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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
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  1.  
    James, as Phil hinted, you'd be greener to charge your EV directly from the grid at 1am, when intensity is lowest.

    Export your PV during the day, or better still, charge a home battery and export it or use it at 6pm, when grid intensity is highest.

    Unfortunately most people are doing the exact opposite of this. They're looking at the financial side and discharging their home battery very late at night, instead of during the early evening peak. The subsidies that the rest of us pay (FIT/ET), are badly set up as they encourage that behaviour.
    • CommentAuthorborpin
    • CommentTimeSep 11th 2019
     
    Posted By: WillInAberdeenExport your PV during the day
    Excess PV of course :bigsmile:

    Posted By: WillInAberdeenThey're looking at the financial side
    Unless you have the desire and the finacial means to be philanthropic, that is inevitable. From the perspective of encouraging the installation of PV to help with CO2 emmissions, the financial setup has always been badly designed. This big generation companiues are not required to be loss making, so why should the small generator?

    With the introduction of the Octopus Agile type tarrif, it seems there should be no reason not to pay exporters a fair rate which will then encourage the use of batteries to charge overnight for local consumption during the day (while still exporting). If the Exporter was paid a fair rate, the need to store woul be reduced.
    • CommentAuthordickster
    • CommentTimeSep 11th 2019
     
    As the sun sets, we use electricity stored in Powerwall 2 to run our house. If the sun hasn't done it's job that day, we charge the battery on E7 overnight to see us through. We have therefore transferred our usage from the grid to overnight and done our bit to balance the grid.

    Not yet worked out what to do if EV arrives on the scene.
    •  
      CommentAuthordjh
    • CommentTimeSep 11th 2019
     
    Posted By: borpin
    Posted By: WillInAberdeenExport your PV during the day
    Excess PV of course :bigsmile:

    No, I think Will means export it all. He doesn't like people diverting it for their own use.
  2.  
    Uhhh... I literally just said "use it at 6pm, when grid intensity is highest", didn't you read before commenting?

    If you're claiming Export Tariff for 50% of your generation, paid for by me but also by people in serious energy poverty, then I'd like you to export at least 50%, thanks very much. Export some more if you want to be greener.

    Or maybe you are not claiming Export Tariff for 50% of your generation? In which case, fill your boots.

    Actually, I don't blame individuals for gaming the system for their own gain, though I chose not to. It's the system that needs changing, and the smart meter tariffs will help, as Borphin said.
    • CommentAuthorphiledge
    • CommentTimeSep 11th 2019
     
    I think the spirit of FIT is(was) that you export what you can over normal daytime usage, where normal doesnt include grabbing it all by way of PV diverters or daytime car/personal battery charging. As I understand it thats what the 50% export payment was intended for.
    • CommentAuthorphiledge
    • CommentTimeSep 11th 2019
     
    A post too late!!
    • CommentAuthorborpin
    • CommentTimeSep 11th 2019
     
    Posted By: djhNo, I think Will means export it all.
    Of course you actually cannot do this (think about it) unless you have zero consumption.
    • CommentAuthorborpin
    • CommentTimeSep 11th 2019
     
    Posted By: WillInAberdeenI literally just said "use it at 6pm, when grid intensity is highest"
    It makes me think that the whole balancing of the grid needs some serious reimagining. If there were lots of micro generation, storing excess during the day, to export it when CO2 intensity would peak, that could have an interesting impact. I do though go back to the need to make it financially sensible for those doing it.

    Those fleecing the 50% but never actually exporting do irritate me. Such a daft setup in the first place.
    •  
      CommentAuthordjh
    • CommentTimeSep 11th 2019
     
    Posted By: WillInAberdeenf you're claiming Export Tariff for 50% of your generation, paid for by me but also by people in serious energy poverty, then I'd like you to export at least 50%, thanks very much. Export some more if you want to be greener.

    You have completely the wrong perspective on the situation. The situation is that even with diversion I cannot use 50% of my generation. So I am subsidising you and people in serious energy poverty, not the other way around.

    To date, I have consumed 37% of my generation. So if I was feeling mean I might switch to a smart meter that did monitor my export, and/or move to a tariff that paid me for my export. So please stop accusing me and other people with PV of unjustified greed.
  3.  
    Once again, please read before commenting, as I think the 'unjustified accusations' are not being made by me. You could start with my last paragraph.
    •  
      CommentAuthordjh
    • CommentTimeSep 11th 2019
     
    I quoted what you said that I responded to.
  4.  
    Just to repeat.
    I was wondering the effect of running high powered loads (3kW+) off batteries in relation to there 'health'
    Rather than the ins and outs grid load matching for environmental benefit etc.
    :-)
    • CommentAuthorFlubba
    • CommentTimeSep 12th 2019
     
    James,

    I think it would very much depend upon the design of the battery pack and arrangement of the internal cells more than anthing else, number of cells ganged up in series vs parallel etc. High'ish draw generally shouldn't be a problem for Lithium battery chemistries as long as they are within a temperature range, more so than other chemistries. The limiting factor for a long life I would suspect is the usual overall cycles per cell although without googling I'd hope an easier life with lower discharge rates should enable a longer life.

