How much current from a "200" watt panel. Is mine fake?

unexpected · July 2019

Wanted some backup power for emergencies and to familiarize with solar.

Got this mono panel:https://www.ebay.com/itm/143284917312

Max Operating Voltage (Vmpp): 21.01Volts Max Operating Current (Imp): 9.52Amps Open Circuit Voltage (Voc): 24.29Volts Short Circuit Current (Isc): 9.89 Amps

Also an Epever 30A MPPT. Small 40AH gel battery. I'm a cheapo.

Still waiting on a dongle to connect to the EPever but looking at the screen I'm not getting IMP.
Have I been ripped? Or was I just too optimistic.

The panel is on the balcony facing directly west. Don't really a choice on direction but I can vary the tilt. I'm shaded until like noon and the sun comes over the roof. Hooked up a fan to my cheapie inverter so that I can max current.

At 1deg I get up to 5A on the LCD of the controller from like 1-4. Later in the afternoon I tilted to something like 50 degrees and saw at most 6.8-7A. This doesn't seem to translate to 200 watts, more like 150 at best and I think the MPPT lowers the volts of the panel too so even less.

So mainly 2 questions here. Is there something up with the panel or the system? EG, over rated, made a bad design? And how should I tilt to get the maximum power? More flat like all the calculators say, or more vertical like I seem to have deduced. I know it will change in the winter. Will test a bit during the prime sun hours tomorrow but since people here seem very knowledgeable (much more than me) I'd like your opinions.

Its not all bad, I mean I can charge batteries run a laptop and a bunch of stuff really. Just wonder if I should have looked harder for a surplus 48v panel or just gotten 2x100watts, etc.

Raj174 · July 2019

@unexpected
From the information you have posted, the panel and charge controller appear to be working fine. The 200 watt rating comes from perfect conditions in a lab. In normal everyday use it may be 20 to 30% less. The panel IMP is 9.52 and your best measured output was 7 amps. That's 73% of the rated output. My own 3600 watt array averages about the same.

The panel needs to be directly facing the sun to get the highest output. Any deviation in vertical or horizontal angle will reduce power. If you have sun from 1 PM to 5 PM and the panel is facing directly west, then a 40 to 45 degree angle would be a good place to start experimenting for best output. Also, check the battery specs for maximum charge amps. A true 40AH gel battery may not like 7 amps, however an AGM battery would be fine with it

Rick

Photowhit · July 2019

You have a lot of things going on, If you truely have a 'Gel' battery they usually can't accept more than 5-10% or 4 amps...
...might want to see if you actually have an AGM battery, some of them can accept 30% of capacity.

The panel is likely in the ball park. Solar panels have a name plate rating. these ratings are based on Standard Test Conditions (STC). In the real world they will produce less. Some now come with Normal Operating Cell Temperature values (NOCT) They are generally about 75% of the name plate.

These means you can expect about 75 watts out of a 100 watt panel. This is what you can expect when the panels are warm/hot. You may approach Standard Test Conditions(STC), in very cold fall days with good direct sun, but it will be rare.

Some manufacturers publish their NOCT values, here are a couple examples, but you can figure around 75%;

Image: https://us.v-cdn.net/6024911/uploads/editor/yk/6m7g1sjvdb70.jpg

unexpected · July 2019

I'll ask the seller for more specs like NOCT/STC. Maybe they have a datasheet because there is no other information on this panel anywhere. Will also see how hot the panel gets with IR. I see people getting 5A out of 100 watts and keep thinking why did I buy 200 if that's the case.

It is a true gel. Deka 8G40. It took all of 8 amps (boost) from the MPPT. In all honesty I think I need to upgrade as the 40ah is not enough with a usable 20ah to 50% SOC. I've been hunting for used lithium or some GC2 batteries. Too much AH and I know it will take multiple days to charge or never make it. This was just the best deal at the time and the seller lied saying it was 50AH AGM.

