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Forum Index : Solar : What do you do with excess solar Power?

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Davo99
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Posted: 10:36am 06 Aug 2019
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I know a lot here are off grid or use solar for battery charging but I was wondering if anyone has any smart uses for their excess solar energy?

I am on grid and have put up a stack of panels. They wind the meters back during the day ( or stop them spinning as fast) and I can use that self generated power at night.
Despite having loads of panels, there is no way to keep up with the usage of our all electric home during winter.

It's especially frustrating atm. I make really good power for a few hours but due to the inherent high mains voltage in the street, the inverters won't stay connected unless I put on a load. That's OK to an extent as I manually switch on the hot water, do the washing or put on the dryer but inevitably I run out of things to use and have to burn off some power in order to stop making a lot less power as the inverters Cycle on over volt.
I have been using a fan heater in the house to try and put a bit of heat into the place and the furniture etc so it's warmer when the sun goes down.

The problem is I make too much power all at once and not less power for longer and am still using more power from the mains than I should given what I can make.

Batteries are going to be a cost rather than give me any savings and I don't know what else to do with that power. I had an idea of heating some sort of storage in the house for night use but the power I want to bleed off would not be enough to do much good. It's coming up a bit now but the last couple of months I only needed to have about a KW load just to pull the mains down a few volts to keep them happy.
The last few sunny days that's coming up closer to 2 KW i need to bleed but it's frustrating to be wasting that power when I don't want it when I could use it later on.

I have realised that because the inverters are so over clocked, the power I'm making in the middle of the day is not that much less than I would make in summer, it's just the days are so much shorter its a time rather than a capacity problem. Looking at what I'm making and how it is ramping up I'll probably be breaking even in another month and have excess for the next 6 months but it would be nice to be able to put the Juice to use for something worthwhile now.

I'd be interested to hear if anyone has any Cunning and smart ways of using their excess power?
 
nickskethisniks
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Posted: 01:47pm 06 Aug 2019
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No smart ways for using that energy. I have the same problem @ the moment because old wiring (long and thin wire). So I buffer the energy with batteries and "only" backfeed 1500w during day and night.

What you can do, is measure the main voltage and pwm your solar panels,this way you don't reach the cut out voltage of your inverter.

Madness made a pcb intended for using a solar inverter to charge batteries through the inverter. Instead of using the battery voltage as reference you could step down ( small transformer) the main voltage and rectify it.

That way you would limit the output voltage.
Edited 2019-08-06 23:50 by nickskethisniks
 
renewableMark

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Posted: 09:42pm 06 Aug 2019
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What is the grid voltage when the inverter cuts out?
Cheers Caveman Mark
Off grid eastern Melb
 
Warpspeed
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Posted: 10:57pm 06 Aug 2019
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Mark's question raises an interesting possibility.

It should be possible to fit a transformer to the incoming grid supply to lower the voltage. If this is done with a "buck" transformer, a small transformer can transmit a much higher power level.

For instance, a 500Va transformer would drop the voltage by ten percent while transmitting 5Kw.

Cheers,  Tony.
 
Davo99
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Posted: 12:15am 07 Aug 2019
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  nickskethisniks said  
What you can do, is measure the main voltage and pwm your solar panels,this way you don't reach the cut out voltage of your inverter.


I have thought of something like this before.
Something I Imagine similar to the stand alone PWM controller I was Discussing with Tony for going direct to a heating element.
Measure the grid voltage and have a PWM that did not exceed a pre set level from the inverter. I was thinking of controlling the AC side but the DC side would do the same thing.

The only thing I came up with that I could manage with my non existent knowledge was a PWM controller for a load which I adjust as I'm around during the day. A dump load would be fine too if I could set it up as something automatic and bled off any excess power and no more at a particular time.

I wish I knew a Lot more about electronics. From what I have learned here, this should be pretty simple using Mosfets... if a person wasn't a complete electronics Dillatante in the first place that is.
 
Davo99
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Posted: 12:45am 07 Aug 2019
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  Warpspeed said  Mark's question raises an interesting possibility.

It should be possible to fit a transformer to the incoming grid supply to lower the voltage. If this is done with a "buck" transformer, a small transformer can transmit a much higher power level.

For instance, a 500Va transformer would drop the voltage by ten percent while transmitting 5Kw.



Tony You have lost me with what I can see is the simplest Circuit Imaginable.
I'm clearly missing something here.

Would this setup have a transformer on the AC and the DC side from the panels?

Your assumption is spot on, the inverters trip at 260V. One will hold 262V for a minute or so but then disconnects.
I thought the problem was the wiring was too light going back to the board. Certainly there is typically a volt or 2 Difference at the inverter and at the board but the voltage shoots up way under what that wiring should carry anyway.
I can feed on one circuit/ phase and every other different circuit on that same phase will be high as well so I don't think it's just an issue of needing heavier wiring. I can see 245+ V on any circuit at any time of night to start with.

