Full disclosure – We are a solar manufacturing company that specializes in RV, marine, mobile and off grid applications. I am not here to promote but to help you find the best solution to your questions regarding solar. Please don’t hesitate to call us and discuss your personal situation.
First off – I’m happy to see you returned the 13 watt solar panel. That panel was made with amorphous solar cells, their life span is roughly 5 to 7 years for the most part. Since those were in a solid structure it likely would have lasted longer. They are also the least efficient solar cell out there. Most quality solar panels will have a 25 year power output warranty. Look for ‘lass A’.
Those smaller solar panels are great for battery maintaining when you park your RV but not for producing a decent charge to replace the energy you’ve used. You would likely need at least 120 Watts of Portable solar power when using that laptop for 8 hours a day and your other smaller draws. However, this is assuming that you will be using this mainly in the summer when the days are longer and you have good lighting
– no shades and not many clouds. If you were to be in an area that is fairly cloudy you would need a larger solar system for your needs.
How I estimate your solar needs.
You gave me some great information regarding how and what you were using electrically. Your laptop is rated at 65 watts – this is the maximum wattage draw that your laptop will allow and unless you’re using it for large amounts of computer processing - you won’t see 65 watts all the time – likely 20% less for the majority of your usage.
65 Watts at 12 volts is 5.41 amperes or a draw of 5.41 amps an hour. 8 hours a day and you could have a potential max of 43 amps for the day – this is potential but generally unlikely. I’d estimate your computer usage to about 30 to 35 amps a day (still considered high). This is just the laptop with no other external electrical
equipment (monitor, hard drive, etc.).
An 80 watt Portable solar panel from Zamp is configured for 12 volt battery charging, it will deliver 4.6 amps of power per hour under optimal sunlight. 80 Watts is about 36 ampere a day for 8 hours of full sun. Again if you have partial sun or might experience partial sun, take this into account when configuring solar. For your specific needs I would recommend a 120 watt Portable Solar Charging System
Your other usage sounds very light
. Typically single battery small RV users are around 15 to 20 amps a day. You’re likely at about 10 to 15. Add that to your 30 to 35 amps a day for the computer and you’ll be at about 45-50 (almost half of battery capacity). A 120 Watt Portable solar system will deliver 6.84 ampere or about 54 amps a day (8 hrs). This should cut it for the most part.
A little bit about batteries. Generally RVers are poor caretakers of batteries. Batteries last much longer if you can keep them topped off when stored and only use 30 to 50% of capacity before you recharge them. This mean on your 115 amp hour batter you should only use between 35 and 57 amps out of your battery before you recharge it. If you follow my recommendations on how to use your battery expect to keep it for 6 to 8 years instead of the 2 to 3 that’s typical. This relates to solar by making sure you have the right amount of solar to recharge your batteries from daily use. Having a solar system that’s about 20% larger than your daily use is an ideal situation to be in.
ANSWERS TO YOUR QUESTIONS:
We recommend that you connect solar directly to the battery to ensure you have the proper wire size, tight connections and quality. Don’t connect solar directly to the battery as it is not a 12 volt battery and thus won’t charge correctly.
For that 13 watt panel you wouldn’t need a solar charge controller on your 115 amp battery. Larger solar panels I would recommend a PWM solar charge controller (smart charger).
Inverters should be connected directly to the battery with the recommended size and length wire. DC (direct current/Battery Power) doesn’t travel well over small wires or longer lengths. Always use the recommended wire length and size for your specific inverter – better yet get an inverter that comes with the wire.
Your inverter will draw a small additional amount of power from just being turned on. Likely 1.1% of the total wattage. 1100 watts at 1.1% is 12 watts or about an amp an hour. It won’t draw the full 1100 watts unless you have more devices powered from it. You can run up to 1100 watts. Turn it off when not using it. Better yet you can get a DC to DC converter for your laptop. I would only get a converter from the manufacture. This can be directly connected to the battery various ways – likely a cigarette lighter adapter. This removes the inverter and works just as well.
Another important factor is making sure you have a pure sine wave inverter. The other cheaper models are modified sine wave. Expect to have about a 1/3 life expectancy decrease on your battery when charging from a modified sine wave inverter consistently. Pure sine wave is the same power source you will find when plugging into a socket in a house or building. It’s considered clean and won’t put added stress on your devices. Pure sine for all sensitive electronics.
You can reach us via email or by phone – just go over to Welcome to Zamp Solar. Power to Explore. if you need to. We’re more than happy to help as you can see form this long post.