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  • #31
    Originally posted by Bintang View Post
    Ok … thought you might be willing to offer some help to a newbie but never mind ….so I have tried to figure it out myself. I found a comparison at the following link though how reliable it is I have no idea:
    http://sagebrushsolar.com/solar-ther...lectricity-pv/

    I cannot see a date anywhere in the article so the costs maybe out-of-date. The article concludes that solar thermal gives bigger bang for the buck but the conclusion is heavily dependent on the assumption of incentives – both federal and state incentives:

    “The installed cost of a typical solar thermal system with one evacuated tube collector and an 80-gallon tank is typically around $8,000. After federal and state incentives, the net investment comes in around $4,300. By comparison, the installed cost of a typical 3.6 kW PV system (eighteen 200W collectors) is around $10,000 ($4.5 per watt installed). After incentives, this system costs about $5,400.”

    In my country there are no such incentives and likely never will be. So the cost to me for the solar thermal system would be the full $8,000 and probably more due to import taxes.
    However, I do have a reliable knowledge of local costs for PV systems and I could install the PV system described for around $5,500 (without any government subsidies). So in my world it looks like PV would give a bigger bang for the buck.

    And all of this analysis conveniently excludes any mention of maintenance costs. I'm sure solar thermal has them but as I have no experience with such systems I have no idea what they might be.

    Each to their own, I suppose.
    Your estimate of $8000 is pretty good. I installed a solar thermal system back in 2010. My house is grid connected and we have used the small electrical heater inside the 80 gal tank during days of rain yet I have seen about $100 per month savings on my electric bill. Depending on how many people live in the house and the length of hot showers (teenagers like to go 30 min or more . LOL) The payback will be more or less.

    As for maintenance. Since I live in Florida I do not have to worry about draining the panel to keep it from freezing since it has a control that will pump hot water back into the panel during a cold night. The only other thing I need to do is drain and flush the system about twice a year since we have hard water. Other than that the system does not need much.

    I certainly recommend it to anyone that uses hot water that has an all electric water heater. It will pay for itself.

    Comment


    • #32
      Originally posted by SunEagle View Post
      As for maintenance. Since I live in Florida I do not have to worry about draining the panel to keep it from freezing since it has a control that will pump hot water back into the panel during a cold night. The only other thing I need to do is drain and flush the system about twice a year since we have hard water. Other than that the system does not need much.
      Suneagle, how reliant are these solar thermal systems on pumping? Presumably any pumping is grid powered, so if there is an extended grid outage eventually there will be no useable hot water even though the heating is from solar. Your grid service is no doubt reliable enough for this to be of low concern but where I live things are different.

      Comment


      • #33
        Originally posted by Bintang View Post
        Suneagle, how reliant are these solar thermal systems on pumping? Presumably any pumping is grid powered, so if there is an extended grid outage eventually there will be no useable hot water even though the heating is from solar. Your grid service is no doubt reliable enough for this to be of low concern but where I live things are different.
        The pump is a very small and runs off of a controller that is powered from 115v house receptacle. It only runs when the tank temp falls below a set point. I'm not sure how many watts it uses but it does not run continuously so a battery system using an inverter will work.

        The backup electric heat element uses more power at 240volts but it only comes on when we do not get enough sun or if someone runs the tank low at night from those long showers.

        The big seller is that there is really no maintenance required and as far as I am concerned it is saving me money and will pay for itself in 5 years after installation. Of course the final price was reduced from our Fed Tax rebate so for you the payback will be longer yet still worth it IMO.

        Comment


        • #34
          Originally posted by Bintang View Post
          Solar thermal is indeed more efficient in terms of the energy it collects per unit area but there are maintenance problems with solar thermal that discourage me from using it.

          I think electric water heating by solar PV has much promise - especially for off grid.
          All it requires is an off-grid inverter with MPPT control which does not need to be connected to batteries.
          Solar thermal does require a bit more maintenance than PV. However, the overall system efficiency including standby, piping and other losses, and the parasitic electric to run a pump still runs about 30% or so for a well designed system. A good PV system will run about 15% or so.

          FWIW, I redesigned my SDHW system 6+ years ago. I've replaces one flex bib gasket in that time. That's it. The system cost $4,200 less 30%. It provides about 92% of my hot water needs on an annual basis, +/- some yr./yr., including all losses. That amount to about $600/yr. to me in savings.

          As an alt., I had considered a heat pump water heater, but the market didn't have what I wanted yet and PV was much more expensive at the time. Things may be better now, perhaps improving the economics and viability.

