Too Much Solar?

[anewbiewannabe]

Okay, so I hate to ask this question, but after reading all the solar stuff I've either missed the answer or not understood that I was reading the answer to it. Is there such a thing as having too much solar for the amount of storage capacity on board? Is it hazardous to have more solar than storage capacity?

I know that I will be using AGM batteries for a couple reasons---one of which is operator forgetfulness so far as remembering to check battery levels.

The following is to give an idea of what I know I'm planning to power and my possible future wish list in case that affects opinions and answers. It's possible that I've forgotten some small need in the basic needs list.

Basic needs:
1 fan vent like fantastic
2 muffin type fans
1 12v convertible fridge/freezer used as freezer
1 cell phone
1 lap top
charging for cordless tool batteries---not daily use
1 Hamilton Beach kcup coffee maker for 2 cups a day if possible
I don't know if the controller for the solar uses power or not....thinking the mppt if I remember right

Possible future wants:
small microwave for occasional use---700w
small toaster oven---only # I could find on one was 1000w

Thanks in advance for any help clarifying this for me!

 

[anewbiewannabe]

I forgot one thing in the basic needs list though it may not be important---some kind of light for under the hood in pack rat territory.

 

[akrvbob]

I'd recommend 400 watts and 4 golf cart batteries to run the microwave confortably.

For vans, the size of the roof limits you so you can't put too much solar on it. On an RV their usage is generally so high that the more the better.

Bottom line, no, you can't have too much solar. But the easy way to know is start with whatever you can afford and if it's enough stop, and if it's not, then when you can afford it, add more. I recommend jumps in 200 watt increments: start with 200, if that's not enough, add another 200. For most vans that's plenty but if not, add another 200.
Bob

 

[LeeRevell]

No such thing as 'too much solar'. It's like having household power in an S&B - you'll never use it all, but it's better too much than too little. Get all you can afford and mount in your space.

 

[ZoNiE]

A good place to start:

Handy Bob (different Bob)

Then here:

AZ Wind and Solar

Another place, but tread lightly:

Solar Panel Talk

And more interesting stuff:

Another Power, where you will find Steve's Saga which isn't really about solar, but this is a good read.

 

[anewbiewannabe]

Thanks all! It just seems like the batteries could be fried or something from my solarly (new word) uneducated brain. It's been a few days since I looked at solar panel sizes, but I figure I can get at least 400w in a 6x10 roofprint. I figured that I'd better go ahead and load what I could on front end expenses because it will be more challenging after that. If things improve greatly and I really decide to act on more wants then I could add more---I'll probably just get used to what I have and forget what I wanted. LOL

Zonie, thanks for the recommended reading. I've read all our Bob's stuff and I've tried to comprehend Handy Bob's stuff too. Also looked at AZ Wind and Solar and some RV solar calculation on some forum---I stopped mathing well when my daughter was a junior in HS and could figure stuff out on her own so it's been a while. Never saw direct discussion, or at least recognized it, for whether a beefy solar bank and an undersized battery bank was risky.

I would say "I think she's got it" but that may still be a bit too soon when it comes to this. I know I'm lots closer now though!

 

[SternWake]

It is very hard to have too much solar for the battery capacity, and far too easy to have too much battery capacity for one's solar.


AGM's enjoy higher charging rates, and their lifespans are shortened when they are tickled to death with low and slow recharge currents which solar is famous for, especially when the discharger thinks that there can be too much solar and only wants the controller to revert to float voltage late afternoon.  Happy batteries go into float by 1PM.

AGM's do tend to hold higher voltages under higher loads, making them a good choice for powering large inverter loads.

But the pure Deep cycle ability of the Flooded golf cart battery cannot be beat, however these  in a single pair, are not great at supporting higher inverter loads.

