Solar Update:
Grid tie results
November, 2002
Well, it's been a long and busy summer over here at the solar shed. A number of changed were implemented as I continued to refine the shed to produce the most useable power.
First things first: The Micro-Sine arrived and was put into service on a Saturday evening. The batteries in the shed were peaked. At first I read the manual, fiddled with the software, and finally just wired it straight into the 24 volt battery core in the shed. It would either work or blow up; I was hoping for work. Well, I did put a 10 amp fuse in series with it on the DC line in the event it tried to dead-short the battery array or something.
A buzz was heard when I plugged it into the grid, and a quick check with the included software showed that I was selling power to the grid.
And selling. And selling.
I went into the house and turned off every circuit breaker with the exception of the one to the shed. The meter slowed down, stopped...
And started turning backwards. Not super-fast, but I watched in amazement as it completed several revolutions in the "other" direction. At this point, I was actually using my solar panels to feed the grid.
Wow. It was an interesting feeling, to say the least.
Finally the inverter kicked off and I took a look at where I stood. The batteries were reading 25 volts even, and the inverter was *off*. It looks like the MPPT software in the Micro-Sine will turn off the inverter when the input voltage is below 25 volts. Which is actually kind of perfect; 12.5 volts is still mostly charged on the batteries; thus the Micro-Sine will not pull the batteries down too very low. Remember that the idea is not to sell *all* my battery power to the grid; just the surplus power generated from the panels each day.
With this setup, I was generating about 600 watts per day and feeding it back into the grid. I now had an extension cord running from the house to the shed across the yard (again) but this time all the power goes in the *right* direction. It's ironic, but I might wind up running a permanent power line between the shed and the house next year to carry the current *into* the house, and not the other way around. Another truth is that I could probably run the critical things in the house (few lights, fridge, and maybe the TV) off the shed's batteries and the inverter in there. I might actually consider trying that if we lose power over the winter :-)
At this point, I re-evaluated the solar shed's panel use. The Elec-Trak was still charging using a dedicated 120 watt panel, and it would typically be peaked in three days or less. Which means that for about four days a week I had a panel up on the roof that wasn't really doing anything. Before this was not a big deal, as the rest of the panels were idle when the shed's batteries were full. However now I had a customer that would take 100% of the power.
The local power company. My new client :-)
So I went up on the roof again and re-wired the panels. The 24 volt bus is now powered by all four of the MSX-120 panels wired in parallel. The 60 watt panel came out of storage, and was wired in series with the 24 volt bus to produce 180 watts of charging power for the tractor. It now takes 7 days to charge the E20 tractor, but since I use it once a week this is perfect. And my power output on the grid-tie system went to about 1,000 watts a day (1kw/hr).
So at this point, all the panels are being used at peak efficiency. Every ray of sunshine that falls on the panels is being used; either to charge the shed (priority one), the Elec-Trak (priority 2) with the cream of the crop going to spin my meter backwards.
And at this point, I think I am going to let the solar shed run in this configuration for awhile. At least through the winter. It has proven that I can use solar to do useful things, and has given me the ability to see what it is like to sell power back to the grid.
It's also time to plan the next step: Installing 1.5 kilowatts of solar on the roof of the house. Along with a grid-tie inverter and maybe a few batteries to keep the house running in the event of a blackout...
Stay tuned :-)