Solar Photovoltaik System Expansion
This year (jup, still 2012!) in February my 1KW grid tied PV system went online. Ever since I was thinking about what to do with the inverters second, unused input. Years ago I had a small Wind Turbine. A small one, it was a Rutland 910. It never produced much energy due the lack of wind and the buildings around. I sold it (for more then I've payed to a guy in Russia. Funny thing). Since my new home comes with a roof much higher then the one I grew up in I gave it another try and purcased a Wind Turbine second hand quite cheap (faulty, but I spend less then 20 bucks on the spare part to fix it). It's a Rutland 913. But to get it to operate with my big string inverter I had to deal with some problems:
In November, while still thinking about the problems I may face when connecting the wind turbine to the String Inverter, I got a Micro Inverter between my paws (an old OK4-E 100). Micro Inverters are designed to run with a single (or two) PV module(s) and operate between 20V and 60V. Usually, they can handle between 100 and 350W. Since it operates with low voltages it could be suitable for using it with the Wind Turbine. Some tests made me abandon this idea, too. The MPP tracker is too slow and in case the wind picks up and the Inverter doesn't draw enough energy from it to keep its voltage low, well, the voltage peak will damage the inverter. More problems to solve.
After running further testes and paying attention to the local wind conditions it quit the idea completely. The generator I'll sale on Spring on ebay. I'll likely get 350 EUR+ for it. That's 270EUR more then I paid for it and the spare parts together. I've read a lot about wind power system, purcased a good book on that topic and gained quite some knowlegde. But that's it. I won't spend a huge amount of money and time on a project that's prone to cause frustration. I still want to play with wind energy. Since spending a lot of money on it would be everything but reasonable I'll build a simple one myself. Just some watts (likely 2...5 from a stepper motor). It's just for fun.
Anyways, suddenly it came to my mind that I still had those 6 panels from my first solar system from my "younger years" on the attic. I did some calulations and the results told me that I can, in fact, connect those 6 PV modules in series and they will work fine with my Inverter (6 x 21,1V = 126,6V. The Inverter needs a 120V threshold to start on each input. 16,0V (worst) x 6 = 96V. Perfect. The Inverter can work with voltage down to 90V in MPPT mode on each string). I'm also glad that I can use them again. They're from my youth where solar panels were quite expensive. I remember that 600 DM for a 50W panel was the common price. I was thinking on selling them on ebay. But I felt uncomfortable about. Because of the money I spend on and for emotional reasons. So, yep, they back in operation soon.
There's not much to say. Theat's what will end up on my roof soon. (likely on Sunday).
But hey. There's still the unused OK4-E Micro Inverter left. Not any longer! In the middle of December I got a 140W Solar PV Module from ebay. For less then 40 Bucks. Nice! Since it comes with 72 cells in series (24V system) it's perfect to operate with the OK4-E Inverter. 140W seems to be a bit too much for the Inverter to deal with since the limit is 120W. Not a problem, there will be have cable losses and a hot module in summer will never produce it's peak power that were measured under test conditions. Like said, thr module and thr Micro Inverter are a perfect match.
That's how the system look like at the moment. I need to shorten the steel legs abit since the angle is too steep. Everything else will stay that way.
That's the test setup to see if everything works (and to use the system already). The whole setup will end up in a junction box with transparent cover later. I'm still waiting for one part (analog AC meter) to arrive.
Today at the first day of operation the 140W Module feed 350Wh to the grid. Nice.
- The Wind Turbine is for a 12V system and it's output voltage swings between 9 and 20V.
- No problem here. I could build a simple DC/DC converter that transfers the Voltage/current ratio of the wind turbine unchanged, still allowing MPP tracking.
- The MPPT may be too slow to catch up with fast changing wind conditions.
- Solving this would be a major task. It would require an µC controlled system and a small power storage system so it can puffer the produced energy until the MPPT catches up.
- The MPPT for Solar modules isn't suitable for wind turbines.
- More issues that only a µC and lots of hardware can solve. If done wrong I would likely end up in an oscillating MPPT condition.
- The Grid Inverter needs about a minute to start up when offline. It would require constant wind for more then a minute to bring it online. Unlikely in my area.
- I could keep the Inverter alive by feeding a stand-by voltage to it so it "thinks" the sun is still out. No problem here (except of wasting energy).
In November, while still thinking about the problems I may face when connecting the wind turbine to the String Inverter, I got a Micro Inverter between my paws (an old OK4-E 100). Micro Inverters are designed to run with a single (or two) PV module(s) and operate between 20V and 60V. Usually, they can handle between 100 and 350W. Since it operates with low voltages it could be suitable for using it with the Wind Turbine. Some tests made me abandon this idea, too. The MPP tracker is too slow and in case the wind picks up and the Inverter doesn't draw enough energy from it to keep its voltage low, well, the voltage peak will damage the inverter. More problems to solve.
After running further testes and paying attention to the local wind conditions it quit the idea completely. The generator I'll sale on Spring on ebay. I'll likely get 350 EUR+ for it. That's 270EUR more then I paid for it and the spare parts together. I've read a lot about wind power system, purcased a good book on that topic and gained quite some knowlegde. But that's it. I won't spend a huge amount of money and time on a project that's prone to cause frustration. I still want to play with wind energy. Since spending a lot of money on it would be everything but reasonable I'll build a simple one myself. Just some watts (likely 2...5 from a stepper motor). It's just for fun.
Anyways, suddenly it came to my mind that I still had those 6 panels from my first solar system from my "younger years" on the attic. I did some calulations and the results told me that I can, in fact, connect those 6 PV modules in series and they will work fine with my Inverter (6 x 21,1V = 126,6V. The Inverter needs a 120V threshold to start on each input. 16,0V (worst) x 6 = 96V. Perfect. The Inverter can work with voltage down to 90V in MPPT mode on each string). I'm also glad that I can use them again. They're from my youth where solar panels were quite expensive. I remember that 600 DM for a 50W panel was the common price. I was thinking on selling them on ebay. But I felt uncomfortable about. Because of the money I spend on and for emotional reasons. So, yep, they back in operation soon.
There's not much to say. Theat's what will end up on my roof soon. (likely on Sunday).
But hey. There's still the unused OK4-E Micro Inverter left. Not any longer! In the middle of December I got a 140W Solar PV Module from ebay. For less then 40 Bucks. Nice! Since it comes with 72 cells in series (24V system) it's perfect to operate with the OK4-E Inverter. 140W seems to be a bit too much for the Inverter to deal with since the limit is 120W. Not a problem, there will be have cable losses and a hot module in summer will never produce it's peak power that were measured under test conditions. Like said, thr module and thr Micro Inverter are a perfect match.
That's how the system look like at the moment. I need to shorten the steel legs abit since the angle is too steep. Everything else will stay that way.
That's the test setup to see if everything works (and to use the system already). The whole setup will end up in a junction box with transparent cover later. I'm still waiting for one part (analog AC meter) to arrive.
Today at the first day of operation the 140W Module feed 350Wh to the grid. Nice.
