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Old 07-10-2019, 08:34 PM   #1
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Need a good power chart to calculate solar

Want to add solar to my small Coachman 16b TT. Doing the planning now but can't find a good chart of what the power usages are on all the 12V items in the camper. I also plan to add a small inverter just for a little TV or radio/CD/DVD occasionally.


Anyone have a link to a good power usage chart?


Thanks.
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Old 07-10-2019, 08:48 PM   #2
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Have a look at the 12V side of life in the electrical section of the library. Library is in the green bar at the top of the page.
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Old 07-10-2019, 09:24 PM   #3
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Need to learn the math.

P=IV. Watts=Amps*volts.

The 1500 watt hairdrye, microwave draws about 14 amps ac. Or about .150 amps dc. Wipes out a battery every 20 minutes.

Batteries are your issue. You need deep cycle preferably six volts, more durable. The more amps the better. Two Costco sixes are 230 amps. Size is always an issue you must deal with. You can only use 50% of the amps or you damage the battery.

100 watts of solar charges a battery 25 amps a day on a good day. That is not a lot. Likely close to your parasitic loads. Fridge, smoke detector, leds on things. etc. With only 1 battery and 100 watt solar there will be no lights the second night.

Plan ahead. Study the chart.
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Old 07-10-2019, 09:47 PM   #4
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Bah, it can be spit-balled easily.
What are you wanting to run and for how long?

I have 420ah of batteries, 600w of solar, and a 2k inverter. I run pretty much whatever, whenever. TV, pocket media computer, charging devices (wireless chargers for phones), night lights, micro for a min or two a day, hair dryer for 3 or 4 minutes every couple days.. battery was charged by the time we got back in the afternoon. Don't think it got lower than 95% SOC. Perhaps I over-did it. However, it's a scaling basis for you.
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Old 07-11-2019, 08:46 AM   #5
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Once you have your daily consumption total (12-volt side of life), you can think about the solar panel specs...but...output is dependent upon the potential solar irradiance available at the panels’ location. That means that in clear weather, on the same day, your panels will generate more watt-hours in southwestern AZ than in northern CA.

HERE is a solar irradiance calculator that can be used to find the potential irradiance for a specific location for each month of the year. Follow the instructions on the website to get a reasonable estimate for the watt-hours you can expect your solar system to deliver to your battery bank in a day. Note, again, that these estimates are based on clear weather.

As mentioned earlier, you will also need to size the amp-hour capacity of your battery bank to support your daily watt-hour draw and charge for the camping duration.

Think about the places you regularly camp (or may camp) and configure your panels to provide the watt-hours needed to cover a portion of your battery bank’s daily draw. Again, you will also need to think about the number of consecutive days you’ll be dry camping in order to size the array and battery bank properly.
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Old 07-11-2019, 09:05 AM   #6
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Another suggestion on sizing is to buy an oversized controller so you can add panels if you find you need more. If installing 300 watts of panel, use a 400 watt controller, etc.
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Old 07-11-2019, 12:24 PM   #7
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If you live in an area with clouds, solar is not so effective. Like most of the United States.

Also, that favored campsite with the beautiful shade trees doesn’t work out well.

Some day we will have better batteries and solar panels.

You need lots of batteries today to cover bad solar days and nights.

Got to do the math. What do you need? Where do you camp.

Easy as stated, just use what you have and turn the generator on.
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Old 07-11-2019, 01:05 PM   #8
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What I read here

Basically solar is for keeping your battery charged as long as you don't use it.



Just another "Hey look at me, I'm solar"
& I am good for nothing.
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Old 07-11-2019, 01:31 PM   #9
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Basically solar is for keeping your battery charged as long as you don't use it.



Just another "Hey look at me, I'm solar"
& I am good for nothing.
Wow another...hey look, I know nothing about solar!


I have 700W of solar, I can recover from multiple days of no sun in one day with my 2 BattleBorn batteries. Never need a generator.
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Old 07-11-2019, 02:02 PM   #10
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See! Got to understand the math.

If you live in a desert state where the sun always shines and ac is not needed.

And, you have $5,000 worth of solar collectors, controllers, monitors, batteries and wire and no residential fridge solar is great. Sign me up.

Last year on spring vacation we needed heat(furnace) and it rained for six days or was cloudy. Plus I like cold beer. For me, it would not work.

