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I don’t want to go off grid as the cost of batteries is OTT,
it more about using Solar without actually using a Grid tie system.
I have picked up 4 x 230w panels and was thinking of using a single battery not so much as storage but as a buffer for stability.
the idea was to get my shed as a start to run from this and then go from there.
I understand that 12v is not the best voltage but a cheap starting point.
Using a user adjustable regulator that I can set the cut out voltage to a conservative 12.6v and a power resume voltage of 12.8v so the load will only really be running direct from the solar panels with a small buffer during sun periods.
The output from the inverter would control a double pole contactor switching both A & N lines between the inverter and mains so power will be uninterrupted while the sun is shinning and mains was up.
Has anyone tried a similar idea?
hotwater Senior Member Joined: 29/08/2017 Location: United StatesPosts: 120
Posted: 04:23am 03 Nov 2017
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I live quite well on a car battery. Solat power is used real time. Wrote a long post and that just got lost. I'll sum it up in one sentence. If you are unwilling to learn to use something like Arduino, your quest is a pointless wasted effort.Edited by hotwater 2017-11-04
yahoo2 Guru Joined: 05/04/2011 Location: AustraliaPosts: 1166
Posted: 07:49am 03 Nov 2017
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Hi Dazza, you are on the right track, that is pretty much the basic principal behind any good solar setup- using power while the sun shines is the cheapest electricity you can get, there is no point charging a battery that you will never use. There is plenty you can do with a smaller system, not that 900+ watts is tiny!.
there are a few areas that can always do with some fine tuning. For example What is the voltage of the panels? if it is 72 cells in series you are looking at a bit over 30 volts for a single panel, there are some quite big losses holding that down to a nominal 12 volt system, if the panel is internally wired to suit 12 volt it should say 16-18 volt on the back. You will basically be turning 1kw of panels into 500 watts throttling a higher voltage panel down to 14 volts. If that is all you need then it is OK but it feels like a waste of potential.
the other issue is battery size, there are limits as to how hard a battery can be charged, so whacking 32 amps in full sun into a very small battery can give it a very short life or it will jump up in voltage quickly and the charge controller will switch off before it actually charges the battery resulting in an even shorter battery life.
I tend to steer people towards higher voltages (48 volts) if they can do it because everything is thinner, smaller and cheaper. 12 volt is going to be a pain unless you can scrounge up thicker wiring and higher amp components for free. It is going to depend on what you have to hand to work with.
Anyway I have to go, I am off baling hay this morning We can chat and walk you through some of the obstacles late.
The sun is shining so not much time and lots to do.
The panels I have are 30v 7.5amp
was wondering if the fancy MPPT type controllers would take advantage of the extra voltage.
Also the small battery capacity was why I was only going to allow it to discharge down a modest 12.6v 20% off the top only to allow for things like clouds passing over as I dont want the contractor switching constantly.
The shed I want to start with is more a man cave for hobbies with LED lighting, a fridge for the drinks and a TV, I spend many hours out there and wish to cut some power costs as its getting over the top at .41c KWH now and second hand panels are quite cheap now.
I have a large roll of 6mm sq I can run a line for each panel and parallel at the battery connection.
I do understand the higher voltages are more sensible than higher currents, part of the reason for staying 12v is I have a caravan that has a small solar panel and a battery, I wanted to use the van battery when not using the van.
will check back in a day or so and will look at what Arduino is all about.
thanks for now
hotwater Senior Member Joined: 29/08/2017 Location: United StatesPosts: 120
Posted: 06:37pm 03 Nov 2017
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I needed a quick conversion from 60-70V down to charge a 12V battery. In 15 minutes I had this. Going clockwise from upper left.
This is a 110-250VAC 12V 1.2A supply I buy for $1, "industrial wall wart". Almost any wall wart will work at 50VDC at reduced current. I don't actually need this. It only supplies high side drive for the FET.
A pair of capacitors from a TV. these store the energy between pulsed and make it efficient. Get yourself an angle grinder with a thin cut off wheel. Make little assemblies from old electronics. A dropping resistor, capacitor and 8V zener supply raw power for NANO.
Transformer from an old UPS used as an inductor. Not ideal but free.
A FET and diode for the buck operation. Cut right out of a TV.
An opto isolator cut out to supply FET drive
A nano controller. $3 shipped. Add a USB cable and free download compiler and the world is yours.
Think you can make one as pretty? I run a whole house on one of these. Two water heaters. two bucks like above, one PWM for for the old odd lot legacy 12V panels and a refrigerator.
Spend a lot of money on professional hardware and you will never get it back.
Edited by hotwater 2017-11-05
oztules Guru Joined: 26/07/2007 Location: AustraliaPosts: 1686
Posted: 08:08pm 03 Nov 2017
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Hotwater......Be proud to call it mine..... very nicely done.... now I want one too.
I have to agree with Yahoo, that 12v is not the best thing in the world.. if you can see your way clear to using 2 batteries, and at least go for 24v, your loss from no mppt will be small, as you have 60 cell panels. ( 48v is better, but you want to start small I guess.. but really, everything is easier at higher voltages )
If 12v, I would extend the working range from 12.2 to 13.7. If you had reliable loads, maybe even a tad higher..... keep an eye on the water levels though. FLA can take a lot of over charge rather than under charge, but it needs plenty of water over the plates, and keep temp down to reasonable levels in summer ( shade, and gaps between batteries, 6v rather than 12v... see if you can track down golf cart batteries second hand etc).
If your thinking of using gell , or glass matt maintenance free , VRLA etc, you will need a better sort of controller.. they dont suffer over charge very well.... in fact I won't use them at all for that reason.
You beaut chargers will all fail some time, and they will generally take girly batteries with them. The newer technologies are very very nice.... until something goes wrong.... then it may get expensive quickly.
Your DPDT relay may cause you to come undone, as there will be almost no time delay at all between the two systems.... you have a fridge with inductance, and a tv with high capacitance, you may get contact arcing with no delay time on a small relay. If it is a manly one, and has a decent air gap, it may be ok. A small HF inverter might baulk at this though.
.......oztulesEdited by oztules 2017-11-05Village idiot...or... just another hack out of his depth
Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406
Posted: 08:38pm 03 Nov 2017
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You don't say if your panels are 12v or 24v type. But lets assume they are 24v (which are more common).
These will have a rating plate that will say something like: Maximum open circuit voltage 38v Maximum power voltage 30 Maximum power 230 watts Short circuit current 7.8 amps
So what you do is hook those up to an inverter that will safely work up to at least 38v which is theoretically the highest possible panel voltage.
Now we do not want to overload those panels by pulling the voltage below 30 (in this example). That is the max peak power point, or very close to it for all operating conditions from total cloud cover to clear blue sky.
We can do that by providing a mains powered dc rectifier that supplies a continuous 30v dc.
At night, or on truly dismal days, the mains rectifier powers the inverter directly through a diode. ANY solar contribution above 30v will drive the inverter and reduce the loading on the rectifier.
On sunny days the panels should be enough to raise the voltage well above 30v and no grid power will be consumed. In marginal conditions the solar panels will work as hard as they are capable of, and any extra load comes from the grid. The grid only supplies any excess load during poor solar days. Even if its 95% grid and 5% solar, the solar panels are still contributing all they are able to produce.
There will be a seamless transfer of power at dawn and dusk as the load gradually shifts from solar onto the grid, and back, without any abrupt switching.
No battery is required.
I have had a system like this running for almost two years without any problems. A battery will eventually be fitted, but a battery is not really cost effective where grid power is available.
Cheers, Tony.
oztules Guru Joined: 26/07/2007 Location: AustraliaPosts: 1686
Posted: 08:41pm 03 Nov 2017
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Fiendishly simple Warp
.........oztulesVillage idiot...or... just another hack out of his depth
Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406
Posted: 09:07pm 03 Nov 2017
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A system like that will produce about 50% of power through mid winter, and about 80% of mid summer power. That assumes there are enough solar panels to produce sufficient power during daylight hours except on exceptionally bad days.
You won't be able to do much better than that, because in winter its like 17 hours of darkness and 7 hours of solar. In mid summer its still dark for 7 hours no matter how many solar panels you have.
