Grid tie and battery together

[SunEagle]

Well I managed to figure out a way with help from a YouTuber by the name of Andy Kirby.

How is I did it was to run the power from the panels to a 40A DPDT 2NO 2NC 24 volt Relay. This is controlled by one of those cheap charge controllers that say MPPT but are really PWM. It has the normal three sets of terminals Solar/battery/load. Only I used the battery terminal to monitor the voltage and the load terminals operate the relay.

I have the load parameters set to 25.5 and 28 volts. This may change if I start using more load.

What happens is if the battery bank drops below 25.5 volts the cheap secondary CC senses the drop and the relay switches the incoming solar power to the main charge controller which will charge the batteries until 28 volts is reached. Once done the cheap CC switches the load off and the relay switches over to providing the Grid Tie Inverter with power which I call the default state. It is fully automatic and works like a charm!!

I get Grid Tie power most of the time with the switchover to battery charging when and as it needs it. So far absolutely no issues with this DIY cobbled together set up! Well pleased!!!!

Hmm. I give it a couple of months before that 24V relay fails. But if it works for you then have at it.

[Tired sparky]

Well I managed to figure out a way with help from a YouTuber by the name of Andy Kirby.

How is I did it was to run the power from the panels to a 40A DPDT 2NO 2NC 24 volt Relay. This is controlled by one of those cheap charge controllers that say MPPT but are really PWM. It has the normal three sets of terminals Solar/battery/load. Only I used the battery terminal to monitor the voltage and the load terminals operate the relay.

I have the load parameters set to 25.5 and 28 volts. This may change if I start using more load.

What happens is if the battery bank drops below 25.5 volts the cheap secondary CC senses the drop and the relay switches the incoming solar power to the main charge controller which will charge the batteries until 28 volts is reached. Once done the cheap CC switches the load off and the relay switches over to providing the Grid Tie Inverter with power which I call the default state. It is fully automatic and works like a charm!!

I get Grid Tie power most of the time with the switchover to battery charging when and as it needs it. So far absolutely no issues with this DIY cobbled together set up! Well pleased!!!!

[josepr]

I’m not sure you can do what you want with your setup. In order to not export power to the grid you need some type of consumption meter and some way to turn off your ‘eBay’ grid tied (GT) inverter. Fortunately, you can connect your grid tied inverter with your solar charge controller (CC) if you are using 24v panels or if your string voltage is supported by both your CC and GT. Your just need a normally open relay (if possible, use a solid-state relay) {Relay need to be 250VAC {or your grid voltage} control and whatever DC voltage is your panels or string for the load side}. When power is available the panel or string will be connected to the GT, when power is out the panels with be connected to the CC. But in my opinion your best option is a small 2k hybrid inverter with a zero-grid option, if you do not want to export to the grid. Others DIY solutions will require a custom PLC or a raspberry pi with a consumption coil (amp meter). I strongly recommend solid state relays. For that try to limit yourself to a 24v battery because 48v solid-state relays are not cheap.

[Tired sparky]

And no the grid tie inverter would just put energy into the house mains (grid). The other CC would deal with the batteries.

[Tired sparky]

Yes the grid tie inverter takes 24 volts straight from the panels. It has four sets of MC4 sockets on the unit for directly plugging in four 300 watt panels.

[Ampster]

I am not sure what you mean by a 24 volt grid tie inverter? Will it take input from your existing solar panels directly? Would it charge your 24 v batteries?

[Tired sparky]

Long term goal.

Have grid tie tie power available for home use only. Don’t want to put any into grid if possible as I’m only capable of producing about 1000 watts presently.

Want a battery back up system for emergency use and to run some 12 volt appliances.

All i I would like is an automatic system that switches between grid tie and battery charging using hopefully one solar array but using cheaper parts and parts available here in the UK. I know there are nice gadgets that do these things but are either too pricey or hard to obtain.

I dont use use hardly any battery power day to day so would like the system to automatically put my hard earned solar energy into domestic use once batteries are topped off.

