Storing solar power increases energy consumption and emissions, new study finds
Homes with solar panels do not require on-site storage to reap the biggest economic and environmental benefits of solar energy, according to research from the Cockrell School of Engineering at The University of Texas at Austin. In fact, storing solar energy for nighttime use actually increases both energy consumption and emissions compared with sending excess solar energy directly to the utility grid.
In a paper published in Nature Energy on Jan. 30, researchers assessed the trade-offs of adding home energy storage to households with existing solar panels, shedding light on the benefits and drawbacks of adding storage considering today’s full energy grid mix.
According to the Solar Energy Industry Association, the number of rooftop solar installations grew to more than 1 million U.S. households in 2016. There is a growing interest in using energy storage to capture solar energy to reduce reliance on traditional utilities. But for now, few homes have on-site storage to hold their solar energy for later use in the home.
“The good news is that storage isn’t required to make solar panels useful or cost-effective,” said co-author Michael Webber, a professor in the Department of Mechanical Engineering and deputy director of UT Austin’s Energy Institute. “This also counters the prevailing myth that storage is needed to integrate distributed solar power just because it doesn’t produce energy at night.”
Webber and co-author Robert Fares, a Cockrell School alumnus who is now an American Association for the Advancement of Science fellow at the U.S. Department of Energy, analyzed the impact of home energy storage using electricity data from almost 100 Texas households that are part of a smart grid test bed managed by Pecan Street Inc., a renewable energy and smart technology company housed at UT Austin.
They found that storing solar energy for nighttime use increases a household’s annual energy consumption — in comparison with using solar panels without storage — because storage consumes some energy every time it charges and discharges. The researchers estimated that adding energy storage to a household with solar panels increases its annual energy consumption by about 324 to 591 kilowatt-hours.
“I expected that storage would lead to an increase in energy consumption,” Fares said. “But I was surprised that the increase could be so significant — about an 8 to 14 percent increase on average over the year.”
The researchers also found that adding storage indirectly increases overall emissions of carbon dioxide, sulfur dioxide and nitrogen dioxide based on today’s Texas grid mix, which is primarily made up of fossil fuels. The increase in emissions is primarily due to the increase in energy consumption required to account for storage inefficiencies. Because storage affects what time of day a household draws electricity from the grid, it also influences emissions in that way.
If a homeowner is seeking to reduce his or her environmental footprint, adding storage would not make the household more green, but it shouldn’t be dismissed either, the researchers said.
“Solar combined with storage is still a lot cleaner than having no solar at all,” Fares said.
For utility companies, the benefits are more clear cut. Solar energy storage reduces peak grid demand by 8 to 32 percent and the magnitude of solar power injections to the grid by 5 to 42 percent. This is good for the utility because it can reduce the amount of electricity generation and delivery capacity required.
“However, if the utility is interested in reducing emissions, incentivizing home storage is probably not a good idea,” Fares said.
In short, the analysis showed that storing solar energy today offers fewer environmental benefits than just sending it straight to the grid, because the energy lost to storage inefficiencies is ultimately made up with fossil-fuel electricity from the grid. “These findings challenge the myth that storage is inherently clean, but that, in turn, offers useful insights for utility companies,” Webber said.
“If we use the storage as the means to foster the adoption of significantly more renewables that offset the dirtiest sources, then storage — done the right way and installed at large-scale — can have beneficial impacts on the grid’s emissions overall,” Webber said.
Journal Reference:
Robert L. Fares, Michael E. Webber. The impacts of storing solar energy in the home to reduce reliance on the utility. Nature Energy, 2017; 2: 17001 DOI: 10.1038/nenergy.2017.1
In the world lacks the egg of Columbus on energy matters, which would produce clean energy for twenty-four hours a day and three hundred sixty-five days a year, in any weather and temperature (even at the north pole), in our apartments in wells, rivers and lakes and on means of transport, without fuel and no solar panels, the system is called pressurized hydroelectricity with water recycling. It is based primarily on the “compressibility” of air and the “non compressibility of water.” In the version with a lesser amount of water that can be used to produce energy in an apartment or on a car to replace the heat engine, are used: A water tank pressurized with compressed air, a motorized valve at the exit of the water that drives a turbine, a reservoir at atmospheric pressure collecting the water drained from the turbine, an electric pump of new conception with the dual separate power supply until to the impeller, complete with feed pipes and one-way check valves, which, has connected the delivery at the entrance of water into the pressurized tank and the two aspirations respectively connected to the outputs of the open water tank and pressurized. Therefore, the feed connected to the open reservoir permit to enter the water discharged from the turbine in the recycling pump with the dual separate supply, while the feed connected to the pressurized tank recycles the water to the interior of the same, by balancing the hydrostatic pressure on suction and delivery of the pump and therefore allowing the external water inlet in the pump impeller and into the pressurized recirculation loop, without the opposition of the hydrostatic pressure. But, being the pressurized reservoir already full of water and compressed air at the highest level, at the same instant, the same amount of water that enters from the outside it is ejected from the compressed air cushion by another output, producing new energy in the turbine. Therefore, maintaining constant the volume of water and compressed air in the reservoir, energy is produced in the turbine with the compressed air pressure, but is not consumed nor water nor air. It only consumes the energy to circulate the water with a very low absorption of energy within the volume of water accumulated without having to win the compressed air pressure on water because the water volume is not changed not even the volume of the compressed air. However, water ejected from the air cushion produces energy in the turbine in an amount proportional to the flow and the compressed air pressure. Assuming you have a small domestic system pressurized to 4.0 bar with a flow rate of 7, 5 L / s, a single-stage recycle dual supply pump DN65 and a multistage pump used as a turbine of equal magnitude, we will have a power generation in ‘alternator coupled to the turbine of 1,76 Kw, but it is produced with the force of the compressed air cushion,without expanding, that leaves the water at the pressure of 4 bars. The power consumption, of 0.183 kW of the system is due only to the operation of the electric pump of the water recycling. Therefore the relationship between expenditure and energy consumed is equal to 9,61 (1,76 / 0, 183). This should not surprise us because the compressed air is an external element to the hydraulic circuit and therefore does not violate the principles of conservation of energy. In addition, these systems have never been made anywhere in the world, because: 1) the pumps with double separate supply are not (have just been patented by the undersigned); 2) the existing autoclave systems do not work as an energy accumulator with the water that circulates in one way, without expanding the air cushion, but doing work expand and compress the air cushion, thus, do not conserve energy; If we use the same system (DN 65 and 7.5 L / s) to replace the thermal engine of a car but with a pressure of 40 bar, we will have an energy production of ten times higher (17.6 Kw) of the domestic system, with an almost identical energy consumption (0.366 kW), so that the ratio between the expenditure and energy consumed becomes equal to 48, 08 (17,6 / 0, 366). If we consider that the average efficiency of heat engine mounted on the car it is about 35% of the lower calorific value of the fuel, we can derive the ratio of convenience between a compressed hydroelectric motor and a thermal engine, which equals 137.39 (48, 08 / 0.35). This relationship of convenience excludes the cost of fuel, the increased complexity of the heating systems, the charges for the filtration of the fumes, etc. So, the actual fossil energy affordability ratio and pressurized hydroelectricity can even double. Not worth it to extract coal, oil, gas from underground but we are doing it for at least 150 years because of the absence of this simple invention, which is met with silence from all those who have not known how to invent, despite having invented things much more complicated and certainly less useful environment and the economy.