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    • CommentAuthorCWatters
    • CommentTimeJan 31st 2017
     
    https://blogs.scientificamerican.co...me-can-increase-energy-consumption-emissions/

    "Storing solar energy in the home can increase energy consumption, emissions"
    "Storing solar energy for nighttime use is less green than just sending it straight to the grid"

    It seems to be suggesting that if you send excess solar PV to the grid then all of the electricity generated is used to reducing C02 emissions. Whereas if you store it in a battery and use it yourself later then some is lost in the charging efficiency. So overall it's greener NOT to use a solar PV backup battery.
    • CommentAuthortony
    • CommentTimeJan 31st 2017
     
    I agree but the economics on an individual basis are tragic and will soon if not already point to the opposite.
    •  
      CommentAuthorSteamyTea
    • CommentTimeJan 31st 2017
     
    Why we need emission taxation.
    • CommentAuthorEd Davies
    • CommentTimeJan 31st 2017
     
    • CommentAuthorEd Davies
    • CommentTimeJan 31st 2017
     
    Yes, narrowly interpreted for the grid as it currently is it's probably less green to store PV output in batteries.

    For the UK grid at the moment (and, I'd assume for Texas) nuclear and renewables do their thing to the maximum extent possible (give or take a bit of wind curtailment for relatively local grid congestion reasons), coal does a bit of ramping up and down but most of the gap between low-carbon and demand is done by relatively efficient CCGT gas plants. Therefore it doesn't really matter from a kgCO₂e/kWh point of view when households take their electricity.

    Maybe in Texas, though, some of this gap filling is done by open-cycle peaker gas plants which are cheaper to build but less efficient in operation so it would matter there. On the other hand, the Texas peak is likely to be driven by day-time air conditioning rather than the evening dinner cooking/watching TV load in the UK.

    There are other considerations, though. As has already been said, financially it might make more sense for an individual and if that means more PV gets installed then it could be a net win. Relatedly, batteries ought to be quite a good way to get round the 16 amps/phase (bit under 4 kW) limit so could also result in more PV.

    That 15% loss in Texas is absolute as very little of the year requires heating whereas in the UK for a chunk of the year the loss will contribute to heating if the batteries are in the insulated envelope (not in the garage, for example).

    You also need to offset the losses in the local distribution network against that. If many of the houses in an area have PV energy will likely have to go back to the DNO's substation before being sent on to industrial or commercial areas during the day. Current losses in the distribution network are typically about 5% which might be doubled in this case.

    Overall, I think domestic batteries aren't an urgent thing but in the long run they're worth encouraging.
    •  
      CommentAuthorSteamyTea
    • CommentTimeJan 31st 2017
     
    Texas produced about the same amount of energy from wind as the UK did in 2015. 42 GWh compared to our 40.4 GWh.
    They have about 17.5 GW installed capacity against our 13.6 GW.
    https://en.wikipedia.org/wiki/Wind_power_in_Texas
    https://en.wikipedia.org/wiki/Wind_power_in_the_United_Kingdom

    They also have about 0.5 GW (510 GWh in 2015 [estimated]) of PV installed compared to our 8.9 GW (7.6 TWh in 2015).
    https://en.wikipedia.org/wiki/Solar_power_in_Texas
    https://en.wikipedia.org/wiki/Solar_power_in_the_United_Kingdom

    Makes you wonder why Texas does not have more PV, but they are doing well on Wind.
    •  
      CommentAuthordjh
    • CommentTimeFeb 4th 2017
     
    Some researchers in a reputable journal (Nature Energy) are suggesting that grid-linked domestic battery storage actually increases emissions:

    https://arstechnica.co.uk/science/2017/02/want-to-minimize-your-homes-carbon-footprint-go-for-solar-forget-the-battery/
  1.  
    Patently absurd. The reasons presented for the increased energy consumption are straw man arguments.

    Home energy storage makes absolute sense in the long run. These studies are looking at the situation as it stands today where home energy storage is in its infancy and not optimised.

    If the majority of homes had home energy storage, smart meters would start to make sense and the could create a truly intelligent energy network.
    •  
      CommentAuthordjh
    • CommentTimeFeb 4th 2017 edited
     
    Posted By: bot de pailleHome energy storage makes absolute sense in the long run. These studies are looking at the situation as it stands today where home energy storage is in its infancy and not optimised.

