
Show HN: $200 Solar Self-Sufficiency  Without Your Landlord Noticing - nikodunk
https://medium.com/@nikodunk/200-for-a-green-diy-self-sufficient-bedroom-that-your-landlord-wont-hate-b3b4cdcfb4f4
======
grecy
I built a very similar system into my Jeep-house.

I have two 100W panels on the pop-top roof, a charge controller and a
dedicated solar battery (isolated from the engine-starting battery) that runs
my fridge, water pump, UV treatment lamp, interior lights, air compressor and
charges all my electronics (laptop, kindle, cameras, etc.) directly from 12V
DC.

I can leave the Jeep parked without running the engine for days and easily
have enough energy to meet my needs.

The system has been amazing, and it's fantastic to be electricity self-
sufficient in remote West Africa, where grid power is often non-existent

More details and photos here: [http://theroadchoseme.com/jeep-build-
complete](http://theroadchoseme.com/jeep-build-complete)

~~~
AnimalMuppet
A question: How much did the solar aspects of your rig cost?

And a comment: You might want the ability to tap your solar battery to start
the Jeep, if you're going to leave it parked that long.

~~~
mod
Wouldn't tapping the other battery be a simple matter of a pair of jumper
cables?

I mean, I guess it'd be nice to have wired in, but I can't imagine the time-
savings would ever catch up to the initial amount of work.

~~~
Washuu
On TJ and older Wrangler the tray on the opposite side battery tray is empty.
People will run dual battery setups that way. There are even options for all
Wrangler models to put dual batteries in the stock location. $100 to $200 on a
TJ Wrangler.

The cost and amount of work to do it is minimal.

------
galdosdi
Cool! The one thing I notice the author gets wrong is (out of modesty perhaps)
claiming the system isn't very financially successful. But it actually is!

> 200W system payback period: $300 / $48 = 6.5 years until payback

> Either way you cut it, this is not a money saving machine. Energy prices are
> just too low.

That represents like a 16% rate of return with little risk, which any investor
would take in a second.

However, the $66 battery expires after about 8 years, you're saving more like
$40, not $48, to amortize the cost of replacing the battery every 8 years. So
the actual rate of return is more like 13%, which is still very attractive.
You'll never find any investment/savings product that returns half that well
at such a low risk and is so accessible to anyone with $300.

We've hit the point where solar is very economical! It's exciting!

~~~
xsmasher
Those calculations also assume he'll use all of the energy it produces, every
day, with no loss; it's a back-of-envelope best-case calculation, at best.

~~~
matt_wulfeck
If we're getting into the nitty-gritty, then let's also include energy cost
inflation into the equation. These numbers are for PG&E which is roughly
equivalent for SF:

    
    
        2001: 0.10c kw/h
        2017: 0.28c kw/h (as per my recent bill)
    

That's an average of 10% increase in energy cost _per year_!

[https://www.pge.com/tariffs/electric.shtml](https://www.pge.com/tariffs/electric.shtml)

~~~
sokoloff
2.8x increase over 16 years is a CAGR of 6.6%, not 10%.

(1.066 ^ 16 = 2.8)

~~~
matt_wulfeck
Correction acknowledges!

------
diafygi
I work in solar, and your panel really, really, REALLY needs to be secured
from wind. Luckily, they make ballast mounts that don't require screwing into
the roof[1][2].

[1]: [http://www.orionsolarracking.com/commercial-roof-
mount/balla...](http://www.orionsolarracking.com/commercial-roof-
mount/ballasted/) [2]: [https://www.civicsolar.com/products/racking-
mounting/applica...](https://www.civicsolar.com/products/racking-
mounting/application/Flat%20Roof%20-%20Ballast/manufacturer/orion-solar-
racking-143/type/Ballast)

~~~
coltonv
Funny that we live in a world where one renewable energy source is powerful
enough to (literally) blow away another.

~~~
ilaksh
Right which is why I believe that after the coming consumer solar revolution
there will be something similar with wind energy. Especially with newer VAWT
designs and areas that have a lot of wind.

They compliment each other so wind can continue producing at night.

