Solar Upgrade

[Ninjabob]

I have a Truma 100watt panel with the SDC10 PVM Controller. I have replaced this controller with a Votronic 250MPPT unit. I intend to add another 100watt panel which appears to be of identical size and specifications. I am charging two 100ahr Halfrauds (Yaesu) batteries and the 1amp Cab battery takeoff. I have the remote meter fitted and everything is working correctly other than I don't seem to have the Bar Graph on the left of the meter. My understanding after hours of trawling the Web is that in series the MPPT controller will perform better with the higher voltage (VOC below 50v) than in parallel especially in low sunlight situations but not happy if one of the panels is shaded. In parallel the shading will not have such a pronounced effect but will forefit the MPPT low light advantage. 4mm wiring for series - 6mm for parallel. Have I understood this malarky correctly? So series or parallel? Would it not be wonderful if someone created a switching unit to allow a swop between series and parallel depending on van location and shading?

 

[tonyidle]

Parallel.

 

[funflair]

I asked Votronic and they said parallel, so that was good enough for me.

The bar on the left side of the solar computer should tell you roughly how many amps are going into your batteries.

Martin

 

[JohnT UK]

I have 2 100w running in para with the votronic 250 not had a problem

 

[Ninjabob]

Parallel it is then - thanks people.

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[Hettie's Crew]

I asked Votronic and they said parallel, so that was good enough for me.

Same here

 

[Lenny HB]

Yep you read it right, don't really need 6mm cables 4 mm will be fine.
You get the biggest voltage drop in mid summer when the panels are producing their max so losing a 5% in stead of 3% won't worry you. In winter when the panels are not producing much the loss will be so small & not worth worrying about.

 

[Off da Grid]

A solar panel can produce more power if its tilted to the right angle for the best sun in the winter as they work better when cold, it is recommended that the controller is rated 10% higher than the max output of the panel for this reason.
In the summer the panel will never produce its rated output because it gets to hot, Hose it down and watch the power go up!
It’s the same with computer chips that’s why super computers have refrigerant running through them

 

[DBK]

Parallel it is then - thanks people.

From a purely electrical point of view series is better but in the real world you won't notice the difference which is why everyone seems to prefer parallel. There is an argument parallel is better if one panel is shaded but either will work.

 

[TheCaller]

I think the series/parallel argument is pretty finely balanced & what is likely to be best depends on what you need from your solar & on how you use the van.

My two 100W panels are mounted next to each other & there aren't many occasions when one would be shaded when the other wasn't. There is nothing sticking up that would always cast a shadow on one panel at some point in the day.

When not in use, my van is outside, but with no access to mains power. So I rely on solar to keep the batteries charged all year round. A controller can only start charging the batteries when it can produce an output voltage higher than the batteries current voltage. I think most controllers switch themselves on once they are receiving about 15V from the panels. I forget the exact figure, but a 100W panel max's out at about 22V. To get that, you need to be in Spain on a hot summer's day. On an overcast UK winter's day, the voltage will never reach the required 15V.

With the panels in series, they only have to reach 7.5V for the controller to see 15V & start charging. Now at that level, it will only be a trickle charge - 1 or 2 amps. But that's enough to keep both the habitation batteries & the starter battery charged up all the time the van is parked.

If you have regular access to EHU, or you spend the winter in Spain, there isn't going to be any benefit in wiring the panels in series. But if you must extract every last watt of power from your panels while in Northern Europe & you can avoid the shading issue, then series is likely to give a better overall result.

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[tonyidle]

I think the series/parallel argument is pretty finely balanced & what is likely to be best depends on what you need from your solar & on how you use the van.

My two 100W panels are mounted next to each other & there aren't many occasions when one would be shaded when the other wasn't. There is nothing sticking up that would always cast a shadow on one panel at some point in the day.

When not in use, my van is outside, but with no access to mains power. So I rely on solar to keep the batteries charged all year round. A controller can only start charging the batteries when it can produce an output voltage higher than the batteries current voltage. I think most controllers switch themselves on once they are receiving about 15V from the panels. I forget the exact figure, but a 100W panel max's out at about 22V. To get that, you need to be in Spain on a hot summer's day. On an overcast UK winter's day, the voltage will never reach the required 15V.

With the panels in series, they only have to reach 7.5V for the controller to see 15V & start charging. Now at that level, it will only be a trickle charge - 1 or 2 amps. But that's enough to keep both the habitation batteries & the starter battery charged up all the time the van is parked.

If you have regular access to EHU, or you spend the winter in Spain, there isn't going to be any benefit in wiring the panels in series. But if you must extract every last watt of power from your panels while in Northern Europe & you can avoid the shading issue, then series is likely to give a better overall result.

