how do I use an off grid module?

System

OK, if anyone could help me with this I would really appreciate it.

Here is what I need, basically. I am going to hook up just 1 solar panel to my rv, and I need help figuring out how to do this. I know that the panel needs to be above 50 watts, at least 24 volts and at least 5 amps.

So if anyone could recommend a good module that would be great !

Also, along with the module I want to get a battery, so that would be nice to have to, and if anyone could recommend one I would love that!

But going further, do I need anything else besides the module and battery? do I need battery monitor? and what about a charge controller? any help would be great!

mike95490

Re: how do I use an off grid module?

You WILL need a charge controller, or risk boiling your battery dry after a couple days of un-regulated charging.

Do you just use the RV on weekends, or 7 days a week ? Lifestyle and future expansion of the solar system, will also determine your choices. Looking at the messages this week, you will need some sort of Low Voltage Disconnect, so if you leave a light or fridge on, you won't destroy your battery.

At first, stick with a name brand 'deep cycle marine' battery. You can add water to it after charging, and it's pretty forgiving of mistakes. When it dies, you can purchase a fancy $$ battery that will work a little bit better. (don't forget to reset the charge controller voltages for each type of battery.)

In an RV, look for a mount that will allow some air flow under the pane while parked, as the panels heat up, their output voltage drops, and you loose power.

If you can read a voltmeter, and have calculated your loads, I'd skip the battery monitor, which can cost more than the battery. As long as you can tell that you get to the float part of the charge cycle several times a week, you should be ok.

System2

Re: how do I use an off grid module?

Thanks, I will only be using the solar panel to power my mobile dish, so that I can connect to the internet. I will probably be running it 7 days a week, and at night, which is why I want the battery. The thing is, I'm going to need a pretty heavy duty battery...

System2

Re: how do I use an off grid module?

The first thing to do is to size your load. Does your dish operate on 120VAC or 12VDC?

If AC through an inverter, then buy a Kill-A-Watt meter for less than $30 and see how much power it draws.

If it operates on 12VDC, it's safe to hook an ammeter in the line to measure the current draw.

If you have a small inverter already, you might want to measure the DC current going into that in order to include DC-AC conversion losses.

After you get your load numbers, you can calculate panel size and battery size based on location, mounting, and temperatures.

icarus

Re: how do I use an off grid module?

My internet dish and router burn ~1.5 amp combined. (12vdc) The dish itself runs on a couple of weird voltages, regulated by the 120vac power supply, so you will need to invert. Assuming you are not charging the computer at the same time, you can do a calc. based on 1.5 amps. On the other hand, my Mac book draws ~5amps while charging and running.

Icarus

System2

Re: how do I use an off grid module?

You MacBook draws five amps? Wow, more than I thought. I have an old G4 tower on the grid running 24/7. I plan to take it off grid and replace it with a MacBook or iMac. I measured a new iMac and found 50 watts AC with the machine running and the display off. What do you think your MacBook would draw if the display was off while running and the battery was fully charged?

Thanks

System2

Re: how do I use an off grid module?

I kind of understand what you guys are talking about, remember, I'm just a begginer. What I really think would be best is if you guys could just tell me everything I need to get this dish running full time off grid. So, I know it takes at least 50 watts, 24 volts, and 5 amps, (although if I hook a computer up to it that will be more amps.) I want to be able to run the dish full time, including at night so I'll need a good battery that stores a lot of power. Anything else that you could recommend would be awesome! thank you guys, remember, I'm just a beginner...:( Oh, and also, money is no objective. Well, just dont make it TOO expensive If you need any more info ask me and I'll try to get it

Windsun

Re: how do I use an off grid module?

Why do you need a 24 volt panel?

System2

Re: how do I use an off grid module?

I've been looking at a very similar thing. Out in sunny West Texas, I'm looking at maybe 6.5 kW/m2/day of insolation. I calculated a simple metric for my estimating. If I want to run 1 watt of load 24 hours, that is 24 watt hours (Wh) per day. If I have an overall system efficiency of 70 percent, then I need 5.3 watts of panel (24 / 0.7 / 6.5). If New York has an insolation of 4.5, then one would need 7.6 watts of panel per watt of constant load.

