1、OVERVIEWI wrote an article for Home Power magazine (issue 136, April/May 2010) that summarizes the project, click here to get a copy, or click here to visit the Home Power web site.My wife and I are committed to sustainable living. I have a separate page devoted to all the efforts we are taking in t
2、hat regard. This section of my web site documents my experience while researching, designing and installing a grid intertied solar power system in the summer of 2009. I have wanted to live a solar powered life but it has always been too expensive to consider. Over the last 10 years I have monitored
3、the costs of installing a system capable of powering a home and that price has hovered around $30,000. I am an active member of a local volunteer organization called the Midcoast Green Collaborative. We are committed to creating a sustainable economy in coastal Maine. In 2009 one of our efforts has
4、been to get legislation passed modeled on the very successful German Feed-in Tariff law. This law levies a small fee of a dollar or so per month on every electric rate payers bill. This creates a fund that the utility uses to pay a significant premium per kWh to small scale renewable energy generato
5、rs. This makes it cost effective to finance the cost of installing solar panels (or a windmill etc.) because the income from the sale of your electricity to the utility covers the cost of the loan. Once the loan is paid off - typically in 20 years you become a profitable electric micro-utility!I tes
6、tified at a hearing for this proposed legislation before the Maine Joint Utility and Energy committee, where I presented a spreadsheet that showed how the financing would work with a 20 year low interest loan and a 20 year generation contract with Central Maine Power - our local utility. I showed th
7、at a minimum payment of 50 cent per kWh would significantly incentivize small scale solar generators on a residential scale. For reference Ontario, Canada is paying nearly 70 cents/kWh and Vermont just introduced a feed-in-tariff bill that would pay 30 cents.Testifying led me to do more research on
8、the cost and feasibility of going solar. My first call was to my friend Naoto Inoue, the owner of Solar Market in Maine. He had helped me to design the solar heating system for my workshop back in 2001, and sold me much of the equipment. He told me of a new technology called “micro inverters“ that w
9、as changing the paradigm of solar installations. Instead of the panels being wired together to create high voltage DC that is sent to a large single inverter that converts the DC to the AC we use in the home, each panel has a micro inverter mounted right behind it. The power is converted to 240 Volt
10、s AC right there at the panel. This makes the system more efficient and more flexible. It eliminates the shading issues that can compromise the performance of DC systems where panels are wired in series - shading any one panel in the series will compromise the whole string. Also one can mix and matc
11、h panels of different capacity allowing one to grow a system with a blend of panels as you can afford them. Overall this system has a slightly better cost/performance characteristic. More about micro inverters on Wikipedia.The only disadvantage of installing a grid-tied solar system like this is tha
12、t there is no battery bank. So when the utility power fails the inverters automatically shut down to protect the line workers. So we will still need to rely on our Generac automatic propane backup generator (purchased from a local big box hardware store) during power outages. In recent years we have
13、 lost power for an average of 5 days each year due to 2 heavy snow storms, Maine winters can be brutal. This cost us several hundred dollars in propane, so the trade-off of a battery-less system can get expensive on occasion. But in the long run it is less expensive than installing and maintaining a
14、 battery bank.Several other factors influenced our decision to go solar now, low mortgage rates, recent drop in the cost of solar panels, and the federal tax incentive that allows us to take 30% of the cost of the system off our federal taxes. (We did not get the credit we expected in the first year
15、 because we are self-employed more on that here)Maines electric supply has one of the highest renewable ratios in the country, at present about 30% of the electricity delivered comes from renewable sources. Read more about other states renewable energy portfolio here. So we already had a very low ca
16、rbon footprint, and we have chosen to purchase electricity from 100% renewable sources. So our electric supply is already carbon neutral.So my next task was to figure out how many panels I would need, and where to put them all. Go to the next page to see what I learned. Also if you want to see a sim
17、ilarly detailed blog about a ground mounted solar power system that also uses Enphase inverters like mine - take a look at Gary Reysas site.Live web cam (updates every 60 seconds)Project timelineDATE ProgressJune 6, 2009Signed loan for project financing (home mortgage re-financing)June 18, 2009 Pick
