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  • #16
    Re: Solar Backup Generator

    well as fast as technology is moving, by the time you measure your roof, figure out how to tie your system into the grid and receive the panels at $1/W, you could be looking at $10,000.

    incentives in places like California will pay for the full system.

    now, after it is installed, find ways to cut back on your usage so you have excess energy to sell to the power companies as everyone's usage goes up as the electric vehicles start filling the roads and you'll be the winner...

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    • #17
      Re: Solar Backup Generator

      Originally posted by Rocky View Post
      you do understand how many of those it would take to run just your refrigerator don't you? the Coleman will light one 60 W bulb during daylight hours which is figured at 7.5 hours for most areas. A large battery can store that for evening use. most energy efficient refrigerators will need at least 250W each hour, 24 hours a day. so you will need ~32 of those panels just to power your fridge each day. So for a little over $10,000 you can buy enough solar panels to keep your food cold. Now measure your roof to see how many panels you can even put on your home...
      If your refrigerator consumes 250 watts on the average, that would be 6 kwh per day (24 hours). That would have to be either an refrigerator of unusual size or a model dating from the 1960s. I have a Maytag 25 cuft refrigerator of 2001 vintage and it consumes slightly under 2 kwh per day. I run that with my small solar system.

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      • #18
        Re: Solar Backup Generator

        Originally posted by Rocky View Post
        well as fast as technology is moving, by the time you measure your roof, figure out how to tie your system into the grid and receive the panels at $1/W, you could be looking at $10,000.

        incentives in places like California will pay for the full system.

        now, after it is installed, find ways to cut back on your usage so you have excess energy to sell to the power companies as everyone's usage goes up as the electric vehicles start filling the roads and you'll be the winner...
        For a 4-6 kw grid tied solar system (without batteries), installed cost after rebates and tax incentives would be $2.50-4.00/watt in most states.

        But, keep in a mind a grid tied solar system is not backup power. The typical grid tied inverter shuts down automatically if grid power goes down. Battery storage is necessary for it to provide backup functionality.

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        • #19
          Re: Solar Backup Generator

          Originally posted by Lizw View Post
          Solar power is a wonderful thing, but it's no substitute for grid power unless you have the money to install a heck of a lot of it, and you can maintain it yourself. I have a friend with a $60,000 grid-tie system he had installed several years ago. His power bill is zero most months, but it will be another five years before the system is fully amortized and his wife won't stay there by herself when he's out of town because something broke one time, the power went out, and she couldn't find anyone to fix it until he got home.
          If your friend has a grid tied solar system, it's failure or shutdown should not make the power go out. That would happen with an off grid system, but not with a grid tied one without batteries.

          Air conditioning is the worst power hog and one that is difficult to substitute for, at least until direct absorption fueled air conditioners become common. Absorption fueled air conditioners use heat (from the sun or other source) to drive the heat pump instead of a electrically powered compressor. In areas that cool off at night, more insulation and thermal mass would reduce air conditioning load, but some places like Phoenix, AZ (where it can often be 100 degrees at midnight) are nearly hopeless unless one wants to live underground or in a cave.

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          • #20
            Re: Solar Backup Generator

            Attached are some quotes for installing a grid tied solar system without batteries in Arizona. That provides an example of the rebate and tax incentives.

            The rule of thumb is a solar system mounted at a fixed angle will produced the rated power for about 2.5 hours per day in the winter and 5.0 hours in the summer. (it's perhaps 10% less at high latitudes) Fixed angle mounts can be mounted to optimize for winter production or for maximum annual total production. A steeper angle increases winter production, but decreases summer production. More grid tied applications just use the angle of the existing roof for aesthetics.
            Attached Files

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            • #21
              Re: Solar Backup Generator

              Originally posted by Zac View Post
              If your friend has a grid tied solar system, it's failure or shutdown should not make the power go out. That would happen with an off grid system, but not with a grid tied one without batteries.
              That's what I thought too, but he said the fault in his system caused the main breaker in his panel to trip.

              Air conditioning is the worst power hog and one that is difficult to substitute for, at least until direct absorption fueled air conditioners become common. Absorption fueled air conditioners use heat (from the sun or other source) to drive the heat pump instead of a electrically powered compressor. In areas that cool off at night, more insulation and thermal mass would reduce air conditioning load, but some places like Phoenix, AZ (where it can often be 100 degrees at midnight) are nearly hopeless unless one wants to live underground or in a cave.
              Only trouble with absorption cooled anything (and I've had plenty of experience with them in refrigerators) is that they're far less fuel-efficient than compressors. But of course if they're solar heated, that's not a concern.

              But I'm always amused at the idea that it's not possible to get by without a/c. I lived in Phoenix once, as it happens, in a small travel trailer with no insulation in the late summer, and the heat didn't kill me. Sleeping at night was less comfortable than if we'd had a/c, but we managed. And I spent my teen and young adult years in Florida, also without a/c. The notion that a/c is somehow a basic human need is a relatively recent one.

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              • #22
                Re: Solar Backup Generator

                Originally posted by Lizw View Post
                That's what I thought too, but he said the fault in his system caused the main breaker in his panel to trip.
                There is likely a design or installation problem with the equipment if that happens. But, there should be a breaker dedicated to the solar grid tie inverter(s). Shutting that breaker will isolate the solar equipment and allow grid power to be restored by resetting the main breaker.

                Only trouble with absorption cooled anything (and I've had plenty of experience with them in refrigerators) is that they're far less fuel-efficient than compressors. But of course if they're solar heated, that's not a concern.

                But I'm always amused at the idea that it's not possible to get by without a/c. I lived in Phoenix once, as it happens, in a small travel trailer with no insulation in the late summer, and the heat didn't kill me. Sleeping at night was less comfortable than if we'd had a/c, but we managed. And I spent my teen and young adult years in Florida, also without a/c. The notion that a/c is somehow a basic human need is a relatively recent one.
                It depends on the climate of a particular location. In San Francisco, or along most of the northern California, Oregon, or Washington cost, AC is not essential. I couldn't survive in Phoenix in the summer without AC. I'm unfortunately very heat sensitive and get sick with migraines and other nasty things when it gets too warm. I currently live in the Sacramento area (101 outside now) and the AC issue has been on my mind the last couple years. I don't think I could survive here in the summer without AC and it's not nearly as severe a climate as Phoenix. This is probably why most of the areas with lousy climates like Phoenix were very sparsely inhabited until AC became affordable and common.

                To run more than the most modest AC system (like a small room air conditioner) would require a large solar system. Running it off grid would require very large batteries. For example, my 3 ton air conditioner eats about 5 kw when the compressor is running. Running a sustained 5 kw load would require around 100 kwh (such as 48V @ 2000 Ah) of batteries if they are to last 10+ years.

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                • #23
                  Re: Solar Backup Generator

                  Originally posted by Zac View Post
                  It depends on the climate of a particular location. In San Francisco, or along most of the northern California, Oregon, or Washington cost, AC is not essential. I couldn't survive in Phoenix in the summer without AC. I'm unfortunately very heat sensitive and get sick with migraines and other nasty things when it gets too warm. I currently live in the Sacramento area (101 outside now) and the AC issue has been on my mind the last couple years. I don't think I could survive here in the summer without AC and it's not nearly as severe a climate as Phoenix. This is probably why most of the areas with lousy climates like Phoenix were very sparsely inhabited until AC became affordable and common.
                  Yes, exactly. Though when I lived there, it was a haven for people with asthma, whose doctors had sent them out there for the dry air.

                  To run more than the most modest AC system (like a small room air conditioner) would require a large solar system. Running it off grid would require very large batteries. For example, my 3 ton air conditioner eats about 5 kw when the compressor is running. Running a sustained 5 kw load would require around 100 kwh (such as 48V @ 2000 Ah) of batteries if they are to last 10+ years.
                  And of course there's the start-up surge. The recent work with capacitors to even that out may help the situation, but absorption units are probably still the way to go in hot humid climates. Or earth-sheltered homes--I have a friend here whose electric bill is almost never more than the minimum, and his home is all-electric. It's also built into a hillside with only two faces exposed.

                  I put up trellis mounted on 4 x 4's along the western face of the 70 foot mobile home I live in, and grow hops and maypops on the trellis. The vines shade the trailer in the summer and die back in the winter so the sun can hit it (I mounted the trellis panels on hooks so I can take them down in the winter). There's about a ten degree differential between the temperature on the sun side and on the shade side, and that really makes a difference in the amount of a/c we use. Given my druthers, I'd turn the a/c off, open the windows and install a solar-powered ventilation fan in the roof, but it's not my property.

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                  • #24
                    Re: Solar Backup Generator

                    Originally posted by Zac View Post
                    Attached are some quotes for installing a grid tied solar system without batteries in Arizona. That provides an example of the rebate and tax incentives.

