Pros and cons of 12V, 24V, 48V system.
Crappy
I am planning on putting up some PV panels on my house to, initially,
run lights and some of the plug circuits but ultimately, run
everything (barring the stove) (Heating is gas)
The panels will be on the first story roof, all the electronics etc,
directly below on the ground floor. Cable run would be about 10m (33
foot).
My question is, all things considered, which is best. To combat the
losses on the low voltage cable, obviously 48V would be better. Or
would 24v system still be ok?
I want to start with 2 or 4 panels. Two would force the 24v option
but if need be, can do 4. I plan to expand it in the near future to
have more panels as well as a wind turbine.
Thinking out loud here, expanding a 12v system means the possibility
to buy one panel at a time. 24 or 48v means 2 or 4 at a time.
Likewise, the turbine will be more expensive.
Is the effort worth going higher source voltages or not really.
Inverters (UK is 230V) are cheap for 24v and have a high enough
rating. I would use two or 3 to run different circuits in the house.
12V inverters are higher cost for high powered ones.
Advantages of 24 and 48 would be less current on the DC side of things
as well. Fewer losses there.
So, after rambling and thinking out loud, 12V is not a good idea (or
is it), 24V is better but 48 would be best provided I can get the
inverters etc.
Is 48 really much better than 24? Can I stick with 24?
Thanks,
Crispin
Bruce Harvey
news:6a406178-2b99-40f9...@r15g2000prd.googlegroups.com...
The length of run you are talking about would be ok for 24v assuming you
have sized your cables correctly for the job. Also because you are using 24V
the cables can be smaller diameter (read cheaper) but to avoid the problem
of needing to upgrade 2 panels at a time you can get 24V (nominal) panels.
So, 24V would be a good option for you to upgrade slowly over time. Would
need more info about loads to help you more but you get the idea. BTW I use
48V system in Australia but is attached to 2.8kW solar PV and MPPT charge
controller. Runs my entire house.
Crappy
What kind of inverter do you have? One or a few of them.
I plan on using at least two 3kw ones.Possibly one 3kw one and a
smaller pure sine wave one for certain plugs.
I'm curious what you run a whole house off. Modified sine wave or tsw?
Regarding the MPPT controller, I had not heard of them before but a
quick dose of wikipedia, they make sense. Are they worth it? Cost a
bit more than "normal" controllers. Me being in the UK, every ounce I
can suck out will help.
I doubt I will have a 2.8KW array anytime soon. Might approach it once
I have wind up and running as well.
Regards,
Crispin
Ron Rosenfeld
<crispin...@gmail.com> wrote:
>Hi All,
>
>I am planning on putting up some PV panels on my house to, initially,
>run lights and some of the plug circuits but ultimately, run
>everything (barring the stove) (Heating is gas)
>
>The panels will be on the first story roof, all the electronics etc,
>directly below on the ground floor. Cable run would be about 10m (33
>foot).
>
>My question is, all things considered, which is best. To combat the
>losses on the low voltage cable, obviously 48V would be better. Or
>would 24v system still be ok?
In order to make a recommendation, one has to know what your ultimate size
will be, and also some idea about the price of the wiring. Copper is
pretty expensive here in the US.
These numbers are rough, only to give you an idea of some of the tradeoffs.
Assume that your ultimate goal is to have 960 watts of PV, and that you can
tolerate up to a 3% loss in the wiring.
If these were to provide that power at 48V, you would be running 20A in the
line, and could run #10 copper wire.
In your 24 V system, you would require #4 copper wire to produce similar
results.
Here, I could probably obtain the #10 copper as scrap from an electrician
for free or for a nominal price. #4 copper I'd have to purchase.
------------------------------
In terms of setting up for what your ultimate size will be, also consider
whether or not your 24V inverter will carry the load that you think you
might want.
The optimum design is driven by energy and power specifications. Without
those, it's difficult to analyze your particular situation. Cost certainly
plays an important role also, and can tilt the decision to one design or
another. But you need the power and energy specifications in order to
evaluate the costs of different approaches.
By the way, I have a 48V system, but my solar panels are nominal 24V and
the array is wired as a nominal 72V array. (I use an Outback MX60 MPPT
controller to get the voltage correct for my system).