(Is this a reasonable way to estimate?)

A 50 watt constant up north would need 380 watts of panel. Panels might cost $1900 ($5 per watt), and the rest of hardware $1140 ($3 per watt?) for a total of $3040 without shipping, taxes, or install.

My point is that another 25 watts of constant load would add another $1520 in PV hardware. In my case, it will be cheaper to buy a new laptop then it will be to buy enough panel to power a free desktop computer.

icarus

Re: how do I use an off grid module?

Sage wrote: »

You MacBook draws five amps? Wow, more than I thought. I have an old G4 tower on the grid running 24/7. I plan to take it off grid and replace it with a MacBook or iMac. I measured a new iMac and found 50 watts AC with the machine running and the display off. What do you think your MacBook would draw if the display was off while running and the battery was fully charged?

Thanks

Perhaps I should be more clear,,, It draws up to 60 watts, when the battery is almost dead, and I am doing something on the machine. I will do a Killawatt test later and post that information. I posted the 5 amps as a worse case "normal scenario".

With the display off, battery charged, if memory serves it draws ~1amp 12vdc. Sorry for any confusion,


Icarus

BB.

Re: how do I use an off grid module?

Sage,

You pretty much have it correct... However, the "derating factor" recommended for a Grid Tied system is roughly 0.77, and my own recommendation for a full, off grid battery backed inverter output system is around 0.52 ...

You can use this link to calculate average production figures for a system in the US or many areas around the world. The website, for some reason, has a floor of 1 kW (STC) of solar panels.... Just enter 1kW and then multiply/divide the results by whatever your less than 1kW system will be (I even the results into a spreadsheet to recalculate all the numbers quickly).

The numbers from this site track very closely to my own Grid Tied system results.

-Bill

Need to add, the numbers from these sites are averages--sometimes you will get more, sometimes less, depending on weather. And remember, the numbers you gave are pretty much for "summer"--in winter, if you want the same amount of power, you may need 2x, or more, solar panels. And with grid tied systems and 1 year net metering, you have "effectively" an unlimited storage battery that can "charge" or "supply" power over a 1 year period... With off grid systems, you have, typically, a three day buffer--so extended cloudy weather can kill you, and extended sunny weather does not let you bank more than your 3 days of power.

System2

Re: how do I use an off grid module?

Thanks BB,

I ran that site recently (Version 2) for my location and got these results:

Month Solar AC kWh
1 5.67 130
2 6.36 129
3 7.06 158
4 7.36 153
5 7.05 148
6 7.01 140
7 6.64 137
8 6.74 140
9 6.36 129
10 6.64 143
11 5.82 126
12 5.40 125

The best month was March. Cold and sunny I guess. The worst month was December at 82% of Max. The average of June, July, August turned out to be 91% of the March maximum. Interesting.

Sadly, I can only get 1 month net metering here.

If I look at the numbers more closely (divide AC watts by insolation), it looks like November through March actually produces more energy per hour due to the colder temperatures.

System2

Re: how do I use an off grid module?

now wait, back to me, I need 24 volts because the power supply for my dish says 24 volts, 50 watts, and 5 amps. Can anyone help me with that? what do I need to buy to have a fully operational off grid system?

mike95490

Re: how do I use an off grid module?

georgesuper wrote: »

now wait, back to me, I need 24 volts because the power supply for my dish says 24 volts, 50 watts, and 5 amps. Can anyone help me with that? what do I need to buy to have a fully operational off grid system?

24V @ 50W = .48amps
24V x 5A = 120 watts

One is wrong.

But you will need a 24V battery system, with a 24 V linear, Low Drop-Out regulator
(charge voltage on a 24V battery could be nearly 30V )

niel

Re: how do I use an off grid module?

that may not be marked properly as 24v x 5a = 120w. that's 70w more than you say it is marked. nobody can truly answer your question as it may need to be measured to be sure of the requirements.
adding you beat me to it by 2 minutes mike.:D

BB.

Re: how do I use an off grid module?

