Breakeven Point of Solar?

[jimdelane]

Using Amp hours as a measure of energy is what makes things confusing.

Amps is a measure of current capacity.
Watts is a measure of energy capacity.

With lead acid/AGM batteries, the Ah capacity is directly related to the the rate of discharge.
A battery rated at 100Ah @ 5A (0.05C) discharge is rated at 82A @ 20A (0.20C) discharge.
Keep in mind that The LA/AGM battery should not be discharged over 50% if you want the battery to last - so you are talking 50Ah @ 5A (600Wh) or 41Ah at 20A (492Wh). Also, at a 50% discharge, the voltage will be 12-12.2V.
Ref Trojan 31-AGM
https://www.trojanbattery.com/pdf/AG...tLineSheet.pdf

With a lithium battery, the discharge voltage is over 12.8V throughout most of the discharge cycle past 50%.
The link has charts showing voltage under a 25A (.25C)
As a result the lithium has more watts available for a longer period. The discharge graph shows that it does not hit 12V until 90% discharged - then it will drop quick.
https://www.solacity.com/how-to-keep...tteries-happy/

Point being, a LA/AGM amp hour rating is a lot of smoke and mirrors. As uncle_bob said - "Simply to be utterly confusing ....."

It does not have to be so.

amps x nominal voltage = watts

A lead acid / AGM battery is 12V nominal.
A lithium battery is 12.8V nominal.

So a 100Ah battery is
LA/AGM 100ah x 12v = 1200Wh (50% discharge = 600Wh usable)
LFP 100ah x 12.8v = 1280Wh (80% discharge = 1024Wh usable) - most LFP can be safely discharged more.

There is more energy in the lithium than the LA/AGM simply because it maintains a higher nominal voltage.
It maintains a higher voltage throughout the discharge cycle. It can be mostly discharged and can remain partially discharged indefinitely without damage to the battery. Because lithium is 99% energy efficient - virtually ever watt that goes in is, is stored for future use.

[uncle_bob]

Originally Posted by jimdelane

Using Amp hours as a measure of energy is what makes things confusing.

Amps is a measure of current capacity.
Watts is a measure of energy capacity.

With lead acid/AGM batteries, the Ah capacity is directly related to the the rate of discharge.
A battery rated at 100Ah @ 5A (0.05C) discharge is rated at 82A @ 20A (0.20C) discharge.
Keep in mind that The LA/AGM battery should not be discharged over 50% if you want the battery to last - so you are talking 50Ah @ 5A (600Wh) or 41Ah at 20A (492Wh). Also, at a 50% discharge, the voltage will be 12-12.2V.
Ref Trojan 31-AGM
https://www.trojanbattery.com/pdf/AG...tLineSheet.pdf

With a lithium battery, the discharge voltage is over 12.8V throughout most of the discharge cycle past 50%.
The link has charts showing voltage under a 25A (.25C)
As a result the lithium has more watts available for a longer period. The discharge graph shows that it does not hit 12V until 90% discharged - then it will drop quick.
https://www.solacity.com/how-to-keep...tteries-happy/

Point being, a LA/AGM amp hour rating is a lot of smoke and mirrors. As uncle_bob said - "Simply to be utterly confusing ....."

It does not have to be so.

amps x nominal voltage = watts

A lead acid / AGM battery is 12V nominal.
A lithium battery is 12.8V nominal.

So a 100Ah battery is
LA/AGM 100ah x 12v = 1200Wh (50% discharge = 600Wh usable)
LFP 100ah x 12.8v = 1280Wh (80% discharge = 1024Wh usable) - most LFP can be safely discharged more.

There is more energy in the lithium than the LA/AGM simply because it maintains a higher nominal voltage.
It maintains a higher voltage throughout the discharge cycle. It can be mostly discharged and can remain partially discharged indefinitely without damage to the battery. Because lithium is 99% energy efficient - virtually ever watt that goes in is, is stored for future use.

Hi

Or you could simply observe that you divide the lead acid amp hours by 2 and go from there ....

Watts are Wonderfull if the voltage is fixed by some basic principle. Unfortunately it's not. It varies and this makes things just as elastic. Amp hours varies as well and it drives the calculation, so you are doubly varying.

Solar watts are no better. You have a peak number, but no real way to know what you actually will get compared to that peak. Again very elastic. Do you want 10X the battery watts in solar watts? How about 5X or 20X? There is no perfect answer other than "put up as much as you can".

Bob

[Barlaws]

I camp almost exclusively in the shade if possible so solar has little value. See how you camp to figure if you'll be in full sun. My 2c.

[Airwave503]

I haven't read any other replies to this, but I strongly recommend solar and forget the cost benefit analysis.

ALL CAMPERS SHOULD BE STRIVING TO MINIMIZE IF NOT ELIMINATE GENERATOR USAGE!!!!

They are noisy (even the quietest ones), smelly and totally wreck the nature experience.

I had 2 100W panels mounted on the roof and unless I dock in a cave, by AGM battery stay topped off. The only time I pull out the gen is to run the microwave for a few minutes or if I am in a snowstorm and can't keep up with sweeping the panels.

QUIET AND CLEAN IS THE FUTURE!

[lewster]

Originally Posted by jnm30327

There are relatively inexpensive ways to add solar. I have a 2018 Flying Cloud prewired with socket for a Zamp solar panel. I bought a 160 watt Zamp suitcase panel and connect it when dry camping. In normal summer use without AC, I use about 45 amp-hrs from 12 V system. The suitcase panel pretty well covers that use. It takes some attention to keep it oriented to the sun but sometimes I just lay it flat on the ground and leave for the day. I went all summer without running the small 1000 watt Honda generator I carry. The longest period of dry camping was 7 nights. NB: no solar is strong enough to run AC.

