28 replies to this topic

[PaulT]

AmSolar.com in Springfield Oregon carries tilt mounts to allow tilting a panel towards the sun assuming you are headed in the right direction. Tilting toward the sun helps a lot in the winter especially when the sun angle is low and the days are short.  

 

There are a lot of tilting panel mounts for RV's if you search for "tilting solar panel mount RV"

The dual tilt mounts look interesting.

 

Paul

[carld]

The problem is that when I park to camp there are already several things that are more important then how I'm facing the sun.  

1. A level place to park

2. Direction facing camp fire or outside table

3. Shade

4. Solar panels facing the sun 

 

If you tilt the the panels you need to be facing solar noon (South), otherwise as the sun tracks across the sky tilting may reduce the overall energy.  If the panels are flat on the roof they will be omnidirectional and so number 4 on my list doesn't matter.  The link http://www.solarelec...calculator.html gives the solar angle at solar noon for major cities in the world.  It looks like on the average you lose about 35% of the available solar energy for 6 hr of daylight for the areas on my solar insolation table, which is another reason to go with the more efficient MPPT controller.  To me tilting mounts just add more cost and trouble.

[Ace!]

Remember though that omni-directional as you've put it is always inefficient, unless maybe when you're nearest the equator.  A flat panel is never at the proper angle for best solar energy.  The ONLY time your panels are most efficient is when they are tilted.

Edited by Ace!, 17 January 2016 - 05:03 PM.

[DrJ]

The best way to overcome some of your issues may be to have both a portable and a fixed panel.

Large Hard Panel on the roof and a flexible panel for the portable one. Best of both worlds. 

 

You can deploy the portable panel and easily tilt it when you need extra power.

 

I have found that my flexible panel I previously bought is very easy to store under my cabover mattress and can be easily tilted when I need a little more solar power.

[carld]

If you tilt and face solar noon it is optimum, but as the sun azimuth angle tracks across the sky the efficiency drops off steeper then for the flat omni-directional case and you only realize 80% to 90% of the full gain.  Otherwise you need to be present and rotate the panels in azimuth over a 6 to 8 hour day.   If you are going to be a passive collector or your just parked, a flat omni-directional mounting is best.  My calculation is you lose 35% energy by not tilting (reduce the efficiency by 65%).  If you are using and inefficient PWM control you are losing 30% and using a MPPT control you are losing 5% of the energy and maybe less if you go to a higher voltage with two panels in series.   

 

Tilting with PWM = .9 x .7 = .63

Tilting with MPPT = .9 x .95 = .855

Flat with MPPT = .65 x .95 = .62

 

Another thing to consider is the time it takes to recharge your battery to above 80%.  It can be 4 to 8 hours with the last hour at the absorption charging voltage of 14.5 V.   Tilting may make this process less efficient in the morning and evening.

[Ace!]

Sounds like you have it figured out.

[carld]

I order my solar starter kit today.  Decided to skip a planed trip from Plano TX, to Santa Fe and Phoenix Jan 26 to Feb 2 to help pay for it.  I'm going to try out the semi-flex 50W panel with a 1 yr warranty.  It only weighs 2 lbs compared to the 9 lbs, so for 2 panels its only 4 lbs.  I don't have lift assists for the roof.  

 

KingSolar 50W semi-flexible solar panel $137

Victron BlueSolar 75/15 MPPT  charger controller $117

Victron MPPT Control $105

 

The MPPT Control looks cool.  It monitors the following:

 

1. Solar panel power, voltage, daily yield kWh, with a 30 day history including total yield and max voltage

2. Battery voltage, current, and charge state (OFF, FAULT, BULK, ABSORPTION, FLOAT) and history includes max voltage, min voltage, max current, and charge times for bulk absorption and float stages.

3. Load current and state (ON, OFF) .

4. Several set up features like battery type, maximum charge current, temperature compensation, bulk and absorption time limits, float voltage level, load high and low switch voltages, history clear, backlight intensity, backlight on/off ...

 

Kind of expensive but over all I think it will be worth it plus I can get some good data on how things are working.   I'll post again when I get things setup.  

[carld]

I updated my schematic and added a current shunt to monitor the current between the truck battery and the camper. 

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[carld]

I installed my solar kit, 50 semi-flexible solar panel,  MPPT controller, and MPPT control.  I had to make a frame out of .125 x .75 x 48 inch aluminum stock that matches the PV panel mounting holes to the existing roof screw.  The panels are 2.2 lbs and the frame  adds 1 lb. It took a day to make the frame and a day to install everything.  I added some pictures.  I got all the parts on Amazon. The control they sell comes with a 9 ft cable that connects the controller to the control. I had about and extra foot of cable and it was vary easy to connect.  The MPPT measures PV power, battery voltage and load current and sends them to the control along with supply power over the 4 wire cable. 

 

 

 

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[carld]

I have some initial data and it that tracks my calculations closely.   An easy with to calculate the optimum angle by add a seasonal adjustment angle to your latitude. The seasonal adjustment angle changes 8 deg every month and is zero in the months of March and September, starting in January its 16, 8, 0, -8, -16, -24, -16, -8, 0, 8, 16, and 24 degrees in December.  For a horizontal panel you take the COS of the latitude plus the seasonal angle times the panel area times panel efficiency times the solar energy in W/sqm.  For a tilted panel you subtract the tilt angle.  In Plano TX the latitude is 33 deg and the average January solar power is 581 W/sqm.  I also lowered the back roof which tilts the horizontal PV panel by 13 deg and made measurements. The table summarizes the measurements.  I added some screen shots of the MPPT control. 

 

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