Hello, new here and to solar as well

bluewickedburner

I'm in the process of trying to get off the grid as much as possible. If I explain what I'm trying to do maybe someone can chime in to tell me I am nuts or on track?

I have a Diesel pusher MH that I bought new 2 years ago. So far I have about 120 hours on the genset only because my trips haven't been frequent or far. That is going to change and we plan on going out often from our permanent location, mostly weekends but longer when time permits. We've decided to try to get off the grid as much as possible. I say possible because reality sets in when there is no sun and I'm open to plugging in when needed (we pay for electric in our space) or running the genset if traveling and we simply run out of sun.

We're using about 15kw of electric from our 50 amp service per day from the pedestal. That includes running any heat and the refer (double door Norcold) on AC along with about 3-4 hours of TV (170 watt LED TV) and a laptop for the same amount of time. We run the water heater on propane and would consider doing the same for the refer. Our interior lighting is LED.

My thinking is to start out with 3 100 watt panels going to a combiner in parallel, to a MPPT controller that charges 4 6 volt J306XC Tojan batteries for about 370 amps (12 volt system). The panels are going on a solar tracker mounted on the roof and I get shadow free sun access all day. I have a 2000 watt quasi sine wave inverter/charger and we rarely run the air conditioner. The micro gets used maybe once a day for 90 seconds. I know that because it is routine.

I'll add panels as needed but those will be on tilt mounts that I'll setup to be elevated and lowered via motorized mounts from inside. My latitude is 38 degrees so that should be my angle of the panels and that of the tracker.

For a controller I was looking at a Midnight 150 (probably overkill) but can't seem to find any. That bothers me a bit since if something goes wrong that means I'll be waiting in line too. That leaves me with Morningstar and there I was thinking about the 60 amp MPPT model since it comes with ethernet connectvity and there I'm in my element. If something needs to be connected to a network, I can do it.

How does that sound so far? I have plenty of space for more panels and could get 8 more panels up on the roof without running out of space since I have basement air.

Since I have readily available grid power at the flip of a breaker I figure I can monitor my usage and insure that even if the solar can't keep up, I can augment with grid power, charging the batteries until I can put more panels up.

So, am I completely in space or just breathing rare air?

Cariboocoot

Re: Hello, new here and to solar as well

Welcome to the forum.

Not meaning to be nasty, but what you're doing is guessing at equipment. That's the second worst way to design a system. The worst way is to buy the stuff and then try to make it work.

So some nomenclature clarification and such.
When you say " using about 15 kW of electricity" I presume you mean 15 kW hours per day?
That is a lot of off-grid power. Anything that heats with electric - get rid of it.

Second, the battery bank's total Amp hour capacity at the 20 hour rate is 370 @ 24 Volts? Or are there parallel connections as well making it 740 @ 12 Volts? I've never heard of that Trojan model and Googling it reveals nothing. This is a very important number to have for adding solar: Amp hours @ system Voltage. The whole solar thing is designed around that!

By "quasi sine wave" I'll assume you mean MSW. Have you considered replacing that? Many things (like the microwave) will run better and draw less power on true sine wave.

Because batteries are the heart of the system, you need to understand your batteries: http://www.windsun.com/Batteries/Battery_FAQ.htm

Basically you want to recharge them at a rate of 5-13% of the Amp hour rating. Trojan recommends 10%, so if you're looking at a 370 Amp hour 12 Volt bank you'd be looking at:
37 Amps * 14.8 Volts charging = 547 Watts, less efficiency derating = 711 Watt array. Just as a staring point; not a carved-in-stone figure. Quite likely you'll be limited to however much panel you can fit on the roof, and it may only be enough to supplement charge rather than completely charge.

Did that help any?

bluewickedburner

Re: Hello, new here and to solar as well

Well, I made sure to say these were my thoughts, not a purchased system so nothing is carved in stone yet. I'll rarely ask a question if something is already done. No worries, no thin skin here.

Some clarifications:

My current grid power usage is about 15 kilowatthours, the difference between two days for a 24 hour period. The service is 50 amp 250 volt. The meter also considers some 125 volt 30 amp use but that is going away so the above will be my max useage. So am I correct in that 15 kilowatthrs from 250 volt 50 amp service (3 phase) is 43.3 amps?