Batteries are really expensive and no deals near me here at 41N. I know some lucky folks out west are getting 230-300watt panels for $100 and plenty of used solar stuff.

BB. · July 2019

Remember that power is P=V*I

A typical 100 Watt panel is ~17.5 Volts Vmp, and your panel is Vmp~35.77 volts

So, in this case, 2x operating voltage = 2x power at the "same current"...

When running solar charge controllers and batteries (and whatever DC loads you may have), it is a bit less clear about where your limitations are... The solar charge controller is modulating battery voltage/charging current and the battery itself changing current based on state of charge, charging voltage, temperature, etc. So the solar panel may have more power than the charge controller+battery bank have decided to "take" when you took the readings.

Add your location and variable weather conditions... It is really surprising how this all affects your solar harvest. I have a GT system which (in theory) always harvests 100% of available panel energy. I look outside and everything seems bright and sunny, go look at the inverter and I am getting 50% of harvest... Go outside and look at the sky and see some very light haze--Enough to block 50% of the sun's energy and not even noticeable by eye.

Other issues like pointing the panel directly at the sun... It is a cosine function... Cosine 0 degrees = 1.00 (100% of suns energy harvested).

Cosine 60 degrees off angle from sun = 0.5 (50% of solar energy harvested).

In general, if your harvest is >50% of nameplate, your system is probably working OK (with ~75-77% of nameplate typical "best" harvest around noontime on cool days).

-Bill

Estragon · July 2019

If there's no NOCT voltage, there may be a temperature coefficient you use to adjust from STC (25°C).

littleharbor2 · July 2019

Are we talking another panel than mentioned in the op?

"Max Operating Voltage (Vmpp): 21.01Volts Max Operating Current (Imp): 9.52Amps Open Circuit Voltage (Voc): 24.29Volts Short Circuit Current (Isc): 9.89 Amps"

BB. said:

A typical 100 Watt panel is ~17.5 Volts Vmp, and your panel is Vmp~35.77 volts

-Bill

BB. · July 2019

I thought there was a question about a 300 Watt panel in comparison.

Bill

unexpected · July 2019

Image: https://us.v-cdn.net/6024911/uploads/editor/pn/yfjk5nxqpdbg.png

Thats at 1degree (almost flat) straight west at 230pm CST.

Image: https://us.v-cdn.net/6024911/uploads/editor/q7/qqhzq6cwobxw.png

Then I moved the panel to ~25 degrees, around the same time and I get a little more current. I know when I tested late the output was a bit higher when I tilted up.

All the guides/calculators were telling me 1 degree and that I'm going to generate $25 of electricity this year

I wish I had a 300w panel. I have the money but not the room. This is a far cry from the 200 watts promised though. I do notice that the back of my panel is 142F taking an IR measurement. It has airflow on both sides so I'd shudder at what a roof mounted one would be.

Estragon · July 2019

There's the tilt, but also north-south angle to consider. Depending on latitude, optimum for both could vary a lot seasonally.

Pointing straight west, power would be near nil at solar noon, as the panel would be at near 180° to the sun on the N/S axis. That angle would get better later in the afternoon, but as it does, the angle of the sun through air in the vertical axis gets worse (reducing insolation available, especially in hazy/smokey/dusty air).

BB. · July 2019

You can play with a couple different solar calculators... Point West and adjust the tilt to see which angle gives you the best harvest per day... (by month/season):

http://solarelectricityhandbook.com/solar-irradiance.html
https://pvwatts.nrel.gov

-Bill

Raj174 · July 2019

Technically, MPPT charge controllers need the PV input voltage to be 1.3 times the battery charging voltage to work properly, and you would think 21 volts would be enough, but PV input is falling to 16.8V and that's no enough for the controller to down convert the higher voltage into increased current. Could be that the panel is too hot. As proposed, two 100 watt panels in series would work much better.

unexpected · July 2019

I used this to find "optimal" degree: https://re.jrc.ec.europa.eu/pvg_tools/en/tools.html

Maybe it would be optimal if there was no buildings blocking from the other directions.

