The price of learning by experience
Posted: Wed May 06, 2009 6:19 am
About a year ago I decided to go "green". I've read a lot about peak oil and the environment and the economy and decided that "it's time".
I bought four 14 watt solar panels for R350 each and a regulator for R180, a total of R1580. I found a supplier of second-hand deep-cycle batteries and bought two 172ah battereies for R450 each. I bought a 2.5kW 12VDC modified sine wave inverter for R2800. I rigged it all up. My panels look quite fancy on the skyline on my rooftop.
Then I proceeded to learn and find out exactly how ignorant I was.
The inverter was a TOTAL disaster and I mean TOTAL and I've subsequently sold it at a firesale price of R1000. What was wrong ??!!! Well one has to do a bit of arithmetic to see where the wheels fell off. The only way to compare the input DC side to the output AC side is to compare the equivalent wattage it would take to perform a given task. The relationship is Voltage (V) X Current in Amps (A) = Work Energy in Watts (W) whether AC or DC.
Let us assume we want to run a fridge which takes 1000 watts for a second or two and then runs at about 300 watt for twenty minutes and shuts off for about twenty minutes and the repeats itself. Ignore the 1000 watts for the moment and concentrate on the 300 watt. OK, on the AC side 300 Watts at 230 V gives us A = W / V or 1.3 = 300 / 230. 1.3 amps sounds OK, no problem, BUT look what happens on the DC side 25 = 300 / 12 !!!!!! 25 amps !!!!!! Nothing in our day to day experience takes that sort of current - your plug rating in your house is only 16 amp max. The only thing that takes that sort of current is the starter motor in your car and that you use for a couple of seconds max and you know what happens when you use more than that - flat battery !!
Good Heavens what would happen if you tried to use that inverter at it's rated maximum of 2500 watts. Do the math 208 = 2500 / 12 or 208 Amps !!!!!!! You need welding wires to handle currents like that and submarine or loader batteries to deliver it. I nearly killed my batteries trying to run my fridge during a four hour "loadshed" - in fact, had I not been monitoring it I would have lost them that day. Within an hour my voltage had dropped to 11 V and my batteries were flat !!!! I sold the bleeding thing - virtually gave it away.
My beautiful solar panels are soooo ineffective. On a very sunny day around noon they will deliver together 52 watt or one-fifth of an amp. At night they do nothing and it takes them a week to top up the batteries if I've run a light or two.
To summarise - my first efforts at going green merely changed my colour. I felt sick.
But subsequently things have picked up and my solar geyser is an enormous success and will even pay for itself. Although I do not expect my wind turbine to pay for itself I think it will give me endless hours of enjoyment and keep me in lights. I'm tackling food supply next but that can wait a month or two.
I bought four 14 watt solar panels for R350 each and a regulator for R180, a total of R1580. I found a supplier of second-hand deep-cycle batteries and bought two 172ah battereies for R450 each. I bought a 2.5kW 12VDC modified sine wave inverter for R2800. I rigged it all up. My panels look quite fancy on the skyline on my rooftop.
Then I proceeded to learn and find out exactly how ignorant I was.
The inverter was a TOTAL disaster and I mean TOTAL and I've subsequently sold it at a firesale price of R1000. What was wrong ??!!! Well one has to do a bit of arithmetic to see where the wheels fell off. The only way to compare the input DC side to the output AC side is to compare the equivalent wattage it would take to perform a given task. The relationship is Voltage (V) X Current in Amps (A) = Work Energy in Watts (W) whether AC or DC.
Let us assume we want to run a fridge which takes 1000 watts for a second or two and then runs at about 300 watt for twenty minutes and shuts off for about twenty minutes and the repeats itself. Ignore the 1000 watts for the moment and concentrate on the 300 watt. OK, on the AC side 300 Watts at 230 V gives us A = W / V or 1.3 = 300 / 230. 1.3 amps sounds OK, no problem, BUT look what happens on the DC side 25 = 300 / 12 !!!!!! 25 amps !!!!!! Nothing in our day to day experience takes that sort of current - your plug rating in your house is only 16 amp max. The only thing that takes that sort of current is the starter motor in your car and that you use for a couple of seconds max and you know what happens when you use more than that - flat battery !!
Good Heavens what would happen if you tried to use that inverter at it's rated maximum of 2500 watts. Do the math 208 = 2500 / 12 or 208 Amps !!!!!!! You need welding wires to handle currents like that and submarine or loader batteries to deliver it. I nearly killed my batteries trying to run my fridge during a four hour "loadshed" - in fact, had I not been monitoring it I would have lost them that day. Within an hour my voltage had dropped to 11 V and my batteries were flat !!!! I sold the bleeding thing - virtually gave it away.
My beautiful solar panels are soooo ineffective. On a very sunny day around noon they will deliver together 52 watt or one-fifth of an amp. At night they do nothing and it takes them a week to top up the batteries if I've run a light or two.
To summarise - my first efforts at going green merely changed my colour. I felt sick.
But subsequently things have picked up and my solar geyser is an enormous success and will even pay for itself. Although I do not expect my wind turbine to pay for itself I think it will give me endless hours of enjoyment and keep me in lights. I'm tackling food supply next but that can wait a month or two.