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

[adoublee]

I thought I remember hearing the engine based gen was a good option as long as it was big enough to absorb excess power. Maybe I'm not remembering correctly and I had never heard of this as a feature of a generator before that point.

Maybe you heard that if the LOAD is big enough to use all the PV generation nothing would be trying to be pushed back into the genset. This could be possible with a commercial/industrial building with a reliable base load, but is not going to happen naturally at a normally operating residence. Maybe with big electric heaters forced to stay on while PV is producing and generator is running. He's probably just been lucky though.

[ButchDeal]

would be more fuel efficient to use the corvair instead of the truck

[jflorey2]

The guy says no batteries on his system. I thought I remember hearing the engine based gen was a good option as long as it was big enough to absorb excess power. Maybe I'm not remembering correctly and I had never heard of this as a feature of a generator before that point.

Generators cannot "absorb excess power." If you backfeed them they overspeed.

However, what may be saving his friend is the fact that while generators cannot absorb extra power, grid tie inverters will generally drop off-line if the frequency or voltage exceeds narrow limits. If you are forcing the generator to overspeed, frequency and often voltage will rise. When that happens the inverter _may_ drop off line and protect the generator. It's something of a crap shoot.

[nomadh]

Guy with the Enphase running off grid sounds like he's using this type of arrangement. Some notes



So the 'grid' then becomes the battery inverter, with the generator as a backup. Your friend has gotten lucky if he just connects the two up. [/FONT][/FONT][/FONT]

The guy says no batteries on his system. I thought I remember hearing the engine based gen was a good option as long as it was big enough to absorb excess power. Maybe I'm not remembering correctly and I had never heard of this as a feature of a generator before that point.

[azdave]

The benefit of the Secure Power supply is not that it's a reliable 24/7 source of power, or that it's just like a generator. It is that it is effectively free and will be available when few other sources of power are - and no maintenance is required to ensure it remains available.

I would just run an extension cord out to my driveway. Start my truck (with the 800W power inverter I use for camping) and I've got enough power to get by, even at night or during a cloudy day.

[Engineer]

Guy with the Enphase running off grid sounds like he's using this type of arrangement. Some notes

• Do not allow the batteries to overcharge. Overcharging batteries can damage the batteries and can potentially cause fires and catastrophic meltdowns. It is smart to provide redundant methods to regulate the charge to the battery.
• Do not connect the Enphase Microinverters to the output of an engine generator. This can cause damage to the microinverters and the generator.
• Design the Enphase Microinverter system so that it does not exceed the pass-through capabilities of the battery-based inverter’s charging system.

So the 'grid' then becomes the battery inverter, with the generator as a backup. Your friend has gotten lucky if he just connects the two up.

[SunEagle]

Isnt that like saying your bank is offering free $35000 life insurance policy but because it isnt 5 times your yearly salary its totally useless so dont do it at all. What if thats all you can afford? I think its pretty self evident that a 35k policy isnt as good as a 250k policy but its soooo much better than the $0 policy and the expensive one is out of the question.
I just spent 17k I didnt have to get a system that only covers half my power currently. I settled on whatever fit on my south roof to maximize the return and did it now to get net metering 1.
I think its unfair to say sps isnt a good feature because some people are too dim to understand it doesnt work in the dark.

I didn't say people were too dim to understand how the SPS works. What I said was that most power outages occur due to a weather related incident which includes clouds. Or like the one I recently had which started at 6:30am and lasted an hour and 1/2. The SPS would have been useless during that event.

But if your area is prone to the grid going down in the middle of the day due to too many AC units running and not enough power generation from the POCO's so you have rolling brown or black outs then I would say it is a good backup power source if it was free or if you paid for it.

[nomadh]

And yet telling them that a simple solution to having power when the grid goes down is to purchase the SPS option, Which IMO is misleading because they will only get power when the sun is shining and maybe 15amps max for a short period of time even though the grid could be down for days.

It would be better to invest in a good grid tie solar pv system as well as an automatically starting whole house generator. Those will not require much in the way of maintenance or costs yet can provide a lot of power anytime the grid is up or goes down.

Isnt that like saying your bank is offering free $35000 life insurance policy but because it isnt 5 times your yearly salary its totally useless so dont do it at all. What if thats all you can afford? I think its pretty self evident that a 35k policy isnt as good as a 250k policy but its soooo much better than the $0 policy and the expensive one is out of the question.
I just spent 17k I didnt have to get a system that only covers half my power currently. I settled on whatever fit on my south roof to maximize the return and did it now to get net metering 1.
I think its unfair to say sps isnt a good feature because some people are too dim to understand it doesnt work in the dark.

[SunEagle]

I wanted to also mention that I know someone who has an enphase microinverter system and he uses a midsize generator and transfer switch to run his solar system during down grid and has done it a few times now. It seems he uses it to start the system off and that kicks on the panels. Then the generator can ramp down as the panlels provide the bulk of the power. It seems that if hes generating to much solar power either the generator somehow absorbs it or the sine wave destabilizes a bit to where some panels start kicking off. Sounds like another great possibility.

Or he has gotten real lucky that the generator has not gone up in smoke.

Maybe the enphase microinverters do not have full anti island software and thus are easily tricked into working without the grid. IMO that is a double edged sword.

[nomadh]

I wanted to also mention that I know someone who has an enphase microinverter system and he uses a midsize generator and transfer switch to run his solar system during down grid and has done it a few times now. It seems he uses it to start the system off and that kicks on the panels. Then the generator can ramp down as the panlels provide the bulk of the power. It seems that if hes generating to much solar power either the generator somehow absorbs it or the sine wave destabilizes a bit to where some panels start kicking off. Sounds like another great possibility.

[nomadh]

Refrigeration, sump pumps, recharging cellphones, recharging power tools, fans for drying out a house. After Sandy I knew several people who had solar who lost the contents of their basement and/or could not do basic repair around their homes due to lack of power.


Generators are great. But you have to maintain them even if they're not used often; a generator that has been sitting with the same oil and fuel for ten years is useless when a long blackout arrives. (And you'll discover as soon as the storm hits that replacement parts, and even replacement generators, are suddenly very hard to come by.)

The benefit of the Secure Power supply is not that it's a reliable 24/7 source of power, or that it's just like a generator. It is that it is effectively free and will be available when few other sources of power are - and no maintenance is required to ensure it remains available.

Thats it 100%. Its zero cost, zero maintenance, long term and short term daytime power. Not as great an answer for east coast ice storms and hurricanes as it is for so cal, rolling brownouts, summer blackouts and earthquakes. Add in the fact that everyone in the know says our power grid is just a sneeze away from a multi week multi state blackout and it makes for a nice plus in an emergency. I still also need a small stand alone generator for winter pumping during a flood. But thats cheap and will only run for an hour here and there.

When I got my sunnyboy I was told we couldn't use sps to power a fridge but after seeing it I expect it can run that or the small AC or possibly both at the same time.

[SunEagle]

I would hate for someone to think their expensive grid-interactive-only system will provide themselves some level of daytime electric support when the grid is down and the sun is shining (most people realize solar is not generating at night), but people think that until they get educated. Then if concerned they are quickly schooled by the high cost of back-up batteries or generator and think those are the only options. I think this is a great feature that is presently undervalued in the market and dismissed to quickly. However, the feature couldn't be effectively used for multiple years in regions with 2014 NEC adopted which was probably a significant setback.

I also agree there are many who could operate a SPS switch with a small listing of instructions, whereas most want nothing to do with servicing a generator or batteries if their grid is relatively stable.

Finally, there is nothing saying the SPS can't be used for some small/medium scale 120VAC battery charging.

All good points.

Maybe in the future the inveter manufacturers can develop equipment that allows a higher usage of the solar panels when the grid goes down. But to be safe and insure someone does not get electrocuted the hardware is limited in output so that the anti islanding software keeps the major portion of the solar generation turned off if there isn't a working grid attached.

[adoublee]

I guess if that option is free and there isn't any expectations of always having power if the grid goes down it could be worth it.

But my concern is that if someone really needed power whenever the grid goes down, I would hate for them to rely only on the SPS function and find out it does not provide what they will need.

I would hate for someone to think their expensive grid-interactive-only system will provide themselves some level of daytime electric support when the grid is down and the sun is shining (most people realize solar is not generating at night), but people think that until they get educated. Then if concerned they are quickly schooled by the high cost of back-up batteries or generator and think those are the only options. I think this is a great feature that is presently undervalued in the market and dismissed to quickly. However, the feature couldn't be effectively used for multiple years in regions with 2014 NEC adopted which was probably a significant setback.

I also agree there are many who could operate a SPS switch with a small listing of instructions, whereas most want nothing to do with servicing a generator or batteries if their grid is relatively stable.

Finally, there is nothing saying the SPS can't be used for some small/medium scale 120VAC battery charging.

[SunEagle]

Agreed. In addition, most automatic start generators can be programmed to exercise themselves once a month or so, and are available in propane or NG versions; these are close to maintenance free. However, when someone doesn't want to shell out the money for something they might use once every 20 years, I strongly recommend the SPS route, since it is effectively free and gives them some power if that day ever comes.

I guess if that option is free and there isn't any expectations of always having power if the grid goes down it could be worth it.

But my concern is that if someone really needed power whenever the grid goes down, I would hate for them to rely only on the SPS function and find out it does not provide what they will need.

[jflorey2]

It would be better to invest in a good grid tie solar pv system as well as an automatically starting whole house generator. Those will not require much in the way of maintenance or costs yet can provide a lot of power anytime the grid is up or goes down.

Agreed. In addition, most automatic start generators can be programmed to exercise themselves once a month or so, and are available in propane or NG versions; these are close to maintenance free. However, when someone doesn't want to shell out the money for something they might use once every 20 years, I strongly recommend the SPS route, since it is effectively free and gives them some power if that day ever comes.