Author Topic: Finally, some use for excess solar power.  (Read 2504 times)

ajaffa1

  • Hero Member
  • *****
  • Posts: 1303
    • View Profile
Re: Finally, some use for excess solar power.
« Reply #30 on: December 10, 2018, 10:12:36 PM »
Hey Glort, what about a plasma/laser cutter or even a high pressure water cutter, CNC controlled. Would use a lot of power and you have three phase on site so you could continue operations on cloudy days. Got to be a demand for precision cut metal components.

Bob

glort

  • Hero Member
  • *****
  • Posts: 2944
    • View Profile
Re: Finally, some use for excess solar power.
« Reply #31 on: December 11, 2018, 04:03:41 AM »
Now who is a mind reader?

That had actually occurred Bob!
Trouble is the word precision is never applied to me or anything I do, ever.  i don't think I could get my head around learning it all now either.

Whatever I do has to be simple for me to get my peanut brain around it.


ajaffa1

  • Hero Member
  • *****
  • Posts: 1303
    • View Profile
Re: Finally, some use for excess solar power.
« Reply #32 on: December 11, 2018, 04:36:30 AM »
Hey Glort, the beauty of CNC is that you don`t have to be a precision engineer or computer programmer to operate it. The designs are emailed to you by an architect, designed or engineer you upload that spec to the CNC cutter and it does all the work. The only thing you need to do is put the correct material onto the cutting machine and tell the client to come and pick it up when it`s done. Most CNC cutters also have the ability to work out the most economical way of cutting sheet material thus reducing cost and scrap.

The brain power of some of the guys operating this sort of equipment is nothing to write home about, I suspect that after the first few weeks you would be bored stupid by it.

Bob

glort

  • Hero Member
  • *****
  • Posts: 2944
    • View Profile
Re: Finally, some use for excess solar power.
« Reply #33 on: December 11, 2018, 04:48:56 AM »

I'll start looking the machines up!  :laugh:

glort

  • Hero Member
  • *****
  • Posts: 2944
    • View Profile
Re: Finally, some use for excess solar power.
« Reply #34 on: March 28, 2019, 02:09:02 AM »
double post
« Last Edit: March 28, 2019, 04:06:59 AM by glort »

glort

  • Hero Member
  • *****
  • Posts: 2944
    • View Profile
Re: Finally, some use for excess solar power.
« Reply #35 on: March 28, 2019, 04:06:02 AM »

Just put up some more panels on the back roof and have now Combined a couple of orphan setups into one substantial one.
Had 3 arrays previously plus this one. I now re wired it all to have 2 outputs from 4 strings which will mate up with the 2 Trackers on the inverter I'm using.

Still learning about this. The very pushed theroy is you have to be very careful about keeping the same size/ output/ voltage panels all together or there are at least very bad inefficiency's.  I find this " questionable". No doubt it's not ideal but when it comes to utilising used panels as one would be normally doing if there was cause to mismatch, I'd say the inefficiency pales into what you get as to not using them at all or the cost of putting them on different inverters.

I have in this system 240w and 190W panels which are all close in voltage. 32 Panels all up so a decent 6.5kw+.
The thing with panels are they are not fixed in voltage or output so there is a lot of flexability in their ability to work with other different panels.
In testing multiple setups on differing panels, the sum of the mismatched panels is about 1+1 still equals 2 so I'm pretty happy with that. While that may seem obvious, a lot of times due to what ever factors of I surmise efficiency, it is more likley to get 1+1= 2.3.
Panels are a lot like batteries. You can put a 100 ah 12V battery with a 50AH 6V battery and get the calculated output only with panels you don't damage anything or have any dangers.

Right now the 2 arrays are doing 7 and 9a at 20V apart and have the inverter maxed out. the water heater is running and i'm still pumping power back to the grid on 2 phases.  Beautiful!

