Panels with more bypass diodes

[sailingharry]

Originally Posted by FlyingScot

Let's start with the fact that I never said calculate power loss as a percentage.

Larger wires for the same voltage you get lower voltage drop percentage. This is a fact. Larger wires also have less resistance as measured or stated in ohms per 1000'. 1 Ohm for 10 awg. 0.62 Ohms for 8 awg. Also a fact.

Three panels in series is raising the voltage to carry the same power without increasing the power loss.

So for the record, does a larger wire = less power loss. If not, please explain how.

A re-read of your initial post makes me wonder just why I responded. You seem to understand the reduced power loss from series. Maybe I responded to the wrong post, or mixed in thoughts form another post. Sorry...


Indeed, larger wires make less loss. And adding panels in series makes more power with no additional losses.

[noelex 77]

Originally Posted by FlyingScot

One thing I haven't seen mentioned is the larger the difference between MPPT input and output the less efficient the MPPT is.

This graph for an Outback controller shows the difference.

As the input voltage from the solar panel array is increased (with series connection), the efficiency reduces (as you would expect).

[sailingharry]

Originally Posted by noelex 77

This graph for an Outback controller shows the difference.

As the input voltage from the solar panel array is increased (with series connection), the efficiency reduces (as you would expect).

A lot to be gleaned there.
* At very low power (less than 10% of MPPT rated power), the efficiency sucks. That's the startup losses.
* As power increases, efficiency drops.
* Peak efficiency is at around 35% of MPPT rated power.
* As input voltage increases, efficiency drops (noelex's point)
BUT...the key take away is the efficiency (after the low power disaster) is amazing. The differences from best to worst are about 98 to about 95. Worst case, in a 400W panel, you are losing 20W in the controller, probably closer to 12-15, and the difference between best case and worst case (3%) is about 12W. That's why PWM is great if your panel Vmp matches your battery volts (and at VERY low power levels), but why MPPT is great all other times.

[s/v Jedi]

Originally Posted by noelex 77

This graph for an Outback controller shows the difference.

As the input voltage from the solar panel array is increased (with series connection), the efficiency reduces (as you would expect).

And as the battery voltage increases, efficiency increases as well. That’s why 48V.

[s/v Jedi]

Originally Posted by sailingharry

A lot to be gleaned there.
* At very low power (less than 10% of MPPT rated power), the efficiency sucks. That's the startup losses.

Yes, and you multiply startup losses times the number of controllers.

I had one of these before switching to Victron. The fan was like a jet engine, must have burned a lot of energy into heat and getting rid of the heat.

[FlyingScot]

Originally Posted by s/v Jedi

And as the battery voltage increases, efficiency increases as well. That’s why 48V.

Unless the entire boat runs on 48V, which is doesn't there are losses to down convert to 24v and 12v. There is no way around that.

DC-DC converters lose 12-15%.

So how is your boat setup to avoid these down voltage conversions?

[sailingharry]

In general, there are a few big draws on a boat. The inverter being the biggie, but the fridge is another. After that, the loads are rather trivial. Winches and windlasses are high power (so a poor choice for a DC/DC converter), but low energy, so losses aren't a major issue (but these items do benefit from an upgrade -- even if the cost may not justify it). If you convert these (relatively few) high power/energy devices to the new voltage, the losses in powering the others are fairly trivial (if my stereo goes from drawing 15W to 18W, who notices?).
On my boat, if I removed the inverter and fridge (and ideally, the winch, windlass, autopilot, and chartplotter) my daily 12V demand would drop from around 200Ah to maybe 50Ah or less -- a 15% efficiency hit is only 8Ah/day. In addition to low energy, it's also low power -- I doubt I'd need more than a 20A DC-DC converter, and if I added a 50Ah battery (lawn mower size) as a surge absorber, I could use a 5A converter.

[FlyingScot]

Originally Posted by s/v Jedi

Yes, and you multiply startup losses times the number of controllers.

I had one of these before switching to Victron. The fan was like a jet engine, must have burned a lot of energy into heat and getting rid of the heat.

Do you multiply the losses times the number of controllers? I don't think so.

The graph shows that by 3-10% input power depending on input voltage the efficiency is alread over 90%.

So a single 435WP panel hooked to a 100/50 which Victron says is max 700w that would mean that by approximately 21W it is operating above 90% efficiency.

Two series 435Wp panels and hook to the same controller and from the looks of that diagram it takes approximately double the input power to reach 90% efficiency.

Conclusion: Both single and series behave almost IDENTICALLY in regards to start up losses.

Actually I'm being generous here, as the curve widens as the input goes up slightly from the 90% giving the single panel setup an advantage.

