Solar panels. Series, parallel or individually wired?

[Roberto]

A follow up question. If I have individual controllers for two panels, is there any issue with having two individual MPPT outlets inputting to the same battery bank?

Check the Victron instructions about Master/Slave Mppts; fwiw I had two simple 75/10 non-smart regulators on two separate panels --> one battery bank and I found no way of making them work together, one of them quickly cut all output; I eventually connected all the panels together and bought one bigger regulator, job done.

 

[Sea Change]

You may want to look at 100W Rigid Mono High Density Solar Panel Kit - PV Logic as they are a bit narrower than the standard panel at 1150 x 460 x 35mm rather than the more usual width of 670 mm. They are a bit more expensive that the £60 quoted above.

I went down this route as they sit vertically between the deck and the top of the pushpit when I am not onboard.

That's a shocking price for it a 100w panel.
The £60 I quoted was for a 400w panel.

Out of the panels listed on that link, I would choose the 125w one, because it has a much higher working voltage.

And that's the key really. One high voltage panel per MPPT is the optimal solution. You don't need to mess about with putting panels in series if they are already 32v or more.

 

[Caladh]

That's a shocking price for it a 100w panel.
The £60 I quoted was for a 400w panel.

Out of the panels listed on that link, I would choose the 125w one, because it has a much higher working voltage.

And that's the key really. One high voltage panel per MPPT is the optimal solution. You don't need to mess about with putting panels in series if they are already 32v or more.

Can you post a link for your 400w £60 panel ?

 

[PaulRainbow]

That's a shocking price for it a 100w panel.
The £60 I quoted was for a 400w panel.

But few typical boats can accommodate such big panels.

Much better price for a 100w panel 12V solar panels charging kits for caravans, motorhomes, boats, yachts, marine

Out of the panels listed on that link, I would choose the 125w one, because it has a much higher working voltage.

Two of those would cost £510 !

And that's the key really. One high voltage panel per MPPT is the optimal solution. You don't need to mess about with putting panels in series if they are already 32v or more.

How much do you really gain by fitting separate controller to a couple of panels ? Not much, if anything, especially taking into account higher overheads of two controllers. Extra cost of two controllers, extra wiring, heavier wiring etc all make it much more expensive for little to no gain.

 

[noelex]

the MPPT reaches its' start threshold slightly earlier in the morning and carries on slightly later in the evening.

Series connection has minimal practical impact on the duration of the charge period, even for nominally 12 V panels. The Vmp remains higher than the battery voltage under quite low light conditions. The charging stops under low light because the panels cannot produce significant current rather than a lack of voltage.

Please refer to the photograph from the solar controller on my previous yacht. The charge controller has been shut down because the current that can be produced by the panels is insufficient, resulting in a current less than the controller’s self-consumption. The Voc remains 18.0 V (these are 12 V panels in parallel).



In essence, the voltage remains satisfactory; however, the current is very low. Series connection offers limited assistance in this situation.

 

[noelex]

How much do you really gain by fitting separate controller to a couple of panels ? Not much, if anything, especially taking into account higher overheads of two controllers. Extra cost of two controllers, extra wiring, heavier wiring etc all make it much more expensive for little to no gain.

As Paul points out, compared to parallel connection, the gains in total energy production are not enormous if you elect for multiple controllers, but for boats where there is little extra space to fit more solar, it remains a useful way to increase production.

The extra cost of multiple controllers is very dependent on the details of the installation. Sometimes multiple small controllers can be similar or even less expensive than a single larger controller. The cabling will invariably be more expensive, but multiple smaller wires are not usually a great deal dearer than a single larger cable of similar total capacity. Series connection enables the use of a single smaller wire, so the wire costs are always lower, but there is a more significant performance loss.

Another advantage to consider with multiple controllers is the added redundancy. This is especially important if solar is the primary means of power generation and you are using high-voltage panels.

 

[Bobc]

For a couple of panels using separate controllers is a waste of money. The difference in yield will be miniscule, or non-existent.