    The main issue I see is the pairing of the overall battery capacity vs the inverter it's connected to, Powerwall 2 is upto 5kW IIRC and 13ish kWh so I would presume it would at least last it's warrantry period loading and unloading at 5kW. Same headache with any storage solution really, I note SSE decided to bump their proposed Coire Glas Pumped storage scheme from 600MW to 1500MW.

    Generally though I agree with Tony, home battery tech is along the lines of eco-bling in my opinion storage at home would be best done thermally or as a side effect of having an electric car. Even once we get to the point of having quantities of used EV battery packs available I feel this would be best managed in bulk with health and usage monitoring done on a 'professional' basis by folk who know what they are doing.

    I think in general storage is best done cost effectively both in terms of money and resources at a grid scale e.g. pumped storage projects or liquid air. We don't really have much storage at all and batteries are a drop in the ocean, they have their uses for grid ancillary services e.g. frequency response but as actual storage we are talking MWh scale.

    For actual grid scale storage to allow for a grid with much higher levels of intermittent renewables we are 100's of GWh's minimum if not TWh's. The obvious place to start would be to get enough storage on the grid to comfortably and reliably peak shave daily demand heading toward enough storage to ride through a few days of low wind.
    • CommentAuthorgravelld
    • CommentTimeSep 12th 2019
     
    Given the energy is most likely used by your neighbours, what if I only want to heat some hot water for my kid's evening bath and the neighbours need the energy for their Agas and hot tubs? Asking for a friend.
    • CommentAuthorowlman
    • CommentTimeSep 12th 2019
     
    AFAIK home batteries don't discharge into the grid unless they are smart and central controls ask them to. Then only a certain agreed % whereas your exported PV does feed local needs, I think. You may know something else.
    • CommentAuthorgravelld
    • CommentTimeSep 12th 2019
     
    Sorry, I'm referring to the "everything should be exported" argument.
    • CommentAuthorowlman
    • CommentTimeSep 12th 2019
     
    OK Dan, understood.
    •  
      CommentAuthorDamonHD
    • CommentTimeSep 27th 2019
     
    I'm now making a definite effort to get a Sunamp UniQ heat battery in, though it probably will not be effective until Feb:

    http://www.earth.org.uk/note-on-solar-DHW-for-16WW-UniQ-and-PV-diversion.html

    Rgds

    Damon
    • CommentAuthorwookey
    • CommentTimeOct 1st 2019 edited
     
    <blockquote>I was wondering the effect of running high powered loads (3kW+) off batteries in relation to their 'health' </blockquote>

    The bigger the battery the less it matters. In general simply using a lithium battery generates negligible wear. The things that generate wear are overheating, sitting at/near max voltage, and overdischarge. You can charge/discharge a cell up and down at rates that do not heat it up, and not going near the 'full' or 'empty' voltages many thousands of times. But charge it or discharge it fast enough to make it hot and its life will reduce.

    Remember that car batteries (20-100kWh) are discharging at 60-150kW (more for fancy cars). So a 5kWh battery discharging at 3kW ought to be fine. However what actually matters here is current per cell, and car batts are 400V (~110 cells in series) or 800V on the fancy cars, whilst home batteries all seem to be ~50V (14 in series), so that's 4 times the current per cell for the same nominal capacity (assuming the same size cells).

    Different cells make different tradeoffs between capacity and max current (and other things - mostly price). So there are 'high power' cells and 'high capacity' cells (and expensive cells that are quite good at both). So all this means 'it depends' on the parallel/series layout of the pack, the exact type of cell used and its chemistry, and also what the connected inverter can do.

    I was just looking at a Darfon 50V 4.5kWh pack and it specifies 1.8kW continuous, 2.3kW peak. That means that 3kW would make it hot and be bad for it. Their standard kit is two of those, for a 9.8kWh batter, paired with a 3kW inverter. That system can supply 3.5kW from the battery alone, or 3.5kW from batt+PV.
    •  
      CommentAuthordjh
    • CommentTimeOct 1st 2019
     
    Posted By: wookeyThe things that generate wear are overheating, sitting at/near max voltage, and overdischarge.

