Solar Panels (how they work)

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Solar Panels (how they work)

Postby teralbabill » Sun May 03, 2015 10:14 am

How does the Solar Panel System work? ( in simple terms)

1) Your Panels produce DC that is converted into AC that is transferred straight into the Grid. Your Electricity Provider pays you for what you produce and then takes this amount off your Bill.
or
2) Your Panels produce DC that is converted into AC.
While your Panels are producing you can utilise that power to run items such as stoves fridges freezers and lights in your home and what's left is transferred to the Grid then Your Electricity Provider pays you for what you produce that is left over and then takes this amount off your Bill.

When discussing this with the salesman. I suggested that the latter 2) is true and he nooded. I suggested that we use as much power as we could during the day ( such as running the pool pump during the day) as relying on the minuscule price of 8 c a kW was false economy and he agreed with that also.
On his company's information sheet it said that a 4kW system costing $5200 would pay for itself in less than 4 years.
BUT if 1) proposition is true 16kW a day at 8c a kW = $1.28 a day , $467 a year it would take 11 years to recoup your investment not taking into account inflation and efficiency loss in the panels. A lot longer that the suggested 4 years!

If proposition 1) is correct and there is no chance of using your own power produced by your panels during the day then it is definitely false economy as the power company is paying you a third of what you are paying them for a kW ....they are making 66% profit as well as charging you the extra kW you use as well as the Supply Charge.

Can anyone on this Forum please enlighten me?
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Re: Solar Panels (how they work)

Postby Gordon-Loomberah » Sun May 03, 2015 11:18 am

Welcome to the Energy Matters Forums Bill :)

Your scenario #2 is closest to how it happens. New domestic PV systems are all on a NET FiT these days, so you only get paid for what is left over (if any) after accounting for your household demand, and is exported. Sometimes this is 8c/kWh, but in some areas it is zero. Exports are a minor to minimal consideration in how long it takes to pay off a system.

The pay off is in the energy you produce yourself offsetting what you would normally purchase from the grid at 30c or 50c or whatever per kWh.

If you use 10kWh of your own power each day instead of purchasing it for 30c/kWh, that's $3 per day that you are ahead - over $1000 per year. If some of that grid power is at a peak rate of 52c/kWh, then a 4 year pay off is entirely possible.
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Re: Solar Panels (how they work)

Postby teralbabill » Sun May 03, 2015 5:41 pm

Thanks Norman. What you have said is encouraging.
What I want to know is how your system ( power source can determine what has been produced by you and not coming from the grid.)
Can the system differentiate between the sources.
In other words I can use my own power to run the electrical systems at home during the day and what's left over goes back into the grid?
So I can put my pool pump system on during the day and maybe put my freezers in the shed on time control so they only come on during the day and feel pleased to run my air con during the day at my hearts content
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Re: Solar Panels (how they work)

Postby Gordon-Loomberah » Sun May 03, 2015 6:05 pm

What I want to know is how your system ( power source can determine what has been produced by you and not coming from the grid.)


The arrangement is: [grid] - METER - [house+PV system], so it measures the net of your usage from the grid. If your load is equal to what you are generating, then the meter wont be accumulating any kWh in its registers. If you are using less than you are generating, then the remainder is exported, and if you are using more, such as at night, then it will be accumulating imported kWh.
The aim these days is to use as much of your PV system's output as possible, and to minimise imports. Time clocks can help with that, and so can the arrangement of your PV array.
Have a read of this thread: solar-wind-gear/topic5064.html
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Re: Solar Panels (how they work)

Postby teralbabill » Sun May 03, 2015 10:45 pm

Norman I know that I could wait and ask the technicians when they install
But it would be lax of me not to take advantage of a man such as yourself ,who obviously is up to terms with the subject that I need to know about.
So let me pick your brains and I am sorry if the questions might sound naive to you.

Firstly, how many devices could a 4kW system run all at once .....say on a sunny day at noon ( say two freezers,one fridge,a pool pump and a small air conditioner ......too ambitious??). How about on a cloudy day?

I virtually have to put all my panels on the western side. I lose 2 hours with the sun rising to hit the panels and lose about half an hour on the set time.
But I have huge tree on the north side that will probably throw a slight shadow on the first panel in the strings for an hour or two.
I understand that that can degrade the whole string but you can correct this with bypass diodes.....do these come standard or do I have to pay extra for these?

I think I understand that the power that you generate goes into the grid ....your load or consumption level is measured at that instant...... if you are using more than you are producing then the grid makes up the difference and you pay for it but if you are consuming less they generously give you 8c for every kW h you produce ......if that is the case......I'm starting to see the light....an ingenious system ( but stingy!)

