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Old 09-19-2020, 11:21 PM   #1
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Cost to add solar (installed) to small class A

Does anyone have any idea of the cost of adding solar to a small class A. Ideally enough to mostly not have to use the generator. I can find some 400w kits online for pretty cheap (under $1k) but 8 have no idea of install costs. Iím guessing the 400w may be enough but obviously please share if you have other experiences. Thanks.
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Old 09-20-2020, 12:14 AM   #2
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It's math and research time... This is way better to do now, before you've spent any money. Installation and the selection of the components is WAY down the line.

Start with the usage side of things. You need to know how much power you actually need and use on a daily basis. Every device you use will have a sticker on it near the power cable that gives you an idea of how much power it needs, times the number of hours daily you expect to use it.

Watts = volts times amps.

You want to know the watts. That's the only rating that won't change, volts and amps vary in relation to each other to produce X watts. So a 1000 watt coffee pot (and a Keurig uses the same amount of power) needs 8.5 amps at 120 volts. BUT if you try to power it off of the batteries... Now you need 85 amps b/c the voltage is only 12.

So for the total wattage to make sense, you need to add up the total of everything in your RV times the number of hours daily it is on. Normally this is expressed in kWh, and that is what you want to try and get to, so that everything is easily understood. Momentary power usage like the water pump can be set aside for the moment. Focus on the bigger things. Is the TV going to be on a lot? That could be 200 watts... If it's on for 5 hours, that's 1 kWh right there. Now the coffee pot is 1000 watts, but only on for a fraction of an hour. To make the math easy, let's say it is on for 6 minutes, which is 1/10 of an hour, so the instantaneous load might be 1000 watts... But the total daily is only .1 kWh.

Lights are on 12v, but they count too. If you have regular lights, those can use staggering amounts of power. Even fluorescent use a lot more than LED. Each LED is good for about 3 watts. Halogens can be 25-30 watts, and most of that is just heat.

So once you have all the numbers added up... That's how many kWh per day you need. Now you need to think about batteries. You can't drain them 100%, and you didn't calculate EVERYTHING that will be using power, and that includes losses in the wires... So you need more batteries than you plan to use daily. I have 8 golf cart batteries in my array, good for 880 amps @ 12v or (if I used EVERYTHING which is not possible) over 10kWh of power. Since I want to try and reduce my total draw-down of the batteries to no more than 50%... I instantly say my cap is 5kWh. But in reality, my daily usage is around 2.5kWh and that is with multiple computers, devices, and a residential fridge.

You will need an inverter to make the 120VAC power, and you want something that isn't going to be running full-out when you have your toys turned on at the same time. Plan for the heaviest usage (microwave or toaster or coffee pot) plus some other things like your TV, and size accordingly. If you need an inverter, PM me and I can make some suggestions. The inverter will also act as your battery charger on shore power, so you want a good one.

Now... The solar. I've got a big class A, and sizing the array is a combination of how many watts you need to put back into the batteries (there's that kWh number again) BUT divided by the average sunlight that you will see per day. Then you need to know how much roof area you have to work with. No it isn't 10 hours of sunlight, or even 7. Five hours is the average. So if you want or need 5kWh into your batteries per day... Then you want an array that can produce 1000 watts if it is only going to see 5 hours of sun per day. Solar is ONLY used to charge batteries, but yes, while the sun is shining some of that power can be directed into the usage devices rather than just the batteries.

The size of an individual solar cell is somewhat fixed, so roughly, a 340 watt panel with 72 cells is going to take up an area of around 40x80 inches. That will give you an idea to measure your roof and see how large / how many panels you might be able to fit. I put 3 panels on my roof, but I have space for possibly as many as 5 with the "roof furniture" up there.

Now charging the batteries (especially lead acid) is an 80/20 calculation. You can put in 80% of the total power in just 20% of the total time, and it can go in quite fast.... BUT when you get near that 80% number, the "fill rate" falls off HARD and that last 20% of power takes 80% of the charging time! Cycling your batteries at a lower total charge amount (say from 80% down to 40% overnight) and back up again with the sun is OK, and probably the most usable way to cycle daily. IF you can keep your usage low enough or the size of the array large enough to make that work. Only you can calculate that. But that is why if you need 5kWh into the batteries... You might get it in just one day's sun with an array like mine, b/c of that charge rate restriction. I've just about maxed out at 5kWh per day of capture, b/c of the slower absorption charging.

IF I was using lithium (WAY more expensive!) I could charge them just about all the way up at full rate, and they would be fine. As it is right now, I can get most of the way full in one day, and only draw down to 40 or maybe 30% overnight, and the solar will get me back to around 90% with a long enough day. I'm usually well into absorption charging by 10am, which is where the rate starts slowing down.

Once you know that much... THEN it's time to think about equipment.
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Old 09-20-2020, 06:40 AM   #3
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Now thatís an excellent explanation!!!
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Old 09-20-2020, 07:52 AM   #4
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From everything I have heard, **not** consistently cycling the batteries to full charge, or at least doing so every few cycles, is an invitation to sulfation and premature failure of the batteries (I killed two sets of AGMs that way, but managed to resuscitate the second set...). I have been planning solar for my rig (but put off installation this year due to the virus).

