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Forum Index : Other Stuff : Use for your excess solar and oil burner heat
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| rogerdw Guru  Joined: 22/10/2019 Location: AustraliaPosts: 852 |
Hey Dave, I think I've found an answer for your heating problems ... as well as your excess solar production ... and you could top it all off with one of your 600kW oil burners. I came across a video in the suggested viewing list on youtube tonight and it looks right up your alley. Seems a new startup in Finland (of all places) has come up with a really simple way to store excess electrical energy as heat ... and to recover that heat up to a couple months later. They simply create an insulated storage container of sand, above or below ground ... run pipes through for airflow ... then use excess solar or wind energy to heat it up to between 300-600 degrees via resistive heating ... though it could be heated as high as 1000 degrees if you have the means! To access the heat, they blow air through and use a heat exchanger. Bit hard to believe, but the claim was ... to heat 35,000 homes ... all they'd need was a volume of sand roughly 40 meters in diameter by 25 meters deep/high. See 17 min mark in the video on their site This is all a bit more than just theory too, as they have a pilot project happening. The founders answer a heap of questions in the video interview ... well worth watching. So, looks like all you need is to dig a decent hole, insulate it and lay in some pipes and heaters ... then fill it with sand. In summer when you have more energy than you can poke a stick at ... use the excess to heat the sand. Once the cooler weather arrives, start drawing heat from the storage ... and in your case ... keep topping it up with your oil burner. You might get away with just hitting it hard an hour a day or something like that ... and yet be able to draw warm air off it continuously over winter. Their 35,000 home system mentioned above works out to a storage volume of 31,420 cubic meters ... so theoretically that means less than 1 cubic meter per home. Somehow I don't think that's right ... but with machinery and some space in the backyard, it wouldn't be hard to manage a 10 cubic meter storage ... then build your greenhouse on top to take advantage of any escaping heat. Not sure how you get the heat from your burner into the sand ... maybe a seperate batch of pipes so the soot and residue doesn't contaminate the sand ... perhaps like a steam engine where you can access the pipes at each end to clean out every once in a while. Whadda ya reckon?  Cheers, Roger |
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| Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1578 |
Well, as usual, quite a lot. :0) To be able to store energy I can produce in summer to use in winter is the holy grail basically. I could easily throw 50 Kwh a day from the solar into a heat bank probably more than 6 Months of the year. Easy to do that in summer even when I am running the AC and even easier spring and Autumn when the generation is less but there is no AC bing used so even more excess power. Firstly, thank you for brining that to my attention. It was certainly thought provoking and interesting. I like to look at these things because they do bring on other ideas even if not entirely applicable themselves. See enough input from the smart people and you can maybe take a bit of everything and come up with something specificity suitable for yourself. The first real thought after watching the vid and perusing the site is I need to sit down and do a "Viability Audit" for my situation. So many hair brained ideas and possibilities. I really need to work out the best, most practical thing I can apply to my situation and forget all the rest.... as interesting as they sound. I need to consider setup cost, Situation ( as in where to practically put it) operating cost, ease of operation, Benefit and Drawbacks. I can see a lot of benefits to the Sand idea and of course many questions and some drawbacks. One thing I think they REALLY glossed over was the insulation part. At first I thought they were saying the sand itself would be the insulation and just heat the core of the pile and the the sand would insulate itself. Going back a few times as I did, I then heard and read mention of the insulation. THAT is a big question for me. What are you going to use to insulate something in the ground that you want to sit at 600oC? I don't know much about industrial insulation but I have an idea that a lot of it would loose it's R value when compressed as would be the case and also when there was water seepage. I can think of ways around this but thinking for my own application, it sure wouldn't be cheap. Thought that comes to mind is Hebel/ Areated Concrete but that is pretty Hygroscopic and having used the stuff in High temps before, It will heat soak and get Damned hot because the base material, concrete, is basicly as dense as sand itself. Heat seeks cold so there are thermal pathways and it warms up at high temps and over longer periods. Being in the ground there would also be the problem of water ingress so I don't see that as being a viable insulator. Anything else I can think of is rather exotic/expensive