How much Solar you should get is dependent on Which particular AGM brand you get, and how much overall capacity.  I would not go less than 1.5 watts per 1 AH of Storage with AGM's.  If other high amp charging sources are used, like a well wired alternator, then the wattage/AH capacity can be less, but if solar is to be the primary /only charging source then the AGMs would be significantly happier with 2 watts per 1AH of storage than the standard 1 to 1 recommendation.

People tend to see the price on AGM batteries, and assume the battery is superior in every way.

AGMs have certain advantages, but if not returned to 100% as often as possible, they are less tolerant than a flooded battery treated equally.

Read a true expert's opinion on AGM's:

 http://forums.sbo.sailboatowners.com/showthread.php?t=124973

It will hurt a lot more to kill a learner pair of AGM's, than it will some cheaper floodeds.

If the offgassing issue is the main desire for going AGM, know that floodeds offgass only when 75% charged  and higher, and do not offgass during discharge.  VW Vanagon enthusiasts over on the Samba forums seem to dismiss entirely the issues of having flooded batteries in the passenger compartment.

Technically, AGMs need to be vented too, as they can offgass if overcharged.

 

[SternWake]

Also, adding more wattage later might require a different charge controller, and likely fatter cabling from panel to controller to prevent losses due to voltage drop. Also one should not add newer batteries in parallel with older ones if one finds they do not have enough capacity.

Changes can always be made later, but getting it close to meet the requirements, getting a well balanced system is not just a matter of slapping on a little more here and a little more there. Adding that little bit more can require as much or more effort than the initial install.

Batteries can accept huge recharging currents. Even the Most timid AGM says 30 amps max per 100 AH of capacity, and Lifeline says one can safely feed their 100AH AGM 500 amps.

There is no danger in having too much solar for too little battery. as long as the voltage is regulated, and that is the job of the solar controller

 

[anewbiewannabe]

SternWake, thanks for your additions. I've been reading along on all that you post on the batteries and I read that link when you shared it on another thread the other day. I know in many ways the wet cell (I had to look up flooded the other day after thinking the wrong thing for so long ) batteries would be a better choice. Though the off-gassing could be an issue the main issue is the known operator problems so far as doing the routine checks and such. I write lists for everything and still forget important things. I need to practice the KISS method as much as possible so hooking up to the alternator without some kind of sentient system that I don't have to think about at all would be a poor choice for me too, at least to begin with. I may not be able to keep the batteries happy but I hope to keep them as content as possible while figuring out if I am capable of doing what it takes to make them happy.

I'd probably notice off-gassing really quickly if it happened. I remember what is was like when dealing with the wet cell batteries and the smells---still deal with them in the barn---so if I don't automatically vent the battery box it will be located where I can do it easily if the need arises.

Thanks again.

 

[ZoNiE]

A lot of good information here. Yes I also agree, you can never have too much solar for the battery. I probably do but you just don't use the excess.

I have a Midnight Kid MPPT controller and if I were to need more charge capacity, I would simply add another one, and connect the comm cable as they "talk" to each other and work together. That is one way to scale a system. You can also use multiple PWM controllers charging the same battery bank, but they are not as efficient.

Also, X2 on the Golf car batteries. They are the best bang for the buck. I have two that are going on 5 years and still running strong, and their first 4 years of life were on an RV charge controller bubbling them a bit too much.

 

[gypsychic]

I was thinking of going with AGM because of the off gassing issue and my asthma. After reading that so many newbies ruin their first set of batteries I looked more closely at the flooded golf cart batteries. Hopefully venting to outside will be adequate.

As far as maintenance, I will put it in my calendar. It's the only way I remember anything of much value. I used to write lists and then forget where I put them and try to rewrite different lists. It just was to chaotic. Now I put anything I want to remember into my calendar, even things like remembering to side dress my garlic and shallots in my garden. I'd be lost without my calendar. It will eventually hold reminders for better maintenance as well. Maybe that my fall into your KISS plan.

