In series vs Parallel?

[EmeraldCoastSailor]

The paperwork that came with my SunPower 110W panels says that SunPower doesn't recommend using them in parallel. I was thinking parallel was the way to go to maximize output given possible shading. The cable run to the controller will be less than 15' and I was planning on using 10 AWG cable. With a roundtrip circuit of 30', 22.8 volts (open circuit rating of the panel, and 12.6 amps (2 panels @ 6.3 A short circuit current each) the voltage drop is 3.23% which I think is acceptable.

Do I need to reconsider and wire the panels in series?

[sailormed]

Just stick to your original plan. Never heard of that installation obligation. As far as I know solar cells don’t have a conscience, they just produce .

[Stu Jackson]

Originally Posted by EmeraldCoastSailor

The paperwork that came with my SunPower 110W panels says that SunPower doesn't recommend using them in parallel. >>>>>>>>>>>>>>>>>>
>>>>>>>>>>>>>>>>>>>>>

sailormed is right, the panels don't care.


Could you quote what you see in the paperwork? Makes little sense without seeing it word for word.

[EmeraldCoastSailor]

I forgot to add that I will use a Victron 75/15 SmartSolar MPPT controller.

[EmeraldCoastSailor]

Here is a link to the SunPower manual document: https://us.sunpower.com/sites/sunpow...on-guide_0.pdf

Here is a cut and paste of the Danger Warning from the document:
DANGER!
• SunPower does not recommend connecting these panels in parallel without proper system and safety protection.
• Connecting panels in parallel will double the current output of the panels. DC Currents may be greater than 12 amps for 100 W, 110 W
and 170 W, and greater than 6amps for 50 W, in high illumination conditions (>1000 W/m2).
• If shading occurs without additional electronic components, such as a blocking diode, the by-pass diodes may be damaged leading to
further panel damage and unsafe conditions including fire.
• If Paralleled panels are attached to a battery for charging, the high current may cause damage to the battery and subsequent safety
issues.
• The charging characteristics of any battery should always be checked for compatibility with the current and voltage output of the panels
prior to use

[sailormed]

Looks like the usual warning all manufacturers put on their products these days to prevent being sued for ridiculous amounts of money decided upon by a totally ignorant jury.

[rbk]

Just a thought on your wire, while the drop is acceptable you may want to consider going to 8g as you can get closed barrel tinned terminals for 8 but not 10 (that I know of). This would give you an even less drop and ensure no corrosion in the ends when used with closed terminals and heat shrink for a few bucks more.

[s/v Jedi]

I agree with Sunpower: you should wire them in series. The information you have was valid 20-25 years ago since when they put bypass diodes in panels to deal with shading.

The limitation you have is the controller: I think it can only deal with 75V open output from the array.

[EmeraldCoastSailor]

Originally Posted by s/v Jedi

I agree with Sunpower: you should wire them in series. The information you have was valid 20-25 years ago since when they put bypass diodes in panels to deal with shading.

The limitation you have is the controller: I think it can only deal with 75V open output from the array.

I will only have two panels so can't see ever getting above 75v.

[mat jam]

I have 2 x 110w Sunpower panels. When I was sizing everything I had direct contact with their (SVB) electrician. Here is a direct quote,

"A single 110w Wp module will deliver max. 6.25 A @ 17.6 V.
Two modules (parallel connected via 22302) will deliver 12.5 A.
This high current will lead on a 2.5mm2 cable to an unwanted high voltage loss.
For a cable length of 5m 2 x 6mm2 cable is required".

So essentially, they are not saying to not do parallel. Just use the appropriate cable. I have them on a Sunware Fox 360 Charge Regulator which is PWM. Now I know some (many?) will swear that MPPT is the way to go, but after an exhaustive research, the conclusion was for my application (read most) PWM was appropriate and MPPT is more geared to large arrays of panels. Note: SVB do not sell MPPT and since they are a major boat supplier I have to assume they know their stuff.

I assumed 5m of cable would be okay since the panels are above the stern and my batteries / regulator under the cockpit / companionway but the distance above the cockpit including wiring following one side down the SS tubing frame required an extra meter. And this was as direct as I could get it. So go longer and cut if you have to.

My panels work well and can say I am impressed with them.

[s/v Jedi]

Yes well with a PWM regulator you can’t put the panelsn series so you’re stuck with parallel and a noticeable reduction in efficiency compared to a MPPT controller. Your supplier sux for not offering any... Victron is available everywhere and the popular choice.

For the OP: just connect in series as manufacturer recommends because your regulator is good to go in that setup. You can always change setup if you want to experiment because the controller can handle two parallel panels as well

[john61ct]

To best handle partial shading, get a second 75/15 and go 1:1.

[s/v Jedi]

Originally Posted by john61ct

To best handle partial shading, get a second 75/15 and go 1:1.

