Solar Electricity Quality

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mikeeastman

Re: Solar Electricity Quality
« Reply #20 on: 26 Jun 2016, 02:41 am »
The Xantrex is not a pure sinewave it just has smaller steps than the inverters called modified sinewave. Also the Xantrex is 90s technology , can't say the newer are better.

HAL

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Re: Solar Electricity Quality
« Reply #21 on: 26 Jun 2016, 03:14 am »
Since the measured distortion with the Fluke 43B was under 2% THD for the older XANTREX ProSine 2KVA unit, might be, but measures very well under load.  Would be interesting to see measurements for newer units.

The PS Audio PPP was measured at under 0.5% THD, still under any of the inverters I could find about 6 years ago. 

JLM

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Re: Solar Electricity Quality
« Reply #22 on: 26 Jun 2016, 10:45 am »
To properly go off grid with solar requires a very large array and lots of expensive batteries to account for cloudy days and nights.  The biggest concern would be low power conditions causing brown-outs leading to burning up of compressors, fans, and motors.  Not economically feasible unless you live without A/C, refrigeration, central heat, pool/hot tub, etc.

We installed a 5 kWp (16 ft x 20 ft) array in lower Michigan last year.  Thanks to the utility incentives and sunnier than normal weather we're ahead of the projected $400 net annual gain and 8 year payback.  Love cashing checks from the utility.

Even when we'd run our portable generator I noticed no sound quality difference in my digitally based (computer/class D amp) audio system.

mikeeastman

Re: Solar Electricity Quality
« Reply #23 on: 26 Jun 2016, 01:55 pm »
The whole idea of an off the grid house is that is designed to be efficient enough so that you can minimize the power consumption.Which means energy efficient appliances and a building with proper design and insulation, which means insulating way above what code is. Ideally you would have minimum R-40 or higher in the walls with at least one reflective layer and R-60 with ideally two reflective layers. I have 2700 watts of solar which gives me gives me 110-130 amphr of AC per day and we are not doing without any conveniences, we have microwave, electric bread maker, 20 cu' refrigerator , ice-cream maker etc. The sun provides 75-80% of my heat in the winter. I have never had a brown out and a properly set up system should never have brown outs. The inverters are designed to shut down if the battery voltage drops below a level that would effect the AC output.

Hal: does the PP Audio PPP actually produce real sine wave or is it like the sine wave inverters and it's just very small steps? My understanding is it is very difficult to make a real pure sine wave from DC. Has anyone put a scope on the PP and verified it is pure sine wave?

Wayner

Re: Solar Electricity Quality
« Reply #24 on: 26 Jun 2016, 04:39 pm »
I used to think this, too, but to my surprise discovered that DC transmission is much more efficient in terms of losses en route and cost of transmission towers and equipment—so much so that it can offset the extra cost of AC/DC and DC/AC conversion at each end. It is the system of choice for very long distance transmission because of this. It also vastly simplifies the connection between different grid systems as must occur to share loads (the AC can be synchronized easily to the local grid during the DC/AC conversion process. Imagine the process of trying to synchronize the AC of all the systems connected in a continent-wide grid system. (I don't want to think about it).
Here's a great encapsulation of some of the considerations:
https://en.wikipedia.org/wiki/Electric_power_transmission#High-voltage_direct_current

There are no DC transmission lines around here. Pretty hard to change voltage without a transformer, and that requires AC.

I was also talking about the early days of electricity and why things are the way they are, even tho there may be changes to some long distance technologies, the usual power grid is of the 3 phase AC variety.

BTW, I live a few miles away from 2 wind farms, each with 12 towers with each tower dumping 1.1 megawatts into the power grid via a sub-station. I did ask some questions to those in the know about synchronization of the sine waves from the tower and was told that there wasn't a need as induction snapped the wind towers to the line frequency. These are enormous towers (100') with 3 blades that are 60 foot long (making a 120') diameter outer rotation. The turbines are housed in a powered turret thats size can only be described as "box-car" like.

Russell Dawkins

Re: Solar Electricity Quality
« Reply #25 on: 26 Jun 2016, 05:10 pm »
There are no DC transmission lines around here. Pretty hard to change voltage without a transformer, and that requires AC.
Did you have a good read of the link? DC high voltage power transmission is more efficient than AC. The twist is that the converters needed at each AC/DC conversion are more expensive than transformers and so AC makes more sense for shorter runs.

