arthuryemi: Is this thread still active

feflo: The 3000W will power a 3bed apartment conveniently and its well protected against major fault that could easily cause damage to it

Call femi on 08023662352, 08165304602

feflo: Recommended Design Practice of Off Grid Solar Power Systems

The design process is a fairly simple and straight forward that doesn’t require a lot of technical knowledge. What follows is based on using MPPT Charge Controllers because they are the most efficient and economical solution for systems requiring a 200 watt or higher solar panel. The initial steps are:

• Determine the load in energy for a 24-hour period. Not the watts, but the watt-hours.
• Determine the size of the solar array to be used.
• Determine the battery size and type.
• Determine charge controller size


DESIGN EXAMPLE

The following example is a rough estimate to take to a system designer to discuss cost and objectives. He/she will then fine tune the system based on actual components, cable distance, etc… Our basic objective in this simple example is to provide power to a 250 watt load (light bulb) for 24 hours per day with 90 % availability. Getting from 90 to 99.99% greatly increases the cost with a larger solar array, larger batteries, and a standby generator set.

1. DESIGN FOR WORST CASE

In this example the worst case is simple to determine because the load is continuous 24 x 7 x 365 of a 250 watt light bulb. So the worst case is during the raining season when the Solar Insolation is at its lowest point of the year.

So in this example we need to determine the energy needed in a 24 hour period. This is done with watt-hours. To determine the watt-hours is straight forward of Watts x Time (in hours). So 250 watts x 24 hours = 6000 watt-hours or 6 Kwh in a day or 24 hours. Make note of this number as it will be needed later.

2. CONSIDER THE LOSSES

To account for overall system losses in the wiring, charge controller, battery charge efficiency, and inverter you multiply the total 24 hour load energy by 1.5 So 6000 x 1.5 = 9000 watts or 9 Kwh. Now take note of this figure. Take Note, if using a PWM Controller the Fudge/losses Factor is 2

3. DETERMINE SOLAR INSOLATION IN HOURS

Most solar map data are given in terms of energy per surface area per day. No matter the original unit used, it can be converted into kWh/m2/day. Because of a few convenient factors, this can be read directly as "Sun Hour Day” The number you want to use in this example is during the raining season when the sun hour day is lowest. For this part of the world, I’ll suggest we use 5.

feflo: 4. DETERMINE THE SIZE OF THE SOLAR PANEL ARRAY.

The size of the array is determined by the adjusted daily energy requirement using the Fudge/losses factor number divided by the sun-hours per day. So for our design, 9000 wh / 5h = 1607 watts, round up to 1800 watts.

5. DETERMINE BATTERY SIZE

Determining battery size is very simple. All batteries will last substantially longer if they are shallow cycled. That means discharged only by about 20% of their capacity in a given day. Whereas deep discharge means that a battery is discharged by as much as 80% of its capacity. Second point is no lead acid battery should ever be discharged more than 50%. Below 50% soft lead sulfate crystals harden on the plates which reduce capacity and shorten battery life substantially. So in real application you have 2 days of usable capacity to allow for cloudy days before reaching the 50% discharge.

To figure the daily load, go back to the original load number before the fudge factor—that is, 6000 watt hours. Battery capacity = Daily Watt Hours x 2. So we need 6000 watt hours x 2days = 12,000 watt hours or 12Kwh.

Now that we have the battery capacity in Watt Hours we need to convert to Amp Hours. To find the Amp Hours we need to select a battery voltage. Amp Hours = Watt Hours / Voltage. To select battery voltage is based on panel wattages vs controller size. MPPT charge controllers have maximum panel wattage input vs the controller’s current rating in AMPS. MPPT controllers typically come in 20, 40, and 80 amps. So selecting battery voltage is very important. As a general rule you want to run the battery voltage as high as economically possible.

I have some general rules of thumb for battery voltage selection:

1. Never use 12 volts. 12 volts is for very small solar installation.
2. Panel wattages 500 watts to 1000 watts use 24 volt battery
3. Panel wattages higher than 1000 up to 4000 use 48 volt



So for our design, we will use 48 volt batteries. So the battery capacity in Amp Hours = 12,000 wh / 48 volts =250 Amp Hours.



6. DETERMINE CHARGE CONTROLLER SIZE IN AMPS

It is very simple, Charge Controller Output Amps = Panel Wattage / Battery Voltage. So for our design the minimum MPPT Charge Controller is; 1800 watts/ 48 volts = 37.5 amps. So it requires a 40 amp MPPT Charge Controller.


7. CONCLUSION & LAST COMMENTS

We need to re-visit batteries for a moment. Flooded Lead Acid (FLA) are the least expensive and last the longest of the lead acid chemistry. However they have one drawback and that is they have the highest internal resistance. What this mean is the maximum charge rate they can be charged with is C/8 where C = the battery 20 hour discharge rate Amp Hour Capacity. So the maximum current we can apply to a FLA 250 AH battery is 250 AH / 8 h = 31.25 amps.

feflo: “If you cannot do great things, do small things in a great way.”
Napoleon Hill

feflo:

Gel batteries are great, they have a longer service life, both under float and cycling conditions. The gelled electrolyte won't spill, even if the battery is tipped upside down or cracked open. You won't have to worry about any messy acid spills or corrosion around the batteries or any of your sensitive electronics. Gel batteries boast greater resistance to extreme temperatures, shock, and vibration.