or wouldn't come near standing the temps. While 600o is given as a number, to put it in perspective, one is talking about a temp that is only 60o below the melting point of aluminium. I have cast 5Kg blocks of ally and it's amazing how long you can spray them with a hose before they stop hissing or how easy it will boil a 20L drum of water minutes after it has solidified. Aluminium is only marginally better thermal capacity than sand and still less than a quarter of that of water. I was a little lost on the thinking of the guys in the Vid. They pointed out that water was not a good working medium for the storage or transport of the heat due to the temperatures. Once again I am confused by the mathematics... I think. Water has 5 times the thermal mass of sand. They pointed out that their sand system has 2.5X the thermal storage by volume of water. I don't get it. Unless the maths is exponential, You would need 5x the volume of sand or, I presume, to get the sand 5x hotter for the same volume to store the same energy. Maybe that's where I'm going wrong BUT, if not, seems their sand would give only 1.2X, maybe 1.3x the thermal storage per volume of water @ 600o. 2 points to that were they said you can only take the water to 95 which I have read before for safety margin and evaporation/ pressure increases rapidly after that and what seems the key to the system is containment, the sand won't leak out. For their anticipated use, that could be a very big Plus factor. For a DIY setup, there are a number of considerations I see. The size of the sand bank. Excavation, getting rid of the spoil, cost of the sand which would be a significant amount to get decent storage. The insulation The piping Heating elements. I think for heating with a burner, this would only be efficient to start with when the pile was at low temps. The exhaust temp from a burner is always going to have to be greater than the storage bank temp so it would be easy to be throwing away gas that was 300o or more. That would be a big efficiency loss and one would have to calculate the point at which that was not viable. Not overly important with free fuel but still, no point in burning 10L of oil to raise the temp of the storage only 10 KWH . There is a lot to this idea that gels with an Idea I already had a while back. Bury a couple of 1000L IBC filled with water that were surrounded and Insulated with Cool room panel. Heat and cool the water which would provide a Good amount of storage capacity. In summer they could be cooled in the early morning blowing air through an external radiator and with a bit of water misting would get the temp down further. I believe I could get down to 17C on average which would be great on a 30+o day. Easy to electrically heat in winter as well as heat with a Burner going through a heat exchanger. I have always had this idea pretty much at the forefront of my mind but held off a bit as we have a spa to put in which could do the same job. Unsure if we will go though with that yet. The other thing they mentioned which I already thought of was having a greenhouse over the top of the IBC's. Seems logical and the losses might even be desirable in that scenario. Plants do a LOT better above 120 Soil temp than below so keeping the GH above that in winter would allow pretty much year round production of anything depending on how hot you kept the enclosure. There is a guy in the US doing that I helped convert his Gas fired heaters for his grow house to Oil and he does summer crops all year round and of course gets premium dollars for his product as no one else is doing it and he is local. Also taps off an amount of exhaust gas to raise the CO2 levels for faster plant growth. The sand concept is pretty much the same principal as the IBC's except the sand idea has the potential to store the heat longer. I perceive though that there would be a heat up period in summer then pretty much a maintenance period in autumn where one was just trying to stop the pile cooling through the losses before the heat was actually wanted. I didn't hear them mention what those losses would be in the vids or see on the site and I think that is a key thing. If you have excess power that may not be so important if it is effectively throw away anyhow but you do have to play cost and yield off at some point. They mention less than 10 Euro per Kwh storage which does not sound that great to me. One thing I LOVED about the people in the vid is they are clearly concerned with saving the planet and associated ideals but they are reasonably realistic about it. One guy said " Once you get to 20% of wind power a Grid Crashes". Least they are honest about that. To their benefit to be but still glad to hear the truth come out with all this zero emissions grid fantasy. Also mentioned the unviability of battery storage at grid level. Another lie of the green obsessed. I can see the sand idea has merits but like all these things, there are a lot of unanswered and key questions. I'd like to know what the insulation they are intending to use is and the thermal losses over whatever period of time. The concept is sound but the devil is ALWAYS in the details. Thanks again for the heads up Roger. Certainly food for thought. Now, for that fantasy Vs. Viability audit of my own..... |