I do understand the difference in amps taken from a 12 volt system and going through the inverter to provide the AC. Also, some adjustments will need to be made on the use side of things because they can be controlled by choice.

I mistated the battery model number, it is the J305H-AC 6V rated at 360 amps at the 20 hr rate. In series and then parallel ( 4 batteries) for a 12 volt system that provides 720 amps in a perfect world. I can't fit 6 T105s because of the battery tray configuration but I have enough space for these. I looked at L16s but there is no way they can fit. My first item on the list was the batteries and then to go from there, adding capacity to charge as I needed it.

I considered changing the inverter but using the microwave for 90 seconds a day at most doesn't seem to justify that. I checked with the manufacturer of the TV and spoke specifically to them about using my current inverter. I sent them the specs and they wrote back saying there would be no problem and indeed, for just over 2 years now, using the inverter there haven't been.

Here is where I am headed. To me it is far better to take care of the batteries and charge controller and then put up three 100 watt panels. I can add as I need more charging capacity and as money allows. While I'd like to say exactly how much power I'll use being away from grid power, like most things, you don't know until you try it. The thoughts are that 1. I'm putting as much battery capacity as I can fit without starting to rebuild things, 2. a 60 amp Morningstar MPPT charge controller lets me expand to more panels as I need. 3. the inverter/charge can be changed at any time and won't affect other system other than getting what benefits pure sine wave has over the other.

I can buy any controller and any type of battery, any kind of panels etc.

Does that give you a better idea of what I'm trying to do?

Cariboocoot

Re: Hello, new here and to solar as well

In this application you're limited by your batteries. Your power usage may dictate needing to start up the gen or plug in to "shore"; there's nothing you can do about that because there's really no room to expand battery capacity, right?

None of that has any bearing on the solar aspect, really. The panels & controller are there to recharge the batteries as best they can.

Ideally, you'd be looking to get 72 Amps @ 14.8 Volts to recharge that bank. That would work out to nearly 1400 Watts of array, and you probably do not have 120 square feet of space to put panels in on the roof of your RV. Now you could put the panels elsewhere and store them inside when on the go. There's been a thread or two about "movable" panels for camping on the forum - along with the safety and security issues that arise. So how much panel can you fit on the roof? Efficiency is about the same for any one of them, +/- a couple percent and excluding the "double sided" ones. Look in terms of cost per Watt, and what ones will actually fit. Some of the larger panels may present mounting difficulties.

Charge supplementing is really all you can hope for, in my opinion. If you were to try for the extreme of providing 15 kW hours per day from solar alone you'd be looking at nearly a 4kW array! And you'd need a 2500 Amp hour battery bank. That doesn't sound very practical, does it? :roll:

bluewickedburner

Re: Hello, new here and to solar as well

First, thanks so much for your help, I really appreciate it.

On my roof I have:

one 9'6"x8" (72 sq/ft)
one 6'x8' (48 sq/ft)
one 13'x3'(39 sq/ft)
one 20'x3' (60 sq/ft)

areas without anything there. The only thing I have on the roof are two vents, black water vent and a satellite dome. All the spaces I've listed are clear of anything.

I realize that since most panels are rectangular (I've seen some odd ball triangle shapes for the frames) all that space wouldn't be usable for panels and there has to be some space to walk to clean the panels, change a vent cover or fan, stuff like that. The 100 watt panels are 41"x21".

In that 9x8 space I could fit 10 panels (2 wide for a total of 6.8' and 5 deep for 105" or 8 3/4') for a total of 1000 watts.

That leaves me the 6'x8' for the tracker with an additional 300 watts on that.

The total then is 1300 watts which is shy of the 1400 watts you stated.

The idea then and all along was to use LP for the refrigerator, heat and hot water. The refer going to LP should help with that.

I was also looking at an LED backlit TV which uses 40 watts/hr instead of the 170 of the current one. Not much savings there but it does come to about 130 watts for the 3-4 hours we use that per day.