 

[anewbiewannabe]

Yeah, calendars. I'm still working on finding a system that's uhm, foolproof? I have a hard time keeping track of days sometimes and lose some here and there. I wish I could say it's getting better, but it's not. So far I've done mostly okay with doctor appointments but the rest of my life is somewhat at the whim of the weather---work outside when it cooperates, inside when I can. Farm life for many years. Luckily the old long-term stuff is still retained.

 

[SternWake]

It should be noted that as flooded batteries age, they will accelerate their water use, and what was once every 6 months in the first year, turns into once every 45 days when their capacity is down to ~60 to 70% of original.


Again it really depends on the battery and how much time it requires at ABSV to get a respectable Specific gravity cycle after cycle, ABSV being absorption voltage, where all the bubbling and offgassing and h20 loss occurs.

Flooded Golfcart batteries also have the option of Hydrocaps or water miser caps which will reduce the watering needed, and these will not fit on most other 12v flooded batteries to my knowledge.

Actual battery maintenance is not time consuming or a PITA, as long as it is not a PITA to access the battery tops.  I had 2 sets of batteries killed near their half life due to accessing them being a PITA, and their increased water usage.  If the tops of the plates go dry then that portion of the plate effectively becomes more than useless and the battery rarely lives much longer at that point, after refilling.

Proper battery cable terminations, which I make a big stink over, are needed to keep corrosion at bay.  Closed end ring terminals, properly crimped and heatshrinked should be practically maintenance free when installed and then covered with grease.

Really, one should have a hydrometer to verify if their charge controller is actually completing the task of returning the Specific gravity up near the maximum cycle after cycle, and adjust their charge controller ABSV settings higher and longer if not. so accessing the battery tops should not be made into a dreaded task when designing the Van interior to accommodate them.

Once Flooded batteries are dialed in ABSV wise, and vented to the exterior properly,  and have quality cable terminations greased, their actual maintenance required is not much at all.

Do be careful when removing the caps, especially when still charging.  Wear eye protection, and clothes you do not care about.  Do not overfill, and use Distilled H20.

Expect a little performance loss, voltage wise, after refilling, as the acid becomes weaker.  The full capacity is still there, it is just the first few cycles after a refill one will notice lower voltages under the same loading as before refilling.  This eventually evens back out.

Some cells will also use more H20 than other cells.  Take note of these.

As far as having more solar than required, At this time of year I basically have that, but in winter I need more.  When my batteries reach ABSV, then there is excess amps available.  At this point I can turn up my fridge to a higher setting,  charge my laptop battery, any other battery, but usually, I do nothing.  Some people freak out if their Solar can provide more than their batteries need, but this is an incorrect way at looking at things.

With more solar than needed, the batteries charge faster, which they like, and they remain at ABSV, and Float voltages longer, which they like, and happy batteries live longer and perform better during that extended lifespan which makes the human all warm and fuzzy, and humans crave the warm and fuzzy.

The person who aims only to reach 'full' charge by late afternoon for fear of wasting any solar wattage, is shooting themselves and their batteries in the foot.

AGM's are great batteries, but their recharge requirements are more fickle, and offset the maintenance aspect of flooded batteries which are more tolerant of less than ideal charging.  If AGM is truly required, then it is more important that the charging source meet the needed ABSV for the required time, and meet it earlier in the day, meaning a higher charge rate via more solar or other more powerful charging sources.

Correctly wiring up a Solenoid to the alternator to charge house battery when driving and not depleting starting battery when not driving, is actually very simple.  But like anything can be made difficult with all the if's and's and butts, and options thrown in.

The alternator as a bulk charging high amp source should never be avoided for fear of the unknown in how to wire it up.  One can add this later without major reworking as might be required if more battery capacity or more solar wattage is required.

