Upsizing Shaded System

[Blackhat]

I have an offgrid network repeater box between my house and ISP, and currently it requires regular battery swaps to maintain.

The solar setup is just a 100W panel connected to a Renogy PWM charge controller. It produces 180 Wh on a clear day near winter solstice, mostly because it's right up against a treeline that shades it starting around noon. I recently did some optimization work on the position and angle and there doesn't seem to be much juice left to squeeze. Moving to another location is out of the question for a couple reasons.

From a load side it uses ~11.5 watts 24/7, which is 276 Wh per day.

That leaves me needing another 100Wh/day at least. The obvious options are a switch to MPPT or the purchase of another 100W panel, and those options seem to be about the same cost ($80 to $100). Which would be a better choice?

Since I only need ~10A of charging max, is there a lower cost MPPT that I should try?

 

[rmaddy]

I don't think buying an MPPT (and nothing else) is going to help. A 100W panel needs at least 3 solid hours of sun to produce 276Wh. The type of controller isn't going to change that. More solar will give you more Wh with everything else being equal.

 

[MichaelK]

The better option I think would be to get both additional panels AND the MPPT controller. Then you can position the panels in a sunny location a hundred feet or more from the repeater, but panels wired in series for higher voltage can send the raw solar power much further distances than with what a PWM controller can do. Let's say you wired three panels in series, and mounted them 150feet away from the controller. You'd get....

 

[Rednecktek]

As someone who has similar issues, I figured that a 100w panel on a PWM would feed my 7w of lights at night. Not so much, and the last month and a half my meter has been telling me that I've only been getting about 6-8Wh per day.

My shed system has 2x 100w panels and a MPPT controller and yesterday I hit a new record (for the month) of 14w.

The MPPT controller wouldn't help enough to compensate for the shading. For the money, a second panel would double your power generation, but a MPPT controller Might get you another 20% at best. Since the amperage on those is so low you can run wire anywhere, so there's the possibility of sticking it into a little better location.

I'd be willing to bet that if you stuck a meter in there, you'd find that your panels are just barely reaching charging voltage (14v or so) and nowhere near the panel VoC (probably 20-ish volts) most of the day.

 

[Hedges]

Shop around for something like a 300W or so panel used, about $100.
It's voltage will be too high, add an MPPT.

I like two panels of different orientations, one South East and one South West, wired in parallel. That spreads power over more hours.

Determine what charge current battery wants, don't exceed what it can handle. Excess PV and an SCC that regulates current to desired amount would be good.

Find an Insolation calculator, determine what panel tilt gives most power on worst day of the year. Size PV array accordingly. Consider how many days without sun, size battery accordingly.

 

[houseofancients]

Shop around for something like a 300W or so panel used, about $100.
It's voltage will be too high, add an MPPT.

I like two panels of different orientations, one South East and one South West, wired in parallel. That spreads power over more hours.

Determine what charge current battery wants, don't exceed what it can handle. Excess PV and an SCC that regulates current to desired amount would be good.

Find an Insolation calculator, determine what panel tilt gives most power on worst day of the year. Size PV array accordingly. Consider how many days without sun, size battery accordingly.

or the santan / ebay 250w panels for ~ 50 USD

 

[Whinny]

As Rednecktek said adding another panel and you double your output, change to a MPPT controller and you add maybe 20%. The MPPT controller also has a higher idle draw than PWM.

 

[Blackhat]

Thanks for the input everybody!

MPPT = 20% is a useful figure to work off. And I didn't realize they had higher idle draw which is important in a low power system like mine. Sounds like replacing a PWM with MPPT only makes sense when you're around 500 watts and/or needing a series connection. Though I would hold out for MPPT if building a new system.

Unfortunately moving it away from the trees is less appealing than buying the panels required to feed the system in the current location for non-technical reasons.

The more I think about it, if I'm generating solidly over 50% of my usage adding another 100W panel is a no brainer. It's basically no work, fairly low cost and is guaranteed to work.

A lot of the other tricks are cool and great considerations on future systems, but a bit overkill for my modest power draw. I certainly would not buy the system I have now if starting over. But that's why it's useful to start small and at this point I've only overpaid by a little bit.

 

[Blackhat]

As someone who has similar issues, I figured that a 100w panel on a PWM would feed my 7w of lights at night. Not so much, and the last month and a half my meter has been telling me that I've only been getting about 6-8Wh per day.

My shed system has 2x 100w panels and a MPPT controller and yesterday I hit a new record (for the month) of 14w.

The MPPT controller wouldn't help enough to compensate for the shading. For the money, a second panel would double your power generation, but a MPPT controller Might get you another 20% at best. Since the amperage on those is so low you can run wire anywhere, so there's the possibility of sticking it into a little better location.

I'd be willing to bet that if you stuck a meter in there, you'd find that your panels are just barely reaching charging voltage (14v or so) and nowhere near the panel VoC (probably 20-ish volts) most of the day.

Man, that's rough. I guess your shed is straight up in the middle of the woods or something? Are you thinking you can get some sun to the panels, or is it a lost cause?

I'll try to check Voc next time I get a chance.

 

[12VoltInstalls]

if I'm generating solidly over 50% of my usage adding another 100W panel is a no brainer. It's basically no work, fairly low cost and is guaranteed to work.

Yes. Mostly. 300W total without the mppt is probably more practical imho. Because it assures the battery is up and the multi-directional hedge helps more.

Another thought: where is your repeater? On a pole? High? On a building? If your repeater is on a mini tower is that tower
1) robust enough to support two 100W panels?
2) more exposed to the sun either longer or less shaded?

I think you know what I’m suggesting.

There’s a piece of property that’s near me. Not for sale per se but the situation…makes it obtainable. I’m considering it but I would need a cell booster or something (no wireless internet around here). With a little playing with my phone I noticed that 40-50 feet nearly vertically up from the usable property there’s a solid 75% signal. It occurred to me a tripod ‘tower’ would provide good cell reception AND a mounting point for a SE and SSW arrays.

Would your situation accommodate a smaller scale of something like this?