During Float Charge - How to use the extra PV power?

72 Posts
Mar 25, 2009 09:33 pm
During Float Charge - How to use the extra PV power?

I have a 700w PV system that is putting my battery array in to float charge for a couple of hours a day.

Other than net metering, What is a good way to use the extra power?

I'm thinking about using the Auxilary Output on my MPPT to trigger a relay, during float charge, to turn on an external device.

But what device? What can I 'turn on' to use the wasted power. So that It gives me some value back?
 
49 Posts
Mar 27, 2009 09:01 am
Re: During Float Charge - How to use the extra PV power?

I would plug in anything that needed charging. In my off-grid cabin I always charge the cell phones, batteries for the electric motor, by plugging in a charger.Or laptop computer.
 Good luck, Jim
 
Mar 27, 2009 01:55 pm
Re: During Float Charge - How to use the extra PV power?

I am curious about the remark you made concerning "net metering." Does this mean you have a grid intertied system with batteries as a back up power supply?
 
72 Posts
Mar 28, 2009 07:35 am
Re: During Float Charge - How to use the extra PV power?

I would plug in anything that needed charging. ...

James, I think that is an excelent idea, except for my situtation ...

As an example:
I have a lot of rechargeable yard tools, so charging them off solar would be ideal, but
... I would only want them to re-up charge during float
... this means I could connect to a relayed circuit
... but, that would mean that while the circuit was inactive, the batteries would be connected to chargers that have no power
... which for some of my chargers, that would mean the batteries would drain the 'other 21 hours of the day'

I could also get more batteries and grow my bank
... collect additional power
... and then add additional load
... but my batteries are past the 1 year add on time
... and replacing is very expensive

so ... for now, I'm trying to figure out what I can actually run, instead of trying to store the energy.

 
72 Posts
Mar 28, 2009 07:44 am
Re: During Float Charge - How to use the extra PV power?

I am curious about the remark you made concerning "net metering." Does this mean you have a grid intertied system with batteries as a back up power supply?

Thomas,
No, This system is not tied to the grid right now. It has a constant light load ( internet, single light, sprinkler system, single phone ), and random short loads ( tools, lights, etc )

I would love to upgrade my inverter, and net meter back my extra power
... I've looked in to it, and it looks like it would cost anywhere between  2k and 5k to upgrade my system and get it certified for net metering.
... on a 700w array with only an hour or 3 of grid feedback, it would take a long time to get return on that!
... If I'm going to spend, I would rather spend on growing the system instead. My next goal would be to double the array and battery bank , but the budget is not there yet :-)

Maybe I do need to think about growing the battery bank?
 
Mar 31, 2009 05:07 am
Re: During Float Charge - How to use the extra PV power?

My bad.

The picture that comes to mind is of the proverbial squeezing and rolling of the tube of toothpaste.
I agree though, it is a waste of potential.

When a PV system is actually planned and designed for offgrid. It usually means there is a surplus of power in the summer months and it just squeaks by in the winter months. This of course is dependent on local.

But what to do with the power from a PV array that, is not, going to the batteries during the float stage of charging and, its still relatively early in the day?

I suppose James A. hit on something there, but what if it was a smaller secondary battery bank sized just big enough to capture the otherwise lost power and then use it at a more convenient time? (May want to oversize the bank a just a little.) It might mean putting the, charge controller to battery, circuit on an automated transfer switch.
Sounds a little "mad scientist" I know but its not as though you will be staring at the battery monitor, yelling to a hunchback named Igor waiting to throw the transfer switch at just the right time.
Thats all I can come up with right now.
 

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