New solar questions/ponderments/opportunities/gotchas

[khigh]

I'm looking to get ahead of schedule for my solar. I have an opportunity to get some older 250W panels for hardly nothing. Specwise for their age, they should be at about 90% capacity or 225W. the price is sure right - my first impulse is to get all I can physically put on the trailer.

But here's the thing and it has to do with my location and region and camping style. I mostly go out in warm weather centered on North GA and the Southern Appalachians and stay in primitive, unimproved, and boondock type campgrounds. Short version: sunlight is in short supply. Most places you can track down a little patch of sunshine if you put your mind to it, but largely under canopy,

Is it even worth doing? It seems like if I'm not getting direct sunlight, I'm not going to be getting much, and if I make it a point to stay under direct sunlight, it would offset the solar gain by requiring more air conditioning.

Another idea might be to not mount them to the top, but make a portable frame system and separate the camping spot and the solar harvesting. Of course then there's something else you have to plan on carrying unless I possibly made them detachable top mount - kind of a hybrid system.

Anyone else faced this challenge and come up with a plan?

[Shadow Catcher]

What is the voltage coming from the panels, I am willing to bet they are high voltage meant for a grid tie system. Not a problem if they are, with the exception that they require a MPPT controller. So what are the specs?

[dustboy]

I reckon you're not going to want to go lugging around your 225w panels to find a patch of sun every time you move sites. Mine is a 190w and it's huge and about 60 lbs. Plus it leaves them vulnerable to theft.

How much power do you need? Can you fit enough panels on the roof to cover your usage if they are outputting 10-20%? Certain types of panels have better output in low-light situations, I forget which, mono or polycrystalline or whatever.

[khigh]

What is the voltage coming from the panels, I am willing to bet they are high voltage meant for a grid tie system. Not a problem if they are, with the exception that they require a MPPT controller. So what are the specs?

Good question and the first one I asked as well. They're 24 Volt, so I'd have to make arrangements for that - either a step down to 12, or a 24V inverter, which are surprisingly affordable.

[khigh]

I reckon you're not going to want to go lugging around your 225w panels to find a patch of sun every time you move sites. Mine is a 190w and it's huge and about 60 lbs. Plus it leaves them vulnerable to theft.

How much power do you need? Can you fit enough panels on the roof to cover your usage if they are outputting 10-20%? Certain types of panels have better output in low-light situations, I forget which, mono or polycrystalline or whatever.

It's kind of a catch-22 with power. I don't use a lot unless I use AC and then it's not going to cut it regardless, but could certainly save fuel otherwise. The main draw other than that is a tower fan, a light bulb if I'm not being lazy by not using my LED lights, charging a laptop every couple days, and then phones and tablets. I have a microwave I can take or leave, but it's always a bonus depending on the amount of power available - never something I'd depend on to eat. There's no refrigeration or electric coffeemaker.

It would also be called upon to power radio equipment in an emergency situation (ARES), but in those cases I could actively seek out full sun if available.

I'm kind of leaning toward "It's better to have it than not to have it even if it doesn't do that great for my primary camping needs" so that I can expand the usefulness of it. Possibly even make detachable roof mounts for even more versatility.

[jss06]

What is the voltage coming from the panels, I am willing to bet they are high voltage meant for a grid tie system. Not a problem if they are, with the exception that they require a MPPT controller. So what are the specs?

Good question and the first one I asked as well. They're 24 Volt, so I'd have to make arrangements for that - either a step down to 12, or a 24V inverter, which are surprisingly affordable.

A mppt charge controller would be way more efficient then a step down converter. It will also not over charge your batteries.

[jss06]

What is the voltage coming from the panels, I am willing to bet they are high voltage meant for a grid tie system. Not a problem if they are, with the exception that they require a MPPT controller. So what are the specs?

Good question and the first one I asked as well. They're 24 Volt, so I'd have to make arrangements for that - either a step down to 12, or a 24V inverter, which are surprisingly affordable.

A mppt charge controller would be way more efficient then a step down converter. It will also not over charge your batteries.

[khigh]

What is the voltage coming from the panels, I am willing to bet they are high voltage meant for a grid tie system. Not a problem if they are, with the exception that they require a MPPT controller. So what are the specs?

Good question and the first one I asked as well. They're 24 Volt, so I'd have to make arrangements for that - either a step down to 12, or a 24V inverter, which are surprisingly affordable.

A mppt charge controller would be way more efficient then a step down converter. It will also not over charge your batteries.

I'm certainly no expert, so I'm honestly asking, but some quick googling puts a conventional 24V controller at $70 and a 24V 900W inverter at $90, where mppt charge controllers start in the high $200s. Even assuming what you're saying is I could do 12V at the battery instead of 24V, it sounds like the more expensive route.

Am I looking at it wrong, or are there other advantages?

[MtnDon]

A so called 24 volt PV panel actually puts out about 30 volts or more at maximum power. On a cold day when the sun first hits the panel the voltage can reach as high as 40 volts. Can the 24 to 12 converter you looked at handle that voltage? IIRC, there are many that can not even safely handle over 28 volts.

The panel specs will have all the data listed. If you are lucky the panels will still have readable labels with the Vmp, Voc, Imp, Isc, etc all listed. That is important data that is needed in order to match equipment to the panels. Then, one panel or more? Parallel or series if more than one.

Yes an MPPT controller will cost close to $300. A PWM controller can be substantially less but if used with the high voltage panels at best will waste a lot of the power and be carrying around un-necessary weight.

Would the source of these panels mind if you took several and sold them, then used the proceeds to buy new "12 volt" panels and a PWM controller? Or sell some and buy a good MPPT controller? Don't even waste time looking at any of the cheap Chinese MPPT controllers. The real cheap ones are not even MPPT; yes people lie.

[khigh]

I've apparently confused at least two people so I'll clarify.

I was never trying to convert 24 to 12v on the charging side.

When I mentioned it, it would have been on the load side, but the 24V inverter is so reasonable, I think I'd go that route, so 12V probably doesn't factor in anywhere.

[MtnDon]

Okay, you have me totally confused.

A more detailed word picture or a diagram of what you are thinking of would help me a lot. Can't say about others.

I envision the high voltage panels feeding some batteries, which then feed an inverter or some direct DC loads. If you have PV panels you need a battery (or 2, 3...) in between the PV and the inverter. If you have a battery you need a charge controller to control the charge rate.

[khigh]

It's my best understanding that's the exact thing I'm describing.

Panels > charge controller > batteries > load

I'm not even aware of another way to do it. What other options are there?

[MtnDon]

What took a while to sink in here is that you mean to use a 24 volt battery system. That was unstated and because almost everyone else uses 12 VDC in a trailer it never occurred to me even though I run a cabin on a 24 VDC system. [slap forehead with palm of hand]

Perfectly feasible to do that with a PWM controller than can handle the volts, amps and the watts that the panels put out.

[khigh]

Oh - yeah

Just hook up in series instead of parallel.

The options come into play for output - whether to drop that to 12 or commit to 24, but everything involving the panels and charger and batteries would be 24V in this case.

[MtnDon]

Just hook up in series instead of parallel.

Not clear again as to what will be connected in series; panels or batteries. Batteries for the 24 VDC I guess.