Geothermal may beat batteries for energy storage • Hacker News Board

Re: Geothermal may beat batteries for energy storage

#221

Post by jonstewart » Wed, Oct 12, 2022, 2:30 AM UTC

mderazon wrote: post #177

2Gkashmiri wrote: post #87

Earlier quoted context omitted.

interesting. i have a PV system. i want to use the half installed central heating system (only piping laid down) (no boiler or FCU/room unit) and i have this crazy idea. use solar water heater to heat water, that feeds into a water storage tank, that water gets heated MORE by an air source water heater and a small circulation pump uses that water storage to heat the house. i am hoping, since we currently have 0 whole…

I am currently looking to do something similar. I have zero heating in my house at the moment and have a 300L (65 gallon) thermosiphon solar water heater [1] (tank plus panels all in one system) that gives me plenty hot sanitary water. I am looking to install an hydronic fan coil [2] radiator in my rooms and need water to heat them - I thought to use the excess heat from the solar heater to supply hot water to the fa…

This is not so complicated, you just need tanks with heat exchanger loops. The solar water heater input comes into your tank at the bottom and goes through a copper coil, giving you domestic hot water.

_Some_ tanks will have a similar coil in the middle/top of the tank. What you can do is then run the cold return from your heating units through this coil. It will heat the radiator water before going to the fan coil unit. This is often done as a precursor "boost" before sending the water through a boiler/heater -- the solar heat is applied to cut the temperature differential and reduce the energy expended by the boiler/heater for the radiant heat, but you're not relying solely on solar heat.

You can get heat pumps that use a water storage tank with extra heat exchanger loops like this, precisely for providing domestic hot water. The DHW and radiator water never mix. There aren't any moving parts, so it's simple.

The only question is what the max temp is from the thermosiphon tank, and whether that exceeds either the max radiator water temp or, if you use some kind of modulating boiler/heater for the radiator, the max input temp.

The math for solar storage gets daunting, however. If your typical max temp for the thermosiphon tank is 120F on a sunny day and the cold return from the FCU comes back at 70F, then with 65 gallons you can store about 26K BTU in your tank. That sounds like a "2 ton"/24K heater, but it isn't because the BTU rating of heaters is _per hour_. So, if your house needs a ~24K BTU system for heating, a sunny day storing heat in your tank will get you about an hour's worth of free heating. 24K BTU/hour is a pretty small heat load for a typical house... (though plenty doable if you invest in insulation, windows, etc.)

So, the thermosiphon is maybe adequate to provide you with domestic hot water, but in a cold climate you'll need 3–5 more of them and a repurposed and well-insulated 500gal milk tank in a shed near your house with insulated below-ground pipes running to it.

Re: Geothermal may beat batteries for energy storage

#222

Post by jonstewart » Wed, Oct 12, 2022, 2:46 AM UTC

distances wrote: post #192

jws wrote: post #134

Earlier quoted context omitted.

It's not as bad as this. In climates where you will have a bed of snow during the winter months, your optimum tilt angle for a fixed solar panel is something like 30° off of vertical or steeper. I find that on mine the snow falls off since it is a south facing, steep, dark surface. You engineer to make sure you have enough energy captured each month to meet that months needs. That might lead you to a tilting mount, o…

Interesting. Last winter my parents' rooftop solar had zero output until April, as it produces nothing until all the panels are clear of snow. Granted their installation is at a fixed angle that matches the roof, and this is in the Nordics. During summer months the production mostly covers and partly exceeds their use, but the sell price is so much lower that it doesn't even begin to pay for the rest of the year. But…

So much of this discussion depends on where you are. In the US, a typical solar installation is on the pitched roof of a house. When the sun comes out, the dark roof and PV panels heat up, and the snow slides off. Rowhomes or apartment buildings in a city might have flat roofs with panels mounted on racks, but most US cities won't get enough snow often enough for this to be a problem.