                    The rule of thumb is a solar system mounted at a fixed angle will produced the rated power for about 2.5 hours per day in the winter and 5.0 hours in the summer. (it's perhaps 10% less at high latitudes) Fixed angle mounts can be mounted to optimize for winter production or for maximum annual total production. A steeper angle increases winter production, but decreases summer production. More grid tied applications just use the angle of the existing roof for aesthetics.
                    so a 5.oi is a 5 KW system costing ~$13K which will produce 25KW in the summer, about half of what a normal household would use?

                    Imagine if the $19,000 in electric company, state and federal incentives were spent a little differently...

                    my 25KW system runs 24/7 expected life 115,000 hours and costs $20K including the grid tie... and that isn't counting what the state will pay in incentives much less the energy being sold to the electric company beyond usage...

                    A 12'x12'x18' room in a school could hold 900+ units and sell enough energy back to the electric company to pay for the school...

                    I'm trying to hurry...

                    PS RV batteries are great backup systems, I have 8. Now if you really want to store some juice, get an electric forklift battery ... weighs half a ton, but it'll power your office...

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                    • #25
                      Re: Solar Backup Generator

                      Originally posted by Lizw View Post
                      And of course there's the start-up surge. The recent work with capacitors to even that out may help the situation,
                      Ultracapacitors for the electricity you will need are outrageously expensive...

                      They load up quick and discharge instantly, perfect for applications like electric trains but still way to pricey for a household...

                      Comment


                      • #26
                        Re: Solar Backup Generator

                        I thought this was a serious thread, not the fantasy room.
                        Rocky, IF you have the solution to the the world's energy and economic needs, get serious and save the planet. I'll quit my job and help you! We'll be rich and famous.

                        Of course, the earth might explode because we are sucking away the gravity flux, but we'll be long gone by then!

                        Comment


                        • #27
                          Re: Solar Backup Generator

                          Originally posted by Rocky View Post
                          Ultracapacitors for the electricity you will need are outrageously expensive...

                          They load up quick and discharge instantly, perfect for applications like electric trains but still way to pricey for a household...
                          Ultracaps are not suitable for mass energy storage because they don't provide energy density (kwh/pound) that is competitive with conventional chemical batteries. They are not needed for a typical off-grid solar power system as adequately sized batteries would provide plenty of surge current capacity. A adequately sized inverter should also have enough surge capacity to handle motor starting and so forth. Keep in mind a small to medium sized inverter as might be found in a typical off grid solar system does not have the surge current capacity of the utility grid so some short duration (milliseconds to perhaps a few tenths of a second) voltage drop and waveform distortion when starting motors is expected. Most electronics are not sensitive to this. If you have electronics that is, the easiest solution is run those items on a separate inverter.

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                          • #28
                            Re: Solar Backup Generator

                            Originally posted by Flufreak View Post
                            I thought this was a serious thread, not the fantasy room.
                            Rocky, IF you have the solution to the the world's energy and economic needs, get serious and save the planet. I'll quit my job and help you! We'll be rich and famous.

                            Of course, the earth might explode because we are sucking away the gravity flux, but we'll be long gone by then!

                            lol... when someone asks what I am using I always say gravity because it spins their mind with the possibilities...

                            I've been working on grants for several years and always end up getting kicked out in the final decision...

                            I'm getting closer to final prototype funding I've raised on my own...

                            once it is complete, it will be a few months before full production...

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                            • #29
                              Re: Solar Backup Generator

                              Zac, you are pretty knowledgeable on electricity, what is the Maximum power that can be sent from a Home into the grid without overheating the lines?

                              each unit maxes out the grid tie inverter - 25KW 220V

                              separate circuit for each unit going into the power box...

                              Comment


                              • #30
                                Re: Solar Backup Generator

                                Originally posted by Rocky View Post
                                Zac, you are pretty knowledgeable on electricity, what is the Maximum power that can be sent from a Home into the grid without overheating the lines?
                                That varies depending on your utility feed. For instance, my house has a 200 amp feed. So, 240V @ 200A is 48 kW which would be the best case. Older houses may have smaller feeds. The limiting factor is usually the transformer in the street. The transformers are rarely, if ever, specified for 100% duty cycle at 100% rated load so every house sending the maximum rated power upstream for hours will probably overheat the transformer. But, few of us can afford or even have space to mount a 48 kW solar system.

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