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| Georgen Guru Joined: 13/09/2011 Location: AustraliaPosts: 462 |
What worries me most that there is lots of energy we could use, but problem is in storage. If it gets solved on acceptable scale before our declared "0" emissions target we are good, if not we are up creek. George |
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| Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1578 |
Making the energy is easy. Storage is the difficult and expensive part which is why Fossil fuels have been the go to. That and energy Density. The agenda pushers talk about more powerful batteries. The practical scientists tell you they will never get near the energy density of liquid fuels as you would effectively making a battery with the characteristics of Nitroglycerin.. very unstable and with a lot of energy that Could run away with a very rapid ( explosive) energy release. No matter how you want to store energy its very expensive. They talk about pumped hydro etc and spin that to cost per KWH but it's still Hundred Million dollar undertakings and very disruptive to the landscape and creates huge emissions in it's construction.... which is inevitably passed off and excused under some green BS. |
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Murphy's friend Guru Joined: 04/10/2019 Location: AustraliaPosts: 648 |
Yes, there are expenses involved but if you use the tides in the right location the effect on the landscape could be minimal. Problem here in WA is where the big tides are there is no big city/ industry to use that power. So its unlikely to happen anytime soon. How about sinking a turbine to the bottom of horizontal falls? you would not notice it from the surface and the tourist boats can do their business as usual. Silly idea, eh? |
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| Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1578 |
It's always a great idea to use whatever natural resources are around you. Unfortunately some places seem to have them in great abundance like Norway that is 99% Hydro and exports a crap load as well and then there are other places that have nothing or intermittent. I was amazed when I went to NZ and saw the Geothermal there. They have a Big stadium/ convention centre in rotoroua on the edge of the lake that is 100% geo powered and I think from memory was only connected to the grid to export? They have an event on and the simply wind up the turbines which only takes Minutes and they can power several times what the pace can draw. They built it with future expansion in mind but hard to fathom where it is why they would ever want to go bigger. Again though, big difference between storage and generation. |
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| Solar Mike Guru Joined: 08/02/2015 Location: New ZealandPosts: 1138 |
Back in the 70s many back yards had a geo thermal steam bore, used to cook, heat water or spa pool. The govt had to shut them all down in the end, supposedly to prevent excessive (FREE) draw off from affecting the geo thermal power station. Some how that doesn't make any sense as the power station had pipes that went down a KM or so, stuff from back yards were quite shallow depths. Its a wonder they don't tax our (FREE) sunlight hitting the PV also... Mike |
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| Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1578 |
I seemed to recall something about people even having micro turbines in their yards but either it was illegal or there were mountains of paperwork that made it neigh impossible. I also seem to recall either seeing a vid or hearing about someone that had a turbine in their Shed making power. All the hotels in Rotorua, even the older, smaller ones advertised free hot spas in every room. Literally a Pipe coming out the ground running in 24/7 and just draining out again. Kids loved that! Remember driving down there looking at the tourist guide and seeing a couple of ads marked " No Sulphur Smell" . Had no idea what that was till we got closer. Started looking at each other as to who Dropped a Sneaky one but then after winding the windows down and driving 10 Km and the pong was getting worse, the penny dropped. Got used to it but when we went to the thermal park In places it was hard to breathe. Incredible seeing an entire boiling lake and the yellow Sulphur Piled up by the ton. I know damn well if I lived where there was any Geo thermal, I'd be sinking a bore on the QT at the back of the shed and running some sort of turbine or at least heating the house or the domestic hot water with it... Seem to recall you can't drink it with the minerals but a Flat plate heat exchanger with the town water would soon take care of that. What an incredible resource that would be to have free Steam like that! |
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InPhase Senior Member  Joined: 15/12/2020 Location: United StatesPosts: 178 |
Places like that make me uneasy. It's super cool but still unsettling. I visited Yellowstone and was struck by its beauty. But those geysers and hot springs mean that there is a churning cauldron of hell not very far below your feet. |
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