It still makes a pretty big impact on power bills !Cheers, Tony.
George65 Guru Joined: 18/09/2017 Location: AustraliaPosts: 308
Posted: 12:27am 04 Nov 2017
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Warp,
While I get the theory ( and appreciate it) for the newbs could you please give some more info on the actual components and setup. For instance, where/ how does one find a supply for 30 V with any grunt to it to power the inverter or how does one build it?
This is a much simpler version of the commercial units I have seen which measure input and output and fill in the gap with mains. At present I back feed the mains with a ( proper not Chinese) grid tie solar inverter. When the panels are making more than the home is using, my old fashioned spinny meters rotate backwards " banking" power for use at night. This won't last forever though as the plan for the power companies is to replace all these meters in the next 4 years.
I also have one phase that has an electronic meter. Any excess current through that one registers as useage. This one will pose more of a challenge to get around. ATM I have taken all the loads off that phase bar the off peak and one leg of the 3 phase AC. I have 6.5KW of solar now. It covers our usage bar the AC and water heating. I want to get another 5 Kw of panels which I think will allow me to take the hot water off the Off peak and run it off the normal back fed phases.
Keen to find a solution to the electronically metered phase that has the same level of simplicity and logic as what you have described here.
hotwater Senior Member Joined: 29/08/2017 Location: United StatesPosts: 120
Posted: 06:22am 04 Nov 2017
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oztules..... They do call it a circuit BOARD don't they. Perhaps there is some misunderstanding. I have a multipurpose board going into production early next year for greenhouses, duck ponds, linear current boosting for pumps with no batteries, refrigerators, dual element hot water heating and house shed systems that will look a little neater.
When I was a kid I was chased all the time out of the town dump stealing parts out of a TV. That has never left me. I have probably 400 TL431 zeners and they only cost 3 cents each. I still go and pull one out of an old PC supply first. Just fun grabbing some old stuff and making it work. The world is a cornucopia of free discarded electronics.
I'm finally getting around to cleaning up the system. Most of the experiments are over. As a manager used to say The optics of a project are everything. It had to be, nothing we made actually worked and the customer never cared if it did.
Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406
Posted: 10:26am 04 Nov 2017
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If you still have the old rotating disc electricity meter and a grid tie inverter you cannot do any better than that. But the good old days are rapidly coming to an end. A smart meter means you have to abide by the rules, receive a pittance for any power fed back, and are about to get royally reamed.
My system is very simple, it feeds nothing back, and it runs if the grid goes down. At least while the sun is shining. There is also no need to synchronize the inverter to the grid, so the inverter only need be very basic.
The first thing to do is decide on a system voltage, the higher the better. I used 30v to 38v as an example only of what could be done.
My own system uses sets of eight 24v panels in series, generating around 220v to 290v dc operating range. As everything has to be built, its a case of using what you have, or can easily get and deciding on a system voltage.
I am using a homemade inverter that is very different to the usual PWM type, but that is not really relevant to this thread. Something could be home made by gutting a commercial grid tie inverter and replacing all the grid tie electronics with something much simpler.
For instance, the 1.5Kw Inspire inverters work over a similar voltage range, 200v to 400v dc. So the original output toroidal transformer, choke, and PWM filtering would work fine with a home brew circuit based on one of those EGS002 PWM generator boards.
Those inspire 1.5Kw toroids have a 135 volt primary and a 230 volt secondary. The primary 135v has a peak voltage of 190v so it will work from anything over 200v incoming dc.
We are both very fortunate in having three phase power available. My rectifier uses three more of those Inspire transformers, 230v primary to 135v secondary. Rectified that gives about 190 to 200v dc as the mains here is usually a bit higher than 230v.
Most people only have single phase available, so the simplest solution might be to try and buy an old fork lift battery charger at an auction or e-bay, and build a system around that. Another possibility would be to wind your own transformer for whatever voltage is needed.
If there are no plans for a battery, then the higher the dc voltage the more efficient it will be. That is especially true of the capacitor bank that will be required for both filtering the rectifier output, and as a low ripple voltage source for the inverter.
