Are these panels a good deal ?? or is voltage low ??

Txrancher

I tried posting in the beginner section, but it said not authorized ?? anyway...I guess mods can move if needed.

Great Forum, some excellent real world knowledge here.

A little background info, My wife and I built our own house here on 20 acres in NE Texas, I did all the electrical also. Currently are on grid at 4.5 cents per KWH, I know thats an unreal rate, at least for now. We use a lot of juice, 2000-5000 KWH per month, at least at this rate my last bill was about 2100 KWH and only $100. We have an old diesel onan generator 12kw hooked to a transfer switch, so we can run almost anything even if grid is out. We also have a complete rainwater system, and a well. propane for heat, stove

Obviously it will never pay to go off grid, BUT

Im a little bit of a survivalist type and want to have a little juice avbl “when the war breaks out”
to run the deep well pump, sceptic.pump, lights. refer, computer, etc. Only have so much fuel for the generator. I want some RE....

I am thinking of a system with about 18 panels 200-245 watts installed on the metal south facing roof.
18 panels is the most that could fit on the roof

I found these Sharp ND-224UC9BX panels locally, new. No shipping for $1/watt, but have been told that the Vmp is low, and could be a problem with a 48v battery bank ?? or does this just mean I need a mppt controller ??

I understand that you cant charge a 48v battery with a panel putting out 29v, but dont you put these panels in series and raise the volts ??

do the folks that told me to pass by these panels know what they are talking about ??
why would sharp make a panel thats not usable ?? or are these only good for grid tie or something ??

If these are a good panel at $1/watt no shipping I should probably get them, would you ???

Thanks

here are the specs



Electrical Characteristics
Maximum Power (Pmax)*: 224 Watt
Tolerance of Pmax: +10%/-5%
Type of Cell:*Polycrystalline silicon
Cell Configuration: 60 in series
Open Circuit Voltage (Voc):*36.6 Volts
Maximum Power Voltage (Vpm):*28.9 Volts
Short Circuit Current (Isc): 8.33 Amps
Maximum Power Current (Ipm): 7.58 Amps
Module Efficiency (%): 14.7%
Maximum System (DC) Voltage: 600 Volts
Series Fuse Rating: 15 Amps
NOCT: 47.5°C
Temperature Coefficient (Pmax): -0.485%/°C
Temperature Coefficient (Voc): -0.351%/°C
Temperature Coefficient (lsc): 0.053%/°C
*Measured at (STC) Standard Test Conditions: 25°C, 1 kW/m2 insolation, AM 1.5

Mechanical Characteristics
Dimensions: 64.6" x 39.10" x 1.8" (994 x 1640 x 46 mm)
Cable Length: 43.3" (1100 mm)
Output Interconnect Cable**: 12 AWG with MC4 Locking Connector
Weight: 44.1 lbs (20.0 kg)
Max Load: 50 psf (2400 Pascals)
Operating Temperature (cell): -40 to 194°F (-40 to 90°C)

mikeo

Re: Are these panels a good deal ?? or is voltage low ??

if these are a good panel at $1/watt no shipping I should probably get them, would you

Yes the price is right and you are correct that you just series panels to get the appropriate voltage. For a 48 volt battery bank, you equalize at around 60 volts. So 3 panels in series and an mppt charge controller would do the job. Yes you are right, they aren't economically feasible looking at it from the money standpoint. But the peace of mind might be worth the cost to you. The panels will be a small part of your overall system price.

icarus

Re: Are these panels a good deal ?? or is voltage low ??

Spend your money on grid tie,, and then build a parallel inverter/battery system for when the grid goes down. The biggest expense of off grid is battery life cycle costs. (especially if they are seldom if ever used).

A better investment might be a good genny, and a stock of fuel,, diesel or propane if you are worried about prolonged grid failure. End of the world scenarios,,, you are on your own, and power might be the least of your problems. Just my opinon.

Tony

BB.

Re: Are these panels a good deal ?? or is voltage low ??

For a 48 volt battery bank, the Vmp-array needs to be ~70 volts (nominal) or higher... For 28.9 volt panels:

• 1x 28.9v = 28.9 volts
• 2x 28.9v = 57.0 volts
• 3x 28.9v = 86.7 volts
• 4x 28.9v = 115.6 volts

For your system, you will probably need a MPPT type charge controller and a 3 in series array. They are more efficient than PWM controllers for Vmp>>70 volts (48 volt bank) and better for larger arrays/systems anyway (although, much more expensive).

