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Grid-Tie with Battery Back-Up

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  • Chris Boyer
    Grid Tie PV systems with battery back up are a solution worth looking into for homes.   A grid-tie PV system most economically generates solar electricity,
    Message 1 of 5 , Nov 1, 2008
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      Grid Tie PV systems with battery back up are a solution worth looking into for homes.
       
      A grid-tie PV system most economically generates solar electricity, running about $8,000 per rated kW size (and each rated kW makes about 1250 kWh per year in Houston).  However, when the grid goes down, the system goes down with it.
       
      To keep the lights on during a power outage, your options are a back-up generator, or a battery back-up solar system. 
       
      GENERATORS
      A portable gasoline generator works well and conomically (~$800 for 5 kW) to keep the fridge and some lights on for the occational long term outage - if you can find 10 gallons of gasoline every day and if you don't poison yourself with carbon monoxide. 
       
      A permanant natural gas generator with an automatic transfer switch is an elegant solution to keep the whole house running (including AC) .  Reliable ones run from $10,000 (15 kW) to $30,000 (45 kW) installed (requires plumbing & electrical permits).  There is about a 30 second delay between the time the grid goes down and the time the generator starts powering the house.
       
      PV grid-tie systems will not work with most back-up generators - I tried it.  It doesn't work because the sine wave and voltage limits of generators are not "grid" quality.  There are high-end, electronic governered generators that may sync with a PV system, but there still needs to be a dump load for excess PV power. 
       
      SOLAR GRID TIE wtih BATTERY BACK UP
      Grid-Tie solar with battery back-up will run about $12,000 per rated kW of solar power.  The power output of the inverter in not the same as the rated solar power, usually it is sized to be almost double.  Loads powered by a battery back-up system will not see any outage when the grid goes down - the switch is instantaneous.  SMA, Outback and Xantrex have good equipment for this purpose.
       
      The recent tax credit makes back-up systems economically attractive.  Look at the following example:
       
      CASE A: 
      PV Grid-Tie Cost:  $28,000  for a 3.5kW (no batteries)
      Generator Cost:   $12,000  for a 18 kW nat gas generator
      PV  Tax Credit:  - ($8,400)
      NET Cost: $31,600
       
      CASE B:
      PV Grid-Tie/Back-up:  $42,000  (including batteries)
      PV Tax Credit: -($12,600)
      NET Cost: $29,400
       
      So, as you can see, if you are thinking about solar and you want back-up power, then a battery back-up system is the way to go.
       
      Sizing your system is a simple excercise, but does take some work and expertise.  Designing and installing a system to integrate into the home takes real expertise - ask for experience and references when choosing a contractor.
       
      Sincerely,
      Chris Boyer
       
       
       
       
       
       
       
       
       
       
    • Stephanie Edwards-Musa
      Chris, Your email reminded me of an article I read yesterday. Solar credit changes the math for homeowners I don t agree with everything in the article, but
      Message 2 of 5 , Nov 1, 2008
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        Chris,

        Your email reminded me of an article I read yesterday.  'Solar credit changes the math for homeowners'

        I don't agree with everything in the article, but it does have some very interesting information.

        http://ecotech.financetech.com/blog/archives/2008/10/solar_credit_ch.html

        On Sat, Nov 1, 2008 at 10:17 AM, Chris Boyer <boyer.chris@...> wrote:

        Grid Tie PV systems with battery back up are a solution worth looking into for homes.
         
        A grid-tie PV system most economically generates solar electricity, running about $8,000 per rated kW size (and each rated kW makes about 1250 kWh per year in Houston).  However, when the grid goes down, the system goes down with it.
         
        To keep the lights on during a power outage, your options are a back-up generator, or a battery back-up solar system. 
         
        GENERATORS
        A portable gasoline generator works well and conomically (~$800 for 5 kW) to keep the fridge and some lights on for the occational long term outage - if you can find 10 gallons of gasoline every day and if you don't poison yourself with carbon monoxide. 
         
        A permanant natural gas generator with an automatic transfer switch is an elegant solution to keep the whole house running (including AC) .  Reliable ones run from $10,000 (15 kW) to $30,000 (45 kW) installed (requires plumbing & electrical permits).  There is about a 30 second delay between the time the grid goes down and the time the generator starts powering the house.
         
