How much solar do I need?

[musicman]

As an retired engineer I would like to add that you actually look and see how many watts each of your items are rated. This will be your watts/ hour you may need. 

Like mentioned in above post your batteries should not be discharged below the 50% level.

 If you have 100 amp/ hour batteries, that's 1200 watts . Taking half of it = 600 watt/hr available at full charge. 

One other item to remember is a solar panel is not  100 % efficient. Meaning you will not get 100 watts out of a 100 watt panel. The standard rule of thumb is 80%. 

Other than the physical requirements of being roof mounted as mentioned in other posts ,  hope this info will help.

 

[Jmel]

As an retired engineer I would like to add that you actually look and see how many watts each of your items are rated. This will be your watts/ hour you may need. 

Like mentioned in above post your batteries should not be discharged below the 50% level.

 If you have 100 amp/ hour batteries, that's 1200 watts . Taking half of it = 600 watt/hr available at full charge. 

One other item to remember is a solar panel is not  100 % efficient. Meaning you will not get 100 watts out of a 100 watt panel. The standard rule of thumb is 80%. 

Other than the physical requirements of being roof mounted as mentioned in other posts ,  hope this info will help.

Great post.

I was just looking at some info last night trying to figure out if I can put a fridge in my van.

I have a 2.3 cubic foot fridge, and it says on the back it uses 1.3a (110v) but like 6.3 max.

I have (2) 35ah batteries in parallel, and (2) 100w panels on the roof of the van. I estimate that on a good sunny day, I can receive 8-11a of 12v power into the batteries. I checked charts for average usable sunlight for solar panels for where I live. It's on average, about 5 hours per day for full charge. I guess that's how I arrived at some of the info below.

So I start thinking... can I run this fridge? How much power is left over. I may update the post later with my crazy math, but what it seemed to boil down to was this -

I have about 660 watts available that come from the solar each 24 hour period. Since it's not sunny 24 hours a day, that was the best way I could account for solar generated watts as a "unit". I end up left with 240 additional watts to "play with" over a 24 hour period, once the battery is fully charged (from dead). 

I arrived at these numbers thinking that if I ran whatever I have, it would take 660 watts of usage to end up at a point where I should not use the battery anymore - 50% used, or 35ah.

I think it's way better to think of everything in watts and watt hours than amps and volts.

I'm thinking I'm undersized on my batteries now, and maybe I should have 150ah or 200ah, but I don't know how folks are running standard 110 fridges off of 200w of solar. Seems like you have almost nothing left over, and really the only thing upsizing the battery does, is to give you a buffer for cloudy days.

Otherwise, you really do have to add more panels. Or spend 500 or so on a really nice 12v fridge/freezer with really low amp draw... like a dometic unit.

Is this right, or have I lost my mind?

 

[frater secessus]

> I think it's way better to think of everything in watts and watt hours than amps and volts.

Probably (and definitely when comparing 12v apples to 24v oranges).  But for whatever reason Amps and Ah are the most commonly used.


> I'm thinking I'm undersized on my batteries now, and maybe I should have 150ah or 200ah, but I don't know how folks are running standard 110 fridges off of 200w of solar.

As you suspected, most folks are running $$$ 12v compressor fridges if they are doing it on 200w of panel.

IMO it is better to be undersized on batteries rather than oversized;  at least they won't be killed by undercharging.  St. Sternwake told us in 1st Absorption, verse 42, that a 2:1 or 3:1 ratio between panel wattage and battery Ah is best for regularly cycled lead-acid.   You are sitting right at 3:1 so he is smiling down on you right now. 

To help a small bank make it through the night it may be necessary to move all time-shiftable loads to periods when there is excess power.  That way they wouldn't compete with the fridge for precious power at night.

 

[laurielovesGary]

Ok we need lots of help Gary and I want to do solar want to get 33 quart fridge and won't know what to do with solar kit when we get them or what kind of battery to get or inverter or what else this is so over our heads.

 

[frater secessus]

Laurie, you may want to start a new thread. 

Here is an intro to solar I'm working on.  It's rough but might help you understand what questions to ask.

