Community Forums

1bigmess · 12-08-2014, 01:21 PM

I am very interested in being able to use solar energy for power when boondocking or dry camping. I'm gonna forget that I think I know anything about solar power and PVs for these questions. My only solar experience up to this point is the house I grew up in that was in SoCal had solar hot water, and I have a small set of PVs that I can use to charge a single smallish deep cycle battery for emergency communications that were bought cheap and look the part.

Is there a risk of damage to system components if there are more solar panels than one really needs? Since it might be difficult to judge average daily usage since for me there is no average day, and I have radio equipment I like to use, I am thinking of making an initial purchase that will provide more power than I will need just for convenience purposes, e.g.: six 6 volt batteries, plenty of PVs to charge them even if they won't all fit on the roof, a little bit of custom wiring to provide power for my toys where I want to use them. I am concerned about the extra weight of batteries and PVs.
Or, is it better to use a small generator to provide extra power and get the usual 4 six volt batteries, three to four panels, and deal with needing to use the generator daily or so? I have a very small generator that provides more than enough power to run the radio equipment and charge batteries that I wouldn't mind using when needed as long as there aren't others around that would be bothered by the noise (I think it's a little loud). Considering that I love staying out in the woods, I know I will need a generator due to the trees and terrain blocking direct sun.
Can batteries in a trailer be charged by the towing vehicle alternator, or is this prohibitively expensive to run the wiring, connections, controllers, etc?

Gordon Dewald · 12-08-2014, 02:21 PM

You have asked a really open ended question. I think you are only limited by the cost of what you can install and the area you have to install it.

More solar means less sun is required to charge your storage. Less sun means shorter charging times for the times it is cloudy or short days.

Yes the trailer batteries can be and generally are charged when the trailer is connected to the car and the car is running.

Nick B · 12-08-2014, 10:02 PM

Yep, this is an open ended question! There's an old saying - you can't be too good looking, or be too rich. True or not, I think you can add an extra one to that: "or have too much solar. Of course, you need #2 to be able to do #3....

I'm big fan of solar for boondocking. I don't have enough on my TT, only 160 watts, but I supplement it with a small generator. I'd like to have enough panels to be self contained even on cloudy days, and intend to get there, a year at a time. There's something very cool about a self contained solar system. So calculate your needs, and go for it! I'd still keep a generator handy, as a back up.... Let us know what you wind up with.

Nick B

1bigmess · 12-09-2014, 02:29 AM

Yes, it's open, but that is because I don't even have the trailer yet.

One thing that I was wondering about is this: does having extra capacity cause any harm to the various components if the batteries are already full or nearly full? In other words, is the controller being damaged because it has to get rid of excess energy that the PVs are sending to the batteries as heat or ??? IOW, as long as the various other components are rated to handle the amount of power that the PVs can produce, but the batteries fully charge while the PVs are still making peak or near peak output, does this potentially cause harm to any system components? I'm hoping the answer is "no".

Thank you for the answers I've gotten so far. I really do appreciate having brains to pick.

jablair · 12-09-2014, 03:59 AM

Some will say you can have to much solar. But they are referring to spending money on unnecessary panels.
No, a properly designed solar system will not be damaged nor damage the batteries or other circuits. By properly designed I mean good quality components such as Morningstar, Outback or Blue Sky. The charge controller will stop charging the batteries once a full charge is achieved. One advantage to having extra solar is the batteries are charged quicker and to a full state of charge. Too little will leave them some percentage short of a full charge. Unless of course, they are topped off with a generator. The excess solar energy is simply not used.

JFNM · 12-09-2014, 05:03 AM

Hi 1bigmess,

I had the same question prior to doing my solar install (here). I can't provide a technical answer but echo what jablair has said. With a good controller, the panels are either shut off or the power flow is stopped (some how??). The result is that the batteries are charged to "full" and no more (actually, voltage is maintained at a 'float' level). This is also true with a good shore power battery converter/charger. These controllers sense battery state and provide the appropriate level of power for the battery.

I've found that my high-voltage "residential" PV panels provide good power even when parked in less than direct sun (in the woods). I understand this is not the case with 12V panels but have no direct experience. Afraid I don't have any quantitative data about this, just my observation. The result is that my generator sits unused (and that makes me happy cause it is not making noise). However; having it for backup feels good.