The voltage doesn't drop off too dramatically in poor conditions but the current available certainly does. Either way an MPPT controller will output charging voltage level even if the panel drops below battery terminal voltage.

 

[TheCaller]

Either way an MPPT controller will output charging voltage level even if the panel drops below battery terminal voltage.

I don't think my Victron MPPT does. The app shows panel & battery voltages & I've never seen the charger in the 'On' state while the panel voltage has been below the battery voltage.

Just found the data sheet:

PV voltage must exceed Vbat +5V for the controller to start.
Thereafter minimum PV voltage is Vbat + 1V

That means that on the standard charge programme, with a fully charged battery at a float voltage of 13.8V, the charger would turn off once the panel output fell below 14.8V.

 

[Ninjabob]

I think the series/parallel argument is pretty finely balanced & what is likely to be best depends on what you need from your solar & on how you use the van.

My two 100W panels are mounted next to each other & there aren't many occasions when one would be shaded when the other wasn't. There is nothing sticking up that would always cast a shadow on one panel at some point in the day.

When not in use, my van is outside, but with no access to mains power. So I rely on solar to keep the batteries charged all year round. A controller can only start charging the batteries when it can produce an output voltage higher than the batteries current voltage. I think most controllers switch themselves on once they are receiving about 15V from the panels. I forget the exact figure, but a 100W panel max's out at about 22V. To get that, you need to be in Spain on a hot summer's day. On an overcast UK winter's day, the voltage will never reach the required 15V.

With the panels in series, they only have to reach 7.5V for the controller to see 15V & start charging. Now at that level, it will only be a trickle charge - 1 or 2 amps. But that's enough to keep both the habitation batteries & the starter battery charged up all the time the van is parked.

If you have regular access to EHU, or you spend the winter in Spain, there isn't going to be any benefit in wiring the panels in series. But if you must extract every last watt of power from your panels while in Northern Europe & you can avoid the shading issue, then series is likely to give a better overall result.

Excellent answer - I think in my web trawlings I read pretty much what you have said. If you have rely on solar in the winter then you are better off with series but generally parallel is the best option for most scenarios. Thank you for your input?

 

[tonyidle]

I don't think my Victron MPPT does. The app shows panel & battery voltages & I've never seen the charger in the 'On' state while the panel voltage has been below the battery voltage.

Just found the data sheet:

That means that on the standard charge programme, with a fully charged battery at a float voltage of 13.8V, the charger would turn off once the panel output fell below 14.8V.

You're correct. I misread the bit about start voltage. My data sheet uses almost the same words. However voltage output is unaffected by the level of sunlight. Sunlight, or lack of it, affects available current. Panel temperature affects voltage.

 

[TheCaller]

However voltage output is unaffected by the level of sunlight.

Can you point to somewhere that I could read more on that? I have noticed that the voltage does tend towards zero as it gets dark. My own observations suggest that both voltage & current increase as light levels increase.

I agree that panel performance decreases with temperature, but if it's hot enough to matter, I'm probably getting a pretty good output anyway.

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[tonyidle]

Photovoltaic Panel Converts Sunlight into Electricity

Alternative Energy Tutorial about the Photovoltaic Panel and how photovoltaic solar panels convert sunlight into electricity for a renewable energy home

www.alternative-energy-tutorials.com

.

- is one source I read.

 

[Misterg]

My own observations suggest that both voltage & current increase as light levels increase.

my Victron MPPT

The current available from the panel changes a lot with light level, but the open circuit voltage doesn't change very much - e.g.

The voltage at maximum power (the shaky blue line) drops away more quickly than the open circuit voltage. The change in voltage you have observed will be mostly as a result of your MPPT controller loading the panels to track the maximum power output.

There are marginal efficiency gains with the Victron MPPT controllers from using as high a voltage as possible (panels in series). In practice, with a MPPT controller, shadowing one panel has a similar effect whether they are connected in series or parallel as most panels are fitted with bypass diodes, so the current from the active panel can still "get through" when series connected. (When panels had to be matched to battery voltage for optimum efficiency, the small voltage drop across the bypass diodes may have have been an issue). The panels do have to have similar Isc if they are to be series connected though (ideally the same type/size of panel).

 

[Just smiffy]

Excellent answer - I think in my web trawlings I read pretty much what you have said. If you have rely on solar in the winter then you are better off with series but generally parallel is the best option for most scenarios. Thank you for your input?

Or you could do what I have, a controller for each panel.... to be sure to be sure...?

 

[barsteward]

I just lurve this analogy. not mine I might add but someone far cleverer than I am.

