CAUTION - Do not use this info until members verify it

[RoadtripsAndCampfires]

DON'T RELY ON THIS INFO - YET

I am wondering if those who know about solar, (when you have time, this is long so I don't expect an instant answer) would read this and tell me where it is wrong.  I've taken notes on videos, websites, etc. and put together this information before I go on to the next step.  Learning all this stuff is hard but I am determined.  The disclaimer is large so no one finds this post and uses it without it being verified.  I know there are going to be options and choices not mentioned here but first I just want to see where I went wrong on the basics of learning it.  Thank you for even taking the time to read it, it took me all day to write up these notes:

Things To Know About Solar

[font=Arial, sans-serif]Sun angle, intensity of the rays, weather, time of day and how many hours of sunlight will all affect the amount of charge the panels will receive so you'll want to be able to store enough power in the batteries to get you through night, clouds, etc. until you can charge again. Where you are on earth will affect all of these factors so there is not one answer for everyone's power needs. But there are charts to help you figure out what you can expect in a given area during a given month. One such chart, or solar map, is available at https://www.nrel.gov/gis/solar.html National Renewable Energy Laboratory.[/font]

[font=Arial, sans-serif]The system will include the necessary number of panels at the necessary wattage, a controller that will regulate the power being received and direct it to a battery to store it in, and the wires to connect it all. Mounting hardware is necessary if they will be mounted to a roof. Some people prefer to carry them in the RV and then lay them out in the sun at camp. This method will work if you can't (or don't want to) mount them on your roof but you do lose any charging one would get during driving time to and from your destination. There are kits that can be bought which will contain the panels, wiring and contoller and sometimes the mounting hardware, or items can be purchased separately.[/font]

[font=Arial, sans-serif]A Sun Hour is an hour of the sun hitting at full strength, generally noon and an hour or so before and after. So in the morning or evening it might take 3 hours to achieve one sun hour of power hitting your panels. And if you are in the middle of cloud or tree cover you may receive very little charge at all, even at noon. You may receive 3 sun hours between the hours of 11 and 1 in June in Arizona but only 1.5 sun hours or less between 11 and 1 in June someplace else.[/font]

[font=Arial, sans-serif]A 12-volt solar panel rated at 100 watts operating at ideal sun conditions will produce about 18 volts and a 5.5 amp current in one hour. Volts x amps = Watts (w):[/font]

[font=Arial, sans-serif]18 volts x 5.5 amps = 99 Watts (rounded to 100, or 100w).[/font]

[font=Arial, sans-serif]A watt is a unit of measurement of the power the device uses. A 100w light bulb requires 100 watts in an hour and a 40w light bulb only requires 40w. Your solar needs will be dependent upon how many watts you will use in a day. Will you power a small fridge or just an alarm clock, radio and phone? Don't figure that out yet but know that there are charts that exist that provide “averages” for things such as TVs, radios, etc. to help you estimate but you'll want to check your appliance ratings to determine the actual amount of power needed based on what you are using.[/font]

[font=Arial, sans-serif]Watt Hours is how much power is generated over a period of time:[/font]

[font=Arial, sans-serif]1 hr x 100W = 100 watt hours.[/font]
[font=Arial, sans-serif]2 hrs. x 100W = 200 watt hours.[/font]

[font=Arial, sans-serif]Using a Solar Map https://www.wholesalesolar.com/solar-information/sun-hours-us-map wholesale solar [/font]

[font=Arial, sans-serif]I charted sun hours six cities that represent areas I will likely travel in (H=high, L=low):[/font]

[font=Arial, sans-serif]THIS PART WAS CORRECTED WITH AN EDIT AS SOME GOT DROPPED:[/font]

[font=Arial, sans-serif]La Jolla, CA     5.24 H, 4.29 L[/font]
[font=Arial, sans-serif]L.A., CA     6.14 H, 5.03 L[/font]
[font=Arial, sans-serif]Grand Junction, CO     6.34 H, 5.23 L[/font]
[font=Arial, sans-serif]Albuquerque, NM    7.16 H, 6.21 L[/font]
[font=Arial, sans-serif]Corvallis, OR 6.34 H, 5.23 L[/font]
[font=Arial, sans-serif]Seattle, WA 4.83 h, 1.60 L[/font]

