How To

How to Calculate Solar Panel Battery and Inverter of RV?

Do you want to retrofit your RV with a solar system? Our solar calculator helps you to make you independent of shore power. An essential requirement for being as self-sufficient as possible is the correct calculation. Only those who know their daily consumption can properly size their Womo PV system.   The battery capacity also plays a role and can be included in the calculations. Also, we show you our PV system and which devices we have additionally installed. In the end, there are a few more tips for installation. 

Calculate the size of the required solar system

Our goal is to be able to stand as long as possible without external power supply and to cover our electricity needs mainly through our PV system. To be able to calculate the right side of the RV solar system, you first have to know your daily energy needs. After that, the required wattage of the solar modules can be determined depending on the location. In the last solar calculator, the battery capacity is included in the calculations. So you know approximately how long you can stand with his stored solar power. Haunting when calculating the PV system does not help here. In the end, the stored solar energy goes out earlier than planned.

Especially in the winter months of the northern hemisphere, it is not so easy to cover its needs only with solar energy. In winter, the power requirement is usually higher than in summer, because the light turns on earlier or operates the fan for heating. The space on the roof, on which the solar modules can be mounted, is limited and maybe the budget. If the daily need is very high, you should think about which consumers you can sort out. Also, the purchase of more economical devices can be saved electricity appropriately.

Solar calculator for the daily power requirement

With the first solar calculator, daily power consumption can be determined. To calculate the size of the required RV solar system, one must first know how much energy is expected to be consumed per day. As already mentioned, you should plan the whole thing realistically and include some reserve. 

You need the voltage of the body battery in volts (usually 12 V), the power consumption in watts, (either this value is noted on the device or in the manual) and the time how long the devices will run per day (eg. For example, 1 for one hour or 2.5 for 2 hours and 30 minutes, separate the decimal places with the dot “.”). If you have entered everything, you can read your expected consumption in ampere-hours per day in the solar calculator.

How many watts must my solar modules have at least?

Now that you know how much power is consumed per day, you can calculate how many watts the solar panels need to have to meet their daily needs. The calculations already include losses due to the heating of the solar panels. Likewise, power reductions, which arise through the wiring and conversion in the solar charge controller. We assume that the solar modules are mounted flat on the roof. Although this is not the ideal condition, it can not be solved otherwise on a motorhome. To save the solar energy you must have an AGM battery. So, you can have a look at our Best AGM Battery Reviews 

Solar calculator for the minimum output of the solar modules

For this solar calculator, you need your previously determined daily consumption in Ah. Since the sunlight changes according to the season and the geographical location plays a significant role, we have evaluated the values for Germany, Portugal, Morocco and Norway. So you can see how much power the solar modules, z. For example, in the case of hibernation in the south, about the month in question. The values for Portugal are similar to Spain or Italy because they are at the same latitude. This also applies to Norway, which is in the amount of Sweden or Finland. The calculations for Germany are also roughly in line with regions such as Poland or the north of France.

Save solar power

What should not be missing when calculating the solar system is the body battery. It stores solar energy, which is needed in the evening or at night. Of course, we would like to have electricity available, even in bad weather. Lead Acid Battery, Gel, AGM, or maybe even a LiFePO4? Each type has its advantages and disadvantages.

Solar calculator for battery capacity and service life

So far, everything has been very theoretical, but now we want to deal with the final calculation of our PV system. You will need your daily consumption in Ah / d again for this solar calculator. Enter the power of the solar modules in watts. Next, you need to enter the desired battery capacity to “survive” even a few days without solar energy. You can also work with different sizes and watch your life change. Choose LiFePO4 or Gel / AGM and your location or vacation destination. The solar calculator determines how long you can stand, or the stored solar energy will last. From which size you are self-sufficient, is also issued.

You can also read our best trolling motor battery for the money.

MPPT or PWM solar charge controller?

MPPT controllers get more from the solar modules than PWM solar charge controllers. For the MPPT technology, we had to spend 1/3 more than for the PWM variant. Of course, both options work, but if you build a new photovoltaic system on the camper anyway, worth the low extra cost in any case. It will be rewarded with up to 20% more solar yield, which means another step towards more self-sufficiency.

temperature sensor

The available accessories temperature sensor monitors the battery temperature and adjusts the charging voltage accordingly. This is useful in all closed battery systems to prevent overcharging and gassing the batteries at high ambient temperatures. At low temperatures, the charge voltage of the solar charge controller is increased to reach a full charge. It is connected to one of the battery poles.

