Quote:
Originally Posted by lancedal
Anybody out there added solar panels to their motorhome?
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Quote:
Originally Posted by lancedal
I have a 40 ft, Endeavor, plenty of room on the roof...Don't do much dry camping, looking to reduce power bill.
Is it worth the investment.?
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Only YOU can answer that.
The electrical needs of an RV depend totally on the lifestyle of the folks that live in it. You won't know if it's worth YOU investing in solar until you determine your power needs / usage and your environment. Someone you is in Texas will have a longer solar day (and therefore more charge in their batteries) than someone in Wyoming. And someone that lives in their RV year around will need more than someone that is summer-only.
It all depends on what YOU need.
And you need to educate yourself as to how solar works...
The biggest problem is that solar generation is variable - it's not like shore power or a generator. Solar charging varies from zero at sunrise to max at local noon to zero at sunset, and depending on the clouds can vary during the day, and clouds can cause variances from hour to hour, and the tilt of the earth (the seasons) will change the strength of the sunlight (called solar flux) from week to week... As such you are not gong to power your RV from it, you are going to run the RV on batteries and the solar is just one more source that recharges the house battery.
I was introduced to solar panels when I worked at NASA-JPL in the 1970s. I actually acquired my first solar panels - four "12 volt" panels - as surplus in the 1980s. When I set them up in my back yard I was seeing anything from 5 to 17 volts, and peaking at almost 2 amps per panel at solar noon. My four panels wired in parallel and mounted in my homebrew panel rack would produce almost 8 amps with the sun directly overhead.
Another variable that you have to consider is the panel mounting method... Most RVs with solar panels have them mounted flat to the roof. You will see some that have tiltable mounts (especially people that park in one spot for weeks or months at a time... they park their RV broadside to the sun in a location where they can tilt the panels to better present the face of the panel to the sun). Tiltable panels can increase the power level by a large amount... in my case from around 3 to 4 amps when flat on the ground to almost 8 amps when peak aligned to the sun. Naturally anything approaching the rated power was only on a clear day in mid-summer with the panels perfectly perpendicular to the sun. "Solar noon" you say? Yes. The sun and the solar panels do not care about time zones or daylight savings time so the term can be reduced to the time when the sun is directly over and perfectly facing the solar panel. BTW, the wattage numbers you see on solar panel specifications are based on these perfect conditions. You will probably never see that performance.
Now to answer the big question "how many panels do I need?":
To properly size a system to fit your requirements you need to FIRST quantify your needs before you install the solar... find out how much power you actually use... and you only get those numbers by installing a shunt-based battery monitor on your existing house battery bank... and logging that info daily for a worst-case month. Or maybe 2 months. No, that's not wasted money, you are going to need that battery monitor in your solar system. A battery monitor like the Victron BMV-712 and the matching shunt will allow you to see exactly how many amp-hours the shore power converter is feeding into the batteries, how many amp-hours is going out (i.e. how much power you are using), how fast you are using it, and how much power you have left at any given point.
Pulling random numbers out of the air, lets say that you used 100AH in 24 hours. Another random number: you have solar day of 8 hours. That means that (in a perfect world) you would need to pump 12.5 amps for 8 hours back into your battery to break even. But it's not a perfect world - you need to pump in some extra in to actually replace all of what you used. And you will never have a 8 hour solar day in the winter. But some people have their RVs in storage for 6 moths of the year, so a winter day doesn't matter - it will be plugged in then...
One friend commented that a single 100-watt "12 volt" panel under optimum conditions can produce about 25-30 amp-hours per summer day and flat to the sun, so if you know what your needs are you have a starting guess as to how much solar generation you will need. If you are going to be a fulltimer (year-round) person you will need to size your solar system for the shorter winter day. That will need more solar panels than someone who stores his RV for half of the year and only uses it in the summer.
To calculate the size of your solar photovoltaic system you need to:
1) Determine your daily kWh energy requirement. You an get that from a Victron (or similar) battery monitor, it's measured in WattHours or KilloWattHours. Call that number EU for Energy Used. Keeping a logbook for 3-4 months and doing the calculations for each month (or even each week) will result in more accurate numbers.
Look here: http: //
www.jenericramblings.com/2017/03/30/battery-meters-an-rv-must-have/
2) Determine how many solar hours you get per day. Call it SH for Solar Hours.
And as said above a winter day will have much less solar production than a summer day.
A good rule-of-thumb SH number for the USA is 5 solar hours per day. That number takes into account the lower quantity of sunlight in the morning and evening. Using 5 hours per day in your calculations will tell you how much power you can reasonably expect in "real world" solar results.
3) Divide your EU by the SH to get the panel output you need. So you are dividing KilloWattHours by Hours and getting KilloWatts.
Call that RE for Required Energy.
Then divide the RE by the Panel Watts rating to get the minimum number of solar panels for your system. If you get a fractional number then round up... i.e. use 14 instead of 13.4
However... that RE number is a constant for every hour of the solar day, and the solar power is not constant! Because you don't have full sunlight for the morning and evening you will have to increase that panel count. And because the panels will be flat to the roof you will have to increase the panel count some more. And unless you park in full sun all the time you will have to increase it even more. People like to park their RV under the trees... and solar panels are allergic to shade.
