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Author Topic: EEVblog #484 - Home Solar Power System Installation  (Read 38755 times)

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Online EEVblog

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EEVblog #484 - Home Solar Power System Installation
« on: June 16, 2013, 10:17:09 AM »
Installing and initial testing of Dave's 3kW home solar power system. With Sunnyboy SMA inverter, 250W LG Mono-X solar panels, and net metering.

Data from the system is here: http://pvoutput.org/list.jsp?userid=22501

« Last Edit: June 16, 2013, 08:05:22 PM by EEVblog »
 

Offline Eliminateur

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Re: EEVblog #484 - Home Solar Power System Installation
« Reply #1 on: June 16, 2013, 10:42:01 AM »
why do you have two power meters in the old installation?
ripple control, wth is that for?
 

Offline Skimask

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Re: EEVblog #484 - Home Solar Power System Installation
« Reply #2 on: June 16, 2013, 11:41:34 AM »
Something I've never been able to grasp...

How does power get fed back into the grid?

Is it as simple as just generating one more volt than the grid has on it at that particular point in time (e.g. keeping everything in phase, etc.)?
Do you monkey with the phasing of the power you generate in relation to that of the phase of the power on the grid itself (e.g lead or lag an equal pk-pk voltage by x degrees)?

If all grids were DC, this would be a no-brainer, but it's not...
I didn't take it apart.
I turned it on.

The only stupid question is, well, most of them...

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Offline c4757p

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Re: EEVblog #484 - Home Solar Power System Installation
« Reply #3 on: June 16, 2013, 11:53:38 AM »
ripple control, wth is that for?

A higher-frequency ripple tone (1050 Hz IIRC) is injected into the mains to mark off-peak hours; that receives the signal and switches a water heater on or off accordingly.
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Offline c6r1s

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Re: EEVblog #484 - Home Solar Power System Installation
« Reply #4 on: June 16, 2013, 12:07:11 PM »
Very nice indeed. I wonder could we modify to increase efficiency of Solar panels. What if we were to put a TEG system along the back of the panels and rails to generate excess DC to feed back into the inverter.? I mean if you harness more of the loses wouldn't that increase your DC feedback to save more money?
 

Offline cthree

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Re: EEVblog #484 - Home Solar Power System Installation
« Reply #5 on: June 16, 2013, 12:17:59 PM »
Amazing how much you pay and how little you get paid wtf. We pay $0.06-$0.12 and get paid $0.53 in Ontario Canada. Used to get paid $0.80 which was stupid so they stopped doing it. Something about encouraging solar generation investment or some such.
 

Offline Deagle

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Re: EEVblog #484 - Home Solar Power System Installation
« Reply #6 on: June 16, 2013, 12:28:34 PM »
Haha Dave, going through the installers toolbag  :-DD
 

Online NiHaoMike

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Re: EEVblog #484 - Home Solar Power System Installation
« Reply #7 on: June 16, 2013, 01:53:14 PM »
Are you going to design some sort of controller to try to match the load to the supply at all times? I suppose the difficulty of actually doing that depends on the time resolution of the measurements.
Something I've never been able to grasp...

How does power get fed back into the grid?

Is it as simple as just generating one more volt than the grid has on it at that particular point in time (e.g. keeping everything in phase, etc.)?
Do you monkey with the phasing of the power you generate in relation to that of the phase of the power on the grid itself (e.g lead or lag an equal pk-pk voltage by x degrees)?

If all grids were DC, this would be a no-brainer, but it's not...
Just generate a waveform that is in phase with and slightly higher voltage than the mains. It's very similar to a synchronous motor drive.

Online IanB

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Re: EEVblog #484 - Home Solar Power System Installation
« Reply #8 on: June 16, 2013, 02:07:59 PM »
When you run a generator feeding a grid you actually have to make the phase angle of the generator lead the grid by marginal amount. The generator will naturally try to synchronize with the grid, and the attempt of the generator to resist being driven out of phase relates to the power you have to feed into the generator to force it into the out of phase situation. The more power you feed into the generator the faster it tries to turn and the more the grid resists it. The generator pushing against the grid is how power gets transferred.
I'm not an EE--what am I doing here?
 

Offline Leon

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Re: EEVblog #484 - Home Solar Power System Installation
« Reply #9 on: June 16, 2013, 02:15:38 PM »
The SMA SB 21-series is fanless. The fan is an option, if you didn't order it you won't find it during a teardown.  ;)
 

Offline Hypernova

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Re: EEVblog #484 - Home Solar Power System Installation
« Reply #10 on: June 16, 2013, 02:43:57 PM »
Why are there no combined elec/water heating setups? You run pipe along the back of the panels to cool them and you get free hot water. Why is it that when ever I see a solar set up it's always either one but never both?
 

