Solar power

Solar power is an excellent fit for those who live on the road. It is silent, nearly maintenance-free, and requires no infrastructure or power grid. Disadvantages include expense, bulky panels, and the daily requirement for access to direct/unshaded sunlight.

Solar power is sometimes referred to as photovoltaic or PV power.

Solar power systems consist of solar panels to collect energy, house batteries to store energy, and charge controllers to regulate how those batteries get/stay charged. Other components are necessary as well, such as wires to go between these, and other optional components can be added to create a more robust electrical system in your vehicle.

Under normal use, solar setups charge fully during the daytime and discharge at night; the lowest state of charge will likely be just before sunrise. On a properly-sized deep cycle system the bank will have used no more than 50% of its capacity at this point. Then the sun comes up and charging begins again. 'Dwellers running small solar setups (or experiencing poor insolation or heavy loads) may have to ration their use of solar power.

The most difficult part of a solar power system (other than paying for it!) is sizing it correctly for your needs.

I'm not sure people always grasp the concept of "minimum" either; they tend to think it means "all that you really need" when it fact it means "the least you can get away with provided everything else goes right". After all, the sun does not shine brightly every day.^[1]

Do you need solar?

Not all vehicle-dwellers want or need a solar power system. No solar may be an option for you if you stay in campgrounds or other places with access to shore power, or you have lithium or carbon foam batteries that do not require regular multistage charging. If you have a small vehicle (cars, etc.) your options are somewhat limited by available space, but portable solar panels or small solar panels are still an option.

Practical considerations

Solar panels take a lot of room on your roof (if you're using fixed solar panels) and must not be shaded. Where will you put them? Panels aren't very expensive, but they can be expensive to ship. Where will you get them? Wiring from the panels will have to enter the camper body somewhere, and the entry will have to be waterproof.

Lead acid batteries (flooded, sealed, AGM, etc.) are extremely heavy and bulky. Where will you put them that is out of the way and that will not negatively impact the balance of your camper? How will you get to them to maintain/inspect them? How will you vent them? Wiring from power sources will need to be fused or fitted with circuit breakers. How will you ensure your batteries don't run your batteries too low and damage them?

Scheduling your use of solar power

When you use power from your system can be as important as how much power you use. There are times (bulk, early absorption) when the system is struggling to charge the lead-chemistry bank; loads should be minimized during these periods. At other times like late absorption and float the system will have surplus capacity that can be used to run loads.

Things that affect solar power

Insolation (Intensity of sunlight) is strongest when there is least atmosphere between the sun and panels: sun is overhead (noon, summer), nearer the equator, and at higher elevations; and weakest when there is the most atmosphere between sun and panels: sun is low (morning/afternoon, winter), higher latitudes, and lower elevations.
hours of sun each day - more in southern latitudes and in summer; fewer in northern latitudes and in winter
clouds - panels make more power on sunny days and less on cloudy days, due to increased current (voltage relatively unchanged).
temperature - panels make more power when cold, due to increased voltage (current relatively unchanged)
physical obstruction / shade - as when in forested areas
physical obstruction / covering - as when covered in dust or snow

How much solar?

Sizing your solar setup

12v vs 24v

Most house banks and accessories are nominal 12v.

Reasons to go 12v:

it is the most common setup: more accessories, more crowdsourced knowledge
you want to charge from alternator
your rig already has a 12v bank

Reasons to go 24v (or higher):

to save on wiring costs; higher voltages do not require thick copper like 12v. Example: a 10' run of 20A @ 2% loss requires 2awg with 12v but only 5awg with 24v.^[2]
more efficient inversion to 110vac. If most of the house will be run off an inverter, it will be more efficient at 24v than 12v.
large arrays and battery banks

Weather-related issues

Weather and shading have serious effects on solar output.

Cloudy weather

Cloud cover can have paradoxical effects:

under full cloud cover current from panels drops significantly while voltage output remains relatively stable.^[3]
under partly cloudy conditions output can be wildly variable.
- When the sun is behind clouds you get diminished current as above
- when the sun is not behind clouds you get max current given the sun's position
- when the sun is near the edge of a cloud you can get spikes in current, called Edge of Cloud Effect (ECE). Here is a YouTube video of a charge controller's out during ECE. Here is a simple drawing illustrating ECE. Here is a demonstration of why it happens.

Rainy weather causes a drop in current due to the cloud cover effect. An upside is it can wash dust off panels.

Dusty or snowy weather can cause a loss of output due to physical presence on the panels.

Temperature

Panels yield the most power in cold temperatures. Since panels are dark and get very hot in the sun they are generally raised rather than directly mounted; this allows air circulation/cooling underneath.

