Feed wire size

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  • lockem
    Junior Member
    • Mar 2024
    • 14

    Feed wire size

    As part of a study of my system I observed the 1.8V * 20A power loss on my 40 foot run of 10gauge wire doesn't sound like a lot of loss, but the incremental cost to have installed 8ga wire instead has a ROI of only 3 years. This ROI is constant for any length run; it is only dependent on the 20A current value and the local cost of electricity. AC or DC does not alter the calculation either.

    I did the upgrade retroactively and indeed the Sunpower monitoring system consistently shows an increase in maximum power of 20W. Even as a retrofit the ROI on the materials is 5-6 years, although I already had a spool just lying around.

    I suspect that going 1 size over size for the wires will have a similar benefit for any configuration, but did not bother to research the numbers.

    So, do any installers out there bother making this calculation?
    Last edited by lockem; 03-12-2024, 12:36 AM.
  • bcroe
    Solar Fanatic
    • Jan 2012
    • 5203

    #2
    My installer did not, but I did. Both my DC and AC feed loops are
    at least 600 ft long. That resulted in an acceptable 1% loss for the
    DC loop, operating at 400V. The AC loop loss was over 3%, which
    besides losing a lot of energy and doing a warm up/cool down cycle
    every sunny day, sometimes would trip inverter line voltage monitors.
    I eventually reduced the AC lose to 1% using greatly oversized but
    economical aluminum direct burial wire. That was the only large
    expense, since I had my own trencher. Bruce Roe

    Comment

    • lockem
      Junior Member
      • Mar 2024
      • 14

      #3
      Originally posted by bcroe
      My installer did not, but I did. Both my DC and AC feed loops are
      at least 600 ft long. That resulted in an acceptable 1% loss for the
      DC loop, operating at 400V. The AC loop loss was over 3%, which
      besides losing a lot of energy and doing a warm up/cool down cycle
      every sunny day, sometimes would trip inverter line voltage monitors.
      I eventually reduced the AC lose to 1% using greatly oversized but
      economical aluminum direct burial wire. That was the only large
      expense, since I had my own trencher. Bruce Roe
      But did you check the cost-benefit analysis, particularly for an even larger wire size?

      In my case the run is 40feet, for 80 feet of wire. For 10ga wire that yields 0.08 ohms of resistance. For 8ga wire that yields 0.05 ohms. At 20.8A RMS that my system produces the power loss = I^2*R is 34.6 watts for 10ga and 21.6 watts for 8ga. The difference is 13watts. My system puts out 4400W, so that is only a 0.3% improvement.

      However, 80 feet of copper 10ga THHN costs about $30 and 80 feet of 8ga TNNN costs about $45 (both prices from these guys: https://www.wireandcableyourway.com/...SABEgLcP_D_BwE) , a difference of only $15. Rounding down, my ground mount system cost $30,000, so the incremental cost of the wire upgrade is a meager 0.05% of the total system cost. It is bound to have a shorter pay off time.

      In my case I have an average of about 5 sun/hours per day and electricity that costs $0.23/kwh. The value of the power is 13*5*365*0.23/1000 = $5.45.
      $15/$5.45 => 2.75 years to break even, at least if you are on NEM1 or NEM2.

      Comment

      • bcroe
        Solar Fanatic
        • Jan 2012
        • 5203

        #4
        More owners should do the analysis you have done. My project starting
        requirements were:
        Reduce AC transmission losses to 1/4
        Use hardware no larger that 200A breaker boxes and 2in conduit
        Not spend thousands on wire.

        To answer your questions...

        The obvious benefit of my upgrade was some 800 kWh extra annual
        energy, without any other change. This helped me run more
        equipment on my generation, such as frequent air circulation for
        evening out heat and fully utilizing my electronic air filter, and
        keeping another building comfortable year around. It will eventually
        help compensate for reduced aging panel output. Note, under good
        sun my inverters run at capacity for 8 hours straight, not 5.

        Here in IL I am not under NEM1 or NEM2.

        With reduced voltages, I no longer have to worry about voltage monitor
        tripouts. Those could be a real problem if my current (11 year old)
        inverters (15kW) were replaced with a different model.

        The major expense for the project was $650 delivered for 300 ft of
        direct burial 4/0 aluminum triplex. It hardly seemed worth trying to
        save a fraction with smaller wire, if all the labor was going to be the
        same. It also helped justify my 2 year earlier purchase of a trencher,
        its long term goal to allow easy trenching on many projects (5 so far)
        without all that strain on my back. It also reduced the width of digging
        to only 3 in, way less dirt to deal with than with a shovel.

        Going for even bigger wire could only save a bit of my 1% loss, but
        would violate my requirement of being physically able to fit into 2in
        conduit inside buildings.

        The project also added a ground wire between buildings, bringing
        the 70s code installation up to date, and fitting into some future ideas.
        And it let me bury a backup Cat5 cable to my radio tower, the original
        cable that supplies my critical internet connection is older and not
        buried deeply enough. It put to work a massive (4 position) 100A
        breaker that had earlier been decommisioned in anticipation.

        I do not know if there can be a cost-benefit analysis of these factors,
        I do not care. The idea of the PV science project was to free me of
        getting the finger from the fossil fuel cos, at a cost I could afford.
        Eliminating electric energy bills is another benefit. Bruce Roe
        Last edited by bcroe; 03-17-2024, 02:18 PM.

        Comment

        • lockem
          Junior Member
          • Mar 2024
          • 14

          #5
          Sun hours is the average amount of sunlight per day, for the entire year:

          TOTAL_SUN_HOURS_IN_ONE_YEAR/365

          The expected value in Illinois is 4.4hours per day. The expected value in the high desert in California is 5-5.5, although that fails to consider raised solar intensity due to reflections off snow covered cliffs and high altitude dry air. The highest in the country is 6. I believe that getting 7 hours at max output is a symptom of an undersized inverter. Based on your numbers, your system is 3 times the size of mine, but produces less than twice as much energy. Part of that is due to location, but some of it is also likely due to an undersized inverter.

          To estimate return on investment in units of time compute

          (cost of upgrade)/(value of electricity saved in a year)

          It is a straightforward computation. It should be done by system installers when they quote the system.

          In your case it seems unlikely that upgrading a 4/0 cables would be economic as it would cost at least several hundred dollars and likely increase electricity production by $20/year. At some point running higher voltage via transformers is going to be less expensive than heavier cables.

          In my case I reduced my loss from 0.011%/foot to 0.007%/foot. Over your 600 foot run that would be an improvement from 6.6% to 4.2%. Since you were already at 4% loss, the level of wire upgrade that I was discussing was already present in your system before you made any changes.

          Comment

          • J.P.M.
            Solar Fanatic
            • Aug 2013
            • 14939

            #6
            Originally posted by lockem
            Sun hours is the average amount of sunlight per day, for the entire year:

            TOTAL_SUN_HOURS_IN_ONE_YEAR/365

            The expected value in Illinois is 4.4hours per day. The expected value in the high desert in California is 5-5.5, although that fails to consider raised solar intensity due to reflections off snow covered cliffs and high altitude dry air. The highest in the country is 6. I believe that getting 7 hours at max output is a symptom of an undersized inverter. Based on your numbers, your system is 3 times the size of mine, but produces less than twice as much energy. Part of that is due to location, but some of it is also likely due to an undersized inverter.

            To estimate return on investment in units of time compute

            (cost of upgrade)/(value of electricity saved in a year)

            It is a straightforward computation. It should be done by system installers when they quote the system.

            In your case it seems unlikely that upgrading a 4/0 cables would be economic as it would cost at least several hundred dollars and likely increase electricity production by $20/year. At some point running higher voltage via transformers is going to be less expensive than heavier cables.

            In my case I reduced my loss from 0.011%/foot to 0.007%/foot. Over your 600 foot run that would be an improvement from 6.6% to 4.2%. Since you were already at 4% loss, the level of wire upgrade that I was discussing was already present in your system before you made any changes.
            Your definition of "sunhours" is different than the usual use of the term and an example of the confusion its use can cause.

            About the closest to being a useful definition for the term is to define a "sunhour" or "sun-hour" as equal to insolation (energy), not irradiance (power) of 1,000 W/m^2 of energy received on a horizontal surface without regard to how long it takes for that energy to be received. So, for example, if at some location 1,000 W of solar energy is received on a horizontal surface over the course of one day, that location has received 1 "sunhour" for that day. If it takes 1 hour instead of 1 day to receive 1,000W of solar energy, the surface has still received only 1 "sunhour".

            The term is of some use when comparing geographical sites one to another for solar potential.
            However, it's of little use in the actual design of solar energy equipment.

            I've been knocking around solar energy for almost half a century and to my experience most knowledgeable solar designers I've known don't use the term.
            In informed circles the usual term (if used at all) is kWh/m^2 per day or W/m^2 with the surface orientation understood to be horizontal.

            To my experience most of the confusion comes about when un- or semi-informed individuals think or assume that if a site or location "gets", say, 5 "sunhours" of sunlight that means a solar energy device will receive that much insolation. Not correct.
            ​​​​
            But, and the point is, the term "sunhours" is not much use in system design or analysis.
            It's a B.S. term that leads to confusion and often to costly errors and/or less than optimal or cost-effective design.

            As far as ROI goes, while that may be your definition, but there's a lot more to it, starting with the idea that ROI takes a longer takes a longer look at the economics than just one year.

            On Bruce's system, and with all possible respect to Bruce, his system is unusual in many respects, starting with its size, orientations and goals. And again, with all respect, it's most likely not cost effective but I recall reading on several occasions over the years that cost effectiveness was not one of his goals.
            If it was I'm pretty sure there would be more systems like his, but I believe his system is unique. And more power to him for what he's done even if I and others may think it's eccentric.
            FWIW, if he's having fun with it, I'm a fan but I doubt many informed people would call it cost effective or practical.

            Comment

            • lockem
              Junior Member
              • Mar 2024
              • 14

              #7
              Originally posted by J.P.M.

              Your definition of "sunhours" is different than the usual use of the term and an example of the confusion its use can cause.

              About the closest to being a useful definition for the term is to define a "sunhour" or "sun-hour" as equal to insolation (energy), not irradiance (power) of 1,000 W/m^2 of energy received on a horizontal surface without regard to how long it takes for that energy to be received. So, for example, if at some location 1,000 W of solar energy is received on a horizontal surface over the course of one day, that location has received 1 "sunhour" for that day. If it takes 1 hour instead of 1 day to receive 1,000W of solar energy, the surface has still received only 1 "sunhour".

              The term is of some use when comparing geographical sites one to another for solar potential.
              However, it's of little use in the actual design of solar energy equipment.

              I've been knocking around solar energy for almost half a century and to my experience most knowledgeable solar designers I've known don't use the term.
              In informed circles the usual term (if used at all) is kWh/m^2 per day or W/m^2 with the surface orientation understood to be horizontal.

              To my experience most of the confusion comes about when un- or semi-informed individuals think or assume that if a site or location "gets", say, 5 "sunhours" of sunlight that means a solar energy device will receive that much insolation. Not correct.
              ​​​​
              But, and the point is, the term "sunhours" is not much use in system design or analysis.
              It's a B.S. term that leads to confusion and often to costly errors and/or less than optimal or cost-effective design.

              As far as ROI goes, while that may be your definition, but there's a lot more to it, starting with the idea that ROI takes a longer takes a longer look at the economics than just one year.

              On Bruce's system, and with all possible respect to Bruce, his system is unusual in many respects, starting with its size, orientations and goals. And again, with all respect, it's most likely not cost effective but I recall reading on several occasions over the years that cost effectiveness was not one of his goals.
              If it was I'm pretty sure there would be more systems like his, but I believe his system is unique. And more power to him for what he's done even if I and others may think it's eccentric.
              FWIW, if he's having fun with it, I'm a fan but I doubt many informed people would call it cost effective or practical.
              I did not make up my definition of sun hours and did not give a complete formula. Plenty of information is available similar to this:

              Yes, it is average over a year insolation per day. It is useful for estimating the annual energy output of a system, and thus useful for determining if a system is performing as expected. My point is that it is not the number of hours of production on the best day of the year.

