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More thoughts on adding solar power

solar battery power

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#1 carld

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Posted 14 January 2016 - 10:35 PM

More thoughts on add solar.  First things are working good without solar.    I can spend 3 nights  using the lights and heater and the battery drops to around 11.8v.  More  then 3 days and I need to idle the  truck for an hr or two.   For summer I park the camper with the fridge on low propane for 3 to 5 days while I’m in the backcountry.  I run a 0.25 A. fan for the fridge while parked and it can drain the battery.   I added a cheep 12 V battery tender that maintains both truck and camper batteries while parked at home and provides a 120V plug to coo down the fridge before the next trip.  

 

I don’t have a lot to spend so I’m considering the following:  

 

How much power can I expect from the solar panels?

 

What size of solar panels?  I’m considering 1 50W, 1 100W or two 50W in series. 

 

What type of charger, PWM  or MPPT?

 

Ideally you would want the solar panels facing maximum sun.  Portable panels would be the easiest but they are only active when you are stopped and they are easily stolen when unattended.  Glueing panels to the roof are omnidirectional, always active and less noticeable.  But just how effective are they?  The website http://www.efficient...calculator.html calculates the solar irradiance kW/sqm per day for each month for cities around the world on the horizontal.  I put together places dates I am likely to go and  came up with an average kW/sqm/day for horizontally solar panel.   The average is 4.7 kW/sqm/day.

 

  See Table 1

 

It is interesting that Santa Fe is at a higher latitude than Dallas it gets more sun.  And Tucson gets more sun than Corpus Christi.  Maybe the Irradiance takes into account altitude and or humidity.  

 

I'm considering SolarKing semi-flexible  solar panels that are thin, light weight and easily glued to the camper roof.  They run about $200 per 100W.  

 

See Table 1

 

Also, what king of charge controller? The PWM is less expensive but overall has about a 70% conversion efficiency so the above AH/day are reduced by 70%.   The MPPT converters are better and have a 90% to 95% efficiency.  The MPPT converters also allow you to stack solar panels in series dubling the voltage so they continue to work on overcast days. 

 

Apply this to the anticipated camper load per day I came up with the following: 

 

  See Table 2

 

Note I set the multiplier for the battery to .9  for aging and the Solar Charger to .9 for a MPPT.  For a PWM the multiplier would be .7.   Also I set the hot and cold factors to 1.29 and .85 assuming that the hot months are in the summer and the cold months are in the winter, the normal is a year average excluding the grayed areas.   The hot and cold factors don’t include the efficiency of the solar cells or battery. 

 

As a result I am think about starting out with 1 50W panel for $125 and a  Victrron Bluesolar 75/15 MPPT controller for $120.  The Bluesolar controller has a blue tooth interface to your smart phone monitoring battery voltage, solar panel power, and charge state.  In the future I can add a second 50W panel in series to boost the power and the higher voltage the panel combo will work better for overcast conditions. 

 

Attached Thumbnails

  • solar schematic 2.jpg
  • Solar Schematic (3).jpg
  • Solar.jpg

Edited by carld, 14 January 2016 - 10:50 PM.

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#2 BillM

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Posted 15 January 2016 - 12:56 AM

Carl,

 

I added my own solar to run lights and a 12v compressor cooler.  I bought a 100w rigid panel and connectors from Renogy for about $140.  Got the MorningStar SunSaver SS10 Solar Panel Charge Controller from Belmont solar for $50.  It will handle another panel if I need it to.   If adding your own wiring I would go big as advised by HandyBob: https://handybobsolar.wordpress.com/

 

So far my setup has worked well and met my needs.  Panels are much cheaper than they used to be so I'd go with 100W and a PWM controller.  The added Watts will make up for the lower efficiency of the PWM and still be cheaper.  Good luck with your install.


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#3 ski3pin

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Posted 15 January 2016 - 01:19 AM

Just my two cents. I have a rigid 100W grapesolar panel on the roof and a mppt controller. Personally, if thinking about going on the roof, I would go rigid and mount up to get airflow under the panel. I would never glue a panel to the roof.


Edited by ski3pin, 16 January 2016 - 11:54 PM.
updated with link

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#4 ntsqd

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Posted 15 January 2016 - 03:05 AM

Concur with not gluing to the roof. Getting cooling air behind the panel does a lot for it's output. With our rigid panel (Grape 100W + PWM controller) I drilled several very large holes in one end of the frame and deliberately made my mounts to slightly tilt that end high.

 

the lower the solar voltage, the more important the wire gauge becomes. Kinda stuck with a PWM on that, but with an MPPT controller you can go series panels to up the voltage and reduce the cable size. Not sure where the break-even point might be.


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#5 DrJ

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Posted 15 January 2016 - 04:47 AM

This website does contain lots of great resource on custom solar setups.

 

I've done several of them and get a little better every time I do one.

 

Just a couple of pointer on your setup.