One of my considerations was to keep the wiring hidden. I had a longer run
than you, and not exceeding the capability of #0 copper was important to
me.
--ron
Crappy
I know I am being vague, but my requirements are such :)
I figure I will stick with 24V system to start as stage one, I will
only run the lights. Once this is settled, I will expand it in both
batteries, inverter and PV.
I will run 3 inverters ultimately. One for lighting, the other two for
plugs. (Possible one for plugs)
As for the cable from PV to batteries, I will run the fattest I can
buy now as I plan to expand.
Question on the charge controllers:
I suspect they are slightly more advanced than simple regulators. I
suspect they would be switch mode to help bring your 72 down to 48.
Will they act as a voltage doubler if the voltage is below the desired
or is that just lost time. Or, is there a sharp climb in PD as light
hits it. (Am I making sense?) Can a panel produce 6v, 1A in dim light
or does it rapidly climb to full voltage?
Are the cheap £30 regulators on ebay a false economy?
Thanks for the help - I am writing my shopping list now. Might publish
it for comment :)
Cheers,
Crispin
Just thought of another question:
If I plan on using 24V, would it be better to have an array producing
36v? Or would 24v array be ok? Would it dip below "chargability" to
often. Would the ±12 (36-24) be wasted or usable?
Bruce Harvey
First let me make it clear that I am not connected to the grid. I use a
Xantrex (Formerly Trace Engineering) SW4548E Inverter charger. This is a
4.5kW 48VDC input 230VAC 50Hz Output unit. These units can be paralleled up
to get up to about 11kW continuous output and somewhere around 30kW for
very short periods if you use the largest SW5548 Inverter chargers. There
are of course smaller models available but keep in mind that you will pay a
lot more for 2 separate 2.5kW units than one 5.5kW unit for example. Anyway
to have a look at Xantrex go here
http://www.xantrex.com/web/id/47/p/1/pt/5/product.asp. To answer your other
question it is true sine wave output. The other thing that will affect your
choice of inverter/charger will be grid or no grid and battery backup or
not.
I and anyone else would need to know what you plan here so that they can
work out what you need. Size of the units will depend on the exact
loads/usage and your GPS location (to work out sun availability. etc. etc.
as you can see this can become very complicated very quickly.
As for the MPPT (Maximum Power Point Tracking) charge controller mine is an
Outback MX60. They can improve the total output by about 10-15% on fixed PV
panels but the gains will be less for the charger and more for the solar
panels if you are using a solar tracker on your panels.
Bruce Harvey
Ron,
Cheers,
Crispin
The voltage (nominal voltage of your PV array/panels needs to be the same as
the inverter input. Keep in mind that the actual output of the panel will
vary depending on sun angle/intensity etc but the charge controller will
take that and transform it into a usable voltage for your batteries/inverter
(this is complicated and needs further information). For example a 24V
(nominal) PV solar panel will output voltage from 0 to about 36V depending
on sunlight. This information is available from the solar panel
manufacturers via their web sites in the form of tables and graphs of their
output at given insolation (sun intensity) values. Go here
http://www.kyocerasolar.com/products/spec_module.html to see a sample of the
info from Kyocera Solar.
Hope this helps a little.
Crappy
As for location, I am in the UK, just north of London. (Stop Laughing.
Ambitious for solar?)
Here is me: http://maps.google.com/maps?f=q&hl=en&geocode=&q=al9+7pa&ie=UTF8&z=16
As I don't have the means to tell the power company right now to go
away, I have to build this slowly.
As such, I plan on isolating certain circuits and feeding them from
the PV / batteries / Inverter. I do not intend (now in any case) to
have this grid tied. (As is becoming common)
My steps are:
1) Lights
2) Plugs - This will be the big jump as I don't want to chance it with
modified sine wave, just go all about and get a big w inverter.
At this point, I can include a disconnect from the grid.
Thanks for the answers on the controller.
The array will be fixed and pointed optimally. (I have a clear view of
the sun from about 8am (summer) to about 8pm. Winter, not sure, not
hoping on much :) Wind will help me here.
As for the controller, it was answered thanks. So when the panels are
producing say 20w @ 18v (instead of 24+) the controller will bring
that up to 24 to continue charging the batteries, albeit at a lower
current.
