Oasis Montana Inc.
Renewable Energy Supply and Design
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Tech. Support: 1 (406) 777-4321 or 4309
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For grid-tied power systems, www.grid-tie.com
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Efficient and DC appliances, www.eco-fridge.com
And our main page at www.oasismontana.com


Solar grid-tie inverter roundup
Oasis Fall 2005 Newsletter

For those of you who aren’t familiar with solar grid-tie inverters, a brief overview of how they work is in order. These inverters allow you to easily connect a solar array directly (i.e. without a battery bank) to your home’s AC breaker box. From there the DC power generated by the solar modules is inverted to AC and it is either used directly by your AC appliances or it is sold back to your utility company which lowers your monthly electric bill. This is the most efficient and least costly way to “go solar” since there is no expensive battery bank to purchase and maintain. The one drawback of this type of system is that it cannot provide backup power during a utility outage since the inverters shut down for safety reasons. 


If you are interested in this type of solar power system, the first thing you should do is contact your utility company to see if they will allow you to connect such a system to their electric grid (as not all utility companies will). The next thing to ask them is if they offer “net metering”, where they pay you the same rate per kilowatt-hour of energy that you pay them. Without net metering, a solar grid-tie system is not very cost-effective. The last thing to ask your utility company is how long they will allow you to carry over any excess energy production (hopefully for a full year). If you get all of the right answers from your utility company, the next step is to determine how much energy you would like the grid-tie solar system to produce. The limiting factors in determining the maximum size of your solar system are either available roof area or budget (also, you can install these on the ground on differing mount structures). After the solar array size is determined, the next step is to figure out which inverter(s) will work best for your chosen solar array. This can be a little tricky due to many factors (number of solar modules, solar module voltage vs. inverter voltage, physical module layout, minimum winter temperature, etc.) so give us a call and we will design the whole system for you. If your solar array size is too large for one inverter to handle, that isn’t a problem because these inverters are modular—so you can install multiple systems on your home if your budget allows, or do it incrementally. A grid-tie solar system is very easy to wire and install since most of the inverters use 1 to 3 high-voltage series strings of solar modules (hence their nickname “string inverters”) along with simple disconnect switches on the DC and AC sides. Some of the grid-tie inverters incorporate these required disconnect switches into their design and all of them have the NEC required DC ground fault detection/interruption protection for roof mounted solar arrays. 


Rather than writing a long and probably boring article (or have we just done that?) about the features of each inverter, we put together the chart below comparing units from SMA, Xantrex, Fronius, Sharp and PV Powered, which we think are the most popular brands for residential and small commercial solar applications. Each unit’s peak power rating is part of the model name so we didn’t list it separately. Hopefully this chart will help you choose the grid-tie inverter that has the features you want and will best meet your needs. Of course if you have any questions about these grid-tie inverters or if you would like us to design a grid-tie solar system for you, please contact us via phone, fax or e-mail. 

 

Manufacturer & model Input  VDC Peak Efficiency AC & DC Disconnects Digital Display Weight  Warranty
SMA SB1800U 156-400 93.6% No Optional 59.4 lbs 5 years
SMA SB2500U 50-600 94.1% No Optional  71 lbs 5 years
SMA SB3800U 200-500 95.6% No Standard 85 lbs 5 years
SMA SB6000U 234-600 >95% No Standard 137 lbs 5 years
Xantrex GT 3.0 195-600 94.6% Yes Standard 45 lbs 5 years ***
Fronius IG 4000 50-450 94.4% Yes Standard 42 lbs 5 years ***
Fronius IG 5100 150-450 94.4% Yes  Standard 42 lbs 5 years ***
PV Powered 2800 200-450 97.6% No Standard 74 lbs 10 years
Sharp JH-3500 110-380 92.4% No Standard**  62 lbs 5 years
*All of the units above have a 240 VAC 60 Hz output with the exception of the SMA SB1800U which has a 120 VAC 60 Hz output. All of the 240 VAC units listed are available for 208V 3-phase applications.

**Sharp’s digital display is designed to be mounted remotely. 

***Optional 10 year warranty available.

For manufacturer's information about these inverters, you can check out these links:

http://www.sma-america.com/index.aspx

http://www.fronius.com/worldwide/usa.solarelectronics/about/index.htm

http://www.xantrex.com/web/id/172/p/1/pt/25/product.asp

http://www.pvpowered.com/inverter_pvp2800.php


   It took 125 years to consume the first trillion barrels of oil; we will likely
 consume the next trillion barrels within just thirty-five years. 

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