anyone know a way to slightly reduce the voltage of solar panels?

[texasjames]

Yep. There is a tradeoff. When you physically attenuate the panel, it attenuates the voltage and amperage which reduces the wattage. My little pump runs on 20 watts, so it's never starved for wattage from the 100-watt panel that is shaded to about 60 watts. There may be a better way to do this but ANYTHING you use (resistors, diodes, etc..) to attenuate the panel is going to attenuate the wattage, voltage and amperage to some extent. Basically, you just have an equipment mismatch that is going to reduce the efficiency of the whole system. You can trade up on your controller/charger or downsize your panels or leave the pancho in place and call it a day. P.S. you can use aluminum foil or an old dashboard shade or plastic matt. I recommend something reflective as the excess heat can damage your panels.

 

[texasjames]

looks like it's gonna charge my unit from 50% to 100% in just under 3 hours. I guess I can live with that.

 

[wme]

OK variation of blocking, go out at high noon and mount a panel in the ground that blocks the needed amount of sun. As the sun moves the panel will unshade and it will make more power, but too much power because the sun is not at the max power point.

 

[fafrd]

looks like it's gonna charge my unit from 50% to 100% in just under 3 hours. I guess I can live with that.

So to be clear, did you bypass teo substrings through a junction box at the back of the panel or did you block two substrings using cardboard or tape?

Bypassing 2 substrings through a junction box is safe and drops Voc_worst-case by 2/12ths (to 50.7Voc nominal @ 25C) but blocking with shade can still expose your SCC to Voc of 72VDC or higher in the morning before the startup.

If you don’t need 33% of your potential power now in summer, I suspect you’ll need it all the power you can get by winter.

With one of these new boost mppt SCCs you will harvest 100% of available power all year long at zero risk of damaging your SCC.

Of course, you could just wait until you’ve destroyed the one you have before buying anything new (or try to sell it used to offset the cost of a new boost mppt SCC designed to do exactly what you are aiming for),

 

[texasjames]

OK variation of blocking, go out at high noon and mount a panel in the ground that blocks the needed amount of sun. As the sun moves the panel will unshade and it will make more power, but too much power because the sun is not at the max power point.

that's......kinda brilliant

 

[gnomie]

OK variation of blocking, go out at high noon and mount a panel in the ground that blocks the needed amount of sun. As the sun moves the panel will unshade and it will make more power, but too much power because the sun is not at the max power point.

Yep, I tried that one too and you're right, the pump starts earlier and runs later but I ran into the maintenance issue of having to adjust the shade panel seasonally as the sun's track moved. I also found that the shade had to be pretty large since the panel face was still exposed to the ambient light reflecting off of everything around it. Eventually I just gave up and taped the shade to the panel surface. More reliable. All my micro system was designed to do was keep a livestock trough full and it does that with some overflow nearly every day.

 

[fafrd]

that's......kinda brilliant

You have not stated what battery voltage you are charging.

This $48 Boost MPPT charger from Amazon can boost your 1S panels to charge 48/60/72V batteries: https://www.amazon.com/dp/B0B4SL5C2...jbGlja1JlZGlyZWN0JmRvTm90TG9nQ2xpY2s9dHJ1ZQ==

Free return rights so you can buy it and try it at no cost.

Boost-chargers for 36V batteries are a little harder to find on Amazon but they do exist: https://www.amazon.com/Controller-A...cphy=9032079&hvtargid=pla-1808085806380&psc=1

 

[fafrd]

Yep, I tried that one too and you're right, the pump starts earlier and runs later but I ran into the maintenance issue of having to adjust the shade panel seasonally as the sun's track moved. I also found that the shade had to be pretty large since the panel face was still exposed to the ambient light reflecting off of everything around it. Eventually I just gave up and taped the shade to the panel surface. More reliable. All my micro system was designed to do was keep a livestock trough full and it does that with some overflow nearly every day.

You are direct-connecting your string to a resistive load (before the motor starts spinning) so you can never reach Voc when there is any current available and your motor cannot be damaged by early-morning voltage.

Trying that trick with an SCC is riskier. There is risk associated with Vmp during high-production hours which can be mitgated with bypassing enough substrings or even by shading.

But at startup, only bypassing substrings through the junctions at the back of the panel can prevent Voc reaching the SCC inputs before solar energy is sufficient to start the charger…

 

[gnomie]

You are direct-connecting your string to a resistive load (before the motor starts spinning) so you can never reach Voc when there is any current available and your motor cannot be damaged by early-morning voltage.

Trying that trick with an SCC is riskier. There is risk associated with Vmp during high-production hours which can be mitgated with bypassing enough substrings or even by shading.

But at startup, only bypassing substrings through the junctions at the back of the panel can prevent Voc reaching the SCC inputs before solar energy is sufficient to start the charger…

I'm not using a controller, charger or inverter in my micro system. The panel is connected directly to the brushless pump motor. The motor starts running when there is enough light and speeds up as the light increases. Without shading the panel, it would push 18V to the 12V motor and probably fry it. I tried some smaller (13V) panels, but they didn't produce enough wattage. Tin foil and tape. Low tech solution.

 

[fafrd]

I'm not using a controller, charger or inverter in my micro system. The panel is connected directly to the brushless pump motor. The motor starts running when there is enough light and speeds up as the light increases. Without shading the panel, it would push 18V to the 12V motor and probably fry it. I tried some smaller (13V) panels, but they didn't produce enough wattage. Tin foil and tape. Low tech solution.

Yes, and a good solution for your use-case (direct-connect to a DC motor).

