Solar panel query - charging battery

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snail

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So, I have the following,

1 x 260w solar panel (Not currently connected)
1 x solar charge controller (Not currently connected)
1 x 102Ah deep cycle battery (12v)
1 x 300w pure sinewave inverter with built in charger
Required output +-50W - 60w

With that being said I currently have the setup as follows,

Main grid -> Inverter (Connected to battery) -> Fish tank (Running through inverter).

I want to do the following (Due to extended power cuts in my area),

Main grid ->Inverter (Connected to battery, while at the same time connecting solar panel and charge controller to battery) -> Fish tank (Running through inverter).

The reason behind this is my battery lasts about 24 hours, however the power cuts have been longer than this, therefore I would like the solar panel to charge battery, therefore if the main grid cuts out and the inverter starts using the battery power, then atleast the battery will continue charging from the solar panel.

With that being said my concerns are regarding having the main grid charging the battery at the same time as the solar panel. Is this possible?
 
Last edited:
You should be able to set the charge voltages on both the inverter and the MPPT. Set the voltage on the MPPT 0.1V higher than on the inverter.
 
Previous message was brief due to posting from phone. More info:
Your proposed setup seems pretty standard - based on the setup you describe (and assuming your components are well paired) you should be able to run the system pretty much without grid input. If the solar regulators are set to charge the battery at the recommended voltage (for your battery type), with the inverter set to charge 0.1V lower, the battery will be charged preferentially from the solar panel. You can possibly also set the inverter to only use battery power / inhibit import during sunlight hours. The nett effect will be that the inverter then preferentially uses solar energy during the day, saving you electricity.

As an example, my home setup: MPPT set to charge @ 0.1V>Inverter. Inverter set to inhibit import from grid from 16:00 -10:00 next day, therefore using the batteries during the night as well as allowing the panels to recharge the batteries during early morning. Inverter therefore only charges the batteries when there has been insufficient sunlight during the morning, and energy from solar panels is used preferentially during the day. In this manner my house is 95%+ independent of grid.
 
I have a simlar setup, but 4 x 300 watt panels, a 4 kw MPPT charger and 4 x 105 a/h batteries. i think you need to beef up the system a bit, it seems rather inadequate for the task you envisage

I run all my (led) lamps and 3 plug circuits off it. My electricity consumption is about 9 units a day. I also have 2 solar water heater panels
 
snail said:
With that being said my concerns are regarding having the main grid charging the battery at the same time as the solar panel. Is this possible?
Click to expand...

Does anyone have a good solution to that part of the problem? I know you can get much more expensive 'hybrid' inverters that will charge from generators, the grid, solar etc... and then obviously it needs quite complicated intelligence / rules to do that.

Anyone got any experience of using/buying something like that? I ask because I've seen some of the Axpert inverters have settings around this, but I'm not sure what the settings should be / what works?

E.g. purely as a bit of a puzzle. It's 3AM sun is out, grid is on, batteries are at 80%; do you take from the grid, or just let the batteries run lower? I guess it depends on your mix of wants / needs - e.g. if your sole-purpose is backup power, then charge from the grid (i.e. charge whenever you can from the grid); if it's 100% about saving money, you may as well cut off the grid... but I guess most people are looking for a bit of both..
 
My MPPT charger/inverter sorts out the mains feed automatically.

During the day there is enough power to supply 900 watts and to simultaneously charge the battery. I generally use 450 - 600 watts during the day

From about 17h00 the PV supply drops off and the battery level drops

At about 20h00 it goes onto "Bypass" which means is switches the incoming power. It will then charge the batteries to about 70%. The next morning, it goes out of bypass at about 07h00 and has fully charged the batteries by about 13h00

You can set these parameters by connecting a computer to the USB port on the device with their software

I got mine from MP Solar in Taiwan. We imported 6 and it came to between R4k and R8k each
 
quick update in terms of responses i have received. My inverter is as basic as it comes. i cant change anything on it. the only indications it gives is the current % usage of the total max watt output capacity (being 300w) and the % charge of the battery. How do i go about this?
 
chrisc4290 said:
From about 17h00 the PV supply drops off and the battery level drops
At about 20h00 it goes onto "Bypass" which means is switches the incoming power. It will then charge the batteries to about 70%. The next morning, it goes out of bypass at about 07h00 and has fully charged the batteries by about 13h00
Click to expand...

That all sounds great. So what do you gain from this set-up? I guess there's backup power available; and you're using Solar for a few more hours every day (from 1700-2000 - so 3 hours?); but does that offset the losses of basically using the grid to charge batteries?

(you're charging batteries in the peak hours... which probably doesn't cost you, but costs the system as a whole!)
 
@snail, I think everybody is giving you advice on equipment you do not have.
You did not say if your inverter can take mains input or not, or charge the battery from mains?
What type of charge controller do you have? MPPT or PWM?

I had a similar set-up to yours some time back.
During the day I ran from solar alone and at night from mains only.
Solar was the only power to charge they battery.
I used a normal day night switch (from any electrical store) to do the switching between mains and invertor power via power relays.
The trick is to run the controls from your battery powerd invertor, so that when the mains fail, your controls will still work.
 
wetkit said:
@snail, I think everybody is giving you advice on equipment you do not have.
You did not say if your inverter can take mains input or not, or charge the battery from mains?
What type of charge controller do you have? MPPT or PWM?

I had a similar set-up to yours some time back.
During the day I ran from solar alone and at night from mains only.
Solar was the only power to charge they battery.
I used a normal day night switch (from any electrical store) to do the switching between mains and invertor power via power relays.
The trick is to run the controls from your battery powerd invertor, so that when the mains fail, your controls will still work.
Click to expand...

when i mean i have a very basic inverter, i mean a real basic inverter. see below link for screen dumps (I cant even find my inverter online to give description),

https://www.tropicalaquarium.co.za/threads/backup-power-supply-at-great-price.22599/
 
Best bet is to connect solar panel with charge controller onto battery with your inverter .
Daytime pannel will supply inverter .
Nighttime it will run from battery.
 
Power Layout.jpg

Hopefully you will be able to understand my basic diagram.
The most difficult part to get right is the Standby / Mains changeover relays.
How is should work is that during the day you running from the Standby relay.
Once it gets dark, the day/night switch will switch over to the Mains relay.
If Mains power falls away for any reason, Standby relay will be powerd again.
You must have an electrical interlock between the two relays, so that they can not be switched on at the same time, as that will blow your invertor.

Have fun :)
 
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