Why Solar?

As fuel costs soar, advocates of dry camping (or boondocking, if you prefer) are looking to the skies for an
alternative to constantly running their generator. Recent advances in solar panels and controls have made them
a savvy investment for the owner desiring a cost-effective upgrade that also improves resale value of the coach.

Some commonly used terms:

Watts=The amount of power that panels produce. This is usually expressed as peak, or maximum output
Ahrs or amp-hours=Current delivered from the panels for dc loads and battery charging
Photovoltaics or PV=An industry term for solar panels
Cross-tied=how batteries are wired for 12/24v combination systems, to allow for even charge/discharge

How do they work?

Solar panels, also known as photovoltaics (photo=light, voltaic=electricity) convert sunlight into direct current
(dc voltage). As sunlight is absorbed by the outer coating on the panel, the material releases electrons that
are steered to a conductive plate. This then transmits the electrical energy from the panel through wiring to an
external controller. The controller regulates the voltage and amps to the batteries.

Design, materials and especially size of the panel will dictate panel efficiency, power output and most importantly,
rated output at temperatures above 100 degrees Fahrenheit. This is not the temperature that you read on your exterior
thermometer. I'm talking about temperatures at the surface of the panel, which can average at least twenty to
forty degrees higher than outside air temperature. Example, if it is eighty degrees outside in bright sunlight, put
your hand on a black car and you'll get the picture!

Dollars and Sense

Solar panels have become popular both in the U.S. and abroad, and demand worldwide has driven panel prices
upward. Prices in the $600 to $1000 range per panel are not uncommon, and you are still looking at purchasing
the controller. This may lead some consumers to purchase lower cost equipment, but beware. Many less
expensive panels are so because they incorporate less silicon in their design, and performance can suffer at
higher temperatures in bright sunlight where panels are supposed to produce peak power. This is so substantial
that power losses can be in the 30-60% range over higher quality panels. When you consider that 4 panels may
only produce 20-30 amps per hour dc in bright sunlight, this is significant. Be sure to read the high-temperature
characteristics in the spec sheets.

Another thing to consider is the controller. Some low cost or mismatched controllers will not maximize the
efficiency of the panels, and in some cases the system will not produce power at all in lower-light conditions.
What you need in a controller is a feature that allows the panels to charge your batteries even during less than
ideal conditions. As sunlight fades and panel voltage drops, the charge controller converts to a pulse charger,
allowing charging of the batteries to continue unabated. Chargers with this feature also function with 3-stage
smart charging, very similar to how newer style inverter-charger combination units operate in the charge mode.
The real beauty of solar power lies in the fact that this is a ONE TIME expenditure. Once purchased, high
quality panels should last for decades. Depending on how the coach is utilized, they can save diesel, and
more importantly, extend the life of your expensive house batteries. Let's touch on this:

Beating the Dead Horse

How long should my house batteries last? Good question, no good answer. It all depends on how often you
discharge your batteries, how low you let them get before recharging, How long you let them recharge before
starting the cycle all over again. Fewer charge/discharge cycles, longer battery life. Less deeply discharged,
longer battery life. Here is a graph depicting battery life expressed in cycles and depth of discharge:

Now along comes solar panels, and voila! Your batteries can charge even when no shore or gen power, and
engine not running. All you need is sunlight. AND you can keep the Prevost chassis batteries topped off, but
we'll cover that later in this article.

More Power!

We'll assume your solar system is producing 25 amps dc per hour, and for 5 hours each day. This is well
within the capability of a 4-panel system. This comes out to 125 amp-hours put back into your house batteries
each day. If you have (6) 8-D AGM Lifeline house batteries, that gives you 1530 amp-hours to start, assuming
they are fully charged. If you pull 250 amp hours out each day and the solar panels put 125 amp hours back in,
you have effectively reduced your battery consumption rate by one-half.

If you discharge your house batteries no lower than the 50% mark (12.25 volts, a good idea if you wish to
maximize the lifespan of your house batteries) then that gives you 765 amp-hours to work with before you would
run your generator. With some prudent power-management techniques and using the example above, at 125
amp-hours used each 24 hour period this would allow for slightly more than 6 days before needing to run the
generator. In one stroke, you have reduced diesel consumption, generator maintenance, and extended the life
of your costly house batteries.

Just for Reference:

If you have 24v house batteries, then you probably have a series-parallel arrangement, with the batteries cross-
tied. Since the system will charge through the 24 volt side, find out how many amp-hours you have at 24 volts.
In this type of arrangement, you can usually figure the amp-hours at 50% of all batteries combined. You will need
a solar charging system rated at a higher voltage to charge 24 volt house batteries.

A Practical Exercise

If you are interested in some figures to see if solar panels will make an impact on your coach, run an amp draw
test. An important thing to remember is that your amp draw will vary as loads cycle on and off. You are looking
for the average draw.

You will need a dc clamp meter that can measure dc amps lower than 20 to within 1% accuracy. If you do not
have a good digital multi-meter and ac/dc clamp amp meter, they are an excellent addition to any coach owner's
tool kit. We'll talk more about that later.

Unplug your coach from shore power, and switch on about half of your dc lights. If you run your inverters when
dry camping, leave them on and switch on your televisions, 110v sconce and bath lights.
Go to the main output lead from your house batteries to the main dc output breaker and inverter(s). Set your
meter to the 200 dc amp range, and clamp your meter around this wire. Take current (amp) readings every minute
for 15 minutes, and write down the results.

At the end of the your test, add all your figures together, and divide by 15. This is your average amp draw per
minute. Multiply this figure by 60 to get your amp draw per hour (amp-hours or ahrs). You can get a good idea
of total draw per day by multiplying that by 12. This is not an exact figure, but it will give you a rough idea of how
much current you pull out of your batteries dry-camping.

Additional Benefits

If you store your coach outside for extended periods without 110v or 220v service, the solar panels will keep the
house batteries topped off, if the inverters are not drawing off of battery power.

For charging 24 volt chassis batteries when your house batteries are 12 volt, you can use a device called a dc to
dc converter to up convert 12 volts to 24. These are normally rated at 10 amps or less, but that it more than enough
charge rate to overcome parasitic draw on the chassis batteries. Even when the chassis switches are off, you still
have a little less than 1 amp of draw present on the chassis side. Couple this with internal loss present within the
batteries, and your chassis battery voltage can drop too low to crank the engine within 2 weeks. Constantly trickle
charging the chassis batteries is the only long-term solution.

Drawbacks

Aside from the initial expense of the panels and control electronics, solar panels are relatively fragile. Most have a
glass cover over the delicate panel material, but that is little protection from large hailstones or tree branches.
Also, you will lose some walk space on the roof for maintenance.