Sizing an RV Solar System

Gone are the days of having to find a camp site with a power outlet to connect into. The world is there to be explored and solar can silently power all of your adventures. Often is all you need are a couple of solar modules, a couple of batteries, a charge controller and inverter to cover your energy needs when you’re away from the utility grid. How perfect to be harnessing the natural power of the sun while you enjoy the best sights nature has to offer!

When sizing a solar system for your RV, the general rule of thumb is: for every 2-6 Volt golf cart batteries you use for your house batteries, you need approximately 100 watts solar power to maintain those batteries. If you have 4-6 Volt golf batteries, your system should have 2-100 watt solar modules. One 80-120 Watt solar module allows you to operate your lights, TV, radio and other basic appliances for a few hours each night without having to turn on your noisy and expensive generator. The following day, the solar module will recharge the batteries the next day.

While this general rule of thumb works for most RV owners, there are however, exceptions to this rule. Some of these exceptions include:

• Battery Voltage, 6 Volt vs. 12 Volt Batteries. Let's face it, trailers and RVs are extremely limited in space. Sometimes, there is only room for a single 12 Volt battery. In this case, a 50-80 Watt solar module will keep that house battery nicely topped off.
• Extended Dry Camping. If you typically dry camp for an extended period of time, 3-4+ days, you live in your RV or you simply prefer not to rely on your generator or shore power, you may find a solar system consisting of 200-400 watts will better accomodate your power needs.
• Short, Quick Dry Camping Adventures or Reliable Access to Shore Power. If you dry camp periodically, 2 days once every two to four weeks, a 100-watt module will keep your house battery(ies) maintained.
• RV Storage and Battery Storage Maintenance. There is nothing worse than getting ready for a new season of fun and adventure in your RV, you turn the ingnition and find out that your batteries are dead. A simple and effective way to maintain your starter battery during the off-season is to add a 10 to 80 watt solar module directly to your starter battery. For most RVs, a 10-20 watt "trickle-charge" module is the perfect size to maintain your battery, however, today's RVs more often than not, have more phantom loads than ever before. If your RV has a lot of these phantom loads, a larger solar module may be required to keep that battery maintained. Phantam loads come from electrical devices that continue to draw power even when they are in the "off" position. Things like GPS systems, TVs, DVD players and other items should be unplugged when not in use. Even being as thorough as you can, there may be additional items that are drawing power that you may miss, requiring a larger module.

One thing to keep in mind when sizing your solar system, is that the solar modules charge your batteries. The amount of power you have depends on how many and the type of batteries you have. The more solar modules you have, the quicker the modules will recharge your batteries the next day. The fewer the modules you have, the longer it will take to recharge your batteries.

Additional items that you want to include in your solar system:

Charge Controller. Don't forget the charge controller... Charge controllers are an inexpensive way to help protect your batteries from overcharging. And because overcharging your batteries can kill them, charge controllers are an essential part for your RV's solar system.

Power Inverter. And finally, the inverter allows you to operate your standard 110 Volt appliances including lamps, radio, TV and even a microwave. Not all RVs need an inverter. If you are hooked up to shore power or if all of your appliance are 12 Volt DC, an inverter isn't needed, but most people find that an inverter is a convenient component to add to your system. If you use a microwave, a 1500 watt inverter is the smallest inverter you want to use.

Generator. Its always a good idea to have a generator when you own a solar system. You may never use it or you may not use it very often, but its an item that compliments any system and can help during an emergency or during those times of extended cloud coverage. Depending on the inverter you have selected, an Automatic Generator Start Module (GSM) can be added. For many RVers, the GSM is a great convenience. When the batteries are low, the generator automatically turns on, charing the batteries and then automatically shuts off when the batteries are charged.

Additional information about proper charge controller, inverter and generator sizing for your RV can be found in future blog entries. If you need immediate assistance, contact us toll free at 1-800-842-5678 or 1-307-635-9205 or email us at solarelectric@gosunsolar.com.

Solar Discovery: How to Take Advantage of the Federal Stimulus Funding

Solar Discovery: How to Take Advantage of the Federal Stimulus Funding

Battery Charger Selection

Most deep cycle applications have some sort of charging system already installed for battery charging (e.g. solar panels, inverter, golf car charger, alternator, etc.). However, there are still systems with deep cycle batteries where an individual charger must be selected. The following will help in making a proper selection.

There are many types of chargers available today. They are usually rated by their start rate, the rate in amperes that the charger will supply at the beginning of the charge cycle. When selecting a charger, the charge rate should be between 10% and 13% of the battery's 20-hour AH capacity. For example, a battery with a 20-hour capacity rating of 225 AH will use a charger rated between approximately 23 and 30 amps (for multiple battery charging use the AH rating of the entire bank). Chargers with lower ratings can be used but the charging time will be increased.

Trojan recommends using a 3-stage charger. Also called "automatic", "smart" or "IEI" chargers, these chargers prolong battery life with their well programmed charging profile. These chargers usually have three distinct charging stages: bulk, acceptance, and float.

