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  • G'day everyone from Victoria Australia

    David here, I'm in my 7th decade now currently I am a part time high school Physics teacher. Next year I want to focus on building the off grid retirement nest. straw bale, evacuated tube solar hot water for both showers etc with gas ( LPG ) boosted and floor heating with separate low pressure evacuated tube primary heat and wood fired boiler for batch heating a water storage tank. Electrical power will be PV and wind and hopefully not too much diesel at all. At this stage I'm unsure what type of batteries to go for as the storage scene is pretty dynamic. Best regards Dave.

  • #2
    Why evacuated tube ? Match the energy production capabilities to the task and don't decrease the fluid entropy any more than necessary.

    If you need 110 C water, evac. tube is what you want. Few domestic tasks require that much heat. Up to ~ 70 - 80 C. simple flat plate solar will be less expensive and more reliable (less complication and less to go wrong).

    Learn the value of insulation and weather stripping. Get the heat loads (and any cooling loads for that matter) as slow as possible before thinking about how to supply the rest of it. Conservation and not losing heat is much more comfortable and cost effective than making more heat. Trust me on that one.

    Welcome to the neighborhood.

    Comment


    • #3
      Hi JPM, evacuated tube is simple. I have it hereat home now. Our 30 tube system meant that last year I only paid for hot water heating for 29 days. I didn't know where the 110

      Comment


      • #4
        Hi JPM, evacuated tube is simple. I have it hereat home now. Our 30 tube system meant that last year I only paid for hot water heating for 29 days. I didn't know where the 110

        Comment


        • #5
          Why do my posts appear truncated?

          Comment


          • #6
            alien characters in your posts. I can use plain window's font and all is fine. Fancy formatting screws it all up. Simpler is better.
            Powerfab top of pole PV mount (2) | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
            || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
            || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

            solar: http://tinyurl.com/LMR-Solar
            gen: http://tinyurl.com/LMR-Lister

            Comment


            • #7
              I see that was my degrees symbol then, Got it. So, It's just your opinion Mike, do you think in my situation NiFe is the go? cheers Dave

              Comment


              • #8
                Originally posted by Colesy View Post
                Hi JPM, evacuated tube is simple. I have it hereat home now. Our 30 tube system meant that last year I only paid for hot water heating for 29 days. I didn't know where the 110
                After and since installation of a plat plate water heating system over 10 years ago which cost about 1/2 or less than an evac. tube system, I've paid exactly nothing to heat water and it didn't take an evacuated tube system to do it. Simple flat plate is completely adequate and appropriate for that application.

                Similar to those who waste money on Sunpower, or similar to killing flies with a sledgehammer, evacuated tube systems are overkill and overpriced for the task of heating water for domestic applications. Money has always been a willing substitute for ignorance. But, your money and time and NOMB.

                Comment


                • #9
                  Round three without the degrees symbols this time! Well flat plate collectors here last year popped all over the place after freezing. My evacuation tubes didn't. I don't know where you are JPM but evacuated tubes here in Oz are not twice as much but are maybe only 25 percent more but the point is they are much better performers on intermediate days that flat panel collectors. I'm a Physics teacher so I do understand about insulation and draught proofing which are actually rather obvious things for people to do. I'm building with straw bales as they have high insulation value, 6-12-6 argon double glazing and very thick batts in the roof area too. Given that I have just joined this forum I didn't expect to get into a p ssing contest so quickly and as you have no idea about me I find it very disappointing that you are prepared to get on my case and call me ignorant so quickly. I might be a recent joiner to tis forum but I am NOT stupid and I spend my hard earned very wisely thanks. I won't be upset if you keep your thoughts to yourself and more friendly members respond to my queries. I know quite a bit about straw bale building and have a lot of experience with small wind generation which maybe I can share down the track. regards Dave.

                  Comment


                  • #10
                    Originally posted by Colesy View Post
                    I see that was my degrees symbol then, Got it. So, It's just your opinion Mike, do you think in my situation NiFe is the go? cheers Dave
                    I've got no idea what your situation is, how much work you are / are not willing to do , if NiFe is a good match. 2 downsides a) high internal resistance b) 50-70% efficient,

                    I will state, that you should ignore wind, unless you have to tie your hat on every time you go outside. Otherwise, the breeze will just make the blades rotate, but not much energy can be harvested.