The inverter I have the house array hooked to is only a 3.6Kw which for the moment is fine.  I have them running through the water heater Circuit atm  which is good for 3600W so not wise to put on a bigger inverter unless I had some switching that would only allow full power ( both strings kicked in) when the water heater was running or when the wattage fell below 3600W.  When I get a HD circuit wired in I can up the inverter to a 5KW or whatever I have at the time.

The other thing with the under rated inverter atm is winter is coming so a lot of the day the thing will still probably not make much more than that as winter fall off is severe and the array is west so won't even to a lot till midday. 

With my excess power problem, the main concern with that is now winter.
Even though last winter I didn't make enough total power, I often made too much peak through the day that went to waste.
I have come up with a solution for that I'm rather embarrassed to admit but pleased I have, so pride will outweigh humiliation....

The big problem has been voltage rise through the regulation but smaller than ideal wiring particularly from the garage where there is 9KW of panels and inverters.  I have 2 Circuits but both tend to go high pushing the power back. I have used dummy loads with the voltage monitoring relays to keep the inverters from tripping on high voltage.  Kicking in the water heater also works but only so much hot water you need before it heats up and kicks out.

My brilliant and cunning ( and blindingly obvious) solution is to take the Voltage monitoring relays from the shed and put them in the house connected to just some cheap fan heaters.  This will help lower the line voltage and put the power to some use as well.  Heating the house will help store the energy in the furniture and walls etc which will mean that the night heating will be reducing it's load by only for the main part trying to heat the air with less heat sink from the furniture etc.

How I didn't think of this before I don't know.  :embarassed: It won't drop the voltage as much as having the load at the inverter but it will certainly help.
The inverter on the house will be fine as I can connect direct to the same junction.

I am also going to look at bringing in a plastic Drum and putting a water heater element in it. Heating the water through the day will allow it to be a passive radiator at night. Found a place to put it in the middle of the house, now just have to think of a way to dress it up to make it look aesthetically pleasing.
I suppose a small fan on that and something like a fish tank pump to stir the water would help to retrieve the heat at night.

mike90045

  • Mendocino Metro
  • Hero Member
  • *****
  • Posts: 1370
  • Mmmm BBQ
    • View Profile
    • Mikes Solar PV page
Re: Finally, some use for excess solar power.
« Reply #36 on: March 28, 2019, 04:19:05 AM »
I like the idea of making hot water in a plastic drum :)

re panel mix & match

In series, the amps will be limited to the lowest amp rated panel, so if you stick a 5A panel into a series string of 12A panels, the whole string gets throttled down to 5A.

In parallel, panels will be limited to the lowest voltage panel in the batch.   mixing 19 & 20v panels is fine, but mixing  27 & 36V panels will limit the group to 27V

The wattage lost depends on how far the data is offset, one 12A panel on a big string of 5A panels is not a huge loss, but put that 5A panel on a 12A string and you loose a lot

glort

  • Hero Member
  • *****
  • Posts: 2944
    • View Profile
Re: Finally, some use for excess solar power.
« Reply #37 on: March 28, 2019, 05:04:22 AM »
I like the idea of making hot water in a plastic drum :)

Do I detect a Note of Sarcasm??  :laugh:

I have heard this before. I remember a veg oil forum lighting up when I showed pictures that I was using plastic fittings on the coolant side of the heat exchanger.( before I woke up to the fact they weren't at all needed.)
 
All the safety sissys and ignorants went into a lot more meltdown than the plastic ever would have and didn't believe it had a far higher melting point than any water could ever get to. I did a Vid with a pipe nipple in a pot of boiling water and pulled it out and showed it wasn't even at all soft but of course never let facts stand in the way of ignorance and fearmongering on the net. Used those Fittings for 3 years and never had a problem with any of them.
Pity few of the other guys conversions ever proved as reliable.  ::)


The drums I would use would have a melting point of around 1500C and probably higher.
As the energy input I would be putting in of around 2KW  for less than 6 Hours, I'm going to be lucky to get 200L of water to remotely near half of that melting point. Of course there is always the minor point that water will never get over 100......