The inverter input current pulses heavily, and solar panels are a high impedance current source. So a large smoothing capacitance will be required. A grid tie inverter will already have that, but a few extra microfarads will not go astray.
If doing all this at a much lower dc voltage, the smoothing capacitance needs to be made much larger.
Its not really possible to give exact instructions how to go about this, as so much will depend on the power level and what parts may be available. But if you can base it around an existing grid tie inverter (working or not) you would be off to a pretty good start. Cheers, Tony.
yahoo2 Guru Joined: 05/04/2011 Location: AustraliaPosts: 1166
Posted: 03:10pm 04 Nov 2017
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MPPT yes and no, yes it can be done but the cheapies will not reliably drop that much voltage, it will either be outside of their max voltage parameters and not work at all or it will blow up. Even some/ most of the PWM controllers will complain about high voltage and not work.
Battery voltage because batteries are a chemical reaction that resist work (lazy like me )you have to think about voltages differently when the battery is charging, resting and discharging.
Batteries are always quoted at rest, that means not having been charged or discharged for 2-4 hours. so the spec sheet is going to say 12.5v or 12.6 volt or maybe 12.7 volt AT REST Here are some state of charge numbers AT REST
if you are discharging the battery the load will lower the voltage further because the chemical reaction cannot keep up and it will recover as soon as the load is removed.
same goes for charging, the harder you push the energy in, the more the battery resists and the higher the voltage rises. so you can trickle the current in over a week at 13.8 volts and the battery will fully charge. To charge it from 60% to full in a few hours you are going to have to be 14.3-14.8 volts to overcome the chemical resistance. As Oztules says once they are very close to fully charged if you dont back things back to an idle you will lose water out the vents. As he also says with glass mat, sealed lead acid and gel batteries things need to be far more precise because once they fill up there is nowhere for the energy to go, lithium even more so, although lithiums have the advantage that they dont suffer degradation if they are not fully charged so we can leave them at 90% for years at a time.
Actually, one idea I was going to try and have not got around to yet...
I was wondering if these modern switch-mode battery chargers that say 90v-250v on the back would power up and run on 4 x 24volt panels in series??? I guess I will leave that for another day.
Looks like Tony and Hot water have given you plenty to chew on!
I would encourage you guys to start a new topic jot down a few notes and explain some of the basics behind your builds and ideas, that kind of thing is what keeps the renewable energy and off-grid part of the forum rolling along.
cheers YahooEdited by yahoo2 2017-11-06 I'm confused, no wait... maybe I'm not...
Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406
Posted: 04:35pm 04 Nov 2017
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[quote]I was wondering if these modern switch-mode battery chargers that say 90v-250v on the back would power up and run on 4 x 24volt panels in series??? I guess I will leave that for another day.[/quote]
Mains voltages around the world vary quite a bit. Japan is nominally 100v but can go as low as 85V. Australia (was) 240v and could go as high as 265v.
So if you want to make some kind of "world" appliance that will plug in, anywhere in the world it needs to operate between about 85v and 265v ac.
Now most things these days rectify the incoming mains voltage with a bridge rectifier to produce a dc voltage which may be from about 120v to 375v. If you are going to run it straight from dc, your minimum input voltage will be 120v dc not 85v dc.
Four 24v solar panels might just about work over that range, but only on a bright sunny day. Under poor conditions I think the switching power supply might have a very difficult time starting up and will pull the panel voltage right down. It will probably cycle on and off until there is sufficient power to keep it running.
And its going to do that every morning, and possibly throughout the whole day if its very cloudy. It will probably work in a fashion but not very well.
These switching power supplies draw higher current when the input voltage is low, and less current when the input voltage is high. That is not going to make a very happy match with a solar panel source.Cheers, Tony.
Warpspeed you have given me a few more ideas in a different direction.
I think I maybe able to pick up a couple of blown (Aroura) GTI's for scrap value
a quick search found some cheap 800v 20a diodes available online? I also have many old CPU power supplies, without checking I would guess they are not upto the currents involved.
