Super Simple Solar Energy

[Rick C]

On Saturday, November 2, 2019 at 6:12:13 PM UTC-4, John S wrote:

On 11/2/2019 4:20 PM, dcaster@krl.org wrote:
On Saturday, November 2, 2019 at 4:12:43 PM UTC-4, John S wrote:
On 11/2/2019 1:25 PM, Rick C wrote:
On Saturday, November 2, 2019 at 9:25:47 AM UTC-4, Klaus Kragelund wrote:
Resistive load won’t operate at the maximum power point

If you overshoot, power goes way down

That is very true. In fact, you need a maximum power point tracking (MPPT) load. If you try to draw a fixed amount of power and the solar cell can't deliver that, the resulting power provided goes down a lot more than it should. Draw too much current and the voltage drops disproportionately..

They make MPPT controllers, but they still will only put out some fixed voltage and for any given lighting condition you won't get optimum power.. So in reality you need a MPPT load device instead. Not hard conceptually. It's basically a switching regulator but the thing being controlled is power to the load rather than voltage or current. Use a low resistance load and a standard buck topology can be used. A small MCU can measure the voltage and current into the load and dither it to find the optimum power point.


Have you read and understood the original requirement?:

"So another idea is using solar panels in a super simple way. Not to
replace electricity, but to provide a little heat to the basement. So
it would just be solar panels connected to a resistive load. No battery
storage, no inverter, no temperature control."

I interpret this as just connecting a resistor to the panel and nothing
else.

That was my original thought. Did not know there were cheap MPPT's on the market. That is what is good about SED. One learns things.

Dan

One poster here said MPPT will not work with a resistive load. I'm not
sure about that so I don't believe it for now.

If you are trying for maximum effectiveness, you should use a maximum
current seeking device. It will work for either battery or resistive
loads. It is very simple. For a battery, you want maximum current to get
it charged. For a resistor, you want maximum current to get maximum power..

MPPT is not a mysterious panacea.

I said the combination of solar panel, MPPT and inverter will not work with a fixed, resistive load.

--

Rick C.

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[John S]

On 11/2/2019 5:54 PM, Rick C wrote:

On Saturday, November 2, 2019 at 3:55:46 PM UTC-4, John S wrote:
On 11/2/2019 1:29 PM, Rick C wrote:
On Saturday, November 2, 2019 at 10:30:00 AM UTC-4, John S wrote:
On 11/2/2019 9:25 AM, John S wrote:
On 11/2/2019 9:03 AM, upsidedown@downunder.com wrote:
On Sat, 2 Nov 2019 08:45:25 -0500, John S <Sophi.2@invalid.org> wrote:

On 11/2/2019 8:25 AM, Klaus Kragelund wrote:
Resistive load won’t operate at the maximum power point

If you overshoot, power goes way down


Overshoot what? I assumed a resistor of appropriate value connected
directly to a solar panel.

If the illumination level drops, the I/V curve "knee" (MPP) will also
move and the fixed resistor will overload the panel.


The panel cannot be overloaded. It is a constant current source and will
survive a short circuit on its output.

I should have said that the constant current is a function of the
insolation. If the insolation drops, the current will go down if the
panel is attached to a resistor.

Look up the I/V curve for a solar array or cell. It is only constant current up to the knee of the curve where the max voltage is approached and the current drops off dramatically. At that point it is constant voltage.

Constant voltage into a constant resistance gives constant current. The
insolation is the source. If it is constant, so is the power hence the
voltage or current is constant for a given load resistance.

That's not what "constant current" means. Constant current means the same current independent of load, in other words, the voltage varies. What you have described is just ohms law.

Okay, then, perhaps constant current is not the correct term.

Maybe power as a function of insolation is a better description. If you
attach a resistor to a solar panel, its power output to the resistor
will be linearly related to the insolation.

Solar cells have a range that is constant current (or nearly so) and a range that is constant voltage (or nearly so) and a knee that joins the two. Forget about your labels and consider that curve. The knee is where the maximum power is obtained.

Yes, I understand that.

>>> Even so, in the constant current range the voltage drops off dramatically. Maximum power is at a point on the knee between the two.

Yes, I understand.

Yes, I know where maximum power occurs on the curve. Where in this
thread was maximum power required? I think I said peak power will be
reached at a certain point with a resistor load.