        PV grid-tie systems will not work with most back-up generators - I tried it.  It doesn't work because the sine wave and voltage limits of generators are not "grid" quality.  There are high-end, electronic governered generators that may sync with a PV system, but there still needs to be a dump load for excess PV power. 
         
        SOLAR GRID TIE wtih BATTERY BACK UP
        Grid-Tie solar with battery back-up will run about $12,000 per rated kW of solar power.  The power output of the inverter in not the same as the rated solar power, usually it is sized to be almost double.  Loads powered by a battery back-up system will not see any outage when the grid goes down - the switch is instantaneous.  SMA, Outback and Xantrex have good equipment for this purpose.
         
        The recent tax credit makes back-up systems economically attractive.  Look at the following example:
         
        CASE A: 
        PV Grid-Tie Cost:  $28,000  for a 3.5kW (no batteries)
        Generator Cost:   $12,000  for a 18 kW nat gas generator
        PV  Tax Credit:  - ($8,400)
        NET Cost: $31,600
         
        CASE B:
        PV Grid-Tie/Back-up:  $42,000  (including batteries)
        PV Tax Credit: -($12,600)
        NET Cost: $29,400
         
        So, as you can see, if you are thinking about solar and you want back-up power, then a battery back-up system is the way to go.
         
        Sizing your system is a simple excercise, but does take some work and expertise.  Designing and installing a system to integrate into the home takes real expertise - ask for experience and references when choosing a contractor.
         
        Sincerely,
        Chris Boyer
         
         
         
         
         
         
         
         
         
         



        --
        Stephanie Edwards-Musa
        Realtor, Certified EcoBroker
        Mobile:  281-635-9444
        Prudential Gary Greene, Realtors
        www.TurningHoustonGreen.com
        Steph@...
      • Russell Warren
        I think this example is missing some key elements. #1 very few solar systems are sized for a households daily needs (even without including AC) Therefore a
        Message 3 of 5 , Nov 1, 2008
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          I think this example is missing some key elements.
          #1 very few solar systems are sized for a households daily needs (even without including AC)
          Therefore a battery backup system is also unlikely to provide the needs of the household.
           
          Furthermore there is a time factor...yes for a blip or even an hour, the system will be fine, but then again my food won't go bad in just an hour either.
           
          Lets say you have the worst case scenario like the hurricane.  Even if you are without power for (only) 3 days, a solar power backup system is unlikely to sustain that kind of downtime.  You have no charging at night, and during the day, your collected energy is re-charging the battery system...and you won't have spare power for actually running your house.
           
          On the flip side, your natural gas generator is going to last a lot longer for those folks who have a natural gas line running to their house.  It will run day and night in this scenario, and provide a ton of power.
           
          I just think for the money, you are better off getting the gas generator, if you need that, or buying a bigger solar system for the 360+ days you are going to be grid tied.
          If my power goes down, I will just rough it.  I can replace the contents of my fridge about 50 times before it would equal the investment of a generator or backup.
           
           
          -----Original Message-----
          From: hreg@yahoogroups.com [mailto:hreg@yahoogroups.com]On Behalf Of Chris Boyer
          Sent: Saturday, November 01, 2008 10:17 AM
          To: HREG
          Subject: [hreg] Grid-Tie with Battery Back-Up

          Grid Tie PV systems with battery back up are a solution worth looking into for homes.
           
          A grid-tie PV system most economically generates solar electricity, running about $8,000 per rated kW size (and each rated kW makes about 1250 kWh per year in Houston).  However, when the grid goes down, the system goes down with it.
           
          To keep the lights on during a power outage, your options are a back-up generator, or a battery back-up solar system. 
           
          GENERATORS
          A portable gasoline generator works well and conomically (~$800 for 5 kW) to keep the fridge and some lights on for the occational long term outage - if you can find 10 gallons of gasoline every day and if you don't poison yourself with carbon monoxide. 
           