As you know in Oz S/H panels are only about $75 - $80 so 8 S/H panels or how ever many are required for around 200 - 250v DC is not hard ask and seems that with your method to rectify the mains seems the simplest method with next to no loses in transformers and minimum currents.
a quick mental calk it should be good for about 1800w minus inverter losses about 1600w?
do you have any reading material on how a old GTI can be repurposed and how is the output V controlled when its not GT
I currently have 4 of these but happy to hunt up another set
230w MPV 29.8v MPC 7.82a SCC 8.26
Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406
Posted: 08:16pm 10 Nov 2017
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[quote]do you have any reading material on how a old GTI can be repurposed and how is the output V controlled when its not GT
I currently have 4 of these but happy to hunt up another set [/quote]
The parts you can use from an old GTI would be the metal enclosure, heat sink, toroidal transformer, choke, and output filter. But these are all major high value parts, and already assembled and ready to go.
What you don't need is the original circuit board, so a blown up or faulty GTI would be ideal for this.
The primary winding on the toroid will determine the minimum dc input voltage that will be required from the solar panels, and the original GTI specifications will tell you that.
Its then a case of building something like an "Oz inverter" to power the primary of the toroid. That will include the required ac output voltage regulation.
Because this will be a high dc voltage inverter, only four mosfets or IGBTs will be required, not a dozen or more as is more usual for a low dc voltage inverter.
All you need to drive that will be one of those low cost Chinese PWM driver boards. I am about to do something like this myself when all the other unfinished projects I have going at the moment are completed. Cheers, Tony.
George65 Guru Joined: 18/09/2017 Location: AustraliaPosts: 308
Posted: 10:02pm 10 Nov 2017
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I thought the simplicity of this idea was brilliant! So I stole it! :0)
I have an old fridge I am using for raising seeds. It has an LED bar light in it which provides Light and warmth at Night. It's rated at 12-24V but handles 30 no probs. I have been powering that with an old car battery charger as a power supply.
I also have a shattered solar panel which I don't want to put in a string but still seems to be providing full voltage and amps. Taking your idea, I put that up on The shed roof behind where the fridge is and just connected it directly to the junction of the charger and light. Works a treat.
I was going to put in diodes but remembered both the panel and the charger have them built in and testing proved one does not try to drive the other when they are the dominant power source.
Very happy with this. It's not a lot of power draw from the light but I had the panel doing nothing anyway and it's a great way to put it to use.
Great idea and thanks for passing it on!
Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406
Posted: 11:14pm 10 Nov 2017
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You are most welcome my friend.
That is the beauty of the internet, and Forums such as this.
One person comes up with an idea, and someone else picks up the ball and runs with it, coming up with something slightly different and better.Cheers, Tony.
thinking about this today and remembered that AC rectified is 1.44 times higher at DC.
so rectified mains will come out at a tad under 350DC and solar input would need to be apx 400v dc
Not sure I want to play with that at those currents.
The idea of useing a transformer has me concerned about losses as transformers are typically only 60% efficient (from distant memories)so running this way 24 hours will cause some serious losses and all but waste the solar power generated.
damned if I do and dammed if I dont.
a thought occurred that the transformer set up could be bypassed by suitable timer relay/contractor between mains and inverter output provided the the inverter didn't object to having mains back fed to it, is this a realistic fix.
starting to think that buying a 3kw solar system and having it installed is a better way to go.
them I still want to play just not with 350 - 400v dc
Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406
Posted: 08:26pm 11 Nov 2017
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No load losses in a 1.5Kw toroidal transformer might be about 12 to 15 Watts, nothing much to worry about. Flat out efficiency is less important because it will very rarely run at full flat out power for any length of time, but I would make a rough guess at about 85% efficiency flat out, and better than that at lower power outputs.
Many grid tie inverters work in the 200v to 400v dc input range. The transformer primary might be typically about 135 volts rms, requiring a minimum dc input of at least 135v x 1.414 = 190v. Cheers, Tony.
Notice. New forum software under development. It's going to miss a few functions and look a bit ugly for a while, but I'm working on it full time now as the old forum was too unstable. Couple days, all good. If you notice any issues, please contact me.
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We can chat and walk you through some of the obstacles late.
)you have to think about voltages differently when the battery is charging, resting and discharging.