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MR NEL Newbie Joined: 03/05/2011 Location: NigeriaPosts: 2
Posted: 03:30am 03 May 2011
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Hi folks, I am new here and very much appreciate the kindred spirit in the house.
I have an ambitious project of powering a 4 bedroom apartment with alternative energy in Africa.
the plan is to use DC airconditioners (4) and fridges (2) and then have the lightings and other appliances on AC.
5KVA for the DC current and then 3kVA for AC (using an inverter)
the Air conditioners comes at approx 700W.
My challenge is which battery system is best for the project and how best do I charge it.
Let's leave out turbines for now before of the geography of the place, with AC power from the grid coming for say 5hours a day. what's my best bet? (budget and qty)
Nelson
VK4AYQ Guru Joined: 02/12/2009 Location: AustraliaPosts: 2539
Posted: 08:07am 03 May 2011
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Hi Nelson
It seems the only option you have for alternate energy is solar panels if you cannot use wind turbines. Solar is more reliable than wind as it is there most times.
You have chosen the most inefficient use of alternate power, to run airconditioning as it is very heavy on power consumption, and therefore solar panels, to use the power grid to charge batteries for the off time is I understand a big part of your system plan, but to do that you will need a large expensive battery bank.
Are you able to use evaporative coolers as they require a lot less power, and can you improve the insulation in the house to even out the temperature on the day night cycle.
You mention it is an apartment you want to improve, is it a ground floor apartment or in a multi story block, rural or city area.
All the best
BobFoolin Around
petanque don Senior Member Joined: 02/08/2006 Location: AustraliaPosts: 212
Posted: 05:39pm 03 May 2011
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In different parts of the world apartment describes different things. In Australia where many of the forum users are based the term apartment is not commonly used.
I am assuming the dwelling is in Nigeria and so keeping cool is the priority rather than keeping warm.
Also there would be times of the year when it would be very humid.
Alternative energy typically is more expensive than conventional power (at least in Australia).
Often there is a long payback period.
Because of these reasons it is very important to minimize energy use if using alternative energy sources.
The battery question (eventually) most people living off the grid in Australia use deep cycle lead acid batteries.
Certainly there are other battery chemistries but what is easily available in your part of Nigeria I don’t know.
With only having mains electricity for 5 hours a day are you in a remote area?
If you are remote it may be wise to design a system that is more likely to be robust and reliable.
If you are starting from scratch passive design issues should be fully investigated.
For instance if changing the design of the house may drastically reduce the need for air-conditioning.
MR NEL Newbie Joined: 03/05/2011 Location: NigeriaPosts: 2
Posted: 06:26pm 03 May 2011
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Thanks folks, Nigeria is in the tropics and cooling is the aim. I chose DC air conditioners and fridges because they are relatively energy efficient and avoids the initial power surge that comes with AC current. assuming that cost is not so much a factor.
what's the best set up for a 4kva load (DC) there won't be need for an inverter. my challenge is how to figure the battery bank that will give a ten hours supply and how to charge that bank.
assume we are using 24V input here, (or 48)
Thanks
RossW Guru Joined: 25/02/2006 Location: AustraliaPosts: 495
Posted: 12:49am 04 May 2011
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4 KVA is an inappropriate term for DC, but if I assume you mean 4KW, thats 166 amps @ 24V, or 83A @ 48V. A lot of current either way.
If you plan to run for 10 hours, and use lead-acid batteries, you'll want to keep the depth of discharge to no more than 10-20% of capacity. So lets say a 48V bank, is 830 amphours of use, would require 8300 amphours of batteries for 10% DOD or 4150 amphours for 20%. That's a LOT of battery.
You might be better served to run a decent chiller when you have power available and "store cold" in brine/water/ice, and use the batteries to run just a small circulating pump and fan instead of the whole aircon.
petanque don Senior Member Joined: 02/08/2006 Location: AustraliaPosts: 212
Posted: 12:57am 04 May 2011
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By 4 Kva I assume you have calculated the maximum load at 4000 w.
The next issue is about how much of the time will the various appliances be running?
Fridges for instance the motor tends to run for a period and then stop for a while.
Air conditioners also have different current demands depending if they are cooling or not.
Both these appliances will use more energy if they are set at cooler temperatures.
Being in the tropics the sun would be strong so a solar system should work well as long as the sky is clear.
Cloudy days can drastically reduce the power output of a solar system.
If you had your 4000w of appliances running 75% of the time this suggests an average power use of 3000 w for 24 hours per day this is 72000w per day
If you were to manage your power by charging batteries from the mains you would need a system that could supply about 15000w
(If the local power supply is up to this would need checking)
I think the supply to my house would struggle to supply this but power blackouts (outage) are rare in Adelaide Australia.
And a battery bank that is large enough to accept charge at the rate of 12000(while the power is on I am assuming there would not be any drain on the battery bank).
Over time the capacity of the battery bank will decrease deep discharge cycles will reduce battery life.
At 24 volts this is 50 amps.
This has assumed there are only small losses in the system.
Often batteries, battery chargers and electrical systems have some losses.
Notice. New forum software under development. It's going to miss a few functions and look a bit ugly for a while, but I'm working on it full time now as the old forum was too unstable. Couple days, all good. If you notice any issues, please contact me.
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