Spose no reason I couldn't use a metal Drum. Going to hide the thing anyway and the metal would probably transfer the heat quicker.  Having the standard 2" Bung may also be an advantage depending on what element I go for.
OToh, I did have some elements that seemed to have a voltage leakage so a plastic drum would be safer in the event of cheap arse elements going haywire.

Better go have a look at elements and see what I have and if I need to order any more.

mike90045

  • Mendocino Metro
  • Hero Member
  • *****
  • Posts: 1370
  • Mmmm BBQ
    • View Profile
    • Mikes Solar PV page
Re: Finally, some use for excess solar power.
« Reply #38 on: March 28, 2019, 06:51:00 AM »
>  Do I detect a Note of Sarcasm??  :laugh:

Irony, as opposed to plasticity !

Many plastics won't melt, but at high heat, they get really soft.    Boiling water will "sit" in a 5 gallon bucket, but don't try to lift the bucket, the bottom falls out.

And if a hot heat exchanger or element touches the plastic, it's likely to melt through.  I doubt a full IBC would hold hot water without a base and sides

glort

  • Hero Member
  • *****
  • Posts: 2944
    • View Profile
Re: Finally, some use for excess solar power.
« Reply #39 on: March 28, 2019, 07:18:19 AM »
I doubt a full IBC would hold hot water without a base and sides

I Filled an IBC tank without the cage the other day with cold water and I noticed it's leaked half the water out already.
They are much thinner plastic than the drums I had in mind.

Getting a heater element that will fit in the bung hole looks to be a challenge but maybe I just won't worry.  Cut a hole in the center of the drum, get a bit of plate and put a hole in to hold the cord and screw that over the hole in the drum with a bit of Silicone.

A removable lid metal drum would be ideal but they are hard to come across now.

I also notice they make metal drums much lighter now. My father has one on his farm he reckons is 40 years old.  Thing is so thick and heavy it's like it would stop bullets.  The ones of today literally wouldn't stop air gun pellets.

glort

  • Hero Member
  • *****
  • Posts: 2944
    • View Profile
Re: Finally, some use for excess solar power.
« Reply #40 on: May 16, 2019, 11:11:38 AM »

Playing around a bit last couple of days with some solar heating of my toy greenhouse.
Temps have been down to 1 oC here already ( Converted for the American readers, thats' ahhh, 1o C !)  and I want to keep some plants alive and growing.
I put in some hedge cuttings I wanted to propagate as I will need about 100 plants that they have been doing fine as well as some tomato plants, Rocket, parsley, passion fruit, a bamboo and Moringa plant.

The little plastic tent can easy hit 40+  during the day but I believe because I have most of the plants sitting in trays and have been keeping a few MM of water in the bottom, the humidity is 101% and the plants never show signs of wilting or any kind of stress.  Quite the opposite in fact. The growth rate has been outstanding and I am pleased that not one of the hedge clippings has faltered and all of them have taken well.

The trick is going to be keeping the plants at a decent temp when we get to the sub freezing temps here as we got too much of last winter.
I could go about this a bunch of ways, the first one was to put a 150W incandescent spotlight in the thing. It was keeping things about 3-5o above ambient but that's not going to be enough. I tried a stove element in a bucket of pebbles but I think that made the element over heat and it burned out. In fact it burned away no doubt due to the arcing of the DC power.  I knew that was never going to be enough thermal mass but something to play with till I got some water heater elements.

Water has far and away teh best thermal retention of any non exotic thermal mass but a long way.  At one stage I had the bright idea of just placing an element in a vessel and pouring 50 Kg of aluminium over it but crunching the numbers found that ally has about 1/4 the thermal mass of water.
Only one way to go with this clearly.


A few pics to add interest to my ramblings.....



My first little greenhouse outside my office window. It is tied to the 400L water heater ( For the US readers, that's a big mutha!)  because a stiff breeze came up here which anywhere else would probably be called a gale and I could see the writing on the wall when the wind did come up here proper.  Might look at re-enforcing that some more.
Structure is about 1.5m Wide, 90cm deep and 1.8 H.




