Welcome to our Information and Learning Guide! If you're new to 12v - 24v solar, don't worry. It's not magic. Basic systems are pretty simple.

BHA Solar on Tiny House

 Install an RV or Off-Grid 12 Volt Solar System that WORKS!

By Bill Andersen

BHA Solar - updated Feb 2024

If you are a beginner and are confused about how a stand alone solar system works, the basics are not complicated. 12v panels have 2 wires, pos and neg, and batteries have 2 connection posts, pos and neg.

If you're a total beginner I always caution to start slowly before investing a lot in equipment and learn from a small starter type system and use it a while to really learn how it works and what to expect. ALL the systems are modular and can be expanded.

Basically the solar panels charge the batteries and you run everything off the battery bank. How big a system depends on what you want to run and for how long.

Large systems can run large loads. Running an air conditioner off a small solar/battery/inverter system has always been the holy grail, but efficient air conditioning units like mini splits and lithium batteries now make it very possible. Many people are successfully running small AC units and window units with inverter / solar / battery systems. Most folks full time off grid are very conservative with power and use propane wherever possible, particularly cooking, propane refrigerators and hot water heaters, and space heaters, but new lithium batteries are becoming the new gold standard for solar/battery/inverter systems. They're easier to recharge (5x faster than lead acid, so a smaller solar array is needed) and they last years longer

A good starting point for running full time loads in an RV is something like this:

600W 12v system, 2 x 100AH lithium batteries, and a continuous 2000W 16.7A output inverter

A separate component added to your battery bank for standard 120v residential power is an inverter. A pure sine is needed for refrigerators and anything with a compressor. Factory installed inverters in large RVs are usually 2000W pure sine. Inverters can be hard wired to an elec distribution panel or a sub panel installed by an electrician, or can be used simply with some inverters that have built in outlets and usb ports

A "solar setup" for an RV can be anything from:
small system for running LED lights, water pump, furnace fan and controls for propane fridge and water heater on weekend camping trips w/o hookups for shore power, to
A large system to be off grid in an RV for weeks at a time, or to living full time and running full sized res refrigerators, freezers, small water heaters etc. (You usually cannot run RV air conditioners off of batteries without a soft start on the AC unit itself and a hefty lithium battery bank.

System sizing isn't an exact science. Its like deciding how much water you need if you're thirsty, but if your set up isn't providing enough power you can always expand it. All solar systems are modular in that respect. (nobody ever calls me and says "Hey! These solar panels are too much power! I can't use it all!")

It's difficult to compute exactly how big a system you should build, but you can narrow it down during your planning

What will your actual usage will be? how many amp hours (ah)?
REMEMBER! 1 amp at 120vac is 10 amps at 12 volts dc, so when living off of solar power you'd want to limit running high amp draw things very long after dark when the solar isn't charging. Compressors, electric motors and anything that gets hot have a high amp draw. Hair driers, toasters, microwaves etc.
A 1200W elec space heater for example? pulls 10 amp from residential 120vac power, but 100 amps off of a 12v battery!

Large amp draw items can still be used, but conservatively after dark. When batteries are full and the sun is shining, you can use the batteries at the same time as they're charging. Often when running large loads while solar is doing max charging, you're not discharging your battery bank at all!

A microwave might be pulling >100 amps while running, but warming up soup for 2-3 minutes is only 5 ah. Your Mr coffee machine is 900 watts and heating elements draw 5.9 amps. So if it was left on for an hour, you use 59 AH out of the battery! Off grid folks will brew for 10 minutes and put coffee in a thermos, using 1/6th of an hour or 9.8 amps
400 watts of solar in full morning sun can replace 9.8 amps in < 30 minutes, because 2 panels can produce 20a. So if you use the coffee machine and the suns already shining, then the battery bank would run the coffee machine with no AH drain and still be getting charged at 10 amps
many things like laptops, iPads cell phones and LED lights are easy to run indefinitely off of a modest solar/battery/inverter system. 8 LED lights running uses less than 1 amp
But predicting usage isn't usually the biggest mistake folks make in planning. It's having wildly unrealistic expectations of how much electricity they can collect
So if you can estimate your future usage, you can estimate how much solar you need to match it.
200W panels are rated at >10 amps, but they harvest the most power from the sun roughly from 10-2 and a conservative rule of thump is to figure 5 hours a day x rated module output. Just because its light outside doesn't mean a 100w panel is putting out 100 watts. Solar panels work in low light, but work better with more sun
It depends on where you're located and average amt of sun, cloud cover etc. The further north you are the lower the sun comes up over the horizon in winter. and shorter days. MPPT controllers are recommended to squeeze every drop of sun early and late in the day in low light, and tilting the panels helps also.
On "average" 6-800 watts can fully recharge 2 x 100ah lithium batteries from max discharge to 100% in about 5 hours.
For maximum lithium life span its recommended to cycle lithium batteries moderately when possible in 30% to 80% range

