Ask HN: What can I do with extra electricity? | Hacker News Reader

Ask HN: What can I do with extra electricity?

27 pointstraverseda60 comments

I'm looking at solar power systems, with the intention of eventually not being connected to the electrical grid at all and only having intermittent internet access.

In order to do that I need to over-provision my solar panels. Solar panels remain a lot cheaper than batteries, so for me at least it makes sense to get a lot of solar panels and only a few "hours" worth of batteries.

Let's assume that some sunny days I have an extra KW of power generation for ~8 hours. On overcast days I probably don't have any extra power, unless I'm not at home and can shut everything down.

What can I use the waste electricity for?

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I'm in Washington state and I'm not sure what latitude you live at, but for my house, my low, without snow on the panels, is about 8 kWh for an overcast day in December or January and my high is 107 kWh for a day in the middle of summer. For me to average out my needs I need a dam... like on the Columbia. In WA state, you don't sell the power, your extra power is future credit to your power needs. I'm on a heat pump and my highest demand is in the winter where lows dip to 15F or 25F. For me to save up enough energy on my own land would require more of a pond pumping scheme and it would be a massive undertaking. On the order of being able to store huge portions of energy for a quarter to a third of the year to get through winter. FYI, my system is Goldilocks's just right. I pay about $25/ year for extra power once my credits run out at the end of winter.

I've bought two different solar systems in two different states and the devil is in the details for your hypothetical situation. You need to understand average overcast days, ~90 percentile run of overcast days in your lowest intensity sun month, intensity of sun, angle of the sun, et c. Also, if you optimize for the worst days of the year, you could be reducing total energy output because your panels would be optimized for a lower sun angle.

I'm in Nova Scotia, Canada. So I'm expecting worse than that, but it's hard to get realistic numbers.

Those numbers are a fair bit worse than the worst cases I was looking at, which assumed winter panels would be ~25% efficient on average....

So that assumes a 3kw system is producing around 4kw-hours per day. I'll need to see if that's realistic.

The middle of Nova Scotia is about same latitude as me, but you guys probably get waaaaay more snow and I am on the desert side of WA state. We get a ton of sunshine. How are you going to clear off the snow? I have 54 panels and it is a big chore to do it without scratching the panels, so I don't even try. Snow slides off like a metal roof, so you have that.

Do you guys get more overcast days? If so your panels may behave more like my place on the west side of the Cascade mountains near Portland Oregon. Looking at production on that 2.2 kW system for this January, I see a non-snow low of 0.4 kWh with an average daily production of 1.6 kWh.

Take a look at my January production, including some days with 0kWh production due to a dusting of snow:

https://i.stack.imgur.com/9qw18.jpg

That system is 6 years old.

So, IFF you get a system, your power storage needs to survive whatever is the longest run you can imagine (+50% ?) of days with overcast or snow coming down.

That program didn't exist last time I looked into it, I'll definitely be following up on it. I actually know some people who would be great candidates for small wind turbines under it, so I'll be mentioning it to them.

Another challenge is that the solar is part of an RV, which makes permanent grid tie challenging, but I'm definitely considering just "donating" it when I can at this point.

Unless you're sure that your donations on will be used on-premise immediately, then you will actually cost whoever is your host. (It may even have to be on the same 120V phase tap from the 240V coming off the street transformer, but I'm not sure.) Standard electric meters are not sensitive to power direction - power going into the residence or power going out. They only detect volume of power movement, but not direction. When you buy a grid-tie system, the power company has to come out and swap your power meter so that the new one will essentially run backwards if you happen to have net power going back into the grid. Anyways, fully solar systems are harder at our latitudes than if you live in California or closer to the equator without the strong winter demands. Maybe just fail-over to propane as needed.

Power inverters need to be manufactured grid-tie style. They have a phase lock loop ( IIRC ) that ties into the phase of the grid and they need to not generate power if power is down on the grid in grid-mode, otherwise guys working on the lines can be electrocuted when they think they have turned off power lines.

Also, if you're donating back, you need to be concerned about amperage on that circuit and it needs to be dedicated, in addition to following all your local power code. If you just so happen to generate 14Amps net and then a device on that same circuit consumes 28A, then the panel 15A breaker may not trip, but parts of your circuit have 28 Amps flowing:

                            Load
                            (28A)
                              ^ <--- exceeding wire load 
                              |      ratings
                              |
     solar_current->---14A--->+<------14A--<--Breaker<--Panel
                                                ^
                                                |
                                      Not tripping cause
                                      it only sees 14A

To minimize battery needs, anything that requires power. Charging power tools, drying clothes, pumping water, washing clothes, cooking food, running the fridge, running the AC, vacuum etc.

You can save a surprising amount of money by just running the most energy intensive appliances during peak solar.

You can sell it to your local utility company. You will get paid for it, and another power plant somewhere (maybe a coal power plant) will need to produce 1 kW less power.

