DIY Solar Power System: Questions & Answers

Hello, I've been building my own solar panel system and throughout this process I've accumulated a lot of questions. If anyone could help answer them I would greatly appreciate it!

First I'll start off explaining what I have.
A polycrystalline solar panel 17V 2.2A and a mono crystalline panel 4.8V 4A (read by multimeter) I connect them in parallel to produce 16.8V 6.2A. Each of them have a "6A axial type" diode connecting the positive line and the solar cells.(I read that you use them to stop power from returning into the solar panels)
I've connected them to a Shunt (which reads 12.9V 1.96A coming from the solar panels) and charge controller using a little less than 50 Ft of 10 gauge stranded copper wires. The charge controller is connected to a 12V 35ah battery that's connected in parallel to a 12V 7ah battery. I have an inverter that I connect to the load of the charge controller. I use that to power lights or charge cell phones. So that's my basic setup. As for my questions, I apologize if they seem a bit random and the large amount of questions I have.

-Why is the shunt displaying 12.9V 1.96A if my multimeter is reading 16.8V 6.2A?

-I bought 10 monocrystalline solar cells (4.8w) and connected them using adhesive copper tape but they produce less than my (2.8w) mono solar panel I built. I had soldered the solar panels up until I discovered copper tape. So does copper tape hold less lots and amps?

-When I tried to connect my 4.8 W monocrystalline solar panel to my regular setup in parallel, it seemed like it actually took away from the power everything was producing, I don't know why.

-Are these diodes actually needed if I have a charge controller?
-Are they just taking away from the power the solar panels produce?

-I decided I wanted to try powering small devices somehow and I found DC to DC converters. But I have no idea how to control the volts and amps enough so that it won't damage the electronics. I'm trying to power things like a peltier and a small fan. Can anyone help me understand how I can use the power I get to power these electronics?

That's all I'll ask for now... it would be easier if I could upload pictures from my iPad or phone but I couldn't figure out how. I apologize in advance for any information I am missing and thank you for reading all of it.

A schematic would be helpful. Connecting the solar panels with different voltages in parallel as you have makes no sense. If it weren't for the diodes the higher voltage cell would simply feed into the lower. With the diodes, only the higher voltage cell is sourcing any current. How did you arrive at 16.8 volts?

Averagesupernova said:

A schematic would be helpful. Connecting the solar panels with different voltages in parallel as you have makes no sense. If it weren't for the diodes the higher voltage cell would simply feed into the lower. With the diodes, only the higher voltage cell is sourcing any current. How did you arrive at 6.2 volts?

I suppose that would help, I've never made a schematic before but I will try to make one and upload it.
Thank you

Brandon91man said:

-Why is the shunt displaying 12.9V 1.96A if my multimeter is reading 16.8V 6.2A?

because the open circuit voltage of the panels is always higher than when loaded

Brandon91man said:

-I bought 10 monocrystalline solar cells (4.8w) and connected them using adhesive copper tape but they produce less than my (2.8w) mono solar panel I built. I had soldered the solar panels up until I discovered copper tape. So does copper tape hold less lots and amps?

without knowing the details of how you hooked them up ... who knows ?

Brandon91man said:

-Are these diodes actually needed if I have a charge controller?

only if there are separate inputs to the controller

Brandon91man said:

-Are they just taking away from the power the solar panels produce?

well there will be around a 0.7V drop across each diode

I have to repeat what Averagesupernova said ...

Averagesupernova said:

Connecting the solar panels with different voltages in parallel as you have makes no sense.

you SHOULD NOT be connecting different value voltage sources togetherDave

Averagesupernova said:

A schematic would be helpful. Connecting the solar panels with different voltages in parallel as you have makes no sense. If it weren't for the diodes the higher voltage cell would simply feed into the lower. With the diodes, only the higher voltage cell is sourcing any current. How did you arrive at 16.8 volts?[/QU

davenn said:

because the open circuit voltage of the panels is always higher then when loaded
without knowing the details of how you hooked them up ... who knows ?
only if there are separate inputs to the controller

well there will be around a 0.7V drop across each diode

I have to repeat what Averagesupernova said ...
you SHOULD NOT be connecting different value voltage sourcesDave

Thank you for replying, the monocrystaline solar panels connected with copper tape are connected in series.

Why should I not connect the solar panels like I have them? It doesn't seem like they are being damaged but I am curious as to why you say that.
Also I am working on completing that schematic to give a clear understanding of my setup.

Brandon91man said:

Why should I not connect the solar panels like I have them? It doesn't seem like they are being damaged but I am curious as to why you say that.

it doesn't matter if it is solar panels, batteries or other type of power sources ... you don't connect ones that are not the same voltage

Brandon91man said:

Why should I not connect the solar panels like I have them? It doesn't seem like they are being damaged but I am curious as to why you say that.