Mounting the panels

[based on this reddit post]

There are a few issues to consider:

solar cells get very hot in sunlight, typically 25deg C hotter than ambient temps. Rating lab tests are performed when the cells are 25deg C (0deg C ambient, freezing)
Panel output is reduced when the cells get hot

hot panels re-radiate heat onto the roof of the van. "On my white van (even with a 5" airgap) it is hotter in the shade under the panels than on the roof in direct sunlight." - secessus

we prefer fewer holes in the van roof when possible
"flex" panels cost ~2x as much as rigid panels and last for years rather than decades
airgapped panels will add height for drive-through adventures
taller racks will likely increase air drag and MPG, particularly if you drive fast

Mounting hard panels to a rack increases airflow (thereby reducing heat-related power losses), reduces heat transfer, and minimizes the number of holes in the van roof.

Mounting hard panels directly to the roof still allows some airgap (the depth of the frame) and the roof corrugations will allow some airflow in the direction of the "valleys". Taller Z-brackets may give a bit more airgap.

Mounting flex panels to the roof allows some airflow in the corrugations but no airgap. Good news: panel derating won't be so bad because the heat is conducted to your van roof. Which is bad news if it's already hot in your van.

Portable panels allow the vehicle to be in shade and panels in the sun. Also can be tilted for maximal yield.

Some or all of the content on this page was originally sourced from this page on RVWiki

Part 2:

Solar panel output will almost never be as high as the claimed output. In fact it will probably hover around 75% of that number under the best conditions; this is called "derating", or correcting output to actual conditions. It sounds like fraud but it's not. A panel's power is expressed as a "nominal" rating like 100W as when tested under laboratory conditions. Since the roof of your van is unlikely to meet those same lab conditions, if you think you need 200W of panel you probably need 250W.

Usable battery capacity is about half of nominal capacity. This is due to a quirk of lead-acid chemistry batteries (flooded or AGM). You can go lower than the 50% mark but it generally leads to early (and $$$) battery death. So if you think you need 100Ah of battery capacity you probably need 200Ah.

PWM charge controllers may not be able to get even the derated power out of the panels. This is because the panel makes maximum power for conditions (Pmax) at a particular voltage (Vmp) which is higher than the voltage PWM controllers can use. (Vbatt) You can work around this issue by using an MPPT controller, but they typically cost 2-3x as much as PWM.

Charge controllers have specific current limitations. Regarding current they are rated by Amps of output: 10A, 20A, 40A, 60A, etc. To protect the controller from damage their nominal output is derated by .80; this assures "headroom" for power spikes due to odd solar conditions. So a 10A controller is safely used at 8A, 20A controller at 16A, etc. If you will be pumping 10A from the panels a 10A controller may not hold up. A 15A or 20A controller may be required. MPPT controllers may be able to cope with excess current.

Controllers also have an input voltage limit which you exceed at your wallet's peril. Going over this limit (usually by wiring too many panels in series) will usually kill the controller and void the warranty immediately. So don't do that.

Vigorously charging a deep-cycled house battery using only solar is expensive. But it takes a much smaller and cheaper setup to charge in combination with alternator, shore power, or generator.

12v systems are not really 12v. We call them 12v (("nominal 12v")) but deep cycle batteries are over-discharged at 12.0V; they should probably never go lower than 12.2V. During some stages of smart charging they might be over 15v. It is very common to hold well over 14v for hours during the Absorption stage.

Shade will clobber your panel output. Even a tiny amount of shade will usually have a drastic effect, losing up to 90% of what you might otherwise harvest. This means no tree shade, no antenna shade, no roof vent shade, no roof rack shade, etc.

Flooded lead-acid (FLA) batteries need to be "watered". They lose water as part of their normal charging and need to be checked and replenished with distilled water regularly.

AGM lead-acid batteries are not well suited to solar-only charging. They cost about 2x that of FLA, have less capacity, require vigorous charging and cannot be charged as high in voltage. They remain popular because people think "$$$ is better" and are loathe to vent their banks.

It is possible (though uncommon) to have one all-purpose battery for both house and starting. This only works when daily power requirements are quite low (40-50Ah/day) or when opportunity loads are aggressively utilized. There are two approaches to such a setup:

the premium battery deep-cycling approach as used by Sternwake^[4] This requires attention and knowledge.
the "make do" shallow-cycling approach. This is more suitable for car dwellers and folks on limited resources.

A gentle introduction to solar

This page is a basic overview of solar power for beginner nomads. There are oversimplifications and concepts skipped for clarity; click on the links for more information on a topic.

If you would like a refresher on basic electronics, see the AltE Intro to Electronics for solar video.

TLDR

Making some power from solar is easy.
- Making sufficient power from solar to cover your daily power needs is much harder.
- Making sufficient power from solar to cover your daily power needs in all conditions, seasons, and locations is so difficult and expensive that few attempt it; instead we augment solar with other forms of charging.
panels rarely make their rated output under real conditions
your location will have a huge effect on solar harvest
shade on the panels will clobber output
panels still make some power under cloudy skies

Benefits of solar

Solar power is silent, works for decades, and is always working when the sun is shining. (portable solar only produces when deployed) It can recharge your batteries and run your loads.