Watering Flooded Batteries

Flooded batteries need water. More importantly, watering must be done at the right time and in the right amount or else the battery's performance and longevity suffers.

Water should always be added after fully charging the battery. Prior to charging, there should be enough water to cover the plates. If the battery has been discharged (partially or fully), the water level should also be above the plates. Keeping the water at the correct level after a full charge will prevent having to worry about the water level at a different state of charge.
Depending on the local climate, charging methods, application, etc. Trojan recommends that batteries be checked once a month until you get a feel for how thirsty your batteries are.
Important things to remember:

1. Do not let the plates get exposed to air. This will damage (corrode) the plates.


2. Do not fill the water level in the filling well to the cap. This most likely will cause the battery to overflow acid, consequently losing capacity and causing a corrosive mess.


3. Do not use water with a high mineral content. Use distilled or deionized water only.

CAUTION: The electrolyte is a solution of acid and water so skin contact should be avoided.

Step by step watering procedure:

1. Open the vent caps and look inside the fill wells.


2. Check electrolyte level; the minimum level is at the top of the plates.


3. If necessary add just enough water to cover the plates at this time.


4. Put batteries on a complete charge before adding any additional water (refer to the Charging section).


5. Once charging is completed, open the vent caps and look inside the fill wells.


6. Add water until the electrolyte level is 1/8" below the bottom of the fill well.


7. A piece of rubber can be used safely as a dipstick to help determine this level.


8. Clean, replace, and tighten all vent caps.

WARNING: Never add acid to a battery.

Battery Discharging

Discharging batteries is entirely a function of your particular application. However, below is list of helpful items:

1. Shallow discharges will result in a longer battery life.
2. 50% (or less) discharges are recommended.
3. 80% discharge is the maximum safe discharge.
4. Do not fully discharge flooded batteries (80% or more). This will damage (or kill) the battery.
5. Many experts recommend operating batteries only between the 50% to 85% of full charge range. A periodic equalization charge is a must when using this practice.
6. Do not leave batteries deeply discharged for any length of time.
7. lead acid batteries do not develop a memory and need not be fully discharged before recharging.
8. Batteries should be charged after each period of use.
9. Batteries that charge up but cannot support a load are most likely bad and should be tested. Refer to the Testing section for proper procedure.
   

% Discharged
100
80
60
40
20
0
0
20
40
60
80
100
% Charged

What Happened to UniSolar's US64 Modules?

Over the past 15+ years, we have sold and installed thousands of UniSolar's US64 modules. They are probably one of the best modules available on the market. They are:

• Unbreakable
• Shadow Tolerant
• Tolerant of Extreme High/Low Temperatures
• Triple Junction Technology (in simple language, the 64 watt module is comparable in daily output to an 80 watt glass module)

The biggest drawback is their size. And depending on the available area for the installation and overall power requirements, polycrystalline and monocrystalline modules are more often used.

For most of our customers, I don't need to sell them on the benefits of UniSolar. Once you have used them, you know exactly what I'm talking about. But it does lead to the question,

What happened to the US64s? Where are they?

UniSolar stopped manufacturing their framed modules about two years ago and their flexible modules in 2005. Why? The solar market has shifted away from small, low voltage applications with an emphasis, first on residential installations and currently, on large scale commercial installations. The module hasn't disappeared... it has simply taken on a new form... a flexible unframed module.

UniSolar's BIPV modules are available in a 68 watt 9 ft version and a 136 watt 18ft version. Architecturally, they are great. They blend into the roofline, allow complete design freedom with ridge to eave coverage possible. They have a "sticky back" that just peels off, making installation easy and cost effective.

They come in rolls that you roll onto your roof or other mounting structure and feature all the benefits of the US64 and a few more:

• Theft resistant!
• No back-ventilation of solar panels necessary (lightweight laminates are easy to handle and can be field applied directly on metal)
• No support structures needed
• UL Listed as prepared roofing cover
• Wind and water-tight roof
• Suitable both for renovation and for new construction
• 20-year power output
• Standard junction box or weather-tight quick connect system
• “Peel & stick” adhesive backing capable of withstanding 160 mph wind loads

The 68 watt version is great for carports and RV roofs. We found the installation to be really simple. But I do have to tell you, once you have taken the backing off and have applied them, they are not coming off again. So you really need to make sure they are going down straight because you only get one try.

If you are a fan of the US64, try the PVL-68. You'll really like it once you've seen it.

Battery Q&A :: What is the Difference Between Marine and Deep Cycle Batteries? And When is the Best Time to Use Each?

We received a question from G. Holmes regarding the difference between a marine deep cycle battery and true deep cycle battery. And which battery type would we recommend using for a system using a wind generator.

Generally, a marine deep cycle and a true deep cycle battery are the same. However, there are differences that do make one type of battery better suited for certain applications and environments than others. The primary differences between the battery types are 1) exposure to environmental conditions and 2) size of the battery's plates.

