Renewables without (or with minimal) Storage

Calliban · 2022-10-16 14:43:49

Renewables without storage?
One thing that would make offgrid RE much more practical, is to develop a system that allows easy demand management (load shedding). This allows the user to adapt his demand to supply, rather than attempting to store ridiculous amounts of energy. For example, when power supply exceeds use, energy could be stored in a small pumped hydro store, say 1kWh, until it reaches capacity. More energy can be stored by activating heating elements in a hot water tank.
Each room in the house, will have green, amber and red indicator lights. When the light is green, heating elements are active, meaning there is plenty of excess power. You can switch on additional loads at that point. Things like the washing machine. The TV. The computer. When the light is amber, there is sufficient power for existing loads, but no more should be added. When the light is red, you are drawing on the pumped store and the diesel generator will soon be starting, or has already started. You shed as many loads as possible at that point. For hydropower, time constants are quite long. For wind power, slew rate can be rapid, losing at much as 10% of power in a few minutes, for a small turbine.
Oversizing the generating capacity reduces the need for load shedding. But it also increases capital costs. So there is an optimum size for a wind turbine for any particular dwelling, depending upon local conditions and demand for power. But controlling load appears to be a more practical solution than storage. We could in fact design a system with a wind turbine and diesel generator alone. Excess power is stored as heat in hot water and is absorbed by banks of heating elements. When demand exceeds supply, the DG starts. However, by appropriately sizing the wind turbine and by shedding loads when demand reaches say 90% of power generation, eventually the householder will learn to postpone energy demands until supply is available. Weather forecasts can be used to schedule high load activities. This would seem to me to be more practical than attempting to store energy. We need to change our behaviours and learn to adapt demand around supply. This article has more to say about that.
https://www.lowtechmagazine.com/2017/09 … ather.html

This thread is to explore how load shedding might be used to apply renewable energy to grids or home networks with minimal energy storage. For example, excess power can be absorbed relatively cheaply by banks of heating elements in hot water tanks. These elements can be switched off when power supply drops off or if additional dispatchable loads absorb the excess power. In the post above, I considered the idea of a three light system. Green light = plenty of excess power / heating elements switched on. You can add heavy loads. Yellow light = add no more loads. Red light = DG about to start. Shed loads. On a grid, these lights would be activated by transmitted price signals. Green is cheap. Amber is expensive. Red is very expensive. By adapting demand to supply, a grid with a lot of additional RE capacity looks more doable. But there are obviously other prices to pay. We are trading operational flexibility for lower capital costs. I can see this being workable in a domestic setting. But much more difficult for industry.

Last edited by Calliban (2022-10-16 14:48:34)

Calliban · 2022-10-16 15:08:51

Is wind power becoming too expensive?
https://oilprice.com/Alternative-Energy … nsive.html

SpaceNut · 2022-10-16 16:53:24

repost

Calliban wrote:

Gravity storage is already used extensively in the form of pumped storage. This involves pumping water from a low reservoir to a high reservoir and then releasing it back to the low reservoir through a turbine. Practical efficiency is about 75% in large scale facilities. Not bad. Relatively low energy density. A cubic metre of water raised through a head of 1km, will store about 10MJ. The energy stored is proportional to height and volume.
The advantage of using a liquid is that it can be pumped through pipes, which is logistically much easier than having to lift blocks by crane and then recover energy using some sort cable winch. That involves a lot of moving parts and is labour intensive.

Calliban wrote:

Gravity energy storage using a raised weight to pressurise a hydraulic fluid, which drives a hydraulic motor coupled to a generator; would be a useful tool for grid frequency control. It can respond very rapidly to changes in load and provides the crucial minutes needed to start gas turbines if wind turbines drop off load rapidly, as often they do. In such cases, you don't need hours of storage. You need small amounts of energy storage that can respond rapidly at high power levels and achieving high power density, whilst the gas turbine picks up speed. And a mechanical system like this could last for many decades of intense cycling. It wouldn't wear out in the way battery systems would.
I think hydraulic gravity storage could certainly have a place in our energy mix. In the absence of spinning reserve, we need systems that can stretch time constants to allow backup powerplants time to respond. This may be just the thing.

SpaceNut · 2022-10-16 16:58:14

A few calculations were done in the other topic post 63 - 67 by tahanson43206

repost 80m / 24 hr = 3 1/3 mhr of movement of the mass for each hour.

Neglecting the mass of the cable to hold the mass at its end as a contributor.

Remember that the length of the mass reduces the distance that you get for each hour of movement.

Deeper wells can be drilled but overall that is just the drilling costs that it impacts for the project.
In New Hampshire, the average bedrock well is between 100 feet and 500 feet deep. However, they can drill as deep as 1,000 feet!

I know that you are looking to create a dry well so it may need to be lined for the entire length and sealed at its end to keep water from filling it.

https://heindl-energy.com/

https://en.wikipedia.org/wiki/Gravity_battery

https://gravitricity.com/

What is Gravitricity's Gravity-Based Energy Storage System?

The typical block and crane design

Mountain Gravity Energy Storage: A new solution for closing the gap between existing short and long-term storage technologies

SpaceNut · 2022-10-16 17:00:46

These systems are pulsed energy systems as the generate a level of power over a short period of time. This is the same as regenerative breaking in the Prius as the duration is factored over the period of time that energy is outputted. The Prius uses a 5-minute duration of 50 whr from breaking such that if you multiply that by 60/5=12 you get the total for an hour if it were to take that long.

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#1 2022-10-16 14:43:49

Renewables without (or with minimal) Storage

#2 2022-10-16 15:08:51

Re: Renewables without (or with minimal) Storage

#3 2022-10-16 16:53:24

Re: Renewables without (or with minimal) Storage

#4 2022-10-16 16:58:14

Re: Renewables without (or with minimal) Storage

#5 2022-10-16 17:00:46

Re: Renewables without (or with minimal) Storage

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