I think most of us know that changing voltages with a transformer requires AC, and that transformers don't work with DC.

My point was that the efficiency of transmission of DC (in terms of transmission losses and construction costs) is so much higher than that of AC, contrary to my (and your) prior understanding, that the extra cost of the converters at each end of the transmission line is more than covered on long runs.

This was a revelation to me when an electrical engineer, father of a friend of mine, who was involved in designing transmission systems was answering some of my queries about 40 years ago. Up until then I also thought AC was the only system used. I was asking about details on the long underwater link between Vancouver Island and the mainland, which carries most of the power for the entire island about 60km underwater. I was surprised that DC was used and also that it was so efficient. I can't remember the figures, but the losses were amazingly small.

Here's a quote from the Wikipedia article on this page: https://en.wikipedia.org/wiki/Electric_power_transmission#High-voltage_direct_current

"High-voltage direct current (HVDC) is used to transmit large amounts of power over long distances or for interconnections between asynchronous grids. When electrical energy is to be transmitted over very long distances, the power lost in AC transmission becomes appreciable and it is less expensive to use direct current instead of alternating current. For a very long transmission line, these lower losses (and reduced construction cost of a DC line) can offset the additional cost of the required converter stations at each end."

also:

"HVDC is also used for submarine cables because AC cannot be supplied over distances of more than about 30 kilometres (19 mi), due to the fact that the cables produce too much reactive power[citation needed]. In these cases special high-voltage cables for DC are used. Submarine HVDC systems are often used to connect the electricity grids of islands, for example, between Great Britain and continental Europe, between Great Britain and Ireland, between Tasmania and the Australian mainland, and between the North and South Islands of New Zealand. Submarine connections up to 600 kilometres (370 mi) in length are presently in use.[22]"

HAL

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Re: Solar Electricity Quality
« Reply #26 on: 26 Jun 2016, 05:11 pm »
Most folks use a DSP based sinewave generator with a DAC to power amp.  That is why they are crystal controlled for the master clock to divide down to 60Hz in the US.  Any 16 bit DAC with an output filter will do better than something like an analog Wein bridge oscillator for stability and lower distortion 60Hz sinewave generation. 

The older Power Plants used that DSP/DAC technology to feed linear PA's for the balanced output.  They had lower distortion, but lower output power than the newer units.  Probably switched to PWM at some point in the newer units.  Much more efficient than the 50% power conversion rate of the original PP's.  My P300 dissipated 600 watts for 300 watts output.  IIRC, the PPP is around 80% efficient at conversion.


JerryM

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Re: Solar Electricity Quality
« Reply #27 on: 26 Jun 2016, 06:26 pm »
Most folks use a DSP based sinewave generator with a DAC to power amp.  That is why they are crystal controlled for the master clock to divide down to 60Hz in the US.  Any 16 bit DAC with an output filter will do better than something like an analog Wein bridge oscillator for stability and lower distortion 60Hz sinewave generation. 

The older Power Plants used that DSP/DAC technology to feed linear PA's for the balanced output.  They had lower distortion, but lower output power than the newer units.  Probably switched to PWM at some point in the newer units.  Much more efficient than the 50% power conversion rate of the original PP's.  My P300 dissipated 600 watts for 300 watts output.  IIRC, the PPP is around 80% efficient at conversion.

What about an entirely solar-power based home???   :scratch:

mikeeastman

Re: Solar Electricity Quality
« Reply #28 on: 26 Jun 2016, 08:16 pm »
I believe for small amounts of power few hundred watts it probably feasible but I think the problem arises when you need 3-4kw, which is what you need for the average off the grid home.

JLM

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Re: Solar Electricity Quality
« Reply #29 on: 26 Jun 2016, 11:36 pm »
I'm in the process of obtaining bids for a fixed backup generator.  As wifey wants to follow through on the hot tub we prepped for when we built 12 years ago and our portable generator has died, I decided to look into this.  We have a 2200 sq. ft. EPA 5 star energy efficient house with finished basement, 3 ton air conditioner, electric oven, well, and freezer.  Our 200 amp panel didn't have enough circuits.

