How to utilize Excess Energy in a system with PWM charge controller

sanat · October 2019

Hi,

I am newly joined this forum and I like the depth of Technical discussions happening over here.

I am planning for a small Off Grid rooftop system, with panel 325Wp X 2 (parallel connection), 150AH X 2 Batteries with a 2200VA solar Hybrid Inverter (24V format) with the in-built PWM charge controller. The Solar charge controller has specification of 24V x 30A . The Panels has max Voltage 37.8V with max current of 8.6A. So during peak hours, I may get maximum 17A current with Avg voltage of 26 V depending on battery charging stage. That leaves with me around 200Watts of unutilized power while battery is being charged.

Can you plz suggest what are the possible ways to tap and utilize this power? I have read about water heater using excess energy. Are there any other possibilities?

Even if any ready-made solution is out there, what do I need to know so as to be able to use it alongside the afore mentioned Solar Inverter?

(Grid Tie is not the option here, it's only Off Grid system)

Thanks,

Sanat.

mvas · October 2019

Pump water from your well into a gravity tank

mike95490 · October 2019

How will your charge controller alert you when there are unused watts sitting around ?

Photowhit · October 2019

I think you don't understand how battery charging works.

The charge controller maintains a voltage above the batteries natural state of charge to allow flow into the battery. with lead acid batteries, this is about 10-15% higher. In addition, you should look for the NOCT values of your solar panels, the actual voltage will be lower than the posted VMP once the panels are warm/hot.

If the 'maximum voltage' represents VOC and it's 37.8 volts, your panels may be 60 cell panels and not create enough VMP (voltage under load) to charge a 24 volt system.

Either way, any extra voltage, above the charging point is just lost with PWM charge controllers. If you want to recover it you need to invest in a MPPT type charge controller.

What I thought you were referring to when you stated 'Excess energy' was once your batteries are charged or nearing fully charged. If you want you can start a load with a timer on sunny days. I did this often when I was using a PWM system and really still do, not taking full advantage of the capabilities of my MPPT charge controller's ability to start loads.

sanat · October 2019

Thanks all for your comments. I like the idea of the utilizing the power for water pumping and the time triggered loads.

Photowhit,

I don't have the NOCT values which I will post once I have it. The voltage(37.8V)/current(8.6A) I had mentioned was VMP and IMP values at STC. The VOC and ISC values are 46.6V and 9.2A. I also confirmed from the SPEC that it is 72 cell panel.

If all the extra energy gets lost during PWM operation, then there is no way to TAP the excess energy. I had raised this point since I was under the assumption (rather a wild guess only) that probably I could add an extra device/load in series (with the Charge Controller input points in the Inverter) so as to utilize the left over Energy. I guess I need to go deep technically in order to think of something like this.

If someone can help technically on how the PWM system works and if there is a feasibility of capturing the excess in-Utilized Energy, then probably something can be thought of.

Of course this can be when PWM is in operation so as to utilize the Excess ones and also when PWM is in passive mode when Battery is fully charged or nearly full so that the complete Solar Panel power can be utilized.

You mentioned of Timer controlled loads on Sunny days. Could you please elaborate where did you get it connected? You had a separate Charge controller which disconnect from the Battery and connect to load, or just directly connect the Solar Panel output to the load or something else. Appreciate if you could share the high level schematic.

sanat · October 2019

mike95490 said:

How will your charge controller alert you when there are unused watts sitting around ?

Well, I am under the assumption that we can have some load that takes the variable DC input and I also assume that after whatever the Power that is used by PWM charger, the rest Excess can be picked up by a system that is connected in series. I did some Google but yet to come across anything to validate if my assumption is wrong or right. I am just using the a crude assumption that when loads are connected in series, the current remains the same in the circuit whereas Total Power (Wattage) get distributed amongst the loads in series with the Priority going to the first Load connected from Positive side terminal.

mike95490 · October 2019

sanat said:

Well, I am under the assumption that we can have some load that takes the variable DC input and I also assume that after whatever the Power that is used by PWM charger, the rest Excess can be picked up by a system that is connected in series. I did some Google but yet to come across anything to validate if my assumption is wrong or right. I am just using the a crude assumption that when loads are connected in series, the current remains the same in the circuit whereas Total Power (Wattage) get distributed amongst the loads in series with the Priority going to the first Load connected from Positive side terminal.

I'm an electronics engineer and I have no idea what you said. So I suspect it's not going to work.

But I'll try to parse it out:

> Well, I am under the assumption that we can have some load that takes the variable DC input

What is the variable DC input ? Are you thinking of the PV output ? That's a pretty stable voltage, with varying current (amps) according to the light intensity. You speak of "some load" but you need to be specific, what load ?

> and I also assume that after whatever the Power that is used by PWM charger, the rest Excess can be picked up by a system that is connected in series.

OK, if you know what that means. Where do you get the "system connected in series" ?

> I did some Google but yet to come across anything to validate if my assumption is wrong or right. I am just using the a crude assumption that when loads are connected in series, the current remains the same in the circuit whereas Total Power (Wattage) get distributed amongst the loads in series with the Priority going to the first Load connected from Positive side terminal.

Wrong. Loads are always connected in parallel. examples: Lights in a house. lights in a car, garage door openers, outlets in a house

How to utilize Excess Energy in a system with PWM charge controller

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