~~~
jsingleton
For anyone curious, a VAWT is a Vertical-axis wind turbine
([https://en.wikipedia.org/wiki/Vertical_axis_wind_turbine](https://en.wikipedia.org/wiki/Vertical_axis_wind_turbine)).
I always thought these were less efficient than the conventional designs but
they're clearly simpler.

~~~
jononor
Conventional designs struggle with low winds, gusty winds and winds coming
from wrong direction. VAWT designs generally fare better with such non-ideal
conditions, which are going to be common in residential sites.

------
ChuckMcM
Fun stuff. I've built several systems just like this one for camping, they let
you keep things like iPads or laptops charged and they aren't noisy like
running a generator.

Something that my wife discovered was that an igloo "lunchmate" cooler was
perfect to hold the battery and charge controller. Makes it easy to carry. I
recommend using Anderson Powerpole connectors
([https://powerwerx.com/anderson-power-powerpole-sb-
connectors](https://powerwerx.com/anderson-power-powerpole-sb-connectors)) to
make it easy to set up and tear down. I typically use one pair of colors for
the connections to the battery, and another pair of colors for the panel to
charge controller.

~~~
dba7dba
During Iraq/Afg conflict, US army started investing in solar systems because
they realized every fuel (alot used for generators) convoy that doesn't have
to make runs to outposts means less exposure to attacks by enemy. Solar
systems can help lower fuel consumption for generators.

I heard fairly high percentage of US veterans back at home are more interested
in solar systems because they saw the high cost of moving fuel around.

Ironic. We supposedly went there to secure our energy source and we learned
solar system is a viable solution...

~~~
kerbalspacepro
I think an argument could be made that, going there to secure our energy
sources forced us to LEARN how to make a better, viable option.

------
pilom
> Unless you live on an RV or a boat it doesn’t make financial sense yet

If you're curious about what a system for an RV does look like, I work
remotely full time in an RV and built my own system:
[https://therecklesschoice.com/2016/04/29/diy-rv-
solar/](https://therecklesschoice.com/2016/04/29/diy-rv-solar/)

6.5 times the solar, 15 times the storage, 20 times the inverter (but mine is
overkill for us honestly).

~~~
rbritton
Are you stationary or do you move around? Four batteries + solar panels can
get somewhat heavy and eat into your total capacity, so I'm curious if it's an
issue.

~~~
pilom
We are very mobile, usually stay in one place for a week at a time and then
move a couple hours away. You're right about weight though, we are right at
our GVWR (11,000 pounds) when fully loaded. The batteries weigh 100 pounds
each and the panels are another 15 pounds or so each. That said though, we get
terrible gas mileage already so the extra 500 pounds for everything doesn't
change it much.

------
mdb333
A couple nice things about SF on this topic:

1\. Davis Stirling (Housing related laws) mandates that building associations
cannot prohibit owners from installing solar panels. Basically, they have to
work with you to find a way and can't just say no.

2\. As of this year, SF is the first city to require that all new buildings
(10 stories or less) have solar installed.

~~~
arcaster
Another excuse to raise rent...

~~~
Dylan16807
It's been clearly shown that they don't need excuses to raise rent.

Solar on an apartment building wouldn't impact the cost too much. The real
issue is whether construction/zoning is allergic to density.

------
sitkack
Please bolt the panel down, if wind picks it up and blows it off the roof it
could easily kill someone.

~~~
Retric
I really doubt the wind is going to pick up a 2'x4' ~20lb panel like that when
it's flat on a roof. Now if he had lifted an edge to try and get a better
angle with the sun that would IMO be a much larger issue.

~~~
trhway
>I really doubt the wind is going to pick up a 2'x4' ~20lb panel like that
when it's flat on a roof.

thus the difference between the air speeds over the panel and under the panel
in this case equals to the wind speed. To compare - Cessna wing loading is
15lb per square foot and it is generated at the minimum no-stall speed
required by the FAA for general aviation of something around 70 miles/hour,
and in that situation the speed difference between over the wing and under the
wing is obviously significantly less than the 70 miles/per hour that wing
moves through the air with. Thus it is pretty possible (to be sure one can
just plug the numbers into any aerodynamics calculator on the web) that this
panel at 8 square feet would generate multiple tens or even like 100lb+
lifting force at storm/hurricane winds of like 70 miles/hour and may pretty
easy lift itself at the 30-40 miles per hour wind (which do happen on occasion
in SF/BayArea). This is basically the same basic aerodynamics (Bernoulli speed
difference) that tears buildings' roofs off in hurricanes.

