Photovoltaics and batteries—an expensive combination

Solar power can cover up to 40 percent of the electricity needs of a typical Belgian household. Going beyond that level becomes really expensive: using batteries coupled with solar panels would be twice as expensive as using the power grid. It is one of the conclusions from a research by ULB researchers recently published on Applied Energy.

Electricity production from solar panels is a recurrent subject in Belgium, especially when it comes down to costs and efficiency. In a new study published in the scientific journal Applied Energy, Guilherme de Oliveira e Silva and Patrick Hendrick, researchers from the École polytechnique de Bruxelles of the Université libre de Bruxelles, bring a new perspective on these questions.

The researchers started by crunching a large amount of data, ranging from meteorology conditions to use, and then ran the numbers through advanced simulators. The results show that, in Belgium, households equipped with solar panels can get a maximum of about 40 percent of their required . Going beyond this value is not possible, no matter how many panels one adds up, given the time mismatch between electricity use and sunshine. Going over that 40 percent level would be possible by storing energy with batteries, but with a heavy price tag: for an average household with an annual consumption of 3500kWh, an installation able to cover 70 percent of the electricity needs would cost about 15000€, almost the double of using the power . Even the future reduction of battery prices will not be enough to make such installations profitable, given that they only represent a fraction of the total installation cost.

Covering more than 40 percent of one's electricity needs with batteries coupled to solar panels is then more expensive than using the grid. To avoid overbearing costs, the researchers indicate that households with solar panels should resort to switching heating and hot water systems to electricity, with a large enough storage tank: a mature technology that can inexpensively absorb excess electricity from the solar panels. Smart appliances, that can switch their consumption to more favourable hours, are also a good option. On the other hand, electric vehicles are not expected to be of much benefit since most will be out of home during the more sunny hours.

Guilherme de Oliveira e Silva and Patrick Hendrick also analysed the impact on the grid of from photovoltaics. The power grid is dimensioned assuming that users have somewhat different use patterns, which end up balancing each other, resulting in a smoother load. On the other hand, solar energy producers can overload the grid given their simultaneous production for a given region, but do not bear the economic consequences of such overload. Therefore, the researchers also introduced in their simulations new grid tariffs, which better reflect the current cost structure of the . The results not only emphasize the advantage of large installations over smaller ones but also pose problems in terms of energy equity: if grid access starts being charged on a mostly fixed basis, households with a worse financial situation, which tend to consume less energy, will be the ones paying a higher average electricity price. The results also show the existence of an indirect subsidy from the typical consumer to those with solar panels, a problem that had already been exposed by the European Commission. The problem is such that Flanders, faced with a growing amount of solar panels, decided to charge producers instead of changing grid tariffs.

The conclusion is that electricity generation from has a certain impact on the grid which should be minimised. The researchers defend that setting limits on the amount of electricity that can be injected on the grid, as already happens in Germany, is a sound strategy. Storage could also mitigate the impact on the grid but, nowadays, grid tariffs present no economic incentive for homeowners to do so.

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More information: Guilherme de Oliveira e Silva et al. Photovoltaic self-sufficiency of Belgian households using lithium-ion batteries, and its impact on the grid, Applied Energy (2017). DOI: 10.1016/j.apenergy.2017.03.112
Citation: Photovoltaics and batteries—an expensive combination (2017, May 15) retrieved 21 August 2019 from
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May 15, 2017
Maybe there's an in-between solution, here. Instead of "full autonomous house" and "fully grid buffered" one could envision insular solutions where neighborhoods feed excess energy into a local, common storage device (e.g. a flow battery) - with larger storage systems at city, county, state and national levels.

May 15, 2017
Good idea, aap, and there are other ways of doing it, too.

But the question is, why impose the entire load on the new technology instead of integrating it as makes sense?

May 15, 2017
Intermediary approaches exist. Storage in Flanders could be done at the village or provincial level. The mix between open space and population density is such that these central power storage nodes, or batteries would work well and prevent overloading the existing dense local grids. Storing electric energy in a larger installation (e.g. molten salt/sodium salt/flow batteries/liquid metal batteries) might allow for interesting economies of scale largely offsetting the storage cost problem.

May 15, 2017
15000 isn't that much. If I were to equip my all electric house with complete standby generating capacity, I would spend nearly that much. Actually using that generating capacity (fuel) increases that cost significantly. That expenditure would make real sense if I can eliminate my monthly power bill at the same time, and never buy fuel to use it. Sign me up.

May 15, 2017
Deciding grid feed-in at the "neighborhood" (substation) level is not workable when individual houses in the neighborhood are acting independently, without coordination between the substation and the distributed generation in its subgrid.

Imposing the "entire load" (har har) on the new technology is natural and efficient, as the new technology is smart and nimble, as opposed to old technology, which is a lumbering megaton network of conductors, electrical steel and capacitors installed in the previous century.

Preauthorized/planned grid feed-in from distributed generation, hierarchically coordinated by the Independent System Operator, eliminates the problems that arise from uncontrolled generation on the grid. When uncontrolled solar generation was a small fraction of the load in a subgrid, this level of coordination wasn't necessary (aside from the anti-islanding provisions), but as solar power becomes more economical and common, feed-in regulation will be inevitable.

May 19, 2017
To avoid overbearing costs, the researchers indicate that households with solar panels should resort to switching heating and hot water systems to electricity, with a large enough storage tank: a mature technology that can inexpensively absorb excess electricity from the solar panels.

It would be much more cost effective to install thermal panels and use these to store the solar generated heat at large water storage tank. Firstly such panels are much cheaper than PV collectors and they have a better collection efficiency.

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