    Seems reasonable that when considering a decision today, I should consider today's situation. In the long run, I might change my decision depending on how the future plays out.
    • CommentAuthorringi
    • CommentTimeFeb 4th 2017
     
    Posted By: bot de paillePatently absurd. The reasons presented for the increased energy consumption are straw man arguments.

    Home energy storage makes absolute sense in the long run. These studies are looking at the situation as it stands today where home energy storage is in its infancy and not optimised.

    If the majority of homes had home energy storage, smart meters would start to make sense and the could create a truly intelligent energy network.


    Not convinced that home energy storage will ever be more "green" then potting the storage on the grid and/or local network. Unless by having storage people are more careful in how much power they use....
    • CommentAuthorEd Davies
    • CommentTimeFeb 4th 2017
     
    Yes, anything which makes people more aware of how much energy they're using and under what circumstances is probably a good thing.

    For a whole lot of reasons I think that the logical “unit” for energy management is about the size of a hamlet or small village; say 5 to 100 homes. Could be completely isolated like Eigg or embedded in a large built-up area like BedZED. Small enough that people can understand what's going on but large enough that individuals are left with a reasonable amount of flexibility in their personal consumption.

    Most importantly, small enough that it's possible to negotiate the financial arrangements to produce an efficient solution. Currently it's in the large power producer's interests to maintain the big asymmetry in prices for import and export, not least because they have to finance the local network costs out of that. This means there's a bigger financial incentive for home energy storage than storage in the network or grid despite it probably being somewhat sub-optimal overall.
  2.  
    The utility companies want us to use energy, period. How else are they and the government going to pay for the upcoming investment in new nuclear power as well as the decommissioning of existing power plants?

    When making a decision of whether to invest today, you need to look to the future or it will never make sense, that goes for most things in general but especially so for large scale infrastructure like national power.

    I dont understand why home storage should consider putting energy back into the grid. Surely the whole point is that you aim to consume the energy as close as possible to the source of generation and avoid transmission losses. The less the utility companies need to send you across the grid with the losses involved, the better.
    •  
      CommentAuthordjh
    • CommentTimeFeb 4th 2017
     
    Posted By: bot de pailleThe less the utility companies need to send you across the grid with the losses involved, the better.

    The losses in a battery storage system are greater than those in the grid.
  3.  
    But the energy generated at home is "free" so it doesn't matter. How many coal power stations operate purely to account for transmission losses??
    • CommentAuthorEd Davies
    • CommentTimeFeb 4th 2017
     
    Posted By: djhThe losses in a battery storage system are greater than those in the grid.
    The “losses” in the battery may well contribute to heating the home (every joule gotta be somewhere).

    Grid losses are indeed small (2%?). Losses in the distribution network are larger (5%?). Depending on the situation domestic PV energy may well finish up going across the whole distribution network twice, once in the direction it's not optimized to flow so could be significant (10%?). Not far short of the battery losses.
    • CommentAuthorringi
    • CommentTimeFeb 4th 2017
     
    Remember, Remember, the article was written for the USA! And in the USA the peak demand is often from AirCon at the time that PV systems are outputting the most. So by storing at these times, the peak is increased.
  4.  
    The research paper makes this caveat about the way they modelled consumer energy usage:


    "Note that both of these operational modes take a customer-
    centric perspective that seeks to minimize interaction with the
    utility as much as possible. Neither operational method explic-
    itly considers other grid-level services that could be offered by
    distributed energy storage or the potential economic benefits of
    those services. While we are aware of the fact that the methods
    of storage operation selected are not optimal from a purely eco-
    nomic or system perspective, our objective is to assess the spe-
    cific impacts of storing solar energy in the home to minimize
    reliance on the utility, because this application is the primary value
    proposition offered to residential customers by storage vendors"

    In other words the research paper does not model home storage when tied into a smart grid managed by the utility companies and the benefits that that would bring. "Minimize interaction with the
    utility as much as possible" is why the paper is a red herring. Home energy storage ONLY makes sense when it is part of a truly integrated smart grid that ties in energy generation with consumer energy use. Ands smart meters ONLY makes sense when they are also part of such a system.
    • CommentAuthorwookey
    • CommentTimeFeb 12th 2017
     
    Therefore it doesn't really matter from a kgCO₂e/kWh point of view when households take their electricity.