              At my location I get about 1080 Watts/m^2 perpendicular to the direction of the sun, except in the spring when snow reflections increase that to about 1200 Watts/m^2.

              ROI is a financial term. Properly it should include cost of money, the changing value of electricity generated (or cost avoided) over time and should be the total yield over the life expectancy of the investment. I simplified that to the time to get back the investment with no consideration of varying electricity cost and money cost (which more-or-less cancel each other out), which is much easier to compute and easier to understand.

              My point is and remains: spend a little extra on wiring and get a little extra in power--it will pay for itself quickly.

              Regarding lots of solar experience, please have a look at my request for information in the Sunpower performance thread. It appears to me that Sunpower has "upgraded" the FW recently in its microinverters to cap max current and as a consequence if one has a bad power factor it degrades the system performance.



              Comment

              • bcroe
                Solar Fanatic
                • Jan 2012
                • 5203

                #8
                Originally posted by lockem
                Sun hours is the average amount of sunlight per day, for the entire year:

                TOTAL_SUN_HOURS_IN_ONE_YEAR/365

                The expected value in Illinois is 4.4hours per day. The expected value in the high desert in California is 5-5.5, although that fails to consider raised solar intensity due to reflections off snow covered cliffs and high altitude dry air. The highest in the country is 6. I believe that getting 7 hours at max output is a symptom of an undersized inverter. Based on your numbers, your system is 3 times the size of mine, but produces less than twice as much energy. Part of that is due to location, but some of it is also likely due to an undersized inverter.

                To estimate return on investment in units of time compute

                (cost of upgrade)/(value of electricity saved in a year)

                It is a straightforward computation. It should be done by system installers when they quote the system.
                In your case it seems unlikely that upgrading a 4/0 cables would be economic as it would cost at least several hundred dollars and likely increase electricity production by $20/year. At some point running higher voltage via transformers is going to be less expensive than heavier cables.
                In my case I reduced my loss from 0.011%/foot to 0.007%/foot. Over your 600 foot run that would be an improvement from 6.6% to 4.2%. Since you were already at 4% loss, the level of wire upgrade that I was discussing was already present in your system before you made any changes.
                I believe you are using micro inverters, so all your long runs are AC?
                Running string inverters here gives 2 loss considerations, DC & AC.
                Here the DC loops vary from around 500 ft for the closest panels, to
                approaching 1000 ft for the farthest. My estimate is around 1% loss
                at full power, at 400V a fair amount of drop can be tolerated. If I wanted
                to get back the loss, just adding a panel or 2 would be a lot easier than
                changing wire. My intent was to ground mount solar completely out of
                view of my house or the neighbors. This is hardly the most cost effective
                per kWh, but it does give a lot more options.

                From the inverters there are a lot of AC restrictions. The 70s house was
                originally an all electric Medalion build, so the service is 200A 240V
                (48KVA) and here in the country I have my own transformer. Long ago
                the previuos owner changed over to propane, my goal was to change it
                back using 2013 technology. Propane bills gave me a pretty good idea
                of how much solar generated energy would be needed, at 25.5 kWh
                per gallon. Solar installers here would go up to 15KW of inverters,
                though some would argue that is overload. I made sure the PoCo
                feed came into the top of each breaker box, the PV inverter power
                into the bottom, so it was physically impossible to overload a box
                busbar. In addition the 4 gauge between the inverters in the shed
                and the house was close to the limit at 60A. Given all this I estimated
                I was close to heating and electrifying the house with PV solar energy.

                There have been regular energy upgrades since startup in 2013, based
                on learning, technology, and the time very economical DIY work takes.
                In 2020 while hiding from Covid, I was doing the upgrade of the buried
                Inverter to house feed from 4ga copper to 4/0 aluminum. I cannot
                change the inverters, as my PoCo contract allows connection of 15kW,
                even the serial numbers are recorded. But there is no limit on hours,
                my DC:AC is around 2.