Solar is nearly mandatory for charging lead-chemistry batteries off-grid, since those require of many hours of charging.(Solar is not mandatory with lithium or chemistries that aren't harmed by partial state of charge.) Failure to charge lead batteries (AGM is lead!) fully and regularly leads to battery murder. Solar helps prevent battery murder and the resulting expensive battery replacements.

For people who can control their power consumption, even a small amount of solar can greatly extend time off-grid and can make a huge difference in quality of life.

Limitations of solar

Solar is not a magic bullet; it is a compromise like anything else. Solar has very high startup costs for the amount of power you get out of it. It could cost several thousand dollars to get the same amount of reliable power one might might get from a residential (or campsite) outlet with a $20 extension cord. Over time, though, the power is "free".

Getting some power from solar is easy. Getting reliable power from solar alone is challenging (and expensive) because solar harvest is greatly affected by real-world conditions: latitude, season, shade, temperature, even battery voltage. It's bit harsh but you need to hear it early on: you won't be getting 100w out of a 100w panel, and you won't be getting it for 8 hours a day. A crude rule of thumb might be meaningful solar harvest is possible only when the sun is throwing well-defined shadows on the ground.

Solar must not be shaded; not by weeds on the the ground or by other objects on the roof. The panel needs to be the tallest object in the general area.

Alternator charging helps address these shortcomings of solar charging (and vice versa) so it is a common combination.

How solar power works

Solar power uses solar panels to convert sunlight into electricity. This electricity goes into solar charge controller, which keeps the battery optimally charged (or attempts to!) and powers any loads (things that consume power). The controller extracts the precise amount of power your batteries+loads demand and no more: in effect the controller is pulling rather than the panels pushing.

Overall it is arranged like this:

panels -> controller -> battery bank -> loads

Excess power (above what you are using for loads) is stored up in a deep-cycle "house" battery during daylight as long as the battery bank can accept it and the power is pulled back out at night. The house battery is electrically separate from the vehicle's starter battery.((unless combined using an isolator, or running a single-battery setup)) In broad terms...

Think of the batteries as a bucket of electricity. It's possible to pour water from multiple sources into a bucket at the same time, and also to do that while water is leaking out of the bucket.^[7]

Battery charging is a topic unto itself, and improper charging can kill batteries prematurely.

Since it looks like magic, beginners tend to worry about whether or not their system is working. The solar setup is usually working as intended, and over time you will begin to learn how your system behaves. In the beginning you may watch it constantly(("solar tv")) then eventually need to check "the gauges" less and less often. At some point you will be able to predict what the system is doing before looking.

Your approach to solar

Since reliable power by solar alone is tough, there are a few approaches to consider:

best-effort power - you take what you can get from the sun and minimize power consumption to make do. No household appliances, at least not often.
reliable power - you need power to keep insulin refrigerated, keep your external heart bypass machine running, etc. Prepare yourself for added complexity and/or cost because now you have to worry about harvest under poor solar conditions.
- massive solar - You can still collect usable solar power under very poor conditions if you have a huge amount of panel. This may require "maxing out" your roof space, tilting the panels, or deploying additional portable panels. Such configurations may be 1000w or more. One of the pleasant side effects of massive solar is that having enough panel to meet needs in poor solar conditions means lots of bonus power in normal and good conditions. You may be able to run non-essential loads without affecting your battery bank's state of charge.
- solar + other forms of charging - Solar can work much better when augmented by additional sources of charging. It can work so well that less solar might be required and overall cost reduced.

What about portable panels?

Portable solar panels: Pro

can be set in sun while vehicle is in shade
can add more power when mounted panels are insufficient
can be tilted easily

Con

panels made to be portable tend to be expensive per-watt.
they have to be deployed in order to work

On the last point: many people believe they will set out their portables any time they are stopped; far fewer actually do it.

What about flexible panels?

Flex panels are very expensive by the watt. They are a great fit for people who need to mount on a curved surface (boat hull, teardrop trailer, etc) or store/lift a portable.

Otherwise framed panels are the standard for many good reasons.

= How much solar do I need?

This question usually means "how much power do I need?" and involves making power (solar, generator, isolator, shore power, etc.), storing power, and using power (12v loads, inverter loads). Unfortunately, you are the only person who knows how much power you will need, and even you may not know yet. Strangers on the internet cannot tell you how much power you need anymore than they can tell you who to date or how many kids to have.