Old Scout · 12-09-2014, 05:50 AM

"All things in moderation grasshopper." Do your homework, assess your need for power, then design a system that meets your needs at a reasonable cost. Solar components can be expensive so incremental costs can quickly out pace increases in performance or capability. You need to "right-size" your panels, batteries, contoller and inverter for what you think you need. Otherwise, the only limits on your questions are: 1] how much money do you have, and 2] how many square feet do you have for panels and storage bats....

1bigmess · 12-09-2014, 12:57 PM

Quote:

Originally Posted by jablair

By properly designed I mean good quality components such as Morningstar, Outback or Blue Sky.

I adhere very strongly to the "Buy Once, Cry Once" philosophy in all purchases of durable anything. Truck, trailer, electrical systems, etc., will all be thoroughly and nearly exhaustively researched before I buy.

Lucky for me, much of this has already been done and the results are fairly easy to find.

BendOR · 12-09-2014, 01:18 PM

1 thing not mentioned yet is that the batts are self-regulating. They will take on as much charge as amps and voltage will allow then the batts themselves will become resistant at about 85-90% full and the charging slows. The excess power that the panels are providing is still available & usable to you. Plan to run some other heavy loads (some of your equipment) during the afternoon and it will not affect the charging.

SteveUpp · 12-09-2014, 03:41 PM

Something else to think about.... when hooked up to shore power, typical RV solar energy is wasted since it is only used to keep the batteries in float. The RV's AC transfer switch would be meeting all the AC demand in the RV with shore power. However, Inverters are getting more sophsiticated. The Magnum Energy Hybrid Inverter has a useful mode that will utilize solar power even when RV is on shore power. The inverter has a Load Support VDC mode where if there is external charging source (e.g. wind or solar), the inverter will use the excess current from the charging source first and reduce the current from shore power to meet AC demands. So your green setup stays green even when plugged into shore power!

nothermark · 12-09-2014, 04:24 PM

FWIW if you go all solar and only solar it's a question of a good controller and a big enough inverter. The point I wish to bring up is to understand your usage. If you want all solar that is a lot of batteries and a lot of PV. If you are really only using high power for the microwave and have a generator as backup you should be running the generator for a half hour on a regular basis to keep it running well. That can translate to a lot less battery and PV and controller but a bit of noise before dinner while the generator exercises and the single big load is satisfied by the gen set. OTOH if you are going to run AC off of PV the rest is moot. Just kill the AC while the microwave runs. You can build an over designed system if you want but you really need to understand what that means.

Smitty77 · 12-09-2014, 10:32 PM

I feel most of the other posters have given you great responses. I'll repeat that you really can't design a full system until you have your unit. Getting to know it, and how much power you consume, is a primary step in the designed finish system.

Can you have too much? Not really, as mentioned an appropriate Controller will handle the SP power output for you well. Lots of variables, so what may seem oversize to some, may be just enough for others.

IMO, SP costs have dropped so low, that adding extra SP capacity above your actual needs, is a good move. The extra capacity can make the difference for those mentioned variables. Say partial shading, or traveling in the Northern regions during the shorter days of the year. It can also make it so you don't need to worry about tilting panels.

I feel the same way about battery bank, in that going a bit larger then you actually need, space and allowing, will give you reserve capacity.

And I also feel that generator power is part of the total design package. And unless you are going to try and build a lithium bank of great capacity, generator power will be needed from time to time. But with a robust SP and battery bank - reduces the need to run the generator.

And all of the design elements, have different costs associated to them - and that can always be an influence on the total designed package

!

Best of luck,
Smitty

mgscott4 · 12-10-2014, 08:17 AM

No, you can not have too much Solar. Your components need to be sized properly for amount of solar being generated.

I would love to have trailer towed behind me with a large battery bank, inverters, and lots of solar panels that would fold out and provide me enough power for my entire rig, Portable 50 amp service, but it is not cost effective.

vsheetz · 12-10-2014, 12:06 PM

Quote:

Originally Posted by SteveUpp

Something else to think about.... when hooked up to shore power, typical RV solar energy is wasted since it is only used to keep the batteries in float. The RV's AC transfer switch would be meeting all the AC demand in the RV with shore power. However, Inverters are getting more sophsiticated. The Magnum Energy Hybrid Inverter has a useful mode that will utilize solar power even when RV is on shore power. The inverter has a Load Support VDC mode where if there is external charging source (e.g. wind or solar), the inverter will use the excess current from the charging source first and reduce the current from shore power to meet AC demands. So your green setup stays green even when plugged into shore power!

I typically turn off my converter when plugged into shore power, and let the solar system do all the battery charging. It's greener, and my Morningstar solar controller is a much better charger than my simple converter.