Staying in an RV, you might get by on just a trickle of electricity, or you might use even more than you do at home. It all depends on your lifestyle. Before choosing solar panels, calculate how much energy you use in a day. The energy consumption of DC electrical equipment is rated in amp-hours — this is, as the name suggests, a measure of how many amps they will use in a single hour.
The capacity of your battery is also measured in amp-hours Ah , with most RV batteries around Ah. A battery rated 72Ah will be able to power a 1Ah light for 72 hours, or a 12Ah water pump for 6 hours. AC electrical usage is usually measured in watt-hours Wh, usually shortened incorrectly to just watts, W , and the watt-hour ratings can usually be seen on the plug casings.
Amps are just watts divided by voltage; in a 12V RV system, you can divide the watt-hour rating of your equipment by 12 to see how many amp-hours it will draw down from the battery. To calculate the total electricity you use in one day, multiply the amp-hours of each piece of equipment by the number of hours you use it. Add up the amp-hours for all your equipment to estimate your total daily power usage, rounding your answer up to cover any power loss within the system. You can also download worksheets which will help you to calculate your usage.
As a rough rule, one solar panel and one or two batteries will enable you to live a frugal lifestyle — lights, water pump, and not much else. Ascetic: running a single overhead light for 2 hours a day light uses approx. No use of the vent fan, and no heating. Charging a phone for 2 hours a day 4Ah but no other electronic entertainment. About 2Ah will be eaten up by miscellaneous items like the carbon monoxide detector and clock and some power will be lost in the system. Cautious: running lights for a combined total of 6 hours 12Ah.
Using the water pump for 40 minutes 8Ah and the vent fan for 5 hours 10Ah every day; 2 hours watching a inch DC TV or 4 hours using a stereo 8Ah ; charging a laptop for 2 hours a day 10Ah and a phone for the same amount of time 4Ah. A frugal lifestyle like this will require around Ah per day. Like home: running lights for a combined total of 10 hours 20Ah and the water pump for an hour 12Ah. Watching a large TV for 4 hours a day 24Ah and using the microwave for 30 minutes 40Ah.
Using your laptop plugged in for 4 hours 24Ah — laptops use more power when plugged directly into the wall than they use to charge the battery. Using the vent fan for 8 hours a day 16Ah. Propane-powered refrigerator and gas stove for cooking. This moderately lavish lifestyle will take Ah per day. Most RV batteries can store Ah. You will need battery capacity to store at least twice as many amp-hours as you use in a day — preferably times more than you need.
So a battery rated 72Ah will be able to power a 1Ah light for 72 hours, or a 12Ah water pump for 6 hours.
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AC electrical usage is usually measured in watt-hours Wh, usually shortened to just watts, W , and the watt-hour ratings can usually be seen on the plug casings. Amp-hours are just watt-hours divided by the voltage, so in a 12V RV system, you can divide the watt-hour rating of your equipment by 12 to see how many amp-hours it will draw down from the battery. Your panels will need to be powerful enough to easily replace the energy you use, or your batteries will gradually run down.
As with AC equipment, divide by 12 if you want to turn their watt-hour production into amp-hours. Solar panels produce the maximum amount of power when the sun is bright and directly overhead. During summer in the southern US, you might get hours a day of ideal strong sunlight, but as little as hours a day during winter in the north. Panels will still produce power when the weather is overcast, but the amount varies — some panels will suffer only a small dip in output, while others will produce only a trickle of power on cloudy days.
The general rule of thumb is to roughly match the amp-hour capacity of your batteries to the watt-hour capacity of your solar panels — so if your batteries have a combined storage of Ah, you will want panels with a total rating of around Wh. Solar panels produce around watt hours per square metre, so there is a limitation to how much energy you can produce: how big is your roof?
For reasons of practicality, most people install a few identical small solar panels rather than one enormous one.
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Panels need to be positioned carefully in full sunlight to maximize their power production. Even a tiny patch of shade — for example, the shadow of a TV antenna — will make most solar panels cut off entirely. There are also portable solar panels available — the panel unfolds like a picnic table and you prop it on the ground next to your RV. A solar panel with a rating of 12V can usually produce up to 18V in strong midday sunlight.