It's not fun but the first step in getting solar is to assess your daily power requirements. Until they sit down to do the math first-timers often have radically unrealistic ideas about power in the campervan. You probably won't be able to run a hair dryer, electric space heater, air conditioner, instant pot, or other high-wattage loads from solar. You can get a ballpark idea before crunching your own numbers by reviewing some existing solar installs.

Why daily?

Power requirements are calculated daily because the solar feeds the batteries (and loads) only in daylight. Then at night the system pulls power back out of the batteries. This is natural rhythm of a solar-powered system and the reason why deep-cycle batteries are used.

A minimal solar configuration will:

meet your daytime needs
then get you through the night without running out of power or over-discharging the battery
meet your needs again the next day while also recharging the battery

People who are off-grid for longer stretches will also have to think about reserve power. It's not so much an issue for recreational campers who will likely camp only in good weather, and can return home to charge in any case.

Should I build or buy solar?

In order from traditional to more recent approaches

DIY

DIY (do it yourself) means selecting component components individually (panels, solar charge controllers, batteries, inverters, isolators, etc) and installing them yourself.

Pro: Typically lowest cost. Components precisely meet your specific needs. You know where everything is, what it does, and how to replace it if it fails.

Con: Time-consuming. You have to learn enough to pick components and install them.

Kits

Kits are usually solar panels, charge controllers, and perhaps related hardware sold in one (hopefully) well-matched package. You will typically need to add your own battery, inverter, etc, as needed.

Pro: some of the product selection is outsourced for you

Con: likely could get better quality and better-matched components for less money with DIY. Packages are often put together by marketing teams instead of engineering or support teams and sometimes the combinations don't work as well as they could.

Portable power stations

Often called solar generators, these devices are neither solar nor generators. They are all-in-one systems packaging a battery, an inverter, DC outputs, and allowing various forms of charging.^[8]

Pro: all of the product selection is outsourced for you. Portable and generally attractive package.

Con: very expensive for what you get, and what you get is someone else's idea of what you should want. Generally not repairable by the end user. People with heavier power needs may find SGs challenging to integrate into camper wiring.

solar ready

RVs that are sold as "solar ready" typically have a connector and wiring from Zamp. It is more apt to call it "Zamp solar kit ready" as normal panels cannot be attached to the Zamp port. Here is Zamp's description of Solar Ready, which uses panels with built-in controllers.

"Solar Ready" doesn’t mean sh*t. It means there is a plug wired to your battery and oh by the way IT IS WIRED EXACTLY BACKWARDS. The polarity on the Zamp SAE style connector is reversed.^[9]

rack mounting

It is common to mount framed panels on a rack. This accomplishes a few things:

allows the panels to always be deployed
where they won't fall over, walk off, or be urinated on by loose dogs
allows underside cooling to minimize heat-related losses and re-radiation from superheated panels into the van interior
to keep from drilling extra holes in the roof
allow changes later; drill new holes in the rack

Note: avoid racks with "ladder retainers" or other vertical elements. Partial shading is brutal on solar harvest, and carrying around your own shade is an "unforced error". If you have inherited a rack with uprights consider cutting them off.

Is my solar working?

One of the challenges of learning solar is that until you understand how it works it can be difficult to be confident that it does work.

Resources

	Resource	Description
	Adding solar panels	Learn how to add a solar panel to an electrical system
	Planning your solar system	How to plan your solar panel installation
	Variation in harvest by region and season	Analysis of variation in solar harvest (PV panel output) by season and geographic area.
	Electrical Solar Forum	Subforum of the Class B Forums
	DIY Solar Power Forum	A very active solar forum with 100k members, founded by Will Prowse. Lots of residential and commercial solar discussion, but the "Vehicle Mounted Systems" sub-forum has plenty of info specific for nomads. Other sub-forums for batteries and solar equipment.
	Vehicle mounted solar forum	A subforum of the DIY Solar Power Forum.
	Hobotech DIY Solar Power forum	Private Facebook group with 10k members as of September 2024. "Official HOBOTECH YouTube channel group about DIY solar power, lithium batteries, generators, solar panels, power stations, power banks, ... LiFePO4, server racks, ... solar generators and their use off grid for RV, van life, camping, trailers ..."
	Solar Camper Van Build Life	Public Facebook group with 10k members as of August 2024.
	/r/RVSolarPower/	Subreddit with 500 members as of October 2024.
	Solar DIY	Subreddit with 67k subscribers as of August 2024. "SolarDIY is a community to share your ideas, projects, inspiration, and look for advice, ideas, and networking."
	Electrical matters forum	A sub-forum of VanLivingForum.com
	Search Amazon	Search Amazon for related products.
	Wikipedia	Wikipedia article on "Solar power".
	Search forums and groups	Search van life discussion groups for "solar power"
	Search related sites	Search van life sites for "solar power"
	Search NomadLife.wiki	Search other pages on this wiki for "solar power"