Upgrading solar (1 Viewer)

[swampsnake]

I'm wondering how straightforward is it to upgrade the solar generating capacity on coachbuilt motorhomes. Most seem to have a single solar panel, 100w or thereabouts. Is it fairly straightforward to swap that to a more powerful panel, plus an extra panel, and replace the leisure batteries with 2 lithium ones?

 

[XxAnthxX]

Roof space and existing cable size permitting, it shouldn’t be a problem....the only thing you might have to think about is if your solar controller has a charging profile for lithium batteries, if not that would need changing too. If you went for lithium that may also mean changing the vans onboard charger too.

 

[pappajohn]

Why remove existing only to replace it with a larger one plus a new one.... Just add two new ones, or one extra large one, and keep the existing panel.
Your only limit is roof space.

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[Sundowners]

Why remove existing only to replace it with a larger one plus a new one.... Just add two new ones, or one extra large one, and keep the existing panel.
Your only limit is roof space.

Given the roof space (which we don't have) I would leave the existing one, complete, exactly as it is and fit whatever i could fit on the roof as a separate system.
Living in Portugal we are going to make do with just the one--- but we do have three batteries to help us through those cloudy days!!!

 

[swampsnake]

But wouldn't two odd sized panels create an unbalanced system? I know nothing on this subject! I believe the inverter would also have to be changed if using lithium.

 

[DBK]

But wouldn't two odd sized panels create an unbalanced system? I know nothing on this subject! I believe the inverter would also have to be changed if using lithium.

Most of the panels used on MHs are all the same voltage so you can wire then in parallel without problem. If you want to be absolutely sure just count the number of cells, which are the rectangular or octagonal shapes which make up the panel. Panels with the same number of cells will have the same voltage.

I suggest plan on a new controller and an extra panel or two and see how you get on. You may find you don't need lithium batteries - most of get on fine without them. As long as the controller (MPPT type of course) has a lithium battery profile in the settings it will be future proof. To install lithium later you will probably need to change the mains charger and fit a battery to battery charger because the vehicle system will be designed for lead acid. This all gets expensive hence my suggestion of a suck it and see approach.

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[Sundowners]

But wouldn't two odd sized panels create an unbalanced system? I know nothing on this subject! I believe the inverter would also have to be changed if using lithium.

The controller,old and new, would just live together charging the battery bank side by side----- it might not be exact enough to give the ultimate charging for the fanatics!! But it will work.
Bit like having a complete spare system incase one has a fault!!
I know nothing about lithium batteries---- sound too complicated and temperamental to me!!

 

[swampsnake]

So is it possible to have a panel with the same number of cells but a higher power output?, and if the number of cells are the same, then the voltage is the same, so the cables should handle the power? I would be happy to upgrade individual components but having to replace the wiring would be a nightmare.

 

[XxAnthxX]

The issue won’t be the cables handling the power.....it will be the voltage drop over the length of the cable run.

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[pappajohn]

So is it possible to have a panel with the same number of cells but a higher power output?, and if the number of cells are the same, then the voltage is the same, so the cables should handle the power? I would be happy to upgrade individual components but having to replace the wiring would be a nightmare.

Most panels are around 20 volts but a slight mismatch won't make any difference as the controller brings it to a nominal 12v.
Connected in parallel (Pos to Pos wires, Neg to Neg wires) the voltage remains the same but the amps from each panel are added together.
So, three x 100watt panel will be
12v 300watts......or a theoretic amperage of 25amps

 

[DBK]

So is it possible to have a panel with the same number of cells but a higher power output?, and if the number of cells are the same, then the voltage is the same, so the cables should handle the power? I would be happy to upgrade individual components but having to replace the wiring would be a nightmare.

Yes although as nicholsong suggests you could connect a second panel to its own controller. This has advantages because it means if one panel is shaded the other will continue to produce maximum power - but it will mean running extra cables. It also assumes the existing controller is an efficient MPPT type which you can't assume - converters have been known to cut corners!

However, even if the existing wiring is a bit thin it probably won't matter in the real world. When the sun is shining strongly in high summer a bit of loss in the cables won't be significant. When light levels are low the current in the wires will be low and that means the loss will also be low. Power loss in a wire increases with the square of the current so losses as a percentage of the total power are much lower with reduced current flow.

I

 

[Sundowners]

Correct me if I am wrong!!
But if you connect the panels to increase the voltage and keep amps the same rather than to increase the amps and remain at 12v -- the power loss would be less on the same size cable---- higher volts req smaller cable to move the same power??

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[pappajohn]

Correct me if I am wrong!!
But if you connect the panels to increase the voltage and keep watts the same rather than to increase the watts and remain at 12v -- the power loss would be less on the same size cable---- higher volts req smaller cable to move the same power??

Yes but, doing it in series you don't increase the watts, only the voltage so you have 36v but only 80watts from 3 x 80watt panels

 

[DBK]

Correct me if I am wrong!!
But if you connect the panels to increase the voltage and keep watts the same rather than to increase the watts and remain at 12v -- the power loss would be less on the same size cable---- higher volts req smaller cable to move the same power??