~~~
Retric
That's not how wings work.
[https://www.grc.nasa.gov/www/k-12/airplane/wrong1.html](https://www.grc.nasa.gov/www/k-12/airplane/wrong1.html)

Most obvious problem aircraft can fly upside down.

~~~
trhway
you're trying to argue with the Bernoulli law. I wouldn't recommend it :) Even
your link clearly states:

"{The upper flow is faster and from Bernoulli's equation the pressure is
lower. The difference in pressure across the airfoil produces the lift.} As we
have seen in Experiment #1, this part of the theory is correct."

Re-read my original comment - it is pretty much stating the same as the cited
text above.

The link you posted refutes the "Equal Transit" Theory which is deriving the
speed difference from the wing asymmetrical shape using very simple approach.
Which has nothing to do with my original comment as i was applying the
[correct according to Bernoulli law and your link] theory of pressure
difference generated by airflow speed difference to airfoils without regard to
whether they assymetrical (Cessna wing) or symmetrical (solar panel).

~~~
Retric
Read the full page.

"The symmetric airfoil in our experiment generates plenty of lift and its
upper surface is the same length as the lower surface. Think of a paper
airplane. Its airfoil is a flat plate --> top and bottom exactly the same
length and shape and yet they fly just fine."

Wings are angled into the wind. The curved shape primarily minimizes drag
rather than generating lift.

As to hurricanes most roofs are sloped. Yes, faster moving air has lower
pressure, but if you run the equation it's a fairly weak effect. So, it has
little to do with stall speed.

------
Cerium
The last place I worked we did this (though with some permission). One of the
guys made friends with some people at a thin film solar plant down the street.
He got a bundle of manufacturing rejects (300w panels that only made 280) for
free. We strung them up on the roof and were raking in the kWh. Enough to
charge 3 electric vehicles without paying the power company.

~~~
jpk
This makes me wonder why the panel manufacturer doesn't bin panels like they
do with CPUs? Surely they could sell them for less than the 300W panels, but
more than zero?

~~~
pilom
Most do. The panels you see on rooftops are all generally exactly the same
size but could generate anywhere from 315w/panel to 250w/panel depending on
binning. No idea why that company didn't.

------
reaperducer
Will the landlord notice? Maybe not. Will the wife notice all the wires all
over the place? You bet!

~~~
bonniemuffin
Because men love electronics projects and women love keeping a tidy house and
ruining their dreams, am I right?

~~~
dlss
> Because men love electronics projects and women love keeping a tidy house
> and ruining their dreams, am I right?

I don't think this is accurate. Personally, I've had a lot of trouble finding
people of either gender who are interested in electronics.

I might be overstepping here, but it sounds like maybe you should talk to you
wife and see what can be done to minimize the negative externalities caused by
your hobby? It's hard to imagine she would actually want to ruin your dreams.
I don't have a wife, but I know my girlfriend became a lot more supportive
once I started keeping half-finished projects in the spare bedroom, and
started putting in an effort to clean up my projects a bit more before letting
them out. Just my $0.02 obviously.

~~~
bonniemuffin
I'm a female electronics hobbyist. Definitely sarcasm. :)

------
gopikori
I have a similar setup at my apartment in India. It is functional since more
than two years now. Its total 140Watt panels, popping out of my bedroom window
[Photo:
[https://photos.app.goo.gl/S4WR5gbrGu0z8IQB2](https://photos.app.goo.gl/S4WR5gbrGu0z8IQB2)].
It has a 12V battery and 10A solar charge controller. It produces good enough
energy to power my room. I hate inverters, all my lights/fans in room are
based on DC 12V. I use car chargers to charge mobile phones and to run a LED
wall clock.

------
adrianmonk
> _Renters don’t need permission from their landlords to place things on their
> windowsill and rooftops if it’s not altering the building_

This has never been the case in any apartment community I've lived in, ever.
Every time I've looked into anything like this, the lease says I have to
follow community rules, and those rules include stuff like pool hours and
parking but also say I can't put foil in my windows, have a window AC unit,
etc.

I'm sure there are _some_ landlords who won't notice or won't care if you do
this, but it's just not true in general that renters only need permission for
things that alter the building.