18、ed up 11 solar panels and the rack mount rails.June 25, 2009 Re-roofing the buildingJune 26, 2009Installed interior load panel for the 240 Volt power from the invertersJune 30, 2009 Picked up 10 more solar panelsJuly 26, 2009 Installed mounting rails for solar panelsAugust 1, 2009Installed grounding
19、 wire for the rails, and roof junction boxesAugust 14, 2009 Installed the first 12 (of 21) invertersAugust 28, 2009 Installed the first 12 solar panelsSeptember 3, 2009 Installed 9 more invertersSeptember 4, 2009 Installed the last 9 solar panelsSeptember 16, 2009More details and real time performan
20、ce statisticsMarch 3, 2010Article I wrote about the project published in Home Power MagazineAugust 18, 2010Installed 2 more 175 Watt panels (now have 23 panels installed)June 29, 2011Installed 2 more 175 Watt panels (now have 25 panels installed)July 29, 2011Installed 1 more 180 Watt panel (now have
21、 26 panels installed = 4.5kW)I highly recommend subscribing to Home Power MagazineHome Power magazine is the Hands-on Journal of Home-Made Power. If you are interested in: making your own electricity from renewable energy, alternative vehicles, or finding out the latest in related technologies and l
22、ife-styles, then this publication can keep you up to date.SYSTEM SIZING To design a solar power system you first need to know how much power you use. Actually before that you need to really work at reducing your usage so that your system costs will be lower. My wife and I have already done all we ca
23、n think of to reduce our energy footprint - read more about that on my Sustainable Living page. By reviewing my past 12 months of electric bills I learned that we use an average of 550 KWh/month. This is pretty good considering that we both have home businesses which use computers and equipment. As
24、a frame of reference the average US household used 880KWh/month in 2006. Take a look at your recent electric bill and see how your home stacks up - there may be room for improvement!So using 550kWh as a design goal was the starting point. For reasons that date back to off-grid solar houses that ran
25、on DC and batteries, solar systems are rated in the total KWh capacity of the solar panels and not the AC power produced. Since the inversion process is inefficient there is typically a derate factor used to calculate the AC KWh of a given solar array. This is typically calculated at .77. So a 1 KW
26、solar array will yield about .77KW of usable AC power. However the Enphase micro inverters I plan to use have better efficiency that is calculated at .819 - a significant improvement!The US National Renewable Energy Laboratory has a web site tool called PV Watts that allows you to calculate the perf
27、ormance of a given solar array based on solar wattage, its location, climate, tilt, orientation and capacity. By trying a variety of panels of different wattages and quantities (see panel siting) I settled on an initial price performance trade-off of using 21 175 Watt BP 175B panels that produce a t
28、otal of 3675 Watts at the panels. That translates into an annual production of around 3923 KiloWatts of AC power depending on weather variables. (I have added panels over the years since the original installation - see below)Here is the result of the PV Watts calculations showing the estimated month
29、ly AC energy production for the current array (29 inverters).Note: I have been adding panels as I can afford them:added 2 175W panels: Aug. 22, 2010added 2 175W panels June 29, 2011added 1 180W panel July, 2011added 3 230W panels June 2012See the next page for more details of the system performance
30、and costing. Click here to see current and historical performance charts since my system was installed.September 2011. Enphase have released a study showing that their microinverters out perform PVWatts calculations by up to 8%. They looked at regular string inverters and found that they underperfor
31、med PVWatts by up to 8%. So this validates my decision to invest in Enphase inverters.Below is an updated system diagram as of June 2012, click on the image to download a full page printable pdf version.If you found the information presented on my web site to be helpful you can send me a donation to
32、 show your appreciation for the many hours I have invested in presenting my knowledge and experience. This is NOT tax deductible and will show as a consulting fee on your receipt.Installing a grid intertied solar electric power systemOverviewSystemsizing FinancingPanelSiting HardwareGroundingRailIns
33、tallationInverterInstallationPanelInstallationReal-timeStatsMoredetails FINANCINGPart of the original impetus to install solar panels came from my experience of watching proposed feed-in-tariff legislation get strangled to death by well intentioned members of the Maine Utility and Energy committee.