Well Norman...........as a fellow who couldn't be bothered to give a power bill a second glance two months ago to a fellow interested in how it all works.....I think I know now .......how it gets you in!
Thanks for your help
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Re: Solar Panels (how they work)

Postby teralbabill » Sun May 03, 2015 10:49 pm

Sorry Gordon...I've been calling you Norman.......its late at night and that's my excuse.
Cheers and thanks
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Re: Solar Panels (how they work)

Postby Tracker » Mon May 04, 2015 8:14 am

..
You have not suggested where you are.. location may affect things.. eg.. in NSW, I UNDERSTAND that when you apply for connection approval, you are pushed onto TimeOfUse pricing which can push your daytime rates from 30 to 50c (odd)...

Prices will determine so much.. eg.. I would normally suggest a smaller system, whilst installers want to do bigger ones..

Are you retired and home during the day.. again as you realise, you need to be there to make best use of the generated power..

The proposed system. WEST facing system .. do you have any East roof.. I would look at some east and more west, to cover power for all of the day, but most in the hot afternoons..

More details of where you are and about the property including shading etc...
..
.
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Re: Solar Panels (how they work)

Postby Tracker » Mon May 04, 2015 8:32 am

teralbabill wrote:......... have to put all my panels on the western side. I lose 2 hours with the sun rising to hit the panels and lose about half an hour on the set time.
But I have huge tree on the north side that will probably throw a slight shadow on the first panel in the strings for an hour or two.
I understand that that can degrade the whole string but you can correct this with bypass diodes.....do these come standard or do I have to pay extra for these?


Again, a better description of the place and why not east.. remembering how the sun moves and especially in winter when a north tree could be most troublesome ..

To prompt thought... is there east roofing that is better than another portion.... you should not be concerned with bypass diodes as they don't do as much as the experts say and I understood that all good panels have them anyway..

Above all, don't jump at the first offer..
..
.
Retired Engineer and keen PV experimenter - Always ready to learn and share.
2 x CMS2000 (fan cooled) GCI and SE 170W panels
1.7kW First Solar/Outback Island circuit - Peak Replacement Power
Governments won't save the world :-) They will just TAX it :-(
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Re: Solar Panels (how they work)

Postby Gordon-Loomberah » Mon May 04, 2015 8:50 am

It's not so much how many devices, it is the total load that is important. A 4kW system will typically produce about 80% of that, ie 3.2kW, through the period when the sun isn't too far off face-on to your panels. In colder weather you will get more from them, less in hot weather. When brightly lit clouds are in the sky near/around the sun, the effective radiation levels can be much higher, so a 4kW array can put out up to 5kW, although a 4kW inverter will probably limit the output to a bit over 4kW. This is known as cloud edge effect. see: solar-wind-gear/topic1507.html

So, lets say we have 3.2kW available, then a small (500W?) AC, plus a 1.5kW pool pump, and say 600W for 3 fridge/freezer compressors leaves you with ~600W spare, which will at least partially be used by lights, standby loads, TV, computer etc, so is probably about what you want to cover your usage. Remember that output will be less when the sun is well off face-on, such as in winter for a west facing roof. If you could put a small string of panels on the east facing roof, and a larger one west-facing, that would help considerably.

In cloudy weather the partial string shading will matter much less, as the light is diffuse, greatly reducing or removing any shadowing, but radiation levels are much lower, so in heavy overcast with rain, you might get zero output for brief periods- chances are you wont run the AC then, and you could limit pool pump use. in thin patchy cloud, you can often get almost the same output for the day as when it is sunny- the thicker cloudy periods are offset by the bright cloud + sun periods. You really need to monitor it with a good metering system showing consumption and production, so that you can get a feel for how much power is available under certain sky conditions and times of day. Manual load control can help match load and output, and there are some automation and remote control (phone or computer) devices becoming available, so you can have some load matching control even when you are not at home.

Bypass diodes dont help much, although most good quality panels have them. If you have a string inverter and one panel is partially shaded, it will really knock your output way down. Micro-inverters such as those made by Enphase would be a much better way to go if you have unresolvable shading issues. With this system, each solar panel has its own inverter, so there is no high voltage DC in the system- just panel voltage and 240V AC.
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Re: Solar Panels (how they work)

Postby Gordon-Loomberah » Mon May 04, 2015 8:53 am

Tracker wrote:..
You have not suggested where you are.. l


Really? Hint, it starts with T ;)
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