Depending on how cold your area gets, 115.6 volts may be too high (Voc cannot exceed ~140-150 VDC for most higher voltage MPPT charge controllers--although there are options for higher voltage arrays).

If you have a long distance between array and battery shed, then keeping Vmp-array high will make the wiring costs much less.

In the end, having a good sized off grid system is expensive. Hardware costs up front and battery replacement every 6-15 years or so. Also, realistically, you should have in your bank account money to replace your major electronics every 10 years or so (charge controllers, inverters, etc.).

For many folks, a genset (or several, run the smaller one for "emergency loads" and use less fuel) is a good solution.

For an end of the world type setup... I would suggest that you measure/document your minimum power needs and size the system to run that. Use a Kill-a-Watt hour meter (or equivalent) to measure your appliance loads. You may need to use other methods to measure hardwired loads (whole house power monitors, some have additional current taps that you can attach to branch circuits).

Basically, unless you expect the power grid to go away in the next few years (for long periods or permanently), you will probably be better off with just enough solar power to "survive" a few months (after a major storm, for example) instead of trying to build out a large backup system.

For example, see what a 100 kWH per month would do for you. It is a good sized system and will run most loads (well pump, sump/septic pump, lights, laptop, washer, lights, etc.) and not cost you an arm and a leg.

For example a 2kW array and off grid power system (using PV Watts, fixed array, 0.52 system derating) for Abilene Tx will give you:

"Station Identification"
"City:","Abilene"
"State:","Texas"
"Lat (deg N):", 32.43
"Long (deg W):", 99.68
"Elev (m): ", 534
"PV System Specifications"
"DC Rating:"," 2.0 kW"
"DC to AC Derate Factor:"," 0.520"
"AC Rating:"," 1.0 kW"
"Array Type: Fixed Tilt"
"Array Tilt:"," 32.5"
"Array Azimuth:","180.0"

"Energy Specifications"
"Cost of Electricity:"," 9.7 cents/kWh"

"Results"
"Month", "Solar Radiation (kWh/m^2/day)", "AC Energy (kWh)", "Energy Value ($)"
1, 4.80, 150, 14.55
2, 5.44, 152, 14.74
3, 6.06, 179, 17.36
4, 6.43, 183, 17.75
5, 6.12, 176, 17.07
6, 6.17, 167, 16.20
7, 6.29, 172, 16.68
8, 6.22, 171, 16.59
9, 5.72, 153, 14.84
10, 6.10, 178, 17.27
11, 5.24, 154, 14.94
12, 4.57, 143, 13.87
"Year", 5.76, 1978, 191.87

Or better than 143 kWH per month or:

• 143 kWH / 30 days = 4.8 kWH per day

A 2kW system may cost your less than $10,000 to install (if you do much of the installation work yourself).... And will, at least, let you live a "civilized" life if your grid power goes away.

Note, the amount of solar power you will harvest is very dependent on local weather conditions If you are near the coast, we will need to use other station data.

Before you buy anything, do a couple paper designs and select the equipment/batteries you would like to use. Usually better than buying stuff "on sale" or from estates if you do not yet have a plan.

-Bill

niel

Re: Are these panels a good deal ?? or is voltage low ??

icarus wrote: »

Spend your money on grid tie,, and then build a parallel inverter/battery system for when the grid goes down. The biggest expense of off grid is battery life cycle costs. (especially if they are seldom if ever used).

A better investment might be a good genny, and a stock of fuel,, diesel or propane if you are worried about prolonged grid failure. End of the world scenarios,,, you are on your own, and power might be the least of your problems. Just my opinon.

Tony

he did say he has a genny, but i will agree with your first paragraph as one can do a backups on certain circuits deemed vital and the pvs would be straight gt for more efficiency. there are some battery backed inverters that are also able to sell to the grid and would serve better than the simple backups as excesses will be sold when pvs are fed into it, but aren't as efficient as a straight gt pv system.

if you go for backing up the whole house and not just a few key circuits, that is allot you'd need to back up with that kind of draw because for what you draw in a day some here use in a month.:roll: