I have finally decided that reading by candle light every second night while the power is down for 3 to 4 hours is not as much fun as it's made out to be. I have therefore taken the second step to reduce my reliance on the Eskom b@stards!
I have had a generator (6.5kVA, 4 stroke petrol) at my place since I moved in about 18 months ago. It works well enough, but it's damned noisy and can become very expensive to run (petrol consumption wise). Also, do you really want all that noise at 23:00 in the night while you are really just using a couple of lights?
Nope - not me. For me the generator is a last resort option. I am happy to run it for a couple of hours during the day to get the fridge and freezer cooled down, warm up the water in the geyser, etc but other than that I am not a fan of the thing.
So, after doing some homework I decided to start building a battery backup system. For phase 1, I only need it to run my light circuits (not the geyser, plugs, etc). In order to design and spec a battery backup system, you need to do some calculations. Firstly decide on what you want to run, and for how long.
Fortunately I have installed mostly LED lights and a couple of CFL throughout my house during the past year to the point where I don't have a single incandescent or other high power draw type light at all.
My lights are as follows:
* Living room: 4x 10W LED (2 banks of 2 which can be switched individually). We mostly only use one bank, so this is 20W
* Kitchen: 2x 10W LED. That's 20W
* Passage: 2x 5W LED. That's 10W
* Bathroom 1: 5W LED
* Bathroom 2: 10W LED
* Bathroom 3: 10W LED
* Bathroom 4: 10W LED
* Outside light (front door): 11W CFL
* Bedroom light: 3x 11W CFL. That's 33W
* Hifi room / Study: 8x 5W LED. (4 banks of 2 which can be switched individually). I mostly use two banks, so that's 20W
I didn't factor in things like the lights inside my garage and outbuildings - these are not critical.
My maximum continuous draw (inside the house) then will be: 189 Watt.
In practice, I would say that we continuously use only the following lights (only the two of us in the house):
* Living room: 20W
* Outside light: 11W
* Hifi room / Study: 10W
That's a very light-weight 41 Watt continuous.
We also use the following lights as needed:
* Kitchen: 20W (about 1 hour per night)
* Passage: 10W (about 1 hour per night)
* Bathroom: 10W (about 1 hour per night)
That's an additional 40W of power needed only 1 hour per night. If we run lights for an average of 6 hours per night, then the total consumption per night would be: (6 x 41W) + (1 x 40W) = 286 Watt. That is an average of (286Watt / 6 hours per night) = 47.67 Watt Hours.
Now the question of how long we want the battery backup to keep these on. I decided that a 18 hours continuous running time would be sufficient - if you use the lights for 6 hours a night, then that gives you a solid 3 days with no charging.
So the total power requirement then is 47.67 Watt x 18hours = 858Watt hours, which is roughly 0.86kwH
The next step is to decide on the battery bank voltage. This is a game of current (Amps). The higher the battery system voltage, the less DC current you need. Common voltages are 12V, 24V, 48V. I settled on 24V because parts are readily available and it seems a good compromise for my low power requirements.
Now that we now the voltage, we can figure out the current capability we need from the battery bank:
858 Watt hours / 24V = 35.75 Amp hours worth of battery capacity. There are some losses incurred in the inverter as heat, etc. The unit I have has a rated maximum efficiency of 93/94%. I will assume a real life efficiency of 80%. Therefore we factor that into the calculation: 35.75 Amp hours / 80% = 44.69 Amp hours.
Next thing to consider is the battery life. I am using two 12V batteries in series to get the 24V. The life of a rechargeable battery is shortened drastically by the discharge depth. Good batteries are expensive, so you really want to look after them so they will last you a long time. Therefore we don't want our 12V battery to discharge to a voltage of lower than 10.5 Volt. Beyond that, the electrolyte starts breaking down, plates start bending, etc.
The batteries I have are rated for 100 Amp Hour from fully charged down to 10.5V; To ensure a long life of the batteries, we really only want to ever discharge them down to 50% of their capacity to 10.5V; Therefore we factor this into the calculation: 44.69 Amp hours / 50% = 89.38 Amp hours.
So from all these calculations then, we have figured our that I need a minimum of 89.38 Amp hours of battery power at 24V to ensure I can run my lights normally for 6 hours per day, and for 3 days straight without any charge. I have two 12V, 100 Amp hour batteries connected in series, so that gives me 24V, 100 amp hour capacity. All good then :2thumbs:
This is what I have: Victon Inverter / Charger. 1200VA, 24V, 16 Amps. This thing connects to the mains feed in the DB board, and to the lighting circuit. While it gets power from the mains, it will apply some very clever charging and maintenance to the batteries, and allow the lighting circuit to work off the mains. As soon as the mains power falls out, it will switch over to battery power. The switch over is claimed to be 20ms and so fast that even a desktop PC will not loose power during a switchover.
Check out the spec sheet here: http://www.victronenergy.com/upload/documents/Datasheet-MultiPlus-inverter-charger--800VA-%E2%80%93-5kVA-EN.pdf
It's an expensive piece of kit, but it allows me alot of flexibility and scale-ability in the future. I can easily add much more batteries to the bank, and if the 1200VA ends up being too little, then I can just add more of these Victron units and run them in parallel. Excellent!
Batteries are Narada GPG 12V 100Ah. This is a deep cycle gel battery with AGM. Made specifically for UPS and emergency lighting systems.
Spec sheet here: http://www.rectifier.co.za/Narada/12v/GPG12V100.pdf
So in theory then, I could potentially survive without Eskom for a good while now. Cooking is off gas. Lights are good for at least 3 days - perhaps more if we use them sparingly. I could fire up the generator every second day for 2 to 4 hours just to cool the fridge and freezer, and warm up the water in the geysers, and recharge my battery bank.
The biggest problem I see is hot water. I have a standard geyser, so I suppose that it will be the focus of my next step when I have some money again.
Going down this route is expensive - no doubt about it, but I just don't see any reasonable alternative if you want to maintain some sort of normality with the power grid being the way it is.
What do you guys think?
Cheers,
Ian.
I have had a generator (6.5kVA, 4 stroke petrol) at my place since I moved in about 18 months ago. It works well enough, but it's damned noisy and can become very expensive to run (petrol consumption wise). Also, do you really want all that noise at 23:00 in the night while you are really just using a couple of lights?
Nope - not me. For me the generator is a last resort option. I am happy to run it for a couple of hours during the day to get the fridge and freezer cooled down, warm up the water in the geyser, etc but other than that I am not a fan of the thing.
So, after doing some homework I decided to start building a battery backup system. For phase 1, I only need it to run my light circuits (not the geyser, plugs, etc). In order to design and spec a battery backup system, you need to do some calculations. Firstly decide on what you want to run, and for how long.
Fortunately I have installed mostly LED lights and a couple of CFL throughout my house during the past year to the point where I don't have a single incandescent or other high power draw type light at all.
My lights are as follows:
* Living room: 4x 10W LED (2 banks of 2 which can be switched individually). We mostly only use one bank, so this is 20W
* Kitchen: 2x 10W LED. That's 20W
* Passage: 2x 5W LED. That's 10W
* Bathroom 1: 5W LED
* Bathroom 2: 10W LED
* Bathroom 3: 10W LED
* Bathroom 4: 10W LED
* Outside light (front door): 11W CFL
* Bedroom light: 3x 11W CFL. That's 33W
* Hifi room / Study: 8x 5W LED. (4 banks of 2 which can be switched individually). I mostly use two banks, so that's 20W
I didn't factor in things like the lights inside my garage and outbuildings - these are not critical.
My maximum continuous draw (inside the house) then will be: 189 Watt.
In practice, I would say that we continuously use only the following lights (only the two of us in the house):
* Living room: 20W
* Outside light: 11W
* Hifi room / Study: 10W
That's a very light-weight 41 Watt continuous.