If you use diodes to prevent reverse current going into the panels, it will be safe, but the 4.8V solar panel can only produce current if the overall output is 4.8V or lower, so you have to use a low resistance load to get this panel to contribute. At this output voltage, most of the power that the 17.2 V panel produces is thrown away.

willem2 said:

If you use diodes to prevent reverse current going into the panels, it will be safe, but the 4.8V solar panel can only produce current if the overall output is 4.8V or lower, so you have to use a low resistance load to get this panel to contribute. At this output voltage, most of the power that the 17.2 V panel produces is thrown away.

I don't quite understand, it seems as though the (17V 2.2A) panel is unaffected and the (4.8V 4A) panel is just contributing amperage. They're feeding into a charge controller that's feeding into a deep cycle battery. Is there a more efficient way of going about this?

Brandon91man said:

A polycrystalline solar panel 17V 2.2A and a mono crystalline panel 4.8V 4A (read by multimeter) I connect them in parallel to produce 16.8V 6.2A.

The schematic really is needed before we go much further. What you have posted above makes no sense (unless I missed a place where you corrected it).

I finished making the schematic and I apologize for how crude it is, its my first time ever making one. If there is any information I left out again I apologize.
I'm apparently terrible with computers too... but I'm trying to learn how to work with them.

So if I wanted to fix the problem of connecting a 17V and a 4.8V panel, would the solution be to connect DC to DC Converters?
I've looked on amazon and it seems like the problem is those converters can step up the voltage into the 30s but the amperage it can handle is too low (near 2-3 amps). The ones that look like they can handle the power my solar panels are producing are like $30. Also I've never bought a transformer or converter before.

Thanks for the drawing.

Another issue involves different amp-hour rated batteries wired in parallel (generally accepted practice is they should be identically rated). Even if they are identically rated, a shorted cell in one battery requires the good battery to discharge into the faulty battery, leading to it overheating and to possibly explode. This potential failure mode ought to be considered in the design.

Brandon91man said:

I finished making the schematic and I apologize for how crude it is, its my first time ever making one. If there is any information I left out again I apologize.

No need to apologize -- you are learning by doing, and working with solar energy systems, which is all great.

This has probably already been mentioned in the thread, but keep these things in mind:

• Stiff voltage sources like batteries need to be rated at the same output voltage before you can hook them in parallel
• PV panels are medium-stiff voltage sources, so you need to only connect them in parallel if they have the same output voltage rating at the same input insolation
• You can parallel-connect different PV panels of the same output voltage even if they are rated at different output currents at that output voltage for the same insolation
• You can series connect PV panels that are rated at different output voltages but the same output currents given the same insolation
• There is typically a Maximum Power Point (MPP) for a PV panel output, where it is producing the most output power for a given insolation. Good PV power converters will help the PV to work at that MPP (a tradeoff between the PV panel's output voltage and current).
• Differently built and rated PV panels may have different MPPs, so it's generally a bad idea to mix and match if you want to build an optimum system

Hope that helps.

Excellent post @berkeman .

@Brandon91man Move your shunt around. Place it in series with each PV panel individually and you will see why paralleling your two particular panels is not doing what you think it is.

Averagesupernova said:

@Brandon91man Move your shunt around. Place it in series with each PV panel individually and you will see why paralleling your two particular panels is not doing what you think it is.

@Averagesupernova
Thanks to the both of you, I will try moving the shunt around and see what I find. Although this is the first time I've used a shunt and I didn't know you could connect it in different ways.
And @berkeman I didn't know mixing different solar panels was a bad idea. So that's good to know. I really was hoping that would be an easy fix with DC To DC converters though.

@Asymptotic

Thank you, That is useful information to know.

Brandon91man said:

And @berkeman I didn't know mixing different solar panels was a bad idea. So that's good to know. I really was hoping that would be an easy fix with DC To DC converters though.

The right solution for mixing panels or panel configurations is really to have a MPP power converter for each contributor panel configuration that can't be easily put in series or parallel with another panel configuration. The output power of the multiple MPP power converters would then be combined in some way, typically after synchronized inverters. That's a fun project to build, but at your level of learning so far, you would need to find packaged inverters that could be synchronized, and buy a couple MPP power converters.

What-all do you want to power? Maybe you could just have two separate PV powered systems that are independent?

Brandon91man said:

@Averagesupernova
Thanks to the both of you, I will try moving the shunt around and see what I find. Although this is the first time I've used a shunt and I didn't know you could connect it in different ways.

There really is only one way to hook a shunt. It goes in series with the current you are trying measure. Don't hook it across a voltage source.

berkeman said:

What-all do you want to power? Maybe you could just have two separate PV powered systems that are independent?

