
Ask HN: What can I do with extra electricity? - traverseda
I&#x27;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.<p>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 &quot;hours&quot; worth of batteries.<p>Let&#x27;s assume that some sunny days I have an extra KW of power generation for ~8 hours. On overcast days I probably don&#x27;t have any extra power, unless I&#x27;m not at home and can shut everything down.<p>What can I use the waste electricity for?
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ldiracdelta
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.

~~~
traverseda
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.

~~~
ldiracdelta
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](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.

~~~
traverseda
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.

~~~
ldiracdelta
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

------
sliken
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.

------
iSoron
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.

~~~
traverseda
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.

~~~
toomuchtodo
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...](http://scitechconnect.elsevier.com/wp-
content/uploads/2016/11/Safety-Disconnects.jpg) (AC disconnect in this image)

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

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

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

------
petermcneeley
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](https://en.m.wikipedia.org/wiki/Gaseous_diffusion)

~~~
traverseda
Looks like a fun weekend project

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

------
mcint
Check out joeyh's stuff, [https://joeyh.name/](https://joeyh.name/), esp
[https://joeyh.name/offgrid/](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.

------
fbhabbed
Distributed computing for citizen science. BOINC, for example

------
aaron695
> 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.

------
vijay_nair
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.

¹[https://www.tesla.com/powerwall](https://www.tesla.com/powerwall)

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

~~~
LinuxBender
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.

------
shoo
[https://en.wikipedia.org/wiki/Aluminium_smelting](https://en.wikipedia.org/wiki/Aluminium_smelting)
?

------
knopkop_
Mine some crypto

~~~
gus_massa
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.)

------
snarfy
Fill a small water tower

------
NoCanDo
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.

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

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

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

------
EADGBE
Solar powered server?

[https://solar.lowtechmagazine.com/about.html](https://solar.lowtechmagazine.com/about.html)

------
programatico
energy efficient server:old link
[https://www.theregister.co.uk/2010/11/11/diy_zero_energy_hom...](https://www.theregister.co.uk/2010/11/11/diy_zero_energy_home_server/?page=1)

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

~~~
traverseda
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.

~~~
rswskg
Hydrogen stoves are in use in homes.

What stops fuel cells being practical?

~~~
traverseda
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.

~~~
rswskg
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.

------
JoeAltmaier
Distill hydrogen for your new hydrogen car

------
boring_twenties
Get a Ryzen CPU and mine Monero with it.

------
jtn_001
Create electric car charging station

------
catwhatcat
Gravity batteries!

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

------
PaulHoule
Heat water?

~~~
traverseda
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.

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

~~~
traverseda
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.

------
Angostura
Get an electric car?

~~~
traverseda
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...

~~~
DeedsMoraine
Something smaller and more bicycular then?

------
yourpalkeith
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.

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

~~~
iSoron
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.

~~~
traverseda
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.

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