34、I testified and then spent many long afternoons in the committee room observing the deliberations. The original bill was drafted by the grassroots organization that I am an active member of here in Maine. The Midcoast Green Collaborative has been very proactive in raising awareness of sustainability
35、 in our region by organizing an annual Sustainability Expo. I had hoped that the bill would pass as drafted and as-such would offer a significant incentive by requiring the electric utility to purchase our power at a very attractive rate for at least 30 cents/kW. In late May, Vermont became the firs
36、t state to pass exactly such a bill. Gainesville, Florida also enacted a similar bill that created a boom in residential solar installations. Maines bill does not offer any real incentive at all, but it is a stepping stone toward a realistic goal.In the process of preparing my testimony for the comm
37、ittee I began to realize that even if the bill did not pass there was another option. Maine has a net metering law in place that credits the customer the full retail value of the electricity they export to the grid. So if we were to install a system that generated all of the electricity that we need
38、 then our annual bill would be reduced to the minimum connection fee of around $8.00/month. In fact it is more prudent to undersize the system so that we would not be giving away any surplus - the utility does not pay for a surplus, just credits for the excess generated power generated in any given
39、month.Below is my bill from Central Maine Power for March/April 2012 - using 26 panels (about 4.0kW peak AC power):Note that since all net metering bills are hand processed, they actually highlighted my credit for me!I looked up the last 12 months of our electric bills and then calculated the antici
40、pated energy production for a system comprising 21 175-Watt panels and from this determined what our electric bill would be on a monthly basis. As you can see below our average bill will be much lower.The way that net metering works is that we would bank any surplus credit in the summer and use it i
41、n the winter. As we eventually add more panels, the credit will be greater.(You can see how my installation is performing compared to the estimated solar power on the Real Time Stats page of this blog.)We began by looking into re-financing our house to lock in a low rate during the “economic downtur
42、n“ (depression) in March 2009. We had an ARM mortgage with a MegaBank that would go from the fixed to adjustable rate next year (2010) and we figured that it was a good time to lock in a 20 year fixed mortgage. We also decided to go to our local bank for the re-fi to keep the money in the local econ
43、omy. I watched the economic indicators and published mortgage rates carefully and then locked in the loan rate at the lowest point in the cycle in late May.We originally budgeted $26,000 for 27 panels that would fill the roof, but decided to reduce our initial overhead and scale the design back to a
44、 more prudent 21 panels. (Panel prices have dropped significantly since 2009 and in 2102 are nearly 50% lower due to the Chinese jumping into the market with massive government subsidies and decimating the US manufacturing capacity by dumping their cheaper products). By asking for an additional $21,
45、000 on the re-financing we were able to lock in a very attractive rate that works out better than an equity loan or line of credit. We also explored the option of a Maine State Housing HELP (Home Energy Loan Program) loan. But they limit these loans to 15 years and $30K so despite the better interes
46、t rate, the net monthly payment would be about the same as the cost rolled into a mortgage. Our loan officer also advised us that the paperwork for these loans is significant and there are a lot of restrictions that could preclude my installing the panels myself.We determined that the added $21K on
47、our loan would cost us about $180 more per month over 20 years than what we were currently paying. When we account for the fact that our electric bill will drop from an average of $100/month (for Clean Power at 18cents/kWh) to about an average of $58.00/month, so I estimated that our monthly budget
48、would only increase by an average of $122 ($89 to $146 depending on the seasonal solar gain - see below). This is not an undue burden for us. After the loan is paid off its all positive cash flow! (after adding more panels our net bill in the spring of 2012 was negative - until we purchased a Chevy
49、Volt electric vehicle.)The Federal Residential Energy Efficient Property Credit (form 5695) allows us to deduct 30% of the cost of the system from our taxes, so we will avoid paying around $6000 in taxes. Maines Efficiency Maine program has a Solar Rebate program, Solar PV systems qualify for rebates of $2.00/watt for the first 1,000 watts, capped at $2,000. Check the DSIRE database of state incentives to learn what you can expect in your state.Update on tax breaks:We got our taxes done by our accountant in 2010, and got a nasty surprise. I had thought we would get the full $6185