I want the solar merit badge.

Got to plug in somewhere.
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Old 07-11-2019, 02:55 PM   #11
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Wow another...hey look, I know nothing about solar!


I have 700W of solar, I can recover from multiple days of no sun in one day with my 2 BattleBorn batteries. Never need a generator.



Never mind. I will not convince you and you will not convince me.
For example, if a 300-watt (0.3kW) solar panel in full sunshine actively generates power for one hour, it will have generated 300 watt-hours (0.3kWh) of electricity. That same 300-watt panel produces 240 volts, which equals 1.25 Amps. Unfortunately, solar panels don't generate a steady stream of electricity all day.
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Old 07-11-2019, 02:59 PM   #12
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Never mind. I will not convince you and you will not convince me.
Sounds like a convo I had with a flat earther!
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Old 07-11-2019, 03:03 PM   #13
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personally, and even though I have some solar myself, I suspect that a small trailer for camping would not be a good subject for the cost of solar, and the fairly small benefit it might provide, especially since, as mentioned, most of us like to 'camp' in the shade, in the woods, and not necessarily 'out in the open', where the sun can do the most good.

Solar is expensive for the typical outcome for most any camper. A few exceptions exists, especially those with very large arrays, large battery banks, and large inverters, but those costs are hard to swallow on a smaller budget for a smaller camping experience.

You could go and spend $300-$500 for a small 2 - 100w panel package and feel 'good' that you have some solar, but if you were to see how that equates and compares in the 'real world' to what you'd have to pay an rv park or campground for that same small amount of 'benefit', you'd run, and fast. It's expensive.


We just purchased a good used EV Nissan Leaf for my son, going off the college at UAH(University of Alabama in Huntsville), for aerospace engineering. He knows how to 'calculate' the cost per dollar of the 'real world' outcomes when it comes to these solar questions... having said that, his mother's first question was: why don't the EV car manufacturers cover the hood and roof with solar panels??
Makes sense, and sounds like a very obvious question. The issue is one of 'cost versus benefit'. Even though you want to buy a 'environment friendly' vehicle, the reality is that it stills comes down to affordability. If manufacturers installed solar panel arrays built-in to these cars, and the wiring and systems needed to 'convert' that power to battery power, the additional 'cost' when purchasing the car might either scare away the public, or never really 'give' any true return on the upfront cost, due to weather, lack of sun, 'where' you park your car, how many miles you drive per day, whether you have 120v charging, or 240v charging, etc., etc. It's not really as 'simple' as we'd like to make it out to be.
The simple truth, though, is that there is just not enough 'acreage' on the roof of an EV vehicle for near enough solar panels to make enough difference.
The same applies for the typical RVing situation - even the largest of motorhomes have difficulty in accessing the amount of 'space' on the roof needed to harvest enough solar power to make a real difference, though many of us try!
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Old 07-11-2019, 03:10 PM   #14
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Comparing putting solar panels on an electric car vs putting panels on a trailer that uses maybe up to 600W hours in a day is a very poor comparison.



I do agree, you have to figure if putting a certain in number of panels in your roof space is worth it. For example, putting up only 200W on a motorhome that has 4 6V deep cell batteries is close to worthless if you have to run your generator anyway.



My goal is to have enough solar so I never have to run a generator. That is how I sized my system.
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Old 07-11-2019, 03:15 PM   #15
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Comparing putting solar panels on an electric car vs putting panels on a trailer that uses maybe up to 600W hours in a day is a very poor comparison.



I do agree, you have to figure if putting a certain in number of panels in your roof space is worth it. For example, putting up only 200W on a motorhome that has 4 6V deep cell batteries is close to worthless if you have to run your generator anyway.



My goal is to have enough solar so I never have to run a generator. That is how I sized my system.

I am sorry, I thought you said the following.


"I have 700W of solar, I can recover from multiple days of no sun in one day with my 2 BattleBorn batteries. Never need a generator."


Also you lead me to believe this was on your RV, correct? Have a great day.
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Old 07-11-2019, 03:16 PM   #16
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personally, and even though I have some solar myself, I suspect that a small trailer for camping would not be a good subject for the cost of solar, and the fairly small benefit it might provide, especially since, as mentioned, most of us like to 'camp' in the shade, in the woods, and not necessarily 'out in the open', where the sun can do the most good.