                As your figures indicate, generating PV energy here under the frequent
                clouds and snow will be less efficient, more costly than in the SW desert.
                I chose to live with some cold months we can deal with, avoiding such
                things as earthquakes, mud slides, floods, droughts, hurricanes, forest
                fires, smoke, extreme real estate prices, overcrowding, and regulations.
                In 2012 my relations with the fossil fuel suppliers were poor, and PV
                technology was looking good. Word was you cannot heat your house
                year around with solar here, but I decided to try.

                Energy varies with the weather, but generally I collect around 29,000 kWh
                a year (Net metering, 1:1). Divide by 365.25 days per year and 15kW,
                that comes to around 5.3 hours a day. If you divide by the .95 efficiency
                of the inverters for the input DC its more like 5.6, since my inverters are
                just into clipping under good sun its even more. Record one day inverter
                output is 158kWh, looks like a 10.5 hour day.

                So how to do that, trackers work very well in the SW desert. But a tracker
                can do nothing about our clouds. But adding more of those now cheap
                panels work. Panels are set up facing east, and my expensive ground
                mount can be made more cost effective by adding another set of those
                now cheap panels facing west. I believe the wind loading is essentially
                the same. Since the 2 sides will never peak at the same time, there is no
                need for more inverters. I get more cost effective use of the plant
                including DC wires, inverters, and AC wires, by keeping them working
                more hours. My long production sunny days are helping make up for
                the cloudy days.

                But what about cloudy days? The light is dispersed, all the panels work,
                output is roughly double the SW desert design if used here. So even
                then, the rest of the facility is twice as effective at the cost of some cheap
                panels. I have seen 4kW output in a rain storm, light clouds will run it
                near 100% capacity.

                Does it cost more than the SW desert setup, yes we said that up front.
                Does it work, 11 years here with the furnace off say yes.

                I will show a curve of AC output under good sun. The inverters are
                clipping at max, but just barely. Removal of just one of 6 strings
                connected to an inverter will drop it out of clipping. Some juggling
                of E, W, and S orientations does this, without any increase of the
                rest of the plant, something not practical with mcro inverters. In
                summer the rising and setting sun is so far north, the 8 hours in
                clipping does not increase, There is a plan on paper to solve this,
                it turns out these methods are also the most snow repellant.

                That is not the end, things like 6 air to air mini split heat pumps,
                non vented clothes drier, and many other details make it all work.
                Cost effective, pretty hard to figure with no starting or ending point,
                huge savings from a lot of repurposed stuff and DIY labor, no detailed
                cost records over 20 years here, with ongoing upgrades. It is well
                within my budget and quite successful, my calculations end there.
                Bruce Roe

                NScurve.jpg
                Last edited by bcroe; 03-17-2024, 02:26 PM.

                Comment

                • lockem
                  Junior Member
                  • Mar 2024
                  • 14

                  #9
                  Thanks for all the interesting details. You had said 4% power loss cost you 800kwh/year, so I just computed 800/0.04 = 20,000kwh/year total output.
                  A ground source heat pump might have been an easier (more cost effective?) way to meet requirements than a huge solar array, but you have already sunk your money into the solar array.
                  When I mentioned transformers, I meant between your inverter and your main panel. Step up to 600V for the run, then back down to 240V at the panel. Transformers are not cheap and have some losses, so the decision is not trivial.

                  The one year that I added up everything, my system produced about 12,000kwh for the year. My home, located in the coldest inhabited place in California used 10,000kwh. My home is insulated similar to a house in Alaska and has a ground source heat pump. I have 5600 DC watt rating (assumes standard light incidence) and 5160 watt inverter capacity.

                  Regarding the insolation discussion with J.P.M., of course actual output of panels is dependent on a lot of factors that I glommed together with the assumption that a reasonably well oriented system will produce roughly average sun-hours*365 per year. Although solar energy varies with the cosine of the angle between the sun and the exposed surface, solar PV output may vary by more than that for several reasons including the variable amount of reflection of the light off the glass.

