Solar help

Lomes · Member

Solar help

Plendo · Guru

Hi Lomes, if I am interpreting the information you posted correctly, you will be generating up to a theoretical 21amps at 24 from your solar panels (2*250 = 500W/24V = 21A), thus on that side of your controller you have the capacity for two more panels.

However you appear to be running your batteries at 12V (4 batteries in parallel), thus the current on that side of the controller is going to be roughly double the current on the input side, so you will be seeing a theoretical 42 amps on the battery side of the controller, thus your controller is maxed out.

There are a number of things that can be done to increase the amount of power you store, but first I would be trying to understand which of the limiting factors is restricting your storage. As in are your batteries full part way through the afternoon, or are they just at 70% at the end of the day. The answer to this would indicate where you should focus your efforts.

In theory you should be able to store about 147 amp hours at 12V.

It is hard to gauge how much power a fridge will draw, because they do not run all the time, it depends how good the insulation is, how many times the door is opened, outside temperature etc. However based on the 110w rating, it should draw about 0.5A at 240V, thus about 11A from your battery when running through the inverter. Thus if it was running 24 hours a day it would be using (24 * 11) 264 amp hours, however fridges stop and start, thus their typical usage is much less maybe 30% so maybe 90 amp hours.

Given you are running your fridge through an inverter, you will have a load to keep your inverter running. This is part of the specs on the inverter, and may be around 1.5A, this is already allowed for while the fridge is running, thus you need to allow for this on the other 70% of the time when the fridge is not running so maybe 25 amp hours.

As you can see from the above I have made a lot of assumptions, but I hope it at least gives you some clues where to look.

Jaahn · Guru

Hi Lomes,

Plendo has given a good considered reply covering most of it so I will not repeat that. biggrin

Why do you want more ? Are you having problems or just the odd dull days ? Had a few here recently for sure. confuse

The MPPT regulator is close to maxed out and could certainly not handle a third similar panel. The output current from the regulator is the spec to watch for with MPPT. In your setup an extra odd sized panel will not work too well. hmm

If you are having problems I would be checking the power(current) draw of the inverter over the day when running the fridge and when not, that is when it is doing nothing. Also the other stuff you have too. Then see what is really happening. Install a meter at the battery to monitor things. Also check the wiring to the inverter is heavy and not loosing the power by resistance losses.

Jaahn

Friar Park · Senior Member

Plendo, thanks for that reply. It wasn't my topic but I was interested in the likely replies. Yours was very clear. I'm as thick as two short planks on electrical stuff but I'm sure I followed your explaination easily enough.

Good onya

Friar

Plendo · Guru

Thanks Friar,

re reading the post it dawned on me that Lomas may just be in the building phase, in which case he may consider changing his battery setup from 12V to 24V, in this case the MPPT controller would then be able to handle another couple of panels without any problems.

There are so many things that could be done, it just needs some more information.

PeterD · Guru

Plendo, I think you should start your calculations afresh. The MPPV of 24 V panels is around 34 V (12 v panels are around 17 V.) 500 / 34 = 14.7 A.....

Lomes, I think this will give give you some idea of how your domestic fridge will work - Fridge comparison - The article refers to the fact that the article may be dated because of fridge improvements. However these improvements will apply to the 12 V fridges as well as the domestic ones.

Lomes · Member

Thx everyone for the great answers my system is very simple . Today I have taken some readings at different times.
At 1 pm soc 79% 13.7v putting 19amps into the batteries
3 pm. 83% 13.6v. 14amps
5.30 pm. 54% 12.8v not charging
6.30pm is one hour after dark soc 50% batteries 12.6v
Now I seen a chart which tells me that at 12.6v is around 80% soc
My moniter came with my 40amp mppt from epsolar so my be it's not right .
Now if I was to wire my batteries as 24v I would need to then convert it back to 12 volts to run the inverta and 12 v appliances.
So I'm thinking would I be better with another 250watt panel up with another controller and run this to the batteries as well and would it better to use a 12v panel instead of 24v panel. And would this give me extra charge to get to 100% soc.

Plendo · Guru

Thanks Peter, did consider the Max power point voltage, but decided to stay away from introducing the extra confusions. If you redo the calcs with the higher panel voltage, it just reduces the current from the panels, and that is not the problem, thus it is easier for teh layman to understand the calculation with nominal voltages.

At nominal voltage the 500 watts produces 21 amps (20.83 actually).

At Max power voltage, likely to be 34.8V, the same 500 watts will produce 14.4 amps. As you can see it is immaterial when talking about a 40 amp controller.