~~~
nikodunk
Good point. I'll clean up the language there. I've never lived in a non-ac
unit and non-satellite dish place, but I probably have friends who do. How to
work around that then? You could only use an ESCO (energy service company) on
the east coast or cleanpowerSF for those scenarios.

~~~
dragonwriter
> I'll clean up the language there. I've never lived in a non-ac unit and non-
> satellite dish place

Well, satellite dishes are legally protected by an FCC order, but that doesn't
apply to other things.

------
Xeroday
Quite a side note: If you're renting in SF, your landlord needs to provide you
with heating ([http://sfrb.org/topic-no-257-minimum-heat-
requirements](http://sfrb.org/topic-no-257-minimum-heat-requirements))

~~~
nikodunk
Thanks for pointing this out! I think our main problem was with the non-
insulation of the property. Though I haven't been here for a winter yet.
There's also the landlord leverage problem though with cheap apartment gems in
expensive places (like SF), as I'm sure you know: "Oh you want more
insulation? Sure, I'll fix your insulation/heating. Woops! The rent just went
up?"

------
cjonas
Obvious Problems:

1: You're not using a pure sine wave inverter so right off the back you are
losing significant efficiency (Most the things you're charging use DC power
anyways so it would be better to just get a nice DC charger).

2: If you are discharging your battery past 50%, you're going to significant
reduce it's life span.

~~~
k__
I asked this myself too.

Aren't most electric devices used today DC?

~~~
cjonas
Everything that runs off a battery is DC.

However, for the past 4 months, I've been charging all my devices off
solar/battery (working-travel vacation in a van). I have run into some issues
with certain devices not accepting charge. I think it has more to do with the
device charges themselves than the power source.

For example, my girlfriends Motorola Droid Turbo won't charge at all anymore
off the 2.1 amp usb chargers. My S7 has no problems. Her cheap windows laptop
will also sometimes refuse charge temporarily. Battery voltage is reliably
between 12.3-13.0, which makes me think it's an issue with the chargers
themselves.

------
maxmax
For heating, you could bring in a small refrigerator rather than a resistive
load. Get something besides heat for your power.

~~~
danmaz74
But then you would need to run the refrigerator even when it's hot...

------
luxpir
He mentions fridge/freezer - I'll just draw attention to this project[0] where
the smart guy uses a chest freezer as a fridge with an external thermostat. It
has better insulation and design (cool air stays in when open), so ends up
much more efficient and can be run on minimal power. Just 90 seconds of run
time per hour.

There are other ways to do this in mobile setups, or with inverters in any
setup, using mini-freezers, simple electronics to turn the inverter on/off and
a small panel. See /r/vandwellers[1].

[0] - [https://www.treehugger.com/kitchen-design/man-retrofits-
free...](https://www.treehugger.com/kitchen-design/man-retrofits-freezer-to-
make-an-ultra-efficient-fridge.html)

[1] -
[https://www.reddit.com/r/vandwellers/search?q=freezer&restri...](https://www.reddit.com/r/vandwellers/search?q=freezer&restrict_sr=on&sort=relevance&t=all)

------
WheelsAtLarge
Nice hack. Can it power a fan for a night? That might save you some money in
cooling, which would help with payback.

I won't be using it for my apartment but it has great potential for an off the
grid light power use workshop. Good job, thanks for showing.

Just a note, the biggest expense these days in solar power installations,
home, is the manpower and incidentals needed to install it. Reduce that and
solar power replacement begins to look good. As we saw here, where there were
no installation costs.

~~~
nikodunk
Hey! It can power a fan overnight no problem. A large box fan uses around 45W,
so this could run it for 10hours on a day's charge. Good point!

