How much solar do I need?

[tripper]

My roof rack is measured roughly 42x60. 42 in the width is the inside edge to inside edge from side to side. Originally I was going to try to fit the panels in between them instead of onto so it was a little more sleek looking. Would the two batteries give me 3 days of power? Granted I won't be living inside of it as it is a camper for road trips and weekend camping trips right now. I could fit a 300w renogy panel up there but they don't sell them where you can just get one and shipping would be really expensive. I figured 2 100w panels would do the job as the only daily items would be charging my phone and the fridge needing to run. The other things would be occasional. Maybe I'm going about building my setup incorrectly for what I want to do? I'm mostly worried about the fridge as the other stuff would be occasional.

edit: The wiki says "200W is not a magic number, but it is the most common size of solar install for vandwellers and boondockers. It is probably more than what's needed for the basics and has enough power to add in a 12v compressor refrigerator if desired.8)"

200 is too small, it will only work well in the middle of summer without clouds, in the winter it won't get your batteries fully charged, and they will die early.  I would suggest using one high voltage 60 cell house panel on your roof, they measure 66 inches by 40 inches, the newest LG panels have up to 340 watts in one panel.  Also one good programmable MPPT controller.

200 watts will work for just a weekender. setting them down inside the roof rack would be bad as the shadows from the racks will be on the panels for most of the day seriously cutting the panels output. To get the large panel without paying for shipping I have I called the local house solar companies and asked them if they would sell me a house panel direct, and they did, and for a good price. The house installers buy them in pallets, and sometimes have a few leftover from each job. I would still make the investment in the single large house panel rather than the renogys

 

[John61CT]

If literally overnight less than 48 hours, maybe OK with zero solar, just need a big enough bank and recharge off mains when you get home

 

[Spaceman Spiff]

Awesome, this seems to be a similar setup to what is like to run and it seems 200w with 2 batteries should do me fine. I'd there anything you would have done differently if you could do it again?

I am very happy with the performance of my system (4 years).  You did not mention where you will be camping.  The one place my system does not work well is under heavy forest canopy.  I would need ~ 600W for heavy shade.  I would recommend getting a good battery monitor (I have a Trimetric 2030).  You will learn a lot by monitoring your system.

200 is too small, it will only work well in the middle of summer without clouds, in the winter it won't get your batteries fully charged, and they will die early.  I would suggest using one high voltage 60 cell house panel on your roof, they measure 66 inches by 40 inches, the newest LG panels have up to 340 watts in one panel.  Also one good programmable MPPT controller . . .

My system runs well all the way into mid November in Northern Minnesota, when I am done for the year.  I get back to 100% daily in all but the most heavily overcast skies (dark grey clouds) or under heavy forest canopy.  When it's cloudy the refrigerator doesn't run as much.

The one disadvantage of one large panel vs. two small panels is in partial shade.  If one part of a panel is shaded it reduces the output of the whole panel.  If you have two (or more) in parallel that doesn't affect the output of the other panel.

I agree with MPPT.  Some of the newer ones have battery monitors that will link to your smartphone (Victron comes to mind).  Might be a better solution for you than Trimetric.

 

[jrose152]

I feel like I'm getting conflicting advice on what will and will not work for me.

 

[John61CT]

Yes that is inevitable.

If you were paying multiple professionals you would get the same.

Over time you learn which members to listen to more than others.

In the end we all must learn enough from the process, in order to sift through the answers and make our own decisions.

 

[jrose152]

So what do I need to make what I want work or can I not do this in my sienna?

 

[John61CT]

Fitting as much solar wattage on your roof as possible (practical) would be a good start.

If you want to try just 200-300W, do it so you can add more later if you find you need it.

You might be fine with a pair of GCs, but IMO two would be better.

Starting your own thread, giving all the relevant data you can think of from the start, and then asking as specific questions as possible, will get more / better answers.

Just don't expect consensus

 

[jrose152]

Fitting as much solar wattage on your roof as possible (practical) would be a good start.

If you want to try just 200-300W, do it so you can add more later if you find you need it.

You might be fine with a pair of GCs, but IMO two would be better.

Starting your own thread, giving all the relevant data you can think of from the start, and then asking as specific questions as possible, will get more / better answers.

