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solarozq

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Posts: 16
Reply with quote  #1 
I have a 3 kw solar inverter to which I added extra panels up to a total rating of 4.25 kw. 
The system seemed to work happily with this arrangement throughout the Queensland summer. 
It is now autumn and I have gradually added a further 750 watts giving a total (manufactures rating) of about 5 kw.
Under winter conditions this all seems to be working fine. Do people think it would be safe to leave the extra panels connected come the next summer?   
The panels are all several years old and the latest ones are not installed at the optimal angle.

solarozq

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Posts: 16
Reply with quote  #2 
In Australia the systems currently advertised feature a 33% greater panel rating. 6.6kw on a 5 kw inverter.
I agree extra heat will be created but if the heat is managed with (low cost) additional thermostatically controlled cooling hopefully the service life will be maintained.
If done currently the additional early and late power is a bonus well worth having, power that is wasted doesn't really matter.
The inverter's temperature, and solar input amps and voltages all need to kept well withing it's rating.
Once an inverter is past its warranty period I suspect the manufacturer wouldn't care either way.
If done correctly the additional early and late power is a bonus well worth having, power that is wasted doesn't really matter. 
I used low cost recycled panels for the additional solar capacity.
They need to be matched to the inverter's voltage requirements and the other panels.
stmbtwle

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Reply with quote  #3 
There's only one way to find out...
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Solar is like the wind. It may be free, but putting it to work isn't!
Willie, Tampa Bay
johnd01

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Reply with quote  #4 
Panels do not generate rated power in real-world conditions. Even if they did they would only do it for a short period of time. As long as you do not overvoltage or overcurrent the inverter it should be able to produce all the power it is rated for or in a lot of cases 10% more than rated power. The inverter should protect its self from overheating. With the price of panels coming down faster than inverter prices, it is better to over panel a system. Inverters are more efficient when they are running close to max voltage. 
stmbtwle

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Reply with quote  #5 

I think the original question was whether or not to disconnect the extra panels in the summer. PV panels actually produce LESS power when they get hot, so the issue may be self-correcting, at least up to a point. The problem is, you don't know where that point is.

Suppose you were to put the additional panels on a relay, and control the relay with a thermal sensor inside the inverter? If the inverter starts to overheat, the relay would disconnect the extra panels, reducing input and heating.


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Solar is like the wind. It may be free, but putting it to work isn't!
Willie, Tampa Bay
solarozq

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Posts: 16
Reply with quote  #6 
I did consider having ground level access DC isolators on the panel strings but in the end wired them direct.
The inverter has two strings of 12 of panels so effectively you would have roof mounted relay contacts to bridge out 2 panels on each string.
The relays would need a serious rating because the DC voltage is about 400v.
I think it would be pretty challenging electrically.
I currently have 12 thermostatically controlled fans around the inverter.
The plan is to leave the panels in string for the winter and if the inverter temperature is getting too high next summer waiting until after daily production finishes then disconnect the extra panels.
Your suggestion has merit, I will look into it.
stmbtwle

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Reply with quote  #7 
It was just a thought. To cut out part of a series string you would have to bypass the panels as well as disconnect them. Yes it would be challenging. Sorry.

It would be nice to have a system that can deliver a relatively steady output all day...




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Solar is like the wind. It may be free, but putting it to work isn't!
Willie, Tampa Bay
colinmcc

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Posts: 174
Reply with quote  #8 
One quick point, using a relay to break a circuit carrying DC is problematic since the plasma arc generated as the points open is not extinguished. (In an AC circuit the current drops to nill every cycle, so the arc is extinguished every cycle) So if you want to break a DC circuit with a relay you can get a DC relay which has a built in magnet that literally blows the plasma arc out by stretching it sideways(!)

I have a couple of these in my self built electric car, one breaks the main current in an emergency (450A DC, and the other turns all the electronics on.

Car details here for anyone interested in the project:

http://pontiacfirefly.com/ecarGallery
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