My inverters are modified sine wave.

Thanks for your interest.

feflo: PWM Controllers:

A FET switch is used, under control of some algorithm, to
rapidly connect a power source, to a battery. The switch "makes" and "breaks"
many times a second, to control the charge. (Pulse Width Modulation)
When the battery is quite low, the FET switch is ON, and the
panels are connected directly to the battery, and since PC panels are a
"current source" their voltage drops (or is pulled low to the battery
voltage) and some power is lost, depending on the difference of the Vpmax
of the solar, and the present voltage of the batteries.
PV voltage - Battery voltage = Difference x Amps = Lost wattage

Note if the array was a 200W array, amps would be 11.11Aa
18V @ 11.11A = 200watts
Assuming the voltage of the battery is 12.2V, then the power loss will be

18V PV - 12.2V battery = 5.8V @ 11.11amps = 64.438W lost
So a 200W panel array will only give 135W of power to the battery



MPPT Controllers: [Maximum power point tracking]

A more sophisticated circuit is used, much like a "DC
Transformer" to dynamically convert the power source (water, wind generator
or PV panels) via an efficient DC-DC conversion process. This can also
down convert high voltage DC, to suitable charging voltage for the battery,
with very low losses, about 95% efficient. This is a good thing if you
have a remote array - you can run high voltage DC to the controller and avoid
expensive high amp wire, and incur lower losses.
The MPPT advantage vanishes when the controller switches
from the BULK charging mode, to ABSORB, and does not need the extra power
recovered from the conversion process, and falls back to PWM for ABSORB and
FLOAT stages. This can be managed in different ways for individual
systems, as many MPPT controllers have user programmable settings.
This is the simple gist of it, the actual workings are much deeper than
I can go into here.

As the system gets larger, the cost trade off between the
simple PWM controller and the expensive MPPT (with possibly shorter
lifetime with more complex innards) and PV panel & rack costs, shifts, and
it's left to each user to decide which controller is most appropriate for
their situation. The tipping point is around 600 - 1,000 watts

feflo:

Gel batteries are great, they have a longer service life, both under float and cycling conditions. The gelled electrolyte won't spill, even if the battery is tipped upside down or cracked open. You won't have to worry about any messy acid spills or corrosion around the batteries or any of your sensitive electronics. Gel batteries boast greater resistance to extreme temperatures, shock, and vibration.

My inverters are modified sine wave.

Thanks for your interest.

feflo: For more contact FEMI on 08023662352 and 08165304602

feflo: PWM Controllers:

A FET switch is used, under control of some algorithm, to
rapidly connect a power source, to a battery. The switch "makes" and "breaks"
many times a second, to control the charge. (Pulse Width Modulation)
When the battery is quite low, the FET switch is ON, and the
panels are connected directly to the battery, and since PC panels are a
"current source" their voltage drops (or is pulled low to the battery
voltage) and some power is lost, depending on the difference of the Vpmax
of the solar, and the present voltage of the batteries.
PV voltage - Battery voltage = Difference x Amps = Lost wattage

Note if the array was a 200W array, amps would be 11.11Aa
18V @ 11.11A = 200watts
Assuming the voltage of the battery is 12.2V, then the power loss will be

18V PV - 12.2V battery = 5.8V @ 11.11amps = 64.438W lost
So a 200W panel array will only give 135W of power to the battery

feflo: “If you cannot do great things, do small things in a great way.”
Napoleon Hill

feflo:

Yes I have 1.2kw (that's 1.5kVa) and its 25k. All my inverters have auto changeover and all the other protective shutdowns to prevent it from developing fault.

alldruns1:
1. Is d auto change-over a separate item frm d power inverter itself or inbuilt.

2. Frm d pic I see, one end of d inverter hs two terminal heads where u connect your +ve & -ve cable heads while d other end is d outlet where u plug your device. How then do I charge d power inverter with Nepa light? Or is it only charged by deep cycle battery? Or is its charger a separate item too
Thnks in adv.

feflo: 2. The end that contains the DC cables (I.e + & - ), also has an AC socket receptacle where the incoming AC supply is plugged

feflo: I will try and upload another pix clearly showing this

alldruns1:
Are u referring 2 d point where u plug in appliances on d inverter e.g. TV, fan, etc? If yes, does it mean it serves dual purposes? As in, u plug in your tv there & u also charge wt Nepa light frm there? Like I'm nt getting something clear.... Pls clarify.

Pls make it asap.

feflo:

The inverter has two ends, the front and the back end. The front end is where you plug your loads, that is the output AC power of the inverter. The other end which is the back end where you connect the positive and the negative cables coming from your battery. That back end also has an AC supply receptacle where your supply from utility or generator is plugged in. Its the same power cable used in computers and some electronics.
I cannot upload the pix now cos I'm using my phone, I can only promise to do before the close of work today.

Thanks so much.

alldruns1:
Alright, d explanation is now clear. Hoping 2 see d pic shortly.