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electrical:solar:gentle_intro
A good solar system is one that meets your needs. – jimindenver1)
The fastest way to bring beginner expectations of solar in line with reality is to assume you will run nothing off an inverter. – secessus

A gentle introduction to solar

This page aims to provide beginners with a basic overview of solar power for nomads. There are oversimplifications and concepts skipped for clarity. If you would like a refresher on basic electronics, see the AltE Intro to Electronics for solar video.

benefits of solar

Solar power is silent, works for decades, and is always working when the sun is shining.2) 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.3) Failure to charge lead batteries4) fully and regularly leads to battery murder. Solar helps prevent battery murder and the resulting $$ 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.

how solar power works

Solar power uses solar panels to convert sunlight into electricity. This power is usually stored in a deep-cycle "house" battery, which is separate from the vehicle's starter battery.5) Electricity from the panels is fed to the battery by a solar charge controller, which keeps the battery optimally charged and powers any loads (things that consume power).

Now that we know how it works we can see where it falls down.

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”.

More specifically, solar-only charging can be unnecessarily difficult and expensive because of the many factors that can reduce solar harvest. Additional sources of charging can be added to increase resilience and decrease cost.

Minimizing power consumption is key to happiness with a simple, affordable solar setup. It requires a change in mindset for most folks. Electrical power becomes a precious resource to be carefully consumed. The path to frustration (or at least considerable expense) involves heating or cooling with electricity or trying to run household appliances in a van.

“…trying to take the comfort level you had in a house into your mobile life [is] tough to do for a boondocker.” – akrvbob6)

The amount of power a solar configuration outputs is greatly affected by things like latitude, season, shade, temperature, and even battery voltage. A crude rule of thumb might be meaningful solar harvest is possible only when the sun is throwing well-defined shadows on the ground.

Since it looks like magic, beginners tend to worry about whether or not their system is working. The solar setup is almost always working as designed.

how much solar do I need?

This question usually means “how much power do I need?” and involves making power7), storing power8), and using power9). 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. It's like writing down all your monthly expenses when making a family budget. As with budgeting, it requires attention and honesty.

Note: you can get a ballpark idea before crunching your own numbers by reviewing some existing solar installs.

Before continuing on, take a peek at factors that will affect solar requirements.

why daily?

Power requirements are assessed as daily because solar power feeds the batteries10) only in daylight. Then at night the 'dweller pulls power back out of the batteries. So a minimal solar configuration will

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

No one but you knows how much power you will need daytime and nighttime. First-timers often have radically unrealistic ideas about power in the van.

adding it up

The best way to do it is with a calculator or a spreadsheet of your own design.

For the purposes of this article, we will assume a fairly normal battery bank size of 100Ah of lead battery (flooded or AGM)11), and 200w+ of solar panel, depending on where the camper will be used.

build or buy?

the easy answer

Kits are available that handle the basics at a reasonable price. 200W of solar is the most common campervan setup, and is sufficient for most campers that do not run inverter (residential appliance) loads.12)

Are kits the penny-pinching cheapest, or the highest tech, or the most tacticool military/marine grade option? No. But the average user doesn't need those attributes. And once users get comfortable with how their system works it can often be tweaked for better operation by adjusting controller setpoints.

For now, let's consider some common kit-based installations. The terms used will be discussed later in the page in case you don't recognize some of them.

