Solar

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Many Westy owners have turned to using solar power to provide modest amounts of electricity while boondocking or camping. This article describes the basic components needed to set up a small solar power system. It is not intended to be a how-to article, rather it is a jumping-off point. For people with no or only rudimentary knowledge of how to do electrical wiring, the go-to book is reputed to be the “Boatowner’s Illustrated Electrical Handbook", by Charlie Wing (ISBN-10: 0071446443).

This article was written by Rocket J Squirrel, based on his system. Others who have designed and built small solar rigs suitable for use in a Westy are invited to correct any errors and make any additions to the article which they feel will be helpful.

Solar Pros and Cons

  • Pro: silent power, energy independence, run a refrigerator for many days.
  • Con: expense, install hassles, no turnkey systems, limited power.

Contents

Power Management

To see if solar power is practical for you, you'll need to find out how much energy you will use in a 24-hour period. From that you can determine how much energy you'll need to get from the solar panel(s) to get that energy, and how big a battery you'll need to provide power for your appliances when the sun isn't shining. Note that everyone's needs are very different. Some folk might want to go for three or four days without giving their battery a charge. Others will be putting in a partial charge by driving each day [1], or a full charge every day from the sun when camping [2]. But maybe there will be a day or two of overcast? All this enters into your design considerations. There's no one-size-fits-all solution.

  • First, determine your energy requirements.
  1. Make a list of the appliances you plan to use (lights, refrigerator, DVD players, etc.) and how many hours you anticipate using each one over a 24-hour period.
  2. For each appliance, use the Battery Demand Calculator to determine how many amp-hours each appliance will need for that 24-hour period. Add them all up to find the total number of ampere-hours you're going to need for that 24-hour period. Then add in another 25%, just to play it safe. This number of ampere-hours represents an approximation of your energy requirements. (Double this number if you want to be able to run everything for two days in a row without a charge, triple it for three days, and so on.)
  3. And here's a consideration. That 800 watt espresso machine you'd like to bring? Using the Battery Demand Calculator we find that it will pull about 85 amps while running and if run for 5 minutes will draw 7 ampere-hours from the battery.
Solar Panels

Solar panels come in many sizes. Kyocera, BP Solar, Sharp and many other companies make excellent panels that will last for decades. Alternative energy companies such as Arizona Wind and Sun, Backwoods Solar (and others, no affliations or implied recommendations) sell panels (AKA solar modules, PV modules) in sizes ranging from a few watts to hundreds of watts. What size will you need? Like everything solar-related, there are no hard answers, just approximations. All that can be provided are suggestions.

Here are some assumptions:

  • You'll need to get at least as much energy from your panels as your energy requirements in order to keep your battery from running lower and lower each day.
  • How many of hours of sunlight can you expect? This needs to be direct, full sun. Light overcasts or even the shadow of leaves on the panels will drop their output dramatically. And the panels will need to be pointed straight at the sun -- if you're thinking that you'll put a panel on your poptop then you'll need to think about how many hours the sun will be shining directly onto the panel.

An example:

Let's say that your energy requirement (above) pencilled out to 24 ampere-hours per day, and that you expect to have 6 hours of full-direct sun on the panel.

  1. Divide 24 by six and we see that the panel will need to deliver at least 4 amps for every hour.
  2. Multiply the current you need by 17.4 volts[3] to get the panel's minimum wattage rating. In this case, 4 x 17.4 = 70 watts.  To play it safe, assume the panel manufacturer is 10% to 15% optimistic, and add on a little extra, giving you something like 75 to 80 watts as a target panel size.

Mounting the panels.
Some folk mount their panel on the roof of the Westy. They are designed to handle the elements and are quite rugged, so this can be very handy, although it limits where you can camp. If camping in full sun works for you, then it's worth considering. Others (Mr Squirrel is one) place their panels out in the sun on the end of a long extension cord. The links at the bottom of this page may provide some ideas.

Batteries

Your solar panels may have enough power to operate your appliances while the sun is shining on them, but without an auxillary battery to store energy in, you'll be without power when it goes dark. Here's another area where things get fuzzy and this article can only provide guidelines.