To your point of expense – the installation cost is what bummed me out, too.
That's exactly why the hack is so effective if someone in your family can
self-install it! I agree. Similar to an AC unit or a satellite dish that most
people just install themselves...

~~~
c8g
we have a table fan specially made for solar is 11.5W, costs about $14.7

------
olegkikin
It better be attached well. If there's a windy day, and that thing flies off
and kills someone, you will not only be liable, you will have to live for the
rest of your life with it.

~~~
nikodunk
Very true. I've tested this thoroughly and it won't. Obviously there's always
a residual risk, which I've mitigated by moving the panel to a window further
back on the roof. Then I'm going to see if the panel's moved after a year.
Another solution would be outdoor glue, but that messes with the ephemeral
nature of the project. Thanks for the input!!

~~~
howard941
What's that puppy's wind loading in an 80mph gust?

~~~
sitkack
It absolutely needs to bolted down.

------
jaclaz
JFYI, the back of the envelope calculation is about energy "created", this
assumes that you actually consume it, i.e. that on average you would use that
energy (while it is within the battery capacity range), if you leave for - say
- 1 month, it is 1/12 less.

~~~
nikodunk
Good point! I think the next step in this project would be to hook it to some
device with high constant consumption, like the fridge, to make sure the
energy gets used up every day. Currently I find it difficult to use everything
it's making, as you say. It's like having more tomatoes in your garden than
you can eat -> sell the tomatoes.

------
SwellJoe
I've been using rooftop solar for many years; I live in an RV (for a total of
about 7 years, spread across two different RVs, both with solar on the roof).
I currently have a 400W system. It makes extremely good economic sense in my
case, because it enables me to live comfortably off-grid for weeks or months
at a time; which can save hundreds of dollars a month in RV park fees, when
I'm traveling.

But, the talk of powering water heater, heating, AC, etc. from a little DIY
solar system is extremely optimistic. I've done the math, and I couldn't run
my AC from the number of solar panels that I could fit on my roof. I can fit
900 watts worth, an additional couple hundred watts on the truck, if I
_really_ wanted to get extreme and was willing to connect/disconnect them
every time I drove the truck away from the RV. That's just not enough. It
could power a small window unit as long as the sun is up, but overnights would
kill a small battery bank dead (like dead dead, not just discharged, as
repeatedly discharging below about 50% reduces the life of lead acid batteries
by a huge amount) in short order.

With a big enough inverter and a bigger battery bank, you can run microwave or
toaster oven for short periods of time (I do). But any big amperage device
that runs for extended periods of time (like heating, AC, and water heater) is
not in the cards for small solar systems.

Battery replacement also needs to be taken into account. In my experience, you
get about 3 good years, and another year of limping along, from this kind of
workload on this kind of battery. He's being more kind to his batteries than I
am to my batteries (I usually end up running down to about 60% each day when
off grid), so he might get another good year. But they probably won't even be
limping along after five years.

But, the good news is that solar panels are _extremely_ durable. They're often
warrantied for 25+ years! And, the expected output after that length of time
is still pretty good. So, if batteries get better, our systems today will get
better just by replacing one component, because everything else is gonna keep
working forever (well, cheap charge controllers die sometimes, but the panels
are practically forever parts).

~~~
adrianN
For water heating, you could skip the electricity step. I suppose that would
gain you a factor two or three at least in the available wattage.

~~~
SwellJoe
Yep, solar water heating is a time-tested way to get energy from the sun and
put it to use. A lot of the earliest solar power deployments (like Carter's
White House) were solar water heaters.

There are even a few cheap off-the-shelf solar water heaters on Amazon these
days (when I first researched the problem a few years ago, it was strictly a
DIY project if you wanted panels small enough for an RV). Getting water to the
roof is usually a difficult problem in an RV (requires breaching the roof
without introducing leaks, and finding a path through the walls from the
existing water heater to get there), but my current RV has an easier path than
my previous one, so I might give it a go next time I've got a free weekend.

------
bvanderveen
Can't imagine why OP has an inverter in the stack when everything connected to
it is DC.

