Solar panel power

[Eugen]

What is the best way to detect that the solar panels are not making enough power and transfer to grid? Current relay and voltage relay seams a bit overkill (which are the most economical ones by the way). Is there a simpler solution?

Thanks

 

[Binaural]

What is the best way to detect that the solar panels are not making enough power and transfer to grid? Current relay and voltage relay seams a bit overkill (which are the most economical ones by the way). Is there a simpler solution?

Thanks

With DC power supplies, you can use a diode unit used with dual power supplies that will allow seamless transfer if one fails. I don't know how many amps you are using but bumplessly switching DC over is probably easier than AC no matter what system you use....

 

[diat150]

HOW MUCH DC CURRENT?

you can use either a current transducer or, if you need higher currents, a dc shunt to measure the current.

 

[Binaural]

The sort of thing I'm thinking about can be seen here: http://www.ab.com/en/epub/catalogs/12768/229240/1151309/1151313/tab10.html

 

[Eugen]

Thanks for the reply's. I want to switch the 110V on the load, with a reversible mechanically interlocked contactor, between the AC power from the grid and that that comes from the inverter that is solar powered. The question is how do I check that the solar panel is producing enough power to feed the load. Load is small and nothing critical, no quick switching is required. How do I check the current when the circuit is open?

 

[leitmotif]

Tell us more about system ie PV to battery then to inverter?

AND what you are really controlling is where you are supplying load from ie PV system or grid?? What size load?

In my mind you should not rely solely on battery voltage BUT get wet lead acid and a GOOD hydrometer and take gravities of all cells weekly. You must know charge level on them - gravity is the only real way to measure.

With the above you could control on battery voltage ie 13.5 to 14 charged and use them for source. Switch back to grid at say 12 or maybe 11.5.

You could also do on amp hour in and amp hour out. You would want initially a formula 1.3 Ah rating in minus 1.0 Ah rating out. Would need very good current monitoring and timing to do this AND the hydrometer. These are just rough number guesses to get you started.

Dan Bentler

 

[nightline]

I don't understand what you like to do.
I've also grid connected solar panels, and I can read every parameter realtime when I'm connected to the inverter.

Jack

 

[Johnster]

Leitmotif is first asking if there are batteries in your solar panel system ?
Thats normally how they are set up - the PV cells charge a battery or bank of batteries, then the batteries are connected to teh inverter which actually makes teh AC power.
The batteries give you some reserve/surge capacity that you wouldnt have with just solar panels.

So IF you have a battery or battery bank, just read battery voltage and switch on that. Most battery banks are 12v (like a car), so 13vdc on the battery is considered charged/charging and 11.5 or 12vdc on the battery means that it is discharged or low.

Measure the battery voltage and if it is low, switch to grid power, but if it is above 13vdc, stay on the inverter (or swtich back to the inverter).

notes: some battery banks may be 24v, 125v or 250v dc busses - adjust your setting appropriately =)

The text about gravities is basically saying - if you have multiple batteries connected in series, you need to monitor their state of charge accurately - the only way to do this is to dip a tester in the battery acid and check the specific gravity of the acid - that is the best indiciator of how much charge is in an wet lead-acid battery. If you dont have lead acid wet cells (most larger batteries are, but my plant has banks of NiMH batteris...) then 'taking gravities' wont work.

If you would have told us how many amps/watts/sq. ft./the size of your stuff, we'd be able to give you some better guesses =)

if you dont have a battery, this wont work.

Most inverters (even the ultra cheap ones at radio shack) have a 'low voltage cut off' which causes them to beep or throw an alarm when their supply voltage is too low to operate. See if your inverter has contacts or an output for this, (if the solar panel gets shaded, this will cause the input voltage to the inverter to drop) and use it to tell you to switch back to grid power.

Does this help ?

 

[rdrast]

How big is your solar array? Unless it is massive, you may as well stop now, as powering up a contactor and inverter is probably more than it can handle anyway.

You MUST have intermediate storage with a solar array, meaning batteries. Use the array to charge the batteries, and run everything off of battery power all the time. Utility power can be used as well to keep the batteries charged.

 

[nightline]

The topic starter doesn't talk about a battery connected system, so I suppose, it's only grid connected by an inverter ( like the system I have ).

Jack

 

[diat150]

phoenix contact makes a dc current transmitter. I think it can read up to 20 amps. its not going to be very cheap though.

 

[seppoalanen]

There is everything you need:
http://www.mastervolt.com/

 

[kamenges]

As nightline said, I don't know why you want to switch anything. You haven't told us the inverter you are using but I am making an assumption. I assume if you connect the output of the inverter to the grid it will sync itself to the grid, much like a regenrative power supply in a drive system will. If you start to get energy from the solar cells the inverter will simply put it onto the grid. But since you are doing it on the "downstream" side of your utility meter the net result is you use less from the grid.

Keith

 

[nightline]

There is everything you need:
http://www.mastervolt.com/

That's exact what I'm using on my solar panels and windmill.

Jack

 

[Eugen]

Thanks, There will be no battery and the inverter I had in mind was not grid tied (that's why the contactor; to switch between inverter and grid) I might go with a grid tied now much better.