# Tag Info

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Because springs have low energy density When storing energy, especially in a residential setting, you want to be able to store a lot of energy, or not take up too much space. To store a reasonable amount of energy with a steel spring, you need a large spring (or a lot of small springs). The 2014 paper "Benefits and challenges of mechanical spring ...

18

Thermal storage Surprisingly to many, conversion of electrical energy from PV (photovoltaic) panels to heat energy and storage in hot water is a potentially excellent use of the energy - provided that you have a use for the hot water. Water stores energy at the rate of about 1 Watt hour per litre degree or 1 kWh per 1000 litre degrees*. So eg a 100 litres ...

12

If your goal is to save money you'll need to do the calculations based on your exact location and costs. In Australia the main use of small battery-backed solar systems is for off-grid locations but people are increasingly looking at going off-grid as the cost of the grid keeps rising (mostly due to cheap air-conditioners) while the cost of PV systems drops. ...

9

This is a question that I've heard several times, though it is the first time I've seen it here. The main problem is, I think, efficiency. Firstly, though, not long ago, when I was a child (OK, quite a few decades ago, but in living memory), energy storage in springs was a common way of powering clocks and watches. Energy stored in weights was used for ...

8

You can easily calculate the maximum strain energy in a material by considering the maximum stress (for metal: yield stress) and stiffness (Young's Modulus). The maximum strain energy in a material is then E = 0.5 x yield stress ^ 2 / Young's Modulus. If you take high quality steel with a yield stress of 1000MPa and a typical Young's modulus of 200GPa, you ...

8

Ok, let's break this down. I will assume photovoltaic solar panels (as the question implies alternatives to batteries) and therefore skip all kinds of solar thermal collectors. Starting from electric energy coming from this PV panels we can convert to various forms of energy. For the purpose of storage this boils typically down to a few used forms only: ...

7

Domestic flywheels are unlikely to happen for 3 reasons: They must be heavy to store significant energy. If you need a crane to install one at your house it’s never going to be super cheap, even with high volume manufacture. The risk of the spinning mass fracturing requires special safety precautions - commercial operators put them in the ground but that ...

7

Lets check the pros and cons on flywheel energy storage and whether those apply to domestic use (source): Compared with other ways to store electricity, FES systems have long lifetimes (lasting decades with little or no maintenance;[2] full-cycle lifetimes quoted for flywheels range from in excess of 105, up to 107, cycles of use),[5] high specific energy ...

6

"Solar panel" includes both thermal panels and photovoltaic panels. A common way to store and use heat is in a domestic hot water storage tank. This is generally cheaper and more efficient than PV panels and batteries, but of course it only makes sense if you need the hot water! Anyone with a heated pool or laundromat should probably be doing this. You'll ...

5

No it is not. Your calculations of 13year ROI is based on the assumption that charging the power wall is free during the day time. It is not. Depending on your locale, either you need to factor in the cost of additional solar capacity or lost feed in revenue. This will easily push your ROI into the 20 year territory. Assuming that your locale supports ...

5

In this question about rooftop hydro I covered the efficiency question almost as an aside. I can't find an actual plant with efficiency over 80%, only claims that that might be possible. The average efficiency will be much lower than the peak, as a lot of plants are old and have efficiencies around 60% (although some have been refitted to boost efficiency). ...

4

Not only is the energy density of such systems low, as other posts explained - stored energy that will be released as mechanical energy immediately in case the storage system fails has been shown to be extremely dangerous in practice. Even the example of a wind-up clock shows it - if you disassembled a fully wound old school alarm clock the wrong way, there ...

4

We were looking into flywheel UPSes for my company and I read up on this a bit. Of note in recent developments: Instead of traditional bearings, they're using magnetic bearings to mostly eliminate friction. To be able to suspend the flywheel on magnets, that requires a lower weight/mass. To counter the lower weight/mass, you have to replace that with ...

3

There is - it just doesn't use metal springs Metal springs have numerous failure modes. In tension, they only remain "springs" for a certain point, after which they simply become wires/rods (which also have a Young's modulus, but in a different way). In compression, they also only remain "springs" until the coils touch, at which point ...

3

Your idea is interesting but would fail in the real world for a number of reasons: The energy embodied in even a moderate storm is staggering. No amount of "Stormbuoys" could make even a dent on a severe storm. Their density would need to be so high that shipping and navigation would be impossible. You will never "mitigate the devastation of storms" with ...