  • 200W kit + a 100Ah wally world learner battery is about $450 at late 2017 prices. This is about $1.75 per solar watt produced13) and would cost ~$750 over 5 years, including expected battery replacement.
  • As above but with AGM: 200W kit + a 100Ah 100Ah Renogy AGM or similar is about $550 at late 2017 prices. This is about $1.75 per solar watt produced14) and would cost ~$950 over 5 years, including expected battery replacement.15)
  • 200W kit + 2 x 6v golf cart battery bank (200Ah+) is about $550 at late 2017 prices. This is about $1.75 per solar watt, and would cost ~$550 over 5 years. Flooded lead acid golf cart batteries are the most tolerant of beginner mistakes, and will take the most abuse.
  • 200W kit w/MPPT controller + 2 x 6v golf cart batteries (200Ah+) is about $675 at late 2017 prices. This is about $2.37 per solar watt, and would cost $675 over 5 years.16)
  • 200W kit w/MPPT controller + AGM battery (200Ah+) bank is about $875 at late 2017 prices. This is about $2.37 per solar watt, and would cost $965 over 5 years~. Note: AGM batteries are not particularly well suited for solar-only charging.17)
  • * 200W kit18) + drop-in lithium bank 100Ah19) is about $1350 at late 2017 prices. This is about $1.75 per solar watt, and would cost $1350 over 5 years. But with proper treatment LiFePO4 batteries can last up to 10 years, bringing the 5 year cost down to $675 if one sticks with it that long and treats the battery well.

200W is not a magic number, but it is the most common size of solar install for vandwellers and boondockers. It is probably more than what's needed for the basics and has enough power to add in a 12v compressor refrigerator if desired.20) When combined with an isolator, 200W is probably all the average camper needs in typical conditions. Folks that want to run microwaves or other power-hogging appliances will have to pony up with more gear and more $$$.

Going beyond the basics, handling the basics more frugally, or running non-trivial loads off an inverter will require more research, planning and patience. Read on, and follow links in the text to drill down to deeper explanations. Beware that some of the links are technical.

a typical DIY setup

A typical DIY setup might run LED lights and roof vent, charge a phone/laptop, and run a 12v refrigerator. It might look like this:

battery

Solar setups require a battery bank of some kind, even during the daytime.21) In simple installs the bank is one or two batteries.22) The battery also stores excess power. At night or any other time your demand is higher than your solar is pumping out, you will be pulling power from the battery.

For reasons related to the chemistry of lead-acid deep cycle batteries, it takes twice the amount of battery bank Ah rating to deliver the daily Ah requirement.

[more batt

total 91
Minimum battery bank23) 182

and that's just to get through a 24hr period with good sun. If you want to get through a day (or more) of terrible solar yield (rain, snow, fog) it requires even more battery capacity (reserve), money, and cargo capacity. These numbers are both very rough but will illustrate the pattern:

Rated Ah cost (flooded) cost (AGM) weight in lbs
Minimum battery bank24) 0 days of reserve 182 $182.00 $364.00 91
1 day of reserve 364 $364.00 $728.00 182
2 days of reserve 546 $546.00 $1,092.00 273
3 days of reserve 728 $728.00 $1,456.00 364

Don't panic! You don't need to spend thousands of dollars. In practice, many vandwellers do not design for extra days of reserve, planning on just not having power (or not much power) on rainy days. And there are other ways to compensate for rainy days:

The most beginner tolerant and value-for-money battery bank is two 6v deep cycle flooded25)“golf cart” batteries wired in series to make 12v. This will provide 200+ Ah (amp-hours) of rated capacity.26) This bank gives one normal day's use and and about a half/day of of reserve (ie, a day with no charging). A set of golf carts like this will be sufficient for most needs and does well with 200-500W of solar panel. Deep cycle batteries are typically discharged no lower than 50% as this is a good usability/lifespan compromise. 50% DoD is about 12.2v for lead-acid chemistries. A Low Voltage Disconnect can help prevent deeper, damaging discharge.

Yes, they should be vented. No, not everyone does.

Sternwake says:

“I don't think any battery is going to out cycle a 6v flooded golf cart battery. These are simply the most tolerant of the type of usage typically seen in this lifestyle.”27)

Because beginners commonly murder their first battery bank, a common beginner's battery is a Walmart "deep cycle" / marine battery, preferably one with removable cell caps for adding distilled water as needed. Often called a “learner battery”, they do not have long lives or much capacity but are widely available nationwide and often have pro-rated warranties. A walmart battery will usually have half the capacity of actual deep cycles, so Bill would get one nights's power with no reserve for rainy days.