Well, for now I'm powering tablets and lights. My ultimate goal is to setup a grid tied system, but I also want to use them in projects and electronics too. For example, I want to eventually get to the point where I can build an electronic system that will use solar power to charge a battery that powers a peltier A/C system (still researching that) and that peltier A/C only turns on at a specific time of the day.

My desires require me to learn and understand thermodynamics, electronics, solar power, power loss, power used, and probably much more. I'm actually extremely happy I found this forum. I didn't even know my panels were connected incorrectly until the other day.

(I know that's more than what you asked for but I feel like there are a lot of brilliant minds here that can help me get to where I want to be)

Brandon91man said:

My ultimate goal is to setup a grid tied system,

One thing to learn early when you are considering building a grid-tied system, is that your local electrical utility will have regulations for how you make that tie. There is special equipment needed (and the utility has to inspect it and sign off on it before you can make the grid connection). One of the biggest reasons is that if the grid de-energizes for some reason (like a breaker blows at your street's distribution transformer), the utility needs you to stop pushing your power back toward the grid. This is to keep repair people from getting electrocuted by what they think are de-energized powerlines on your street.

This is called Anti-Islanding protection:

https://solectria.com/blog/anti-islanding-protection-with-grid-tied-pv-inverters/

berkeman said:

This is called Anti-Islanding protection:

https://solectria.com/blog/anti-islanding-protection-with-grid-tied-pv-inverters/

Thanks for the heads up!

Does anyone have feedback on making separate off grid solar power for large appliances that use up a lot of energy? (Like A/C & Heating, Washer/Dryer, Water heater, etc.) Any opinions on if it's worth the effort? Maintaining systems? A rough cost to savings ratio?
I'm just looking to see if I should go further with my solar interests.

There are some things better left to gasoline or propane power or perhaps wind. Windmills were likely first used to pump water.
-
Try this: www.otherpower.com.
Lots of info there.

Brandon91man said:

Thanks for the heads up!

Does anyone have feedback on making separate off grid solar power for large appliances that use up a lot of energy?

Join the club? As far as I can tell, there are no off the shelf products that you can buy at Walmart to do such things. So it's DIY hell...

(Like A/C & Heating, Washer/Dryer, Water heater, etc.)

You forgot your refrigerator.
Each of these devices/problems deserves a thread of its own, in a solar powered world.

Any opinions on if it's worth the effort?

I'm retired, and my effort is currently close to nil.

Maintaining systems?

Since it's all DIY at the moment, maintaining the systems will be dependent on the quality of your duct tape.

A rough cost to savings ratio?

Just finished up some washer and dryer experiments this morning.
My wash machine consumes 250 watt hours of energy over the course of 40 minutes, with a maximum output of around 900 watts. (Not counting surge current).
My solar powered clothes dryer consumed only my time. Which non-retirees will tell you is a waste of time and money. Unless they are poor, and then they are probably already ahead of you and me.



Obligatory sciencey graph:

I'm just looking to see if I should go further with my solar interests.

I've been doing it for about 11 years. It's still interesting.
But, please be advised, that people, even hippy looking tree hugging people, will call you stupid.
Take my advice, and just ignore them, the best you can.

@OmCheeto thank you! I appreciate your post.

Brandon91man said:

Does anyone have feedback on making separate off grid solar power for large appliances that use up a lot of energy? (Like A/C & Heating, Washer/Dryer, Water heater, etc.) Any opinions on if it's worth the effort?

PF 'er @BernieM is doing it. Here's a recent thread about his battery troubles.
https://www.physicsforums.com/threads/solar-series-battery-charging-problem.918209/
Maybe he'll share some of his knowledge and experience on this thread...

My advice is this -
anything involving heat is a power hog.
Heat water directly with flat panels,
get a gas dryer and gas stove and gas furnace or burn wood,
air condition only your sleeping quarters,
and get a chest freezer not upright.
Better yet- were i going off grid i'd get a gas fridge and gas freezer. Maybe gas water heater too.

Build for the climate .
I grew up in South Florida before middle class people had air conditioning . Houses then were designed for cross ventilation from prevailing SE wind, with big windows and four foot eaves to shade them. Before WW2 most had a flat panel thermosiphon solar water heater on the roof . They worked great in that climate.

You'll find energy from the electric company is a bargain . They buy fuel by the ton and convert it at 40% efficiency or better. You can't do that.

my two cents worth of opinion

old jim

So I made a mistake and I'd like to ask everyone else's opinion about it.
I have a 50 ah battery that I don't usually use with my solar power system, but I decided to charge it since my 35 & 7 ah batteries were fully charged.