George,

You need to accurate measure/predict how much power you will need to operate first... So, guessing (these numbers may be a bit high--but will give you an incentive to reduce your power usage once you see the size of the system required):

24 hour x 50 watts = 1,200 Wh satellite system
24 hour x 50 watts = 1,200 Wh computer system + printer, etc.
8 hour x 26 watts = 208 Wh for two 13 watt lights
===============================
2,608 Watt*Hours per day.

NOTE: Sometimes below I change between Watt*Hours and kWHrs... 1,000 WH = 1 kWHrs.

Lets assume that you will use a very nice 85% efficient pure sine wave inverter to power all of this stuff (using 12 or 24 volt battery bank and the conversions to other voltages are going to be just about as ineffecient as using an inverter in the first place--plus many DC to DC supplies--like a 12 vdc laptop power brick--don't do well with the wide voltages experienced by a properly operating deep cycle battery bank).

So, the size of the battery bank--assuming 3 days of no sun and 50% maximum discharge level... And assume 12 volt battery bank (24 or 48 VDC will require the same "weight/cost" of batteries):

Batt= 2,608Whperday * 1/85% inv-eff * 3 days * 1/50% discharge * 1/12 volt bat = 1,534 AH (at 12 volts) (see below, will be 767 amp*hours at 24 volt)

And you will need to size the solar panels... Lets assume you are in Syracuse NY (center of state), and you will be using a 92% efficient charge controller, 80% efficient flooded cell Lead Acid batteries, 85% inverter (derating factor = 0.52 for off-grid system), and the rest of the defaults from the Solar Calculator website (fixed panels tilted at latitude, etc.). To generate 2,608 Whrs per day for ~8 months of the year (March through October), that would require

2,608 WH * 30 days = 78.240 kWhrs per month of solar power

Using 1kW of solar panels, we find that October is 57 kWhrs per month (per 1kW of panels). To get 78.240 kWhrs per month, we would need:

Panels=78.240 kWhrs per month * 1kW/57kWhrs per month = 1.37 kW of solar panels to run your system 24x7 for 8 months of the year...

Looking at the wattage of 1,370 watts--I am going to choose a 24 volt battery bank to get the charging current to under 60 amps. And because we will need an even number of Evergreen panels, we will have to bump them up to 8 panels to charge a 24 volt battery bank (even though only 7 are required)

For the winter months, you will need to generate ~30-40 kWhrs per month (call it ~6-10 gallons of gasoline per month).

So, now you can go price the components...

1,370 watts of solar panels = 8x195 watt Evergreen = $7,120
8x195w/24v batt=65 amps -> 80 amp FM-80 Outback charge controller = $580
Exeltech XP250 24-volt 250 watt sine wave inverter = $398
8x Crown 395 Amp-Hour Deep Cycle Battery, 6 Volt = $2,146
=============================================
$10,244 for basic off-grid system

You will need to add an AC battery charger, generator (electric start if unintended operation), maybe a battery monitor, and such to the system to get true 24x365 days operation....


You can see you are pretty close to a $15,000 system for operation in central New York state... If you are in sunnier weather, or use less power for your communications/computer equipment, only run 6 months out of the year (summer time +/-), change to AGM batteries (deeper cycling capable, more efficient, fewer panels, etc.), you can get the size/cost of the system down quite a bit.... And choosing different panels to better match your system (right now, I have one extra 195 watt Evergreen panel, or 14% more solar power than you may need), and other similar choices can bring down some of the costs.

Does this sort of help?

-Bill

icarus

Re: how do I use an off grid module?

georgesuper wrote: »

now wait, back to me, I need 24 volts because the power supply for my dish says 24 volts, 50 watts, and 5 amps. Can anyone help me with that? what do I need to buy to have a fully operational off grid system?

Most internet dishes that I know of (Xplornet KU Band) have a dual voltate 120vac power supply. One voltage is for the modem, and the second is for the TRIA (The broadcast head). Unless the dish is meant to be wired directly to 24vac (I doubt) I would not run it that way, as peak voltages could damage the delicate electronics. I suggest a battery system with an inverter to power the dish.

Icarus

System2

Re: how do I use an off grid module?

Bill - thank you so much for the help, it really does help, and even though its expensive, I think I understand how it all works now

Icarus - Thank you too, I'm begining to wonder if solar energy is really worth it though...