Solar/Inverter Question...too much power!

[BobJones]

Hi Folks!

Sorry for yet another solar/inverter question. I got lots of responses in my other thread but am still trying to get my head around it. So now, a much more basic question...

Our two solar panels put out a LOT of power. It was my first solar install and I've seen it hit 48 amps with no issue. In fact, we cannot draw enough power because we do not have an inverter, so the solar system more/less idles along only providing about 10 amps for powering our DC fridge. Point being, we have something like 40 amps to spare that's not being used....

This brings me back to an inverter, which we do not have. Question, since we have upwards of 40 amps coming from the panels, if I installed a large inverter could we then use the solar to run AC etc?

We have 225 AH in batteries. To me, if the solar can put out +40 amps then should be not be able to draw a similar amount of power?

And with respect to the inverter, if we installed one, could we not replace the existing two-way transfer switch with a 3-way one, run the output of the inverter to that side of the transfer switch and then just power the entire AC side with solar using only devices which are appropriate for the output of the panels?

I'm just curious, and for sure, these are newby questions so I may be out to lunch. But when the batteries were low at one point I saw the array put out 48 amps with no problem. Our problem seems to be that we generate WAY more power than we are using, which seems to be a real waste to me.

[SLOweather]

I'd like more details, please...


What type solar panels (48 amps at what voltage (48 amps and 12 volt panels is 576 watts, 48 amps and 56 volt residential panels is 2,688 watts). What kind of charge controller (PWM or MPPT).


What kind of batteries (lead based or LiFePO).


What do you want to run on the inverter?



Adding an inverter takes a little more thought than just connecting everything to it and trying to manage the load yourself. If you have a propane/AC fridge set to auto, it will run off the inverter on AC and it's a big load. Similarly, you won't be able to run the roof air conditioner on it.

[BobJones]

Certainly!

There are two panels each at 41.1v they are wired in series so 82.2v although the Vitron app routinely shows them at 90v. 10.71 amps each panel.

The charge controller is MPPT (Victron 100/50) and the batteries are Trojan T105's.

The Victron app for the solar controller is what shows the 48 amps if the batteries are low enough.

Periodic use of the microwave for reheating would be nice but my thinking is, and perhaps I'm wrong, if the solar controller is able to put out just about 50 amps, as we've seen, then why couldn't we run one of the AC units on it as well? The DC fridge uses ~9 amps.

Point being, it seems we can generate way more power than we use, unless I am out to lunch (entirely possible!).

[Fffrank]

You're getting 40amps of 12v power/hr peak (or 4amps of 120v.)

That's not going to be enough to run anything of interest (and especially not the AC.)

Inverter will help you run things for short periods of time (coffee maker, microwave, etc) or that require small draws (TV, wifi-router, chargers, etc.)

[SLOweather]

OK, you have a similar system to what I installed in my Sunstar, except I don't have an ATS. I unplug the house cable from the generator outlet to plug into a pedestal.


2- 250 watt residential panels (56 volt) wired in parallel (better output if one is partially shaded), Renogy MPPT controller, 2 Battle Born 100AH batteries, and a Victron battery monitor.



And I also have an inverter, a 2kW Xantrex PWS inverter/charger.



First, a little perspective. Think of the solar panels putting out water instead of electricity. Think of the batteries as the water storage tank. You can use a lot of water for a while from the tank, and then the panels refill it.


By themselves, as Fffrank noted, the panels don't put out even enough to run the microwave. But the batteries do. So, you have the solar panels constantly keeping the batteries charged during the day, and replacing whatever you use in lights, computer, TV, M/V, as long as there is light.



When I did my installation, I did what you are sort of talking about. I disconnected all of the outlets in the coach except the one for the fridge from the coach breaker panel. I installed the inverter/charger and connected it to the A/C panel, the batteries, and to a breaker subpanel for the outlets. There is an ATS for AC in the inverter/charger that switches the outlet side from generator/pedestal to the inverter as needed, and a sort of another ATS that automatically charges the batteries when connected to shore or generator power.



It works so well, I hardly ever mess with it, except to shut off AC loads at night when dry camping. Last year, the inverter ran continuously for a 3 week trip keeping the microwave clock and a PC running through maybe 30 or so shore power transitions, running off the batteries whenever the engine was off, and the alternator when driving.