Just don't expect consensus

I'm waiting to start that thread around when I am ready to order so I can ask what parts specifically to order. Are you suggesting I get 4 batteries rather then 2? How much of an actual advantage will 4 give me over 2?

 

[John61CT]

Depends on many factors, but basically gives you a longer buffer of power in between charging opportunities.

How often / how many hours driving?

How many Watts solar, what sort of weather patterns?

How easy is it to get to shore power overnight?

When you are stationary boondocking in cloudy weather, what % of battery capacity do you use even when conserving as much as possible?

If you get an AH-counting meter and learn how to measure input vs usage, you could start with one pair, and then decide whether it's worth getting the second within a couple of weeks.

Since ideally all batts in the bank are identical, mfg date.

 

[jvriffel]

My first post and have read and watched hundreds if not thousands of solar information.

I keep reading put "as much on roof as can fit" but my questions would be. Is there any reason to use certain watt(or sized) panels or can I use "as much as I can fit" in larger or smaller watt or sized panels? Preferably keeping them all the same or is there reason not to?

Looking at whats out there they range in watts from very little to I think 435 watts. Obviously cost would be an issue.

 

[tripper]

My first post and have read and watched hundreds if not thousands of solar information.

I keep reading put "as much on roof as can fit" but my questions would be. Is there any reason to use certain watt(or sized) panels or can I use "as much as I can fit" in larger or smaller watt or sized panels? Preferably keeping them all the same or is there reason not to?

Looking at whats out there they range in watts from very little to I think 435 watts. Obviously cost would be an issue.

High voltage (i.e. house panels, 24v panels) have a lot less amperage loss/better at pushing the energy to the controller and usually much more efficient for the space used. The only reason to use the 12v/RV panels is if you are on a super budget and cant afford the MPPT controller needed for the house panels,if you can't fit a house panel on your vehicle, or can't afford the house panel/shipping price.

All flat top vans can fit the house panels , automobiles you have to find custom sizes to do it efficiently.

 

[John61CT]

Is there any reason to use certain watt(or sized) panels or can I use "as much as I can fit" in larger or smaller watt or sized panels? Preferably keeping them all the same or is there reason not to?

All the panels per controller should match if not going 1:1.

Panels that put out more watts per total sq ft are better.

Then you have your length and width to juggle the different dimensions to further optimize, squeeze say another 300W.

And as you say the cost issue

 

[Bridgestreet]

I am by far no expert, I feel it’s more of battery capacity. In my case, 2- 100 watt panels, It’s about having more battery to store the energy.


Sent from my iPhone using Tapatalk

 

[tripper]

It is a balance between battery capacity and solar wattage. Too little solar for the battery capacity and you will rarely get the battery fully charged; this will lead to the battery having to be replace every 2-3 years.

For example:
100 watts of solar for 100 ah of battery - BAD, most of the time the battery will never get fully charged

200 watts of solar per 100 ah of battery - OK, the battery will sometimes get charged fully, not really enough for wintertime use.

300 watts of solar for 100 ah of battery - GOOD, the battery will get fully charged most days.

This is assuming you are using about 30% of your batteries AH every day.

This is a lot my personal experience, plus reading others opinions.

 

[John61CT]

This is only true for users who either

A. do not have and use an AH-counting meter, or
B. do not have a supplemental charge source

As long as you follow The Rule:

use less than you will produce in your charge cycle,

you could have an enormous bank and a small amount of solar.

It is true that the percentage of users with this degree of knowledge, control and gear is rare, but if you do then you have a lot more options, are free to make exceptions when needed occasionally, without reducing your bank lifespan much.

And of course, the third approach, never mind about these details, just have a cheap bank and replace it when needed.

 

[jasper]

I hope this is not out of place in this thread.

Our van is a pop-top that limits roof area for solar panels. It came originally with a house battery and solenoid for alternator charging.  The battery box was just large enough for a 100AH AGM. Our main load is a 63qt Edgestar 12vdc/120vac chest refrigerator set to 34 degrees.