The unit I have seems to no longer be available. Currently a 180 watt suitcase system from Zamp costs $800.

May I take exception to part of the above "NB: no solar is strong enough to run AC." This statement is basically untrue! Any A/C system can be run from solar and lithium batteries. It just depends on the size of your solar system and the amp/hours in your lithium batteries.

We have built systems for larger Airstreams that can operate an A/C unit for up to 8 hours. Unfortunately, your statement does not hold true for many Airstreams and definitely for larger 5th wheels and Class A models.

[kscherzi]

Originally Posted by lewster

May I take exception to part of the above "NB: no solar is strong enough to run AC." This statement is basically untrue! Any A/C system can be run from solar and lithium batteries. It just depends on the size of your solar system and the amp/hours in your lithium batteries.



We have built systems for larger Airstreams that can operate an A/C unit for up to 8 hours. Unfortunately, your statement does not hold true for many Airstreams and definitely for larger 5th wheels and Class A models.

Yes you are very correct. With enough money and hardware the AC can be made to run from solar panels and batteries. The OP was asking about break even. The suggestion regarding portable panels is a plausible break even solution.

[DaveP]

Originally Posted by kscherzi

Yes you are very correct. With enough money and hardware the AC can be made to run from solar panels and batteries. The OP was asking about break even. The suggestion regarding portable panels is a plausible break even solution.

So, the true "breakeven" is when you run out of disposable income!!

[1StreamDream]

Originally Posted by mikeinca

On a strictly cost basis it's probably difficult to justify solar over a generator. However there are intangibles that are harder to quantify in dollars and cents.

There's a lot to be said for not compromising a quiet boondocking site for yourself (and your neighbors) with a generator. I don't know how you put a dollar value on that but it's worth something, to me anyway. Also, unless you're planning to run the generator a lot you may want to upgrade to lithium batteries and an uprated converter in which case you've probably invested half of what it will cost to go all the way to solar. Plus installing solar on your RV qualifies for a tax credit.

You've done the research so you know the numbers. I don't think having solar is an economic decision so much as a lifestyle choice to have a clean, quiet power source. Only you can decide if that's worth the money.

FWIW, we're headed out tomorrow for Grand Tetons NP and we're staying at a minimal services NP campground that does not allow generators. I'm looking forward to the peace and quiet.

X2 on all the points offered by mikeinca

I took the point of view that it is more valuable for what it enables me to do vs the pure economic analysis. I also like quiet extended boondocking stays. For me I think the biggest gain was made when I switched over to lithium ion batteries (battleborn). Unfortunately that was also probably my most expensive upgrade segment (I did mine gradually in small increments, over time). I do also carry a set of portable panels so I can get some sun from a mostly shaded site, and also a Honda 2200i generator but use it very sparingly, mostly just 5-10 min or so around dinner when the DW wants to use the microwave. We both try to avoid that, but we will do it on occasion. I don’t think I can say I break even from a pure cost point of view but that’s ok … I now have the flexibility I wanted.

[ejami5]

Hi Mitch - I have an Airstream and recently acquired a 1964 Silver Streak which will be a complete renovation. I use both portable solar (2 100 watt panels) and travel with 2 2400w dual fuel generators with the Airstream. This covers me when I'm on the road for 4-5 months which is not your situation. My preference is to use solar when boondocking but need the generator(s) if I want to run the AC or if it's been too cloudy for the solar panels. I view the generator as a back up.



For my Silver Streak, I started thinking about the changes to the original footprint (primarily air conditioning). This may not matter to you, but I don't want to change the original look of the exterior. Partly because I like it and partly for resale value in the distant future. That said, I will not put solar panels or an AC unit on the roof.



The Airstream and Silver Streak will probably not be in the same state. This means I will have to decide between solar or generator for the Silver Streak. Previous comments have covered lots of the pros and cons of both. For me, the bottom line is the peace and quiet and the beauty of nature. This means solar to keep the house batteries topped off. I don't miss using the microwave or the blow dryer and so not start the generator for those items. I have a power bank to charge the laptop, phone and other small electrical devices.



Congrats on your Silver Streak. I'm excited about mine.

[Sylvain]

Here is my 2 cents on this controversial topic.



Choosing solar; be it for trailer, RV or residential; is not and should not be about breaking even as for most of the cases it will be most likely more expensive than alternative options. Both generator and solar have a decent cost and some maintenance required.

It is more a question of independence, inconvenience and power requirements.
Solar:
- will virtually not produce any noise, except for the few cooling fans of the electrical equipment, with all the benefits that brings.
- does not need to be refilled every few hours in gas or propane, therefore no need to run to the refill station.
- can charge while driving and most of the day.

- can power anything and last for days if sized properly.
Generator:
- will be a lot smaller for the amount of power generated
- can easily provide large amount of power
- will work in low sun exposition (night, winter, rain, smoke etc...)


In your case (3 to 4 weeks a year) it is really up to you to see what makes more sense.

[Sylvain]

Follow up on my previous post:
For my personal case I am rebuilding an 30ft long Airstream for full-time living, I chose the a large solar system with a backup 2000W generator that I should not need to use in theory. When I say large I mean 1kW of panels on the roof (+ portable solar panels on the ground if necessary) and 31kWh of battery hidden in the frame.