Grid-Tie Power Systems

The terms grid-tie, grid interactive, and net metering all loosely refer to a power generating system (solar, wind, hydro-electric, or other) that is somehow connected to the electrical power distribution network ("the grid") in a way that allows the system to feed electricity into the grid.  This is a long-winded explanation for "spin your meter backwards", which seems to be a common, and often misleading, phrase these days.

There are good reasons for owning a grid-tie system for your home or business, and today's lower prices for solar power equipment make the payback time a lot more realistic.  If your only objective is to save money on your power bill, consider that the break-even point for your installation might well exceed a decade.  Tax incentives can make a major impact on the installed cost of your system, but you need to have a tax burden to reap the rewards of these incentives.  The payback time on your investment is directly related to the price that you pay for electricity, and therefore gets shorter as electricity costs rise. For now, grid-tie systems have to be seen realistically as a long-term investment.  It is also important to note that a simple grid-tie solar power system becomes inactive whenever the utility grid is offline. So no matter how many solar panels you have installed, you home will be as dark as the neighbor's house when the utility power is out. To lower your power bill, it is much more cost-effective to save or conserve energy by upgrading doors, windows and insulation.  Buy energy-efficient appliances and lighting, and make an effort to waste less power.  Buy a Kill-a-Watt Meter for just $38 to find out exactly how much energy your appliances use.


What about when the grid fails?  If you are in an area where grid power is present but unreliable, or you are concerned about the long-term stability of the utility grid,  a grid-tie with battery backup  system might be a smart choice. This is a grid-tie solar power that stores electricity in batteries for use when the utility is offline.  The solar array keeps the battery charged and sells any excess power to the utility. When utility power is not available, it functions as a completely independent electric power system. Electrical power is always available without interruption for computers, refrigeration, lighting, and other "critical loads".  The limitation of this type of system is that in most homes the central inverter is not capable of powering the entire household to the same capacity as the utility grid, so the "critical loads" are usually separated electrically from the other circuits of the house. This usually requires a bit of professional rewiring at the circuit breaker box, but when the utility power is out the most important functions of your home will still be operational. If this sounds like the system that you need, call us and we'll probably recommend the proven Xantrex XW system. We custom design these solar electric systems to meet your needs. Solar panels + inverter + charge controller + batteries = working system.

Another choice would be for emergency, standby, or backup power.  This system differs from the one just mentioned because it does not use a solar array or any other energy collection source.  It simply consists of batteries and power inverter.  The grid keeps the batteries charged.  When the grid goes down, the inverter is instantly activated and your home is running on battery power without interruption.  This system can be designed to carry you through short to moderate outages if your power usage is conservative.  The main distinction to this system is that it does not produce energy in any way, and it is the least expensive type of system. Add a propane or diesel generator to this system and you have a longer-term solution. The generator powers the bigger household needs and recharges batteries simultaneously. The battery then provides electricity when the generator isn't running. This makes the system more efficient, provides electricity day and night, and saves enormously on generator fuel. These simple power systems are easy to get going, and most have the capability of adding solar panels either now or later. Contact us for details.  Batteries + inverter + generator = working system.


Probably the best reason to own a grid-tie system is because it eases the load on the power grid and reduces our national consumption of finite energy sources.  By producing your own clean electricity you are doing a good thing for our planet and mankind.  There is much talk about a "smart grid" where all of the grid-tie systems in the USA would be monitored through the internet, giving utilities better control of their energy resources.  Some of that technology is available today, though widespread implementation of smart grid is still in the future.  But it is very important to know that simple grid-tie systems stop working when the utility power fails.  That means during a power outage, your home will be without power of any kind and your solar panels will be useless until the grid is energized again. I find this to be a peculiar irony.  The primary advantage to a straight grid-tie system is it's simplicity and lower cost. If this sounds like what you need, keep reading and watch the Enphase videos below. We rely on Enphase inverters for our simple grid-tie systems: solar panels + grid-tie inverter = working system.

For the handyman types out there, or anyone interested in a simple grid-tie installation, there's the Enphase system. Enphase uses one micro inverter for each solar panel, making the entire installation very easy and eliminating the need for potentially dangerous, high-voltage DC circuits.  A homeowner can successfully install the simple plug-and-play Enphase system. In most states, connecting your power system to the grid requires approval from your utility, local permits, and final connection by an electrician licensed in your state.  There may be other requirements. The simplicity of Enphase also provides a convenient way to get a ballpark idea of grid-tie costs. The following formula is for a simple enphase grid-tie system using Enphase inverters, USA-made 225 watt or 230 watt solar panels, and mounting structure (roof or pole mount):

1. Check your monthly utility bill to see how many Kilowatt-hours of electricity you use on an average month. (example: 900 KWh per month)
2. Divide that number by 30 to see how many kilowatt-hours you use in a typical day. (900/30 = 30 KWh per day)
3. Multiply the number of KWh per day times $1,000 to find the total cost for the equipment needed without labor costs. (30 x $1,000 = $30,000)
   

These numbers are only estimates. Your final installation costs will vary depending on how you choose to mount the solar array, and special construction costs that may apply to your installation. How much average energy harvest you get will be influenced by several factors:

1. Latitude. This has an effect on the number of hours of sun you receive on an annual average.
2. Climate. Areas with generally sunnier climates will have more days of useful energy harvest in an average year.
3. Solar array mounting. Northern climates benefit from pole-mounted arrays where the array can be adjusted for seasonal sun angles, and so the solar panels can be cleared of snow in winter. Warmer climates in lower latitudes offer good performance with roof mounted arrays, but performance can be increased substantially with pole-mounted solar tracking systems.
   

ENPHASE GRID-TIE COMPONENTS	VOLTAGE	PRICE
M190 for MC4 connections	240	$190
M190 for TYCO connections	240	$170
EMU Energy Management Unit		$320
Branch circuit connection kit	240	$70
Typical 230 watt solar panel (spring/summer 2011 prices)		$560-$660

Enphase  is a great way to build your grid-interactive system.  With Enphase, there is a separate micro-inverter for each solar panel, and they plug together in a series string. It is impossible to connect the inverters incorrectly. We usually specify 220 to 230 watt USA-made solar panels for Enphase installations. Although each Enphase inverter is capable of only 190 watts output they will work with panels up to 230 watts. The extra panel wattage provides better performance in morning and evening hours and on cloudy days, giving the system better overall performance and greater average electrical yield.  One solar panel, one Enphase inverter, and the required mounting structure bring the overall cost to about $1000 per panel/inverter/mount unit. Each string of 15 solar panels requires an Enphase branch circuit kit for about $70.  Since the system is modular, you can potentially start with a single solar panel, and more solar panel/inverter pairs can be added easily to increase output.  If you want to start with a large array, let us quote a complete system price for you, with shipping costs included.  This is about as simple as solar can get!  The Enphase EMU Energy Management Unit communications gateway is easily installed to connect your system to the internet to monitor your energy production from any internet-connected computer.  Envoy comes with a 90-day subscription to the Enlighten website, which is required for viewing data. It is said that a picture is worth a thousand words, but sometimes a video is even better, so we have included a couple of official Enphase videos below.

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