  • Sizing. The battery has to be big enough to keep everything running when the panels aren't delivering power. In the Energy Requirements section the total number of ampere-hours per day were calculated. Some of those hours are during the sunlit portion of the day while the battery is getting a charge. The rest of the time, that energy will come from the battery. Assume that you will have six good hours of sunlight (modify this based on your experience).
  1. 24 hours less 6 gives us 18 hours without sunlight. If we need 24 amp-hours per day, that means that when the panels aren't providing power, the battery will need to provided 18 amp-hours -- right? Not necessarily: if you're running a refrigerator then it might use less power at night when it's cooler. But you may be running lights. You're going to have to figure this out. But for the sake of this example, let's assume the battery will need to provide 18 Ah unaided.
  2. It's not a good idea to discharge a battery more than 50%[4], so get a battery with a 20 hour ampere-hour rating of twice that, or at least 36 amp-hours. If you don't expect any sun during a 24-hour period, then get one rated to supply twice your daily energy requirement. And so on.
  3. Add on some extra "just in case." Like another 10%.
  • Battery Types. Of the battery choices out there, a conventional flooded cell-type deep cycle, such as a golf cart battery, will be the most tolerant of use and abuse and provide the longest life. Most of the 12 volt deep cycle batteries are beefed up starting batteries and may have short lives of one or 2 seasons. Good for space savings and simplicity. Limited to about 110 A/H. 6 volt golf cart batteries are a lot more tolerant of heavy use. Two 6 volts in series will work better than two 12 volt batteries in parallel. Of the common, reasonably-priced brands, the Trojan T-105 is the best out there: best plates and a lot of active material in the plates. Yes there are better, such as Rolls Surrette, but bring money. Only problem is you will have to check and add water, they can spill if turned over, and they can give off hydrogen gas[5]. Typical capacity will be ~220 Ah which will also support a 1,000 watt inverter. AGM and Gel are still emerging technologies and the advertising is a lot of hype. While sold as sealed, they are not truly sealed. All of them have some type of pressure relief vent. Temperature changes can cause the vents to weep and once the electrolyte is lost it can not be replaced. Most cell failures are the result of dry out. Unless you truly have an application requiring a sealed battery, avoid AGM unless you really feel the need and also like to empty your wallet. Most likely you will have much better results with a Wal-Mart stock battery at ~ $55 and when it fails in less than 2 years, get the free replacement with the warranty starting again (Dennis Haynes).

Also see Joel Walker's post "How to Select the Right Battery" from the gerry.vanagon.com archives.
And here's a good deep cycle battery FAQ.

  • Locating in the Westy. Any battery can boil, off gas from a failure, whatever. For an RV application, the batteries should be installed in some type of sealed and vented compartment, especially if you plan to sleep while the batteries are being charged. This is not always practical so consider a flammable gas detector. They will pick up hydrogen. Plastic battery boxes are available for most any sized battery. They can be placed under the seat and you can install drain and vent of desired. At least if a battery boils out, the acid will be contained (Dennis Haynes).
  • Maintenance, including off-season (needs to be written).
Solar Charge Controllers

In the simplest form a solar charge controller protects the battery from the high voltage that a solar panel generates. Even a 10 watt solar panel can bake a lead acid battery. Solar panels operate in the 16 to 20 volt range while lead acid batteries only need a little more than 14 volts to reach a full charge. 

Cheap solar charge controllers get rid of the extra volts from the panel by forcing them to the lower voltage battery voltage by shunting current to ground -- throwing it away. Shunt-type controllers are rare these days, having been replaced by more advanced designs which waste less of the panel power. Such controllers don't have a place in any modern solar system. Like Earth's.

Of the more advanced designs are the "three stage" PWM (pulse-width modulation) types and the MPPT (maximum power point) types. The three stage controllers let the panels work at the higher voltages they are happy at, which means that almost every amp the panels put out get to the battery. MPPT  types are even more efficient (and expensive): they actually send more current to your battery than the panels are providing.

Good solar charge controllers are also good deep-cycle battery chargers. Unlike the Vanagon's charging system, which is designed to keep the starter battery happy, a good solar charge converter will top off your deep cycle house battery without overcharging it.

Charge controllers are available from dozens of online vendors. The Alternative Energy has listings here for PWM and here for MPPT controllers (no affiliations or implied recommendation here, just an example).
 

Wiring

Obviously it doesn't matter what kind of panels you get or the size of the battery if you can't wire everything up! The subject of how to wire things together so it's all safe and tidy and does what it is supposed to do is outside the scope of this article. If anyone wants to write about that, click here and go for it.

Wiring your van up for solar can be roughly broken down into three areas: connecting the panels to the controller and the controller to the battery, connecting the Vanagon charging circuit to the battery, and making the battery power available for your use.