Basics of how you set it up:

put the panels in FULL sun.

connect the pos and neg wires to a charge controller (Morningstar is the best by far and all we've sold for 14 years)

keep controller as close as possible to battery connections with heavy battery cables. This is critical to prevent voltage loss.

connect an inverter to batteries for 120va 

Once you've been using your solar power a while you'll be able to zero in on what your actual daily AH (amp hour) usage is and increase the size of the solar charging appropriately.

Then you can size your battery bank for however many days you'd want to go with continuous power without any charging. (solar panels produce zero power when covered by snow) most folks try to have 3-5 days autonomy.



Install by Durand C. in Maine 800 watts


Our kits are designed with 12v solar panels which can be configured for 12v by connecting in parallel (pos to pos and neg to neg) or 24v by connecting pairs of panels in series (pos to neg) and to be fairly easy and uncomplicated to put together yourself. Don't pay too much attention to forums or you-tube videos. Many if not most don't have a clue and some are totally wrong, giving bad advice

There is no one size fits all system design, but the basic rules are the same. RV and small off grid solar systems typically can supply power for most everything up to and including a microwave or small air conditioner. Folks off grid full time typically use propane for cooking, heat, hot water and propane fridge. Batteries easily power the elec controls for gas appliances, and everything 12 volts in an RV like lights, water pump and furnace fan. An inverter supplies 120vac power. When air conditioning is needed many RVers either move north, pay for shore power or run a generator. Hybrid solar systems can run large loads using a much smaller gen as a supplement with the inverter/batteries

To simply replicate shore power off grid like your on the grid house requires a large solar array charging a large battery bank. 
The future gold standard for batteries seems to be lithium, but cost is high so many folks still use flooded deep cycle batteries like golf cart batteries. A huge advantage with lithium batteries is that they can be deeply discharged without harm and recharge 4-5 times faster. Always check to make sure there is a 5-10 year warranty. (some advertisers state "10 year possible lifetime" but only have 1-4 year warranties.

Solar panels and a Tristar controller can recharge Lithium batteries 4-5x faster than lead acid. REFILL your battery bank easily every single day!



Larger off grid systems are usually 24v, but RVs come from the factory for everything 12v.


We want you to have a system that actually works well and lasts for years, but here's a critically important thing you should know

Your Off Grid or RV Solar panel system is only as good as the charge controller, the heart of your system and all controllers are far from equal.

Besides complete system failure when a controller goes bad, the chronic undercharging of your expensive batteries will cause them to fail and need replacement much sooner. Morningstar is an American company and has had over 2.5 million controllers installed in 112 countries over 25+ years. MANY are still in operation today. The finest charge controllers in the world are Morningstar MPPT. Amperage and voltage ratings differ, but more importantly, charging algorithms, protections, warranties and advanced features vary greatly between brands. The finest charge controllers in the world are the Morningstar MPPT    LEARN MORE HERE  -  5 REASONS TO USE MPPT (OR NOT)

BHA SOLAR      5 year warranty and 15 year expected life




The following 2 links are experts and provide a massive amount of RV / OFF GRID 12v solar knowledge.

These sites haven't been updated lately but still have mostly applicable information and are great free learning sources and a good place to start

HANDYBOB - Making off grid RV electrical systems work

I really like Bob and owe him many thanks for all his knowledge. A retired electrical engineer very compassionate about RV solar, who was off grid by 2003. He is aimed at the "frustrated, technologically challenged and budget minded RV owner who needs basic education about battery supplied electrical power."

It takes hours to read, he's long winded, and rants on the state of the RV manufacturing and RV Solar industries but If you read all of it and follow his advice, you will have a great system that works and gets the batteries 100% full so they last longer! Read it more than once, (it's free, but he welcomes donations!)