          Using PV directly as a D.C. heating element is like cutting butter with a chain saw.

          Comment


          • #35
            Originally posted by J.P.M. View Post

            Using PV directly as a D.C. heating element is like cutting butter with a chain saw.
            Agreed, but I’m considering an inverter with module level MPPT control that does not require batteries and is also not grid-tied. The input to the hot water heater will still be AC - not DC. There are no high voltages or currents on the DC side and the setup is very simple. The inverter output can connect direct to the existing water heater. Total cost for a 2.4kW system should be less than $4000 (< $1.70 per watt) and the estimated LCOE should be less than US 7 cents/kWh - all without any subsidies/incentives.

            In deference to Russ, I know the PV modules will take up more roof space than solar thermal collectors would for the same output but I have more than enough roof space.

            Comment


            • #36
              Everyone should do as they feel best - sometimes it will be. The pump for my system is one small Wilo - I am not at home now and don't have the file with me where I have recorded consumption.

              The PV plus heat pump style water heater may be winner. The heat pump style alone wins over solar thermal in the long term. That style of heater has a COP in the 2.5 to 3 range as I remember - in a tropical climate there wouldn't be a location problem.

              With my system I turn off the electric connection to the tank heater sometime in March and will turn it on in late November.
              [SIGPIC][/SIGPIC]

              Comment


              • #37
                Originally posted by Bintang View Post
                Agreed, but I’m considering an inverter with module level MPPT control that does not require batteries and is also not grid-tied. The input to the hot water heater will still be AC - not DC. There are no high voltages or currents on the DC side and the setup is very simple. The inverter output can connect direct to the existing water heater. Total cost for a 2.4kW system should be less than $4000 (< $1.70 per watt) and the estimated LCOE should be less than US 7 cents/kWh - all without any subsidies/incentives.

                In deference to Russ, I know the PV modules will take up more roof space than solar thermal collectors would for the same output but I have more than enough roof space.
                Understood. I'd still sketch up a PV system w/ a heat pump H2O heater, run the #'s and LCOE's on both for the hell of it. Off grid may make the heat pump a no go, depending on heat pump power requirements and considerations however.

                Good luck.

                Comment


                • #38
                  Originally posted by J.P.M. View Post
                  Understood. I'd still sketch up a PV system w/ a heat pump H2O heater, run the #'s and LCOE's on both for the hell of it. Off grid may make the heat pump a no go, depending on heat pump power requirements and considerations however.
                  JPM, I've followed up your suggestion. As with solar thermal it is difficult for me to find reliable costs so if my stated cost of the heat pump is way-off please go easy.

                  I’m comparing a PV system and heat pump each of which need to generate 3,000 kWh per year heat energy - excluding any hot water boosting using the grid.

                  The heat pump system capacity is 325 liter with coefficient of performance (COP) = 3.4 Therefore energy input to the heat pump will be 882 kWh/yr

                  Heat pump cost including install: $3,000
                  Cost of grid electricity : $0.14/kWh

                  Maintenance costs are not included.

                  The LCOE estimates are summarised in the table below. For the PV system the LCOE is 6.7 cents per kWh. For the heat pump it is 9.1 cents per kWh if the cost of grid electricity is assumed to be constant for 20 years – which is unlikely. Including an escalation rate for electricity prices of 3% per year increases the heat pump LCOE to 12.9 cents per year. So it looks to me that the PV system wins hands-down.

                  Table PV vs Heat Pump.jpg

                  Comment


                  • #39
                    Have fun - your analysis is useless.

                    The maintenance on the PV will have to include a new inverter over time - the solar thermal type would have no real charges - especially in the tropics.

                    The 3% escalation rate is just blather posted by a ghost.

                    If you have the grid available then hands down the heat pump is cheapest if worked out correctly.
                    [SIGPIC][/SIGPIC]

                    Comment


                    • #40
                      Originally posted by russ View Post
                      Have fun - your analysis is useless.

                      The maintenance on the PV will have to include a new inverter over time - the solar thermal type would have no real charges - especially in the tropics.

                      The 3% escalation rate is just blather posted by a ghost.

                      If you have the grid available then hands down the heat pump is cheapest if worked out correctly.
                      So what is the correct way to work this out?
                      Is my cost estimate for the heat pump way too high?

                      I have no idea what your comment about escalation means. Are you implying that electricity prices never increase?

                      Where I live electricity prices were increased by 5.7% in the last financial year and a 7% increase has already been announced for the coming year so I think using 3% price escalation for the analysis is reasonable.