 

[highdesertranger]

you can break it down to 3 basic steps,

1. figure out your daily power usage.
2. size your battery to your daily power usage.
3. size your solar to your batteries.

that's it, it's easy. well not that easy but as you go through the steps you will gain knowledge and understanding. we will help. try to avoid an inverter most things can run 12v. also remember it's always easier and cheaper to conserve energy then it is to make it. highdesertranger

 

[willprowse]

I personally tell people to fill the roof with as many solar panels as they can (because on a vehicle, it is the largest constraint), then build a battery that can charge at a safe rate with the solar panels that you put on the roof, then buy the largest solar charge controller they can. Then buy the largest inverter they can afford.

Try to build the biggest system you can. Solar panels are cheap. If you need to scale your system in the future, be sure to have a larger than needed solar charge controller so you can continue to make your system bigger if you need to.

 

[Annie W]

I like your thinking on this Bob.

Panels mounted with tilting mounts on the side of the rig , some  over the windows like awnings and some others on the walls. All removable to go on the ground etc when shade parking.

After watching Bob's video on Solar, am still Wondering what Bob is talking about in his OP, as well as what this above means ?

 

[Weight]

A basic answer, get as much solar as you can fit or afford. My example, I have 4 x 100 watt Renogy panels as that fills the roof leaving room for the exhaust fan.

 

[John61CT]

And being able to get the face of the panel aimed so perpendicular to the sun's path can double production.

 

[Rolling BnB]

Does anyone know if this Renogy 400 Wh power pack would be enough for basic van needs?  Am I right in saying that this power pack takes the place of a battery, charge controller and inverter? 

Mod edit, the link has been removed see the link in post #116

All you need are, 2  x 100W panels to connect to it, or plug it into your cigarette lighter as you are driving.  It seems so much easier than buying the separate components and it is very reasonably priced.

My needs are: small household refrigerator, lights, coffee maker, recharging a phone and laptop.  Everything else is propane.

 

[Canine]

Rolling BnB, Depends on what you mean by basic. This unit provides 15 to 20 amp/hours of stored electricity. Your fridge would eat that up in as little as a couple of hours. Your coffee maker would put such a high demand on the surge start that it wouldn't even work. The AC output is 300 watts max; your fridge may not run on that. Without the sun lights, phone, and maybe your computer would be the best you could get out of it. It says to use one 100 watt panel, so two 100 watt panels would be too much. Maybe the battery management system would not allow the unit to burn up. At best it would clip off a good portion of electricity making the second panel largely a waste. It shows a picture of a 110 volt coffee maker plugged in, but that's misleading. Most coffee makers are 600 watts+. A 300 watt coffee maker would take a while and then I would do it only when the sun is shining. Or maybe make only one 8 ounce cup of coffee then that would work.

So pretty basic. Good enough for one day without sun and then you would have to do without the fridge and the coffee maker until the sun charges it up again. But I have a system that is 16 times larger than that, so I might be overly harsh. Some people do without a fridge or other high-demand items and they do just fine.

 

[sushidog]

After watching Bob's video on Solar, am still Wondering what Bob is talking about in his OP, as well as what this above means ?

Sometimes a picture is worth a thousand words.

Chip

 

[John61CT]

For 200w solar input, would take a ~100-200AH battery bank to make the most of it, depending on weather etc conditions.

Erring on the side of "too much" solar never hurts more than your wallet, but 10x is def overkill.

Really you want at least a rough AH/day usage budget to figure out sizing.

 

[Rolling BnB]

Rolling BnB, Depends on what you mean by basic. This unit provides 15 to 20 amp/hours of stored electricity. Your fridge would eat that up in as little as a couple of hours. Your coffee maker would put such a high demand on the surge start that it wouldn't even work. The AC output is 300 watts max; your fridge may not run on that. Without the sun lights, phone, and maybe your computer would be the best you could get out of it. It says to use one 100 watt panel, so two 100 watt panels would be too much. Maybe the battery management system would not allow the unit to burn up. At best it would clip off a good portion of electricity making the second panel largely a waste. It shows a picture of a 110 volt coffee maker plugged in, but that's misleading. Most coffee makers are 600 watts+. A 300 watt coffee maker would take a while and then I would do it only when the sun is shining. Or maybe make only one 8 ounce cup of coffee then that would work.

So pretty basic. Good enough for one day without sun and then you would have to do without the fridge and the coffee maker until the sun charges it up again. But I have a system that is 16 times larger than that, so I might be overly harsh. Some people do without a fridge or other high-demand items and they do just fine.