    Not sure I follow you here. UK grid intensity is typically _much_ lower overnight (1/3rd to 1/4 of what it is during the day), so it does matter what time of day you use electricty from a kgCO₂e/kWh POV.

    It is overall more efficient to put batteries in the local grid, than in individual homes, because the (very expensive) resource then benefits from diversity and gets higher utilisation. But at the moment, much of the incentive is about grid independence, so it's more likely to happen at the individual level. (It's still expensive enough that it doesn't make simple financial sense for many (any?) yet, but it's likely to within not too many years.

    I'm going to have to read that paper more carefully. At first glance it sounds like bollocks. I can see how overall emissions might increase due to less residential-PV being sent to the grid, but I can't see how it would increase local consumption (and thus emissions) (Unless you assume that the batt and inverter are in series and _all_ the leccy goes into and out of batt - but that would be a dumb design).
    • CommentAuthorEd Davies
    • CommentTimeFeb 12th 2017
     
    Posted By: wookey: “Not sure I follow you here. UK grid intensity is typically _much_ lower overnight (1/3rd to 1/4 of what it is during the day), so it does matter what time of day you use electricty from a kgCO₂e/kWh POV.”

    But it's not the average grid intensity that matters, it's the marginal intensity: the amount that emissions increase for each extra kW taken. Currently, that's supplied mostly by gas pretty much whenever you take it, whether it's during the evening peak or in the deepest deadest hour of the night. Low carbon generation never displaces all the fossil generation (in the UK, yet).

    https://edavies.me.uk/2016/07/grid-intensity/
    •  
      CommentAuthordjh
    • CommentTimeFeb 12th 2017
     
    I think this 'marginal' thing is overdone. A person who switches on a light, or charges a battery, doesn't get electricity at the marginal rate. Instead every consumer gets electricity at a slightly worse average rate. The instantaneous average rate is a better measure than the marginal rate.
    • CommentAuthorEd Davies
    • CommentTimeFeb 12th 2017
     
    Clearly whatever a single consumer does is not going to be resolvable by any real instrumentation operating at the grid level.

    But suppose a million households charge their 3 kWh batteries overnight (at 220 g/kWh) and use the contents during the evening peak (saving 320 g/kWh). Would that really save (320-220) × 3 × 1000 kg of CO₂ emissions? There are lots of second order considerations like the battery efficiency and the higher efficiency of the grid under low load (lower I²R losses) but basically those 3 GWh are going to be generated by CCGT plants at some time so there's no practical CO₂ saving involved.

    The only saving I can see is that you might have to build less generation plant in the first place.

    Of course, if there's enough wind overnight that electricity would otherwise be dumped then it's a completely different story.
    •  
      CommentAuthordjh
    • CommentTimeFeb 12th 2017
     
    When a large change in behaviour takes place, then clearly it will affect the averages and the new average will still inform us better than the marginal rate. But a million people don't change their mind overnight, these things take time to happen. It's planners' jobs to ensure we have enough generating plant to meet the anticipated demand. In this case, I suppose it would be pretty simple to spin up more low-emissions generators at night to deal with the 3,000,000 kWh demand. No need to do much planning at all, just notice the new average demand pattern.

    Saying that those million people charging their batteries are doing so at marginal rate doesn't make sense to me. The implication is that the 63 million other people are getting their electricity at a different emissions regime.
    • CommentAuthorEd Davies
    • CommentTimeFeb 12th 2017
     
    Posted By: djhI suppose it would be pretty simple to spin up more low-emissions generators at night…
    But that's the point; all the available low-emissions generators are already spun up as far possible.
    •  
      CommentAuthordjh
    • CommentTimeFeb 12th 2017
     
    Posted By: Ed Davies
    Posted By: djhI suppose it would be pretty simple to spin up more low-emissions generators at night…
    But that's the point; all the available low-emissions generators are already spun up as far possible.