          A permanant natural gas generator with an automatic transfer switch is an elegant solution to keep the whole house running (including AC) .  Reliable ones run from $10,000 (15 kW) to $30,000 (45 kW) installed (requires plumbing & electrical permits).  There is about a 30 second delay between the time the grid goes down and the time the generator starts powering the house.
           
          PV grid-tie systems will not work with most back-up generators - I tried it.  It doesn't work because the sine wave and voltage limits of generators are not "grid" quality.  There are high-end, electronic governered generators that may sync with a PV system, but there still needs to be a dump load for excess PV power. 
           
          SOLAR GRID TIE wtih BATTERY BACK UP
          Grid-Tie solar with battery back-up will run about $12,000 per rated kW of solar power.  The power output of the inverter in not the same as the rated solar power, usually it is sized to be almost double.  Loads powered by a battery back-up system will not see any outage when the grid goes down - the switch is instantaneous.  SMA, Outback and Xantrex have good equipment for this purpose.
           
          The recent tax credit makes back-up systems economically attractive.  Look at the following example:
           
          CASE A: 
          PV Grid-Tie Cost:  $28,000  for a 3.5kW (no batteries)
          Generator Cost:   $12,000  for a 18 kW nat gas generator
          PV  Tax Credit:  - ($8,400)
          NET Cost: $31,600
           
          CASE B:
          PV Grid-Tie/Back- up:  $42,000  (including batteries)
          PV Tax Credit: -($12,600)
          NET Cost: $29,400
           
          So, as you can see, if you are thinking about solar and you want back-up power, then a battery back-up system is the way to go.
           
          Sizing your system is a simple excercise, but does take some work and expertise.  Designing and installing a system to integrate into the home takes real expertise - ask for experience and references when choosing a contractor.
           
          Sincerely,
          Chris Boyer
           
           
           
           
           
           
           
           
           
           

        • Jay Ring
          Russell, You make a good point. If you size a solar install for, say, 75% of your normal use (as a grid tie usually does), when the battery doesn t help much
          Message 4 of 5 , Nov 1, 2008
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            Russell,

            You make a good point.

            If you size a solar install for, say, 75% of your normal use (as a
            grid tie usually does), when the battery doesn't help much because you
            depend on external power. Batteries never charge since you are still
            a net-consumer. If you are going to depend on external power, you
            might as well just depend on a generator.

            I think I might have to reluctantly agree that if you have an
            undersized system, money might be better spent buying extra panels
            before adding batteries and counting on a generator in an emergency,
            but I am not 100% sure yet.

            One thing to consider is buying just one day worth of batteries, so
            that the solar can operate about 1/2 of your house, or maybe just the
            refrigerator. That way you don't lose the entire benefit during that
            duration. Then instead of sizing your battery bank for the worst
            expected case of cloudy days, you are just sizing it for one
            refrigerator and maybe a TV after a storm. Might be cheaper than a
            generator after all.

            One thing that analysis leaves out is that power outage is not the
            only risk solar can protect you from. Solar also reduces the risk
            from rising energy prices which is a big part of my reason for buying!
            That would tend to push you even further towards "extra panels before
            batteries".

            Anyone else have any thoughts on this? The more I think about it the
            more complex it seems :)