I have never seen under 238V even at night with the Big AC and other loads running.
The 3.6 Kw water heater will still have 236V Min at the element when it's running.
I have tapped into that circuit ( non off peak) and as soon as I put more than about 2.5 Kw into that during the day it's on the edge. I switch the hot water on manually when I'm here about 11-11:30 so that keeps the voltage for that inverter down but the other one on the same phase but a different circuit will still go high.
Pole Transformer tap needs to come down about 10V.


If you could explain the transformer Idea for an idiot and what I might need to try it, that would be great. I have a couple of heavy transformers up the back that were given to me and I have no idea what they are as there is no markings on them.
Spose i could get them out and hook them up and see what I get but wouldn't know how to test amperage output. Load them up till the output Voltage starts to rapidly fall off?

Anyway, if the idea is plausible for me I'd be happy to buy what I needed for the Job as it would have a worthwhile ROI over wasting power as I do now.
Won't be long before I'm making more power than I can use every day and switching inverters off.

Playing with this stuff really does give a very sobering insight to the idea of all Renewable grids. Given storage is going to be token at best for at least another 50 years, the size of any solar or wind generation would also have to be so oversized to allow for bad weather and even just winter drop off it would be completely impractical from a number of perspectives.
 
Warpspeed
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Posted: 01:22am 07 Aug 2019
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O/k Dave.

Suppose your mains voltage is 262 volts, and you want to drop that down to say 250v.

You find a transformer that has a 12v secondary winding on it.
You then connect the high current secondary in SERIES with one side of the incoming 262v on the primary.

Depending which way around the secondary is connected, that 12v is either going to add to the 262v or subtract from the 262v.

Now the really nice thing about this, is that if the secondary is rated to carry 10 amps, you can draw ten amps from the whole thing.

So in this example if the transformer had a 12v 10 amp secondary, it will convert 262 volts to 250 volts at up to the full ten amps.

If you have a few big trannies with output voltages between about 12v and 24v, give it a try
Cheers,  Tony.
 
Warpspeed
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Posted: 01:26am 07 Aug 2019
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Connect this between your grid tie inverter and where it plugs into the mains.
The grid tie inverter will always see a voltage less than is on the mains, regardless of which way power is flowing.
Cheers,  Tony.
 
Davo99
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Posted: 11:53am 07 Aug 2019
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Geez this makes me feel dumb.

Let me see if I have got it right in my head....

One side of AC goes to a secondary ( low) side. Other low side goes to the inverter.
Other AC side goes straight to inverter with the AC side of the transformer tapped in.
Is that correct? Your diagram doesn't have the dot / circle on the straight through AC side but I assume that's what you meant as it couldn't be unconnected?

I'm really hoping those Trannys I have up the back somewhere are suitable. They are Big heavy things about half the size of a house brick but I have no idea the ratings. Mate said he was going to do a guitar amp out of them and I -think- they may have been 24V but somehow I also seem to recall a figure of 60V.

Looking on fleabay I'm almost wondering if " Transformer" is the right word to use still. I assume I'm looking for those lumps of metal cores with 2 sets of windings in the traditional configuration?
A search on fleabay for transformers gets about 95 switch mode power supplies and about 5 ( relatively) of the type I'm looking for. All in pretty low ratings. There are also a few toroids again of pretty Diminutive outputs on the low side.

These traditional transformers must really have gone out of fashion!
 
nickskethisniks
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Posted: 12:25pm 07 Aug 2019
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Wow Tony, clever design --> keep it simple!

I would be thinking about a step down transformer like 260--> 240V but then the whole inverter power need to go thrue the transformer.

The only downside of using the transformer is that you have no monitor about the maximum voltage (272V when using 12V).

So your appliances need to be rated well above the normal 240VAC. Or connect your mainbord after that transformer...
Edited 2019-08-07 22:26 by nickskethisniks
 
Warpspeed
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Posted: 09:13pm 07 Aug 2019
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A bit of experimentation with a multimeter should tell you which way around the secondary needs to be connected.
It probably does not need to drop the voltage by much, 12v or 15v might be enough.
Cheers,  Tony.
 
Davo99
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Posted: 10:08pm 07 Aug 2019
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Spoke with mate last Night about transformers.
Number he came up with was 56V so looks like we are in the same ball park.
I guess I'll have to drag one out and fire it up to measure it but probably not going to be what I want. Bugger!

Anyone have any suggestions where I could buy a tranny of the right Voltage and size?
 
Warpspeed
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Posted: 10:19pm 07 Aug 2019
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What power is your grid tie inverter rated ?
Cheers,  Tony.
 
Davo99
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Posted: 03:45am 08 Aug 2019
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I have 3 at the present time Tony with another to put up and probably replace the small one.