That amount of power puts me past the capacity of the Morningstar 60 amp charge controller so I'd need to run two 45 amp models (parallel systems) or go to something like the Midnight Solar Classic 120 right? The Midnight Solar Classics are nearly impossible to find though.

Again, thanks for your input, that was a lot of good info.

mike95490

Re: Hello, new here and to solar as well

Your usage is HUGE, and will be difficult to have solar as you describe, make a dent in it.

15KWh from the electric company, at 20c ea KWh, is $3 worth daily.

600W of PV, on a tracker, could harvest, in a 5 hour solar day, about 2.4KWh, or about 50 cents.

If you feed that into batteries, and use it at night, you only have about 1.5KWh to work with, because of battery recharge and inverter losses.

You are talking about only having 300W of PV. That will barely run a decent 18CF Energy Star fridge.

Think on these numbers, and what the PV, Tracker, Charge controller will cost, and having to dismantle it each time you move.

bluewickedburner

Re: Hello, new here and to solar as well

Then perhaps I'm reading the meter wrong. BTW, this system is going on the roof of a motorhome, no disassembly needed, just lower the tracker and go.

Without any solar and having only 4 group 31 batteries (12 volt) we've never run out of battery power during weekends. That is taking the batteries down to 12.2 volts after use but with no load on them.

So, something might be up with the way I'm reading the meter. Our electric bill runs 45 dollars per month.

I'm near sea level with nothing between me and the horizon so we get more than 5 hours of sun easily, winters are a different story. The tracker points directly at the sun from the moment it breaks the horizon until it sets.

The 300 watts would be just to start, I can add more as needed.

icarus

Re: Hello, new here and to solar as well

Just FYI,

The 130 watt savings from the TV change, saves ~400 WH/day, not insignifincant for a small off grid system.

The general rule for off grid PV, ( and it is worse feor RV installations) is, take the name plate rating of the PV, divide by 2 to account for all cumulative system loses, then multiply that number by 4 to account for good sun. That give good daily kwh/day averge, over the course of the year.

So y our proposed 300 watts of PV might look like this,, net/et out of the inverter.
300/2=150*4=600 WH/day.

Just as an FYI, we live off grid, with no tv, no micro, no electric heating elements at all. We have 400 watts of PV, feeding 450 ah of batteries. On the averag day we use between 5-800 WH of power. On an perfect, cold winter day, we can make 1.5 kwh, but on averge, we keep nicely even.

If you haven't read the following, I suggest you do so:

http://www.batteryfaq.org/

http://www.windsun.com/Batteries/Battery_FAQ.htm#Lifespan%20of%20Batteries

Tony

bluewickedburner

Re: Hello, new here and to solar as well

Thanks for that. Very practical info.

I just read the usage fro my refer and it consumes 3.8 amps per hour on AC and about 5 when running on propane (for temperature control, cycling or whatever else it does. My plan was to put it on propane since it has that feature. On AC from what I've read, on AC that 3.8 amps becomes 38 taken out of the batteries via the inverter. Save quite a bit of electricity putting it on propane.

I know that there is a cost for the propane but it is still close to what the electricity from the grid costs (we pay nearly $3.20 per gallon of propane, crazy.) For us though it is also a lifestyle choice too, being able to stay away for extended periods without plugging in.

Eventually we will have 1300 watts of solar on the roof and might go with 2 trackers for a total of 6 100 watt panels on a dual axis tracker for maximum exposure to direct sunlight and the rest with tilt mounts that are operable from inside.

Being near sea level without obstructions maximum sunlight isn't a problem except for inclement weather and then we have other options. Reality says that unless we want to give up nearly every convenience, we'll use multiple sources of power, just limiting our grid power as much as possible.

Thanks to all for the help.

Cariboocoot

Re: Hello, new here and to solar as well

Just a heads up about putting a tracking array on the roof with flat panels: shadows. It's inevitable that some will fall on the flat panels, reducing or negating their output.