[font=Arial, sans-serif]If I were to base my below calculation of my needs on the lowest amount of daily sun hours, it would be 1.60 for Seattle. However, I will likely only be there once in the next several years and probably for only 2 days. For my purposes I plan to be sure my batteries are charged before I get there and put us on a low consumption plan during our stay rather than base my calculations for number of panels to install on the lowest amount of average Seattle sunlight. Likewise, La Jolla will be visited in the summer and only for a few days so I am tossing that one out. I am going to use 5 sun hours to figure out our initial solar panel setup for our needs.[/font]

[font=Arial, sans-serif]100w x 5.0 Sun Hours = 500 Watt Hours (Wh)[/font]

[font=Arial, sans-serif]Deductions[/font]

[font=Arial, sans-serif]The next part of the process is determining energy lost by traveling across wires, the amps used by the charge controller and any cell obstructes due to things such as dirt or snow. Deduct 1/3 of your total watts for these losses by multiplying .70:[/font]

[font=Arial, sans-serif]500Wh x .70 = 350Wh (represents 70% of the total power allowing for 30% loss).[/font]

[font=Arial, sans-serif]The charge controller sends the power generated by the solar panels to the battery which stores it for later use and it has an amp rating which varies according to the conroller.[/font]

[font=Arial, sans-serif]Determining Amps[/font]

[font=Arial, sans-serif]Watts divided by volts equals amps. We are using a 12v system so:[/font]

[font=Arial, sans-serif]350wh divided by 12 volts = 29 amp hours.[/font]

[font=Arial, sans-serif]Battery[/font]

[font=Arial, sans-serif]A standard car battery is meant to be rapidly discharged for starting the car and then recharged as the car is driven by the alternator. The amount of discharge at time of start is a short high-current charge and normally only discharges a small portion of their stored energy.[/font]

[font=Arial, sans-serif]A deep cell or deep cycle battery is designed to be drained of more power and is in use more often as your devices draw from them. It is a good idea to avoid discharge below 50% so if one chooses a battery system capable of twice the amp hours needed this avoids going below 50% of the full battery charge. [/font]
[font=Arial, sans-serif]29 x 2 = Ah x 2 = 58 Ah required.[/font]

[font=Arial, sans-serif]Temperature and De-rating[/font]

[font=Arial, sans-serif]Temperature affects the amount of power a battery can store. Manufacturers can provide you with information on how much to de-rate your amp hours based on temperatures. Here is an example of a battery de-rating:[/font]

The first number below is the temperature (F) followed by the percentage to de-rate:
80, 0%
70, 2%
60, 5%
50, 10%
40, 15%
30, 20%
20, 35%

[font=Arial, sans-serif]One would want to increase the battery by the percentage of derating according to the chart based on the temperature the battery will be stored at. If the temperature averages 60 degrees F multiply the Ah by the percent shown, in this case 5%:[/font]

[font=Arial, sans-serif]58 Ah x .05 = 2.9. [/font]

[font=Arial, sans-serif]Add the 2.9 to 58 and we round out to 60Ah.[/font]

[font=Arial, sans-serif]The Inverter – Another Deduction [/font]

[font=Arial, sans-serif]The inverter converts the DC power of the battery where you have stored your power into AC power so that it can be used by your AC appliances and devices. The inverter uses about 5% of power:[/font]

[font=Arial, sans-serif]60Ah divided by .95 = 63.1 so we'll call that 63Ah.[/font]

[font=Arial, sans-serif]Storing Power For 2 days without sun:[/font]

[font=Arial, sans-serif]I you can't charge the battery during two days of no sun you would need to multiply the amp hours by that many number of days and have it fully charged before you arrive at camp:[/font]

[font=Arial, sans-serif]63Ah x 2 = 126Ah.[/font]

[font=Arial, sans-serif]So one would need a 126Ah battery.[/font]

[font=Arial, sans-serif]- - - - - - - - -[/font]

[font=Arial, sans-serif]SO – IS THIS ALL CORRECT?  Or?[/font]

 

[Trebor English]

In theory, theory and practice are the same.  In practice, they are different.  Theoretically what you have is close.