So? Consider my posts to be information to the OP if you don't like what they say.

I don't dislike what you say. But please consider the OP:

"So it would just be solar panels connected to a resistive load. No
battery storage, no inverter, no temperature control."

 

[John S]

On 11/2/2019 6:23 PM, Rick C wrote:

On Saturday, November 2, 2019 at 6:12:13 PM UTC-4, John S wrote:
On 11/2/2019 4:20 PM, dcaster@krl.org wrote:
On Saturday, November 2, 2019 at 4:12:43 PM UTC-4, John S wrote:
On 11/2/2019 1:25 PM, Rick C wrote:
On Saturday, November 2, 2019 at 9:25:47 AM UTC-4, Klaus Kragelund wrote:
Resistive load won’t operate at the maximum power point

If you overshoot, power goes way down

That is very true. In fact, you need a maximum power point tracking (MPPT) load. If you try to draw a fixed amount of power and the solar cell can't deliver that, the resulting power provided goes down a lot more than it should. Draw too much current and the voltage drops disproportionately.

They make MPPT controllers, but they still will only put out some fixed voltage and for any given lighting condition you won't get optimum power. So in reality you need a MPPT load device instead. Not hard conceptually. It's basically a switching regulator but the thing being controlled is power to the load rather than voltage or current. Use a low resistance load and a standard buck topology can be used. A small MCU can measure the voltage and current into the load and dither it to find the optimum power point.


Have you read and understood the original requirement?:

"So another idea is using solar panels in a super simple way. Not to
replace electricity, but to provide a little heat to the basement. So
it would just be solar panels connected to a resistive load. No battery
storage, no inverter, no temperature control."

I interpret this as just connecting a resistor to the panel and nothing
else.

That was my original thought. Did not know there were cheap MPPT's on the market. That is what is good about SED. One learns things.

Dan

One poster here said MPPT will not work with a resistive load. I'm not
sure about that so I don't believe it for now.

If you are trying for maximum effectiveness, you should use a maximum
current seeking device. It will work for either battery or resistive
loads. It is very simple. For a battery, you want maximum current to get
it charged. For a resistor, you want maximum current to get maximum power.

MPPT is not a mysterious panacea.

I said the combination of solar panel, MPPT and inverter will not work with a fixed, resistive load.

Can you please explain why it will not?

 

[Rick C]

On Saturday, November 2, 2019 at 4:25:01 PM UTC-4, Whoey Louie wrote:

On Saturday, November 2, 2019 at 2:40:55 PM UTC-4, Rick C wrote:
On Saturday, November 2, 2019 at 12:34:13 PM UTC-4, jla...@highlandsniptechnology.com wrote:

Sunlight looks bright, but it's low density intermittent energy and
hard to apply. It's even worse in winter. Better to insulate the
basement, probably.

Basements are typically not insulated because being below ground they are close to the optimum temperature. Only above ground walls are insulated..

Only if you think ~55F is the optimum temperature. Otherwise a basement
is like having an uninsulated living space when it's 55F outside.
Actually it's worse than that, because when it's 55F outside, sunlight
is a big help in warming the living space. In the basement you don't
have that. IMO, it most of the US if you're going to finish the basement
and use it as living space, you'd be nuts not to insulate it.

It would appear the majority of homes built in the
US were built by nuts then. The thermal load of a concrete wall with 55°F on the other side is not so large really. In fact, most spaces need to be cooled if they don't have a path for the internally generated heat to escape. Don't try to compare an insulated wall with a huge thermal hole in it (windows) to a basement wall. Temps inside don't really need heat until the outside temps get fairly cool, below 55°F. As someone mentioned, it is the dampness of basements that gets to you more.

--

Rick C.

--+- Get 1,000 miles of free Supercharging
--+- Tesla referral code - https://ts.la/richard11209

 

[Rick C]

On Saturday, November 2, 2019 at 3:55:46 PM UTC-4, John S wrote:

On 11/2/2019 1:29 PM, Rick C wrote:
On Saturday, November 2, 2019 at 10:30:00 AM UTC-4, John S wrote:
On 11/2/2019 9:25 AM, John S wrote:
On 11/2/2019 9:03 AM, upsidedown@downunder.com wrote:
On Sat, 2 Nov 2019 08:45:25 -0500, John S <Sophi.2@invalid.org> wrote:

On 11/2/2019 8:25 AM, Klaus Kragelund wrote:
Resistive load won’t operate at the maximum power point

If you overshoot, power goes way down


Overshoot what? I assumed a resistor of appropriate value connected
directly to a solar panel.