Another expert, he wrote a book about RV Solar and has it available for free. His information is a little more complicated, and from the viewpoint of one who can afford to spend more money. It's well organized and has a LOT of expert advice and instructions with photos

We've distilled down and summarized a few of the most important points below



Just shading on one small square on a panel drastically reduces the output of the ENTIRE panel

See those little shadows?
Surprise! Minus 6.4 amps
from these two panels! This is 90 % of the output of a full panel. When solar panels are configured in series then the entire string will be effected, but in parallel only the panel shaded will be effected


Voltage loss is the enemy in these systems, and is especially critical from charge controller to battery. Keep wire runs as short as possible, and use the proper cable size. (Don't waste money on wires bigger than needed for 2% drop on MPPT systems or 5% on PWM systems)  Use a wire sizing calculator like this one


Distance under 3' with large wire. Max wire size accepted: 10 AWG for Sunsaver controllers, 6 AWG for ProStar, and 2-4 AWG for TriStar. Splicing a piece of 10ga onto larger wire is OK and won't get hot if done properly, or simply clip some of the fine wire strands off larger wire until it fits. This won't affect anything.


It will send more voltage when batteries are cold so they still get 100% charged. It'll reduce the voltage when batteries are hot so they don't overcharge. (A temperature sensor on a controller that is located in a heated area will not see the battery temperature, so it will not work.) The Sunsaver controllers do a good job in cold weather with built in temperature compensation, and the ProStar and TriStar remote temperature sensors are a must. (adding the temp sensor to Prostar controllers requires soldering 2 wires)


Every 12 volt solar system should have a real battery monitor that includes percentage (%) of charge. Not just voltage. This is the only way to ever be confident that your system is really working. learn more

                                                                                          Trimetric 2030-RV


*check with the battery manufacturer

If you can get a TriStar controller it has volt set points as high as 14.8 , or Bogart SC2030 can easily be set to any voltage at all.  It is even smarter than a Tristar. It will charge better and faster than any other PWM controller. The smaller Morningstar controllers are 14.4 volts with built in temperature sensors, which will get the batteries full, but it takes a little longer. The RV Battery Charging Puzzle

BHA RV Solar kits save you money. Top quality parts that maximize charging and life of your batteries


       Awesome 1200 watt solar Off Grid system installed  on Bainbridge Island in Wa. by Doug H.


BATTERY INFO from solarseller.com




Electrolyte  ELECTROLYTE

VRLA (valve regulated lead acid) Battery  VRLA BATTERY

Gel Cell Battery  GEL CELL BATTERY

AGM (absorbed glass mat) Battery  AGM Battery

Flooded Type Deep Cycle Battery  FLOODED TYPE BATTERY

Self-Discharge Rate  SELF-DISCHARGE RATE

Charge Rate  CHARGE RATE

Electrolyte Level  ELECTROLYTE LEVEL

Equalization Charging  EQUALIZATION CHARGING

State of Charge  STATE OF CHARGE


Battery Location  BATTERY LOCATION

Used Batteries  USED BATTERIES

Battery Safety Battery Safety


How to wire 6v and 12v batteries together in series and / or parallel



Wiring of fuse / breaker devices is covered in detail in this article


Fuses/Circuit Breakers:

"In-line fuses or circuit breakers are important to protect the wiring and components in your system from shorts and other catastrophic failures. Place one on the positive wire within a foot of your battery and another in between the combiner box and the charge controller. The size of the fuse or breaker depends upon the size of wire used in your system. Place no larger than a 30 amp fuse or circuit breaker for 10-AWG wire; no larger than a 48 amp fuse for 8-AWG; no larger than a 74 amp fuse for 6-AWG; and no larger than a 120 amp fuse for 4-AWG wire." 

Fuses for Inverters to battery: Always use the exact factory recommended size fuse stated in the installation instructions


More good info and pics:

From Kelly's RV Solar Blog - Great blog with lots of interesting info and good photos.

Excellent complete wiring diagrams of 2 systems

Diagrams From Jack Mayer w/ reading at  RV Solar Electric  

Integrating a system with inverter & subpanel

System powering main load center w/ inverter

All charging sources integrated

Typical Wiring Examples below


_wsb_211x353_2panel+branch                             _wsb_337x319_3$2Bpanel$2Bbranch$2Bconn

How to install Spider Wire to parallel panels video


yago100-f2 yago100-f3



                                                        Typical Wiring Examples above


Build your own combiner box with parts from home depot

_wsb_219x163_project1_double      _wsb_327x261_overview_project1      _wsb_216x162_project1_done

Build A Mini Junction Box

minibox_items    minibox_wiring

System photos below from HANDYBOB






DISCLAIMER : Always make sure that all of your equipment is properly fused and grounded for safety. Also, be sure to read and follow the advice and instructions that come with your equipment. While our projects have actually been constructed and tested under actual operating conditions, we do not guarantee that they will meet all electrical codes in all locales. Nor do we suggest that our advice supercedes the recommendations of a licensed electrician. Hey, we're just trying to help!