You have calculated that a 100 watt panel needs 126 amp hours to take what the panel produces.  Some of the power generated will get used during the day so it doesn't all need to be stored in the battery.  Roughly the rule of thumb is about 100 amp hours of battery for 100 watts of solar panel.  Your calculation matches that.  Some AGM batteries do better with higher charge rates.  An occasional plug in shore power charge could meet that need.  Some people recommend 150 or 200 watts for a 100 amp AGM battery.  Lead acid batteries don't charge at a constant rate.  When deeply depleted they can take a lot of current while the last 20% takes many hours to complete.  As you noted visiting Seattle increases the panel size requirement.  Thee are more variables than you can shake a stick at.  What yo need to do is get the battery back to 100% charge often to keep the battery capacity from fading away.  Daily is best, weekly is not very nice.

Most people start with what devices they have and how much they use them to figure out how much electricity they need.  If you want to use high power devices like food grinders, microwave ovens, or coffee makers then the peak demand needs to be considered as well as the long running low peak devices like CPAP machines, TVs and fridges that take a lot of amp hours slowly.

Inverters have been known to consume 20%, 5% is being generous.  

Most of what is used does not need to be processed by an inverter.  For efficiency you want to get 12 volt devices.  Phone chargers that use 12 volts typically require less power than an inverter running a 120 volt charger.  For laptop computers you can get a power supply brick that makes the 19 volts the computer uses directly from 12 volts.  That is more efficient than making 120 volts from 12 and then making 19 volts from the 120.  Fans, led lights, refrigerators, etc are available in models that use 12 volts directly.  Some things like microwave ovens and electric shavers are typically used with inverters.

Temperature derating for low temperatures is not nearly as important as keeping batteries cool.  Heat is a battery killer.

 

[BradKW]

I'm not sure where you got the inverter number of 5% ...could be that is what the parasitic draw from a powered inverter under no load might draw in a system spec'd as you have.

But unfortunately you might have missed the -20% loss from conversion inefficiency...so anything running off 110v wastes around 20% versus 12v appliances.

20% is a ballpark number, but you can look at the specs when shopping inverters to see exact amount. Definitely worth swapping to 12v for as many things as possible...

 

[tx2sturgis]

Christine you are doing great!
I only saw one very minor point that needs a technical correction:

[font=Arial, sans-serif]A watt is a unit of measurement of the power the device uses. A 100w light bulb requires 100 watts in an hour and a 40w light bulb only requires 40w. [/font]

The 100 watt bulb is consuming 100 watts, but that in-and-of-itself is not 100 watts in an hour.

If you have it burning for an hour, THEN it has consumed 100 wh. (watt-hours).

But if it only was lit for 30 minutes, then it has used 50 wh.

Clear as mud?  

Others have or will address the practicality of your plans.

 

[RoadtripsAndCampfires]

Trebor English wrote:​

“Some of the power generated will get used during the day so it doesn't all need to be stored in the battery. “​

Christine: This is a very helpful point! I did not think of that and none of the sites I read brought that up. But of course, the whole reason to get solar is to use it. Thank you ​

Trebor: Some AGM batteries do better with higher charge rates.  An occasional plug in shore power charge could meet that need.  ​

Christine: We are hoping to get hookups with electrical at least twice a month in order to charge everything (although most things will be charged ongoing with the solar panels), bring out all the fancy cooking plug-in stuff, etc. so we can cook up a storm and freeze it for later (and take showers, do laundry, etc.). We are probably going to end up with a small trailer fridge which means small freezer so that is the main reason I am looking at that 12v fridge/freezer Bob showed. ​

I think the only every-day high powered appliance we will use will be a juicer cause I know no other way to get juice out of a carrot.​

Trebor: ​

 Lead acid batteries don't charge at a constant rate.  When deeply depleted they can take a lot of current while the last 20% takes many hours to complete. ​

Christine: I have noticed this before when charging in the past. I'm going to take a good hard look at batteries after I figure out all of this solar stuff and before we do an install. I will add your note though as it is appropriate.​