            --- In hreg@yahoogroups.com, "Russell Warren" <rrwarren@...> wrote:
            >
            > I think this example is missing some key elements.
            > #1 very few solar systems are sized for a households daily needs (even
            > without including AC)
            > Therefore a battery backup system is also unlikely to provide the
            needs of
            > the household.
            >
            > Furthermore there is a time factor...yes for a blip or even an hour, the
            > system will be fine, but then again my food won't go bad in just an hour
            > either.
            >
            > Lets say you have the worst case scenario like the hurricane. Even
            if you
            > are without power for (only) 3 days, a solar power backup system is
            unlikely
            > to sustain that kind of downtime. You have no charging at night,
            and during
            > the day, your collected energy is re-charging the battery
            system...and you
            > won't have spare power for actually running your house.
            >
            > On the flip side, your natural gas generator is going to last a lot
            longer
            > for those folks who have a natural gas line running to their house.
            It will
            > run day and night in this scenario, and provide a ton of power.
            >
            > I just think for the money, you are better off getting the gas
            generator, if
            > you need that, or buying a bigger solar system for the 360+ days you are
            > going to be grid tied.
            > If my power goes down, I will just rough it. I can replace the
            contents of
            > my fridge about 50 times before it would equal the investment of a
            generator
            > or backup.
            >
            >
            > -----Original Message-----
            > From: hreg@yahoogroups.com [mailto:hreg@yahoogroups.com]On Behalf
            Of Chris
            > Boyer
            > Sent: Saturday, November 01, 2008 10:17 AM
            > To: HREG
            > Subject: [hreg] Grid-Tie with Battery Back-Up
            >
            >
            > Grid Tie PV systems with battery back up are a solution worth
            > looking into for homes.
            >
            > A grid-tie PV system most economically generates solar
            electricity,
            > running about $8,000 per rated kW size (and each rated kW makes
            about 1250
            > kWh per year in Houston). However, when the grid goes down, the
            system goes
            > down with it.
            >
            > To keep the lights on during a power outage, your options are a
            > back-up generator, or a battery back-up solar system.
            >
            > GENERATORS
            > A portable gasoline generator works well and conomically
            (~$800 for
            > 5 kW) to keep the fridge and some lights on for the occational long term
            > outage - if you can find 10 gallons of gasoline every day and if you
            don't
            > poison yourself with carbon monoxide.
            >
            > A permanant natural gas generator with an automatic transfer
            switch
            > is an elegant solution to keep the whole house running (including AC) .
            > Reliable ones run from $10,000 (15 kW) to $30,000 (45 kW) installed
            > (requires plumbing & electrical permits). There is about a 30
            second delay
            > between the time the grid goes down and the time the generator starts
            > powering the house.
            >
            > PV grid-tie systems will not work with most back-up
            generators - I
            > tried it. It doesn't work because the sine wave and voltage limits of
            > generators are not "grid" quality. There are high-end, electronic
            > governered generators that may sync with a PV system, but there
            still needs
            > to be a dump load for excess PV power.
            >
            > SOLAR GRID TIE wtih BATTERY BACK UP
            > Grid-Tie solar with battery back-up will run about $12,000
            per rated
            > kW of solar power. The power output of the inverter in not the same
            as the
            > rated solar power, usually it is sized to be almost double. Loads
            powered
            > by a battery back-up system will not see any outage when the grid goes
            > down - the switch is instantaneous. SMA, Outback and Xantrex have good
            > equipment for this purpose.
            >
            > The recent tax credit makes back-up systems economically
            attractive.
            > Look at the following example:
            >
            > CASE A:
            > PV Grid-Tie Cost: $28,000 for a 3.5kW (no batteries)
            > Generator Cost: $12,000 for a 18 kW nat gas generator
            > PV Tax Credit: - ($8,400)
            > NET Cost: $31,600
            >
            > CASE B:
            > PV Grid-Tie/Back-up: $42,000 (including batteries)
            > PV Tax Credit: -($12,600)
            > NET Cost: $29,400
            >
            > So, as you can see, if you are thinking about solar and you want
            > back-up power, then a battery back-up system is the way to go.
            >
            > Sizing your system is a simple excercise, but does take some
            work
            > and expertise. Designing and installing a system to integrate into
            the home
            > takes real expertise - ask for experience and references when choosing a
            > contractor.
            >
            > Sincerely,
            > Chris Boyer
            >
          • Gary Beck
            This is an interesting discussion with lots of great comments and useful information. Here are more food-for-thought comments. Current events and trends are
            Message 5 of 5 , Nov 1, 2008
            • 0 Attachment

              This is an interesting discussion with lots of great comments and useful information. Here are more food-for-thought comments.

               

              Current events and trends are making people finally start thinking more about self-sufficiency. The market will react and follow this trend.  Forward-thinking home designer/builders in grid loss areas will start to include standard Solar PV systems plus natural gas standby generators as ‘standard appliances’ for new homes. The ones that push the envelope will even offer other self-sufficiency options such as rooftop hydroponic vegetable gardens above the garage. The garage will likely become a home’s utility/mechanical center for residential energy, recycling, and self-sufficiency efforts.  Designers and builders that don’t follow such trends may lose standing due to a perceived lack of innovation.  