Online IanB

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Re: EEVblog #484 - Home Solar Power System Installation
« Reply #11 on: June 16, 2013, 02:52:01 PM »
I don't think you would get much hot water if most of the sun's energy is being converted to electricity. By energy balance you can get hot water or electricity, but not both at the same time. If you did run water cooling you would get low grade heat (lukewarm water only) and then you would need a heat pump to raise the water to a useful temperature. I doubt that the improved efficiency of the cooled panels would generate enough extra power to run the heat pump. Not to mention the considerably increased complexity and capital cost of the installation.
I'm not an EE--what am I doing here?
 

Offline Eliminateur

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Re: EEVblog #484 - Home Solar Power System Installation
« Reply #12 on: June 16, 2013, 03:10:37 PM »
panels should already include piping for that, and you run the water for your overhead water tanks that you have anyway so it doesn't matter if they get lukewarm only (or the downpipe from the tank to the house)
 

Offline Hypernova

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Re: EEVblog #484 - Home Solar Power System Installation
« Reply #13 on: June 16, 2013, 03:30:19 PM »
I don't think you would get much hot water if most of the sun's energy is being converted to electricity. By energy balance you can get hot water or electricity, but not both at the same time. If you did run water cooling you would get low grade heat (lukewarm water only) and then you would need a heat pump to raise the water to a useful temperature. I doubt that the improved efficiency of the cooled panels would generate enough extra power to run the heat pump. Not to mention the considerably increased complexity and capital cost of the installation.

The panels are not that efficient, most of the light is still turning into waste heat and the panels can get to 50+ degrees easily.
If you are already using electric based water heaters you already spend power on the heaters, so giving the heater warm water to start with will save power. Solar water heater installations are often augmented by electrical heaters already. What I'm proposing is free cooling for the panels and free preheating for the heaters.
« Last Edit: June 16, 2013, 03:33:24 PM by Hypernova »
 

Offline snoopy

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Re: EEVblog #484 - Home Solar Power System Installation
« Reply #14 on: June 16, 2013, 03:33:39 PM »
Something I've never been able to grasp...

How does power get fed back into the grid?

Is it as simple as just generating one more volt than the grid has on it at that particular point in time (e.g. keeping everything in phase, etc.)?
Do you monkey with the phasing of the power you generate in relation to that of the phase of the power on the grid itself (e.g lead or lag an equal pk-pk voltage by x degrees)?

If all grids were DC, this would be a no-brainer, but it's not...

Yes the inverter generates a sinewave with the same phase but with a higher voltage than the mains and it also has a high output impedance approaching current drive. If there are too many inverters on the grid it can drive the actual mains voltage too high and all inverters have an over voltage limit to shut them down when this happens. They also have a feature called anti-islanding which means that if the grid and mains fails the inverter will shut down thus making the grid safe.

regards
david
 

Offline snoopy

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Re: EEVblog #484 - Home Solar Power System Installation
« Reply #15 on: June 16, 2013, 03:35:30 PM »
Installing and initial testing of Dave's 3kW home solar power system. With Sunnyboy SMA inverter, 250W LG Mono-X solar panels, and net metering.



6 cents per KWh gives new meaning to daylight robbery ;)

cheers
 

Offline notsob

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Re: EEVblog #484 - Home Solar Power System Installation
« Reply #16 on: June 16, 2013, 03:37:38 PM »
When dave grabbed the installers meter - I was waiting for a 'mine is bigger than yours' segway
 

Offline Skimask

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Re: EEVblog #484 - Home Solar Power System Installation
« Reply #17 on: June 16, 2013, 03:38:06 PM »
When you run a generator feeding a grid you actually have to make the phase angle of the generator lead the grid by marginal amount. The generator will naturally try to synchronize with the grid, and the attempt of the generator to resist being driven out of phase relates to the power you have to feed into the generator to force it into the out of phase situation. The more power you feed into the generator the faster it tries to turn and the more the grid resists it. The generator pushing against the grid is how power gets transferred.
Is "super-synchronous" the word I'm looking for?
If it is, then unless I'm wrong, it appears to me that a purely mechanical solution would be a relative piece of cake compared to designing/programming/using a solid state inverter.
I didn't take it apart.
I turned it on.

The only stupid question is, well, most of them...

Save a fuse...Blow an electrician.
 

