Portable Solar Panels

[Bill]

As Wayne says, your hose-and-tank analogy is a good one. The solar panels don't know/don't care/can't tell whether they are pushing charge into the battery or into the loads or both. The loads don't know/don't care/can't tell whether they are being powered by the battery or the panels or both.

If the loads pull less water from the tank than the panels are pumping in, then the tank will fill up (i.e., the batteries will charge). When the tank is full, the controller will throttle back the filling so the tank doesn't overflow.

There is a tendency to make electricity more complicated than it is (thank goodness! I make my living from understanding electricity!)

Bill

Originally Posted by harveyrv

We bought a Coleman, propane coffee maker last year and that took care of our need to use the inverter (during quiet hours) to make coffee. In fact, we no longer bring the generator with us at all anymore.

That's great, you must feel pretty good about spending the time and efffort in order to reap the rewards of a well configured solar system for your new RV...OH!, I hope you are enjoying your new RV, I completely missed that small detail

Originally Posted by Bill

As Wayne says, your hose-and-tank analogy is a good one. The solar panels don't know/don't care/can't tell whether they are pushing charge into the battery or into the loads or both. The loads don't know/don't care/can't tell whether they are being powered by the battery or the panels or both.

If the loads pull less water from the tank than the panels are pumping in, then the tank will fill up (i.e., the batteries will charge). When the tank is full, the controller will throttle back the filling so the tank doesn't overflow.

There is a tendency to make electricity more complicated than it is (thank goodness! I make my living from understanding electricity!)

Bill

Very good, thanks a bunch for the recap Bill. That is how I hoped and assumed it would work. I am fairly optimistic this system will be very useful and should actually be fun to "behold" the power of the sun.

Thanks again,

Bob.

[Wavery]

Originally Posted by Mr Geek

Very good, thanks a bunch for the recap Bill. That is how I hoped and assumed it would work. I am fairly optimistic this system will be very useful and should actually be fun to "behold" the power of the sun.

Thanks again,

Bob.

You're right.....it is "Fun". I wish that more people would view it that way. I think that too many people find Solar power to be intimidating. The reality is, it's so simple that your "Water in the tank" analogy is very fitting.

Just don't drive yourself crazy "chasing the Sun". I did that when I first set up my 1st 320W system on my sailboat in 1985. I soon realized that one adjustment per hour is all that is need for optimum performance and once every 2-3 hours is just fine. I don't adjust at all now (on the TM). They are where they are and have served me well.

I will second Bill's comment on Arizona sun and wind. I have panels for camping and for some home use and got all my stuff from them. In simple terms, a PWM controller is simply a high speed switch. It turns on and off rapidly with the time it is on vs off being controlled by the demand (battery voltage). as a load or discharged battery presents a lower voltage, the on time is increased and current is pumped into the battery up to the panel output max. As the battery voltage increases, the amount of time the switch is on is decreased. This happens at a very high speed. An MPPT controller is somewhat like a transformer in that it takes total power into (V*A)the controller and coverts it to the charging voltage (approx 14V) at the same total power ( V*A) out which results in a higher output current than the input current. For this benefit, you will pay approx 2x the price.


The answer to your two questions depends on if he load is connected to the load terminals of the controller or the battery. If connected to the controller load terminals any demand greater than the panel output comes from the battery while any panel output not used by the load is used to charge the battery The total current available to the load is limited by the controller max output capability. If load is connected to the battery the charging is the same, but you can draw a higher output current. The controller load limit is usually very close to the max panel current capacity spec. (ie a 20W panel usually has a 20W limit on the output terminals)
I have not seen a controller that can be connected directly to a load with no battery. The controller is an electronic device that needs continuous power to operate, most panels will have times of no or limited output ( Clouds)
Depending on the device, a cloud limited output could damage the device.