 

[anewbiewannabe]

Thanks SternWake. I learned a lot about flooded batteries a long time ago but didn't learn all of it because the person teaching didn't know it either---like why the different cells use different amounts. Always have used distilled water. I agree, proper protection of eyes and person is necessary when dealing with battery acid and even had to teach some boys about that after they couldn't figure out why all the sudden their clothes had all these holes in them. I won't tell you how many flooded batteries on equipment ended up with low survival rate around here in more recent years because of operator issues.

What is ABSV? Sometimes I get lost in the acronyms around here. Oops, I found it---absorption voltage. Nevermind.

The only concerns or fears I have are related to my short-term memory being in a position to cause me to strand myself. Hence the KISS method until I am able to devote more attention to learning about the solenoid or other methods. I've worked with solenoids long ago but never really learned much about them or understood them so the learning curve would be higher than I can deal with to start with. Until I program the other basic stuff into auto pilot I want to avoid having to remember more.

To start I'm going to just run a down and dirty best solar/battery setup I can afford and not have to think about much and avoid the other hookups. Running wires for solenoid or shore charge later will be possible and more price accessible than the original setup once I decide which direction to head with it.

Great information about flooded batteries that I'm sure will be useful, if not to me then to someone else.

 

[gypsychic]

It should be noted that as flooded batteries age, they will accelerate their water use, and what was once every 6 months in the first year, turns into once every 45 days when their capacity is down to ~60 to 70% of original.


Again it really depends on the battery and how much time it requires at ABSV to get a respectable Specific gravity cycle after cycle, ABSV being absorption voltage, where all the bubbling and offgassing and h20 loss occurs.

Thanks for that reminder!

 

[anewbiewannabe]

So my mental absorption value might have had a higher spike of understanding again. :idea: Sorry my brain is about like a starved battery.

So, if I have to move let's say every 12 days and I have the wires/solenoid? hooked up to the alternator to charge the batteries while driving. If I drive an hour, shop an hour, and then drive an hour is that going to be deleterious to the uhm, prime charging that would get the batteries where they need to go to keep them happy? Do I need to have all the hours at once at the start I guess is what I'm asking? Is there a way to calculate the hours assuming that I never went below 50% at the very least on solar only?

Is there an automatic switch that can be put on to shut of connection to alternator? Or is that the solenoid?

This might be doable. Especially since whenever I do the install I'll have to figure out someone or another to help me somehow.

Thanks for your patience and understanding. If we all learned the same way it would be so much easier on those helping us out. :blush: I'm sure some feel about like I did when I was trying to help my daughter understand algebra.

I can't wait for the day when somebody can say "By George, I think she's got it!"

 

[Canine]

No,yes yes no no no

 

[Seraphim]

I don't think you can have too much solar. We have 400 watts of panels and 210ah of battery storage. In the morning our batteries are down to about 92%, and with any sun they are recharged in about two hours, average. Often times faster. The panels are flat mounted. I estimate we can handle about four days with no sun before the batteries hit about 50%, and we'd need an alternate source to recharge them. Battery levels during the day don't drop for us.

More panel wattage offers quicker recharge times. Larger battery capacity offers more time available between necessary recharges, for a given amount of usage. For our usage, our setup offers us pretty much independence from external power sources, as we also charge the house batteries from the alternator when driving. No generator. Can't stand them...

Considering adding power points inside the camper for recharging devices during the day, when we are out and about. Four devices (two phones, two iPads) would be a significant addition to power usage for us, but we always recharge when driving and a charge lasts several days, so the addition may not be that significant.

 

[Seraphim]

More capacity (panels and batteries) offer more options, flexibility, and leeway, but the key is adjusting one's usage to what's available.

 

[Spaceman Spiff]

My 2¢:

The only downsides to too much solar is investment cost and weight.  Solar panels are about $1.00 per watt and batteries ~$1.00 and ~1 lb. per usable amphour.  If you are short on $$ or GVW, then you have to shortchange somewhere else for the excess capacity.  OTOH, having too little power sucks.  -- Spiff