So far, I have opted for this:
http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=320286111891&ru=http%3A%2F%2Fsearch.ebay.co.uk%3A80%2Fsearch%2Fsearch.dll%3Ffrom%3DR40%26_trksid%3Dm37.l1313%26satitle%3D320286111891%26fvi%3D1
It is cheapish, is a starting point. I will get two and series them. I
have opted for a 24v system.
As for batteries, I have opted for two 150ah floated. (They are deep
cycle, marine apparently) (I thought only sealed and Gel were deep
cycle capable)
While the PV will be very underrated for the batteries, they a good
starting point (or not?)
Thanks again, you've answered some of the questions I have swirling
around in my head. (There are many more...)
As I have got bye-in from the boss (aka: Wife) I don't particular want
to end up with a white elephant...
Why are you not on the grid? No possible or just because you liked the
idea of free power. (Free after paying a sh1t load for it....)
Cheers,
Crispin
Ron Rosenfeld
I'm heading out of town for a few days so can't respond in depth to your
questions. But here's a link to a controller similar to what I use:
http://www.outbackpower.com/products/charge_controllers/flexmax/
And the panel voltage does need to be above the battery voltage in order to
get any charging. Voltage does climb rapidly, however. See PV mfg
detailed specifications for more info.
The minimum voltage for you array should be above the equalization voltage
for your batteries, which may be, for a nominal 24V system, as much as 32V.
A panel marketed for a 24V system will usually put out more than that at
it's maximum power point. Probably it will be in the range of 34-35V.
I have no idea about or experience with the Ebay regulators. But you
generally get what you pay for. Because of the higher voltage of my array
compared with the batteries, I did not consider anything other than the
MX60. Also, you should be able to harvest more power from the array with a
MPPT type controller. I doubt the Ebay controllers do that. (Something
more for you to read up about <g>).
Good luck.
--ron
wmbjk...@citlink.net
<crispin...@gmail.com> wrote:
>As for the controller, it was answered thanks. So when the panels are
>producing say 20w @ 18v (instead of 24+) the controller will bring
>that up to 24 to continue charging the batteries, albeit at a lower
>current.
Controllers such as the MX60 only boost current, not voltage.
>So far, I have opted for this:
>http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=320286111891&ru=http%3A%2F%2Fsearch.ebay.co.uk%3A80%2Fsearch%2Fsearch.dll%3Ffrom%3DR40%26_trksid%3Dm37.l1313%26satitle%3D320286111891%26fvi%3D1
Negatives for that seller
http://toolhaus.org/cgi-bin/negs?User=%09koekraf&dirn=Recd&v=b1
Wayne
Bruce Harvey
news:f0h8a4d4spl7jvu4m...@4ax.com...
> On Thu, 14 Aug 2008 02:57:56 -0700 (PDT), Crappy
> <crispin...@gmail.com> wrote:
>
>>As for the controller, it was answered thanks. So when the panels are
>>producing say 20w @ 18v (instead of 24+) the controller will bring
>>that up to 24 to continue charging the batteries, albeit at a lower
>>current.
>
> Controllers such as the MX60 only boost current, not voltage.
Yes and no. The controller scans the entire pre-programmed voltage range
available from the solar panels and uses the voltage that gives the maximum
POWER (VoltsxAmps) available anywhere in that range. Obviously this is more
efficient to some extent than setting the charger at the theoretical Maximum
Power Point and expecting it to stay at the same voltage throughout the day.
Frequency of scans can be programmed from 1 min to almost any amount of
time. Mine scans every 10 minutes)When the batteries are fully charged or
close to it the controller raises the voltage to a point where the output
power is reduced to maintain the batteries at a 'float' charging level. The
other thing that the MX60 (and many other MPPT charge controllers) does is
give flexibilty to you panel array wiring. The MX60 has a maximum input of
140VDC @ 60A (This can be programmed up to 80A but is not recommended).
Therefore a number of different panels can be arranged in series to give a
usable voltage as long as the Voc total in each string of the array does not
exceed 140VDC. There are some limitations on this but you get the idea.