I have a 5, 4 and 3.6 KW inverter atm. I may replace the 3.6 with another 5kw when I get either a 4 or 6MM circuit installed for it as I don't want to be pumping that much power down a 2.5MM cable. I actually don't think it's dangerous at all, the voltage will just climb with the resistance and the inverter will trip out so not much to worry about but the 3.6 is making often more than the other 2 atm thanks to better orientated Panels.

All the inverters are about double over panelled, or more, to make the most of the ramp up and down periods.
I have another 16 190W panels on the shed roof atm that arent connected because they are on the south side of the roof although fairly flat. They keep getting filthy with Bird crap and leaves and I'm thinking of taking them down or maybe having them there just for solar experiments. I could easy tilt them north but not worth the trouble. They won't make much difference in winter and I don't need them in summer so....

I have another 25 250W panels to put up which will replace a number of smaller 190W panels so everything is 250W and that will cover the west house roof.

The 5KW inverter is the most problematic atm because it's the furthest away from the board and the most sensitive to over voltage and trips out the second it hits 258V which can often only take 2 Kw to send it over. I'm tossing up wether to put 3 phase up the back or just a heavy duty single phase.
Guy is coming Monday morning to give me some quotes as i'm not brave enough to try and pull the cable through myself and I HATE running cable down walls and crawling in ceiling spaces.

Ran a bunch of extra power points in the house and outside last year and that was enough. Rather pay someone else for these real crappy jobs.
 
Solar Mike
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Posted: 04:03am 08 Aug 2019
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If the ac voltages in your mains switch board are already getting to 258 and with the aid of a step-down transformer to your inverter, they will be pushed even higher, isnt that going to damage some of the AC stuff in the house (motors in fridges etc)....


Cheers
Mike
 
Warpspeed
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Posted: 04:05am 08 Aug 2019
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  Quote  
I have a 5, 4 and 3.6 KW inverter atm. I may replace the 3.6 with another 5kw when I get either a 4 or 6MM circuit installed for it as I don't want to be pumping that much power down a 2.5MM cable. I actually don't think it's dangerous at all,


Not unless you consider a house fire not to be dangerous.

I believe the max rating for 2.5mm is 28 amps or 6.4Kw. At that rate the voltage drop will be about one volt per metre of cable length, and that can quickly add up.
Cheers,  Tony.
 
mackoffgrid

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Posted: 07:38am 08 Aug 2019
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  Davo99 said  I'd be interested to hear if anyone has any Cunning and smart ways of using their excess power?



I have 5/6kW on-grid and 10kW off-grid. (2 sites)
On-Grid: During summer we consume a good chunk of the solar power produced with Air Cond.

Off-Grid: During clear days, most power is wasted. I wish I could produce and store hydrogen or something for later use. I will put more hot water tanks in. I'm thinking of three tanks.

The other idea we've recently come up with is to convert a car (4wd ute) to electric. At 100v the batteries can augment the house battery, and what is now excess solar can be used to charge the car battery.

We'll be kicking that can around over the next year or so.

Cheers
Andrew
 
Davo99
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Posted: 11:52am 08 Aug 2019
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  mackoffgrid said  
  Davo99 said  

Off-Grid: During clear days, most power is wasted. I wish I could produce and store hydrogen or something for later use.


I tried that last summer.
I realised I'd need a lot even to boil a kettle and as much power as I had In summer, storing enough for meaningful winter use would be impractical but thought I might learn something and I sure did!

Made up some plates, Mixed up some Naoh, used an inverted drum inside another to catch the Hydrogen with the Oxy emitting plates on the outside so there could be no O2 in with the hydrogen.

All went well, had a couple of hundred Litres of Hydrogen in a few days. Sweet.
Then I bled some Hydrogen into a plastic Sandwich bag and Lit it.
Rather than the lazy, lopey flame I was expecting like one would get with LPG or Methane, the bag went off with a bang that had my ears ringing for hours and I was surprised no one called the Police.

I then did the smart thing of looking up the LEL of hydrogen. Ya!
Rather than like with most gases where there is a fairly narrow window where the stuff will burn( slow or violently) Hydrogen goes off like a bomb at nearly any mixture.
I'm not too bright but no way in hell I'm going to have hundreds of litres of that stuff sitting round compressed or not.

If I could set something up all in pressure tanks with proper compression fittings and money was no Object, Might be OK but for backyard hackery.... Not wanting to give the wife and Daughter need to go buy new black dresses quite yet.

I'm sure it's safe on an industrial manufacturing level but it's way too dangerous and easy to make a sizeable Bomb for a backyarder with some simple mistake like a little air getting into a tank.

I Bled the first Few hundred litres off to make sure there was no air left before I started really saving it and having played with Browns/ Hohoho gas before, I made damn sure to set up the tank so there was no possibility of OZ contamination.
Just a bit of air in about 100Ml of the gas in that bag was like shooting a .357 at an indoor range without ear muffs.