Roof rack with round bars between. One of the cheapest available online.  175 watt swiveling panel (via u-bolts, L brackets and hose clamps), with an underneath 100 watt panel that can be removed (slid out) for placement elsewhere if needed. Removing four nuts from the two u-bolts on the 175 watt panel allows it to be placed elsewhere, also.

We have a generator, and one of these cheapo completely dumb power supplies with an inline ammeter if needed for quick bulk charging. They can be adjusted to 15vdc or for current (amps) output.

Not full-timers, and the system is only a little over a year old, but generator and dumb charger only needed twice with little to no direct sun for two or three days. There is a digital voltmeter inside the van that gets a lot of attention.

 

[kyra1958]

Being an engineer, I always recommend starting with a needs list (not likes or wants).  Especially if you have a medical condition that requires power for equipment (CPAP, nebulizer, refrigeration for medications, etc.).  Determine how much power your needs require.  Now you can go up on the roof and see how much solar you can fit (and measure you wallet to see how much you can afford).  If you can't meet your needs, you need to get creative or find a different solution.  And remember, you must build margin into your system for that inevitable week of rain 

Other than where you start from, I think you are giving great advice.

Personal experience: I have 200W of solar and 208 AH of battery.  My big loads are a 12 volt, 2.1 ft³ refrigerator and a Maxxfan.  I am seldom below 90% battery capacity in the AM.  Additionally, I am usually up to 100% by noon on an overcast day.  My system hardly notices my charging a cell phone, laptop, digital camera or running LED lights (all on 12V, I don't have an inverter).

-- Spiff

You sound like the perfect person to ask my question too. I have an old Dometic 3 way fridge that was cut out of a trailer, it works with the plug in regular house current, I tried it lol, And it still has the wires to hard wire it right into a trailer, unfortunately, they cut the propane line and I haven't been able to get it off and don't have the knowledge to see if I could hook it up to a hose for propane, even if I could get the old metal conector off. Now I was going to purchase a 200 watt system since that is what I can afford, would it be better to get it hardwired into the trailer or just use the plug-in to a converter. Its a 12 v 1.3amp. Also with the 200 watt system do I need to install a fuse panel if so can you recommend one, newbe here, I only ask who I think sounds like they know what their talking about.

 

[MarleyPumpkin]

:huh: 
Hi Everyone,
I'm a newbie & to be honest this forum is an absolute lifesaver for me. Even though at the moment my head is about to explode with all the info. BUT I'm truly thankful for it. With that being said, I NEED HELP, please. 
My main goal is to boondock as much as possible. This is going to be long sorry...

I'm confused about the size of inverter I will need. And there's a few other questions I'm tossing in at the end.
Here's my plan, 
I'm either going with a Whynter Dual sided fridge/freezer (92 qt) OR run my RV fridge (on solar/AC) while driving & propane when parked), 
LED lights, 
a laptop, 
charge my cell, 
smart tv, (4.16 DC Amps)
DVD player (@ times) (.75 DC amps)
Fantastic Fan,
a Road Pro fan (when needed)
there's also a few days where I will use my instant pot but those aren't everyday things, (when used it will be for about an hr)
and my microwave (700 Watt) for about 5 minutes a day.

I will be using a Honda 2000 watt generator to run a small easy start A/C, like the Frigidaire off Bob & Jim's new video. (when needed)

The Solar system I'm looking at- 
(4)-100 watt Renogy Mono Panels) 400 watts of Solar (wired in parallel) Would this be sufficient?
(4) 6 Volt 200AH GC2 Photovolatic Renewable Energy AGM Soalr batteries. Wiring the batteries in Series and then using a parallel bridge giving me 400AH. If I'm understanding this right I can only use 200AH or less to save my batteries, Right? Because I don't want them going below 50%. I also don't want to overshoot on my batteries, would 2 work or do I need 4? Or am I wrong and need 6?

What size inverter should I get? I was thinking a 2000 watt pure sine with 4000 peak would be sufficient BUT don't want to get the wrong thing. 
Please if I typed some incorrect information, I apologize, I'm hoping I have at least everything down so far. 
Of course my heavier usage of power will be during the day when I'm getting the most solar. 

There is one more thing that confused me. I've also seen where they have inverter chargers. And in one video I seen they actually suggested against using the combo/all in one's and to buy separate items (Smart converter charger, transfer switch, & inverter) in case one component goes bad it's more cost effective than replacing the whole thing. Anyone have any suggestions on this?