Unfortunately that won't work in my municipality, as they only do that for larger customers. The problem is that it's not a "smart" grid, and having random customers pump power back into the grid can cause lines that they thought were dead to actually be energized during repairs. They need some way to shut off the buyback during repairs, and right now they don't have that.

Also I'm not sure that the amount of power I'd be putting back would actually pay for the basic connection fee. It would during the summer months, but during the winter it likely wouldn't, and seasonal connections aren't much cheaper.

I think that's generally the best bet if you can do it.

Most net metering arrangements require a manual power disconnect switch for your rooftop generation [1] for utility workers or first responders, and NEC requirements require inverters to shut down ("rapid shutdown") if they can't sync to the utility to prevent backfeeding power during maintenance (caveat: if you have local energy storage, the inverter will island and continue to provide power from local storage). I would encourage you to ask your municipality and their utility department what their net metering arrangements are; I would be happy to make such a phone call/inquiry on your behalf if you would prefer.

Is your utility Nova Scotia Power by chance? It appears they support net metering [2].

Everything I mention above will be cheaper than storage (which will start around $13k CAD).

[1] http://scitechconnect.elsevier.com/wp-content/uploads/2016/1... (AC disconnect in this image)

[2] https://www.nspower.ca/your-home/save-money-energy/make-own-... (Nova Scotia Power: Enhanced Net Metering)

Thanks, the net meter looks to be a new pogrom. I wasn't previously aware of it.

Happy to help. Please share the net metering info to anyone who might be considering rooftop solar/distributed generation in your area!

This is exactly why many grid tied inverters like the SMA Sunnyboy range won't start or auto shutdown if it doesn't detect power coming from the grid.

That's going to be hard if he's literally off the grid.

I can highly recommend Gas diffusion. It consumes electricity like one might expect from a multistage refrigeration unit. The results will guarantee your permanent "off the grid" independence comparable to any other nation. https://en.m.wikipedia.org/wiki/Gaseous_diffusion

Looks like a fun weekend project

Grow some plants or algae faster by shining extra grow lights on them, in addition to sunlight?

Check out joeyh's stuff, https://joeyh.name/, esp https://joeyh.name/offgrid/

Energy storage, whether purchased batteries or built gravity storage is likely most useful.

Having consistent access to power through predictable reserves makes energy way more useful to you. You can do laundry at night, or run a heater, etc.

Storing energy allows you to adapt your power usage to your needs and preferences, instead of adapting your needs and preferences to power availability—which has daily and seasonal limitations.

Distributed computing for citizen science. BOINC, for example

> What can I use the waste electricity for?

You can't. That's really the end of it.

Lots have tried and failed. You can pick a fun project that you might get some skills from but it's not really a real answer.

It won't beat batteries which you've already spec'd out.

Best you have is move chores when you have extra electricity. Washing, download torrents, watch TV, run the pool pump, heat water, dry food.

I'd buy Tesla Powerwalls¹ and charge 'em up. One of them can store upto 13.5 kWh of energy and going by your comment below (190 kWh/30 days = 6.3 kWh/day, which seems in line with "I have an extra KW of power generation for ~8 hours" for peak days), it seems two of them costing $14k as per their calculator can handle 4 days worth of surplus.

Not sure if the economics would work out in your favor² but I personally consider going off-the-grid worth the cost.

¹https://www.tesla.com/powerwall

²subsidies: https://www.tesla.com/support/energy/powerwall/learn/incenti... (could potentially knock off 50% of the cost if you qualify)

For some time, Tesla were not selling the power walls to people that were off-grid or unwilling to put power back into the grid. Is this no longer their policy?

background: this is second hand knowledge based on watching hundreds of videos people have made, documenting their experience and all the steps to go off grid, so this could be outdated. Learning every facet of this is one of my hobbies.

I'm paying about $2200 CAD for 4.8KW hours of lifepo4 batteries, after taxes and charge controllers. I'll be putting that to the test, but even so I'd rather have more solar than more batteries most of the time.

I don't need any large AC inverters, so a big part of the appeal of a power wall is lost on my. Also I'd rather something with user-serviceable parts, as for me at least that goes hand-in-hand with going off grid.

https://en.wikipedia.org/wiki/Aluminium_smelting ?

Mine some crypto

I agree. I think that the OP must look carefully for a coin that is profitable when mined intermently (perhaps using common hardware instead of ASICs?). (I think most of the cost analysis assume that you are mining 24/7, and that is important for the amortization cost of the ASICs.)

Fill a small water tower

Gravity batteries. Get a million gallon Tank on 10-20m stilts, pump water into it with ONLY waste electricity.

Let water flow out of it and power a turbine during times where electricity is needed.

But then OP still has too much electricity — s/he just has too much electricity at different times!

Seems like a good opportunity to donate some power to the neighbors.

Wood pellets, irrigate, fill-up battery powered tools, turn on AC.

Solar powered server?

https://solar.lowtechmagazine.com/about.html

energy efficient server:old link https://www.theregister.co.uk/2010/11/11/diy_zero_energy_hom...