I disconnected the two smaller batteries from my charge controller and hooked it up to the car battery in reverse by accident, It made a pop/spark and I pulled the probe away.
Because I'm curious, I tapped the probe back on the battery terminal and it did nothing.
I disconnected everything and opened up the charge controller, I found out that the 35 amp fuse in the charge controller was blown so I replaced it with a 30 amp fuse (because that's all I had) everything seemed ok besides the fuse being blown and some white-ish area around the temperature sensor (which has never worked in the first place)

The shunt & display were displaying some very odd numbers so I opened the digital display too. It seemed like there were no signs of damage inside it but I replaced the wires connecting the meter and the shunt (I thought they might be throwing off the reading because two were 18 gauge and two were 20 gauge).

The display used to show 12.9 V, 1.96 A.
but now it shows between 19 - 23 V, 0 - 2 A.
I disconnected and read the solar panels with a multimeter 17 V, 5 - 7A.
I connected my inverter and a 36 W load to the (35 & 7ah) battery, and it went from 13.8 V to 12.5 V in about two minutes.

Would anyone have advice on what to do or know what's happening?

I have a system that runs my entire household, off-grid in Arizona near Phoenix. It takes a LOT OF POWER to do it.
Most of the people around where I live do not even have the ability to run a/c, and live in homes that have huge insulation values, and have adapted to hot temps through the years living here.
I can't do that unfortunately, so I had to opt for power to run a/c's and stuff. By far the largest power use is air conditioning here, but if you live in the northern states, it may not be that much power use compared to say heating. But I do my heating using propane as well as run my refrigerator off propane. Small refrigerators and freezers do not actually use that much power, however. My small chest freezer uses just 84 watts, and a small dorm type refrigerator will use about 100 watts or so. Even a larger refrigerator may only use 150 to 200 watts.

If you want to live off grid, you will have to put out a lot of money and economize everywhere you can. It's also helpful if you can get away with propane powered equipment which will reduce your electric needs, saving you money. But if you have to run everything off electric (dryers consume huge amounts of power!) you will need a system even larger than I have.

My system is 4.4KW of solar panels, with 10 banks of batteries, each bank is 2 batteries in series for a 24 volt system (higher voltage saves on conductor costs and reduces losses in transmission of power from roof to inverter.) @ 200 Ah each battery pair @ 24 volts, the array theoretically is in the range of 48KWH of power storage. However one never depletes the batteries past 50% if one can help it, 30% if possible (extends battery life.) So in reality I have around 24KWH of power stored for use at night or when solar input is low (cloudy days.)

With this system I am able to run up to 4 a/c's during the day (generally I never run more than 2 except when I am working in the shop which isn't too often in the summer,) my chest freezer, lights, tv, satellite internet dish, water pump, microwave oven, pc, washing machine (but not an electric dryer, I use propane or the sun) and just about anything else that I need to run when I want to as long as it isn't a huge load for a long time.

Thanks, @BernieM

Averagesupernova said:

@Brandon91man Move your shunt around. Place it in series with each PV panel individually and you will see why paralleling your two particular panels is not doing what you think it is.

So I have moved the shunt to each solar panel individually. What I found is that the shunt powers on with the poly panel but not the mono panel. When I measure the panels with my multimeter, the values come back pretty close to what I've measured before: (mono = 5V 5A) (poly = 16V 2A). When I read the display from the shunt, it shows anywhere between 25 - 32 volts and 0.5 - 2 amps. These numbers bounce back and fourth between these values a lot. The batteries I'm charging show a steady 13.1.
Does it do this because the power cannot be pushed into the battery and that makes Voltage go up while current goes down?
Or do I have a faulty shunt?
Also there is no shade or anything blocking sunlight to make this happen.

Brandon91man said:

So I have moved the shunt to each solar panel individually. What I found is that the shunt powers on with the poly panel but not the mono panel. When I measure the panels with my multimeter, the values come back pretty close to what I've measured before: (mono = 5V 5A) (poly = 16V 2A). When I read the display from the shunt, it shows anywhere between 25 - 32 volts and 0.5 - 2 amps. These numbers bounce back and fourth between these values a lot. The batteries I'm charging show a steady 13.1.
Does it do this because the power cannot be pushed into the battery and that makes Voltage go up while current goes down?
Or do I have a faulty shunt?
Also there is no shade or anything blocking sunlight to make this happen.

How can you have a 5A reading from a multimeter when the shunt told you the opposite?
-
Concerning the 25-32 volt reading with current draw of .5 to 2 amps, I will assume that the higher the current the lower the voltage assuming you always have the same amount of sunlight on the panel? A solar cell is not a perfect voltage source so as you draw more current from it, the voltage on the output terminals will fall. Do the same thing with a couple of AA dry cells and resistors to vary the load around. You will find the same thing happens. The more current you draw, the lower the voltage will fall.

@Averagesupernova Thank you, I will try out that experiment later.

I came here to help with answers but see that there were quite a few and this was a while back. I'm curious, how did it turn out? Hopefully you learned a lot.