I got a rough calculation of about ten 135 Watt panels (about 2.5' by 5') fitting in the space available. Only your fine time with a tape measure will tell for sure.

bluewickedburner

Re: Hello, new here and to solar as well

Thats a good point about the shadows. Our permanent spot allows for a southern exposure and the tracker will be toward the rear and flat laying panels would be forward. We are more fair weather travelers and want to stay away from commercial RV parks. We rarely use the AC and figure that if it is that hot, we can find a place not so. Hopefully we'll have more choice about how we park and in that way keep the flat panels forward of the tracker.

One thing I have noticed is that when we travel we use far less power than in our spot. My hope is that even if we need to run the genset that we'll reduce that to a minimum. In our spot we tend to watch some TV and do other things that use more electricity.

I've been informed that running panels in parallel instead of serial would reduce the effect of shadows on all panels and that running them in serial would cause shadows on any single panel to significantly lower output of all.

icarus

Re: Hello, new here and to solar as well

Be careful with your current rating comparisons. Your fridge (Assuming it is a typical Dometic type 2 or three way, will draw say 3.8 amps of 120 vac or ~ 450 watts. (Remember, we don't measure power in "amps per hour" we talk about amp/hours or watt hours.) A typical 10 cu.ft. Dometic will have a ~ 350 watt heating element, plus a bit for the control board, and the defrost. (off grid, turn off the defrost mode!)

On propane, my guess it that it would only use 5 (60 watts) amps if you have the defrost cycle or the light on. It should use less than 1/2 amp when of 12 vdc to power the control board. (Most propane fridges controls run on 12 vdc, even if they are 120vac elements).

As for propane use, a full size Dometic RV fridge will burn ~1500 BTUs an hour. It is important to realize that there is a typical duty cycle (on any fuel source, 120vac, 12vdc, or L/P) that will vary, but in general the fridge (if it is well vented) will only run ~ 1/2 time or 50%)

A gallon of propane contains ~79,000 BTUs, so at a 50% duty cycle, that would allow the typical fridge to go ~ nearly a week on a gallon of propane. If you add insulation to the cabinet, condenser fans, you can reduce the cycle to less than 50% with out too much trouble.

Tony

PS Get a kill-a-watt meter and actually measure you average daily consumption.

T

bsolar

Re: Hello, new here and to solar as well

i'll break in with my 2 neophyte to solar cents .. forget a tracker and plaster every square inch of roof with panels, 12v should be fine imo just use a mean cable like 4/0 from bat to inverter. If you can get a 1300 watt array going im guessing you will be sustainable on the fridge a tv an a couple of low wattage lights and running your water pump .. if your thinking about running ac's and turkey fryers i dont really think that is going to be realistic, now an induction hotplate and an evaporative cooler i think would be feasible, in a low usage situation charging a second bank just for the nights xbox marathon and burrito rolling may be better than a roof bristling with trackers .. ok i'll shut up now

bluewickedburner

Re: Hello, new here and to solar as well

Thanks all. Good info on the refer figures. I currently have 4/0 cable running from inverter/charger to battery bank.

My refer is a Norcold 1211M 2400 BTU AC/Propane model, 12 cu'ft model with ice maker although I turned that off since we don't use ice. It is double insulated, they did quite a good job on that at the factory. 2 sheets of 2" thick insulation (styro over some hardboard material and an aluminium skin)

We don't use the AirCon and only turn it on once in a while to maintain it, (about once a month for a little while).

I did put on a Kill-A-Watt monitor yesterday and came up with this after 16 and 1/2 hours:

528 watts
4.14 amps.

Approx .30 amps /hr
Approx 32 watts/hr

for 24 hrs that would be (I've left the monitor on to see if I'm correct):

7.2 amps
768 watts

From the battery bank via the inverter that would come to 72 amps according to the 10x approximate conversion I've aways heard about. That easily covers the laptop and TV use, especially after I toss the standard LCD (Sharp 37") and put in a 40" LED backlit LCD that run 40 watts instead of 170.

When it comes to the cost of propane vs electric only the grid power remains pretty static since I can fill up on propane on weekend trips at far less than my local 3.20 per gallon. Usually I can get it for about half that price. The solar electric costs will vary some according to available sun but if I put the refer on propane and that gives me more available electricity from the battery bank, it is an easy choice in my situation.