                  Earthquakes are not much of a risk in Bridgeport, Ca. Neither are floods. Snow avalanches, volcanoes and wildfires are a risk, but there are risks anywhere you go.

                  Comment

                  • bcroe
                    Solar Fanatic
                    • Jan 2012
                    • 5203

                    #10
                    Originally posted by lockem
                    Thanks for all the interesting details. You had said 4% power loss cost you 800kwh/year, so I just computed 800/0.04 = 20,000kwh/year total output.
                    A ground source heat pump might have been an easier (more cost effective?) way to meet requirements than a huge solar array, but you have already sunk your money into the solar array.
                    When I mentioned transformers, I meant between your inverter and your main panel. Step up to 600V for the run, then back down to 240V at the panel. Transformers are not cheap and have some losses, so the decision is not trivial.

                    The one year that I added up everything, my system produced about 12,000kwh for the year. My home, located in the coldest inhabited place in California used 10,000kwh. My home is insulated similar to a house in Alaska and has a ground source heat pump. I have 5600 DC watt rating (assumes standard light incidence) and 5160 watt inverter capacity.

                    Regarding the insolation discussion with J.P.M., of course actual output of panels is dependent on a lot of factors that I glommed together with the assumption that a reasonably well oriented system will produce roughly average sun-hours*365 per year. Although solar energy varies with the cosine of the angle between the sun and the exposed surface, solar PV output may vary by more than that for several reasons including the variable amount of reflection of the light off the glass.

                    Earthquakes are not much of a risk in Bridgeport, Ca. Neither are floods. Snow avalanches,
                    volcanoes and wildfires are a risk, but there are risks anywhere you go.
                    Yes good to go thru the numbers.

                    Actually best estimate of AC transmission loss was 9V out of 260V
                    generated, or near 3.5% peak. I cut that to more like 0.9% with bigger
                    wire. 2.6% of 29,000kWh is 754kWh, just an estimate because line
                    voltage and output power both vary, changing the instantaneous loss.

                    Earlier the ground source heat pump was about the only solution. I
                    did look at them earlier, expensive and difficult on this terain. I did not
                    like the idea of using plastic tubing either in a horizontal land sink,
                    which might some day require a very difficult replacement, and a friend
                    after some decades is having leak problems with it in his concrete floor.

                    By 2017 I was reading the latest Mini Splits with a SEER of 36, low
                    temp capability far below 0F, and lending themselves to (economical)
                    DIY. I started out with 3 of these in 2018, at $1400 each for the basic
                    1 ton (heating) units. These saved so much energy, I eventually
                    bought 3 more, could now nicely warm (or cool) the car shop, run
                    my dehumidifier summers, and keep the air nearly dust free running
                    the furnace blower air thru the electronic air filter often. I did have to
                    replace that well worn propane furnace blower motor, a common part.

                    One goal here was an HVAC that could not be completely disabled by
                    a single component failure, and leave me in a desperate winter
                    situation. I also put in enough capacity that it would likely never be
                    necessary to turn on any auxilary heat on the coldest day. Again a
                    bit oversized by some standards, not very costly to me.

                    This 70s ranch is a poor candidate for saving energy, but I am not
                    going to tear down a functional brick house. Work to better insulate
                    it is slowly underway, but I was not going to wait to finish that
                    (probably never) before installing PV solar. As a consequence all
                    the equipment is scaled up quite a bit to cover the extra losses. If
                    the time comes the solar is to be shut down, more insulation will rise
                    to a much higher priority.

                    I did consider the transformer idea, but it had so many problems.
                    It would have to be a dual auto transformer at both ends, to keep
                    the inverter neutral voltage monitor happy. The more line loss I
                    wanted to save, the bigger the auto trans would have to be, adding
                    a lot of clumsy equipment at both ends. It would consume idle
                    current 24/7, which would probably cancel or exceed my line gains.
                    And it might add enough impedance to the apparent line that the
                    inverters think they have been islanded, and shut down. No.