Opened up  the little greenhouse is quite full and the water tank doesen't take up that much useable space really.
The element I screwed and siliconed into the side can be seen. It's a 3.6 Kw, 240V rated element I measured at about 15 ohms. Picked up 2 of these and 2 4.8 Kw units from the local friendly scrap yard.

The tank is 110l Capacity and I have 100L  in it to make the heat calcs simple.  The 150W lamp can be seen at the top. I'll probably use that in a month or so to extend the light the plants get.  I did take Bruce's idea on board and get some LED strip but it is disappointingly dull  so I'll have to do some research for some better type. I have a couple of small LED Ligh bars up the back so I might put them on the sides facing in and across.  The 150 Light throws quite a glow in teh yard at night, I can Imagine what these light bars will do. The sheep next door that happily came back today won't know what's going on!

I have a bit of styrofoam over the top of the drum to stop too much moisture loss and avoid cooking the tray of plants sitting on the top.



This is the panel array across about 3M from the greenhouse.  The panels are set up 5 in the string with the 2 strings paralleled to get the right ohms for the heater element.  The panels are 250W so 2.5Kw in total. Matching the Ohms is very important when using panels and mains rated elements.  It's not a matter of half input equals half power. One needs to match the resistance reasonably closely to get decent output.  If this is not done it would not be unusual to have say 1 Kw of panels and an actual heat output from the element of 150W.

My panels work out at about 10.8 ohms and the element is 15 Ohms. From what I read having a 40% over rating on the element aids in the power levels during ramp up and fall off in solar production.  It seems to work

Today I took some measurements of temp and power input.

The position of the panels although facing north ( Being down under as we are is correct)  is such they don't get complete sun till about 10 am being shaded by the house till about then.
At that time and after putting about 25L of water in the tank I had heated somewhat yesterday, the water temp was 30.5oC.
Electrical input to the element was 11.4A @ 132V into the 140V element for a heating input of 1508 W which I was really happy with.

By 11 am the water was up to 42oc and the element was getting 13.7a @141V for a total of 1931W.

Unfortunately I didn't get to check the 12 Pm time as the mrs summoned me to come hold her hand at the dentist. So much for appreciating my putting my day aside to be with her. Not my fault If I laughed at the way she jumped when he put the cold spray on her cracked tooh and then tried to curl up in a little bally in the chair, it was funny as fk and even the dentist and the nurse were laughing. As the dentist pointed out, with hat he had done to me over the last couple of years, I had well earned the right to laugh at anyone in that chair.

Returning home at 2:30 ( no, you can never go just one place with my wife once you are out the house)  The tank temp had risen to 69oC and was getting 12.3A @ 105V for a total of 1291W

By 3 PM the panels were back in shade and producing next to nothing.  I hooked in an array of 16 Panels on the roof but probably due to the ohm Mismatch and the failing light, I was only getting about 800W input  from 3.8 Kw of panels.  These are wired in series so the open voltage is a bit over 300 but it fell to around 60 when the element was connected.

All input would hae stopped by about 4:15 and I measured the tank temp at 5 at 64o. This may have been because the temp of the pots inside when I checked at 2:30 was up around 40oc so I left the door open to give the plants some air and cool them off a bit.
I'll go out about midnight and shoot the temps now the tent is sealed up again and see how it's going.
I noticed last night I had a tank temp of over 50oC and the temp of the pots was around 18-20 . The heat loss through the plastic would be huge but if I can keep the soil temp of the plants no lower than 15 I'll be a happy camper. I suppose I could also throw a blanket over the thing at night to slow the heat loss and I'd also probably have to partially wrap the tank as well as I wouldn't want the soil temp getting too high.