Also common are AGM batteries, a sealed type. They do not have to be vented under normal conditions and have very high charge/discharge rates. On the downside they cost 2x as much, require vigorous charging one generally cannot get with solar charging alone, cannot be charged to as high a voltage, and have less capacity.28)

About these Sternwake says:

“While AGMs are considered a no maintenance battery if they were a person… they would be considered high maintenance… and only with a surplus of everything they want could they be kept happy.”29)

A single 12v AGM would get Bill through one night; two can be paralleled to double capacity to nearly match the capacity of the golf cart batteries.

panels

A common rule of thumb for solar-only charging is that one needs one watt of solar for every Ah of rated battery capacity. 2:1 is recommended for winter or other challeging conditions, and 3x is even better for off-grid folks.30)

So about 200w of solar is a good fit for Bill's 200Ah golf cart bank if he stays in a sunny area like the desert southwest. In the Pacific NW he'd be better off with something like 600w.

Ratio W:Ah Panel watts
1:1 solar 182
2:1 solar 364
3:1 solar 546

Considering the solar panels themselves, there are framed panels (mono, poly), and semi-flexible (mono, poly, or amorphous) panels. Buy whatever:

  1. fits on your roof
  2. is the cheapest per watt

This usually means framed panels, as flex panels are usually 2+ times more expensive per watt and are less rugged. Flex panels do have legitimate uses but they are specialty panels and are not recommended as a default panel for most builds.

Arrays of two 100W panels are popular because 100w panels can be shipped individually by UPS/FedEx. Larger panels may require $$$ truck shipping; try to buy those locally if possible to avoid shipping fees.

100W panels are usually nominal 12v; there are also 20v and 24v panels one can source from the solar grid-tied market. The higher voltages panels are paired with a MPPT controller31) (see below) but tend to be cheaper per watt.

The two main types of panel in 2018 are monocrystalline (mono) and polycrystalline (poly). The technical details are unimportant but you will see panels described as mono or poly when you are researching. Due to relatively small differences in their voltages, poly panels are slightly better suited to PWM charge controllers, and mono panels32) are slightly better suited to MPPT controllers. These controllers are discussed next.

charge controller

The charge controller stands between the panels and battery bank and takes care of charging. There are two types of controller commonly found in vans and RVs:

  • PWM - simple, inexpensive, cannot make complete use of the panels' capabilities.
  • MPPT - more complex, 2-3x more expensive, can run the panels at max power, optional with 12v panels and mandatory when nominal panel voltage is higher than nominal battery voltage.33)

PWM are cheap enough that it is common to start with PWM and upgrade to MPPT later only if necessary. After one upgrades from the PWM unit it can be kept as a spare/emergency part.

Folks in areas of limited sunlight (like the Pacific Northwest) or heavier power use might be better served by investing in MPPT right away.

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.

This information will help you tell if it's working or not.

1)
paraphrased
2)
portable solar only produces when deployed
3)
Solar is not mandatory with lithium or chemistries that aren't harmed by partial state of charge.
4)
AGM is lead!
5)
unless combined using an isolator, or running a single-battery setup
11)
or 50Ah of lithium
12)
Yes, you can run inverter loads. The problem is not with the inverter; it is with users who do not realize how much power residential appliances consume. Planning to have no inverter will build in realistic expectations from the beginning. – secessus
13) , 14)
actually going out of the controller into the battery
15)
MPPT suggested for AGM, which would add another $75 or so
16)
using a locally sourced 24v panel with the MPPT controller would bring the cost down to $1.25/solar watt
18)
no MPPT required
19)
roughly equivalent to 200Ah of lead
20)
assuming good conditions like the desert southwest
21)
this is to help the controller stay stable
22)
not including your vehicle's starter battery
23) , 24)
except lithium
25)
you can/must add water periodically
26)
100+ Ah of usable capacity
30)
1:1 is usually sufficient if solar charging is augmented with alternator or other sources. 2:1 might still be required in areas lihe the Pacific Northwest.
32)
and “high voltage” 20v/24v panels
33)
e.g., 24v (72 cell) panels with a 12v bank
electrical/solar/gentle_intro.txt · Last modified: 2021/06/11 12:08 by frater_secessus