More thoughts on adding solar power

[carld]

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.efficientenergysaving.co.uk/solar-irradiance-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.

 

[BillM]

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.

 

[ski3pin]

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.

 

[ntsqd]

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.

 

[DrJ]

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.

 

[Bigfoot Dave]

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

 

[carld]

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.

 

[iowahiker]

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.

 

[Ace!]

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.

 

[carld]

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.solarelectricityhandbook.com/solar-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.

 

[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.solarelectricityhandbook.com/solar-angle-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.

 

[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.

 

[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.

 

[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.