What panel should I buy for dry camping flexible or the largest watt panel available

Re: What panel should I buy for dry camping flexible or the largest watt panel avail

Our host, NAWS, has good products, prices, and service. But, frankly, shipping and local service and support are important too. As always, you will have to research what is the best for you--including shipping/insurance to your front door.

Picking your appliances for conservation is always important with solar. But, starting with normal rules of thumbs and 4x 110 AH @ 12 volt batteries. First rule of thumb for off grid systems, try for 5% to 13% rate of charge on battery bank with 10% a healthy amount:

• 4x 110 AH * 14.5 volts charging * 1/0.77 panel+charger deratings * 0.05 rate of charge = 414 watts "minimum"
• 4x 110 AH * 14.5 volts charging * 1/0.77 panel+charger deratings * 0.10 rate of charge = 828 watts "nominal"
• 4x 110 AH * 14.5 volts charging * 1/0.77 panel+charger deratings * 0.05 rate of charge = 1,077 watts "maximum cost effective"

Using PV Watts for Boston MA, 1kW (1,000 wattss) fixed array mounted flat to roof, and 0.52 system end to end efficiency:

"Station Identification"
"City:","Boston"
"State:","Massachusetts"
"Lat (deg N):", 42.37
"Long (deg W):", 71.03
"Elev (m): ", 5
"PV System Specifications"
"DC Rating:"," 1.0 kW"
"DC to AC Derate Factor:"," 0.520"
"AC Rating:"," 0.5 kW"
"Array Type: Fixed Tilt"
"Array Tilt:"," 0.0"
"Array Azimuth:","180.0"

"Energy Specifications"
"Cost of Electricity:","11.8 cents/kWh"

"Results"
"Month", "Solar Radiation (kWh/m^2/day)", "AC Energy (kWh)", "Energy Value ($)"
1, 1.85, 26, 3.07
2, 2.79, 39, 4.60
3, 3.79, 59, 6.96
4, 4.61, 69, 8.14
5, 5.58, 83, 9.79
6, 6.03, 84, 9.91
7, 6.03, 86, 10.15
8, 5.43, 78, 9.20
9, 4.25, 59, 6.96
10, 3.15, 46, 5.43
11, 1.89, 25, 2.95
12, 1.58, 21, 2.48
"Year", 3.92, 675, 79.65

Note that for northern locations, tilting the solar array to your latitude (~42.37 degrees), on average, will collect a heck of a lot more energy during winter:

"Station Identification"
"City:","Boston"
"State:","Massachusetts"
"Lat (deg N):", 42.37
"Long (deg W):", 71.03
"Elev (m): ", 5
"PV System Specifications"
"DC Rating:"," 1.0 kW"
"DC to AC Derate Factor:"," 0.520"
"AC Rating:"," 0.5 kW"
"Array Type: Fixed Tilt"
"Array Tilt:"," 42.4"
"Array Azimuth:","180.0"

"Energy Specifications"
"Cost of Electricity:","11.8 cents/kWh"

"Results"
"Month", "Solar Radiation (kWh/m^2/day)", "AC Energy (kWh)", "Energy Value ($)"
1, 3.36, 55, 6.49
2, 4.36, 65, 7.67
3, 4.79, 76, 8.97
4, 4.92, 74, 8.73
5, 5.33, 79, 9.32
6, 5.41, 74, 8.73
7, 5.60, 79, 9.32
8, 5.64, 81, 9.56
9, 5.13, 73, 8.61
10, 4.65, 71, 8.38
11, 3.14, 47, 5.55
12, 2.98, 47, 5.55
"Year", 4.61, 820, 96.76

Normally, for a cabin/home, I like to suggest that you design for "no generator use" for 9 months of the year (the last 3 months is normally winter and, for most locations, it is more cost effective to use a small genset during poor weather).

So, from above, February is the "9th month" and for a 1,000 watt array tilted to latitude (second table), you would collect ~65 kWH per Month (65,000 WH per month), or for the above suggestions:

• 65,000 WH per Feb / 28 days per Feb = 2,321 Watt*Hours per day in February

If you choose the minimum solar array of 414 watts, then the amount of power per day per February, here is the math:

• 2,321 WH per day per Feb * 0.414 kW array = 961 WH per day (Feb)
• 961 WH per day / 12 volt battery bank = 80 AH @ 12 volts per day (Feb)

That is not a lot of power, but it is enough to for lights (CFL/LED), small fan (mix heat), and a laptop computer/modem. And if you use a flat mounted array, you will get 1/3rd less power.

Hope this helps.

-Bill

Re: What panel should I buy for dry camping flexible or the largest watt panel avail

God (or the devil) is in the details... Where will the system be? Can you tilt the array? Seasons/months of the year? etc...

So, just to make some basic assumptions. 220 AH @ 12 volts per day, assume a minimum 3 hours of sun 8 months of the year for Boston area (~ 8 months of the year), AGM bank with 90% efficient batteries, and 77% derating for solar panels + charge controller, mounted flat to roof.

• 220 AH * 14.5 volts charging * 1/0.90 eff battery * 1/0.77 system derating * 1/3 hours of sun per day = 1,534 watt solar array

From our host NAWS (does not include shipping/insurance costs--which can be substantial):



Kyocera 235GX-LPB


$395.00 per panel

$1.68 per watt

• 1,534 watt array / 235 watt solar panel = 6.5 = 7 solar panels (235 watts per panel (~66" by ~39" rectangular panels)

For various reasons, you may end up making a choice of 6 or 8 panels to give you a higher Vmp array (smaller wiring).

You will need a fairly large charge controller:

• 8 panels * 235 watts * 0.77 system derating * 14.5 volts charging = 99 amps "nominal" into a 12 volt battery bank.

So, you would need a pair of 60 amp (or larger) solar charge controllers (around $500 to $600+ per controller).

Does this look like the system you need?

-Bill

Re: What panel should I buy for dry camping flexible or the largest watt panel avail

In the simplest of terms, an MPPT charge controller can match a 12 volt battery to a 100 volt solar array. It is, sort of, like a computer controlled version of a DC Variable Transformer.

So, either you pick solar panels with Vmp~17.5 volts or so with a PWM type controller, or if you choose panels with a much higher Vmp, and install a MPPT type charge controller.

You are not going to be able to setup 7-8 big solar panels on your trailer--Only one or two(?). You need to evaluate your loads/needs, or figure out how you will use a genset / shore power to meet your needs.

One way, use a smaller battery bank for a few lights, radio, cell phone charger, laptop computer, etc At night/during quiet times, and use the genset when your loads are heavier and shore power when you have it (and to recharge the battery bank, if needed).

-Bill