One of the contractors used Generac's software to estimate (conservatively) the power demand.  According to the software we'd need a 25 kW generator to cover the entire house, but he demonstrated that a 22 kW generator would cover the entire house as the software assumes every circuit in the house was fully loaded and every device/appliance started up at once.  Since a 15 kW generator has nearly as high an operating and up front cost we'll go with the 22 kW.  Note that a smaller generator, like an 11 kW unit would save maybe $2000 but limit use us to 12 preassigned 20 amp circuits (and wouldn't cover the hot tub).

Peak and average power demand are vastly different, probably a 3 to 1 ratio.  In our case the power produced from a 6 kWp solar installation would match our demand on an annual basis, yet we're looking at a 22 kW generator.  To cover for a week's worth of totally cloudy weather (we are very cloudy in the winter) we'd probably need 150 kW of batteries or fuel cell/storage tanks (about $50,000 at today's cost) on top of the $16,000 solar installation.  That's why going off the grid is so impractical.

mikeeastman

Re: Solar Electricity Quality
« Reply #30 on: 27 Jun 2016, 12:07 am »
I would recommend you stay away from Generac generators they don't have a good rep in off the grid.

JLM

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Re: Solar Electricity Quality
« Reply #31 on: 27 Jun 2016, 10:41 am »
I would recommend you stay away from Generac generators they don't have a good rep in off the grid.

Don't understand your comment, what do you mean by "rep in off the grid"?  If you addressing 24/7 use (off the grid), that's a whole different game.  Generator lifetimes are limited by engine run times, regardless of how much load is on them.  Based on 12 years here I estimate the generator will see less than 50 hours of use per year, including weekly 12 minute testing.  In discussions with the contractors have given estimates of the expected life of the engine of 2,000 - 4,000 hours which for us would be roughly 60 years of service.  But running 24/7 that expected lifetime drops quickly.  Few small engines are designed to run 24/7.  Again you have to size for peak demand to avoid burning out motors, etc.  In our case average demand is 0.7 kW/hour but peak demand 99% of the time is probably close to 10 kW and once in a blue moon peak (house full of dinner guests on hottest day of the year) maybe 15 kW. 

So a better (but far more expensive) solution for off grid power would be to add a battery bank that the generator charges while serving the house.  When fully charged the generator would automatically rest and the batteries take over.  When the batteries are nearly depleted the generator automatically starts up again and the cycle repeats.  Or just learn to live without refrigeration, wells, A/C, hot tubs, etc.


I've inspected hundreds of nursing homes here in Michigan and many use Generac.  In fact it's about the only residentially sized fixed generator you can find around here.  The only problems the contractors indicate (if properly maintained) are lack of a cold weather kit, lack of sufficient gas/propane supply, and nuisance calls from the wireless reporting option.

Wayner

Re: Solar Electricity Quality
« Reply #32 on: 27 Jun 2016, 11:59 am »
Did you have a good read of the link? DC high voltage power transmission is more efficient than AC. The twist is that the converters needed at each AC/DC conversion are more expensive than transformers and so AC makes more sense for shorter runs.

I think most of us know that changing voltages with a transformer requires AC, and that transformers don't work with DC.

My point was that the efficiency of transmission of DC (in terms of transmission losses and construction costs) is so much higher than that of AC, contrary to my (and your) prior understanding, that the extra cost of the converters at each end of the transmission line is more than covered on long runs.

This was a revelation to me when an electrical engineer, father of a friend of mine, who was involved in designing transmission systems was answering some of my queries about 40 years ago. Up until then I also thought AC was the only system used. I was asking about details on the long underwater link between Vancouver Island and the mainland, which carries most of the power for the entire island about 60km underwater. I was surprised that DC was used and also that it was so efficient. I can't remember the figures, but the losses were amazingly small.