The tracker lets me put up 300 watts in a very small space. If I park with a southern exposure, the tracker can't shadow any panel laying flat. In the winter months or when we travel I can set it up so that even if a part of the day is shaded I can maximize the available sun light regardless of my location.

The cost of the tracker could easily pay for lots of panels but that 300 watts takes up virtually no roof space. The money wasn't part of the equation since we plan to add flat panels anyway.

Here then is my next step since batteries are going to be maxed out with 4 Trojan J305 for 720 amps (6 volt serial/parallel for 12 volt):

I could go with AGMs for more capacity if it is possible to place them in the same bay as the inverter/charger. That bay is vented very well but I know flooded batteries there is a no go. If AGMs could go there I could increase my capacity quite a bit. My rig is not even close to gross weight so that isn't the issue, safety is.

Do I use a single larger capacity charge controller or use a smaller one to start with and then break up additional panels into sets and use multiple controllers?

mike95490

Re: Hello, new here and to solar as well

bluewickedburner wrote: »

.......
Do I use a single larger capacity charge controller or use a smaller one to start with and then break up additional panels into sets and use multiple controllers?

Depends, each batch of panels in parallel, needs to be fairly close in the Vmax power spec. for a 12V system, that would be about 17- 19V . If you go panels in series for a MPPT controller, you want to closely match the Imax power spec.

If you can be sure of getting panels to match your existing, the next batch you buy, you can add to the same controller. Or, each batch of panels can go on it's own controller, it's legal to have several controllers on one battery bank, as long as their setpoints are pretty close to each other.

TheBackRoads

Re: Hello, new here and to solar as well

How are you going to mount a tracker on the roof of an RV? Just curious..

icarus

Re: Hello, new here and to solar as well

You are still seemingly not getting the hang of wattHOURS AND ampHOURS.

for example a 100 watt light bulb, burning for one hour will consume 100 watt/hours!

A fridge may burn 32 watts, but it probably won't burn 32 watts each nd every hour. ( Swme with propane consumption. It might burn 2500 BTUs/hour, but most fridges will either go to low flame, or shut off as the tsat calls for or doesn't call for heat.

Tony

bluewickedburner

Re: Hello, new here and to solar as well

TheBackRoads wrote: »

How are you going to mount a tracker on the roof of an RV? Just curious..

A base plate holds the tracker onto the roof. Standard roof mounting methods will work although I'll back that up with 3M's thin carrier VHB tape that I've used for many other projects. I'm using the VHB you get from special order and the same kind used to put together large trailers instead of rivets. No chance of it coming off.

Tracker rotates 360 degrees and tilts from flat to 45 degrees. Plenty for any latitude where I could possibly go.

By itself the VHB would work. I have projects on a larger scale than a tracker and over 10 years old exposed to the weather, not a single failure and to date can't be pulled apart through shear, tear or pull. Amazing stuff. I now use VHB for any relatively smooth surface mounting situations. The other thing it does is make a weather proof seal so liquids can't penetrate the seal even if wind driven.

I'm going to document the install and I'll share it here, hopefully in the next few weeks.

bluewickedburner

Re: Hello, new here and to solar as well

icarus wrote: »

You are still seemingly not getting the hang of wattHOURS AND ampHOURS.

for example a 100 watt light bulb, burning for one hour will consume 100 watt/hours!

A fridge may burn 32 watts, but it probably won't burn 32 watts each nd every hour. ( Swme with propane consumption. It might burn 2500 BTUs/hour, but most fridges will either go to low flame, or shut off as the tsat calls for or doesn't call for heat.

Tony

So if the Kill a Watt reported 4.14 amps @ 125 volts doesn't equal 518 watts? That was reported over 16 and a half hours accumulated (the version of the Kill A Watt device I have.

I then took those figures and divided by the 16.5 hours. That isn't correct? If so then maybe I am not getting it. I gave a little extra for more use. I know that some time it will use more or less per hours but I was trying to get an average.

What would be the correct math in this situation?

BB.

Re: Hello, new here and to solar as well

There are "Instantaneous Readings" and readings over time...

