"RV SOLAR POWER"

With RVs and RVers getting more sophisticated every day, or perhaps I should say more power hungry, RV solar power is an alternative also getting more and more attention by the day. And why not? What could be simpler than harnessing some of our suns energy , storing it in our battery banks, and using it to either charge our batteries, keep our 12 volt systems operating, and for the bold and those who can afford it even powering up their 110 volt systems such as microwaves, stereos, tv's, computers, etc. etc. In addition they are environmentally friendly as they do not produce waste or pollution, are quiet (unlike a generator), and require little maintenance.

RV SOLAR POWER BASICS

Solar power gives rv'ers another degree of independence, and independence is something we love. There are two components in today's systems, the solar panel and a power controller. Of course you need batteries to store this energy your harnessing from the sun, but I assume you already have those. If you don't you've been living at the end of your shore power chord.

RV Solar panels come in all different sizes and you can add on to them later if you want to boost your capacity (just keep your systems compatible in terms of voltage output), they're usually mounted on the roof but they don't have to be, and the trickiest part is determining what you want to accomplish with them. Oh, and one other minor point! You do need sunlight so where you will be using them is critical along with what season you will be using them. Winter users in areas with not so friendly skies will want the capability to tilt them and aim them at the sun.

BASIC CONSIDERATIONS

Like anything there is a right way and a wrong way of working with rv solar power. Your needs and objectives will determine how "right" you need to be to end up with a system that will meet your objectives. There are three basic considerations and they are as follows:

#1 Battery temperature compensation

Since you can find RV'ers and their rigs just about anywhere they can maneuver them to, all the way from the desert floor to the mountain top temperature compensation needs to be addressed.

  • To reach 100% charge lead acid batteries(at 80 degrees) need to be pushed to their "gassing threshold" which is 14.1 to 14.4 volts.
  • Keep in mind deep cycle batteries charge and discharge at different rates at different temperatures.
  • The gassing threshold is higher for a cold battery and lower for a warm battery and when the gassing threshold is not met you will not reach "full charge" which leads to battery sulphation.
  • The flip side of the coin is if the battery is gassed for too long it boils off its water. Low water level means plates exposed to oxygen which also leads to sulphation.
That's also why inside battery storage is always better than outside storage as it at least "helps" in avoiding extreme temperature variations. Its also how a mediocre charging system can boil over an already warm or hot battery...not a good thing when you want to maintain as long life a life span as possible for your batteries.

(For an in depth explanation of deep cycle battery charging see my E-Book on Deep Cycle Batteries.)
#2 SOLAR OUTPUT

Here's something MANY are not aware of:

    Flat lying solar panels operate at higher than normal temperatures... resulting in a voltage drop.

You might think the opposite would be the case, but not so. So at the point of the day when your receiving the highest degree of direct sunlight its possible to loose a couple volts of output.

Think about this. If you're in the bulk charge state (reaching gassing threshold) in the heat of the day and your entire solar system losses a couple volts your batteries may not achieve full charge. Also note deep cycle batteries efficiency and longevity rely on reaching "full charge". To alleviate this happening your system should be rated at least 17 volts. #3 CHARGE CONTROLLER

Charge controllers aren't what they used to be and for good reason. As energy needs have escalated battery banks have grown and inverters size has increased to the point that the old fashioned "on/off" (shunt type) controller is no longer sufficient to keep our large battery banks up to snuff.

    The charge controller is the brains of the system...or in other words your system is only as advanced as your controller is.

The shunt type will get you by for a small trickle charge system for 1 or 2 batteries but if your battery bank is any larger than you need a more sophisticated controller.

Pulse Width Modulation(PWM)

  • PWM controllers control the current going to your batteries.

They will sense the charge cycle required by your battery bank and adjust the current (to a degree at least) to help attain a "full charge". These are also available with external temperature compensation sensors which should alleviate the old problem of boiling off your batteries.

Maximum Power Point Tracking (MPPT)

Currently MPPT controllers are the most sophisticated available. MPPT controllers constantly read:

  • battery voltage
  • solar panel output
  • and adjust for optimum voltage and current flow required at that moment to maintain batteries at the highest state of charge with the least amount of water loss
Solar power systems are not cheap but can be affordable depending upon your needs. The following provides general criteria to help determine your needs. Solar manufacturers do provide worksheets for those who need to calculate as close as possible what their needs are but the following will assist getting you in the ball park of what your needs are.

SOLAR POWER AND BATTERY BANK REQUIREMENTS BASED ON SYSTEM OBJECTIVES

System Objective: Battery Maintenance
Light duty only, keep batteries charged in between 110V hookups. Energy usage: lights, rv appliances (except furnace) roof vent fans
Solar Panel Required
Minimum 65 watt for travel trailers/5th wheels
Minimum 100 watt for motor homes
Battery Bank 1 to 2 Group 24 or 27 batteries
System Objective: Moderate Energy Usage

Battery maintenace PLUS use of lights, rv appliances, (except furnace) roof vent fans, radio, tv, some computer usage.

Solar Panel Required

150 - 300 watt
Battery Bank
200 AH (amp hour) battery storage Group 24, 27, 31, golf cart

Inverter 300 watt


System Objective: Heavy Energy Usage

Energy use as stated above PLUS microwave, satellite, coffee maker, dishwasher

Solar Panel Required

300 - 500 watt

Battery Bank

400 AH (amp hour) storage Group 24, 27, 31, 4D, 8D, golf cart

Inverter 2000 watt

System Objective: Extended Boondocker

Energy use as stated above plus furnace

Solar Panels Required

500 - 800 watt

Battery Bank

600 AH (amp hour) storage MPPT current boost controller

Inverter 2500 watt


Battery Amp Hour Storage Capacity
(Note: these are "always" exaggerated 10-20%)
Battery Storage Capacity (Amp Hours) (Usually exaggerated 10-20%)
Group 2480 AH
Group 27100 AH
Group 31120 AH>/td>
4D180 AH
8D220 AH
Golf cart *220 AH
L 16 *400 AH
two 6 volt batteries connected in series

As mentioned previously the above is all stated in general terms. Reality of course can sometimes be very different beginning with the very unpredictable variable of hours of available sunlight. Another is charge time. You can compute and run numbers till the cows come home but you have to have some idea of how long it is going to take you to get your batteries charged again once they're discharged to 50% capacity. (You don't want to discharge over 50% whenever possible) The following gives general charge times at full sunlight for batteries 50% discharged.


Battery Charge Rates at Full Sunlight (50% discharged)
Battery Size Solar Panel Output
75 watt100 watt150 watt225 watt300 watt
Group 24 8 hrs6 hrs4 hrs3 hrs2 hrs
Group 2710 hrs7 hrs5 hrs3 hrs3 hrs
Group 3112 hrs9 hrs6 hrs4 hrs3 hrs
4D18 hrs13 hrs9 hrs6 hrs5 hrs
8D22 hrs16 hrs11 hrs7 hrs6 hrs
Golf Cart22 hrs16 hrs11 hrs7 hrs6 hrs
L 1640 hrs30 hrs20 hrs13 hrs10 hrs









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