[Wavery]

Originally Posted by rumbleweed

I will second Bill's comment on Arizona sun and wind. I have panels for camping and for some home use and got all my stuff from them. In simple terms, a PWM controller is simply a high speed switch. It turns on and off rapidly with the time it is on vs off being controlled by the demand (battery voltage). as a load or discharged battery presents a lower voltage, the on time is increased and current is pumped into the battery up to the panel output max. As the battery voltage increases, the amount of time the switch is on is decreased. This happens at a very high speed. An MPPT controller is somewhat like a transformer in that it takes total power into (V*A)the controller and coverts it to the charging voltage (approx 14V) at the same total power ( V*A) out which results in a higher output current than the input current. For this benefit, you will pay approx 2x the price.


The answer to your two questions depends on if he load is connected to the load terminals of the controller or the battery. If connected to the controller load terminals any demand greater than the panel output comes from the battery while any panel output not used by the load is used to charge the battery The total current available to the load is limited by the controller max output capability. If load is connected to the battery the charging is the same, but you can draw a higher output current. The controller load limit is usually very close to the max panel current capacity spec. (ie a 20W panel usually has a 20W limit on the output terminals)
I have not seen a controller that can be connected directly to a load with no battery. The controller is an electronic device that needs continuous power to operate, most panels will have times of no or limited output ( Clouds)
Depending on the device, a cloud limited output could damage the device.

Actually, my controller has connectors for direct output to devises like irrigation systems or other loads that you want to use during daylight hours. It also has a timer for those connections. I don't use them but they are there. I think that they are on most controllers.

Originally Posted by rumbleweed

...
The answer to your two questions depends on if he load is connected to the load terminals of the controller or the battery. If connected to the controller load terminals any demand greater than the panel output comes from the battery while any panel output not used by the load is used to charge the battery The total current available to the load is limited by the controller max output capability. If load is connected to the battery the charging is the same, but you can draw a higher output current. The controller load limit is usually very close to the max panel current capacity spec. (ie a 20W panel usually has a 20W limit on the output terminals)
I have not seen a controller that can be connected directly to a load with no battery. The controller is an electronic device that needs continuous power to operate, most panels will have times of no or limited output ( Clouds)
Depending on the device, a cloud limited output could damage the device.

Thanks Rumbleweed, great information, makes perfect sense. Recapping a bit more to further complete the understanding...

Any solar system must have a battery...period. It both powers the solar panel controller (must have some power to become active/pass power) AND it stores and outputs power used by the RV appliances (load devices).

The power from the sun/solar panels is 100% dynamic, never truly constant and can't be reliably utilized/allocated for powering many/most things. It is a FREE power source that can be stored into batteries, like RV batteries, and output in usable form for use when needed.

Being new to solar, I really appreciate all the input. It's reinforced to me that solar is pretty darn simple. The solar panels supply available power into the power storage device (battery) and the load devices (appliances) draw that power as needed. That's the system backbone.

Typical System Components:

Solar Panels

Solar Panel Controller - Passes power to batteries, switches prevent overcharging.

Battery Monitor - Displays warnings when batteries are too low.

Inverter - DC to AC - For AC power when needed. From what I can tell, inverters are power hogs, very inefficient.

I am not new to electronics, it's a huge part of many things I enjoy, always has been. But I always like to feel "familiar" with any project I undertake and this forum has been very helpful.

Another question I had was WRT sun angle versus ouput for the panels. I know Wayne has mentioned very good results with his static mounted roof panels. I also just found this middle school lesson on this topic that is actually very good. I am sure there's better information, but this is interesting reading. See attached document (the Photovoltaic Panel Simulation is a nice tool).

I have 2 - 80W portable panels coming soon (see PDF file below for the Panel Manual). They have the controller built onto each panel. I will be testing them soon with some backyard camping to see what is actually doable with winter time sunshine on these panels. I will post back with results from my backyard testing.

Thanks again for all the great information.

[Wavery]

Originally Posted by Mr Geek

Thanks Rumbleweed, great information, makes perfect sense. Recapping a bit more to further complete the understanding...