If they are wired in series they just become a bigger panel, as far as the controller is concerned. The voltage doubles, so voltage drop is less, allowing lighter, cheaper, easier to route cabling. The voltage required to start the controller is reached sooner and they will work better in low light, where the voltage of a single panel might not be enough for the controller to work with. Only downside is, if one gets shaded it will affect the overall yield.

Wiring in parallel loses the advantages of series connection (higher voltage etc), but if one panel suffers some shading the other is unaffected.

Exactly what I was going to say.

 

[Sandy]

That's a shocking price for it a 100w panel.
The £60 I quoted was for a 400w panel.

Out of the panels listed on that link, I would choose the 125w one, because it has a much higher working voltage.

And that's the key really. One high voltage panel per MPPT is the optimal solution. You don't need to mess about with putting panels in series if they are already 32v or more.

You should see the prices in the chandlers!

As stated above the 125 watt panel is too wide for my design requirements; I really do not want panels protruding over the pushpit. Why do I need a higher voltage? I use AGM batteries and the Victron MPPT does what it needs to do.

My power requirements are tiny compared to some boats, basically nav and internal lights plus instrumentation. My consumption is less than 10 amps per hour.

 

[noelex]

One notable advantage of employing multiple controllers that has not been explicitly mentioned is the avoidance of confusion that can arise when attempting to monitor the output voltage of solar panels. This confusion can occur due to the presence of multiple peaks and valleys in the output curve. In such instances, a single controller may become erroneously locked onto a specific portion of the output curve. This factor can sometimes be more pronounced than the compromise in power point selection that is necessitated when multiple panels are connected to a single controller.

 

[Sea Change]

Can you post a link for your 400w £60 panel ?

Take your pick:
Solar PV Panels | City Plumbing

 

[Sea Change]

But few typical boats can accommodate such big panels.

We all have different ideas of what the 'average' boat is.
We fitted two domestic type panels to our 39ftr, plus another six 100w panels. We're often the smallest boat in a given anchorage.

How much do you really gain by fitting separate controller to a couple of panels ? Not much, if anything, especially taking into account higher overheads of two controllers. Extra cost of two controllers, extra wiring, heavier wiring etc all make it much more expensive for little to no gain.

You're right, it won't always be the best option.

But my point remains- all else being equal, my preferred installation would be high voltage panels wired to individual controllers.

 

[Sea Change]

Why do I need a higher voltage?

If you don't need a higher voltage, then stop worrying about series wiring.

 

[Sandy]

If you don't need a higher voltage, then stop worrying about series wiring.

Who said I was worried about it?

 

[Sea Change]

Who said I was worried about it?

Apologies, it was the OP who brought up series wiring. A non issue if using higher voltage panels to start with.

 

[requiem]

As I've been playing with solar panels and power stations at home, one warning that stuck out was that voltage should be considered an absolute limit. (I.e. do not feed more volts than the charge controller can handle!)

For my small power station, it has a 60V limit. My solar panels have an open circuit rating of 57.6V. This means I cannot connect them in series unless I wish to damage something. Instead I need to connect them in parallel which will keep the voltage the same and double the current. (In series the current would remain the same but the voltage would double.)

 

[noelex]

For my small power station, it has a 60V limit. My solar panels have an open circuit rating of 57.6V.

You are correct; the maximum voltage rating of a solar controller is generally the absolute limit. Voltage over this value, even very briefly, will damage most controllers.

In some circumstances, such as cold temperatures, the input voltage can rise above the Voc. Therefore, most companies advise a 10-15% buffer between the Voc of the solar panels and the input limit of the solar controller. Using this criterion, a solar panel with a Voc of 57.6V is not suitable for a solar controller rated for a maximum input voltage of 60V.

 

[requiem]

Therefore, most companies advise a 10-15% buffer between the Voc of the solar panels and the input limit of the solar controller. Using this criterion, a solar panel with a Voc of 57.6V is not suitable for a solar controller rated for a maximum input voltage of 60V.

