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Solar panels generate a predictable
amount of power each day. A typical 80 watt (4+ amp) panel on a good sunny day
can produce over 30 Amp Hour (AH) of power daily-- that is about 1/3 of a full
RV battery. To overcome battery resistance and line loss you should produce
about 10% more power that you actually use. If you continually use more
power than you produce, you can cut back on consumption or generate more
power. Fortunately, these solar systems are modular and you can add on at any
time without replacing existing equipment.
To determine how much of a system you need, you can use the
general rule of thumb (what other Rvers find acceptable) or try to
determine what is your daily consumption:
1. Make a list of items normally used daily. EXAMPLE: a one panel system
2. Multiply amp draw by hours (or fraction) of use to give total AH.
| Item | Amps | x Hr/day = | AH/day |
| 15 watt fluorescent light | 1.0 | 6.0 | 6.0 |
| Two 12v incandescent lamp | 1.5 | 2.0 | 6.0 |
| TV (9" color) 12 volt | 3.0 | 4.0 | 12.0 |
| Water pump (12 min/day) | 8.0 | 0.2 (12/60=.2 hr) | 1.6 |
| 12 volt stereo | 0.8 | 2.0 | 1.6 |
| Total AH used per day = | 27.2 | ||
In this example, extra power generated can be stored in the battery or used for other purposes. We deliberately left out electric appliances that produce heat. They are extremely wasteful. Use propane to cook and heat in an RV. Compare fluorescent tubes with incandescent auto lamps. "Flours" use a bit less electricity but give far more illumination. One "flour" will equal 2-3 "incads." Shop carefully. Read labels for amp draw or calculate using the WATTS formula (Amps x Volts = Watts). Some 9" color sets only draw 2.5 amps, while other may use 6 amps.
Don't forget "hidden or phantom" power users not listed: Propane refrigerators use 12 volt for the igniter brain even when on 120VAC. Digital stereos and TV use 12v, even when turned off, to maintain memory circuits. Gas & CO detectors use 12v also. The RVer's Guide to Solar has more listings in greater detail.
SOLAR SIZING "RULE OF THUMB" for the average Rver:
Whether or not you choose to install a solar system, we encourage you to measure and calculate your energy requirements. It will show you how to better manage your situation. But, based on the thousands of systems we've been involved with, the average Rver, one without unusual needs, generally finds that one 80 watt panel and one 105 AH battery (or equivalent) per person provides an adequate system for long term outings. An extra panel and battery provides insurance during bad weather and enough power to handle the unexpected.
The Custom Design Worksheet will help you discover how much energy you use.