I am on the lookout for some large sheets of styrofoam to put on teh bottom of the tent to stop the cold radiating up from the pavers.  If i could put some styro on the back of the structure  where it goes up against the house and on the south side opposite the direction of the sun, that would be helpful in slowing heat loss and probably reflect the light around a lot better as well. I think If I start insulating I'm also going to need to put in a small fan ducted to the outside attached to a thermo to start cooling things when the temps go up during the day. Better air Circ wouldn't hurt the plant development Either.



This is the south end of the rear of the house which faces west. There is a clear 7x4.5M clear, square area there not counting the diagonals on the ends where I can put more panels. easy enough for another 5Kw+. Being west facing, I'd probably need that much at least to get the same daily total generation as I have from half of that which now faces north.  The west panels did pretty poorly last winter but brute force of adding a load more since is yeilding some good numbers on the other end of the house and there is still room for another 2.5 K up there at least and another 5 KW on the north roof.
In several minds about putting them on the north end.  Dor the moment I think I'll hold off.

If they change my meters to smart arse meters I'll look at getting a " legit" system put there and see if it's possible to get certified for 10Kw and only install 3 or so and then hook my current system back in.  Save on the costs of having a certified system installed but allow me to feed back from my present setup without causing too many problems.  From what I read repeatedly, They don't even bother with the amount you have installed, power co is only interested in what you are approved for and aren't going over that.  Don't want to loose any more profits than they have to.

For this winter and untill I finish the outdoor tropical bathroom I'm putting down that end of the house the panels can stay in their present temporary position.  Next winter I'd like to have a bigger greenhouse or even a shed would do me.   Easy to put in clear panels in teh roof or insulate it and just light it with LED's and have better winter heat retention.

This setup is interesting but I am mindful at the end of the day, I'm probably better off all round just hooking the panels to a GTI, feeding them back to the mains and powering a heater, be that a thermostatically controlled fan heater or a storage setup like I have than having a dedicated array.

It's SOOO much easier and cheaper to control things with AC than DC. I could use a thermostat or 2, a PWM controller to regulate the input to the heater element and incorporate an earth leakage detector as a life preserving measure to run it all and it would all be cheap, off the shelf stuff.
Dc is fun but one is limited with power control above 100V, there are no earth leakage devices I am aware of to stop one getting a heart stopping belt in case of brain fade and DC thermostats become more complicated as the whole lot is far more exy than AC. One thing to have your house on DC where the cost and setup is worthwhile but the perspective is this is a cheap arse Greenhouse with highly questionable Longevity.
Expenses need to be looked at accordingly and I already have EVERYTHING i'd need made up in AC.

The other thing with this is where does the point come where I don't have the solar to spare and it's more valuable in the home?  In a larger and more permanent setup it would be easy to install a water heater with a draft oil burner and run the whole thing off 12V which is easy to work with.

For the meantime though this is proving to be a lot of fun and an interesting learning curve.
be interesting to see what the temp inside in the morning is.  only going to get down to about 7 tonight so not really cold but i will get an idea what to expect in about 6 weeks when there is frost every morning.

I think I might do well to find some styro to insulate the little structure with by then.  :0)



glort

  • Hero Member
  • *****
  • Posts: 2944
    • View Profile
Re: Finally, some use for excess solar power.
« Reply #41 on: May 16, 2019, 11:42:55 PM »

7 Am Observations.

Ambient temp outside was 6 oC.  Water tank was 30oC ( again!)  Temp of various pots in the greenhouse was  12o C.

My conclusions are I simply need more heat or less heat loss to keep the temps where I want them when the weather get cooler as it is set to do.
I'm reluctant to increase the temp of the water any higher because the initial temps will make the GH too hot.   I'm limited in the amount of thermal mass I can store, could add another 10L of water which will hold about a KW of energy but probably not enough and then one is limited by the input from the panels anyway.

Insulating the structure seems the best way but depends on materials.  Seems styro is very hit and miss to find and surprisingly and over the top expensive here.  I did see a place giving away  thin corflute, wonder if that would be any good at all?
I might try an old blanket over the top tonight and see how that goes but would be of limited help in wind and if it rains.