It seems to be difficult to get enough solar onto a given rig to completely charge every day (can be done, but takes a lot of relative roof real estate). My current thinking is to put in enough solar to get most of the charging done during the day, leaving an hour or maybe two on generator in evening to get the batteries to float ... or even the other way around ... run generator an hour or two in morning, thus giving the panels a shot at getting the batteries to float during daylight.

Once you get past that fast bulk charge, you are into that long-slow charge to full capacity... and you are thus not using the full output of the panels anyway ... so what you put on the roof I guess depends on how you intend to use the panels vs. genny... (more if you want the panels to handle the bulk charge in the morning, less if you run the generator in the morning, then let the panels handle the long slow (lower current) approach to full charge)
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Old 09-20-2020, 08:52 AM   #5
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I'll try a shorter version of geordi's in-depth reply.

There are three steps to answering this:

1.Determine how much power you consume on a normal day, either in watt-hours or 12v amp-hours.

2. Then figure how much battery capacity you need to supply the amount calculated in #1. And maybe add some reserve capacity for heavy use days or days when you may not be able to recharge the batteries..

3. Lastly, figure how much solar capacity is needed to replace the charge in those batteries every day.


Lead acid batteries get charged at a voltage rate of [roughly] 13.6v-14.4v. 400 watts at that rate delivers about 27-30 amps/hour of full sun. In 6 hours you would put about 180 amp-hours back into the batteries. Is that enough for your daily usage? Only you can answer that. If the 180 AH is enough for daily needs, you will require about 360 AH of battery capacity so that your normal use doesn't deplete the batteries below about 50%. If you buy the pricey lithium ion batteries, you can get away with less AH capacity because you can discharge to around 20% instead of just 50%.
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Old 09-20-2020, 09:16 AM   #6
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Here were the costs for my system. I did the work myself. My vendor was Continous Resources.
Four 200watt solar panels $185 each (price has dropped a bit)
Victron 100/50 mppt controller $323
Victron Bmv712 (battery monitor) $206 not really part of solar, but it tells you exactly what is going on with power into and out of batteries (it can also help figure out how much power you are using in your rig so you right size your solar system) - for solar it passes battery temperature and voltage to the mppt.
Solar mounts - I self made mine $50 -
Wires - probably about $100

So for for about $1500 in parts for the solar part of my system I have an 800 watt system. (Max charging in bulk is 700 watts). I oversize my panels to the solar controller slightly because i wanted more watts when the condition were not ideal and it worked out that way. In perfect conditions my panels will produce 800 watts but it gets clipped my the charge controller to 700 watts.

This setup usually provides all the power I use. Plus it cuts down on my propane usuage because I switch the fridge to electric when I have plenty of sun.

Good luck with your project
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Old 09-20-2020, 10:55 AM   #7
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So .... let me see if I can try to make my point/question again:

All of the above discussion basically assumes that you have a certain capacity of the batteries to fill, and (this is the big assumption) that the charging rate of the batteries is constant. But it is not (as has been noted). Bulk charge takes maybe about 25-35% of the total charging time to get to float. If you assume that your whole charge occurs during daylight, then when the day is 80% over, you will get to 80% charge on the batteries (end of bulk charge), BUT, with the 20% of the day remaining you dont stand a chance of getting to float because you would need 2-3 times as much daylight as is actually remaining.

So .... if the objective is to get to float by the end of day, are you better off thinking in terms of using solar to meet (if you can) the max bulk charge wattage for your battery bank (thus minimizing the time to get to end of bulk, and giving you a running chance at getting most of the way to float from the panels (this is more expensive) .... OR are you better off thinking of running the generator for a couple hours in the morning (which will give you max bulk current), and buy a smaller (and less expensive) solar setup which can just sit there quietly all day and handle the lower current but longer (timewise) approach to float condition?????

taking the latter approach would reduce cost for the solar setup, and (I am now thinking) would give you a better chance at getting to float at the end of the day
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Old 09-20-2020, 03:58 PM   #8
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Quote:
Originally Posted by MN_Traveler View Post
So .... let me see if I can try to make my point/question again:
You are missing the middle stage in a quality charger, absorption.

The charge stages are:
Bulk - Constant voltage, high amperage (total battery array amps divided by 10)
Absorption - Higher voltage, reducing amperage until saturation is reached.
Float - meant to overcome self loss but also can be final finishing charge just above static voltage.
Storage - 4-stage chargers add this level, which maintains at full to account for self discharge of approximately 1% a day

Now most chargers (less advanced converter/chargers especially) will default to lower bulk rates to protect the batteries. At the risk of some heating and gas production (requiring water refilling) the higher bulk rates can be used which will accelerate the first stage.