Offline Leon

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Re: EEVblog #484 - Home Solar Power System Installation
« Reply #18 on: June 16, 2013, 03:43:19 PM »
Why are there no combined elec/water heating setups? You run pipe along the back of the panels to cool them and you get free hot water. Why is it that when ever I see a solar set up it's always either one but never both?
There are plenty attempts:
http://solarwall.com/en/products/pvthermal.php
http://www.tessolarwater.com/index_en.html?zeuspv-t.html&2
But the problem is, you need to be able to get rid of the heat accumulated by the thermal part of the panel. Solar thermal collectors are often stagnating in the summer, they heat up to the point steam is produced and the collector is actually getting dry as the fluid is pushed out of the collector. Temperatures of 170 degrees celcius and up are possible, this would seriously harm PV cells or at least reduce production significantly.
 

duskglow

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Re: EEVblog #484 - Home Solar Power System Installation
« Reply #19 on: June 16, 2013, 03:48:50 PM »
I was just reading up on 1050hz ripple today - or more accurately, watching youtubes of it.  There are some interesting ones of the ripple actually being generated.  Here's one:

 

Offline jnissen

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Re: EEVblog #484 - Home Solar Power System Installation
« Reply #20 on: June 16, 2013, 04:05:13 PM »
Your net metering pay back is awful. Here we get paid 12.8 cents/KWH generated. It used to be very poor like that when it was first installed but last year they changed from a net metering to a gross type. I have to pay for whatever I pull from the grid at from 1.8-11.8 cents/KWH but every KWH I generate it's paid at the higher 12.8! Went from a payback of 8 to 9 years to less than 5 for me. In fact I sized my system and have yet to pay for bill since January! As our summer cranks up I suspect I may soon have a bill as the AC is running often.

So your sunny boy communicates via Bluetooth to the PC? My system uses power line communications and a receiver box plugs into the AC line and then an ethernet cable to that. I like the idea of directly to bluetooth. Hopefully you can figure out the communication issue so the data can be seen live. Does Sunnyboy offer a web service to view the data?

 

Offline Strada916

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Re: EEVblog #484 - Home Solar Power System Installation
« Reply #21 on: June 16, 2013, 04:07:51 PM »
Dave download Sunny Explorer from SMA website. Also there is an android app so you can connect to the inverter via Bluetooth.

Why they did not install an import/export meter instead of two meters is beyond me.
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Offline KedasProbe

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Re: EEVblog #484 - Home Solar Power System Installation
« Reply #22 on: June 16, 2013, 06:33:44 PM »
Here in Belgium your meter (before solar panels installation) is the same and will turn backward when you generate more than you use. You don't get money if the total is negative.
So you try to get the average use to 0 or a little lower when they check your usage. They did just add a tax though on using the net to put energy on. (as a buffer)
(53 Euro/installed kW each year, with an extra meter they will tax you with what you really put on the net)
« Last Edit: June 16, 2013, 06:49:44 PM by KedasProbe »
Not everything that counts can be measured. Not everything that can be measured counts.
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Offline michaelc

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Re: EEVblog #484 - Home Solar Power System Installation
« Reply #23 on: June 16, 2013, 08:55:36 PM »
Just watched your solar install video... very interesting. 

I wonder why the installer didn't adjust the height of the rails on the brackets to offset the "undulating" roof structure.  I know in the end it doesn't really matter... but the brackets have elongated holes, why not use them to make the rails straight?

I have 3.04 kW (16 x 190W) of ET panels and a SMA SB5000TL-20 inverter.  My system was registered with the South Australian distribution company (SA Power Networks) as a 4.94 kW system, I can add another 10 x 190W panels without losing my feed in tariff...  IIRC 44c/kWh from the governemnt FIT scheme and 6c/kWh from my energy retailer.

I use software called PV Bean Counter to read solar info from the inverter, this then uploads to www.pvoutput.org in five minute intervals.

http://www.pvoutput.org/intraday.jsp?id=5514&sid=5863

The next step is to transfer the Bluetooth read and upload functions to a Raspberry Pi and eliminate the need to keep a power hungry PC running!

Michael.






« Last Edit: June 16, 2013, 09:07:22 PM by michaelc »
 

Online EEVblog

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Re: EEVblog #484 - Home Solar Power System Installation
« Reply #24 on: June 16, 2013, 09:08:29 PM »
I use software called PV Bean Counter to read solar info from the inverter, this then uploads to www.pvoutput.org in five minute intervals.
http://www.pvoutput.org/intraday.jsp?id=5514&sid=5863
The next step is to transfer the Bluetooth read and upload functions to a Raspberry Pi and eliminate the need to keep a power hungry PC running!

Exactly what I'm doing:
http://pvoutput.org/list.jsp?userid=22501
Using a netbook at the moment, and it's not live feeding, have to sort that out. But yes, I want to transition to a R.Pi or something.
Or could just let it update once every day instead of live.
Next step is consumption data with a Watts Clever unit.
 


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