Supply and consumption in Kilowatts

Can you solve this equation for me please?
Given that I am in Cambodia where there is abundant sunshine.
1) What is the maximum consumption of the following:
a) 10 x 3 Watt LED lights for 8 hrs
b) 1 x domestic fridge for 24hrs
c) 1 x computer for 8hrs
d) 1 x internet router for 24hrs
Therefore:
How many solar panels of how much wattage?
What size (amp size) controller?
What voltage?
Plus what size inverter (wattage if pure-sign wave)?
How many batteries of what Ah rating?
Thank you in anticipation of your reply.
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1) What is the maximum consumption of the following:
a) 10 x 3 Watt LED lights for 8 hrs
b) 1 x domestic fridge for 24hrs
c) 1 x computer for 8hrs
d) 1 x internet router for 24hrs
Therefore:
Add everything up... My suggestion is to keep the energy usage to ~3.3 kWH per day as a "reasonably" cost effective system that should be large enough to live a "near normal" electric lifestyle (conservation is your friend here).
1 kWH per day refrigerator
0.24 kWH per day Lighting
0.24 kWH per day computer
0.72 kWH per day modem+router (you can probably do better):
==============================================2.2 kWH per day above... Leaves ~1.1 kWH per day for charging cell phone, water pumping, washing machine, etc.
Next, size the battery bank--I will assume 3.3 kWH per day--But you can use your own numbers (more or less energy). Pick 24 volts (experience). 1-3 days storage, pick 2 days. 50% maximum discharge:
- 3,300 Watt*hours per day * 1/0.85 AC inverter eff * 1/24 volt battery bank * 2 days storage * 1/0.50 max discharge = 647 AH @ 24 volt battery bank
I suggest that you keep the battery bank to 800 AH or less, if possible. If your battery bank is larger, then go to the next higher voltage.Next, sizing the solar array. Two calculations. One is based on 5% to 13% charging current, the second based on hours of sun per day. First charging current:
- 647 AH * 29 volts charging * 1/0.77 panel+controller derating * 0.05 rate of charge = 1,218 Watt array minimum (part time/seasonal use)
- 647 AH * 29 volts charging * 1/0.77 panel+controller derating * 0.10 rate of charge = 2,437 Watt array nominal (full time living off grid)
- 647 AH * 29 volts charging * 1/0.77 panel+controller derating * 0.13 rate of charge = 3,168 Watt array typical "cost effective maximum"
Continued on next pagehttp://solarelectricityhandbook.com/solar-irradiance.html
Phnom Penh
Measured in kWh/m2/day onto a solar panel set at a 78° angle from horizontal:Average Solar Insolation figures
(For best year-round performance)
- 3,300
WH per day * 1/0.52 end to end AC system eff * 1/4.01 hours of sun per
day = 1,583 Watt array minimum (based on loads and sun)
I suggest that batteries are expensive and have a "short life" and solar panels have never been cheaper and have a long life--So, if possible, you should add as much solar panel as your budget would allow... But somewhere in the 1,583 to 2,437 Watt range minimum would be a good start for full time off grid living. Of course, your actual hours of sun will vary with weather conditions--You should plan on your "base loads" using ~66% to 75% of the predicted output--And on clear/sunny days you can run more loads (pumping, computer, etc.).How large of AC inverter--That really depends on both your loads and your battery bank size. For a typical Refrigerator, a 1,200 to 1,500 Watt (good quality) AC inverter minimum.
And based on the battery bank, a "workable" AC inverter would be (based on flooded cell lead acid battery bank):
- 647
AH * 24 volts * 0.85 AC inverter eff * 1/20 hour discharge rate = 660
Watt average load (5 hours per night, 2 nights, 50% maximum discharge)
- 647 AH * 24 volts * 0.85 AC inverter eff * 1/8 hour discharge rate = 1,650 Watt inverter maximum continuous discharge
- 647 AH * 24 volts * 0.85 AC inverter eff * 1/5 hour discharge rate = 2,640 Watt inverter max continuous discharge (minutes to an hour or so)
- 647
AH * 24 volts * 0.85 AC inverter eff * 1/2.5 hour discharge rate =
5,280 Watt inverter max surge (seconds to minute--Remember that most
good quality AC inverters will support 2x rated output for surge load)
So--realistically, you would need (guessing) a minimum of 1,500 Watt AC inverter--And not much more than 2,000 Watt based on a 647 AH @ 24 volt flooded cell lead acid battery bank.Of course, my numbers are based on an estimated usage of 3.3 kWH per day system. Your actual loads may be more or less than my suggested starting point.