~~~
nikodunk
Because it's easier and I don't want to fry my $1500 laptop with some hair-
brained project's DC-power spike. But I admit that's not really well thought
through and an earlier version of this project was DC only. Also, the main
inspiration for this project was DC only, as I mentioned in the article (but
reposted here: [https://arstechnica.com/gadgets/2015/08/op-ed-how-i-gave-
up-...](https://arstechnica.com/gadgets/2015/08/op-ed-how-i-gave-up-
alternating-current/))

------
mrbill
After Hurricane Ike (and 8 days without power) I built almost this exact setup
to power my CPAP machine in case of another long-term power outage.

------
agumonkey
I've been chatting a bit about thermal building design. This article reminds
me that for most entertainment or work, we don't need much energy.

Cost comes from AC, heater, fridges. Other household appliances too but these
are transient.

But with carefully dimensionned walls, you can slow the heat spread enough to
avoid AC most of the time.

Surely we could keep our energy needs low if we wanted to.

------
URSpider94
Have you talked to your landlord about adding solar panels to the roof? He/she
could install them and connect them to your apartment's service, which means
you would get the power and the savings -- though you might reasonably expect
some of the savings to go towards higher rents in the future. With the tax
advantages, it's almost a no-brainer.

It's even possible to apportion power between multiple units with PG&E in
California. They even allow "neighborhood solar", where you can benefit from a
larger system installed elsewhere, like over a parking lot.

I would also +1 the other comments about thinking really hard about whether
your system is safe in the event of high winds. Solar panels are basically
large sails, you'd be surprised what a 50 or 60 mph wind gust (likely to
happen once or twice a year) can do. If you plan on doing this, check your
lease - many landlords forbid putting things on the roof or hanging outside
windows, or running wires on the exterior of the building.

~~~
rosser
Doesn't PG&E charge customers who have residential solar installs a higher
rate, _because_ they have residential solar installs?

~~~
URSpider94
In a word, no. They do now tack on a monthly minimum fee that only applies if,
over the course of a year, you use less than the sum of the monthly minimums.
So, if you install a project so large that it zeros out your bill, you'll end
up paying $100 or so per year to be tied to the grid. Otherwise, the rates are
the same as you would pay without solar.

------
anderspitman
I'm hoping to build a similar system in the next year or two. Biggest
difference is I plan on building battery banks out of lithium-based 18650
cells. You can salvage them from old laptop batteries, even dead ones (one bad
cell can bring the whole battery down, even if the other cells are fine).
18650s are also used in Tesla's car batteries [0] and Powerwall. They
literally just cram thousands of them in there. There are some youtubers who
have done tons of stuff with them [1][2].

[0] [https://youtu.be/NpSrHZnCi-A](https://youtu.be/NpSrHZnCi-A)

[1]
[https://www.youtube.com/user/jehugarcia](https://www.youtube.com/user/jehugarcia)

[2]
[https://www.youtube.com/user/nocrf50here](https://www.youtube.com/user/nocrf50here)

------
winter_blue
I wonder if you can mount this over a roof rack for a plug-in hybrid car like
he Chevy Volt/Bolt. It'd be an amazing way to charge your car.

Although, 200 W might be a bit too low for the Chevy Volt. It draws circa 100
W when charged via the slow charger that you plug in to an outlet.

~~~
taneq
> It draws circa 100 W when charged via the slow charger that you plug in to
> an outlet.

1kW - 2kW, surely? 100W would take days to charge.

------
gwbas1c
These already exist as self-contained kits:
[https://www.amazon.com/dp/B00GV3XRDW/ref=asc_df_B00D5RVMAM50...](https://www.amazon.com/dp/B00GV3XRDW/ref=asc_df_B00D5RVMAM5086472/?tag=hyprod-20&creative=394997&creativeASIN=B00D5RVMAM&linkCode=df0&hvadid=167143550553&hvpos=1o1&hvnetw=g&hvrand=16267220506877723508&hvpone=&hvptwo=&hvqmt=&hvdev=m&hvdvcmdl=&hvlocint=&hvlocphy=9001821&hvtargid=pla-308511758090&th=1&psc=1)

What I think would be interesting is to use a relay to fall back to grid power
once the battery dies.