If the illumination level drops, the I/V curve "knee" (MPP) will also
move and the fixed resistor will overload the panel.


The panel cannot be overloaded. It is a constant current source and will
survive a short circuit on its output.

I should have said that the constant current is a function of the
insolation. If the insolation drops, the current will go down if the
panel is attached to a resistor.

Look up the I/V curve for a solar array or cell. It is only constant current up to the knee of the curve where the max voltage is approached and the current drops off dramatically. At that point it is constant voltage.

Constant voltage into a constant resistance gives constant current. The
insolation is the source. If it is constant, so is the power hence the
voltage or current is constant for a given load resistance.

That's not what "constant current" means. Constant current means the same current independent of load, in other words, the voltage varies. What you have described is just ohms law.

Solar cells have a range that is constant current (or nearly so) and a range that is constant voltage (or nearly so) and a knee that joins the two. Forget about your labels and consider that curve. The knee is where the maximum power is obtained.

Even so, in the constant current range the voltage drops off dramatically. Maximum power is at a point on the knee between the two.


Yes, I know where maximum power occurs on the curve. Where in this
thread was maximum power required? I think I said peak power will be
reached at a certain point with a resistor load.

So? Consider my posts to be information to the OP if you don't like what they say.

--

Rick C.

---- Get 1,000 miles of free Supercharging
---- Tesla referral code - https://ts.la/richard11209

 

[Rick C]

On Saturday, November 2, 2019 at 3:08:07 PM UTC-4, Winfield Hill wrote:

Rick C wrote...

Yes, my lazy solution: $100 150W stick on flexible
panel + $100 300W micro inverter + $10 heater.

Too bad it won't work.

Of course it can "work". If he controls the heater
carefully enough, he can match its on-average energy
use to the solar energy from his panel into the grid.
But it may not heat up his basement, very much.

So what does the inverter do when the input power is less than the load would draw at the output voltage? From the data sheet for a microinverter...

Nominal (L-L) voltage/range 240V/211–264V 208V/183–229V

For the output power to match the input power the output voltage has to roam with the input power. That ain't happening with an inverter designed to supply AC to the line.

To get the max power from the solar panels to the load the power at the load has to vary. With a resistive load this means a variable voltage. What type of DC/DC or DC/AC converters do that?

--

Rick C.

+++ Get 1,000 miles of free Supercharging
+++ Tesla referral code - https://ts.la/richard11209

 

[Rick C]

On Saturday, November 2, 2019 at 5:15:20 PM UTC-4, Winfield Hill wrote:

John S wrote...

On 11/2/2019, Rick C wrote:
On November 2, 2019, John Larkin wrote:
On 2 Nov 2019, Winfield Hill wrote:
dcaster@krl.org wrote...

You understand the trade offs. I had not seen anything
about MPPT'n and it sounds adding one of them would be
cost effective. And easy to add at any time.

You will see a dramatic difference between using a fixed
load resistance, and some form of MPPT. But I was able
to create of form of pseudo MPPT, that's only about 10
to 15% worse than perfect MPPT. To illustrate my scheme
I'll use the values I implemented, to charge the Li-ion
battery in my bee-hive monitor. My sources are nominal
12V solar panels with various capacities. An important
first step is an electrolytic cap charged by the panels.
This holds the node voltage during high converter current
pulses. I used 470uF 25V to handle up to 20W panels.
Next a Schottky diode to handle reverse polarity wiring.
Followed by an efficient buck converter setup to create
a 4.6-volt charging voltage. Next an important item, an
accurate UVLO to shutoff the buck converter whenever the
470uF elec voltage drops below 10 volts. I used a TI
TPS54202H, which has an accurate 1.28V cutoff, with two
1% resistors to set the 10V (or maybe 11V). It's the
hiccuping of the buck converter that implements MPPT.