3

China, Japan, and South Korea are buying hydrogen that is either made using renewable electricity or that has the carbon from production then captured. Hydrogen is easier to ship and store in the form of ammonia-gas. Then ammonia-gas can be converted back into hydrogen with only the release of nitrogen. The electric powerplants in Japan are just burning the ...

3

STES (Seasonal Thermal Energy Storage) is, in most cases, too expensive to really be practical because of the huge quantity of the storage medium needed to supply the seasonal demand. Typically, you loose a good portion of the heat through conduction or have to invest heavily in insulated containment. I find it difficult enough designing thermal stores for ...

3

Energy Storage Association cites round trip efficiencies above 80% http://energystorage.org/energy-storage/technologies/pumped-hydroelectric-storage As for the evaporation question. I don't know of any specific data on it, but would expect it to be minimal if you charge the reservoir during off-peak (cheaper) hours and discharge it during the morning ramp. ...

2

I hate to sound glib, but have you considered abandoning solar panels in favor of biomass, storing solar energy in a natural form? Trees are a fantastic way to store solar energy; so is some sort of oilseed like rape. Of course, it takes long-term planning to get a sustainable cycle going, but you can figure out how much energy you use continuously (kWh/...

2

Adding Power-to-(natural-)Gas, since no one mentioned it yet: By now, it's also possible to transform the energy from solar panels not only to hydrogen, but further into methane, 'the main component of natural gas'. Edit: This might not be possible to do for a single home yet, see below. Then you could either store the gas at home or feed it into the local ...

2

I've been doing quite a bit of reading and other research in the area of using solar for hot water tanks. There are quite a few Youtube videos by people who have been using PV (Photo Voltaic solar panels or arrays) to either produce or supplement their hot water tanks with solar electricity. I think this may currently be one of the more productive ways to ...

2

My knee jerk reaction: From what I know of mechanical systems, anything mechanical introduces losses due to friction in the form of heat, sound, and vibration. How would you even begin to use the mechanical energy stored in a flywheel? Simply storing the energy induces massive losses. Transferring the energy to its appliances introduces transfer problems ...

2

It may be technically feasible. But in reality, for places that do desalination, it's never going to be economical, because there's already an easier way to do things. Storage on the grid is useful because it enables more supply to be matched to more demand. It does that by shifting energy from the time it is generated to the time it is used. There is ...

1

I have done this sort of, in reverse. I'm a tree farmer. I get seedlings and to extend the time I can plant them I have made a cold room. This is a 12x12 foot room with 4" fiberglass + 12" strawbale insulation. Inside are 10 45 gallon drums of water on sections of pallet and 4" of styrofoam chips on top. In the winter, the door is left open and the fan on....

1

The article you linked says that the salt content of the seawater released by the desalinization plant is increased by 20%, not that the effluent is 20% salt. This means that normal 3.5% salt seawater becomes something like 4.2% salt seawater. Plug that difference into your mgh equation and desalinization plant numbers you get 110 kwH per day of desalinated ...

1

This all seems highly inefficient. Your one calculation based om m*g*h is meaningless, g is not 9.8 here. You have to displace the sea water which is almost as dense as the saltier water you want to descend. I do not understand how you regard bringing slightly heavier water down as "energy storage". Once the saltier water is down, you want to have caught ...

1

TL;DR - Because of how flywheel energy storage scales it is unlikely that significant efforts will be made to develop the technology for home use. This is similar to the case for windmills, where the power output increases as the square of the diameter, and the cube of the wind speed (which itself doubles roughly every 20m of elevation). From the ...

1

As a Mechanical Engineer, I know the efficiency of the pump(s) and generator will be a function of the head or the height difference between the upper and lower reservoirs. Also, the line losses will increase with distance. Finally, an uncovered reservoir in an arid climate will suffer evaporation losses. Therefore, there isn't a single answer to this ...

1

Very good idea of storing heat energy in water. Since I expect my biggest use of solar energy to be in the form of heat this might be a good idea for me. One can increase the storage capacity of water by adding Glauber's salt. It absorbs a lot of heat going into solution and gives it off going out of solution. I myself planted a small patch of sunflower ...

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