~~~
nikodunk
Nice! 600 bucks though?! I guess I'd have to sell this package for 600 for any
kind of profit margin... Reading the reviews on Amazon of the Yeti system
though, I'm not sure they've solved all the issues for 3x the price.

------
ruffrey
How safe is it to keep that battery indoors? Don't batteries need some
ventilation?

~~~
canoebuilder
It's a sealed lead acid(SLA) battery which is different from a wet/flooded
battery, which do require periodic topping off with water and ventilation.

For a project like this, SLA is the way to go.

[https://electronics.stackexchange.com/questions/175649/are-s...](https://electronics.stackexchange.com/questions/175649/are-
sealed-lead-acid-batteries-safe-to-use-indoors)

------
wfunction
This is awesome. The one question on my mind is: is there really no barrier to
doing this, like regulation of some kind? I would imagine there's an added
fire risk with that kind of battery at home?

------
SingletonIface
> I wish I could run a water heater, heating or fridge off this system to use
> the excess 270Wh of the daily energy production.

Or better yet, be able to sell the excess power. In the future power grid this
will be possible.

~~~
URSpider94
It's possible today, almost everywhere in the USA. In fact, the power company
will usually buy it from you at the same rate that they are charging. My house
is turning the meter backwards as we speak.

To do this, you need extra components to protect your house, the power grid,
and the electricians who work on it.

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sand500
If we are talking about being green, what is the carbon footprint of
manufacturing all those things vs the equivilent carbon to geberate thr
electricity the solar panels provide?

~~~
seveneightn9ne
That's at the bottom of the article:

Production footprint PV multicristalline: 4200kWhee/kW [1] * 0.1kW = 420kWh
embodied energy

Production footprint lead-acid battery: 321kWhee/kWh [1] * 0.5kWh = 161kWh
embodied energy

Total Footprint: 581kWh

Annual energy production system: 155kWh/y

Payback period: 581kWh / 155kWh/y = 4+ year footprint payback

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lubujackson
Cool. One caveat in SF (and elsewhere, I'm sure): since I work from home my
electricity usage is way higher than the PG&E norm (which itself seems
aspirationally low). Of course, PG&E uses this to charge me huge "overage"
charges so using a solar panel to offset some of those charges might actually
make this economically viable.

~~~
mindslight
One of the biggest cost/safety/longevity factors here is the usage of a
storage battery. This is necessary because OP presumably uses most power at
night, and is unable to use the grid as virtual storage due to all the
complexity that brings.

If one's usage was mostly in the day or even constant, they could forgo the
storage batteries and setup a system to supply specific loads, making up any
shortfall from the grid. This would take a different type of "inverter" to
avoid becoming grid-tied. I'm imagining a production circuit being based
around a 170VDC bus (power factor? who cares!), but that's probably currently
rare/custom/expensive. You could DIY the same type of thing with a nominal 12V
bus (or 48V, depending on your loads) and DC distribution, from off the shelf
components.

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snowwindwaves
I find the title kind of click baity, "$200 solar self sufficiency for my
bedroom" would be more accurate

~~~
nikodunk
Hey. You're completely right :) My original title was was "Solar Self-
Sufficiency for Renters", but my mates in marketing told me to clickbait it
the f up. Would you have clicked on the former, though?

~~~
TeMPOraL
Personally, I would. What you wrote is very interesting, and interesting
content can stand for itself. No need to clickbait things up.

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scotty79
You could save some energy by driving Led lights directly from the 12V
battery. Not through an inverter.

Doeasn't matter in this case though since one of the things he's running is
electric heater. When you are usin lights you are just getting bit more
heating comming from inverter.