Thanks so much for your reply, Canine.  All this solar stuff makes my head spin.  I wish someone would just say 'I have this much solar/# of batteries/size of inverter and this is what I run on it.'  I have watched so many videos and read so many articles and they just make it more confusing.

 

[highdesertranger]

I had to edit the link out of the original post. here it is it's for a Renogy power pack,

https://www.amazon.com/Renogy-Rugge...=1520793376&sr=8-3&keywords=renogy+power+pack

that power pack has a very small battery. here's what you need to do,

1. add up what your planned usage per day is.
2. size your battery bank according to your usage.
3. size your solar to your battery bank.

now there are limits how big is your roof? how much weight in batteries do you want to carry? remember it's always cheaper and easier to conserve energy then it is to make it. heating anything with electricity is very inefficient. highdesertranger

 

[Almost There]

I wish someone would just say 'I have this much solar/# of batteries/size of inverter and this is what I run on it.'  I have watched so many videos and read so many articles and they just make it more confusing.

Okay, I'll start with mine for you.

I have 4 -Trojan  T105RE batteries that give me 450 amp hours of storage (225 a/h usable.) That powers a couple of LED lights, my roof vent fan used occasionally (when cooking mostly), charges my Kindle, cell phone and laptop at least daily. The main power draw is my pair of Whynter 65 qt refrigeration units. One of those babies is set at 0 F for a freezer, the other at 40 F as a fridge.  Without the freezer I would only need about half this amount of batteries.

I have a built in 400 W pure sine wave inverter so I can power the occasional use of stuff like my food chopper and immersion blender. I also carry a 120W plug in inverter that I normally use to charge my laptop. Both the cell and the kindle are charged with 12V chargers. If I need more power for something like power tools I draw power straight from the generator. The 400W inverter has a power switch so that when I'm not using it, it draws nothing.

To charge those batteries I have CHOSEN to only have 200 W of solar...I should really have at least 400 watts but since I only use solar 6 months of the year I made the choice not to invest in double the solar. I do use the 200 W as portable so I can tilt and angle them - it makes a huge difference.

To supplement the solar because it's not nearly enough, I use a 55 amp Iota battery charger hooked up to 2000 W of generator every second day for at least 2 hours, sometimes longer if it's hot out or if it's been cloudy/raining.

I can also charge my house batteries via the solenoid/alternator if I'm driving. I keep track of the hours the engine is running so I know what I need to do to supplement the charging.

I do not ever use my battery system to heat anything..that's what the propane heater and the butane stove are for. My shower system is solar supplemented as needed with hot water heated on the stove and poured in to the shower unit.

Everyones' needs are different...there is no one simple solution to any of it. I know my eyes rolled clear around my skull when I had to start figuring it all out.

As has been pointed out in several places here on the forum...the only way to do it without it being nothing more than a guess is to figure out what you absolutely have to power,(check that with us so we can offer advice as to whether it's practical or not), add up the usage (we can help with that). That becomes the basis for figuring out how much battery storage you need. Then and only then can you match the amount of solar/battery charger you need. Sometimes you have to work back and forth because you run in to financial and roof size factors that mean you can always have what you thought you wanted...

 

[Motrukdriver]

Probably the first question you need to ask or determine the answer to is how much solar can I have? In other words how much real estate you have to mount panels. With panels being x wide by y long and your roof or mounting surface being x wide by y long wouldn't it make more sense to first determine how many panels can actually fit up there. It would truly suck if you did all your calculations and came up with the right number of panels and batteries and charger to do every single thing you want only to find you can't mount all of the panels. So I'd probably determine how much solar I could reasonably have first and then base everything off of that. Might not need all that room but it would be nice to know for sure.

 

[Almost There]

Mo - that's a nice way of looking at it but not totally the absolute be all and end all.

For example, I  have absolutely no panels mounted on my roof, never measured it, never will!

I use a portable set up for a bunch of reasons - height of my van and my inability to get up to clean them for one. My distaste for putting holes in my roof for another. My seasonal time in either coastal rain forest or northern boreal forest means that solar is wasted for me for probably 6 months of the year. And I don't want to  have to be scraping pine sap off of my solar panels on a regular basis.

Strict needs assessment is a better place to start IMO...then you can figure out how to achieve that goal.

 

[tx2sturgis]

 And I don't want to  have to be scraping pine sap off of my solar panels on a regular basis.

Not to mention bird poop.