Useful additions to our motor home solar system

In addition to the PV system, which takes over the main task of our efficient power supply, we have installed a few more devices that make our lives quite easier.

Shore power, charger and priority circuit

Whenever we need shore power because long-lasting rainfall minimizes solar yield, a battery charger has been installed to ensure our power supply. The electrical system was adapted so that when fed from shore power, the refrigerator is operated with 230V, a charger starts and the supply batteries are charged. At the same time, the voltage converter is controlled by a priority circuit separate from the 230V sockets and the shore power fed into the electrical system.

DC converter

Of course, we also have a 230V power supply integrated. The whole thing is realized by a voltage converter, which makes 12V 230V pure sine and can deliver permanently 1000W. This is definitely enough to operate our Flex, charge the cordless screwdriver and use our notebooks or the electric toothbrush. The vacuum cleaner is performed on it. For this purpose, the construction of several 230V outlets was donated.

Battery to the battery charger

If solar energy is insufficient in lousy weather, we use a B2B charge booster. So we can load our body battery while driving. After our truck has a 24V power supply and the construction was realized with a 12V power supply, the charging voltage has to be transformed from 24v to 12V. Also, the charge booster takes over. Also, our alternator does not create a full charge of the battery due to the design. This requires a corresponding IUoU charging characteristic, which is also provided by the device. Among other things, the booster also separates starting batteries from the body batteries when the alternator is no longer supplying power. Separation is necessary to prevent discharge of the starter battery by the body battery.

If it’s all about a separation of the two batteries, a sufficient battery disconnect relay, in our oldtimer but still, a DC alternator is installed with little power. So our vehicle was allowed to keep its old alternator and we get enough energy into our body battery during the journey.

LED ceiling lights

The entire structure is equipped with LED ceiling lights to keep power consumption low and to supplement the efficient power supply. There are a total of 12 lamps installed, which record at 12V per 1 Watt of power. The control of the light takes place via a cross-connect with three switches. One at the entrance, one at the passage and one at the bed.

USB sockets

We have recently retrofitted USB sockets under construction. Most devices, such as mobile phones, GoPro and routers, can be conveniently charged via USB cable. An absolute enrichment in our structure.

Installation of the mobile home solar system – Tips for fitting and retrofitting

When we have got our components, it’s time for assembly. If you have a bit of manual skill, you can install your mobile home solar system yourself. We want to give you a few more tips to make the installation work.

Required tools:

  • Cordless Screwdriver
  • drill
  • screwdriver
  • side cutter
  • Crimping Tool
  • hammer
  • grains

Gluing or screwing?

Gluing is preferable to a screw connection. On the one hand, every hole in the outer skin poses a risk of leaks; on the other hand, bonding is much more stable. One should opt for a fastening variant. Simultaneous gluing and screwing does not make sense, because by tightening the screws, the adhesive is displaced under the holding corners. This makes the bond virtually useless.

Clean the roof

To ensure a reasonable bond, the roof at the mounting positions must be thoroughly cleaned. For this purpose, the coarse dirt is removed with sponge, water and detergent and then cleaned with alcohol, the splices. The durability of the adhesive bond depends on clean preparation. If the stains are very persistent, you can also work with fine sandpaper. The splices must then be completely free of dirt, dust, and grease.

Apply adhesive and install solar modules

Before the adhesive is applied, the splices must still be treated with the enclosed activator. Now, the sealant can be applied caterpillar-shaped on the splices. The best advice is to follow the instructions carefully. Especially the processing temperature should not be exceeded or fallen below. The drying times must also be observed.

Shading during installation

If we install our solar modules outdoors, you should, for. B. be shaded with cardboard. This prevents short circuits because the modules deliver power in the sun.

Save electricity

Despite our mostly self-sufficient power supply, we try to save electricity. Batteries for mobile phones, laptops and razors are best charged during the day when there is enough solar power available. Chargers should be taken off the grid when not in use. If necessary, you can also switch off the voltage converter, if just no 230V voltage is needed. It is even better to use 12V chargers because the sine converter itself also swallows power and you can save even a few amps.

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