Finally there's a charging-controller IC, setting the
maximum Li-ion charging current, limiting its voltage
to 4.3 volts. The equivalent in your case would be a
fixed resistor on the 4.6-volt output. When there's
insufficient solar, the buck converter cuts out and
the 4.6-volts drops, but the solar panel is always
operating with a load from 10 to 13 volts, even with
an overcast sky, and it's delivering close to its
maximum available power.

It would make more sense for him to install a standard
solar system, into the AC line, and go to Walgreens
and get a little electric heater for the basement.

A classic illustration of completely not understanding the problem.

A classic illustration of not understanding the original requirement:

"So another idea is using solar panels in a super simple way.
Not to replace electricity, but to provide a little heat to
the basement. So it would just be solar panels connected to
a resistive load. No battery storage, no inverter, no
temperature control."

We've outlined why a spec that lacks, or even forbids, an
MPPT component, would work poorly. But let's see how it
could work if we allow one simple addition, a 300W boost
converter. The I-V curves for my Hyundai HiS-S280RG 280W
solar panels show an MPPT point near 32 volts. We can add
a 15A CCM boost converter, having an enable with hysteresis,
set to say 28 to 30V, and an input capacitor, say 2200uF 63V
(dV/dt=I/C, 2V/300us = 15A/2200uF). The boost converter will
run when the cap voltage is above 30V, and continues until it
drops below 28V. If the boost is set for 120Vdc output, and
intermittently powers a 500W heater, most all the available
solar panel energy will go into the heater.

https://www.dropbox.com/s/g84quuwc5446t4c/Hyundai_HiS-S280RG.pdf?dl=1

Yeah, this can work. But when you say "most", that means more than half. Your choice of trip voltages will pretty much keep operation on the constant current portion of the curve. That will certainly work a lot better than a simple fixed resistance directly tied to the solar cells, but it does give up a significant portion of the available power.

I'm not adverse to using an MCU device to work with the direct tied load through a switch. It would monitor the voltage and current and control power to the load to get the full potential power from the solar cells. This can be done with fairly simple components on the low side only requiring a filter cap on the solar array output.

--

Rick C.

--++ Get 1,000 miles of free Supercharging
--++ Tesla referral code - https://ts.la/richard11209

 

[Rick C]

On Saturday, November 2, 2019 at 4:03:49 PM UTC-4, edward...@gmail.com wrote:

On Saturday, November 2, 2019 at 12:34:01 PM UTC-7, whit3rd wrote:
On Saturday, November 2, 2019 at 12:03:47 AM UTC-7, Martin Riddle wrote:

On Fri, 1 Nov 2019 13:19:32 -0700 (PDT), "dcaster@krl.org"
dcaster@krl.org> wrote:

... Seems like a good project,...t to provide a little heat to the basement. So it would just be solar panels connected to a resistive load.


Hot water solar collectors are the most efficient out of all solar
things. Most bang for the buck too. They move more heat than PV'S
could.

Absolutely, if you want area heat, solar HEATING of water for pumped circulation
to the basement is a good idea. It's as effective as a south-facing basement
window... except you can turn it off in the summer. Mirror area is cheaper
than solar-panel area,

Yes, mirrors or fixed panels are cheaper, but flexible panels are easier to install without risking damages to the roof. It's a much simpler solution as requested by the OP.

Why would they need to be on the roof. At my place I would consider making them into an awning. Putting them on a roof means complications when the roof needs replacing.

--

Rick C.

---+ Get 1,000 miles of free Supercharging
---+ Tesla referral code - https://ts.la/richard11209

 

[Bill Sloman]

On Sunday, November 3, 2019 at 11:27:05 AM UTC+11, jla...@highlandsniptechnology.com wrote:

On Sat, 2 Nov 2019 17:17:27 -0500, John S <Sophi.2@invalid.org> wrote:

On 11/2/2019 5:14 PM, jlarkin@highlandsniptechnology.com wrote:
On Sat, 2 Nov 2019 15:07:49 -0500, John S <Sophi.2@invalid.org> wrote:

On 11/2/2019 11:38 AM, jlarkin@highlandsniptechnology.com wrote:
On Sat, 2 Nov 2019 09:25:12 -0500, John S <Sophi.2@invalid.org> wrote:

On 11/2/2019 9:03 AM, upsidedown@downunder.com wrote:
On Sat, 2 Nov 2019 08:45:25 -0500, John S <Sophi.2@invalid.org> wrote:

On 11/2/2019 8:25 AM, Klaus Kragelund wrote:

<snip>

So you have not read the original requirements.