Any solar system must have a battery...period. It both powers the solar panel controller (must have some power to become active/pass power) AND it stores and outputs power used by the RV appliances (load devices).

The power from the sun/solar panels is 100% dynamic, never truly constant and can't be reliably utilized/allocated for powering many/most things. It is a FREE power source that can be stored into batteries, like RV batteries, and output in usable form for use when needed.

Being new to solar, I really appreciate all the input. It's reinforced to me that solar is pretty darn simple. The solar panels supply available power into the power storage device (battery) and the load devices (appliances) draw that power as needed. That's the system backbone.

Typical System Components:

Solar Panels

Solar Panel Controller - Passes power to batteries, switches prevent overcharging.

Battery Monitor - Displays warnings when batteries are too low.

Inverter - DC to AC - For AC power when needed. From what I can tell, inverters are power hogs, very inefficient.

I am not new to electronics, it's a huge part of many things I enjoy, always has been. But I always like to feel "familiar" with any project I undertake and this forum has been very helpful.

Another question I had was WRT sun angle versus ouput for the panels. I know Wayne has mentioned very good results with his static mounted roof panels. I also just found this middle school lesson on this topic that is actually very good. I am sure there's better information, but this is interesting reading. See attached document (the Photovoltaic Panel Simulation is a nice tool).

I have 2 - 80W portable panels coming soon (see PDF file below for the Panel Manual). They have the controller built onto each panel. I will be testing them soon with some backyard camping to see what is actually doable with winter time sunshine on these panels. I will post back with results from my backyard testing.

Thanks again for all the great information.

I'm not sure that it is a good idea to use 2-separate controllers on one battery bank.

The controller reads the state of charge from the battery to determine the controller's output. If you use 2-controllers on the same battery, each controller's output may cause confusion to the other controller.

I'm not sure about this and you may want to contact the manufacturer of those particular controllers. I would simply run one controller for both panels that will handle 10 or 20 amps. I have a 20A controller but you can probably get away with a 10A. You just don't want to exceed the controllers maximum rating. I would imagine that each of your panels comes with a 10A controller (I may be wrong).

As far a Sun angle is concerned +/- 15 degrees will not make an appreciable difference. after ~15* the output diminishes at a relative state of angle to the Sun. These are not "Lab-Facts", they are just my experience. Again, "Sun chasing" will get old sooner than you think.......

Originally Posted by harveyrv

As far a Sun angle is concerned +/- 15 degrees will not make an appreciable difference. after ~15* the output diminishes at a relative state of angle to the Sun. These are not "Lab-Facts", they are just my experience. Again, "Sun chasing" will get old sooner than you think.......

Hi Wayne, yes I called the dealer on this very issue, they advised these are designed to be connected as multiple units and they are simply connected all to the same place. He even recommended grouping the two connection wires into a single ring terminal connector simplifying the process. BUT I feel as you do, I want to make certain the controller will work properly and I plan on contacting the manufacturer.

I am already inline with your thinking about chasing the sun, I expect I will move these a few times a day at most. I suppose it all comes down to how much of a difference it makes. If I can get the power without moving them I won't. It sounds like you get very usable capacity from your static setup. I like that.

Just to be politically correct, there are some controllers that can be directly connected to things such as pumps etc in remote areas, but you need to be sure that is the case. Many of the lower cost ( basic) controllers use voltage on the load side to control the charging and can get confused if there is not a battery present. Check the manual. Some of the mid range controllers actually have 4 stage charging with an equalizing mode that is time based. The key thing to remember on solar is the energy is free and portable, but collecting and storing it is relatively expensive due to efficiency.
Below is a link that will give you a fairly good estimate of the useful power you can expect from your system. You can try various angles to determine the best one and they will change from summer to winter.

http://www.nrel.gov/rredc/pvwatts/version1.html

Another calculator if you just want to calculate the angle.

http://www.macslab.com/optsolar.html