Solar PV (now with grid backup)

Following my previous post there was some discussion about the need for grid backup of solar PV to deal with extended periods of overcast weather. It’s obvious that storage will help with this to some extent, since batteries can store electricity from the grid as well as from distributed solar. I thought I would try to put some numbers on this (slightly changed from last time to simplify the numbers).

I’ll focus on 1 kW of solar PV generating an average of 4.8 kWh per day, with (as before) 2 kWh of storage. If there is zero solar generation and no demand management, the entire 4.8 kWh per day must be drawn from the grid. In the absence of storage, we might suppose that 1kW of backup capacity is needed to match the peak output of the solar PV system. But with storage, all that is needed is enough to supply 4.8 kWh over the course of a 24-hour day, that is, 0.2 kW.

The optimal backup choice is a fully dispatchable technology such as hydro or gas. Hydro resources are pretty much fixed, so I’ll focus on gas. According to the US Energy Information Agency, the capital cost of gas-fired power plants is around $1000/kw so our grid backup will have a capital of cost only $200 for each kW of distributed solar. There’s also the need to take account of fuel and distribution costs. Fuel costs will be low since the system is only used as backup, while distribution costs will be around 20 per cent of what would be need if peak loads were to be met by centralised generation.

To sum up, if battery storage becomes available at a sufficiently low price, there’s no obvious problem with a system in which over 80 per cent of capacity, and an even larger proportion of generation is distributed solar PV.

60 thoughts on “Solar PV (now with grid backup)

  1. @Will Boisvert

    Sorry Will, you are wrong on all counts. There are studies which show over-building redundant renewable capacity is indeed fully energetically and economically feasible.

    These guys from Stanford have done a lot of work in this field.

    Graeme R.G. Hoste
    Michael J. Dvorak
    Mark Z. Jacobson

    This is not their only paper on the general topic.

    http://web.stanford.edu/group/efmh/jacobson/Articles/I/CombiningRenew/HosteFinalDraft

    Also look up “Stanford engineers develop state-by-state plan to convert U.S. to 100% clean, renewable energy by 2050”.

  2. It’s a wonderful thing that despite all the claptrap from conservatives over climate change and negativity from so called experts over domestic solar so many people have voluntarily put their hands in their pockets and invested in a roof top system.

    And look at just how many roofs are sporting an array.

    Meantime the PM is tying himself in knots over moral policy.

  3. Will Boisvert,

    “Well, yes, what you’re proposing is an energy system where we have natural gas generation, capable of running the whole grid as “backup” and then build more and more intermittent capacity to try to abate as much gas generation and CO2 as possible.”

    The idea is not to use natural gas but to use biogas for back up energy, as we have plenty of materials we can convert to biogas in Australia.

    There are at least three reports on 100% renewable energy for Australia where they use modelling of weather over a year to see how their ideas work.

    The only one I’ve read is by Mark Diesendorf in NSW who proposes to replace the current baseload system with an energy system with a first level of variable electricity provided by solar p.v. and wind turbines, and to even this out a second level fluctuating electricity provided by concentrated solar thermal which can go in there desert (but you don’t want too much as it will spoil the desert ecologies) and also biogas turbines in long grey spells in Winter.

    Beyond Zero Emissions here in Victoria have a slightly different plan, with more of an emphasis on concentrated solar thermal.

    I have never heard a discussion on why the different reports have made their different choices and which is better, but I guess having 3 or more will give the government more choices when they begin to act properly and more rapidly to mitigate climate change.

  4. “But let’s be clear that the notion of comprehensively decarbonizing the grid with intermittents has now gone out the window. I’m not sure that’s good. World electricity usage will soar in the future and even a 20 percent residual fossil component over time will approach unsustainable absolute levels.”

    No this is not correct. As I said there are at least 3 reports for Australia showing 100% renewable is possible.