Of course I have. But in the brutal reality world of engineering,
numbers matter. Some things won't work.

One of them is burning every more fossil carbon to power the ever larger air-conditioners requred to cope with rising global temperatures.

It's funny to hear people talk about how they would re-imagine our
power systems, with solar cells and batteries and power lines from
Florida.

There aren't talking about "re-imagining" it. They are talking about re-engineering it. John Larkin find's it funny because he doesn't understand that it is necessary now, and getting more necessary with every year that every American dumps their 15 tons of CO2 into the atmosphere.

The fact that he and Donald Trump can't see the necessity isn't in the least funny. If they weren't such fatuous clowns it would be tragic.

--
Bill Sloman, Sydney

 

On Sat, 2 Nov 2019 17:17:27 -0500, John S <Sophi.2@invalid.org> wrote:

On 11/2/2019 5:14 PM, jlarkin@highlandsniptechnology.com wrote:
On Sat, 2 Nov 2019 15:07:49 -0500, John S <Sophi.2@invalid.org> wrote:

On 11/2/2019 11:38 AM, jlarkin@highlandsniptechnology.com wrote:
On Sat, 2 Nov 2019 09:25:12 -0500, John S <Sophi.2@invalid.org> wrote:

On 11/2/2019 9:03 AM, upsidedown@downunder.com wrote:
On Sat, 2 Nov 2019 08:45:25 -0500, John S <Sophi.2@invalid.org> wrote:

On 11/2/2019 8:25 AM, Klaus Kragelund wrote:
Resistive load won’t operate at the maximum power point

If you overshoot, power goes way down


Overshoot what? I assumed a resistor of appropriate value connected
directly to a solar panel.

If the illumination level drops, the I/V curve "knee" (MPP) will also
move and the fixed resistor will overload the panel.


The panel cannot be overloaded. It is a constant current source and will
survive a short circuit on its output.

At some illumination level, there is an optimum load current. Anything
else wastes power. A solar cell is not a constant-current source.

For a (silly) resistive heater, one could add a big cap and PWM the
heater to find the sweet spot.

Have you read and understood the original requirement?:

"So another idea is using solar panels in a super simple way. Not to
replace electricity, but to provide a little heat to the basement. So
it would just be solar panels connected to a resistive load. No battery
storage, no inverter, no temperature control."


If cost doesn't matter, use a roof full of solar panels inefficiently.

I like Win's link:

https://www.builditsolar.com/Projects/SpaceHeating/Space_Heating.htm

"Solar space heating can be 25 or more times more cost effective than
solar electric (PV) systems"

but there no limit on how inefficient a PV heating system can be made.


So you have not read the original requirements.

Of course I have. But in the brutal reality world of engineering,
numbers matter. Some things won't work.

It's funny to hear people talk about how they would re-imagine our
power systems, with solar cells and batteries and power lines from
Florida.



--

John Larkin Highland Technology, Inc

lunatic fringe electronics

 

[Klaus Kragelund]

Any resistive load needs to be regulated to the power level of the solar array

If you load less, you loose some power (constant current part of the curve). If you load more, no power since you operate on the constant voltage part

Resistive load must be changed dynamically since solar arrays change power point according to ambient temperature and sun intensity (fast transients from clouds etc)

 

[Winfield Hill]

Rick C wrote...

Your choice of trip voltages will pretty much keep operation
on the constant current portion of the curve. That will
certainly work a lot better than a simple fixed resistance
directly tied to the solar cells, but it does give up a
significant portion of the available power.

I discovered that doing experiments in sunlight, comparing
different possibilities, can be a frustrating experience.
That's because the solar radiation is constantly changing.
10 or 20% changes due to a little haze, etc., are seen by
the instruments, even though the sky looks clear. Add a
few little puffy clouds, forget it. I came to realize that
eking out every last 10% was an exercise in futility, and
simplifying the electronics instead was a reasonable goal.