Assumpitons: Victron curve is similar to Outback Flexmax. Use the same controller on both scenarios.

I didn't compare 3 panels because that would require a larger controller and the startup numbers to reach 90% efficiency would go up.

Can you explain how you think more controllers means more startup losses?

[noelex 77]

Originally Posted by FlyingScot

Assumpitons: Victron curve is similar to Outback Flexmax. Use the same controller on both scenarios.

I have never seen similar data from Victron, but having owned both an Outback controller and several Victron controllers I suspect there are some differences.

The Outback has a very high parasitic draw even for a very large controller. In other words, once the controller has woken up, the power to run the tracking and conversion circuitry is quite high even if this solar panel has zero output. This is what causes the very steep drop off in efficiency with low input powers.

The Victron controllers are the opposite with a very low parasitic draw. This is one reason why they are ideal for installations with multiple controllers. The parasitic draw can reduce the efficiency when multiple controllers are used although the difference between multiple small controllers and one larger controller is usually small.

The ultimate conversion efficiency is much harder to gauge without some controlled experiments. The all important tracking efficiency is better on the Victron controllers (at least compared to much older Outbacks), but the adjustable start up parameters are better than the non adjustable (and rather pessimistic value) that is part of Victron’s algorithm.

[jsanton]

I didn’t read the entire thread but I do have a novel, I think, solution for partial shading on my vessel.
First, SV Jedi knows his stuff.
Second, I’m a BSEE who studied solar engineering in the 70s. Never worked in the field.
On my vessel I have 3 panels in series and one mppt. I have a switch which selects whether or not the panel under the radar is included. Requires some thought, but it’s a cheap easy shade manager as it’s mounted near the panels.
On my house, each panel has it’s own inverter.
On my RV, I have only one panel, but it’s easily movable to chase around the sun.
So, I think the best fix is situational.

[Pete7]

Originally Posted by jsanton

I didn’t read the entire thread but I do have a novel, I think, solution for partial shading on my vessel.
On my vessel I have 3 panels in series and one mppt. I have a switch which selects whether or not the panel under the radar is included. Requires some thought, but it’s a cheap easy shade manager as it’s mounted near the panels.

Why didn't you read the whole thread?

Why have you mounted a radar above a solar panel?

What sort of differences do you see with no shade, shade from the radar and then using the switch?

Pete

[jsanton]

Hi Pete!
Busy retired EE here…
With panels in series I find the current drops significantly if only a portion of the cells are under shade.
I have a radar mast at the stern quarter. The 3 series panels (100w each) are mounted over the helm on the Bimini. There’s about a foot separation between the edge of the closest panel and the radome center. It’s roughly a 12” diameter dome. Close, but not quite above.
A bit of shade on panel 3 and I get almost no power from the set if all 3 are used. Switch to 2 and I get the full 200w.

[s/v Jedi]

Originally Posted by jsanton

Hi Pete!
Busy retired EE here…
With panels in series I find the current drops significantly if only a portion of the cells are under shade.
I have a radar mast at the stern quarter. The 3 series panels (100w each) are mounted over the helm on the Bimini. There’s about a foot separation between the edge of the closest panel and the radome center. It’s roughly a 12” diameter dome. Close, but not quite above.
A bit of shade on panel 3 and I get almost no power from the set if all 3 are used. Switch to 2 and I get the full 200w.

100W panels? Flexible? Do they have bypass diodes at all? You could simply mount a diode per panel externally.

In a series setup with partial shading, voltage should drop according to shaded strings/panels but current shouldn’t drop.

[jsanton]

Jedi,
Flex panels, no bypass diodes.
I thought the body diodes would function as bypass diodes, but no.
The panels do have discrete blocking diodes.
I doubt the forward voltage for the panel would drop low enough for an external bypass diode to conduct.
Are there flex panels made with bypass diodes? My panels are several years old. I still get good power from them, but I expect to need to replace soon.
Cheers!
John

[noelex 77]

Originally Posted by jsanton

Jedi,
Flex panels, no bypass diodes.
I thought the body diodes would function as bypass diodes, but no.
The panels do have discrete blocking diodes.

Almost no panels have blocking diodes as standard. They decrease the STC output numbers and no manufacturer wants that. In addition, blocking diodes are only very rarely a good idea and easily added later in the rare cases when they are helpful.

On the other hand, bypass diodes are essential to prevent hotspots and damage to the solar panel. Manufacturers need to install these to ensure panel durability. The bottom line is that if you see diodes installed by the solar panels manufacturer, they are almost always bypass diodes and not blocking diodes.