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There are a wide range of solar panels on the market and costs can vary widely. Apart from the obvious concerns — wattage and size — how can you pick a quality panel? The very best solar panel manufacturers are vertically integrated that is, they make the individual components as well as assembling the panels and invest heavily in research and development.
Good solar panels are generally made by an automated assembly line, as robots can handle delicate electrical components more precisely than humans. The longer a manufacturer has been producing solar panels, the better — look for producers who have been in business for five years or more. Do they make their own silicon chips? Do they have patents on any of their products? The money you spend now will save you power outages and costly repairs in the future.
I went with three no brand name Watt monochristalline panels. A charge controller is a device which prevents your batteries from being overloaded. It monitors the current power levels in the battery, and controls how much power flows down from the solar panels. Think of it like the handle on a faucet, which is used to turn off the water flow once the sink is full.
The higher the amp-hour rating of your batteries, the more power can be stored. Some RV full-timers use two 6V golf buggy batteries, which will have the same footprint as one 12V RV battery but store twice the amp-hours. How is that possible? Hooking up two electrical items in parallel means their amps are doubled, but their voltage stays the same.
See the section on wiring for a bit more information about parallel and series connections. Golf buggy batteries have an amp-hour capacity of around 75Ah, so two of them connected in parallel will give you around Ah of power, with an unchanged voltage of 6V.
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Of course, connecting two RV batteries the same way will give the same power boost, but will take up more space. Golf buggies batteries have a smaller footprint than RV batteries but are usually about 3in taller, so not all RVs have enough vertical space to accommodate them.
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The higher the price of a battery, the longer it will usually last. The cheapest may need replacing after a couple of years, whereas high-quality batteries will give you ten or more years of service for your initial outlay. In this case, a cheap battery might be a good temporary choice. Another surprising indicator of quality is weight. If two batteries have the same amp-hour rating, but one weighs 50lb and one weighs 60lb, then you can assume that the heavier one contains higher-quality components. A monitor is connected close to the battery and tells you information like the current level of battery charge and the rate at which power is being used.
With a monitor, you can see how well your panels are working and check that you have enough power in your batteries. An inverter is a gadget which converts DC power to AC. A common example of an inverter are the portable three-pronged power sockets you can plug into the cigarette lighter of your car, designed for charging your phone or laptop on the move.
Inverters have a watt rating, which tells you the maximum power they can provide.
To find the amount of power you will need, add up the watt ratings of all the AC equipment you plan to use concurrently. To give an idea of scale, 75W is usually enough to run a inch TV. The smaller the inverter, the less power is lost.
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This type of inverter turns DC power into a gently rippling wave which is an exact replica of the power you would get from the mains. It is much easier to convert DC into flat steps rather than smooth waves, so modified wave inverters are much cheaper. However, sensitive equipment will only work with pure sine wave — some computers, stereo equipment, and oddly electric toothbrushes can be temperamental when confronted with a modified sine wave. Wiring your solar system carefully can make your system work more efficiently, providing you with a power boost.
Electricity can flow more easily through a thicker cable, in the same way that water can flow more easily through a wider pipe. Most RVs are fitted with standard gauge wire, which is just about the thinnest you can get away with, to save weight and cost. Trading in for thicker wire can seriously improve the performance of your solar panel system. There are two ways to connect electrical equipment together — in series and in parallel.
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In parallel, positive is connected to positive and negative to negative — if you look at parallel connections on a wiring diagram, they look like the rungs of a ladder. When batteries or panels are wired in parallel, their amps are added while their volts stay the same. When they are wired in series, their volts are added, while their amps stay the same. Parallel wiring is considered more reliable. That can happen with your solar panels if they are connected in series. If you have two panels connected in series, then both panels will stop if you cover a small area of just one.
There will always be some inevitable power loss from the wires, so using shorter lengths of wiring can help maximize power. This means keeping your panels, battery, charge controller, and inverter close to each other so you use less wire to connect them. There are two ways to get your solar equipment: you can either buy a kit that contains everything you need, or pick up individual pieces to create a customised solar setup.
Most beginners choose to buy solar kits.