--
Thanks,
- Win

 

[Jasen Betts]

On 2019-11-02, John S <Sophi.2@invalid.org> wrote:

On 11/2/2019 6:23 PM, Rick C wrote:
On Saturday, November 2, 2019 at 6:12:13 PM UTC-4, John S wrote:
On 11/2/2019 4:20 PM, dcaster@krl.org wrote:
On Saturday, November 2, 2019 at 4:12:43 PM UTC-4, John S wrote:
On 11/2/2019 1:25 PM, Rick C wrote:
On Saturday, November 2, 2019 at 9:25:47 AM UTC-4, Klaus Kragelund wrote:
Resistive load won’t operate at the maximum power point

If you overshoot, power goes way down

That is very true. In fact, you need a maximum power point tracking (MPPT) load. If you try to draw a fixed amount of power and the solar cell can't deliver that, the resulting power provided goes down a lot more than it should. Draw too much current and the voltage drops disproportionately.

They make MPPT controllers, but they still will only put out some fixed voltage and for any given lighting condition you won't get optimum power. So in reality you need a MPPT load device instead. Not hard conceptually. It's basically a switching regulator but the thing being controlled is power to the load rather than voltage or current. Use a low resistance load and a standard buck topology can be used. A small MCU can measure the voltage and current into the load and dither it to find the optimum power point.


Have you read and understood the original requirement?:

"So another idea is using solar panels in a super simple way. Not to
replace electricity, but to provide a little heat to the basement. So
it would just be solar panels connected to a resistive load. No battery
storage, no inverter, no temperature control."

I interpret this as just connecting a resistor to the panel and nothing
else.

That was my original thought. Did not know there were cheap MPPT's on the market. That is what is good about SED. One learns things.

Dan

One poster here said MPPT will not work with a resistive load. I'm not
sure about that so I don't believe it for now.

If you are trying for maximum effectiveness, you should use a maximum
current seeking device. It will work for either battery or resistive
loads. It is very simple. For a battery, you want maximum current to get
it charged. For a resistor, you want maximum current to get maximum power.

MPPT is not a mysterious panacea.

I said the combination of solar panel, MPPT and inverter will not work with a fixed, resistive load.


Can you please explain why it will not?

the inverter-resistive load pair poses is a newgative resistance load
on the mppt.

panel-mppt-resistor should work.


--
When I tried casting out nines I made a hash of it.

 

[Jasen Betts]

On 2019-11-02, Whoey Louie <trader4@optonline.net> wrote:

On Saturday, November 2, 2019 at 10:09:08 AM UTC-4, dca...@krl.org wrote:
On Friday, November 1, 2019 at 5:18:33 PM UTC-4, John Larkin wrote:


Solar cells are inefficient, and resistive heaters are inefficient.
The sunlight is hot already, so maybe use a hot water loop, basically
a solar water heater.

I guess a solar cell could run a small circulating pump.


--
On Friday, November 1, 2019 at 5:18:33 PM UTC-4, John Larkin wrote:


Solar cells are inefficient, and resistive heaters are inefficient.
The sunlight is hot already, so maybe use a hot water loop, basically
a solar water heater.

I guess a solar cell could run a small circulating pump.


--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com



John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

You are right. Solar cells are inefficient. The ones thaOn Friday, November 1, 2019 at 5:18:33 PM UTC-4, John Larkin wrote:


Solar cells are inefficient, and resistive heaters are inefficient.
The sunlight is hot already, so maybe use a hot water loop, basically
a solar water heater.

I guess a solar cell could run a small circulating pump.


--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com


t caught my eye say just over 20 %. But solar collectors are not 100% efficient. And plumbing solar collectors is a lot more work. Here ( Delaware ) you either have to drain the system at night so it does not freeze or have an expansion tank to so you can use antifreeze .

Dan

How is the need for an expansion tank dependent on whether the fluid is
water or a mix of water and antifreeze?

if you don't use antifreeze it can be directly connected to the house
water supply.

--
When I tried casting out nines I made a hash of it.

 

[stratus46]

On Friday, November 1, 2019 at 4:48:24 PM UTC-7, Bill Sloman wrote:

On Saturday, November 2, 2019 at 9:41:03 AM UTC+11, John Larkin wrote:
On Fri, 1 Nov 2019 15:24:21 -0700 (PDT), Phil Allison
pallison49@gmail.com> wrote:

John Larkin wrote:

------------------


Solar cells are inefficient, and resistive heaters are inefficient.


** Really ?

Other than heat, what do resistive heaters convert electricity into ?