Trebor:
Most of what is used does not need to be processed by an inverter.  For efficiency you want to get 12 volt devices. ….  For laptop computers you can get a power supply brick that makes the 19 volts the computer uses directly from 12 volts. ​

I did plan on getting 12v whenever possible but am glad you brought that up because it is an important point. I'll also be taking a good look at laptop power options because in the past I've read that the power source is important to pay attention to and I know nothing yet about that pure sine wave stuff – another thing I want to take a look at after I get the basic solar down. I did not know about the “brick” you mentioned so that is very helpful at this stage.​

Trebor:​

What you need to do is get the battery back to 100% charge often to keep the battery capacity from fading away.  Daily is best, weekly is not very nice. ​

Christine: ​

Getting it back to 100% daily is the reason to insure you have enough solar power I think. That's why I am diving into this before I decide on what I need. (I mention a 100 watt solar panel but plan on 2 to 3 on the pickup and 3 to 4 on the trailer, depending upon trailer size). First I am trying to understand the basics before figuring out the actual needs cause that's how I roll when I am not being stupid or in a hurry.​

Trebor: ​

Inverters have been known to consume 20%, 5% is being generous.​

BradKW:​

I'm not sure where you got the inverter number of 5% But unfortunately you might have missed the -20% loss from conversion inefficiency...so anything running off 110v wastes around 20% versus 12v appliances.  ​

Christine: ​

I got the figure from Alt-E solar. It is good to know there are such differences among brands. Another item I'll need to take a long look at. Maybe they are quoting the figure for just being plugged in and not being used?​

Tx2sturgis /Brian:​

A watt is a unit of measurement of the power the device uses. A 100w light bulb requires 100 watts in an hour and a 40w light bulb only requires 40w. ​

Christine:​

I did know that but will make that clear on my notes. Sometimes I think I think things are obvious when they are not and that's what I am looking for here – getting EVERYTHING as close to right as I can.​

- - - 

Thank you for taking the time to read through my post and respond. When I get all done I am going to send it to a solar company and ask them to check it out and note anything wrong. I may not get an answer but I think I will. It's not as complicated as learning to rebuild a carburetor or something and because they offer kits with all the wires I don't have to learn too much to do a self install.​

I'M GETTING THERE!! THANK YOU AGAIN!​

 

[Trebor English]

I recommend reading: 
https://handybobsolar.wordpress.com/
In a nutshell, there are mistakes that make a solar installation not work well.  More money, panels, batteries, etc won't overcome things like programming your charge controller to a voltage that is too low, a common mistake.

 

[RoadtripsAndCampfires]

Handy Bob's site is a bit overwhelming for me. but thank you for the link. His project far exceeds my needs and a page I thought would be useful is dated 2011. I will be diving into the actual components of the system once I get the basic writeup but just right now I want the basics. He's building solar for houses, large amounts of solar, I just need to power my life in a trailer or van. Once I understand the basics then I can go on to types of cells, batteries, controllers and such. Since I know I will be buying a kit, I will be looking closely at the reviews to gain info on specific offerings.

 

[akrvbob]

I think this is a very good idea, but it is so large as to be overwhelming. I'd strongly suggest you break it down into multiple, logical sections and post each on in its own thread. You will get much more information in response.

 

[akrvbob]

[font=Arial, sans-serif]A 12-volt solar panel rated at 100 watts operating at ideal sun conditions will produce about 18 volts and a 5.5 amp current in one hour. Volts x amps = Watts (w):[/font]

[font=Arial, sans-serif]18 volts x 5.5 amps = 99 Watts (rounded to 100, or 100w).[/font]

No, you've made a common mistake. If you have a MPPT controller this is correct, but if you have a PWM controller it's wrong.

No 12 volt battery can take 18 volts, it'll destroy the battery so the controller MUST step down the voltage to protect the battery, that's its job. 

So lets say at that moment the battery can only take 13 volts, that means it takes 13 volts X 5.5 amps = 71.5 watts. You've flushed 28 watts down the toilet. Why?

A PWM controller is dumb, it can only reduce volts, it can NOT increase amps. 

If you have a MPPT controller, it is smart and will increase the amps to get you all the power your panel is producing. So it will put in 13 volt at 7.6 amps = 99 watts. You get all the power you paid for.