 

Figure out how much energy you need and plan for 2-3 days of battery coverage with no sun.

Batteries don't last very long if they are deeply discharged - like below 12 volts.

 

Size your solar based on where you live and the size of your battery back.

You want to be able to recharge your batteries to 100% daily if possible.

 

Get an adequate solar controller (MPPT is nice but can be overkill for some of our systems) that covers some expansion

 

Use lower gauge wire to avoid voltage loss

 

Rigid panels seem to last longer and have better performance long term

I've had both and I will stick with rigid now. 


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#6 Bigfoot Dave

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Posted 15 January 2016 - 07:55 PM

BillM's reference to Handy Bob RV is a great one. It takes a bit to read but you will learn things. I went with the Trimetric RV2030 monitor(a must before you do anything else) and their SC2030 solar controller. The monitor will help you understand your power usage and when coupled with the SC2030 allows you to maximize the battery life as Bob will explain. Good luck, Bigfoot Dave


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#7 carld

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Posted 16 January 2016 - 09:16 PM

Ok Thanks.  I looked at the flex panels again.  Their reliability is questionable, their power degrades in 5 years, and their warrantee is only 1 yr.  So now I like the Renogy 50W mono-crystalline panels. Their less expensive more reliable with a warrantee for 5 yrs and their power is guarantee for 25 yr.  Only problem is they add 9 lbs to the roof.  I thinking starting with one and the Victron BlueSolar 15/75 MPPT controller for $120 and one panel with the options to add another in series.  The controller can some how be connected to a computer to monitor panel power, battery voltage and current, battery charge state (absorption, bulk, and float) and load state (on, off).  l still have a month or two to consider my options. 


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#8 iowahiker

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Posted 16 January 2016 - 09:50 PM

I may be "preaching to the choir" but:  Converters and Controllers are not the same for handling solar panel output.  A converter can "convert" high voltage to additional amperage to charge a battery while a simple controller just wastes the extra voltage.  Solar panels in series need a converter (sized correctly) while solar panels in parallel can use a simple controller (sized and wired correctly).  Controllers and Converters can be combined in a single device making things a little confusing.  Panels in series increase voltage while panels in parallel increase amperage.

 

Full disclosure:  I am not an expert and do not have a solar panel.  

 

The design of a converter capable of handling two panels in series is an amazing device with less complicated wiring while controllers with panels in parallel is a much simpler device but more complicated wiring.


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#9 Ace!

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Posted 16 January 2016 - 10:44 PM

Costco offers a 100W Grape Solar rigid panel for $149.  Sometimes they have them on sale for less.  You can buy a Zamp Solar Controller for less than $100 and an SAE wire for another few bucks.  That gives you a panel you can use as a portable, or if you'd rather, you can mount it on the roof.


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#10 carld

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Posted 17 January 2016 - 01:40 AM

I mislabeled my table as solar irradiance.  It should be solar insolation per day.  Irradiance is the instantaneous power in W per square meter falling on a flat surface.  Insolation is the total solar energy falling on a flat horizontal surface in a day in kWh/sqm/day.  The table is just labeled wrong the results are correct. The link http://www.solarelec...irradiance.html gives the average insolation for major cities around the world.  I think the averages account for average atmospheric absorption so results in desert areas and at high altitudes show some improvement.  

 

I want to mount the solar panel flat on the roof so that it doesn't matter how I park with respect to the solar angle.  This allows me to park any direction for leveling and enjoying the camp site.  Also if the panels are on the roof they are always available for charging. 

 

The way I understand it there are two major types of solar to battery charger controllers.  The pulse width modulator PWM and the maximum power point tracker MPPT.  The PWM matches with 12V panels ( that usually run at about 18V) to a 12 V battery system and the conversion from solar to battery energy is around 70% efficient.  The MPPT can match 12V to 36V panels (that run as high as  70V to a 12 V battery system and the conversion is 90% to 98% efficient.  The MPPT 75/15 is good for a maximum open circuit solar panel voltage of 75V and a maximum load current of 15A.   The advantage of higher voltage is that the solar panels can still provide a charging current to the batteries for low light conditions and the solar panel electrical current is lower reducing losses.   The PWM are lower cost but the MPPT are reasonable.  

 

The more modern solar battery chargers are microprocessor controlled so that they charge the battery system  in 3 or 4 stages.  To do this correctly they need to sense the battery voltage, charge current and temperature.  An algorithm adjusts the battery charge to fully charge the batteries to 100% charge over an extended 2 to 8 hrs depending on the initial battery voltage. Monitoring only the voltage can come up short at 60% to 80% of full charge.  After the battery is fully charged the charger maintains the battery in a float state at around 13V.  The MPPT 75/15 provides a 3 or 4 stage charge profile, although it doesn't have an external battery temperature sense it does have an internal temperature sense and needs to be mounted close to the battery. 

 

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  • Solar Insolation.jpg

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