Solar is expensive for the typical outcome for most any camper. A few exceptions exists, especially those with very large arrays, large battery banks, and large inverters, but those costs are hard to swallow on a smaller budget for a smaller camping experience.

You could go and spend $300-$500 for a small 2 - 100w panel package and feel 'good' that you have some solar, but if you were to see how that equates and compares in the 'real world' to what you'd have to pay an rv park or campground for that same small amount of 'benefit', you'd run, and fast. It's expensive.


We just purchased a good used EV Nissan Leaf for my son, going off the college at UAH(University of Alabama in Huntsville), for aerospace engineering. He knows how to 'calculate' the cost per dollar of the 'real world' outcomes when it comes to these solar questions... having said that, his mother's first question was: why don't the EV car manufacturers cover the hood and roof with solar panels??
Makes sense, and sounds like a very obvious question. The issue is one of 'cost versus benefit'. Even though you want to buy a 'environment friendly' vehicle, the reality is that it stills comes down to affordability. If manufacturers installed solar panel arrays built-in to these cars, and the wiring and systems needed to 'convert' that power to battery power, the additional 'cost' when purchasing the car might either scare away the public, or never really 'give' any true return on the upfront cost, due to weather, lack of sun, 'where' you park your car, how many miles you drive per day, whether you have 120v charging, or 240v charging, etc., etc. It's not really as 'simple' as we'd like to make it out to be.
The simple truth, though, is that there is just not enough 'acreage' on the roof of an EV vehicle for near enough solar panels to make enough difference.
The same applies for the typical RVing situation - even the largest of motorhomes have difficulty in accessing the amount of 'space' on the roof needed to harvest enough solar power to make a real difference, though many of us try!

Thank you so much for your reply. Very educational.
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Old 07-11-2019, 03:17 PM   #17
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Thanks for the good input.


Yep, I know that solar is not for everyone, that also it can be expensive, and needs to be well planned in order to work well.


We are somewhat of minimalists in most things. Small camper, in general we boondock only 3-4 days at a time, no big TVs or sound systems or hair dryers so I think we can make it work for us if I get the design right. I've studied it a good bit starting with "Handy Bob's" stuff.


Thanks again.
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Old 07-11-2019, 03:21 PM   #18
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I am sorry, I thought you said the following.


"I have 700W of solar, I can recover from multiple days of no sun in one day with my 2 BattleBorn batteries. Never need a generator."


Also you lead me to believe this was on your RV, correct? Have a great day.
Yep on my RV. I can discharge my batteries over many days of shade or clouds and recharge 100% with just one sunny day.


Of course I won't convince you that solar actually works.


Your example of a 300W panel and the current produced at 240V is kinda in left field for what we are talking about here regarding 12V RV systems.
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Old 07-11-2019, 03:23 PM   #19
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Yep, I know that solar is not for everyone, that also it can be expensive, and needs to be well planned in order to work well.
Also keep in mind that any solar system you install on your RV allows you to claim a 30% tax credit in 2019. For 2020 and beyond, it starts to go down and eventually dissapears. This includes the batteries and inverter you purchase for your solar system.
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Old 07-11-2019, 03:26 PM   #20
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Yes, everyone has a slightly different 'goal' when it comes to their thoughts about 'what' solar can do for them... and bringing in the typical need to have to 'use the generator anyway for air conditioning' creates even more ambiguity to many calculations since you then that time effectively is removed from any time calculations for solar.
Traveling also presents a different approach to the calculation, at least those with motorhomes, or situations where the alternator from the vehicle is charging the House batteries while the engine is running.

If you look at how to 'calculate' the effectiveness of solar, it can be all of the place since so many things comes into play.
While driving, your motorhome may itself be taking care of 12v charging to the battery bank.
While on shore or generator power you obviously don't 'need' the solar power, except for the few who have hybrid inverters that can use some of the solar to offset incoming needs for shore power, if they are being charged 'extra' for it, etc.

So, only when parked, and the sun is 'out', can you really make use of using, and most urgently, STORING solar power, which is really only effective IF you have the storage capacity, i.e., battery Amp Hours(number/size/type of batteries).

This is not to say that, like many things in life, we prioritize other things ahead of 'economic calculations', but most of us want to know the truth about things, even if we gloss over them on our way to buying into it anyway... it's all good...
not having a generator running is enough reason for many.
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