Here's a quote from the Wikipedia article on this page: https://en.wikipedia.org/wiki/Electric_power_transmission#High-voltage_direct_current

"High-voltage direct current (HVDC) is used to transmit large amounts of power over long distances or for interconnections between asynchronous grids. When electrical energy is to be transmitted over very long distances, the power lost in AC transmission becomes appreciable and it is less expensive to use direct current instead of alternating current. For a very long transmission line, these lower losses (and reduced construction cost of a DC line) can offset the additional cost of the required converter stations at each end."

also:

"HVDC is also used for submarine cables because AC cannot be supplied over distances of more than about 30 kilometres (19 mi), due to the fact that the cables produce too much reactive power[citation needed]. In these cases special high-voltage cables for DC are used. Submarine HVDC systems are often used to connect the electricity grids of islands, for example, between Great Britain and continental Europe, between Great Britain and Ireland, between Tasmania and the Australian mainland, and between the North and South Islands of New Zealand. Submarine connections up to 600 kilometres (370 mi) in length are presently in use.[22]"

This was probably DC required because the power was run underwater. A severed line here, would electrocute almost any living creature's soul if such a thing were to happen as an AC power feed. (This reminds me of the early days of lighting (I have 30 years in the lighting industry) when swimming pool lighting was powered to run 120 volt AC lamps. Very stupid and very dangerous. Now they are all low voltage). I believe that most DC power lines are for "special" situations. I can certainly ask my pal at the utilities.

The submarine comment is understandable because many older (WWII) submarine's  lower bowels were filled with batteries. My wife was a tour guide aboard one anchored in Wisconsin. They needed DC for submerged operations and silent running.

'ner
« Last Edit: 27 Jun 2016, 03:21 pm by Wayner »

mikeeastman

Re: Solar Electricity Quality
« Reply #33 on: 27 Jun 2016, 01:25 pm »
I have been working on off the grid solar systems for over 20 yrs and any system I worked on that had a Generac had problems with it. My generator guy that has be doing it for over 40 years tells me there junk in his opinion.  Your contractors said engine life 2000-4000 hr, the generator I have now has over 20,000 hrs on it and I rebuilt the engine at 14,000 hr. As far as the weekly test of 15 min a week goes, it's not good idea to only any run an engine for that little of time as they doesn't get a chance to warm up properly, I have all my customer run their gen once a month for a hour. Most off the grid system are designed for the gens get run 60-100 hrs per year. Provided nothing changes in the next 20 yrs and you only run it 50 hrs a year it will probably work just fine for you.

HAL

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Re: Solar Electricity Quality
« Reply #34 on: 27 Jun 2016, 01:48 pm »
What about an entirely solar-power based home???   :scratch:

There is no reason that the same DSP technique for sinewave generation cannot be used and sync'd to the grid with digital phase locked loops. 

Instead of using Class AB amps like PS Audio did in the original P300, P600 and P1000, a PWM power amp can be very large, low distortion, with high efficiency like the PPP.  Basically the same technique is used in HiRez DAC's all the time for digital to analog conversion.   Same sort of technology used in motor controllers.  Most microcontrollers these days like the Arduino have the PWM output capability.   

Speedskater

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Re: Solar Electricity Quality
« Reply #35 on: 7 Jul 2016, 12:27 am »
Jim Brown the go-to EMI/RFI expert writes:

Solar Power Systems can be very strong noise sources as a result of poor design, poor installation,
or both. The best charge current regulators are DC-DC converters, and most are noisy. DC – AC
inverters that provide 120VAC are also often noise sources. Both charge and discharge circuits
carry large pulsed currents with strong harmonics; those harmonics will radiate if the current flows
through large area magnetic loops.

and
Uninterruptible Power Supplies (UPS) come in two basic types: On-line types are always regenerating
power, while Standby units monitor the AC line and regenerate power only when AC power
fails. Both types include batteries to provide the power when power fails, a DC power supply to
keep those batteries charged, and a DC-AC inverter that operates when the unit is producing AC
power. If the DC power supply is an SMPS, it will likely produce RF noise while charging the battery.
All of the comments about DC-AC Inverters and SMPS apply equally to UPS units.

mikeeastman

Re: Solar Electricity Quality
« Reply #36 on: 25 Aug 2016, 05:20 pm »
I just got an Alphalabs EMI meter to check out my power (live off the grid ). When I test my dedicated circuit, for my audio gear, that comes straight off the inverter the power is so clean the meter doesn't even read, when I test the other circuits in my house I get the same readings as I get on the grid in town. So at least my inverter is producing pretty clean power. There maybe other garbage on my power that this meter doesn't read, I don't know. If someone has any other suggestion for other tests I could try let me know.