                      All systems can break down and require repairs/maintenance.
                      One advantage of a PV powered system is that on the day the inverter goes belly-up the hot water tank can simply be reconnected to the grid.
                      Presto ….. no down time while waiting for the new inverter.

                      But on the other hand I guess with a heat pump you could achieve the same level of convenience by keeping a spare heat pump on hand.

                      Comment


                      • #41
                        Originally posted by Bintang View Post
                        JPM, I've followed up your suggestion. As with solar thermal it is difficult for me to find reliable costs so if my stated cost of the heat pump is way-off please go easy.

                        I’m comparing a PV system and heat pump each of which need to generate 3,000 kWh per year heat energy - excluding any hot water boosting using the grid.

                        The heat pump system capacity is 325 liter with coefficient of performance (COP) = 3.4 Therefore energy input to the heat pump will be 882 kWh/yr

                        Heat pump cost including install: $3,000
                        Cost of grid electricity : $0.14/kWh

                        Maintenance costs are not included.

                        The LCOE estimates are summarised in the table below. For the PV system the LCOE is 6.7 cents per kWh. For the heat pump it is 9.1 cents per kWh if the cost of grid electricity is assumed to be constant for 20 years – which is unlikely. Including an escalation rate for electricity prices of 3% per year increases the heat pump LCOE to 12.9 cents per year. So it looks to me that the PV system wins hands-down.

                        [ATTACH=CONFIG]4561[/ATTACH]
                        Actually, my suggestion was to use both: A PV system to generate the electricity at about 15% system eff. and a heat pump to use that electricity to generate hot H2O. Assuming a somewhat conservative C.O.P. of 2.0 for the heat pump, such a system would approach or surpass the overall system efficiency (~30%) of a solar thermal water heater by itself. Either will provide hot H2O by itself. Depending on the duty (how much hot water is required), motor starting and other heat pump elec. requirements, combining the two may be a way to generate more hot water with a smaller PV array than using PV alone for hot H2O. The economics are a separate and equally important matter.

                        Sorry for the lack of clarity.

                        Comment


                        • #42
                          Here is a quick note on projected maintainance.
                          PV- projected life for an inverter 10 years- 2500 watt $1279.00 . 50 gallon Tank and elements - 7 yrs $500
                          Differential controller 10 yr.life expectancy - $200. Stainless steel Taco 009 pump $379 projected life 15 yrs. Tank - Super stor SS with cupronickel HX life time warranty.
                          You make the choice.

                          Comment


                          • #43
                            Originally posted by LucMan View Post
                            Here is a quick note on projected maintainance.
                            PV- projected life for an inverter 10 years- 2500 watt $1279.00 . 50 gallon Tank and elements - 7 yrs $500
                            Differential controller 10 yr.life expectancy - $200. Stainless steel Taco 009 pump $379 projected life 15 yrs. Tank - Super stor SS with cupronickel HX life time warranty.
                            You make the choice.
                            In 10 years time the replacement inverter cost will have increased. I'll include 3% per year cost escalation and use $1700 instead of $1279.
                            LCOE for the PV system with this additional cost is 9.5 cents per kWh - still less than the heat pump system at 12.9 cents per kWh.

                            Comment


                            • #44
                              Originally posted by Bintang View Post
                              In 10 years time the replacement inverter cost will have increased. I'll include 3% per year cost escalation and use $1700 instead of $1279.
                              LCOE for the PV system with this additional cost is 9.5 cents per kWh - still less than the heat pump system at 12.9 cents per kWh.
                              Notice that I did not include the Heatpump water heater. That is because they have many controls & motors prone to failure, plus the sealed refrigeration system will leak. The projected maintainance is just to high to even consider these units.
                              The most reliable system is the simplest one, with the least amount of electronics and moving parts.

                              Comment


                              • #45
                                Originally posted by J.P.M. View Post
                                Actually, my suggestion was to use both: A PV system to generate the electricity at about 15% system eff. and a heat pump to use that electricity to generate hot H2O. Assuming a somewhat conservative C.O.P. of 2.0 for the heat pump, such a system would approach or surpass the overall system efficiency (~30%) of a solar thermal water heater by itself. Either will provide hot H2O by itself. Depending on the duty (how much hot water is required), motor starting and other heat pump elec. requirements, combining the two may be a way to generate more hot water with a smaller PV array than using PV alone for hot H2O. The economics are a separate and equally important matter.

                                Sorry for the lack of clarity.
                                That is what I understood you to be saying.
                                [SIGPIC][/SIGPIC]

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