Far IR light?

Some people claim that resistive heating is 100% efficient. Then a
heat pump must be 400% efficient.

John Larkin doesn't understand efficiency.

The heat pump extracts low level heat from the outside world, and delivers slightly higher level heat to your environment.

You get more heat delivered (in joules) per joule of electrical energy invested, but any "efficiency" calculation would have to take the change in outside world into account.

--
Bill Sloman, Sydney

The bottom line is to get heat where you want it. While you're correct about efficiency you're being a bit pedantic. The heat pump will get more heat into the house than the resistor. That's all most folks want.

G²

 

[Bill Sloman]

On Sunday, November 3, 2019 at 2:31:03 PM UTC+11, Jasen Betts wrote:

On 2019-11-02, Whoey Louie <trader4@optonline.net> wrote:
On Saturday, November 2, 2019 at 10:09:08 AM UTC-4, dca...@krl.org wrote:
On Friday, November 1, 2019 at 5:18:33 PM UTC-4, John Larkin wrote:


Solar cells are inefficient, and resistive heaters are inefficient.
The sunlight is hot already, so maybe use a hot water loop, basically
a solar water heater.

I guess a solar cell could run a small circulating pump.


--
On Friday, November 1, 2019 at 5:18:33 PM UTC-4, John Larkin wrote:


Solar cells are inefficient, and resistive heaters are inefficient.
The sunlight is hot already, so maybe use a hot water loop, basically
a solar water heater.

I guess a solar cell could run a small circulating pump.


--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com



John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

You are right. Solar cells are inefficient. The ones thaOn Friday, November 1, 2019 at 5:18:33 PM UTC-4, John Larkin wrote:


Solar cells are inefficient, and resistive heaters are inefficient.
The sunlight is hot already, so maybe use a hot water loop, basically
a solar water heater.

I guess a solar cell could run a small circulating pump.


--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com


t caught my eye say just over 20 %. But solar collectors are not 100% efficient. And plumbing solar collectors is a lot more work. Here ( Delaware ) you either have to drain the system at night so it does not freeze or have an expansion tank to so you can use antifreeze .

How is the need for an expansion tank dependent on whether the fluid is
water or a mix of water and antifreeze?

if you don't use antifreeze it can be directly connected to the house
water supply.

You don't really want to. The "water" circulating through our radiators in our houses in Cambridge UK and Nijmegen in the Netherlands was dosed with anti-corrosion chemicals as well as anti-freeze - I bought mine from Fernox.

https://fernox.com/about-us/

The pipes were mostly copper, and most of the radiators were pressed steel, but there were also a couple of cast aluminium radiators below low window sills. I still had to vent a few millilitres of hydrogen gas from the systems every month or so, but the additives were pretty effective.

--
Bill Sloman, Sydney

 

[Rick C]

On Saturday, November 2, 2019 at 7:34:17 PM UTC-4, John S wrote:

Okay, then, perhaps constant current is not the correct term.

Maybe power as a function of insolation is a better description. If you
attach a resistor to a solar panel, its power output to the resistor
will be linearly related to the insolation.

Ah, but it won't. That's the problem. Look at the curve for the current vs. voltage. Win posted a line for a data sheet of a panel. It shows the IV curve for different conditions including insolation. If you pick a resistor that is optimal for one level, it won't be optimal for any other insolation level, not even close. Win suggested a constant voltage on the output of the panel which is still not optimal, but it's not bad, much better than a resistor. The main problem is it doesn't compensate for the variation in voltage. It is likely a suitable thermistor could be incorporated into Win's circuit to adjust that threshold voltage to suit a given panel for temperature variations and be very close to an MPPT device without actually measuring the output power. It would require a larger capacitor on the input to the regulator than otherwise, but it is simple.

Solar cells have a range that is constant current (or nearly so) and a range that is constant voltage (or nearly so) and a knee that joins the two.. Forget about your labels and consider that curve. The knee is where the maximum power is obtained.


Yes, I understand that.

Even so, in the constant current range the voltage drops off dramatically. Maximum power is at a point on the knee between the two.

Yes, I understand.

Yes, I know where maximum power occurs on the curve. Where in this
thread was maximum power required? I think I said peak power will be
reached at a certain point with a resistor load.

So? Consider my posts to be information to the OP if you don't like what they say.