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msangi
Does the panel produce the same amount of energy every season? I know that in
most of Europe the production during summer months is way higher than during
winter and that needs to be taken into account

~~~
kerbalspacepro
San Fransisco is at about the same latitude as Gibraltar, so while he will see
seasonal fluctuations unless he changes its angle of incidence (but hes laying
it flat, so...) However, he will not see as big a difference as, say, somebody
in Germany.

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PascLeRasc
Very cool project and great writeup! It seems like every week I learn about a
new Google microservice (Google Sunroof here).

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kogepathic
The author's calculations for the capacity of the battery are very wrong and
the battery will not last many years the way he's using it.

Deep cycle lead-acid batteries should not be discharged below 50% (known as
Depth of Discharge, or DoD) unless you really want to kill them quickly. The
author's calculations assume he can drain the battery 100% (35Ah), which while
technically correct, will kill his battery very quickly.

Unfortunately the manufacturer doesn't provide any data on the capacity over
discharge cycles at different DoD's [0], but I can guarantee the author will
significantly shorten the battery's lifespan by discharging it so deeply.

If you want some idea of the effect of DoD on battery health, Hoppecke have a
very good chart in their datasheet on page 43. [1] At 50% DoD, the battery
will last for approximately 3000 cycles, or 8 years. At 90% DoD, the battery
will only last for 1500 cycles or 4 years.

If you want to go for 100% DoD in solar, you're looking at Redox flow or
Lithium battery technologies, both of which are more expensive than Lead-Acid.

There are other problems with this setup as well. At $17, the charge
controller is very unlikely to support an equalization charge mode, which is
required to periodically balance the cells within the battery to ensure a long
lifespan. The author would be better off skipping AC entirely and charging
their MacBook/iPad from a car charger which operates on 12V. DC lights can
also be purchased quite inexpensively. The AC inverter is likely putting out
something closer to a square wave than a sine wave, and the low voltage cut-
off is far too low to avoid damaging the battery.

This is really a case of "you get what you pay for" and for such cheap
components, the system will not perform well or last for very long.

If this sounds really negative, I'm sorry. I want more people to become energy
independent, but if you follow the author's example, you're going to have a
very bad time. If you are seriously interested in going off grid, you should
invest in quality components like Victron, Outback, Studer, Hoppecke, etc.
Something like the Victron EcoMulti would be a good choice for someone who
wants an easy to use system that's been designed for longevity. [2]

[0] [http://www.expertpower.us/exp12350](http://www.expertpower.us/exp12350)

[1] [https://www.hoppecke.com/fileadmin/Redakteur/Hoppecke-
Main/P...](https://www.hoppecke.com/fileadmin/Redakteur/Hoppecke-
Main/Products/Downloads/Montagehandbuch_verschl_EN_final.pdf)

[2] [https://www.victronenergy.com/solar-pv-
inverters/ecomulti](https://www.victronenergy.com/solar-pv-inverters/ecomulti)

~~~
mindslight
To be fair, the DoD vs cycle numbers aren't as dire as they first look. Even
an ideal deep-discharge battery would have a 1/x curve, as the real metric is
total energy stored, which is proportional to DoD*ncycles vs DoD.

For instance, for the two datapoints you gave. At 50% DoD, the battery will
have stored 1500 times its capacity over its life. At 90% DoD, the battery
will have stored 1350 times its capacity over its life. This is only a 10%
degradation.

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agumonkey
How hard would it be to add regenerative braking to that ? if not already
installed.

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arcaster
Why not build a small super-capacitor or lithium ion bank that you'd charge at
work?

Also, unless you have perfect weather (I.e. the Bay Area) and require no
energy for HVAC this system is almost useless.

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mchannon
Far more cost-effective would have been to skip the battery and just put a
cheap chinese pure-sine-wave grid-tie inverter to bridge between the wall
outlet and the panel.

It's simple- it has a 110V line cord and plugs into the outlet, sending
current the opposite way of normal. Do a search on your favorite e-commerce
site for "grid tie inverter" and you'll see what I mean.

These cheap inverters have most of the same safeties as the UL 1703 certified
variety, and as long as you don't exceed current ratings (not likely with a
little 200W panel) you're able to apply the power to your electric bill,
without futzing with a lead-acid battery.

~~~
cmac2992
Does that work with a regular meter? My internet sluething says some people
have been charged for the electricity the produce because they don't have a
"compatible" meter.

~~~
ldiracdelta
If you hook up a ton of these and actually generate _more_ than you consume at
any time, you will actually _pay_ the power company for the power you push
back into the grid. You have to get a special meter that can measure the
direction of the flow. I have bought two residential roof-mounted solar
systems and this is what they told me. If you never generate more than you
use, maybe you're ok.