Other options are simply more power.  Adding panels is a very Limited option as I need to stay in the resistance rage of the panels and the element.  I could go to a 6 panel array but that's not going to do a lot and the effect would be merely to heat the water hotter. The panels stop producing much earlier in the day than i'd like so even a limited intput to maintain temps longer would also help.

I could go back to turning the light on which would negate some heat loss and I could put a 2nd element in the tank with a thermo that kicked in when the water got down to say 40o C to maintain the inside temps.

As usual, extra insulation would be the best solution but not necessarily the most economical or easiest to implement.
Not sure where I would look to find it as a waste product and whom might have sheets of it they wanted to get rid of.

 I'm also wondering about just a tarp or a second cover over the top. I have seen replacement covers available and they seem generous enough sized.  the one on there is quite loose so I may well be able to put another over the top. If I put some " Spacers" in the form of small foam blocks between the covers on the top particularly, I could trap some air which would act as insulation. If I found some foam would work nicely to keep that in place.

In the mean time I'll see how much difference the light and a blanket would make.

BruceM

  • Hero Member
  • *****
  • Posts: 2740
    • View Profile
Re: Finally, some use for excess solar power.
« Reply #42 on: May 17, 2019, 12:00:56 AM »
Mike was right about plastics- HDPE is often used for barrels, and it's going to very slowly start to deform at boiling, just give it time, it's strength is greatly reduced at higher temps. It will just ooze. You will see that buried rotomolded HDPE tanks will rarely be rated for over 130F.   

Polypropylene is much stronger, especially at higher temperatures, the buried tanks are often rated to 150F or better.

So if you're bargain shopping for tanks for hot water, look for a PP stamp, though even that isn't going to take 100C for extended periods without some deformation unless it was overbuilt.


mike90045

  • Mendocino Metro
  • Hero Member
  • *****
  • Posts: 1370
  • Mmmm BBQ
    • View Profile
    • Mikes Solar PV page
Re: Finally, some use for excess solar power.
« Reply #43 on: May 17, 2019, 12:14:14 AM »
Do you get any stratification in the water tank ?  I ask because my Listeroid barrel can be scalding on top and cold at the bottom.

glort

  • Hero Member
  • *****
  • Posts: 2944
    • View Profile
Re: Finally, some use for excess solar power.
« Reply #44 on: May 17, 2019, 04:37:56 AM »
Do you get any stratification in the water tank ?  I ask because my Listeroid barrel can be scalding on top and cold at the bottom.

I did get huge stratification but not any more.

At first during the initial mucking around, I suspended the element in the top of the drum with a bit of wire. Covered the element but had the electrical terminals above.
 Seemed the top of the drum was near boiling and the bottom had no detectable heat increase. I was really amazed the difference was so great.

The element is now is probably about 10 Cm off the bottom of the drum. The element steps down a fair way so is much closer to the bottom on the inside than it appears on the outside. I noticed that the element is marked one direction for solar, another rotation for mains. The solar  orientation is as I have it, with the element down. The AC direction has it basically flat.  I surmise this is so one gets more water heated from the solar input.  Not sure why you wouldn't want it the same way for AC but that what's on all the elements I recovered.

Shooting the temps now the whole drum is even temp to within the error margin of the temp gun I am using which is about 1o . I think having the offset to one side works as well as it rolls the water slightly with the convection current. I was thinking and could have easily Centred the element in the bottom of the drum as the red ring stops it contacting the ground but I thought it would be good to have as much of the element as lot as possible and having it to one side to create a rolling turbulence would also be beneficial.

 It also seems the water at the top is NOT the hottest if there is any variation. Maybe it's evaporating a bit and bleeding energy through that.

I was thinking to put an air bubbler in the tank to stir it if need  be but seems there isn't.
I think the hot water rises easy enough but it is VERY reluctant to go down.  From an engine cooling POV, this is probably a good thing in most circumstances. A small airpump or electric motor with a prop might be good to activate on a timer if you wanted to even out the drum temps.