What has been said in other replies to this thread is also true. The output
voltage from the solar panels must be higher than the charging voltage of
the batteries. For example a 24VDC battery array would normally need to
charge to about 29.2V (dependent on the batteries used) to reach the fully
charged level of the batteries and hold the batteries on 'float' once they
are fully charged. The output voltage open circuit (Voc) of a 24V solar
panel or 2 12V solar panels in series is around 32-36VDC depending again on
the panels used. Some solar panels have also been designed for grid
connected sytems and have a lower Voc bur depending on how you set up the
panel array and the charger these can be used in similar ways as long as the
panel voltage is higher than the battery voltage.
Hope this helps more than it adds to the confusion.
wmbjk...@citlink.net
<bl.h...@bigpond.com> wrote:
><wmbjk...@citlink.net> wrote in message
>news:f0h8a4d4spl7jvu4m...@4ax.com...
>> Controllers such as the MX60 only boost current, not voltage.
>
> Yes and no.
No, it's "yes" only. :-)
>The controller scans the entire pre-programmed voltage range
>available from the solar panels and uses the voltage that gives the maximum
>POWER (VoltsxAmps) available anywhere in that range. Obviously this is more
>efficient to some extent than setting the charger at the theoretical Maximum
>Power Point and expecting it to stay at the same voltage throughout the day.
>Frequency of scans can be programmed from 1 min to almost any amount of
>time. Mine scans every 10 minutes)When the batteries are fully charged or
>close to it the controller raises the voltage to a point where the output
>power is reduced to maintain the batteries at a 'float' charging level.
Just to be clear, the controller switches out of MPPT mode once it
enters absorption stage. When absorption is finished, the voltage is
lowered to float.
Wayne
Eeyore
Crappy wrote:
> Hi All,
>
> I am planning on putting up some PV panels on my house
Spend the money on more insulation and other energy SAVING measures
instead. You are using all CFLs for example I assume ?
You'll do FAR better that way.
Graham
Eeyore
Crappy wrote:
> Ron,
>
> I know I am being vague, but my requirements are such :)
>
> I figure I will stick with 24V system to start as stage one, I will
> only run the lights. Once this is settled, I will expand it in both
> batteries, inverter and PV.
You do know about wiring regs I hope ?
Graham
Bruce Harvey
news:rcoba45j01o3ag862...@4ax.com...
Yes Wayne, sorry, my bad. The charge controller on the MX-60 changes the
current (Amps) to cause the output voltage across the batteries to change so
as to reduce the output power to a point where it only maintains constant
voltage across the batteries (Float). This output voltage can of course at
no time exceed the input voltage from the panels and is only lowered by the
load created by the batteries. My apologies for the poorly worded
information.
Bruce
Bruce Harvey
news:48A61D80...@hotmail.com...
I agree with Graham on this. If your aim is to reduce your electricity bill
or save the environment then make your house more efficient/less power
hungry first. If your aim is to experiment and learn then go for your life
and have fun with it. Financially you will be better off with the former,
educationally you will be aiming for the latter.
Bruce
Crappy
While there are many many questions, I feel I am in a position to make
a start. It will be small(ish) and only power the lights and some
plugs.
As for energy saving, I'm fresh out of ideas. I have 62 50W (GU10)
spot lights in my house including 6 in the shower (Not bathroom,
shower!)
I have, at great cost replaced 12 of them with 1W LED spots (Dim but
workable for the passage), 22 with 7W CF spots, 9 with 11W CF spots.
The remainder are in the process of replacement. For some areas, I
will be ripping out the spots and putting up normal lamps. Previous
owners had a spotlight fetish.
House is fully insulated, walls and ceiling / roof and I use wood
fires for winter. So, as far as savings go, I am pretty much there.
Solar heating is also in the pipeline (pun intended)
The solar project? Part want for free electricity, part cool project,
part first person in the street / neighbourhood / county to run
totally free.
Mostly, Part "I can do it".
As for the environment? Could not care less. Sort out industry,
nuclear etc etc before forcing me to spend money. Spend money on R&D
for better cars before waging war in Iraq etc etc. Oh, penalise
Americans for driving 5L gas guzzlers to the local shops. (Crispin
puts soap box away)
As for my initial purchase, http://www.orionairsales.co.uk/2-x-kyocera-solar-panel-200-watt-kc200ght-345-p.asp
is what I will get.
Two 200W 24v panels. Not the cheapest supplier out but not the worst.
When I have working model, I will look at getting a pallet load. :)
You've all been helpful - thanks.