So in order:

Connecting the panels to the controller and the controller to the battery.

As current flows through wire, a certain amount is lost in the form of heat due to the resistance of the wire (it's not a perfect conductor). The skinnier the wire, the more it resists the flow of current. As current is resisted, volts are lost. If you have a long skinny wire connecting your solar panel to your controller, the panel might be putting in 17 volts at the one end, but only 16 volts might be coming out the other. That 75 watt panel might only deliver 70 watts to the controller if one volt is lost, so the idea is to use wire fat enough so you won't lose too much power. How much is "too much"? That's up to you to decide.      Let's do an example. Say you elect to put a 130 watt panel on the roof of your Westy and figure that it will take 15 feet of wire to bring the power to the controller, and another five from the controller to the battery. And say that you don't want to lose more than 5% of the power, or 6.5 watts. What gauge wire should you use?

    1. Start by finding the panel's current rating from the manufacturer's data sheet. For the purpose of this exercise, we'll use the Kyocera KC 130 as an example. The manufacturer claims 7.39 amps (at ideal conditions, but we have to use some number).
    2. Use Ohm's Law to find out the resistance that loses 6.5 watts at 7.39 amps: R = P / I2 ("I" is current in EE-speak). This is 6.5 / 54.8 = .11 ohm.
    3. The actual wire length is 40 feet because the current flows out of the panel on one of the two conductors, through the controller, and back to it on the other of the two conductors; and the current from the controller to the battery also has two conductors involved so you're looking to find what wire gauge will have a resistance of .11 ohm over a run of 40 feet.
    4. Go to the Wire Resistance and Voltage Drop Calculator and midway down the page you'll find a wire chart where you can enter 30 feet and 7.4 amps. Hit the "calculate" button and we see that 14 gauge wire has .10 ohm over 40 feet, so it will work just fine. If you have fatter wire, you can use it -- the lower the resistance, the more power reaches the battery.

If the wire run is longer, or more powerful panels are used the wire has to be fatter in order to keep the losses down. Some folk, like Mr Squirrel, don't like to park in the sun and might have as much as 60 feet of wire out to two 45-watt panels. He has his controller mounted behind the driver seat, and the house battery is under the bench seat. There's 140 feet of wire there. He uses 6-gauge wire because he's crazy that way. See his link with the others at the bottom of this page.

Connecting the Vanagon charging circuit to the house battery.

There is a lot of discussion about this, and it's fair to say that there are a lot of ways to skin a cat - not that cats are in need of skinning. What you want to do is protect the engine's starter battery (under the passenger seat in the Vanagon, maybe elsewhere in different models) from being discharged by the appliances and other loads while parked, yet allow the engine alternator to charge the house battery when current is available.

GoWesty.com and busdepot.com sell kits for hooking up auxiliary batteries. It has been argued that the relays and wiring in the kits are not large enough to reliably handle the current a big aux battery needs for charging if it is deeply discharged. Dennis Haynes (2007) comments that "you want a truly reliable relay. Most important that it disconnects when expected. You want double break contacts like in those solenoid type cans. Not a small lighting relay." Such devices are usually called "power contactors." One manufacturer is Stancor, and their Type 120-901 contactor has contacts rated for 100A continuous, 400A inrush.

This is important -- if you're camping for a few days and expect that engine to start when you want to leave, you don't want to find that you have a dead starter battery.

The article "Battery Isolater/Starter Solenoid," by David Schwarze and Jim Arnott, is worth a read.

An oft-mentioned option is the Surepower 1315 battery separator which is said to do a fine job of connecting the aux battery to the charging circuit when it makes sense to do so, and disconnecting it when it doesn't. It's really just a relay system, with some additional "smarts." One Westy owner has kindly given permission to steal the content of his personal webpage about adding a 1315 to his Vanagon to use on this wiki, for more information, click here.

Similar to the Surefire 1315 are the Yandina battery combiner and the Power Stream Smart Battery Isolator. They are both relay-based products with "smarts." (if anyone has any experience with these products, please edit this page).

With regard to how fat the wire connecting the auxiliary battery to the alternator needs to be, some feel it to be important that the wire and relay be sized so that the battery can be charged quickly. Haynes (2007) writes that, "For wiring and charging, the circuit needs to sized for both charging the battery and any load connected to it. This includes inverters. The GC-2[6] size battery will pull about 40 amps off the alternator during the bulk charge. Add your other loads. Best results will also be a direct line from the alternator. 6 gauge."