Don't forget - I have a large array of batteries, 880 amps worth. When pulled low overnight, the solar is at max production (bulk rate) and enters absorption within about 2 hours of the sun coming up. So it has the next 7 hours to be at absorption. I actually could go harder on the charge rate, I have mine set for 50 amp rather than 80 and it STILL is out of bulk before I wake up.

You are asking the question if it would be faster or better to use the generator either before or after bulk.... It doesn't matter, it will be the same time either way. If the solar can produce a 40 amp charge rate (around a 600 watt array and an MPPT can do this) then you are likely matching what the generator can do and the time will be the same - just a lot quieter. The solar can "wake up" with the sun and start working before quiet hours are over, rather than having a couple hours of lost production waiting for the humans to get up and start the generator.

The only places the generator wins is in the rain, at dusk or at night, b/c it makes power in all these conditions. But the charging time will be the same in all cases.

There is also a misconception that you had above, where you mentioned hurting the batteries if you don't get them fully charged each day. Lead acid doesn't have a "memory" effect, and sulfation happens at the BOTTOM of the power curve, not the top. When the battery is discharging, tiny crystals do form. If the battery is run low, these can grow. If the battery is LEFT LOW or drained too much, they can get larger - that's the problem, b/c then they start to insulate the lead and prevent full charging.

BUT avoiding draining the battery too low (stop draining at 50% SoC and it is just about eliminated, but you can be OK with dropping to 40% or 30% and recharging soon after) and the effects are minimized. The lowest point in the cycle will conveniently be right before the sun comes up and the solar starts making power, so there's a minimum of time spent at the bottom SoC. You don't need to get it to the float every day to keep the battery happy, but it wouldn't hurt to try for that at least once a week and certainly before going into storage. Now if you have a solar setup maintaining everything, the batteries can be left on while in storage (just shut down all the power users with a disconnect switch) and let the solar provide the final float and storage charge over a couple days, and the batteries will be ready to go when you are for your next trip.

Even now, I'm at home and my RV is stored with the solar maintaining everything - but I actually left my inverter ON as I now have a Victron CerboGX controlling everything, and the inverter is powering my router and tethered cellphone so I can monitor it remotely. I just checked it now, and I'm showing a 41 watt usage through the inverter, the solar (at 5:50pm EST) is producing 10 watts b/c there's no place for the power to go and the battery is showing 95%. It must have been cloudy today, b/c it's been consistently right at 100% for the last week since I put it into storage. I'll be back to it toward the end of this week, so this is a good test for leaving it alone with the solar maintaining everything. It is producing a daily total of around .36 kWh... B/c there's just not that much usage. For storage, obviously a 400 watt array would be just fine!
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Old 09-20-2020, 04:01 PM   #9
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Here's a battery chart I just found - it says you should only need absorption for about 2-4 hours, so if you can get out of bulk in around 2 hours.... You should be good topping up with solar during a normal day.

http://www.lichty.org/MiscImages/Int...e-Charging.pdf
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Old 09-20-2020, 10:19 PM   #10
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Geordi - I am not missing anything. When I commented on getting from bulk to float, I am expressly talking about the time in absorption. sorry if I did not use that word.

I think you are not hearing my point/question. your setup is impressive, and clearly matches the generators capability in full bulk charge current. My comment is focusing onthe other end of the spectrum. might it make sense to spend less money for a less powerful solar system, but one that is capable of reasonable absorption power input .... and use the generator to cover the bulk charge part of the curve, then let the less powerful solar system to cover the longer absorption part of the charge curve. the OP asked about cost. your approach maxes out the capability of the solar system, but at a $$$ cost. Is what i am commenting on also a viable approach, with a reduced dollar outlay to install the system....

just meant to be food for thought.
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Old 09-20-2020, 10:21 PM   #11
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Can someone please give a backchats idea of coat for what a general solar setup would cost on a smaller class A. They all have roughly the same appliances so I,m looking for a quick concise general answer if someone has one
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Old 09-21-2020, 06:53 AM   #12
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Depending on what you do, something like $1-2k
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Old 09-21-2020, 07:52 AM   #13
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Originally Posted by wannaclassc View Post
Can someone please give a backchats idea of coat for what a general solar setup would cost on a smaller class A. They all have roughly the same appliances so I,m looking for a quick concise general answer if someone has one


It still depends upon how you USE your RV on whether the system is adequate for your needs. Just saying ďmy rig has solarĒ doesnít mean you could actually rely on it to power anything.

Also you havenít said if you have the skills to do yourself, or need to pay for expertise and skills and produce a finished system.

I you are like most, pay a knowledgeable and quality company to do an expert job..... AM solar is but one example.

Try filling out their quote form for a custom quote.

I would plan on ballpark at least $5K

https://amsolar.com/quote

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Old 09-21-2020, 12:16 PM   #14
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Original costs are high, but lithium will take all your panels puts out till they are fully charged, same with inverter or converter, max amps until full.
Don't have to worry about bulk, absorption and float times. If I use 100 amp hours out of my lithium batteries, and charge at 100 amp hours, they are recharged in one hour, so you can go a little smaller on your solar and still get your batteries topped off in less time than lead acid.
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