The same thing is true on the other side of the charger, where the charger will be charging anywhere between 11.5 and 14.3 volts, and on this side the current is a problem because the same 500 watts will produce anywhere between 35 and 43.5 amps. While theoretically over the capacity of the charger, how often would you see a solar array running at 100% (never).

Hence the reason I tried to keep it simple, and stay with nominal and rated numbers.

Sorry it was a deliberate decision to keep it simple, and understandable.

Plendo · Guru

Hi Lomes, thanks for the extra numbers. It looks to me as if you have the following setup:

2 panels connected to a 40A Tracer from Ep Solar, with a display panel attached probably an MT5 (or maybe 50).

I suspect your inverter is connected directly to your battery, NOT through your Tracer MPPT controller, thus the controller does not know about the load being taken out of the battery by the inverter.

If I am correct, it is likely that the charger is getting confused, and it may even be thinking the battery is full, and turning off the charge while the battery is only partially charged.

Most this type of charge controller have logic built into them to track how full the battery is, and to reduce the charge to a trickle either when the battery reaches a certain voltage OR when its own tracking says the battery is approaching full.

Some keep a running total, which they reset when the battery has been full for a period of time (usually programmable), some of them reset on first light based on battery voltage (rare now). From that point onwards the controller tracks how much current goes in to the battery, and also how much current is taken out of the battery to track the state of charge (SOC). I believe your SOC is getting confused, and I suspect it is because the controller does not know about the current being taken from the battery.

Why do I think it is confused?

Note that the voltage drops from 1pm to 3pm readings, yet the SOC rises.

Lomes · Member

Thx Plendo for all your input to my questions
You are right my inverta is wired directly to my batteries . I have the controller set for charging 420ah of Gel batteries
The batteries being charged are 4x105ah AGM batteries .
The controller is Epsolar Tracer 4210rn with the mt5 remote display I have read the manual many times so I hope I have it set up wright

Plendo · Guru

Thanks Lomes,

I have a similar setup, with 1,200 Watts of panels feeding through a 50A MPPT into 200Ah of Lithium battery at 24V, My 3,000w inverter is also direct connected to the battery.

When I set mine up I was in touch with a group who were very knowledgable in the management of Lithium batteries, and that helped me a lot. Even with the help it took me a while to get my head around the whole thing, and to get it working the way I knew it should work.

I now no longer us the SOC tracking built in to the charger, but have fitted a separate battery monitor a BMX 600 from Victron, and it works and stays accurate.

I decided to go with 24V to overcome the problem you are facing now, it allows me to put 1,200w of solar through a 50A charger, it also reduces the amps going to the inverter which is a 24V inverter. Everything else in the van is still 12V, running from the standard house battery which is charged by a 24V to 12V charger capable of providing 40a at 12V.

So the 12V system runs the 230l compressor fridge (about 90ah per day in summer), lights, pumps, TV, radio, laptops, etc. The inverter is turned on for the aircon, microwave, coffee machine, washing machine, hair dryer, and induction cooker.

It is rare for our battery to go below 70% SOC, but it does occasionally, but I have never seen it below 40%. We can do things like run our air conditioner for five hours after the sun goes down.

Now back to your system, given the numbers you provided I believe you probably have enough battery, and are probably limited by the amount of power you are getting into the batteries. It would be possible to add a second charge system in parallel, BUT MPPT chargers do not play very well together, they tend to confuse each other, they will still charge, but not as efficiently as they do individually.

Given your dependence on electricity (electric fridge), I would explore moving your system to 24V. It would mean buying a new inverter, and probably a 24v to 12V converter to feed the rest of the system. Worth a thought.

Jaahn · Guru

Hi

Plendo is going well on the replys. wink However he answered while I was typing.

My thoughts for consideration,

Set the controller to sealed battery type not gel. This gives a small increase in the set voltage(0.2)and a boost phase too.

The inverter has to be wired direct to the battery as it draws too much current to come through the controller. That is always a design glitch that seems to be universal !!

The controller is confused if there are other currents that it does not see. However it really only affects what it shows as the state of charge. The set point voltages are the same and it charges the same no matter.

The current from the controller from the panels seems low but we do not know what the solar input was or how the panels face the sun either. With your 500w panels you should be doing more than "At 1 pm soc 79% 13.7v putting 19amps into the batteries" IMHO. MPPT systems are sensitive to wiring losses despite what some say. They need proper size wires to work properly.

Cheers Jaahn

-- Edited by Jaahn on Wednesday 20th of May 2015 09:02:46 AM