So for a 400 watt array of solar panels (four 100w panels) for 5 hours you can reasonably expect about 2 kilowatt hours per day....
That panel count you actually need will be about four to six times larger than you calculated in the step above because your numbers for Energy Required were generated during a 24 hour period and your Solar Hours is only for the daylight period. And think about this: What will you do if you have a solid week of overcast days? Or even two weeks? I suggest you keep your generator connected and maintained... real life isn't always sunshine and 75 degree F / 25 degree C weather.
Here is a very basic calculation page intended for a sticks-and-bricks home but the concepts and techniques are the same:
https: //
www.solarpowerauthority.com/how-to-size-a-solar-pv-system-for-your-home/
However the panel watts numbers you see on solar panel spec sheets or advertisements is naturally for an ideal situation: flat facing the sun (i.e. directly overhead) in the summer. Those numbers are peak numbers that are only useful to marketing staff to write brochures from. And they always round the numbers up. I always discount spec sheets by 40% to 50%.
The following link is for a 6-times-a-year magazine that was devoted to home-made power. They went under recently but the index and all of their back issues are available for download.
There is a tremendous amount of information on solar systems here... however some is dated. https: //
www.homepower.com
Before you start laying out $$$ you should learn about solar charge controller technology (PWM or MPPT), low voltage disconnects, state of charge and how to measure it, how wire size can make or break a system, and a lot more. A low voltage disconnect saves your batteries - a lead-acid battery doesn't like being over-discharged (yes, you need at least twice as much battery as you expected), where as a Lithium based battery can be discharged to a much lower percentage. But both still need a Low Voltage Disconnect to prevent battery failure from self-destructive overdischarge. Most lithium battery modules have an internal LVD.
Another charging issue is that the average battery bank can only take full charging current for a certain amount of time - usually this is described as an 80/20 relationship. 80% of the charge can be stuffed into the battery in 20% of the total time... But that last 20% of the charge takes 80% of the time! The charge rate of the battery bank is one of the limiting factors in solar - you have to have someplace to put the sunlight-generated power right away, or it is gone...
Many lead-acid battery manufacturers have literature that says that for best life do not discharge below 50% state-of-charge. One manufacturer statement is at
https://www.trojanbattery.com/tech-s...ry-maintenance under the section titled "Discharging". Yes, you can go to 80% but it will reduce the total number of charge / discharge cycles.
I suggest that you download and read the writeup called "The 12 volt side of life".
There are 2 versions out there - one version is a single long PDF and the other version is a pair of PDFs titled "Part 1" and "Part 2".
Part 1:
The 12volt Side of Life (Part 1)
Part 2:
The 12volt Side of Life Part 2
Then there's the HandyBob writeups... also well worth reading... they (all of them) should be required reading for anybody that is going to go solar (or has solar).
https://handybobsolar.wordpress.com
Learn two basic formulas: Power (watts) = volts multiplied by amps. Rearrange the formula and you have Amps = watts divided by volts.
A 1200 watt microwave on 120vAC translates to 10 amps.
That same microwave plugged into a 120v inverter will pull 100 amps at 12v... and you have to figure on some conversion losses, so figure around 110-115 amps... That's large diameter wire (read: expensive) from the battery to the inverter.
As I said above, back in 1978-1980 I had a small system in my back yard... four 2 foot by 4 foot panels totalling 100-150w on a homebrew charge controller and two deep cycle golf cart batteries... yeah, panels were pretty inefficient 35+ years ago. I later relocated them to my workshop roof... learned a lot... but I learned a bunch more by reading those documents above.
Another couple of links you may want to check:
Northern Arizona Wind and Sun:
www.solar-electric.com
Will Prowse's site at
www.mobile-solarpower.com
He won't answer emailed questions but there is a ton of good information there and the folks on the board will help. There is a newbies section. I would suggest you read it first.
DO NOT think that a basic solar system will allow you to live like you are in a sticks and bricks house. A simple device like a 1500 watt hair dryer can pull a LOT more power than you initially expect... Plug it to an inverter connected to a 12 volt battery and flip it on and it will suck over 125 amps! (1500 watts at 12 volts is 125 amps, then you have conversion losses in the inverter... 130 to 140 amps is more like it. A typical 200 ah house battery is going to deliver 100 ah of usable power (remember the rule of don't discharge it to less than 50%?) and 2 minutes is 1/30 of an hour... 130 amps for that time is 4.3ah. Your 100% battery charge just dropped to about 95% in 2 minutes.
And that's not discussing lights, TV, electric blanket, or any other devices that suck electrical energy.
Here's a good comment thread on a new solar system:
https://www.irv2.com/forums/f44/new-...em-517041.html
And we haven't touched on the installation... will you be doing it yourself? Or paying someone's labor costs?
Or touched on the materials... panel racks, cabling, connectors, etc.
Mike
Linear Mode