No thanks.

Maybe this year I'll try something much safer with the excess power like making Chlorine. Least it will be good for cleaning and killing weeds rather than blowing everything up at the slightest slip.



  Quote  I will put more hot water tanks in. I'm thinking of three tanks.


I have been thinking about this too but I can't see an advantage to it.
I have a 400L tank now which is more than we ever come near using. We can get away with not heating it at all for 2-3 days in winter. In summer I fire it every day to use the load as inverter ballast.
In summer I make so much power I boil water in an urn to pour on weeds. I boil a LOT of water sometimes like over 100L a day easy.

I can't see where having more hot water in summer will help and in winter even though I get excess power, it's only for 2-3 Hours so won't make much difference to a pre heat tank which I thought about. I could raise the temp of 400L of water about 10oC in 3 hours with 1500W input but it seems a lot of mucking round for little benefit.
Would store about 4 Kwh of energy less losses which would probably near halve that I imagine.

If you see a different angle, I'd be interested to hear it as I'm bound to have missed something.

Today I put 5X 190 panels up the back and connected them direct to a 3600W element and put that in 10L of water in an old fridge. I want to use that as a thermal mass to put seeds in the fridge to keep it warm to raise seedlings. Around Midday I was getting 400W into the element which was more than I thought and might well be more than I need.
I'll probably put another panel up and wire that to a LED light bar for when the seeds sprout. I want to get a good start on some tomatoes, corn, beetroot and Sunflowers for Christmas and later I'll do some lettuce.

I discovered I had an AC PWM controller in my box like I ordered and I tested that with a couple of panels in series. It was blowing a gale and my testing was very precarious. I could get about a 10V variation in voltage with a small load but when I connected some larger elements there was no PWM at all. Not sure if I blew something in the controller or it was my crappy test setup. I'm thinking more the former.
I'll hook it up to AC and see if the thing still works and go from there.

With the 5 190 Panels I was getting 122V open circuit ( Which I was surprised I could only just feel when I held the bare wires in my hand) and 80V connected to the element. I'd really like to be able to throttle that even manually to see how much difference it could make.

Getting anything to control higher voltage DC is a real Pain in the backside.
 
Davo99
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Posted: 12:16pm 08 Aug 2019
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  Warpspeed said  
  Quote  
Not unless you consider a house fire not to be dangerous.


I don't consider it at all likley.
I have felt the cable so many times I don't bother any more. Never felt any warmth in it at all.
I also have a number of breakers that are in fact under rated but as long as they hold, no problem but it wouldn't take much to get them to trip. One of my Inverters has some stupid breaker rating printed on it as to what must be used on the AC side.
I think it is the 5KW. It says to use a 40A breaker when the thing is not capeable of generating much over 20 amps if that depending on the voltage. Why would one want to over spec a breaker that much? I have pulled the full 5kw out the thing when running loads up the shed plugged into the sub board and the 16A breaker I have on it didn't trip. Probably because the voltage was up but I want a breaker to trip at the first sign of trouble not when everything is on fire!

  Quote  I believe the max rating for 2.5mm is 28 amps or 6.4Kw. At that rate the voltage drop will be about one volt per metre of cable length, and that can quickly add up.


I thought about 5 KW was the limit for 2.5 But there are a heap of ways of calculating it. It's my limit put it that way.
Voltage rise can add up too and that is why the inverters trip. They can only push so much before the voltage gets too high and they cut out. The voltage is highest at the inverter rather than with load it's farther from the consumption point.

My 3.6 and 4 Kw inverters are less than 10M from the board so again the voltage rise would take them out well before any overload of the wiring they are on seeing neither are capable of more than about 2/3 that rating.

Anyway, I'll have at least 4mm cable run to them in a few weeks so won't have to worry. I'll try for 6 MM to the shed but depends what I can get in the conduit.

In reality I don't think I'm going to gain much if anything with heavier cable. I don't think it's cable size that's the problem now, it's the voltage that's high here even at 3am.
 
Davo99
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Posted: 04:27am 12 Aug 2019
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Wasting power again today.

Burning off 2Kw just to keep the inverters on the thin end of staying connected and it's after 2 Pm>

Sparky came this morning. Seems a real nice guy although the fact he told me he just had a power wall put in at home was a worry!

Going to have 2x32A circuits put at the back of the house and run 10MM 3 phase up to the shed. Will cure any voltage rise problems in the house but with only 16mm to the pole and a high transformer tap.... Who knows how effective it will be.

Driving me nuts I am still pulling more from the grid than I can push back even though I strongly suspect I am making enough to break even.

Voltage rise seems to be getting worse as well. Be interesting to see what happens when summer comes although I still believe there will be plenty chance there will be periods with no power at all.
 
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