obala's solar panel + charge controller questions

Re: obala's solar panel + charge controller questions

Obala,

I moved your question to its own thread--easier to keep track of your setup.

-Bill

Re: obala's solar panel + charge controller questions

Obala,

I am sorry--that paragraph was about something else--and I forgot to delete it (should have been commenting on the PWM controller to 12 volt battery bank miss-match).

So, If you want a 24 volt bank, either a 24 volt PWM or 12/24 volt MPPT controller would work... To quote the previous post for MPPT 12/24:

Place the two 180 watt panels in series put that in parallel with other 3 panels placed in their own series string:

• Vmp 180 watt panels = 2x 23.7 volts = 47.4 volts
• Imp 180 watt panels = 7.59 amps (series connection)
• Vmp other 3 = ~17 volts + 16.9 + 17.1 volts = 50.9 volts
• other "3" series current 3.8 amps max

Maximum average output power from MPPT controller (assume 0.77 derating for "real" power) which would support either a 12 volt or 24 volt battery bank(note: I forgot to multiply by the 0.77 derating factor--the 415 watts is the correct value--I will fix my previous posts):

• 47.4 volts * (7.59 amps + 3.8 amps) * 0.77 = 415 watts
• 415 watts / 14.5 volts charging = 29 amps into 12 volt bank
• 415 watts / 29 volts charging = 14 amps into 24 volt bank

And the same setup running a PWM controller into a 24 volt battery bank:

• (7.59 amps + 3.8 amps) * 29 volts charging = 330 watts
• 330 watts / 29 volts charging = 11.4 amps into 24 volt bank

You are in Morocco? I assume that the temperatures are not too extreme for most of the country--but with any controller you need to check the Voc (voltage open circuit cold) and Vmp (voltage maximum power hot) to make sure that the high voltage (very cold solar array can over voltage controller) and low voltage (very hot solar array may not charge battery) do not exceed your working range.

In your case, your voltages should be fine for most controllers. You have to find what is appropriate for your location (availability and price)... Do yo have any you are looking at?

One of the controllers (15-30 amps depending on PWM/MPPT) Xantrex, Morningstar, and probably Outback would be fine for your setup. You should have other choices from Europe.

If you have access to products from the US, our host NAWS has a webstore you can look through.

-Bill

Re: obala's solar panel + charge controller questions

Obala,

From my previous calculations:

Maximum average output power from MPPT controller (assume 0.77 derating for "real" power) which would support either a 12 volt or 24 volt battery bank (note: I forgot to multiply by the 0.77 derating factor--the 415 watts is the correct value--I will fix my previous posts):

• 47.4 volts * (7.59 amps + 3.8 amps) * 0.77 = 415 watts
• 415 watts / 14.5 volts charging = 29 amps into 12 volt bank
• 415 watts / 29 volts charging = 14 amps into 24 volt bank

You need to find out your average amount of sun for your location.

One common term is "hours of sun per day"... The average full noontime sun is around 1,000 Watts per square meter... So, Hours of Full Sun is assuming 1,000 watt/sqmtr... Some approximate numbers:

• 2 hours of sun in winter/coastal areas
• 4-5 hours of sun average for regions with decent sun
• 5-6 hours of sun for average clear summer days
• 6-7 hours of sun for some desert regions

From this presentation (solar radiation map in presentation):

Morocco has an excellent Solar potential :
4,7 - 5,7 kWh/day (2800 hours/year in the North, more than 3000 hours/year in the South of Morocco).

So, if you are in the coastal region, more towards 4.7 hours of sun per day and more towards the higher number for central-eastern Morocco.

Now, note that that is the average over one year... It is very easy to have 2 hours of sun in winter and 5+ hours in summer. Frequently the "cost effective" estimate is to toss out the three months of winter and size the system for the other 9 months of the year.

For example, using the PV Watts website for the city of Nouasser Morocco, 1kW (1,000 watts) of solar panels (sorry, minimum accepted by website), and 0.52 derating (solar panel, charge controller, battery bank, inverter losses), we get:

"Station Identification"
"City:","Casablanca/Nouasser"
"State:","MAR"
"Lat (deg N):", 33.37
"Long (deg W):", 7.58
"Elev (m): ", 206
"Weather Data:","IWEC"

"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:"," 33.4"
"Array Azimuth:","180.0"

"Energy Specifications"
"Cost of Electricity:","-99.0 dirham/kWh"

"Results"
"Month", "Solar Radiation (kWh/m^2/day)", "AC Energy (kWh)", "Energy Value (dirham)"
1, 4.24, 62, "N/A"
2, 4.80, 65, "N/A"
3, 5.91, 87, "N/A"
4, 5.50, 79, "N/A"
5, 5.83, 85, "N/A"
6, 6.52, 91, "N/A"
7, 6.67, 96, "N/A"
8, 6.73, 96, "N/A"
9, 6.01, 84, "N/A"
10, 4.95, 72, "N/A"
11, 4.40, 63, "N/A"
12, 3.58, 53, "N/A"
"Year", 5.43, 935, "N/A",

We get about 63 kWhrs per month of useful 240 VAC per 1,000 watts of solar panels. Your systems rating is approximately:

• 47.4 volts * (7.59 amps + 3.8 amps) = 540 watts rated

To work out your system's output for November:

• 63kWH per 1kW * 1/30 days * 1,000 W/kW = 2,100 Watt*Hours per day per 1kW of panels
• 2,100 WH per day per 1,000 watts of panel * 540 Watts of panel = 1,134 WH per day

If you plan on using the system during summer, you can get almost 50% more power...

But, how much power can you use... What you need to know is how much power your AC appliances consume. Say you have a 13 Watt CFL (compact florescent lamp--"twisty bulb") and a 30 watt laptop.

• 13 watts + 30 watts = 43 Watt load
• 1,134 WH per day in November / 43 Watt load = 26 hours of use

Your 300 watt inverter is too small to power a refrigerator (you probably would need a 1,000-1,500 watt inverter minimum to handle the starting current of the compressor motor in the refrigerator). Also, 1,100 Watt*Hours per day is just about what a small / energy efficient refrigerator uses in 1 day--so with the correct inverter, your system would only be able to power a fridge in the summer months.

You also have to size the battery for your system... The starting rule of thumb is to plan for 3 days of no-sun and 50% maximum battery discharge...

Say your average load is 1,100 WH per day and you have a 12 volt 85% efficient inverter:

• 1,100 WH * 1/12 volt batt * 1/0.85 eff inv * 3 days * 1/0.50 max discharge = 647 Amp*Hour battery bank @ 12 volts

Notice that the battery bank is fairly large and expensive--if you want a full time off-grid system for power.

To really know what the power usage of any of your appliances are--you need to measure their usage (labels on appliances are usually very high estimates of power usage). A Kill-a-Watt meter is one very nice way (and reasonably inexpensive) to measure the Watt*Hours per day usage of your devices. Kill-a-Watt meters are now available in 230/240 VAC models now.

In general, an Off-Grid solar electric system is a fairly expensive way to generate electric power... It is always best to conserve as much power as you can (small, efficient appliances) first.

I hope this all helps.

-Bill

Regarding a refrigerator... Here is an example of how you can really save power by "thinking outside the box"... This project uses about 1/4 the amount of power vs a regular refrigerator.

Chest freezer as a chest refrigerator

Saving power is always cheaper vs building a larger solar array + battery bank...