                    J.P.M. is quite technically correct, we sometimes kick around goals.
                    I should add snow avalanches, tsunami, sink holes, and volcanoes
                    to my list. About the only real threat here is the Byron Nuke plant,
                    just minutes away.
                    Bruce Roe
                    Last edited by bcroe; 03-15-2024, 04:15 PM.

                    Comment

                    • lockem
                      Junior Member
                      • Mar 2024
                      • 14

                      #11
                      My ground source loop is outside of the house. Putting it under the house seems a bit fool hardy to me. I used 1800W "heat cubes" as backup. They are cheap and only a few of them can keep my house warm.

                      I would not consider an autotransformer for this application due to the balance issues. The bigger problem with transformers is that you are going to have a loss of several percent per transformer, so it isn't going to "fix" a 4% loss.

                      In these more-or-less constant voltage systems it is easier to use the following to compute wire loss:

                      Loss = I^2*R
                      W = I*V*power_factor
                      I = W/(V*power_factor)
                      Loss = R*(W/V*power_factor)^2

                      So step up the voltage and scale down the loss in inverse SQUARE proportion. Double the voltage, 1/4 the loss. At the same time, the loss scales with the resistance -> wire size linearly.
                      Also note that squared power_factor in there. You may or may not have any ability to control it, but it is something to be wary of.

                      What mini-split heat pump has an SEER of 36 and costs only $1400?

                      If a tsunami reaches my house at 7500' elevation, it is likely to not stop before it gets to your house.
                      Southern Il has a similar earthquake risk as my house:
                      Earthquakes are one of 18 natural hazards included in the National Risk Index.


                      Tornados are so rare in California that it is fair to say "they never happen". OK San Diego averages something like 2 per year, while the entire rest of the state manages to average not much higher.

                      Comment

                      • bcroe
                        Solar Fanatic
                        • Jan 2012
                        • 5203

                        #12
                        In 2018 I ordered a mini split on line from
                        Budget Heating & Air Conditioning Inc. 813 885-7999
                        To the inside and outside units I added several things like a wall
                        mount, tubing and cable kit, electrical whip and disconnect box,
                        brought me to $1662, shipping to the door was $200. Still testing
                        on this new item then, was the SEER 36, or 33, or 30.5? It has
                        served me well for 5 winters. I decided I did not like the metal wall
                        mounts offered, for later units made my own from the same 6061
                        aluminum and 18-8 stainless hardware I used to mount panels.

                        Note, units tend to be rated in cooling capacity, which sends the
                        motor operational power outside. But in heating mode that energy
                        goes inside, so heating is more powerful than cooling. COP does
                        decrease with outside temp, but I have enough capacity to cover it.
                        3 of these smaller units got me thru a winter unaided, but I then
                        added more to cover severe cold or any failures.

                        An auto transformer could be much smaller than a full isolated
                        transformer, since it only handles the DIFFERENCE in voltage
                        I need. And losses would be proportionately smaller. That
                        thought was based on getting down to a level to avoid tripping
                        inverter voltage monitors. But the idea of using units at both
                        ends was never seriously considered. Can only DIY so much
                        in a year, I lived with high AC line losses for 7 years. Bruce Roe

                        Comment

                        • lockem
                          Junior Member
                          • Mar 2024
                          • 14

                          #13
                          Bruce,

                          What is the brand name on those split units? I have another house that has air flow issues causing temperature balance issues. I was quoted about $5000 to install a SEER 10 unit.
                          Some mfgs refuse to ship to California with our out of control "everything causes cancer" labelling requirement and all. Did you know that wood saw dust causes cancer--just inhale an entire tree ground down to a fine powder and you are in trouble? How about stainless steel metal dust--this is a real thing, but mostly from factory processed foods?

                          Another hazard we don't have in California is large hail. I can reasonably expect my panels to last the length of the warranty, rather than until hail breaks them. 400W microinverter based Sunpower panels here are $1440 each, so pretty far from cheap.

                          A trencher will not work at my home. The "soil" is 25% rocks; often 6" or larger. I have a backhoe for digging. It can move rocks up to 6' round by 3' thick and pick up rocks up to 3' more or less spherical.