I'd have to run a 4A load all day or something and see what collected the most watts (1 deg or 25deg).

Also confused as to why the panel isn't in float by now, does it never float if there is a load?

:

Estragon · July 2019

The panel doesn't float. The battery will float if/when the controller thinks it's full. The panels will supply current for the combination of loads and battery charging/floating to the extent it can. To the extent it can't, any aditional current drawn by loads will generally be supplied by discharging the battery.

With no load, the pv will "float" in the sense it will only supply as much current as needed to float the battery.

Wheelman55 · July 2019

Unexpected. Your panels are likely rated at STC (Standard Test Conditions”. Here’s an explanation:

PV manufacturers use Standard Test Conditions, or STC, to rate their PV products. STC are 1,000 Watts per square meter solar irradiance, 25 degrees C cell temperature, air mass equal to 1.5, and ASTM G173-03 standard spectrum.

The conditions on your westward facing balcony are likely less optimal than STC. You can buy a solar irradiance meter to check how many watts the sun is kicking out on your balcony if you are curious.

Photowhit · July 2019

unexpected said:

It took all of 8 amps (boost) from the MPPT.

Be careful, Looks like you are searching for cheap options. In other countries "Boost" refers to an equalizing charge and should NOT be used with Sealed batteries.

In general "Boost" is not a term in common use in the US.

unexpected · July 2019

I'm talking about charging state. It goes bulk (high amps), boost (higher V, like 14.2 lower current), float (13.8v, almost no current) at least according to EPever manual. Equalize is its own thing and I have it turned off. I took their gel profile and raised the cutoff voltage to 12.2 volts so I could hit 50% soc.

I did see float eventually but at small loads .3-.5a it causes the battery to lose some charge even though the panel could technically be putting out high enough current to cover it. Everything is hooked to load so I don't know why this is a thing.

littleharbor2 · July 2019

I started to question your graphs yesterday , then deleted my post. Now with your last comment on "everything is hooked to load" I need to ask. Is your entire load connected to your charge controller load terminals? One of your earlier graphs shows 120 watts in from PV and a load of 120 watts. The load terminals on charge controllers are not really intended for powering much more than a lighting circuit, which is why they have all the on and off options. Your loads need to be connected directly to the battery. If you need to monitor your load this can be done with a shunt based battery monitor.

unexpected · July 2019

Yes, its going through the charge controller. It has a 30A load capability and the system is well below that.

littleharbor2 · July 2019

unexpected said:

Yes, its going through the charge controller. It has a 30A load capability and the system is well below that.

Regardless if your loads are less than the max allowable limit that is not what the load terminals are intended for. If your combined loads are all running and for whatever reason a surge pulls down the battery voltage momentarily the low voltage disconnect may shut down the output. While that is what it should do, some of your devices may not like being shut down and may need to be manually restarted. Do what you like here, this isn't any kind of large highly dangerous system, just bear in mind that you should be running your multiple loads from the battery, not the load output terminals.

unexpected · July 2019

True, well aware of that. I actually call the shutting down a feature so I don't over discharge the battery. I have a separate low voltage disconnect but its only 20A rated. That load was also run specifically to stress. Most of the things I actually want to run don't pull over 3A tops. I couldn't even get over that until I got the inverter and plugged in nono things like the fan. With the panel I have nothing over 7A is really worth running anyway except for a short amount of time.

littleharbor2 · July 2019

The one thing you definitely DON'T want connected is an inverter. What is the problem with connecting directly to the battery?

unexpected · July 2019

Lack of low voltage disconnect. Kinda not getting it here. The load terminal is rated for 30A. My load is 20 amps short of the rating. There is also a fuse inside. Electrically this all makes sense and its not just some "30A" rated ebay PWM.

