increase from the older model sunnyboy to the newer?

Sunnyboy claims its new power point tracking technology still collects 99% of the unshaded string output, not the Volts but the power . This would seem to make very similar output to enphase or solar edge. I'm still not convinced and see no tests to prove or disprove it..

https://www.youtube.com/watch?v=bxIi4GiZakE

[russ]

I believe that the efficiency of both micro and string inverters have gotten at least a bit more efficient the last few years.

Marketing hype and BS for a great part

[NKetch22]

Is this true in your experience? This is the exact question I have been seeking to get answered in this thread. I have seen this repeated elsewhere, that if a small cloud comes in the output from the Secure Power Supply would go off. But it doesn't seem to me like this would be the case. Say I have a 6 kW PV array and the Secure Power Supply, there is an outage and I'm drawing 500W powering some loads. The Secure Power Supply would not go off unless it is no longer able to produce that 500W AC, which means that the array would need to be producing maybe 800W DC (or not even). In your experience, if a cloud goes over your array will its output drop by 85% (6kW to 800W)? I'm not trying to argue this point -- I really do not know if it would, as I do not currently have a solar PV system, but I'm looking to find out that answer because this seems to be key in how well this system would work. When I read online about the effect of cloud cover on PV it seems as though the entire sky would have to be quite cloudy for it to drop that much.

For me personally, I'm interested in this system because I want SOME sort of backup in case of a long-term power outage. I have a generator, and that is very useful, but I have friends who went without power for 2 weeks a couple of years ago, and it would be really really nice to have even a little power for things like lights, radio, phone, etc, during a time like that. During Hurricane Sandy, gas was nearly impossible to come in certain areas. A PV solution would not provide power during the storm, but in the aftermath, it could be very useful.

It would be great to have a fully islanding system with batteries during a time like this, but unfortunately it seems like these systems are really really expensive. Unless there is an inverter I haven't read about, even without batteries they are expensive because the inverters cost so much more, and they usually restrict the panels you can get.

The Secure Power Supply seems to me like it provides some of the benefits of an islanding system, with a lot less cost, and also more restrictions. But with a UPS and a generator, it seems like it could be a good choice, and that's why I'm interested in finding out more about it. Thanks.

This is not true. I just had my 5.889 kW system installed with an SMA Sunny Boy 6000TL-US-22 with Secure Power. While I await my new meter, I have played with the secure power. I took a sick day last week on an overcast cloudy day. For kicks I decided to plug in a jig saw. I ran it flawlessly for a few minutes. I then decided to run an extension cord from the secure power outlet to my entertainment center. Since both items were the only draw on the system, the Sunny Boy display lists the draw coming from the secure power. Running the jig saw for a minute was a 500 watt draw. The tv/cable box/sound bar was a 450 wall drawing which was maintained for about three hours until night was starting to fall upon the panels. The constant cloudiness kept the power at a constant rate and did not result in any shutdown/restarts until it got late. If you overload the secure power it will restart itself on it's own. No going back to the switch.

So in summation; I think the secure power supply is a great add-on. With occasional hurricanes and blizzards, I just need enough power to charge phones, laptops and perhaps run a tv or bring the internet up for a little while.

[nomadh]

This is not true. I just had my 5.889 kW system installed with an SMA Sunny Boy 6000TL-US-22 with Secure Power. While I await my new meter, I have played with the secure power. I took a sick day last week on an overcast cloudy day. For kicks I decided to plug in a jig saw. I ran it flawlessly for a few minutes. I then decided to run an extension cord from the secure power outlet to my entertainment center. Since both items were the only draw on the system, the Sunny Boy display lists the draw coming from the secure power. Running the jig saw for a minute was a 500 watt draw. The tv/cable box/sound bar was a 450 wall drawing which was maintained for about three hours until night was starting to fall upon the panels. The constant cloudiness kept the power at a constant rate and did not result in any shutdown/restarts until it got late. If you overload the secure power it will restart itself on it's own. No going back to the switch.

So in summation; I think the secure power supply is a great add-on. With occasional hurricanes and blizzards, I just need enough power to charge phones, laptops and perhaps run a tv or bring the internet up for a little while.

There are a few reports on the web like yours. I too am very tempted by this feature even though string inverters seem completely wrong for my roof. The reports I've seen claim its very linear. It seems as long as your 5.9 wk system is just limping along even at 1.7 kw you can still heat 1.5. and even into the night or storms if the system is making say 1k you can use 7 or 800 watts it seems.

btw enphase has their answer here http://enphase.com/wp-uploads/enphas...Brochure-1.pdf
10 yr 1.2 kw modular battery plugnplay. Kinda poor substitute but if its 10 years and the inverter only lasts 10 years. its an answer to backup islanding.
Any guesses how much?