Solar Power for your Camper – Where to Start (Hint: The Solar Panels are last in this list of steps

[ckent323]

I have the impression that a number of people start with the Solar panels when planning to add solar power to their camper (like I did). So I thought it might be helpful to write a short set of steps to start to process, with the hope that it will help minimize iterations and confusion for folks wanting to add Solar.

Caveat emptor: I am not an expert on this subject but I have read a lot on the topic and I have installed my own Solar System on my camper. I hope I have not omitted any significant steps or considerations.

Solar Power for your Camper – Where to Start (Hint: The Solar Panels are last in this list of steps)​

Note: - This has been edited to include recommendations from Rando's comments in the reply thread (below)

1 [SIZE=10.5pt] [/SIZE]Determine your daily power consumption from all sources. Make a spreadsheet and estimate power use by device per day in winter and in summer. Determine typical and worst case power consumption.
[SIZE=10.5pt]- Better yet [/SIZE][SIZE=10.5pt]measure your power usage (assuming you already have the camper and are currently using it without solar). Do this to avoid over estimating power needs. There is tendency to add up everything in the camper and worst case run times, then call that number the typical usage. [/SIZE]
[SIZE=10.5pt]- [/SIZE][SIZE=10.5pt]To accomplish this consider investing in a battery monitor first ([/SIZE][SIZE=10.5pt]Victron BMV-712[/SIZE][SIZE=10.5pt]) or break out your voltmeter and do some careful state of charge (SOC) measurements to see what your actual usage is. Your loads may not actually add - when it is hot out, the fridge runs a lot, but you don't use the furnace and don't use the lights much. When it is cold out the fridge and fans don't run much, but you run the furnace and lights more. 30-40Ah /day seems to be a pretty reasonable average, but everyone's usage varies based on equipment and lifestyle. [/SIZE]

[SIZE=10.5pt](Note: If you use a CPAP as well as the humidifier and power it from the house battery your power needs could easily be another 40 or 50 Ah a day on top of the other items included in your measurements or estimates above. You may want to consider a separate portable [/SIZE]rechargeable[SIZE=10.5pt] CPAP battery, especially if you have access to shore power or move around frequently and can recharge from your vehicle while driving).[/SIZE]

2 Determine the environment you will most often be in and how many nights a year you will use your camper: clear, cloudy, on pavement (modest vibration and bouncing), off pavement (perhaps significant vibration and bouncing). The answers to this will help you choose the battery type and the storage capacity you need. It will also help you determine the size of the Solar panel bank that you need to recharge the battery bank.

3 Determine what kind of battery storage and capacity you need/want.
- Deep Cycle, mixed or starting type,
- Flooded lead acid (FLA) , Absorbed Gas Matt (AGM), Gell, or Lithium Iron Phosphate (LiFePO4). Each type has its pros and cons.
- Look at Depth of Discharge (DOD) vs Charge Cycles (lifetime) curves relative to your typical power needs and the type of battery you choose. (This may lead you to considering a different battery type). If you do not use your camper more than 20 or 30 nights a year you can draw your battery down significantly further on a routine basis than if you use it 60 or more nights a year (see discussion in the comment/reply thread below).
- Look at battery orientation, venting and shock protection requirements (for example sealed batteries can be mounted on their sides and do not require venting - Gell may be more resistant to shock bouncing than AGM)

4 Think about where you will house your battery bank
- Weight and volume (size) of the batteries
- Where will they fit and where will you run the wires and place the Solar control panel?

5 Think about where you will place the Solar Panels
- [SIZE=10.5pt]Weight and size (length and width) [/SIZE]of the solar panels
- Do you want the Solar panels to be fixed in place, deployable or a combination
- Where will you run the wires to connect to the charge control panel and the batteries?

6 Determine how much Solar Power you need each day and the number of panels that requires
- How much power per day will the house batteries receive from the vehicle? Do you tend to move around a lot or stay in one place. Sizing of the wires from the vehicle to the camper is important and wires smaller than around 4 ga or 6 ga can significantly reduce the amount of power available to the batteries (cause recharging to take longer)
- Solar panels (like Batteries) are rated by full or max capacity. On average a solar panel only provides about 75% - 80% of peak output during the day on a clear sunny day and even less on cloudy days so factor that into your calculations. Also keep in mind that any shadow, even a small shadow from a branch or even a leaf can significantly reduce the output from a solar panel, so where you park your camper is important if the panels are fixed on the camper.
- Look at the cost performance trade between using fewer higher output capacity solar panels (larger in length & width) with output nominally 24v versus more, lower output capacity panels (smaller in length & width) with output nominally 12 v. Note: Your Solar Charge controller will need to be able to support the type of panel you choose (12 V or 24 V as well as the max current output of the Solar Panel array).

That about covers the steps to start with.

What charge controller and what configuration is best for connecting your battery bank and Solar Panels are among the next set of steps but beyond the scope of this set of initial steps of where to start.

I hope this is helpful.

Regards,
Craig

[SIZE=10.5pt]- [/SIZE]

 

[Wandering Sagebrush]

Craig, great information. Thanks for sharing.