Vmp and peak power production is your only concern - you cannot ever reach Voc.

Different story when feeding an SCC with maximum voltage ratings on the DC inputs that can damage transistors if exceeded even when no current is flowing…

 

[efficientPV]

I was running a 6V outdoor fan for my wife with half a 100W panel and a resistor in series. It is a Coleman fan designed to work on 4 D cells. Was looking for a quick solution. This year I mounted a buck converter in the base of the fan and used full panel voltage. She likes that a lot better. Now when a cloud passes over the speed never changes. There are buck converters for $4 that can be adjusted to 12V and that pump will run a lot longer thru the day.

 

[texasjames]

You have not stated what battery voltage you are charging.

This $48 Boost MPPT charger from Amazon can boost your 1S panels to charge 48/60/72V batteries: https://www.amazon.com/dp/B0B4SL5C2...jbGlja1JlZGlyZWN0JmRvTm90TG9nQ2xpY2s9dHJ1ZQ==

Free return rights so you can buy it and try it at no cost.

Boost-chargers for 36V batteries are a little harder to find on Amazon but they do exist: https://www.amazon.com/Controller-A...cphy=9032079&hvtargid=pla-1808085806380&psc=1

its a lion energy safari me - 30-60 volts but the mpv must be 36+

 

[kendive]

I have 2 solar panels, they are 275 watts, 38 VOC and VMP 31
what I NEED (for a specific solar generator) is:
watts: 550
VMP > 36
VOC < 60

if I connect them in series, my volts reading is about 64
so I assume that covers the requirement "VMP > 36"
but violates "VOC < 60"

is there any way I can make them work? maybe a way to slightly lower the volts to just under 60?

I have 2 solar panels, they are 275 watts, 38 VOC and VMP 31
what I NEED (for a specific solar generator) is:
watts: 550
VMP > 36
VOC < 60

if I connect them in series, my volts reading is about 64
so I assume that covers the requirement "VMP > 36"
but violates "VOC < 60"

is there any way I can make them work? maybe a way to slightly lower the volts to just under 60?

Add a long wire run. That will reduce the voltage.

Voltage Drop Calculator

This free voltage drop calculator estimates the voltage drop of an electrical circuit based on the wire size, distance, and anticipated load current.

www.calculator.net

.

 

[fafrd]

its a lion energy safari me - 30-60 volts but the mpv must be 36+

The manual states:

‘PV charge range 30-60 VDC; Solar panel must be >36 VMP <60 VOC’

Have you tried hooking it up to a 1S string? I’m guessing voltage will increase to 36VDC with no current flowing and then the MPPT will kick-in and will drop voltage back to 30 - 31V.

The Voc upper limit is a real limit that can cause damage if exceeded.

The Vmp limit is a soft limit that at most will impact how early the Safari Me starts charging in the morning.

I would definitely try running this at 1S2P if you have not already done so.

If it never starts charging then you need to deliver maximum power at a voltage of > 36V (for whatever strange reason).

Looks like your Safari ME cost you over $2000 - before I did anything that risked exceefing max I put voltage limits and could cause damage, I’d consider it a tiny investment for peace of mind to pick up one of these: https://www.amazon.com/Renogy-Contr...renology+boost+mppt,aps,159&sr=8-3&th=1&psc=1

Set to put out 48V, you’d be all set.

Or alternatively, you can spend only 4.8% of what you spent on your Safari ME rather than 8% by picking up one of the cheap 48V Chinese boosters that can output 48V such this: https://www.amazon.com/color-Charge...mzn1.fos.006c50ae-5d4c-4777-9bc0-4513d670b6bc

Either way, cheap insurance for the piece of mind…

Note that if you do decide to use one of these Boost MPPT chargers to feed your Safari ME, you may need to add a 50mOhm or 100mOhm power resistor in series to make the SCC ‘look’ more like a solar panel…

 

[gnomie]

I was running a 6V outdoor fan for my wife with half a 100W panel and a resistor in series. It is a Coleman fan designed to work on 4 D cells. Was looking for a quick solution. This year I mounted a buck converter in the base of the fan and used full panel voltage. She likes that a lot better. Now when a cloud passes over the speed never changes. There are buck converters for $4 that can be adjusted to 12V and that pump will run a lot longer thru the day.

Good idea. I'm not using the micro pump at this time, but I will definitely grab a buck converter that I can fit in the back of the panel frame when I decide to restore it.

 

[DIYrich]

I have a 12V brushless pump motor that I run off of (1) 100W panel that is rated at about 18V. I'm wired direct from panel to pump so to attenuate the voltage down and keep it from frying my pump I went completely "old school" and taped some cardboard over part of the panel until I got a meter reading of 12V in full sun. Since it's a brushless motor it will still run (slower) at voltages <12V so clouds/partial shade etc... rarely shut the pump down but "hobbling" the panel protects it from spinning up beyond its design parameters and burning out.

Victron Orion TR 12/12-9 will convert 8-17v to 12v.

 

[ungrounded]

I have 2 solar panels, they are 275 watts, 38 VOC and VMP 31
what I NEED (for a specific solar generator) is:
watts: 550
VMP > 36
VOC < 60

if I connect them in series, my volts reading is about 64
so I assume that covers the requirement "VMP > 36"
but violates "VOC < 60"

is there any way I can make them work? maybe a way to slightly lower the volts to just under 60?

By running extra long wire you can drop the voltage. Maybe 40ft?

 

[timselectric]

By running extra long wire you can drop the voltage. Maybe 40ft?

That would only reduce the voltage while loaded.
VOC would not be affected.