Make hydrogen (H2)with electrolysis. Need to found a good technology for that, and be careful hydrogen is very explosive.

Running a server isn't really a predictably intermittent load, and there are plenty of servers/computer already in my power budget.

Not sure what I'd do with a bunch of hydrogen. Fuel cells still aren't really a practical thing. I'd thought about maybe some kind of wood-gas biodiesel thing, but I don't know of any way to do that on a small scale with intermittent power.

Hydrogen stoves are in use in homes.

What stops fuel cells being practical?

Mostly the bit where I can't actually buy them. Do you know of any good suppliers of kw-scale fuel cell systems that are cost-competitive to lithium or lead-acid batteries? Because that would be great, I just can't find them.

I think hydrogen storage is still one of the difficult parts.

I've never done any analyis on the performance of them. I should, the dual nature of hydrogen usage (cooking and power) makes it very intersting to me.

Hydrogen storage tank seems to be available but keeping it all under pressure, i've not seen many people talk about that.

Distill hydrogen for your new hydrogen car

Get a Ryzen CPU and mine Monero with it.

Create electric car charging station

Gravity batteries!

This. Best idea so far. If you can implement it.

Heat water?

There are some intermittent things like drying my laundry that it makes sense to do only when I have extra power.

I'm probably going to go tankless propane for hot water heating though. Heating water takes a lot of power, storing hot water produces a lot of waste heat, and in the winter when I could most make use of that waste heat is when I'm expecting to not have much of a power surplus.

If I could get a hot water tank that was well enough insulated...

It's a good point, I'll need to do some math, and it would probably need to be in addition to some type of tankless/propane heater, since I still need to shower in the winter when I don't have as much extra power.

Similarly, you could distill water for drinking if sources are not pristine.

Probably a "water maker" for a boat, my understanding is that they use reverse-osmosis to desalinate water, so it's easier to have them take up small amounts of extra load. It's a nice self-contained unit that you can start and stop pretty much instantly.

Get an electric car?

At 190kw hours it would take me like a month to get a full charge. Also probably peek hours would be when I'm not at home, and neither is the car.

I also worry that I'd end up filling it up in town and using the power at home.

Still, it would certainly fix my battery situation...

Something smaller and more bicycular then?

Please don’t increase your energy consumption just because you are generating an excess. As a world, we need to lower our energy use (as I’m sure you are well aware). I’d urge you to consider those extra watts as a much needed contribution to the cause.

That makes no sense. If the energy is here, what's the benefit of not using it?

It makes a bit of sense. If you use all energy, you a) generate heat b) increase your energy consumption habits. The alternative is of course to reflect the sunlight. Not that this one case would make a difference, but still makes sense as a mindset.

Instead of consuming the extra energy, OP could also provide it to another customer through the grid, by selling it back to the utility company. This would reduce the total amount of energy that needs to be generated from non-renewable sources. If OP increases their own consumption instead, those non-renewable kWh are still being generated and causing environmental impact somewhere.

This is being mounted on an RV, which is explicitly off-grid, and would only be intermittently connected at best. In my municipality they only do power buy-back from larger generators.

Also most of it isn't going through an inverter, I'm using direct DC-DC, which is much more power efficient for what I'm doing. So that means more cost for inverters, which I'd consider paying even if at the scale I'm working at it would take years for the equipment to pay for itself, but...

You can't simply tie an inverter into the grid and sell back to the power company, as that could mean that during repairs lines they thought had no power were energized by some residential customer. You need special hardware that the power company can shut down remotely, and that's only available for larger customers.

Also I'm not sure if the price I'd be getting for that power would actually offset the monthly connection fee, making connecting to the grid and selling back extra power very likely cost more than just wasting the power, which is unfortunate.

So unfortunately grid-buyback that isn't really an option for me.

Which is why I'm looking at other options. I like the wood pellet one, in an ideal world I'd be able to do some kind of carbon capture or something, but I'm not seeing any good power-to-gas tech right now.

Thanks for the reply - makes perfect sense in your case.

Assuming the panels are connected to the grid, then the power will be consumed by neighbors - not wasted.

EDIT: I see it was right there in the first line of the post that the plan is to unplug from the grid. I would reconsider this decision. If you stay connected, you can share your excess capacity - if not then you use it or lose it. Why put yourself in that position?

I personally support municipalities making it illegal to go completely off the grid.

It's an RV, so good luck.

Well that certainly changes a lot. Probably would have been helpful in your question to specify.

Out of curiosity why?

Creating and maintaining a electric grid requires scale, it's one of the main reasons municipalities grant exclusive monopolies to power companies, because competition doesn't really work in the space. At certain low thresholds the system can absorb people going "off the grid", but too many and it becomes economically unstable. Forcing a rise in rates and a cascade effect. By requiring people to remain attached to the grid and sell off their unused power the benefit to all is clear.

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