The charger side will put out an honest 100 amps on the generator or shore power, and the Battle Borns will accept a 1C charge rate, so I've seen the battery bank 100AH down in the morning, be completely recharged in an hour on the generator.

[Mark_K5LXP]

Point being, it seems we can generate way more power than we use, unless I am out to lunch (entirely possible!).

That is, until it clouds up or there's some other unforeseen or unanticipated load you need to run.

I see this controller has some user configurable load and sense conditions you can set up. Maybe come up with a passive load like a water heater element you can activate when your batteries are full and you have excess capacity. It doesn't amount to much power in terms of heating water and it's debatable you'd ever recoup the cost of the hardware in propane savings, but it's a way to always have your panels doing "something".

Mark B.
Albuquerque, NM

[Talloaks]

Originally Posted by BobJones

Hi Folks!

Sorry for yet another solar/inverter question. I got lots of responses in my other thread but am still trying to get my head around it. So now, a much more basic question...

Our two solar panels put out a LOT of power. It was my first solar install and I've seen it hit 48 amps with no issue. .

Bob...where are you measuring the 48 amps? It has to be on the 12 vdc side of your controller, i.e., your battery feed. At a nominal 13 volts, that computes to 624 watts. From your previous threads describing the design of your solar system, yo have 2- 440 watt residential panels that operate at approximately 41 volts and 11 amps output, which lines up with your 440 watt rating. Given you have 2 panels, total design output is 880 watts (you stated 900). You contemplated connecting them in parallel, which would give you about 22 amps at 41 volts (900 watts) but I believe you opted to connect in series, which would give you double the voltage but still limited to the 11 amp current. Again, about 900 watts capability.


As another poster mentioned, 900 watts is not enough to operate any 120 volt ac appliance over about 7 or 8 amps. Definitely not your A/C, probably not your refrigerator and almost certainly not your microwave. Compare this with your rig's so-called 50 amp shore power capability; that is 12,000 watts. Typical 8KW RV generator is (obviously) 8000 watts. All in comparison to your 900 watt (max) solar panels.


Remember you have many factors that can derate you to less than your 900 watt capacity, which is why you are seeing only 624 watts (based on your observed 48 amps @ 12 vdc). Also remember your production varies with time of day and weather (intensity of sunlight).


What I am saying is, you don't actually appear to have an exceptionally large amount of power, beyond what you are capable of using. Focus on the power being developed and used in your system, which is measured in watts, not amps, and it will be more clear to you and to those of us trying to help you on this forum.


Best of luck---

[SJ-Chris]

Originally Posted by Fffrank

You're getting 40amps of 12v power/hr peak (or 4amps of 120v.)

I think this is the main point you are missing Bob.


Here's another data point... If you have a 1200w microwave (120v) and you are powering it from your batteries through your inverter, it will draw approximately 100amps (12v) from your batteries. If your solar was generating 48amps going into your batteries while that is happening, then your solar will be providing about 1/2 of the power and the other half will be coming from your batteries.



Welcome to the wonderful world of solar! Glad to hear your system is up and running. 48amps (12v amps) going into your batteries sounds like it's working great. Congrats! Now go camping!


-Chris

[SJ-Chris]

Originally Posted by BobJones

The charge controller is MPPT (Victron 100/50) and the batteries are Trojan T105's.

Just curious...how many T105s do you have? 2 @ ~225AH? 4 @ ~450AH? More?


If you have 800-900w of solar, that should be more than enough to keep 4-6 T105s ~fully charged every day when you have sunshine.


If you are only using batteries for lights, propane fridge, water pump, TV/DVD/Computer, phone/tablet charging, and the furnace on a cold night, you are probably only using 50-75AH in a day. Your 800-900w of solar have the ability to produce about 200-250AH of 12v power every sunny day. Sounds like you do have plenty of extra sun power...a good problem to have.


Happy Camping!
Chris

[astrocamper]

One may have too much solar when the solar output exceeds the recommend charge current for your batteries. Easily fixed by added more batteries in parallel or going with LiFePO4 batteries which can handle larger charging and discharging currents.

Having more storage is a way to make use of excess solar. An inverter is a good way to use power that you have stored in your batteries. Useful for microwave, blender, toaster, water heater, etc...