               

              From: hreg@yahoogroups.com [mailto:hreg@yahoogroups.com] On Behalf Of Russell Warren
              Sent: Saturday, November 01, 2008 1:09 PM
              To: hreg@yahoogroups.com
              Subject: RE: [hreg] Grid-Tie with Battery Back-Up

               

              I think this example is missing some key elements.

              #1 very few solar systems are sized for a households daily needs (even without including AC)

              Therefore a battery backup system is also unlikely to provide the needs of the household.

               

              Furthermore there is a time factor...yes for a blip or even an hour, the system will be fine, but then again my food won't go bad in just an hour either.

               

              Lets say you have the worst case scenario like the hurricane.  Even if you are without power for (only) 3 days, a solar power backup system is unlikely to sustain that kind of downtime.  You have no charging at night, and during the day, your collected energy is re-charging the battery system...and you won't have spare power for actually running your house.

               

              On the flip side, your natural gas generator is going to last a lot longer for those folks who have a natural gas line running to their house.  It will run day and night in this scenario, and provide a ton of power.

               

              I just think for the money, you are better off getting the gas generator, if you need that, or buying a bigger solar system for the 360+ days you are going to be grid tied.

              If my power goes down, I will just rough it.  I can replace the contents of my fridge about 50 times before it would equal the investment of a generator or backup.

               

               

              -----Original Message-----
              From: hreg@yahoogroups.com [mailto:hreg@yahoogroups.com]On Behalf Of Chris Boyer
              Sent: Saturday, November 01, 2008 10:17 AM
              To: HREG
              Subject: [hreg] Grid-Tie with Battery Back-Up

              Grid Tie PV systems with battery back up are a solution worth looking into for homes.

               

              A grid-tie PV system most economically generates solar electricity, running about $8,000 per rated kW size (and each rated kW makes about 1250 kWh per year in Houston).  However, when the grid goes down, the system goes down with it.

               

              To keep the lights on during a power outage, your options are a back-up generator, or a battery back-up solar system. 

               

              GENERATORS

              A portable gasoline generator works well and conomically (~$800 for 5 kW) to keep the fridge and some lights on for the occational long term outage - if you can find 10 gallons of gasoline every day and if you don't poison yourself with carbon monoxide. 

               

              A permanant natural gas generator with an automatic transfer switch is an elegant solution to keep the whole house running (including AC) .  Reliable ones run from $10,000 (15 kW) to $30,000 (45 kW) installed (requires plumbing & electrical permits).  There is about a 30 second delay between the time the grid goes down and the time the generator starts powering the house.

               

              PV grid-tie systems will not work with most back-up generators - I tried it.  It doesn't work because the sine wave and voltage limits of generators are not "grid" quality.  There are high-end, electronic governered generators that may sync with a PV system, but there still needs to be a dump load for excess PV power. 

               

              SOLAR GRID TIE wtih BATTERY BACK UP

              Grid-Tie solar with battery back-up will run about $12,000 per rated kW of solar power.  The power output of the inverter in not the same as the rated solar power, usually it is sized to be almost double.  Loads powered by a battery back-up system will not see any outage when the grid goes down - the switch is instantaneous.  SMA, Outback and Xantrex have good equipment for this purpose.

               

              The recent tax credit makes back-up systems economically attractive.  Look at the following example:

               

              CASE A: 

              PV Grid-Tie Cost:  $28,000  for a 3.5kW (no batteries)

              Generator Cost:   $12,000  for a 18 kW nat gas generator

              PV  Tax Credit:  - ($8,400)

              NET Cost: $31,600

               

              CASE B:

              PV Grid-Tie/Back-up:  $42,000  (including batteries)

              PV Tax Credit: -($12,600)

              NET Cost: $29,400

               

              So, as you can see, if you are thinking about solar and you want back-up power, then a battery back-up system is the way to go.

               

              Sizing your system is a simple excercise, but does take some work and expertise.  Designing and installing a system to integrate into the home takes real expertise - ask for experience and references when choosing a contractor.

               

              Sincerely,

              Chris Boyer

               

               

               

               

               

               

               

               

               

               

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