Instantaneous:

• Voltage
• Current (Amperes)
• Watts
• Volts*Amps
• PF (power factor)
• Hz (frequency)

And over time:

• Time (Hours)
• kWH (kilo Watt * Hours)

Voltage, Current, and Hz are pretty straight forward.

Watts and Volt*Amps starts getting a bit more complex by adding PF (Power Factor) into the mix...

Basically, for AC power, Volts and Amps may not be "linear" relationship. And one way to represent that is by:

• Power (Watts) = Volts * Amps * PF

PF (Power Factor) is one way to represent if Volts and Amps are not "in phase" with each other... Think of pulling a car with a rope. If you stand right in front and pull, the Cosine of the angle (zero degrees) equals 1.0 ... Basically all of your force pulling forward on the rope is moving the car forward.

If you stand off to the side and pull forward (say 60 degrees to the side), Cos 60 degrees = 0.50 --- Or 1/2 of the force pulling on the rope is moving the car forward and the rest is pulling the car to the side--and not doing you any useful work... So, to stand to the side, you have to pull 2x harder to move the car forward the same speed vs standing in front. That is Cosine and Power Factor relationship between VA and Watts.

VA is how you define the wiring, inverters, transformers and how heavy the "wiring" needs to be.

How much energy comes from the battery is Watts... And if you take VA * PF that will equal Watts for Battery Bank sizing (and solar array).

The "over time" measurements are the Hours (how long the Kill-a-Watt has been running). And the kWH (kiloWatt*Hours)... That is the amount of work.

• Watts = Rate ~ Miles per Hour, Miles per Gallon
• Watts*Time = Amount = Watts*Hours ~ Miles driven, Gallons used.
• kWattHours = 1,000 Watt*Hours (kilo=1,000 factor)

So, if you have a an "average" power (like 150 Watts) running for 16 hours:

• 150 Watts * 16 Hours = 2,400 Watt*Hours = 2.4 kWH

So--The Watt and VA ratings are instantiation values... The kWH reading it totalizing over time.

From you--We kind of need to know the exact readings and "units" from the k-a-w meter...

Amp*Hours is used a lot with battery systems--but we also need to know the Battery Bank Voltage--Such as:

• 14 amps * 10 hours = 140 AH
• 14 amps * 10 hours * 12 volts = 1,680 Watt*Hours = 1.68 kWH

You can do the same thing at 125 VAC--But we generally do not--Just use Watt*Hours and kWH instead--and you can use WH/kWH for the battery bank too--just not everyone will understand what you are saying (AH * Volts = Watt*Hours).

Just to give you an idea--A off-grid home may use around ~100 kWH per month of power or ~3.3kWH per day. That is pretty efficient. A "cabin" may be down in the 0.5 kWH per day type range.

Grid homes use around ~500-1,000-2,000+ kWH per month... I work at keeping my power usage down and can get aroud 200-300 kWH per month for my home--natural gas for all heating, no Air Conditioning.

-Bill

bluewickedburner

Re: Hello, new here and to solar as well

Thanks for that. The MH uses 451 kWH per month if everything is turned to electric including the hot water, refer, furnace and some 30amp service which is also measured at the pedestal as part of the total. The rest is all from the 250 volt 50 amp service side.

I can reduce that quite a bit to around the 200 range if I go to gas for the heat, refer, water.

For me, everything has always been mechanical and I never even bothered dealing with electrics so this is all brand new to me. I'll get it eventually but that reply really helped in the understanding.

Thanks again.

icarus

Re: Hello, new here and to solar as well

Just an FYI, a kill-a-watt meter will read, instantaneous watts, volts, VA and PF? But it will also read cumulative loading, in KWH. So, for example, if you plug in a 100 watt light bulb, it should show 100 watts,~ 1.2 amps PF of 1 (assuming a incandescent bulb for this example) instantaneously. Leave that same load plugged in for 24 hours,(it will still read the same instant load) but change the scale, and it will read 24 KWHs.

So it is a valuable tool for finding instant loads, but arguably most useful for finding cumulative loads. I believe some models reset when you unplug them, others will keep logging in memory.

Tony