Re: Geothermal may beat batteries for energy storage

#223

Post by manholio » Wed, Oct 12, 2022, 2:49 AM UTC

Retric wrote: post #212

manholio wrote: post #157

Earlier quoted context omitted.

> at basically no cost for the EV owner? Only if you have a battery with unlimited charge cycles. This doesn't seem possible with current technology - and even if it were, manufacturers would still optimize for higher density and reasonable longevity after 100,000 miles. Most people would average a charging cycle a week, so they can't see the difference between a 2000 cycles battery and a 50,000 cycles one in the lif…

The idea is you wait to charge until prices drop, rather than charge as soon as possible which adds zero charge cycles or degradation. Discharging into the grid is unlikely to ever be profitable for the average consumer but it isn’t impossible for the economics to work out just look at how high Texes Grid prices have gotten during extreme events. Delayed charging is already a common feature on many EV and could shift…

There is some talk about virtual energy providers that could agregate a large number of home users, receive an availability fee and only physically discharge during emergencies; that could work out economically and allow owners a positive revenue after depreciation, that could translate, for example, in lower prices for energy. That being said, I still think the whole fixed costs of the scheme (smart bidirectional meters, EV and charger support, coordination and administration costs etc.) would make it a money-losing proposal. A nice idea in theory, like say IP multicasting, but that cannot be made to work effectively in the real world.

The benefits of delayed charging are limited by the electric consumption of the transport sector. For an average family driving no more than 800 miles/month at 4 miles/kWh it works out less than 200kWh/month. If half of that charge is time flexible (with the rest being achieved at fastchargers or when the owner is in a hurry etc.), you get a 100 kWh/month dynamic load, a sizeable yet small fraction of the total household consumption. I would earmark that under smart-grid approaches, if correct pricing incentives are set at the meter it will happen automatically and not just for the EV charging loads.

Re: Geothermal may beat batteries for energy storage

#224

Post by jonstewart » Wed, Oct 12, 2022, 2:53 AM UTC

aidenn0 wrote: post #138

LinuxBender wrote: post #67

Many of the greenhouse Youtube channels I watch do a smaller DIY version of this. They have either dark barrels of water in the greenhouse with the windows facing south to the sun, or a thin metal wall filled with clay and pipes acting as a sun-heat-battery. They pump the water through the barrels or clay battery into pipes that are under ground to store the heat. In winter time they extract the heat from the ground…

Forget geothermal, I'd love an air-exchange system for the summers where I live. It's not uncommon for the low to be in the 50s, with the high in the 80s. If I could just store some of that overnight cool in water and then run it through the central air system, I almost wouldn't need AC.

There's work being done on incorporating paraffins and other such materials into walls, so that they go through a phase change close to room temperature. That way they act like heat mass, but without all the weight: https://www.doityourself.com/stry/phasechangedrywall

Re: Geothermal may beat batteries for energy storage

#225

Post by kjs3 » Wed, Oct 12, 2022, 2:56 AM UTC

jonstewart wrote: post #224

aidenn0 wrote: post #138

Earlier quoted context omitted.

Forget geothermal, I'd love an air-exchange system for the summers where I live. It's not uncommon for the low to be in the 50s, with the high in the 80s. If I could just store some of that overnight cool in water and then run it through the central air system, I almost wouldn't need AC.

There's work being done on incorporating paraffins and other such materials into walls, so that they go through a phase change close to room temperature. That way they act like heat mass, but without all the weight: https://www.doityourself.com/stry/phasechangedrywall

So...I'll save on energy by turning my walls into candles. Interesting.

Re: Geothermal may beat batteries for energy storage

#226

Post by adrianN » Wed, Oct 12, 2022, 4:43 AM UTC

LinuxBender wrote: post #67

Many of the greenhouse Youtube channels I watch do a smaller DIY version of this. They have either dark barrels of water in the greenhouse with the windows facing south to the sun, or a thin metal wall filled with clay and pipes acting as a sun-heat-battery. They pump the water through the barrels or clay battery into pipes that are under ground to store the heat. In winter time they extract the heat from the ground…

This reminds me of this article: https://www.lowtechmagazine.com/2015/12/reinventing-the-gree...