Not made of money here BUT I have a small nest egg to put towards my future home and want to get what I need and not waste.  and I do't have my rig just yet, I'm deciding between a 22' or 24' Class C or my son has said he would help me convert a step van into my new home (20'). 

Thanks

 

[Canine]

Marley, you are on the right track. You have the correct amount of solar assuming you don't live in a place like Alaska or Oregon in the winter or you don't run your TV and other items all day and all night. I have more solar/battery, but would be comfy with the solar and battery bank you have.

You also have the correct amount of batteries, although, those look a little on the cheap side and probably won't last too terribly long. However, I still think that is the right choice since there is a good chance you could charge them incorrectly (which happens to A LOT of us) then ruin them. Then you aren't out $2000 or so. You will probably get your money's worth out of them if you take care of them. I would totally get those batteries if I were a neophyte. I did just that and purchased used AGMs and am still running off of them. Will do lithium next time.

You can run your batteries to 50%, but that is the edge of heading into damaging territory. I don't like to ride the edge like that. I prefer my system to get no more than 30% discharged. The batteries last longer and if I make a mistake or something happens, I still have a buffer of 20% to use. I never find myself without power. Also, at, say, 40% your batteries may not run a microwave due to Peukert's Law.

More solar and more batteries is often better, but not always. You can upgrade in the future.

2000 pure sine will easily do what you want it to do. You are smart to stay away from modified sine wave.

Get separate components if you want to charge the batteries the best you possible can. I'm a Blue Sky Energy fan all the way, but there are other good brands like Victron or even Renogy. Get an MPPT if you want to utilize the solar energy as much as possible. Then use a charge controller with the optional temperature sensor that attaches to the battery itself. Very important. You would be throwing money away not using a $30 temperature sensor especially with AGMs. Also get a controller that can be networked if possible. You can run non-networked charge controllers in parallel as well, but you will get better results with a networked system should you decide to expand. It's nice to leave that option open as you don't know what the future holds for your system. It may grow as you grow.

While I don't have all the facts, if you had went ahead with the system you described and had not asked for feedback from us, you would have likely been just fine; I can't see anything wrong with it.

 

[MarleyPumpkin]

While I don't have all the facts, if you had went ahead with the system you described and had not asked for feedback from us, you would have likely been just fine; I can't see anything wrong with it.

Thank you Canine,

I thought I would have enough but the inverter threw me for a loop. I thought about getting (3) 350 watt solar panels BUT I got lost trying to figure up the right amp of MPPT controller to get. I was going to get 6 batteries and a 3000 pure sine but again I have looked at so many different set ups I was thinking less is more. Guess not. 

I will definitely look into the smart charger and buy separate components because I will be living on a limited income & won't have a lot of money to correct errors. 

I have 1 cup of coffee in the morning & will alternate between my little 1 cup maker or just thinking about omitting that all together and getting the coleman stove top one for 30$. I just cannot get over the taste of instant coffee YUCK...sorry to those that drink instant.

My TV will be on for a bit BUT not all day and night, depends on what I will be doing that day. And I can also use my laptop if I want to watch a DVD or YT vid's.

I won't have the roof top AC those things weigh a flippin ton. That's why I was just going to do the little 5000 BTU mounted in the back some where and then again that won't be run on solar. Nor will it be ran all the time as I will have the Fantastic Fan going and the RoadPro Fan. I cannot breathe when it gets too hot so having that small A/C for back up is a necessity. 

Also not having a water heater, using solar shower bag, 5 gal bucket, and the Zodi shower pump. (For showers & running water into a dish pan)
For days that are cold or just not enough sun I can heat some water on the stove and add a little cool water if needed. 

What batteries would you suggest? I want something that is going to last but lithium I believe is out of my budget. 

Thanks for the heads up on the the temp sensor & networked controller. I hadn't came across a video yet that mentioned that, or if I did I must have forgotten. I usually take notes. 

OK how do you charge batteries incorrectly? Even those cheap batteries are gonna smack my wallet pretty hard, so please tell me what NOT to do 

Thanks
Maggie