Photowhit · July 2019

unexpected said:

Lack of low voltage disconnect. Kinda not getting it here. The load terminal is rated for 30A. My load is 20 amps short of the rating. There is also a fuse inside. Electrically this all makes sense and its not just some "30A" rated ebay PWM.

If it was a top name charge controller, they would tell you specifically NOT to connect an inverter!

In fact In the Epever manual they say specifically;

"CAUTION: If an inverter is to be connected to the system, connect the inverter directly to the battery, not to the load side of the controller. "

They also provide this handy diagram;

Image: https://us.v-cdn.net/6024911/uploads/editor/dj/54wwmcm014qj.jpg

Page 12
Link to manual;
https://www.epsolarpv.com/upload/cert/file/1811/Tracer-AN-SMS-EL-V1.0.pdf

unexpected · July 2019

Sure I get that. A large inverter would overwhelm the load port. And one could use a 30A tracer to charge a large (ish) bank of batteries that would support such an inverter. In that case you would definitely want to hook it directly to the battery. Failure to do so would pop the fuse or trip the overload protection. In my case, not sure how I would do that if I wanted to. I have a PC that can draw 8 amps and the fan at 10 so at best I would be pulling 18. If I plugged in a power strip I could probably get there but I'm not planning on it any time soon, much less with this tiny 40ah. Inverter itself is 40A fused so it probably tops somewhere around there -5?

So in my case the risk of battery drain is greater than overloading the port at the current juncture. Besides hearsay, what is the electrical reason to not use the advertised capacity of the port?

unexpected · July 2019

Heh, as far as trusting manufacturers. The gel profile in the epever looks to cause overcharge at least according to specs from the battery maker:

http://language.mkbattery.com/images/GELBatteryCharging.pdf

This is what I changed it to from that PDF:

BatType: 0
BatCap: 40
TempComp: -3
OVCutOff: 14.30
ChargLmt: 14.10
OVRcv: 14.10
EquilV: 14.10
RaisV: 14.10
FloCharg: 13.50
RaisRcv: 13.20
LVRcv: 12.60
WarnRcv: 12.30
LVWarn: 12.20
LVCutOff: 12.20
DischaLmt: 12.00
RatedLv: 0
EquilDur: 0
RaisDur: 120
BatDisch: 30
BatCharg: 100
ChargMode: 0

Estragon · July 2019

Doesn't really matter in your case, as the loads are well under the load terminal limit, but to use the controller LVD or other load control features on larger loads, you'd just use the load terminals to control a relay which would switch battery power to the load on/off.

Photowhit · July 2019

unexpected said:

Sure I get that. A large inverter would ...

I missed where they say anything about a large anything...
I tried, good luck.

littleharbor2 · July 2019

Photowhit said:

unexpected said:

Sure I get that. A large inverter would ...

I missed where they say anything about a large anything...
I tried, good luck.

When it comes to a 12 volt system and a 30 amp max loads terminal there really isn't a "small" inverter.

We have all tried.

mike_s · July 2019

littleharbor2 said:

When it comes to a 12 volt system and a 30 amp max loads terminal there really isn't a "small" inverter.

Sure there is. I run everything in my camper through the controller 40 A load terminals (except the power jack and brakes), to ensure the batteries can't be over-discharged while in unattended storage. Also because my controller will track energy usage through the terminals, so I have a better feel for SoC than just monitoring the voltage. I also occasionally use a small (rated 300 W, but have never used more than 100) inverter for things like a laptop. Works perfectly fine, and well within the capacity of the controller.

It's not clear why you're being so critical of @unexpected. He's using the load terminals appropriately, has shown he understands his needs and the limitations better than you, and the system is clearly working for him.

Photowhit · July 2019

mike_s said:

It's not clear why you're being so critical of @unexpected. He's using the load terminals appropriately, has shown he understands his needs and the limitations better than you, and the system is clearly working for him.

So another person who can't read?

The Frickin' manual says NOT to...
NO he is NOT using the load terminals "appropriately".

How much current from a "200" watt panel. Is mine fake?

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