Hmm... in this case the company was selling the panels bundled with the power station (same vendor). The panels themselves have an operating current of 48 volts, which I know is a different thing entirely, but conveniently 57.6 is 120% of that number. I'm wondering if the vendor is simply playing closer to the limit (I saw mention of 3.5% headroom on another random site, which would be under 60), or if there is padding baked in elsewhere.

 

[Baggywrinkle]

Series connection has minimal practical impact on the duration of the charge period, even for nominally 12 V panels. The Vmp remains higher than the battery voltage under quite low light conditions. The charging stops under low light because the panels cannot produce significant current rather than a lack of voltage.

Please refer to the photograph from the solar controller on my previous yacht. The charge controller has been shut down because the current that can be produced by the panels is insufficient, resulting in a current less than the controller’s self-consumption. The Voc remains 18.0 V (these are 12 V panels in parallel).

View attachment 188712

In essence, the voltage remains satisfactory; however, the current is very low. Series connection offers limited assistance in this situation.

That is Voc ... the open circuit voltage of the panel, which is measured under no load. The voltage the panel delivers under load is Vmpp (the voltage used in Victrons excel MPPT calculator spreadsheet and their online calculator). ... in low light, when Voc goes above the start voltage, the MPPT tries a scan to find the MPP, the voltage drops to Vmpp if the panel can deliver enough current, and below this if it can't, The the MPPT then gives up and tries again later (10 mins on Victron), the panels return to Voc. When in series, the voltage is higher, so a voltage drop is to the sum of Vmpp of both panels, allowing the MPPT to remain above it's start and run voltages in less light and at higher temperatures, albeit with less current than parallel. It works similarly to a weak battery as I understand it, voltage is fine until a load is applied, then it drops as the battery can't deliver enough current. Because Vmpp also drops with rising temperature, it is also important to understand the way the panels behave in relation to the start and run voltages required by the MPPT to charge the battery bank.

Playing with the calculator here ...

MPPT Calculator - Victron Energy

.... using single, smaller 12v panels, the calculator can't find a suitable MPPT for panels @ 70°C. Pick a larger panel which can maintain Vmpp due to being larger, and check out the graph showing startup and run voltages and voltage delivered based on panel temperature (max 70°C) and you will see the voltage reduce as temperature rises. A healthy setup has the 70°C voltage well above the run voltage of the MPPT. Not all small single panels are capable of driving an MPPT @ 70°C, even wired in parallel, but put them in series and it works every time - or choose a higher voltage panel.

 

[PaulRainbow]

You are correct; the maximum voltage rating of a solar controller is generally the absolute limit. Voltage over this value, even very briefly, will damage most controllers.

In some circumstances, such as cold temperatures, the input voltage can rise above the Voc. Therefore, most companies advise a 10-15% buffer between the Voc of the solar panels and the input limit of the solar controller. Using this criterion, a solar panel with a Voc of 57.6V is not suitable for a solar controller rated for a maximum input voltage of 60V.

Victron controllers have over voltage protection, exceed the rated voltage and they just shutdown.

 

[noelex]

Victron controllers have over voltage protection, exceed the rated voltage and they just shutdown.

Paul, you are confusing current protection with voltage protection.

Most solar controllers, including the Victron units, have a safety mechanism that will limit the maximum current to a safe level, but even brief over voltage will destroy most controllers.

The Victron questions and answers website confirms that Victron does not have any voltage protection. Responding to the question:

"Does the MPPT 150/35 Controller have Over Voltage protection if the Max input is over 150?"

The Victron community manager responds:

"Exceeding the maximum PV input voltage rating will destroy the MPPT.

It is also important to be aware of the role that temperature plays with panel voltage. Increasing voltage as temperature decreases. So even if a system appears to work for some time, if you are too close to the limit, it can appear to be working and then, the conditions for a particular day can destroy the MPPT."

Does the MPPT 150/35 Controller have Over Voltage protection if the Max input is over 150? - VictronEnergy