 

[Casa Escarlata Robles Too]

This info would have helped 9 years ago when I made my system. But since I didn't have it what I did seems to have filled my needs.
Thanks for taking the time to share the info.
Frank

 

[rando]

Good idea for a topic. I guess I would change things around a little bit - in stead of starting with a spread sheet to estimate your power usage, actually measure your power usage (assuming you already have the camper and are currently using it without solar). Pretty much every spreadsheet calculation of power usage I have seen ends up in way too high a number. There is tendency to add up everything in the camper and worst case run times, then call that number the typical usage.

Consider investing in a battery monitor first (Victron BMV-712) or break out your voltmeter and do some careful SOC measurements to see what your actual usage is. I have found that my loads don't actually add - when it is hot out, the fridge runs a lot, but I don't use the furnace and don't use the lights much. When it is cold out the fridge and fans don't run much, but I run the furnace and lights more. For me, 30-40Ah /day seems to be a pretty reasonable average, but everyone's usage varies based on equipment and lifestyle.

Second, I would go with much less conservative DOD numbers for the various battery types. For my previous AGM batteries I used 50% as a target and was OK with drawing them down to 80% DOD on occasion. For lithium batteries 90% DOD on a regular basis is totally fine, and you can take them down to 100% DOD on occasion with no real concern.

 

[ckent323]

Rando,

Good suggestions.

However, I paused at " For my previous AGM batteries I used 50% as a target and was OK with drawing them down to 80% DOD on occasion. For lithium batteries 90% DOD on a regular basis is totally fine, and you can take them down to 100% DOD on occasion with no real concern."

All the curves I have seen for AGM show that routine DOD to 50% and LiFePO4 to 90% significantly reduces battery life. Those curves were based on testing.

Do you have any data that substantiates your assertion that less conservative DOD draw down will not significantly reduce battery life? I would sure like to see the data. I am no expert here but being an engineer I do like to see data that backs up assertions.

That written I suspect you are better educated on this stuff than I am so I am hoping you have data to share.


Regards,

Craig

 

[rando]

Here is a fairly typical cycle life vs DOD plot for LiFePO4 batteries:

Even at 100% DOD you still get on the order of 2-4000 cycles out of the batteries. You are correct that if you only took them down to 50% DOD you would get a longer life (11,000 cycles), but then you would need twice as many batteries for twice the weight and cost. For me (and most people here), 4000 cycles (or even 1000 cycles) would be far more than we would ever need.

Here is the same sort of chart for a high quality AGM battery:

1000 cycles down to 50%, or even 500 cycles down to 80% DOD is still more than enough (in ~45 nights of camping last year, I did 19 cycles below 40% DOD on my 75Ah AGM, according to my BMV-702).

If you are a full timer or living off the grid in a cabin where you cycles your batteries 365 days a year, you would probably view these numbers a little differently, but for most of us couple month a year type folks in weight limited campers the calculus is a lot less strict.

 

[ckent323]

Rando,

Good discussion. I concur.

We are using our camper about 40 - 50 nights a year now but even at that we should get 10 years out of the batteries drawing them down to 50% or even more.

Accounting for the likely number of cycles a year and then how many years the battery should last is a better, more pragmatic way to think about this rather than just thinking about how to maximize battery life based on the DOD vs charge cycles.

Of course all this assumes a charge controller with appropriate voltage settings applying the manufacturer recommended charge profile as well maintenance (float) charge as well as avoiding high or low temperatures that are applicable to the particular battery type .

Thanks for the follow-up discussion.

Regards,

Craig

 

[Vic Harder]

some great info here guys. I love the practical view gained by looking at DOD & anticipated usage = life of battery. After 42 days of camping last year, I had 1 = ONE = cycle on my batteries. And that was a test I did on them by intentionally draining them.

By that reasoning, they should last forever. I wonder if there is another factor to consider - what is the life expectancy of a well stored battery? ;-)

 

[rando]

To be clear, I think most of the manufacture spec'd lifetimes are very optimistic, particularly for lead acid batteries. This not nefarious, it is just that there tests are done in a lab with automated test equipment (hopefully, or I feel really bad for their technicians). The batteries get perfectly charged with the optimum settings back up to 100% immediately after discharge, then are discharged at a constant rate, all at 25C. In real life, the batteries are discharged and charged at various rates and under variable conditions and not always back to 100%, so you unlikely to see the same performance as in the lab. However, even if the real life results are a factor of 2 or 3 lower than the lab tests, the the cycle lifetime is still way more than most of us would ever use.

I would guess that abuse is more of an issue with battery lifetime than the inherent cycle life, and why people often see shorter battery life than the specs would indicate. Over charging, leaving discharged for extended time, improper temperature compensation etc all eat into these numbers.

That all being said, I had an odyssey AGM in my prior camper, and the same battery in the camper before that for ~10 years and it was still working well when I sold that camper to buy my FWC, so it outlived my ownership of two campers. I expect the LiFePO4 battery (or the Exide AGM it replaced) to outlive my ownership of my FWC.

 

[PaulT]

This page gives one some things to ponder about battery life. http://www.mpoweruk.com/life.htm

Paul

 

[rando]

That is an excellent resource!

 

[Squatch]

Other than bad charging habits I think the biggest killer of batteries is vibration. The bumps and bangs of being in a vehicle don't do the plates any favors.