    Well that's a planning failure then. Build another low-emission generator.
    • CommentAuthorEd Davies
    • CommentTimeFeb 12th 2017 edited
     
    Right now people are modifying their behaviour on the assumption that using electricity when the average grid intensity is low is a good thing [¹]. This thread is about the effects of home energy storage on the availability of electricity to the grid which, at least partly, will be to do with affecting the overall emissions. The assumption of many (including Wookey) is that the instantaneous average grid intensity matters.

    To a good approximation we have a grid with the following characteristics:

    1) A certain (varying) amount of available low-carbon electricity (nuclear, wind, etc) which is pretty much used to its limit.

    2) A mix of carbon-intensive generation (gas and coal) which is varied up and down to follow the gap between the low-carbon generation and the demand.

    There's biomass, hydro, pumped storage, interconnectors in there as well to fiddle around at the edges but they don't make a huge difference to the big picture.

    As a result the total emissions in, say, a 24 hour period will simply be a multiple of the total carbon-intensive generation (GWh) which in turn will be the difference between the total demand over that period and the total available low-carbon generation over that period. So, so long as we don't run out of power stations or ever have demand go below the generation of the low-carbon generation, it doesn't currently make any difference to the total emissions over that 24-hour period when the demand happens.

    Therefore I think anybody who's taking that EarthOrgUK feed seriously is kidding themselves. Similarly, batteries aren't going to make much difference to emissions, either, at least until there's enough of them to invalidate my assumptions made above.

    [¹] https://twitter.com/EarthOrgUK has 1080 followers just now. I assume at least some are cluttering up their Twitter feeds with the idea of actually acting on the information posted.
    •  
      CommentAuthordjh
    • CommentTimeFeb 12th 2017
     
    Posted By: Ed DaviesSo, so long as we don't run out of power stations or ever have demand go below the generation of the low-carbon generation, it doesn't currently make any difference to the total emissions over that 24-hour period when the demand happens.

    Right but that decision is the planners' to make, not the consumers'. Equally, it doesn't make things worse if consumers try to spread the load more evenly, so if they want to send a signal to the planners by doing that en masse then fair enough. Or if they do it, like me, because we're encouraged by tariffs that financially reward us for doing so then fine. Or even if they do it through a perhaps misguided attempt to save the planet then wonderful.

    If we're serious about decarbonising, then we do clearly need a low-carbon grid that can sustain the full baseload.
    • CommentAuthorEd Davies
    • CommentTimeFeb 13th 2017
     
    Just to be clear, I do think there's a lot to be said for moving consumption out of the evening peak where possible to avoid the risk of the grid having to go “desperate” generation (diesel, etc). Also that things might be different in the future as the grid evolves.

    Posted By: djhOr even if they do it through a perhaps misguided attempt to save the planet then wonderful.
    Yep. But not so good if it actually increases consumption. See examples in my blog post linked above.
    • CommentAuthorringi
    • CommentTimeFeb 13th 2017
     
    If the aim is to charge at night, and use the power to reduce the evening peak, why not have electric cars that can discharge into the home in the evening?

    However if the aim is to use home generated PV (that is worthless due to low export prices) then we are talking mostly about saving money, not reducing CO2 output…..

    If phase change thermal stores every become reasonably prised, heat pump could be run at night, but that only helps in winter. (Apart from DHW)
    •  
      CommentAuthorDamonHD
    • CommentTimeMar 4th 2017 edited
     
    FWIW, I took a call from the guys who do this fine site, covering everything that my page does and more:

    http://www.electricitymap.org/

    and we will be discussing which metrics we *should be* collecting and providing signals for, in real time and as forecasts, to help people achieve the best outcomes. Could be minimising I^2R losses in distribution, peak shaving for infrastructure and fuel costs, etc, etc.

    I think that we may all agree with Ed's thesis re gas actually filling in an extra kW demand on the GB grid, though less so elsewhere in Europe. Though the intensity figure is still a decent proxy for a number of other parameters for now IMHO.

    Rgds

    Damon
    •  
      CommentAuthorSteamyTea
    • CommentTimeMar 4th 2017
     
    Interesting, as I type this (04/03/2017 9:44), the UK has an intensity of 228g/kWh, Denmark, 405g/kWh.
   
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