Indeed, but much smaller MPPT controller could be used in that case. We had a member doing that and getting very good results in line with theoretical calculations

[john61ct]

I believe Victron's smallest is 75/10?

If money is the issue, not much cheaper, especially in a BT enabled version.

I don't think other lines offer such good value at the low-end, $130 is pretty cheap IMO, usually that sort of feature set costs hundreds of dollars more per SC.

To maximize that value, buy the panel (if possible) to get the most out of the SC; for the 75/15, that would be 40-60V at 240-300W

Getting the optimum watts per limited square area is the other side of the challenge though.

[mat jam]

Would be interesting if knowledgeable cruisers could weigh in on these comments from Quora by industry experts. My so called inefficient PWM is via a company that has been in the industry for about 30 years and has an efficiency of 98.5% but the argument appears to be I have used an inefficient system. Appologies if this method of quoting is not appropriate.


Paul Millott, 25 years in the PV industry, PV system designer and PV system integrator.

The most efficient solar charging is only obtained when the solar panel, open circuit voltage, (Voc) is matched to the battery voltage. Most people do not know this, so they have to use PWM or MPPT chargers to correct the mismatch and both cause losses in charging.
To charge a 12 volt, Lead acid battery, the Voc of the solar panel has to be between 21Voc and 24Voc. This will charge the battery very efficiently with no losses. Make sure the solar panel maximum amps is no more than 25% of the battery capacity to avoid losses from charging too fast. Use an analogue charger to avoid the MPPT and PWM losses.
PWM stops the battery from over charging by switching off the current to the battery between pulses of power. The solar panel is still producing power during the off pulse but this power is lost completely if it does not reach the battery, causing a very inefficient charging. The current from the solar panel varies all day long from zero to maximum current, which only occurs at mid day. Also most PWM chargers use a 24 hour battery charging regime, which is obviously useless when a solar panel only works a few hours a day and gives very low current on rainy days to zero current at night. Losses vary with weather conditions so I don’t have an average loss.
MPPT should never be used for charging batteries but since most people use the wrong voltage solar panel, there is no choice but to use the MPPT to correct the mismatch and get a working system. Average 12% losses occur with MPPT chargers, compared to using the correct voltage solar panels.
Always use the correct Voc for your battery with a good analogue charger to prevent losses from MPPT or PWM chargers.


Phil Karn, Have had grid-tied PV since 1999, long before it became fashionable

Because the MPPT is somewhat more complex than the PWM controller, the efficiency of the controller may be somewhat lower. But efficiency depends more on engineering choices like the switching transistors used, transformer/inductor design, switching frequency and especially the output current. (Efficiency usually peaks at some particular current and falls off below and above that value.)
I think you’re really after the overall efficiency with which the system converts sunlight to electrical power. Again, it depends. What is the panel’s peak power point voltage in relation to the required output (e.g., battery) voltage?
If they are already closely matched, a MPPT may not be much better than a PWM controller.
But a panel’s peak power point voltage increases with decreasing temperature, so a MPPT may provide considerable benefit during a cold winter. Also, if you’re discharging your battery at night (as in an off-grid system), its terminal voltage will be relatively low when the sun rises, and a MPPT will provide greater benefits.
Another situation where a MPPT can really help is when an array is partly shaded. Panels include bypass diodes to shunt current around them when they’re shaded. This is primarily a safety mechanism (a panel could conceivably burn up otherwise) but it also lets the array continue to produce reduced power at a lower voltage. If this voltage is below the required output voltage with a PWM controller, you’ll get essentially nothing. A MPPT will adjust to the lower voltage and get as much power out of the unshaded part of the array as possible.
An MPPT also makes it possible to operate the array at a much higher voltage than the required output, acting like a DC stepdown transformer. The resulting reduction in current in the array wiring lets you use lighter and cheaper wiring and/or decrease wiring losses. With modern panels each typically producing 7 amps or more, and wire runs of tens of feet, this can actually be significant.


Prathmesh Karmarkar, works at Enertech

An Enertech MPPT controller enables the greatest capacity to be gathered. The nuts and bolts of an MPPT Solar Charge Controller are to streamline the effectiveness of the charge controller utilized in a photovoltaic system.
PWM charge controllers are, basically, a switch that demonstrations between the sun based cluster and the battery and its capacity is to pull down the voltage of the exhibit to close to that of the battery to guarantee that the battery is legitimately charged. The PWM charge controller is reasonable for little frameworks.
MPPT framework is regularly utilized when the PV cluster voltage is generously higher than the battery voltage. It is the best answer to higher power frameworks.


Kevin Cameron, B.Sc. Electronics & Physics, University of Edinburgh

You are confusing acronyms, PWM (pulse width modulation) is a technique used in power electronics for multiple purposes, MPPT (maximum power-point tracking) is used in conjunction with PWM. Losses in PWM for DC/DC conversion on solar panels will be single digit %.


To be fair I posted all the comments.