    There needs to be similar work done in other countries too, for instance someone told me they were in Vietnam and there is a big data gap on the renewable energy potential there. But even if as they are tropical they have a lower renewable energy potential, as they are part of Eurasia all of Eurasia can share an energy grid so as to accomodate the needs of tropical countries. In return tropical countries can preserve and increase their rainforests to draw down carbon.

    Here is a report you can read that is for the least cost energy grid so you should be pleased with it

    Least cost 100% renewable electricity scenarios in the Australian National Electricity Market
    By Ben Ellistona,?, Iain MacGilla,b, Mark Diesendorf

    http://www.ies.unsw.edu.au/sites/all/files/profile_file_attachments/LeastCostElectricityScenariosInPress2013.pdf

    Mark Diesendorf also writes as well as energy efficiency we will need energy conservation, and has written a couple of papers with Lawrence Delina on A Wartime Mobilisation For Rapid Mitigation Of Climate Change , as it is going too slow at present

    Is wartime mobilisation a suitable policy model for rapid national climate mitigation?
    By Laurence L. Delina and Mark Diesendorf

    http://www.ies.unsw.edu.au/sites/all/files/DelinaDiesendorf_EnergyPolicy-v2%5B1%5D.pdf

  5. @John Quiggin
    OK.
    I dimly remember from looking at linear programming as a graduate student that the practical way you solve a real-life optimisation problem is to establish a solution that works, and then fiddle around in the neighbourhood to improve on it. That was the way Soviet central planners did it. Their system worked, in the sense that the reason it fell apart was not failures of coordination but of quality and innovation. If the system isn’t conveniently convex, you may approach a local optimum that isn’t a global one. The substitution relationship between domestic and grid storage doesn’t a priori look eccentric in this way.

  6. This article touches on a number of debates in this thread.

    http://cleanenergytransmission.org/stanford-study-u-s-can-move-to-100-renewable-energy-much-sooner-than-you-think-transmission-infrastructure-is-critical/

    The study apparently shows that in a fully renewables grid;

    ” – More than 90 percent of renewable generating capacity is utility-scale – including a large majority of solar PV; virtually all generation is connected to the grid.

    – Transmission and non-battery storage balance the natural variability of wind and solar to provide 24/7/365 power to everyone, everywhere.

    – Electrifying everything, including transportation, together with energy efficiency, demand response, and distributed generation make are essential to the ultimate goal.”

    Also;

    “Utility scale photovoltaics (PV) produce power at half the cost of rooftop installations. Wind power is only economical at large scales. The overwhelming majority of solar and wind power produced in the U.S. today comes from grid-connected, large scale facilities owned by or under contract with utilities.

    Jacobson’s vision of the future is no different, with large scale renewables providing about 93 percent of the power: 50 percent wind (30.9% onshore; 19.1% offshore); 30.7% utility-scale (PV), 7.3% concentrated solar power (CSP) with storage, 7.2% rooftop PV, 1.25% geothermal power, 0.37% wave power, 0.14% tidal power, and 3.01% hydroelectric power.”

    “ow does Jacobson turn myriad variable renewable generators into smooth and reliable 24/7/365 power in all 50 states? Transmission and storage – batteries not included. Transmission lines slash natural variability by blending diverse wind and solar resources over large regions:

    “. . . while the study bases each state’s installed capacity on the state’s annual demand, it allows interstate transmission of power as needed to ensure that supply and demand balance every hour in every state. We also roughly estimate the additional cost of transmission lines needed for this hourly balancing.”

    More transmission, Jacobson notes, would make it even easier and cheaper to achieve 100% renewable energy, by allowing the best quality, least cost resources to serve more customers in more states:

    “ . . . if we relax our assumption that each state’s capacity match its annual demand, and instead allow states with especially good solar or wind resources to have enough capacity to supply larger regions, then the average levelized cost of electricity will be lower than we estimate because of the higher average capacity factors in states with the best WWS resources.”