                    Powerfab top of pole PV mount (2) | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
                    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
                    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

                    solar: http://tinyurl.com/LMR-Solar
                    gen: http://tinyurl.com/LMR-Lister

                    Comment


                    • #11
                      Thanks for that Mike. It is windy, I can do wind site assessments and I know probably 95 percent of small wind turbines should not have been installed. Wind in the less sunny months can be a real help for the batteries. I suspect I will have to dump energy from the wind turbine, that can go into the thermal store too. I should rephrase the query. As someone who has gone off grid and knows the ins and outs of NiFe would you install NiFe batteries today in a new set up or would you choose another battery option given recent developments.

                      Comment


                      • #12
                        Originally posted by Colesy View Post
                        .... As someone who has gone off grid and knows the ins and outs of NiFe would you install NiFe batteries today in a new set up or would you choose another battery option given recent developments.
                        Today, with existing tech, I would install NiFe again. In my situation, we often go 3-15 days of solid cloud/rain/drizzle in winter, trying to maintain a FLA bank in those conditions, would consume a lot of diesel (I slow charge with a 3Kw genset) The long gloomy periods tilted my install toward NiFe, since varied states of charge don't bother them.

                        In 3-5 years, I expect to see MAJOR improvements in LiPo4 BMS systems, and the prices should be lower than the stratosphere. So not knowing your site conditions, off the top of my head, I would say: Consider a 5 year FLA bank, and re-evaluate the state of the art batteries & BMS in 4 years and see if any make sense.

                        Powerfab top of pole PV mount (2) | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
                        || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
                        || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

                        solar: http://tinyurl.com/LMR-Solar
                        gen: http://tinyurl.com/LMR-Lister

                        Comment


                        • #13
                          Originally posted by Colesy View Post
                          Round three without the degrees symbols this time! Well flat plate collectors here last year popped all over the place after freezing. My evacuation tubes didn't. I don't know where you are JPM but evacuated tubes here in Oz are not twice as much but are maybe only 25 percent more but the point is they are much better performers on intermediate days that flat panel collectors. I'm a Physics teacher so I do understand about insulation and draught proofing which are actually rather obvious things for people to do. I'm building with straw bales as they have high insulation value, 6-12-6 argon double glazing and very thick batts in the roof area too. Given that I have just joined this forum I didn't expect to get into a p ssing contest so quickly and as you have no idea about me I find it very disappointing that you are prepared to get on my case and call me ignorant so quickly. I might be a recent joiner to tis forum but I am NOT stupid and I spend my hard earned very wisely thanks. I won't be upset if you keep your thoughts to yourself and more friendly members respond to my queries. I know quite a bit about straw bale building and have a lot of experience with small wind generation which maybe I can share down the track. regards Dave.
                          Do as you wish, but you seem to have misread or read into (inferred) what I wrote. I'd respectfully suggest you reread it. Nothing I wrote was directed at you personally. I did not call you ignorant. Ignorance is when someone doesn't know something. When used in the usual sense, or at least as I learned it and use it, there are no pejorative connotations. It's a condition, not a personal or moral failing.

                          Nor did I call you stupid. Infer that upon yourself, but know that it's your call or perhaps the call of others upon you, but not mine. I wouldn't do that. Besides, how can I even presume to call someone stupid without knowing they exist ?

                          FWIW and not that it matters, but I've found ignorance is a lot easier to change than arrogance induced stupidity.

                          As for what you know, and also because like most, I'm ignorant of about 99.44 + % of most everything, I'm sure you know more than I do about many things. Most everyone does. However, my guess is that how to lower heat transfer between the inside and the outside of a dwelling as well as maintaining indoor air quality, and also solar thermal applications are not two of them.

                          That flat plate systems fail in freezing weather may say more about the poor design and/or maintenance of those systems than any design superiority of evacuated systems in cold(er) climates. I had a flat plate system in a very cold climate and it worked well (never froze) in ~ 15 years of continuous service. I'd also note, that was what is called a direct system, that is, a flat plate system that operated without a heat exchanger.

                          As for performance in sunny vs less than sunny conditions/climates, while evac. tube systems can have a higher % efficiency under less than clear skies, overall, depending on something called the "clearness index" which is one way to quantify how "sunny" a place is and a few other parameters flat plate systems often and usually do perform as well or slightly better on an annual basis than evac. tube systems in terms of useful heat delivered to the load. Most, or at least a lot of that is due to the idea that while the lower overall (loss) heat loss coeff. of evac. tube systems results in higher efficiency of evac. tubes under less intense irradiation, that higher efficiency comes at the very time when that irradiance is, by definition, lower. Most production of thermal solar systems, both evac. tube and flat plate, happens under clear(er) conditions. Under those clear(er) conditions, an evac. tube system will usually deliver less heat to a load than a flat plate system due to the lower optical efficiency of those evac. tube systems compared to flat plate systems.

