Thinking about 500 watts of solar

[newmarokie]

I have been kicking around the idea of installing 5-600 watts of solar panels. I know I will have to do some measuring and layout planning. A couple of questions: 1) If I go 600, what would be required to convert down to 12v if I put 6 100 watt panels and wire them 2s3p? 2)I am thinking in terms of keeping the batteries charged while traveling and mild weather boondocking. Is 5-600 watts adequate? And 3) Is anyone familiar with Renogy's 100 watt panel? Are they a decent quality panel?

 

[Kevin D Pem]

Lot of stuff on this site about solar!!!
500w can be handled by a 50amp controller
600w you should use a 60amp controller
Although you can put 600w on a 50amp controller, that gives no margin.

Why 100w panels? If you can put larger panels on the roof, that would be cheaper. My panels are 250w used panels and are worth investigating.

Renogy makes good equipment!

 

[newmarokie]

what brand are you using, Kevin and where did you find used ones? What are your thoughts on wiring them up 24v and then reducing to twelve at the batteries?

 

[Kevin D Pem]

I purchased at SanTan solar. They have more than one location, bought mine in Gilbert, AZ

I have two systems at this time. A 12vdc system, and a 48volt system.

Both systems have panel voltage at 67 volts. That voltage is only required on the 48volt system due to the the 53 volt charging requirements of the rack mount lithium battery being used. I am not a fan of lithium but salvaged, helped make my decision. Still I wonder about my choice.

The 12vdc batteries (all 400ah of them) are Northstar blue+. The inexpensive PowMr controllers convert the power from the panels close to the batteries.

I made the choice for multiple controllers for duplicate systems design. A decision I have not regretted! Had it not been that way my refrigerator would have been full of spoiled food on a couple of occasions.

MPPT controllers are required to use a "24" volt solar panel for 12vdc systems. The house panels I use are 3x volts likely 35 volts. This they would call a 24volt panel. 19 volts would be what they call a 12vdc panel. The choice has only to do with the fact a 19 volt panel will not charge a 24volt battery, yes it can in a series connected panel array. It surprises me how some people in the industry are so poorly educated in their field they don't understand what works. Anyway, as long as the controllers will handle the peak voltage of the panel(s), the higher the voltage to the controller, the smaller the wire can be. For an RV my system is quite large. Even still, my wires are 10 awg, excepting those wires running from the cargo trailer, those are 6awg.


I tell people 500w is a minimum system. Not because you can't do with less. However when people see what I do, they start buying stuff I use and say " how can you, and I can't ".

Here is an example:

I have a chest freezer, an apartment size refrigerator. I make my espresso in the morning, and dilute it to taste with water I heat with an electric tea kettle. I use an instapot to precooked meals every 4 days or so, and warm them with an electric rice cooker.

I have a lady friend who I am showing the ropes, that is plugged into my rig till we have her setup with her own system.

When something needs modification I use my table saw and planner as needed.

I do have a poor boy generator should my batteries take to much of a hit. But running it is more of a maintenance thing.

Hope that dissertation is useful!!!

 

[Joe Hogan]

Here is a discussion of the basics of solar power

Solar Panel Voltage: What Is It & Does It Matter? – Solair World

solairworld.com

 

[Kevin D Pem]

Here is a discussion of the basics of solar power

Solar Panel Voltage: What Is It & Does It Matter? – Solair World

solairworld.com

Wow Joe! If that article were correct, I would have to relearn everything I know about solar panels!

 

[Roadglide117]

I think it all depends on what you want your system to do for you and what is your budget. 500 w will not get you much.

 

[LMHS]

HandyBob's Blog

Making off grid RV electrical systems work

handybobsolar.wordpress.com

You want to hook up your battery bank like Method 4 SmartGauge Electronics - Interconnecting multiple batteries to form one larger bank

 

[Kevin D Pem]

SOLAR CELL BASICS!

so as my title says, I get very basic here!
everyone knows that a lead cell has a value of 2 vdc. Put 6 together in series you get 12v. Change the chemistry, change the voltage! Changing the number of cells required for your desired voltage.

Somehow the translation gets lost when looking at solar panels! But the same principles apply! Just like with batteries, the individual cell of a solar panel has a set voltage it produces. When a load is applied that open circuit voltage drops depending on how severe the load is. When you follow current vs. Voltage you can establish the maximum power point (mpp). This is listed on your panel and is the value required to supply the rated wattage listed on the panel! Your MPPT controller finds this point and tracks it using a computer program, not a preprogrammed value.

Although the panel environment may cause the mpp to vary the computer in the controller tracks for best output from the panel. That is why it is called an MPPT controller. Because the voltage coming into the controller can vary due to environment, a controller is rated in amps based on system (battery) voltage.

I don't know what the configuration of a 12v panel is. I don't recommend such panels. S&B panels are what I suggest! The size panels that are common are 60 or 72. Cell panels. The number of cells set the output voltage of the panel, and at rated wattage output, that will be the MPP rating, and only has minor voltage fluctuations, that a MPPT controller adjusts to. The size of the cell determines wattage!

Why this matters:

The above information posting is wrong!
The only significance voltage plays in this balancing game is how much power (watts) can be pushed into the load. This is the voltage differential that determines this. And once again is determined by the controller while it determines what stage to charge at (think 3 stage charger). This is designed to save the battery, and is the controller's primary job.

The voltage is fixed based on the number of cells, and will not change while the controller has a place to dump the power.

Summary:

While you research this topic disregard any sites you reference that offers anything contrary to this dissertation. Although the dissemination of information may be an effort to be helpful. The fact that it was published without correction, means you should go elsewhere for further help.

As an aside: the electronics lab that taught me about the theory presented here I complete before I entered high-school, it is not rocket science, so avoid those that can't explain it!!!