    Storage and demand response take care of the remaining variability – but not batteries – which are exclusively reserved for their higher value use in transportation:

    “Solutions to the grid integration problem are obtained by prioritizing storage for excess heat (in soil and water) and electricity (in ice, water, phase-change material tied to CSP, pumped hydro, and hydrogen); using hydroelectric only as a last resort; and using demand response to shave periods of excess demand over supply. No batteries (except in electric vehicles), biomass, nuclear power, or natural gas are needed.”

    In Summary.

    According to Jacobson et. al.,

    (1) utilities will remain the mainstay of power generation even with renewables;
    (2) battery storage of power will not needed except in vehicles.
    (3) distributed generation and state interconnectors will play a big role;
    (4) most grid energy storage will be as heat reconvertable to power.

    Look at the graphic in the article for percentages of contribution. I agree with the idea of avoiding biomass burning as a contribution to power though niche applications could still happen like sugar mills burning bagasse. I have my doubts that off-shore wind would be economically efficient or necessary at such a high percentage rate. I would question CSP (concentrating solar power) being so low. I would question no mention of solar updraft towers which solve the storage problem by generating power 24/7.

    One final point which many people forget. A fully electrical economy in the transport sector is four times more energy efficient than an oil economy. Thus it will need 1/4 of the net energy (EROEI in “gathering” energy) to do the same transport work. Electric motor energy efficiency approximately equals 80%. Internal combustion motor energy efficiency approximately equals 20%.

  7. @Will Boisvert

    Your argument about capacity is still stuck in “baseload” mode.

    In the setup I’ve described, solar PV will be first in the order of merit, followed by stored power from batteries, followed by gas-fired grid backup, used only during long periods of overcast weather. So, the 80 per cent solar PV capacity will translate into more than 80 per cent solar generation (either directly or via battery).

  8. Siemens has a neat product which users renewables to create hydrogen, which is then used to fuel gas power plants. Once scaled, solar pv could supply 100% of loads. This system is economic when retrofitted to existing gas plant.

  9. Will Boisvert,

    ““But let’s be clear that the notion of comprehensively decarbonizing the grid with intermittents has now gone out the window. I’m not sure that’s good. World electricity usage will soar in the future and even a 20 percent residual fossil component over time will approach unsustainable absolute levels.”

    No this is not correct. As John Quiggin said you are thinking of the old style energy system thinking.

    As I said there are at least 3 reports for Australia showing 100% renewable is possible using models of real weather to make sure it is feasible.

    There needs to be similar work done in other countries too, for instance someone told me they were in Vietnam and there is a big data gap on the renewable energy potential there. But even if as they are tropical they have a lower renewable energy potential, as they are part of Eurasia all of Eurasia can share an energy grid so as to accomodate the needs of tropical countries. In return tropical countries can preserve and increase their rainforests to draw down carbon.

    There is no reason that energy grids need to stop at arbitrary national boundaries and not be shared.

    Here is a report you can read that is for the least cost energy grid so you should be pleased with it

    Least cost 100% renewable electricity scenarios in the Australian National Electricity Market
    By Ben Ellistona,?, Iain MacGilla,b, Mark Diesendorf

    http://www.ies.unsw.edu.au/sites/all/files/profile_file_attachments/LeastCostElectricityScenariosInPress2013.pdf

  10. Mark Diesendorf also writes that as well as energy efficiency we will need energy conservation, and he has written a couple of papers with Lawrence Delina on A Wartime Mobilisation For Rapid Mitigation Of Climate Change , as it is going too slow at present

    Is wartime mobilisation a suitable policy model for rapid national climate mitigation?
    By Laurence L. Delina and Mark Diesendorf

    http://www.ies.unsw.edu.au/sites/all/files/DelinaDiesendorf_EnergyPolicy-v2%5B1%5D.pdf

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google+ photo

You are commenting using your Google+ account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

w

Connecting to %s