                          If you need heat at process temps., maybe > 100 C or better, the lower heat loss coeff. of evac. tube systems makes them superior to flat plate systems for such applications. For DHW applications, that capability of evac. tube systems is wasted in several ways. Using a flat plate and larger storage for DHW applications will be safer, more environmentally appropriate, more cost effective and, if properly designed and maintained, a better deal.

                          All that said, a PV system coupled to a heat pump water heater is probably a better way to go than solar thermal, at least for heating water for domestic use.

                          On straw bale insulation systems: I've talked with a lot of folks who tout straw bale systems. Just opinion here, but it seems to me most of them are not as technically and practically astute as those who think there are better ways to reduce heat transfer in a building envelope. I have run across a lot of folks who read, or heard from some peddler or someone with skin in the game that straw bale design is the cat's pajamas. I've not heard good things about straw bale design from those whose opinions about such things I respect. I never got a good answer to the question of what happens to the building heat loss when the straw settles and creates gaps at the top of wall sections or at fire stops or horizontal barriers (and just like all loose fill, it does settle). Another concept lost on most straw bale backers I've spoken with is what happens (more so in colder climates) when the colder straw, that is, colder than the interior dew point, being hydroscopic - similar to most loose fill substances, absorbs moisture. Seems to me that what I learned was that the condensate will just kind of hang around and either wick and get absorbed by the straw and have the dual effect of allowing bacteria growth as well as reducing the insulating value of the straw. There are ways to reduce in/exfiltration, but most straw bale backers if talked to about it seem ignorant of the problem much less its mechanisms or how to mitigate it.

                          I'm wondering, if straw bales are so great, why don't you use that systems for ceiling insulation instead of what reads (to me anyway) like fiberglass batts.

                          As for argon fill in multiglazed windows, first of all, the slightly lower thermal conductivity of argon makes little difference in the thermal performance of fenestration systems. Air is almost as good as an insulator in fenestration systems and a lot expensive to the point of often making argon filled window systems less cost effective for the slight benefit afforded by argon filled systems. Run the numbers - not simply compare mfg. published stuff - and compare costs.

                          All that about argon may be moot anyway. Ever see moisture between glazings in a multipane window ? Happens all the time, particularly in cold(er) climates. Just a matter of time when. Know or ever wonder where the moisture between the panes comes from ? It comes from outside the space between panes. That means what was once between the panes ain't there anymore - including the argon. The argon got replaced by air. So, after a few years, you're back down to air. Measure some temps. and calc. your glazing's actual heat transfer coeff. when the windows are new (and while your at it, see how it compares to published data). If you're really curious (as I assume you are, being a student as well as a teacher of physics), measure it again in a few years. In the meantime, enjoy your argon while you have it.

                          If you get into a pissing match, it'll be because you choose to engage in such things with someone else, but you won't do it with me.

                          This is, among other things, a place to exchange opinions. Some of my opinions about perhaps better or at least different ways to save energy/money, and the best uses of alternate energy to further those ends seem different from yours. I believe my opinions about such things as discussed in this thread may be better than those of some others, maybe even some of yours, as well as being more practical, and based on academic study, but equally or maybe even more importantly, based on work and experiment during and after academia.

                          Whether you and I ever see eye to eye matters not a whit to me, and without rancor. What is important to me, FWIW, and among other things, is that others who may be reading what you write get a chance to look at what may be some of the possible shortcomings and less than optimal outcomes from reading what you write of your opinions.

                          Lastly, everyone who tells you what you might not like, or what you may disagree with, or what you think might be embarrassing, or bruise your perhaps thin skin isn't out to hurt you.

                          Take what you what of the above. Scrap the rest.
                          Last edited by J.P.M.; 08-10-2018, 12:24 AM.

                          Comment


                          • #14
                            Mike, thanks for that thought. I'm currently building temporary accommodation for myself and the lady wife to live in while we build the main house. I think it will be about 2 years before I need to actually choose storage so I do have a bit of a buffer before I need to make the final decision. I was too thinking along the lines you suggest but it is a bit like buying a computer, you know that soon they will be faster etc etc however with newer technologies the knowledge of longevity is less well known. the area I am moving too also does have periods of dull days but has the advantage of steady winds too. I installed an 11 kW turbine on a 27m tower for a grid connected house a few years back a few km from where I'm heading and it produces about 120 kWh's a day to give you an idea so I think the balance between solar and wind will work quite well. I'm still leaning in the NiFe direction at the moment. Best regards and thanks for your helpful input.

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