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Rooftop solar could provide nearly half of US electricity demand

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A major new study has significantly lifted the potential of rooftop solar PV in the United States, saying rooftop solar alone could provide 40 per cent of all the electricity needs of the world’s biggest economy, and around half if module efficiencies continued to improve.

The study by the National Renewable Energy Laboratory says the estimated potential from rooftop solar has been revised upwards by more than 80 per cent since the last study in 2008, mostly because of improvements of module efficiencies, building availability and solar modelling.

In all, NREL estimates potential rooftop solar installed capacity at 1,118 gigawatts (GW) and generation of 1,432 terawatt-hours (TWh). This would account for 39 per cent of all electricity sales, but could go higher – to around 50 per cent – if higher module efficiencies were taken into account.

The report underlines the likely transition of the world’s major electricity systems from one dominated by central, fossil fuel generators, to a largely locally supplied pool of electricity, much of it from rooftop solar, augmented by storage and community based projects using solar and other technologies,

 

NREL solar potential

As this map above shows, the greatest potential for rooftop solar as a share of total electricity supply is in California, where NREL estimates it could supply 74 per cent of all demand.

A cluster of New England states – Maine, Vermont, Rhode Island, New Hampshire, Connecticut and Massachusetts –  could generate more than 45 per cent of their electricity needs from rooftop solar PV, despite the below-average solar resource of these states.

The NREL says a common feature of the top six states – in terms of potential PV generation as a percentage of total sales –  is the significantly below-average household consumption, suggesting the role an energy-efficient residential sector could play in achieving a high penetration of energy from rooftop PV.

The worst performing state – Wyoming – has the highest average households electricity consumption, at more than 30kWh a day.

nrel solar states

NREL points out that these are not predictions, just potential output. But is also says its own estimates could be highly conservative.

Firstly, it uses an average module efficiency of 16 per cent, when most modern rooftop systems have efficiencies of around 20 per cent. If this average was used, it would lift its figures by around 25 per cent, meaning that rooftop solar had the potential to meet half the country’s electricity demand (and nearly 90 per cent in California).

The study also did not take into account the enormous potential of ground-mounted solar, nor did it take into account other installations such as car parks, or integrating solar PV into building facades. Only 26 per cent of “small  rooftop” spaces were considered suitable for solar PV.

While the NREL study does only focus on the potential of rooftop solar capacity, many in the industry believe that rooftop solar costs will fall so much that installations will be at “saturation point” – meaning that they will be intalled on nearly every building available.

A study by the former WA energy market operator suggested that 70 per cent of all homes and 90 per cent of all businesses could install rooftop solar. Similar forecasts are made for South Australia.

Rooftop solar in both W.A. and S.A. is forecast to meet all of daytime demand in certain periods within the next decade, underlying the shift from the old-fashioned but long standing system of centralised “base load” generation to a localised system of “distributed energy”.

Institutions such as the CSIRO, and utilities such as RWE, E.ON, and Engie have all forecast that half of all electricity generation could be supplied locally within a few decades.

This includes rooftop solar and battery storage systems, but also “community” projects and micro-grids that might use other technologies too – such as wave, hydro, biomass  and wind.

 

   

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  • Rob G

    If Trump succeeds in keeping Republicans out of the White House for a decade or two, we may see solar let ahead at an even greater rate. I suspect this will indeed happen. After solar is the easiest thing to sell and it plays a vital part in climate change action.

  • suthnsun

    3kw PV supplies more than my household + EV demand. (2 pax)

    • solarguy

      Like to know what appliances you use and when you use your power? I take it that you have SHW as well?

      • suthnsun

        All electric house (no gas). Induction cooktop, all normal appliances. 4kwh average pd all year for cooking fridge etc. Another 4kwh avg for heating /cooling and hot water boost in winter (ET HW) Clearly total energy over the year is supplied from PV (and ET), not peak power.

        • hydrophilia

          Impressively frugal. I take it there are no teenagers running hair dryers or taking long showers and that you don’t do much baking.

          • suthnsun

            Not so frugal feeling really, discipline turning off parasitic loads is the ‘frugal’ part. My wife bakes judiciously every few days. Teenagers long gone but grandchildren are present quite often! Replacing as needed with LED and cost effective low energy appliances has been very beneficial.

  • Mike Dill

    Adding wind and hydro to these figures, with some efficiency, gives us all the energy we need. Some of the ‘rooftop poor’ states have other resources in abundance.

  • The Wiseman

    Let’s remember that solar only works during the daytime! If you intend to use power during the hours of darkness, then you still must have “the grid” attached to your home – with all the attendant poles, wires, transformers, generators, interconnections et al – that we have today. That grid is hugely expensive and – because you are generating all that solar power yourself, during the day, and not buying electricity from the grid during the day, then your night-time electric bill will be much more expensive than it is right now, in order to pay for maintaining all those grid-related equipments.
    It ain’t all cake and wine, folks! Solar isn’t the perfect solution.

    • Bob Fearn

      Lets remember that it only rains sometimes, that coal is only delivered at certain times, that natural gas wells run out.
      It is completely possible and reasonable to run your house on solar. First you need an energy efficient house, secondly you need to use energy wisely and third you need electrical storage.
      Not only is this energy less expensive, if the true cost of the alternatives are actually calculated, but is is far better for our future.
      Don’t let the ‘can’t do it gangs’ tell you otherwise.

    • Jonathan Prendergast

      The electricity grid works hard to balance instantaneous supply and demand throughout the year, for example by having network controlled household hot water. But there is so much more potential through methods like pumped hydro, dispatchable renewables (eg. biogas, landfill gass, waste to energy), dispatchable demand and battery storage. A lot of it is already in place but is not utilised to balance renewables yet. Solar is a great solution for the % figures quoted, but agree it is unlikely to ever be 100%, but 100% renewables is certainly achievable.

    • hydrophilia

      Solar definitely has its issues, as does every other technology. Still, with efficiency, demand management, and a bit of storage, one can get by. Perhaps with a little 1kw generator for the 50hrs per year that you need it. In this case, screw the grid!

      On the other hand, a recent study of the USA found that, with a large and expensive grid upgrade, we could get rid of most FF power at a lower over-all cost than biz as usual… without storage.
      http://spectrum.ieee.org/energywise/energy/renewables/noaa-model-finds-renewable-energy-could-be-deployed-in-the-us-cost-effectively-without-storage-to-cut-carbon-emissions

  • Tami Chapman

    It would provide all of it if we weren’t so wasteful.