Re: Geothermal may beat batteries for energy storage

#227

Post by adrianN » Wed, Oct 12, 2022, 4:51 AM UTC

londons_explore wrote: post #139

jandrese wrote: post #135

Earlier quoted context omitted.

However, the ASHP can also be used to cool your home in the summer. In the past this has been a dubious benefit for most of northern Europe, but heat waves have been getting stronger, last longer, and happen more frequently as time goes on. This is turning into a serious consideration. Also, you can theoretically power a ASHP with renewable energy, while there are few if any carbon neutral replacements for natural ga…

Most boilers purchased today allow use with a Hydrogen mix, and some under development allow 100% hydrogen. Before the widespread extraction of natural gas, towns were powered with 'town gas', which is ~50% Hydrogen, so this is very much proven tech. There are a bunch of potential ways to make green hydrogen too. So, there very much is a path to green with a gas boiler.

But making green hydrogen has pretty bad efficiency. It could never compete with a heat pump using the same electricity source, even if it had an efficiency of 100%, since the heat pump has an efficiency of 200-400%.

Re: Geothermal may beat batteries for energy storage

#228

Post by adrianN » Wed, Oct 12, 2022, 4:55 AM UTC

bergenty wrote: post #168

tyfon wrote: post #34

There is a school close to where I live that does something like this. During the summer they heat the bedrock using solar panels (thermal and electric via a heapump) to heat the bedrock far down using water pipes. In winter they extract this energy for heating, electricity and hot water making the school self sufficient for energy. Here is a write-up from the municipality about it, but it's in Norwegian https://www.…

Wait how long does that heat last. I wouldn’t imagine more than a week since it’s not insulated?

You don't have to dig very deep for the soil on top to be decent insulation.

Re: Geothermal may beat batteries for energy storage

#229

Post by nasmorn » Wed, Oct 12, 2022, 5:34 AM UTC

dahfizz wrote: post #179

smileysteve wrote: post #130

Earlier quoted context omitted.

This seems like a (regulated) pricing error. There should be no economic way that a high efficiency turbine produces and distributes electricity to heat homes at a greater than 1:1 ratio compared to storing, pressurizing, and delivering, then burning in irregularly maintained consumer homes. Likely the error is that gas pipes to the house are subsidized (albeit the electrical likely is too, with heat pumps and induct…

"high efficiency" turbines are not all that efficient. Burning gas releases 100% of the available energy as heat. Converting that gas to electricity is Also, electricity from gas is relatively expensive. Other sources like coal or hydro are cheaper, which lowers the average cost of electricity.

If you combine gas turbines with district heating you can recover almost all of the heat energy. If you use the produced electricity for heat pumps you come out ahead. For climate change purposes it is way better since gas pipes to homes leak way more methane than those to central power stations

Re: Geothermal may beat batteries for energy storage

#230

Post by Schroedingersat » Wed, Oct 12, 2022, 6:25 AM UTC

killjoywashere wrote: post #31

jillesvangurp wrote: post #24

Earlier quoted context omitted.

It can work, it's just a cost equation. You need a large amount of mass to get meaningful amounts of energy stored. So pumped hydro is nice because you are basically using natural reservoirs and some cheap pumps and pipes. A water tower needs to be built first and only stores a limited amount of potential energy. The problem is not the efficiencies but the cost of building a big enough tower. A tower with the same ca…

Why would you need a water tower? If you're in flat geography at sea level, you could probably access tidal energy to drive generators. If you're flat and far from water, couldn't you dig a shallow hole and a deeper hole, and put the generator and pumps in between? I mean, even in Kansas it's not that hard to find an elevation difference of 50 feet.

Digging 100m deep holes isn't cheap.