Getting a Kill-a-Watt type meter and/or AC+DC Current Clamp DMM can help you get better measurements:
http://www.reuk.co.uk/Kill-a-Watt.htm (230 VAC 50 Hz version)
http://www.sears.com/craftsman-digital-clamp-on-ammeter/p-03482369000P (Sears "good enough" $60 clamp meter)
-Bill
The reason why I posed the question is in reference to providing power in Cambodia.
I wanted to make a model which showed the typical usage for a small household.
Here in Cambodia the base rate for power is 2 dollars a KW
I want to take the cost of the equipment needed, (including replacement of batteries and upgrading of controllers every 2 years) during the 18 years lifespan of the panels and come up with a cost per kilowatt.
My target figure is 1.5 dollars
Can this be achieved?
Prices here are as follows:
Panels are 1 dollar a watt
100 amp hour Narada deep cycle battery is 175 dollar each
Suitable controller about 200 dollars
1500 pure sign wave inverter about 300 dollars
Bulb plus holder about 2 dollars each
Plus wiring, switch gear, breakers and fuses estimated allowance is 100 dollars
I know I am asking for an algorithm to be written but I am interested to know the economics
Again thank you in anticipation of your reply
[$2,437 panels + 4x 18 batteries * $175 each * 4x $200 charge controllers + 4x $300 AC inverters + $100 misc] / [3.3 WH per day * 0.65 ave usage * 365 days per year * 18 years] = $1.21 per kWH over life of system
Batteries--I would like to see you use better/different/larger batteries (at least for 3.3 kWh per day system). Charge controllers and AC inverters (at least good ones) should last 10+ years, with some early life failures in 5+ years.
In the end, batteries are the weak part of any off grid power system... It is very easy to kill batteries with improper operation/maintenance (you can kill batteries in weeks or months pretty easily).
-Bill
With the equation, you can see where your expenses are and what can be changed to (hopefully) reduce the costs... But, in general, you will be paying much more for off grid power than for utility power.
In the US, Grid Tied solar (panel+GT inverter connected directly to the grid) is as cheap as, and even less than utility power (can be less than $0.10 per kWH). Notice, that there is no Battery, no backup/off grid power, and no extra stuff (like DC charge controllers, battery chargers, etc.).
However, GT Solar really only makes sense when subsidized by utility customers. In the US, we are presently on a path where subsidies for home based GT solar is slowly going away (for example, they just doubled my minimum metering charge--Other companies are dramatically reducing payouts for GT Solar power and or raising minimum billing fees).
-Bill
However I am not deterred from providing power to rural communities in Cambodia. These people are completely off the grid and in much need of good quality lighting for a start.
I am using Tweet as a mediam for networking and I have a facebook page called oursolarpower it will have in brackets (Siem Reap)
Perhaps you would be so kind as to follow me on tweet@Solar4Cambodia and or 'like' my page and become a FB friend.
Social media will help me to expose my crusade, thanks.
http://zoneblue.org/cms/page.php?view=off-grid-solar
Prices vary, I understand that we have somewhat inexpensive prices on a lot of our equipment and environments vary as well! A 3 kwh a day system in a rural area where, it is being introduced, ...that would be an area that closes down with the sun and this is routine, would have far fewer storage requirements than a system that is used where people come home at night and start using power.
I likely used 3kwh a day with my 1500 watt array and 4 golf cart batteries during the summer, when we have regular sun with the heat that I was running an A/C. I could see that system reliably producing 3 KWhs a day in the southwest, particularly if much of that energy was used during the day. Quick Estimate would be $1500 for array, $150 for mounting, $150 for a C60 CC, $400 for a battery bank, $500 for an inverter, $150-200 for a combiner box and breakers, $150 for assorted wiring. Around $3000...
If electric runs 20 cents a KWh and there is no, or minimal installation expense, it is NOT worth considering. If the rural energy is 40 cents or higher then you might look into solar energy.
P.S. I've never gotten around to buying my 'big inverter' so I have @ $8000 (before tax incentives) in my current 4KW array system and it has been reliable for the last 3 years, battery on it's 5th or 6th year, inverter on it's 8th year (Prosine bought used, but was really new/unused) I use much more than 3 KWh's a day. Having some knowledge and background does help, but owning a system is the best teacher.
Please see my new topic: A design for a 12 volt supply in rural communities.