Yes, that's what I did as the cables in mine were a bit thin. But it doesn't work well if the panels are different sizes as the smaller panel will restrict the maximum current flow.

 

[XxAnthxX]

Yes in series the voltage increases but the amps from ‘each’ panel remain the same.

This site explained mixing panels in both parallel and series quite well....

Mixing solar panels – Dos and Don’ts • SOLAR POWER SECRETS

Mixing Solar Panels: Discover Now Dos and Dont's of Mixing the Same Types or Different Types of Solar Panels. Act Now to Save Your Money!

solarpanelsvenue.com

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[autorouter]

Correct me if I am wrong!!
But if you connect the panels to increase the voltage and keep amps the same rather than to increase the amps and remain at 12v -- the power loss would be less on the same size cable---- higher volts req smaller cable to move the same power??

Correct. But you must make sure the controller can handle the higher voltage. Many of the smaller systems have a controller with a voltage limit of around 35v. Two panels in series would exceed that voltage. There's plenty of controllers that will handle the voltage, but you have to check the specs.

 

[autorouter]

So is it possible to have a panel with the same number of cells but a higher power output?, and if the number of cells are the same, then the voltage is the same, so the cables should handle the power? I would be happy to upgrade individual components but having to replace the wiring would be a nightmare.

The power depends mostly on the total area of the cells. In larger panels each cell is larger than the cells of smaller panels. The cable thickness is decided by the current flow (amps) rather than the voltage. If you really really want to not change the wiring, you could wire two panels in series. This means the voltages add but the current (amps) stays the same, so the wire thickness can stay the same.

Since you are intending to more than double the solar power, the existing solar controller will probably need upgrading anyway. You could sell the old panel with its controller. You will need a high voltage controller, but there's plenty of good ones available. For example the Victron SmartSolar 75/15 will handle 75V and panels up to 200W total. There's a wide range of similar ones for larger or smaller powers and voltages.

Also it's best to get MPPT type rather than PWM if you want to get the best yield when it's cloudy, or in early morning/late evening.

 

[Sundowners]

Yes but, doing it in series you don't increase the watts, only the voltage so you have 36v but only 80watts from 3 x 80watt panels

Yes but, doing it in series you don't increase the watts, only the voltage so you have 36v but only 80watts from 3 x 80watt panels

But when those 36v go through your mppt it will give you the same power to the battery---- it is capable of turning volts and watts to the correct power to charge battery. That is one reason to insist on mppt, it can normally handle a wider range of power.

Another advantage of connecting solar panels to get higher voltage is that when light is poor, a"12volt " panel will produce ,say, 7volt--- this not enough to charge---- but connecting 3 panels together you would get 21 volt, this would give you a charge------ that is how I understand it??

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[autorouter]

Another advantage of connecting solar panels to get higher voltage is that when light is poor, a"12volt " panel will produce ,say, 7volt--- this not enough to charge---- but connecting 3 panels together you would get 21 volt, this would give you a charge------ that is how I understand it??

A '12 Volt' panel has a maximum voltage of 18 to 26 volts. A controller needs about 5V more than the battery voltage to convert the power. It's called '12 Volt' because it's not enough for 24 volt batteries. Larger panels have a voltage of 35 to 45 volts, suitable for 24V batteries. But with a suitable controller they are fine for 12V batteries too.

Two '12Volt' panels in series can easily exceed the maximum voltage of some controllers, which is often 35V or less.

Three 80W panels will produce 240W total whichever way they are wired, series or parallel. Series gives 3 times the voltage but the same amps. Parallel gives 3 times the amps but the same voltage. Power is volts x amps, the same for both.

 

[Minxy]

Most panels are around 20 volts but a slight mismatch won't make any difference as the controller brings it to a nominal 12v.
Connected in parallel (Pos to Pos wires, Neg to Neg wires) the voltage remains the same but the amps from each panel are added together.
So, three x 100watt panel will be
12v 300watts......or a theoretic amperage of 25amps

Do you mean join them individually to the existing cable?

 

[autorouter]

Do you mean join them together? That would surely be in series not parallel?

All the positives connected together, all the negatives connected together - that's parallel.
Connected one after another, in a string, positive to negative - that's series.

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[Minxy]

All the positives connected together, all the negatives connected together - that's parallel.
Connected one after another, in a string, positive to negative - that's series.

See my edited post, I pressed 'post reply' before I'd finished so just shortened/reworded it instead ... you 'nabbed' it before I'd done so.

I was concerned whether the cable itself would be good enough for the extra input from the panels being joined together as we don't know what the cable is that's already installed.

 

[RobL]

But wouldn't two odd sized panels create an unbalanced system? I know nothing on this subject! I believe the inverter would also have to be changed if using lithium.

Odd sized panels aren't a problem.

 

[RobL]

See my edited post, I pressed 'post reply' before I'd finished so just shortened/reworded it instead ... you 'nabbed' it before I'd done so.

I was concerned whether the cable itself would be good enough for the extra input from the panels being joined together as we don't know what the cable is that's already installed.

Cables should have the size embossed on them. If not(cable may need replacement) there are online calculators to work out the size of cable required related to panel output and length of cable required to reach the controller.

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