    I noticed in the instructions for some of my battery-powered garden tools that it says not to leave the batteries fully charged for long periods (e.g. over winter). That's made me a bit worried as to how far I should charge and discharge the batteries in regular use? I'd been assuming that the BMS would be designed to protect them and make them work so naive users could get the best? use out of them.
  5.  
    Posted By: DamonHDI'm now making a definite effort to get a Sunamp UniQ heat battery in, though it probably will not be effective until Feb:

    http://www.earth.org.uk/note-on-solar-DHW-for-16WW-UniQ-and-PV-diversion.html" rel="nofollow" >http://www.earth.org.uk/note-on-solar-DHW-for-16WW-UniQ-and-PV-diversion.html

    Rgds

    Damon


    Thanks for the link Damon. I was going to share our experience of SunAmp but it looks like you might already have a smaller one installed?

    Agreed with your points on the website about the lack of display on the unit. We have an Eddi controller which gives us an idea of how much we've diverted to the UniQ and has a boost button (which appears to address a few of your points). What it doesn't do is say how much is already 'in the tank' so we've had to learn when to boost on demand or set timers in the week, still a bit of a mystery and the odd cold shower as a result...
    • CommentAuthorborpin
    • CommentTimeOct 1st 2019
     
    Posted By: djhI noticed in the instructions for some of my battery-powered garden tools that it says not to leave the batteries fully charged for long periods
    I think it is Tesla that say that the most efficient and life prolonging pattern for lithium batteries is to keep the charge between 10-80%.
    •  
      CommentAuthorDamonHD
    • CommentTimeOct 1st 2019
     
    I think that range is probably good for many lithium-chemistry rechargeables. For example, I usually aim not to go much above 80% for my phone and batteries in storage, etc, where I can.

    But in general I trust the BMS to be sensible in decent equipment, less so in cheap equipment.

    Rgds

    Damon
    • CommentAuthorjamesingram
    • CommentTimeOct 1st 2019 edited
     
    Yes it appears the BMS pretty much does all the management out of the users hands in the better systems to control them within the recomended boundaries, I guess this allows the 10 warranties ( or number of cycles) they offer.

    I'm looking at the LGchem RESU 10H batteries with Solaredge kits.
    Its controls do offer a few interesting options, so it's better than I expected
    such as,
    Prioritising self consumption,
    controlled Timed charge / discharge period (15minute slots) to suit variable peak/low import tariffs
    power backup
    controlled export levels ( for over sizing systems and keeping under G98 limits (3.6kW) in the simply UK domestic situation)

    Doesn't seem to have a charging via the grid option though. ( which would be good for grid load balancing and varible tariff savings during the lean winter months, ie charge over night and use at peak)

    Wookey
    LGchem and Telsa powerwall are 400Vdc set ups
    LGchem use a flat cell stacking setup to reduce heat build up

    They both charge DC direct from the PV and use the PV inverter to switch it to AC
    I presume this is to reduce unnecessary DC-AC-DC-AC transformation .
    I'm not sure it would do anything with regard to what you where suggesting and I'm presuming most EV chargers
    wouldnt be direct DC but 240Vac-400Vdc.

    Solaredge do do a invereter with a direct EV charge point which may deal with this issue you mentioned , that's my next topic of reading up on :bigsmile:
    • CommentAuthorwookey
    • CommentTimeOct 2nd 2019
     
    I think it is Tesla that say that the most efficient and life prolonging pattern for lithium batteries is to keep the charge between 10-80%.


    Everyone says that, and it's correct.

    The standard charge level for battery storage is 40% (that's what a decent RC charger will charge to if you do a 'storage' charge). Determined by voltage, not actual capacity, so somewhat approximate.

    Dave, your power tool BMS will not do this for you - it's way stupider than that. All it will do is stop the pack being overcharged. If it's not too cheap it'll stop individual cells being overcharged, and it'll prevent charging if any cells are too far undervoltage. If it's good it'll stop discharge so you can't get them undervoltage accidentally.

    I have a pile of Makita 14.4V batts (4S2P packs). The early ones only check voltages of the two halves, rather than each cell. Only later ones do it properly. They do have overtemp cutout during charging (but not discharging). None of them prevent undervoltage by overdischarge. If a charge on an undervoltage pack is attempted 3 times it disables the battery forever (because Makita are cynical wankers who want to sell you more batteries). Ripping out this stupid system and dealing with the cells individually is the only way to get good longevity of the packs.

    That's how smart power-tool battery designs are. Not necessarily in your interest at all.

    If you know you aren't going to use it for 6 months or a year, then some discharging down to at least 80% is a good idea, but it's not a huge deal.

    Fancier BMSes in car batteries or home storage batteries (or really the charge controllers rather than the BMSs) will often distinguish between 'normal full' (80%) and 'really full' (100%), in the interests of preserving battery lifetime.
    •  
      CommentAuthordjh
    • CommentTimeOct 2nd 2019
     
    Thanks, Wookey. These batteries appear to have an overdischarge prevention cutout (some are Bosch and some are Parkside). You run the mower until it stops, then charge it and start again. But at the end of the year it says not to fully charge. So it seems they're more user friendly than the Makita ones.
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