We also use the following lights as needed:
* Kitchen: 20W (about 1 hour per night)
* Passage: 10W (about 1 hour per night)
* Bathroom: 10W (about 1 hour per night)
That's an additional 40W of power needed only 1 hour per night. If we run lights for an average of 6 hours per night, then the total consumption per night would be: (6 x 41W) + (1 x 40W) = 286 Watt. That is an average of (286Watt / 6 hours per night) = 47.67 Watt Hours.
Now the question of how long we want the battery backup to keep these on. I decided that a 18 hours continuous running time would be sufficient - if you use the lights for 6 hours a night, then that gives you a solid 3 days with no charging.
So the total power requirement then is 47.67 Watt x 18hours = 858Watt hours, which is roughly 0.86kwH
The next step is to decide on the battery bank voltage. This is a game of current (Amps). The higher the battery system voltage, the less DC current you need. Common voltages are 12V, 24V, 48V. I settled on 24V because parts are readily available and it seems a good compromise for my low power requirements.
Now that we now the voltage, we can figure out the current capability we need from the battery bank:
858 Watt hours / 24V = 35.75 Amp hours worth of battery capacity. There are some losses incurred in the inverter as heat, etc. The unit I have has a rated maximum efficiency of 93/94%. I will assume a real life efficiency of 80%. Therefore we factor that into the calculation: 35.75 Amp hours / 80% = 44.69 Amp hours.
Next thing to consider is the battery life. I am using two 12V batteries in series to get the 24V. The life of a rechargeable battery is shortened drastically by the discharge depth. Good batteries are expensive, so you really want to look after them so they will last you a long time. Therefore we don't want our 12V battery to discharge to a voltage of lower than 10.5 Volt. Beyond that, the electrolyte starts breaking down, plates start bending, etc.
The batteries I have are rated for 100 Amp Hour from fully charged down to 10.5V; To ensure a long life of the batteries, we really only want to ever discharge them down to 50% of their capacity to 10.5V; Therefore we factor this into the calculation: 44.69 Amp hours / 50% = 89.38 Amp hours.
So from all these calculations then, we have figured our that I need a minimum of 89.38 Amp hours of battery power at 24V to ensure I can run my lights normally for 6 hours per day, and for 3 days straight without any charge. I have two 12V, 100 Amp hour batteries connected in series, so that gives me 24V, 100 amp hour capacity. All good then :2thumbs:
This is what I have: Victon Inverter / Charger. 1200VA, 24V, 16 Amps. This thing connects to the mains feed in the DB board, and to the lighting circuit. While it gets power from the mains, it will apply some very clever charging and maintenance to the batteries, and allow the lighting circuit to work off the mains. As soon as the mains power falls out, it will switch over to battery power. The switch over is claimed to be 20ms and so fast that even a desktop PC will not loose power during a switchover.
Check out the spec sheet here: http://www.victronenergy.com/upload/documents/Datasheet-MultiPlus-inverter-charger--800VA-%E2%80%93-5kVA-EN.pdf
It's an expensive piece of kit, but it allows me alot of flexibility and scale-ability in the future. I can easily add much more batteries to the bank, and if the 1200VA ends up being too little, then I can just add more of these Victron units and run them in parallel. Excellent!
Batteries are Narada GPG 12V 100Ah. This is a deep cycle gel battery with AGM. Made specifically for UPS and emergency lighting systems.
Spec sheet here: http://www.rectifier.co.za/Narada/12v/GPG12V100.pdf
So in theory then, I could potentially survive without Eskom for a good while now. Cooking is off gas. Lights are good for at least 3 days - perhaps more if we use them sparingly. I could fire up the generator every second day for 2 to 4 hours just to cool the fridge and freezer, and warm up the water in the geysers, and recharge my battery bank.
The biggest problem I see is hot water. I have a standard geyser, so I suppose that it will be the focus of my next step when I have some money again.
Going down this route is expensive - no doubt about it, but I just don't see any reasonable alternative if you want to maintain some sort of normality with the power grid being the way it is.
What do you guys think?
Cheers,
Ian.