I have an Epever 40 amp mppt charge controller. 900 watts of solar panels. 8 x T105 in series and parallel to make a 24 volt battery bank. Also have a 1200 Watt 24 volt grid tie inverter sitting unused. Saving for a nice 24 volt pure sine inverter for emergency use.

As as this is all diy experimentation, part hobby and maybe useful one day and not really critical for life stuff it just needs to work, not work perfectly.

Thanks.

[Ampster]

Sometimes when trying to solve a problem the details get in the way. What happens is i find myself incrementally making a couple of small decisions that take me down the wrong path. Let me ask a few questions to see if I can understand the big picture;

What is your long term goal? I understand your roof has limited space for lots of panels and that you have a grid connection, correct? What existing equipment do you now have that you would like to continue to use?

[Tired sparky]

Ok thanks, I didn’t think this would work with the two units competing for power. I think I will have to either separate the two systems which will be problematic due to lack of panel space or try to use a relay to switch the power from the charge controller to the grid tie when the batteries are full?

Ideally I would like to get a Victron battery monitor which has an output for a relay built in. These are pretty expensive though.

One idea deal is to use a second cheap charge controller to monitor the battery voltage and use its pre-set-able on/off controls to power a relay that will switch the incoming solar from the main charge controller to the grid tie inverter when the batteries are full.

Im thinking this should work mechanically tho whether it would interfere with the charging cycle I don’t know? Maybe set the relay to switch to grid tie at 28.8 volts battery level and switch back to charge controller when battery drops to 24 volts? Or something like that??

[SunEagle]

I think Morningstar makes an inverter that does this, take a look here:

https://www.morningstarcorp.com/retrofitting-grid-tied-solar-systems-backup-power/

Ampster: You may be thinking of the battery side of charge controllers. Many are capable of much higher PV Voc inputs, 150V is common and some as high as 600V. Outback and Morningstar for example.

I would say that Morningstar is a hybrid inverter that can be connected to both the grid and battery. I don't think the OP's equipment is designed for that operation.

[Ampster]

Ampster: You may be thinking of the battery side of charge controllers. Many are capable of much higher PV Voc inputs, 150V is common and some as high as 600V. Outback and Morningstar for example.

Yes, I am not as familiar with most standalone charge controllers. The one integrated in my hybrid inverter does operate at those voltages.

[sdold]

I think Morningstar makes an inverter that does this, take a look here:

https://www.morningstarcorp.com/retrofitting-grid-tied-solar-systems-backup-power/

Ampster: You may be thinking of the battery side of charge controllers. Many are capable of much higher PV Voc inputs, 150V is common and some as high as 600V. Outback and Morningstar for example.

[SunEagle]

What I should have said is can I have one of those small 1200 Watt grid tie inverters (micro-inverter) that run off 12 or 24 volts and have MPPT, looks like the inverter has MC4 plugs for a direct connection?

I was wondering if the supply from the panels could be paralleled into both the inverter then into my Epever charge controller.

As both units are MPPT controlled would they compete and interfere with each other but more importantly would the electricity from the panels go through the charge controller when the batteries need a charge, then go through the grid tie when that has a load demand or would the power get divided between the two depending what load is on each?

Maybe this just isn’t possible and I would need some switching gear to alternate between the two?

I think you will have to split the panels so some are connected to your MPPT CC and batteries and the rest are connected to the grid inverter. I just do not see a way to "parallel" the inverters to the same set of panels.

[littleharbor]

Output from a micro inverter is AC power, Your CC wants DC power.

[Tired sparky]

What I should have said is can I have one of those small 1200 Watt grid tie inverters (micro-inverter) that run off 12 or 24 volts and have MPPT, looks like the inverter has MC4 plugs for a direct connection?

I was wondering if the supply from the panels could be paralleled into both the inverter then into my Epever charge controller.

As both units are MPPT controlled would they compete and interfere with each other but more importantly would the electricity from the panels go through the charge controller when the batteries need a charge, then go through the grid tie when that has a load demand or would the power get divided between the two depending what load is on each?

Maybe this just isn’t possible and I would need some switching gear to alternate between the two?