I don't dislike what you say. But please consider the OP:

"So it would just be solar panels connected to a resistive load. No
battery storage, no inverter, no temperature control."

Yeah, so? If he does that he will get a really crappy system. He asked and he has been told it will be crappy. Now people are trying to help him figure out how to make a better system that is still pretty simple.

I'd rather bang out a little code on an MCU or FPGA than construct a frame for some solar cells. I think that is the part of the system that will need significant attention and effort. So rather than design and construct the array myself, I'd save on the money for the electronics by building that myself and buy the solar panel.

Just my opinion.

--

Rick C.

-++- Get 1,000 miles of free Supercharging
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[Rick C]

On Saturday, November 2, 2019 at 8:14:34 PM UTC-4, Winfield Hill wrote:

Rick C wrote...

Your choice of trip voltages will pretty much keep operation
on the constant current portion of the curve. That will
certainly work a lot better than a simple fixed resistance
directly tied to the solar cells, but it does give up a
significant portion of the available power.

I discovered that doing experiments in sunlight, comparing
different possibilities, can be a frustrating experience.
That's because the solar radiation is constantly changing.
10 or 20% changes due to a little haze, etc., are seen by
the instruments, even though the sky looks clear. Add a
few little puffy clouds, forget it. I came to realize that
eking out every last 10% was an exercise in futility, and
simplifying the electronics instead was a reasonable goal.

I don't understand your point. Eking out the last 10 or 20% is exactly what a MPPT does for you. In this case it is even easier since you are only trying to make heat. You don't even need a regular MPPT converter. You just need a MPPT load. The required circuit couldn't be much simpler. Switchers make noise and your design is suboptimal because it leaves power in the solar array. A linear MPPT load would not make significant electrical noise, use very few parts and be very easy to design and build.

--

Rick C.

+--- Get 1,000 miles of free Supercharging
+--- Tesla referral code - https://ts.la/richard11209

 

[Rick C]

On Saturday, November 2, 2019 at 7:37:33 PM UTC-4, John S wrote:

On 11/2/2019 6:23 PM, Rick C wrote:

I said the combination of solar panel, MPPT and inverter will not work with a fixed, resistive load.


Can you please explain why it will not?

Because the inverter operates with a fixed voltage output into a fixed resistance which will be a fixed power level. How can that possibly track the optimum power point?

An MPPT designed to charge a battery might work since it is designed to drive different currents. It depends on whether the MPPT is designed to output a constant voltage or if it just lets the battery set the voltage.

The easy way to design an optimal circuit would be to optimize the power going into the load... or have no MPPT converter at all and connect transistors as loads with the control coming from a circuit designed to optimize the load power which in this case would be exactly the same as the power from the solar cells.

While measuring power is not so easy in discrete components, it is duck soup in an MCU. Solar cells on roof, two wires to the basement, an MCU and some transistors are all you need... oh, and a heat sink. A linear regulator would provide power to the MCU. As soon as the solar cells start to make power the MCU boots up and drives the transistors to the MPPT.

--

Rick C.

-+++ Get 1,000 miles of free Supercharging
-+++ Tesla referral code - https://ts.la/richard11209

 

[Martin Brown]

On 01/11/2019 20:19, dcaster@krl.org wrote:

I think about doing a lot of things that I never actually undertake. And Solar Collectors are one example of this. Seems like a good project, but it also seems like a bunch of work. So another idea is using solar panels in a super simple way. Not to replace electricity, but to provide a little heat to the basement. So it would just be solar panels connected to a resistive load. No battery storage, no inverter, no temperature control.

AliExpress or maybe it is Ebay has ads for 100 6 inch by 6 inch solar cells for about $100. So could make 4 panels , 2 feet by 3 feet to hold 24 solar cells on each panel. Maybe run lines for each panel to the basement.

Anyone see an obvious fault with the idea?

The poor intrinsic efficiency of the PV cells means that a well
insulated black painted flat radiator under glass perhaps followed by a
parabolic trough with a black pipe at the centre will capture a far
greater proportion of solar energy and deliver it as hot water (or
antifreeze mix). Kingspan, a pump and mild steel radiators are cheaper.

Plenty of designs about usually for heating swimming pools or bulk
thermal stores.

--
Regards,
Martin Brown