Others feel differently. Mr Squirrel feels that while the battery might want 40 amps of current, putting it on a "diet" by using thinner wire which would slow how quickly the battery is charged initially won't make much difference when driving for a few hours, and his loads are never great enough to cause much of a voltage drop in a few feet of 10-gauge wire. As wire size goes down, resistance goes up which will result in heating of the wire when passing a lot of current. Wire's ability to handle current without overheating is called its "ampacity" and you want to stay below the wire's rated carrying current. A table can be found here. In short, to be able to quickly charge the aux battery then fat wire will help assure that the battery and any connected loads receive full alternator voltage. This applies not only to the wire connecting the starter battery to the aux battery, but the wire -- and connectors -- between the alternator and the starter battery since the charging current for both batteries must flow through that one wire.

Charging Deep Cycle Batteries when Household Current is Available

Use a good microprocessor-controlled multistage charger with bulk, absorption and maintenance/float stages. A good article on this subject can be found here.


Charging Deep Cycle Batteries with the Vanagon Alternator

The alternator is designed to charge the engine starter battery. Starter batteries have thin lead plates so they can deliver a lot of current quickly, and in routine usage they don't get very deeply discharged. The alternator provides a constant voltage (usually around 13.8V or so) backed up with a lot of current in order to quickly recharge the starter battery. It's an effective match.

Constant voltage chargers like an alternator aren't very good for recharging deep cycle batteries with their thick plates. Such batteries are best charged by multistage chargers which take the battery through several steps of voltage and current in order to wring out the best performance and operating life; such batteries like to be taken to more than 14 volts to completely remove sulfite deposits from their plates. When driving, the best an alternator can do is take the deep cycle to around 85% of full charge, which means that one may arrive in camp with a battery that is less than fully topped off. That missing 10 to 15 percent can matter even more if one is trying to avoid discharging the battery below, say, 50% to help prolong its life.

With sunny conditions in camp, a good multistage solar charge controller will do a good job of charging deep-cycle batteries to 100%, and when household AC current is available a good smart charger will keep the battery fully-charged. But to fully charge a deep cycle battery while driving the alternator isn't so smart. One solution is to use an inverter to convert the alternator's voltage to 120VAC, and use that to power a household smart charger to charge the deep cycle battery. Another approach is to use a charger designed to operate directly off the voltage the alternator provides. One such device is the Powerstream PST-BC1212-15, a four-stage DC input charger which operates off the alternator. It operates at input voltages ranging from 10 to 15VDC, and provides up to 7.5A charging current (current model - Mr Squirrel has one of their early models which can be switched to provide 15A maximum charge current. The newer ones don't have the switch, but the cutout in the case to mount the switch into still exists, covered with a sticker; and the circuit board pads are still present to which the switch can be wired. It's not known why the manufacturer deleted the higher current capability). There may be other brands of suitable DC-DC multistage chargers [if found, add them here].

Making the battery power available for your use. (cigar lighter receptacles, etc.)
Living on limited power
  • Low power appliances (lighting, etc.)
Existing Setups
Notes
  1. ↑ The Vanagon alternator is intended to bring your engine's starter battery back to full charge, it is not designed to fully charge the types of deep-cycle batteries that are needed for solar power applications.
  2. ↑ Solar panel charge controllers are designed specifically to fully charge deep cycle batteries.
  3. ↑ Solar panels put out more power at a higher voltage than the battery's 12.6 volts. It is the job of the solar charge controller to match the panel to the battery. 17.4 volts is around where most panels put out the most power. MPPT-type controllers extract the most power from panels, standard controllers a little less.
  4. ↑ 50% is a simplification for the purpose of this article. You can discharge a deep-cycle more than 50% if a shorter life is acceptable. For longer life, then shallower discharges are desirable. See "Cycles vs Life" for more information.
  5. ↑ One or two small lead-acid batteries will not emit Hindenburg-levels of hydrogen. Besides, the stuff is lighter than air so it will rise up to the underside of the poptop, and the molecules are so small that they will easily drift out through the fabric and cracks up there.
  6. ↑ These are serious batteries. Each 6v GC-2 (T-105 profile) "golf cart" battery packs about 225 amp-hours of capacity. Each also comes with a nearly 70-lb penalty and two are needed to make 12 volts.
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