COMMON ARGUMENTS FOR PAR ALLEL OVER SERIES.
Recently we’ve been getting a ton of comments arguing for wiring solar panels in parallel and they always go something like this:

“I want max solar output from my solar panels and if I wire in series, park under a tree, and get shading on part of my array, It significantly decreases power to the entire array.”

and…

“I want max solar output from my solar panels and if I wire in series and a panel breaks It significantly decreases power to the entire array.”

In our 3+ years of being on the road, neither of these have been a problem.

Fortunately, I’ve developed a highly-sophisticated strategy for solving both of these problems and still wiring in series and lucky for you, I’ve made diagrams for both of them.

The first diagram fixes the problem in regards to getting max solar output when your camper is parked near a tree that’s causing partial shading to your solar array.

This next diagram fixes the problem in regards to getting the max solar output of an array with a broken panel.

There have been tests done showing how one bad panel or shading on one panel will decrease the output of the entire array. All of that is true; I’m not debating that.

My point is this: If you are TRULY worried about getting the maximum output from your solar panel array; park in the sun and maintain your solar panels.

 

[Ninjabob]

Or you could do what I have, a controller for each panel.... to be sure to be sure...?

Now your talking - the cheap option! - like to see you Bluetooth to that lot with your phone ?

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[TheCaller]

Photovoltaic Panel Converts Sunlight into Electricity

Alternative Energy Tutorial about the Photovoltaic Panel and how photovoltaic solar panels convert sunlight into electricity for a renewable energy home

www.alternative-energy-tutorials.com

.

- is one source I read.

Interesting, and it's confirmed by other sources - I had a look. So that should mean that the time of day a controller switches on or off should vary little whether wired series or parallel - certainly when only two panels are involved, because as daylight increases/decreases, the voltage will rise/fall very fast over a very small change of light intensity.

However, I've noticed that in winter, the output from my two series wired panels spends quite a significant time between mid-teens volts & low thirties volts. That's the area where the charger would by turned off if parallel wired. Now as said earlier, the output to the batteries at those light levels is tiny, an amp or two at best. But a trickle charge is all that's needed when the van's just sitting there.

Although I use the van all year round, before I had solar, I had to ensure that it didn't stand for more than a couple of weeks, or the starter battery would start to get uncomfortably low. Since fitting the panels, all three batteries are always fully charged. So even though solar will never provide enough power to match usage in winter, at least when I do use the van, I start the trip with two full habitation batteries, prolonging the period before I either need EHU or a longish drive.

 

[tonyidle]

It's a little too dynamic to draw any firm conclusions from charge observations. Panel voltage drops when a load (charging for instance) is applied due to photo cell internal resistance. In series there's a drop over the whole number of cells at a certain current draw. If the panels are in parallel the drop is halved at the same current. So the voltage at the combined panel terminals may not be much different whether series or parallel.

 

[DBK]

It's a little too dynamic to draw any firm conclusions from charge observations. Panel voltage drops when a load (charging for instance) is applied due to photo cell internal resistance. In series there's a drop over the whole number of cells at a certain current draw. If the panels are in parallel the drop is halved at the same current. So the voltage at the combined panel terminals may not be much different whether series or parallel.

That doesn't make sense. The easiest way to look at is to consider the voltage drop as lost energy. So the voltage drop times the current equals a certain wattage lost internally. When in series the current is the same through each panel but the overall the voltage drop will be double but this is the same as having two panels in parallel as each generates a loss equal to the current times a voltage drop half that of the series array - but there are two panels so the overall loss is the same either way.

Where there is a greater loss is in the cables linking the panels to the controller as the current will be double with a parallel array so the losses will be double for the same cable. It won't be significant if the cables are well sized but if they are a bit thin it is something to take into consideration.

 

[Ninjabob]

It is interesting because if you read advice from the Victron site they say series with their MPPT controllers and yet people here have had advice from Voltronic that parallel is best. I have gone parallel and all is working.

 

[tonyidle]

That doesn't make sense. The easiest way to look at is to consider the voltage drop as lost energy. So the voltage drop times the current equals a certain wattage lost internally. When in series the current is the same through each panel but the overall the voltage drop will be double but this is the same as having two panels in parallel as each generates a loss equal to the current times a voltage drop half that of the series array - but there are two panels so the overall loss is the same either way.

Where there is a greater loss is in the cables linking the panels to the controller as the current will be double with a parallel array so the losses will be double for the same cable. It won't be significant if the cables are well sized but if they are a bit thin it is something to take into consideration.

Yeah - that's pretty well what I was trying to say and it doesn't make much sense to me now. I think we are agreed that series or parallel is only significant for long cable runs and/or inadequate cabling.

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