 

[frater secessus]

Handy Bob's site is a bit overwhelming for me. but thank you for the link.

I've attempted to summarize HandyBob's solar info.

 

[RoadtripsAndCampfires]

Thank you for this. I have been away from computer a lot lately due to company and working on finishing Class B. I will catch up soon and be back. Thought I had better pop in and see if I needed to respond. Really appreciate this.

Christine

 

[Zerpersande]

The Inverter – Another Deduction

The inverter converts the DC power of the battery where you have stored your power into AC power so that it can be used by your AC appliances and devices. The inverter uses about 5% of power.

As has already been pointed out the inverter losses are probably higher than 5%. But something that has not been pointed out is that an inverter draws power when idle. The amount of power varies from nothing to be worried about it all to a very big concern and that depends upon the inverter you were using.

For my purposes I keep the inverter turned off. This means I don’t have to worry about those losses. However there is another issue regarding inverters that must be taken into consideration and that is that when left unpowered for extended periods (not going to try to define that) the capacitors can discharge. And depending on the size of the inverter those capacitors may need to be charged. It’s easy enough to do and you can find it on YouTube.

Again for my purposes I don’t want to worry about the simplest process required to charge the capacitors. To avoid this I bought a blue Sea three-way battery switch. From the off position I can cycle through 1 only, 1&2, and then 2 only, the final position fully connecting the inverter. I wired a resistor (25W/12Ohm) into the ‘1 only‘ circuit which means that when I turn it to position1 it charges to the capacitor without energizing the inverter. When I change it to 1&2 the inverter is energized and the resistor is still in the circuit. You don’t want to leave it in this position however. This shouldn’t be a big deal because all you do is just passed through the 1&2 position on your way to 2.

I’ve included a couple of pics of the device I made. Details on how to construct this device can be found on YouTube. Details on how to move from 1 to 1&2 to 2 are detailed in the following clip. Simply considered the labels of 1, 1&2, and 2 to be equivalent to 1, 2 and 3. And there you go.

just as with your initial warning…
Actual mileage may vary, batteries not included.

 

[Zerpersande]

I’ve included a couple of pics of the device I made.

And here’s a wiring diagram and a link.
https://diysolarforum.com/resources/inverter-disconnect-switch-with-precharge.60/

 

[Gr8ful]

You do see the post is 5.5 years old, right? But good info. I'd charge from the alt as well when driving with one of a couple devices you can use.. The MOTOR HOME ex-AMBO has a new 250 watt alt. I left the master switch on for a month & it started OK but was putting out 150 amps for a short while. Glad i start & drive it once a month except in the winter with salt on the roads I just start it.

 

[maki2]

Getting burnout from overthinking is a real thing and a real drag. This stuff is way simpler than the approach you are taking.

My solar power setup is limited by the physical size of what I own for traveling in. Both in terms of space for batteries and wall space for the controller in the interior and roof space for fixed panels as well as the weight. I am way too lazy to play at being a “sheep herder” tending an array of portable panels. Setting them up, putting them away, moving them during the day for optimal input, securing them from strong winds, etc. That is not living a simple life, it is just chores that give little in the way of results unless you have no roof space for fixed panels in which case it is a necessity.

My power consumption HAS to fit within my means of generating and storing it. That makes calculations a whole lot easier than trying to learn all the technical stuff.

Figure out how many panels you can fit on your roof and what wattage that small array adds up to. That is what determines the size of solar controller you need.

The third factor is the physical space you have for a battery bank. Your battery size for capacity is related to the amount of power your panels generate. You want to be sure it gets fully charged to capacity pretty much everyday and not drained too low by over consuming its storage capacity. You have to live within your means and you can adapt to that.

 

[bullfrog !]

^^^ ”Different strokes for different folks!” I use both permanent and portable panels. The mounted ones are much easier to deal with especially if you have more room for more panels than you need. Needs or daily usage is the determining factor in figuring out what you must have for it to work for you. If budget, space, physical ability or mental attitude limit you from doing what you need then things have to change. For us it has meant not boondocking as much, seasonal jobs with full hookup sites and base camps where solar panels can be mounted so portable panels are not necessary.