I a larger system with 1440 watts on the roof and another 640 watts that help when we are running the air conditioner late in the day as the sun gets lower. When I don't need the air conditioner I also have more power than needed. I run my water heater on electric in those situations. I also replace my propane fridge with a 12 volt compressor fridge that keeps a steady temperature where it is hot or cool outside.

I have 700 amp hours of LiFePO4 batteries so I can go several days with little solar production if it is cool enough not to need air conditioning. If I am parked in a heavily tree covered area for several days I may use the portable panels to get some solar production.

[hclarkx]

You've probably heard enough .. but to summarize, that 40 amps at 12V is 480 Watts. An inverter drawing only that 480 Watts would produce about 408 Watts at its 120V output terminals (i.e., about 15% goes to heat .. losses .. in the inverter). So you would need about 3.5 times as much solar as you have to run a typical roof top A/C (up around 1400 Watts).

And if you had that 1400W from solar when the sun is high, and wanted to run the A/C into the late afternoon, you are talking considerably more battery energy storage.

For those that run A/C on solar, typically, morning solar is used to re-charge the batteries after the previous day's late afternoon and overnight use then in early afternoon when the batteries are full, the A/C goes on and works wholly from solar .... until 3 or 4 pm when solar wanes and the A/C needs to start making up for less solar by drawing from the battery.

Then there's the problem of lead acid batteries being quite inefficient so losing Watts in heat during charging and when feeling a high load like an A/C. I.e., needing more solar to cover the battery losses and more battery to cover the battery losses.

Most that run A/C have large banks of LiFePO4 batteries that can be drawn down to lower levels without much loss of life and that have almost no losses so store all of your solar and return all of that energy later. And thus need less solar.

Mini-split A/C units have been installed by some RV'ers. A mini split uses about half as many Watts as a typical roof-top A/C and are much more practical for use on solar and battery.

[sibe]

Inverter splits will draw 65-70% of what a RV AC draws.. start surge is a bit less,,
15K RV 1350-1450 watts,, 14K splits 1030-1240,, but many find a smaller like 10-12K split does a good job, now you are in that 800-900 watt range,,,

for poops,, but 480 watts at 12vdc going into an Inverter will give that 400ish watts at 120,, 40A in maybe 4 amps out..

1440 wattS AT 12V... 120AMPS... you gonna need some HD wiring..

Many have run AC on solar as mentioned... not for me... if i was..
I mapped my roof and with being careful I can get 8 large panels running 150 watts at 31-34 volt each.. So in theory on a perfect day with a nice big bank of batteries,, I can use AC and still store,,, right...?? 2000 watts should be close... still not enough for 24 hr AC... Run AC , 8 hours,, 4000 watts stored,, maybe 3 more hour ????

random thoughts....

[TravelSolo]

Unless it's really hot the A/C isn't going to run constantly. You need to get some typical run times per hour and then factor that into your calcs.

Admittedly I have small trailer and smaller solar setup compared too yours but I can run my A/C off my batteries for about 3.5-4 hours with no other input from solar, the DC-DC or genset. At 50% "duty cycle" that's 8 hours or having my A/C. Add solar at 25-28 amps during the day it adds about two hours of run time

[hclarkx]

Originally Posted by Mark_K5LXP

That is, until it clouds up or there's some other unforeseen or unanticipated load you need to run.

I see this controller has some user configurable load and sense conditions you can set up. Maybe come up with a passive load like a water heater element you can activate when your batteries are full and you have excess capacity. It doesn't amount to much power in terms of heating water and it's debatable you'd ever recoup the cost of the hardware in propane savings, but it's a way to always have your panels doing "something".

Mark B.
Albuquerque, NM

I have this same frustration. My RV sits at home all summer in one of the sunniest places on earth. Additionally my RV roof slopes to the south so gets near optimum solar energy through the summer. And it's all going to waste.

I've thought about using a line commutated inverter to put the excess into my side of the power company meter, but I already have more solar on my house than I can use, and I don't do illegal stuff like that anyway.

I've thought about installing some rock polishers that have to run for months, but I'm not into polished rocks or jewelry. I don't have a well. My pool does not need heating this time of the year. My son has used his RV solar to do bitcoin mining, but I'm not into that either.

Any suggestions?