There are (6) 260 watt German made panels from Hanwa. They are each tied to a microinverter made by Enphase, model M250. They are Grid-Tie inverters which means that they require you to be hooked up to grid power in order for them to work. If the grid goes down, so do the panels. This ensures that no one working on the power lines down the road gets hurt by the power we're generating and feeding back into the system. Enphase has a trunk cable that will tie all of AC power together into one line. This is not a backup for times when the power goes out. This is a sytem to offset our electric use. Instead of feeding a battery bank, these panels feed our house and the excess power goes into the grid for credits against future use. The cost (and maintenance effort needed) of batteries led us to use grid power. We have a generator for backup power should we need.
Our Power Company (Farmers Electric Co-Op) has several requirements for grid-tie systems. 1) Must use UL1741 compliant inverters (change DC power from panels to AC so it can feed into your house). This ensures that if the grid goes down, the array turns off. 2) You must have a cut-off box with a lockable external switch installed to shut down the array when needed. 3) You need to install a meter base next to the array. They will provide the meter so that we can monitor how much power is being generated monthly.
Past that, it's just common sense. I put in a double pole breaker into our breaker box for the incoming 240v power. You must use a double pole breaker, not 2 singles, so that if there is a problem, it will shut down both 120v legs of the incoming power. this also ensures that your 2 120v legs are in phase and will combine to 240v. You should mount this breaker at the far end of the bus bar (opposite of the power company's incoming lines) in your breaker panel to help evenly distribute incoming power. The inverters put out AC power at a higher voltage than the power company lines. This allows the voltage to push back into the power lines and into your house. This power is taken 1st as your appliances need it. If your household demand is higher than your array is producing, then it pulls the remainder from the grid from the power company. If you are making more than you are consuming, this power (since it's a higher voltage) pushes back into the grid and feeds your neighbors houses.
Since the system requires a bi-directional billing meter, your meter runs backwards as long as you're pushing excess power onto the grid. Thus, the electric company is buying the power that you're generating. Currently, we get full retail value for this excess we make but only against our usage in the current month. They reset the credits on each monthly billing cycle. We never get a refund check for excess power generated but we are getting full retail price for it. I am pushing for them to allow a longer period of credit accumulation, possible 6 months or a year. This would even out the seasons for the consumer. They have been pretty responsive so far to other requests. They earlier dropped the requirement for additional insurance coverage since they also required that the inverters automatically shut down in case of power outages. This meant that there should be no additional risk from the home based solar array.
System Costs:
Hanwa Q-Cell 260Watt Panels (6) at $213 ea. (no freight as I picked them up locally)
Enphase M250 Inverters (6) at $158 ea (changes DC power from panel to AC power for house)
Enphase Trunk Cable (6) connections at $20 ea (this is what combines the inverters)
Enphase Trunk Cable Terminator (1) @ $15 (caps off the trunk cable at the end)
Usage Meter Base (1) at $37 (power company provides the actual meter for free)
Midnite Solar Cut-Off Switch (1) @ $185 (provides disconnect of array)
20 Amp breaker Cutoff Switch (1) @ $25
20 Amp Double Pole Breaker for Main Breaker Box (1) $8
Mounting Rack (1) @ $250 (put together myself from Home Depot materials)
Conduit and wiring from panels to breaker box $80
Grounding Rod & #4 bare copper $40
Misc conduit connectors $12
Trencher rental 1 day @ $120 (to bury the wire from the panels to the breaker box 100' away)
In all, I have about $3,000 into the system. Our electric company is giving us a $1,000 rebate for installing solar since it eases their demand. Nice to have a power company that's not profit-driven! They also gave us a $3,000 credit when we installed our grid power lines and transformer. That would have just about covered the cost of installing overhead lines but I hate them and would have had to cut down some of our gorgeous 60' Oak trees to accomodate. That wasn't going to happen! So, we installed underground service 750' from the road to our meter base. Kim and I ran cabling (additional 100') to the house where we installed another breaker box to feed all of the household circuits. Here, I ran 100 amp service and put in 12 breakers and 250' of 12 gauge wire for our 240 sf house. :) Every outlet, light switch and appliance is on its own breaker. :)
The solar array generates about 1,500 watts. That's 1.5 KWHrs for every hour that the sun's shining on the array. It gets about 5 hours of direct sunlight now. The Enphase inverters are MPPT (Maximum Power Point Tracking) which allows for varying output from each panel. If one is in the shade, only that one slows down production.
Right now, we're only at the house part time. That means that it will be generating power for credits on 4-5 days that we're not there. We have propane for our stove and water heater so hopefully our power needs will not exceed what the panels can produce for now. As we're ready to relocate here permanently, we can add additional panels to offset the additional demand. Since all of the wiring and infrastructure are in place, it should be pretty cost effective to expand. Buy a pane, an inverter and trunk cable. No telling what solar panels will cost in the next 3-4 years as they have dropped by half in the past 4 years. Currently we expect a payback in about 5 years of service. The awesome part is being able to put together your own power generating station and know that you control your electric costs for the next 30 years. This should set our electric bill at $15/mo for the rest of our lives. :)
Here are some pics of the system as we put it together.
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| Built stand out of fencing materials and steel from HD |
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| Panels from front view |
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| Added meter base for usage meter from power company. Enphase inverters (gray box on under each solar panel) |
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| Enphase 250 watt microinverter. One for each panel. |
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| Double Pole breaker in breaker box. (yes, I have a breaker to add to the open slot! :) |
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| Billing meter on left. Main Breaker box on top right. Cut-Off switch wired in below. Everything labeled for safety! |
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| Specs on the Solar panels |
(May 12) Finally got our bi-directional meter and new Net-meter installed from the electric company. Happy to report that our solar array is in full production. :) Very exciting to see your electric meter count backwards.
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| Our 1st 4 Kilowatt hours produced! Cool knowing that we'll be in production for the next 30 years. :) |
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| Panels with production meter in place. |
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