                          Comment

                          • bcroe
                            Solar Fanatic
                            • Jan 2012
                            • 5203

                            #14
                            Hail sometimes happens here, not on my list because it is generally not
                            life threatening. Only once did I see some orange size that damaged
                            cars, very rare.

                            Get the tools you need. A mile from the Rock River, there is a lot of that
                            layered yellow rock. My trencher works its way through, pieces come up
                            from gravel size, to hand size that may jam things and require removal.
                            Have encountered those hard egg shaped rocks that the trencher cannot
                            cut, dug them out and dumped on my rock pile. The pile started with the
                            solar array, now is bigger than my rooms. Have a mini back hoe too.

                            Abiout the time my solar went in, my ancient AC went bad and I had an
                            air to air heat pump replacement installed for about $5k. This old school
                            unit was about 14 SEER, would only work down to around 20F, had a
                            very noisy fan and reversing valve, and the compressor vibrated the
                            whole house. I was not very successful trying to supplement heat with
                            it. After a couple failures I gave up, but was looking at new school hps.

                            You should carefully research a heat pump to fit your needs. I started
                            looking for low temp capability to below -10F, that for the car shop is rated
                            -25F. COP or SEER is pretty important. The small air to air mini splits
                            were extremely quiet, efficient, and fit my DIY skills. Basically one at
                            each corner of the house and one in the exposed wall of the basement
                            met my needs, enough capacity to cover the coldest temps, and with
                            independent operation one could not take down the whole system. I
                            avoid larger units serving multiple locations for that reasoning. Running
                            the old furnace fan evened out temps and cleaned the air.

                            The car shop has a 1.5 ton heat pump that can maintain about 65F
                            working temp at least 9 months of the year. Ceiling fans run all
                            winter to keep the heat down where I am. The very coldest months
                            the hp may only manage low 40s, but that is enough to keep my
                            snow blower melted clean after each use. Very little is done there
                            those days, but I stlll can if needed, more capacity would be a waste
                            of energy.

                            No brand loyalty here, I have different sizes, MITSUBISHI, FUJITSU,
                            SENVILLE.

                            My panels are varied brands and configurations, just made sure each
                            string had 720 cells so they would play together nicely. An advantage
                            of string inverters, it is not necessary to add an inverter every time a
                            panel is added. So any cheap panels on the market work. Bruce Roe

                            Comment

                            • lockem
                              Junior Member
                              • Mar 2024
                              • 14

                              #15
                              Thanks for all the info. In Silicon Valley a heatpump only needs to be efficient down to 35F. I have seen it get down to 21F once, but nothing below 30F for the last 20 years.
                              In the Bridgeport California area lows are -20 to -10F, it is the coldest inhabited place in California. My 5 ton ground source heat pump never works very hard and is clearly over specified. Actual heat load at the typical 20F outside temp and 72F inside temp is about 12,000 BTU/hr (measured). This demands about (12/(3*3.4))*24 = 28kWh in energy to run the ground source heat pump, while at least on winter sunny days I typically get over 30kWh from my little array. That heat load increases to about 20,000 BTU/hr at -10F outside temp, which is still only 1/3 of the heat pump capacity.

                              Under NEM2, my excess power output from summer counts against my power deficit in the winter, so I end up getting an end of year check from the power company. I expect that once I am living full time in the house my consumption will exceed my production, but not by a large amount.

                              Sunpower panels are compact relative to their output and even though I have plenty of space, I only have a small area where the panels do not become an eye sore. Besides, ground mount support frames with a reasonable snow load capacity are expensive. Everything needs to handle up to 150PSF snow load. After all, Sierra Nevada is Spanish for snowy mountain or some such.

                              I don't think any trencher would chew through the local granite, andesite and mystery iron bearing rocks. They are hard and likely to damage a trencher. No one in the area uses trenchers, including public utility companies. Explosives or expanding chemical rock crackers are required if the rock cannot be moved via backhoe or excavator.

                              I have a grizzly to bulk separate large rocks from dirt. I have enough large rocks to build a fire barrier rock wall, and have plenty left over.

                              Comment

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