Corrosion Resistant. Marine batteries have been designed to withstand the harsher environments often associated with a marine environment that often speed the corrosion process including:

• exposure to water
• exposure to salt

Battery Plates. Another difference between these battery types are the sizes of the plates. A marine battery has a thinner plate for higher cranking amps--or in other words--the thinner plate is better for the rigors of starting a battery. Deep cycle batteries have a thicker plate for slower discharge.

Applications. These differences in plate size allows you to use a marine deep cycle battery as a house and starter battery for boats and RVs whereas a deep cycle battery is better suited to be used as a house battery or as energy storage for battery based, stand-alone, solar and renewable energy systems.

Wind Generator Recommendaton. For a wind generator, we'd recommend using a true deep cycle battery, such as a golf cart battery. However, if your wind generator is located on a boat or near the coast with exposure to marine conditions, you may consider the marine version.

Equalizing Flooded Batteries

Equalizing is an overcharge performed on flooded lead acid batteries after they have been fully charged. It reverses the buildup of negative chemical effects like stratification, a condition where acid concentration is greater at the bottom of the battery than at the top. Equalizing also helps to remove sulfate crystals that might have built up on the plates. If left unchecked, this condition, called sulfation, will reduce the overall capacity of the battery.

Many experts recommend that batteries be equalized periodically, ranging anywhere from once a month to once or twice per year. However, Trojan only recommends equalizing when low or wide ranging specific gravity (+/- .015) are detected after fully charging a battery.

Step by Step Equalizing:

1. Verify the battery(s) are flooded type.
2. Remove all loads from the batteries.
3. Connect battery charger.
4. Set charger for the equalizing voltage (See Table 2 in the Charging section).
5. Start charging batteries.
6. Batteries will begin gassing and bubbling vigorously.
7. Take specific gravity readings every hour.
8. Equalization is complete when specific gravity values no longer rise during the gassing stage.

NOTE: Many chargers do not have an equalization setting so this procedure can't be carried out.

Battery Charging

Charging batteries properly requires administering the right amount of current at the right voltage. Most charging equipment automatically regulates these values. Some chargers allow the user to set these values. Both automatic and manual equipment can present difficulties in charging. Tables 2 & 3 list most of the necessary voltage settings one might need to program a charger. In either case the original instructions for your charging equipment should also be referenced for proper charging.

Here is list of helpful items to remember when charging.

1. Become familiar with and follow the instructions issued by the charger manufacturer.
2. Batteries should be charged after each period of use.
3. Lead acid batteries do not develop a memory and need not be fully discharged before recharging.
4. Charge only in well-ventilated area. Keep sparks or flames away from a charging battery.
5. Verify charger voltage settings are correct (Table 2).
6. Correct the charging voltage to compensate for temperatures above and below 80o F. (Add .028 volt per cell for every 10o below 80o F and subtract .028 volt per cell for every 10o above 80o F)

Table 2. Charger Voltage Settings for Flooded Batteries

System Voltage
Charger Voltage Setting
6V
12V
24V
36V
48V
Daily Charge
7.4
14.8
29.6
44.4
59.2
Float
6.6
13.2
26.4
39.6
52.8
Equalize
7.8
15.5
31.0
46.5
62.0

Table 3. Charger Voltage Settings for VRLA Batteries
Charger Voltage Setting
System Voltage
12V
24V
36V
48V
Daily Charge
13.8 - 14.1
27.6 - 28.2
41.4 - 42.3
55.2 - 56.4
Float
13.5
26.4
39.6
52.8

1. Check water level (see the Watering section).
2. Tighten all vent caps before charging.
3. Prevent overcharging the batteries. Overcharging causes excessive gassing (water breakdown), heat buildup, and battery aging.
4. Prevent undercharging the batteries. Undercharging causes stratification.
5. Do not charge a frozen battery.
6. Avoid charging at temperatures above 120o F.
   

Additional VRLA Charging Instructions:

1. Become familiar with and follow the instructions issued by the charger manufacturer.
2. Verify charger has necessary VRLA setting.
3. Set charger to VRLA voltage settings (Table 3).
4. Do not overcharge VRLA batteries. Overcharging will dry out the electrolyte and damage battery.

Battery Storage

Periods of inactivity can be extremely harmful to lead acid batteries. When placing a battery into storage, follow the recommendations below to insure that the battery remains healthy and ready for use.

NOTE: Storing, charging or operating batteries on concrete is perfectly OK.

The most important things to avoid:

1. Freezing. Avoid locations where freezing temperature is expected. Keeping a battery at a high state of charge will also prevent freezing. Freezing results in irreparable damage to a battery's plates and container.
2. Heat. Avoid direct exposure to heat sources, such as radiators or space heaters. Temperatures above 80° F accelerate the battery's self-discharge characteristics.
   

Step by step storage procedure:

1. Completely charge the battery before storing.
2. Store the battery in a cool, dry location, protected from the elements.
3. During storage, monitor the specific gravity (flooded) or voltage. Batteries in storage should be given a boost charge when they show a 70% charge or less. See Table 1 in the Testing Section.
4. Completely charge the battery before re-activating.
5. For optimum performance, equalize the batteries (flooded) before putting them back into service. Refer to the Equalizing section for this procedure.