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Author Topic: Solar export controller, DIY suggestions.  (Read 2628 times)

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Fellow members.

My modest 2 KW solar system has just passed its second year of operation with an output of 2.75 MW hours. Most of which has been given away to the national grid. Don't get me wrong, I've already saved so much that another 2 years will see the system paid for.

I've been watching the fuel prices steadily rising lately and considered the purchase of an export controller to heat my water rather than use my oil fired boiler/furnace, particularly during the summer months.

These things are ridiculously expensive for what they do, I found one on eBay today at a starting price of £130.00 I placed a bid and found others were already at £200.00+!!

Can we put our heads together and design a simple unit that can made for a fraction of the cost? I'm pretty sure both other members and guests could benefit.

Cheers Graham.


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Dear Graham

I've only a small understanding of what an export controller is supposed to do. Maybe a definition would be good and how you intend to use this feature to heat water.

As I understand it, this is a device that caps the amount of power put onto the grid due to regulations . But how do you use the excess? Seems like an excess power transfer device would be needed that redirects the excess into the heaters of your electric boiler. But that too must be limited to prevent overtemp condition.

Is there an output on the export controller that sheds the excess into a side load?

Regards



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Dear ION.

The device I looked at this morning was quite clever. It can be programmed to switch on up to three resistive heating elements when there's a surplus or export condition.

What I'm looking for is a single load ( 1 KW ) immersion heater element to be activated once my system produces over a kilowatt.

Here's a link to the device that was on sale earlier today.

https://www.immersun.co.uk/wp-content/uploads/2014/08/Instruction-Manual-v1.1.pdf

Cheers Graham.


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Dear ION.

The device I looked at this morning was quite clever. It can be programmed to switch on up to three resistive heating elements when there's a surplus or export condition.

What I'm looking for is a single load ( 1 KW ) immersion heater element to be activated once my system produces over a kilowatt.

Here's a link to the device that was on sale earlier today.

https://www.immersun.co.uk/wp-content/uploads/2014/08/Instruction-Manual-v1.1.pdf

Cheers Graham.

Graham
Im a little lost here==maybe our grid tie systems work different over here?

In Australia,where you have grid tie solar systems,the home draws the power it needs from the solar system via the grid tie inverter,and the grid tie inverter sends the excess back to the grid.

If we have electric water heaters with grid tie systems,then a timer is fitted to the water heater,so as it only comes on during the day. (They do have an over ride switch should you need to switch it on at night.)
So the solar system powers the electric water heater-along with the rest of the home,and the excess is automatically sent to the grid.
Should your home need more power during the day than the solar system can deliver,then the grid tie inverter draws the needed excess from the grid.

If your system works the same,then all you need to do is wire up the heating element,that has a thermostatically controlled switch,to your homes wiring,and the grid tie inverter takes care of the rest.


Brad


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Dear ION.

The device I looked at this morning was quite clever. It can be programmed to switch on up to three resistive heating elements when there's a surplus or export condition.

What I'm looking for is a single load ( 1 KW ) immersion heater element to be activated once my system produces over a kilowatt.

Here's a link to the device that was on sale earlier today.

https://www.immersun.co.uk/wp-content/uploads/2014/08/Instruction-Manual-v1.1.pdf

Cheers Graham.

Dear Graham

I have read the manual and believe I understand it's operation.

Question Is that 1kW transfer over and above what you are back feeding the grid or just kicks in when your system reaches over 1kW, even if you are using domestically the 1kW?.

It would not work to use a simple current controlled switch, as this would put the full 1kW heater load in all at once, whereas you need a proportioning system so that only the overrage is sent to the heater. This can be done by monitoring the current threshold and direction as I assume you do not want this transferring during a cloudy day when you are using (drawing from the grid) over 1kW and proportionally sending the overrage to the heater be it 1 Watts or 1k Watts. So direction control is a "must have".

Since you are feeding the overrage into a resistive heater, you can probably get away with phase control using a thyristor (Triac as in light dimmer) that has a filtered feed and setpoint adjustment from the current transformer. You don't need a pure sine wave inverter for this type of resistive heater load, only for sensitive inductive loads, as that is where most of the money is spent in the unit described in the pdf. The direction control is still a problem we need solved.

Do I understand the problem yet? or am I still confused?

Regards


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Hi Brad.

Well, I really don't know. My grid tie inverter is sat firmly onto the grid via a permanent Live and Neutral. When the sun shines, not very often, we get some energy. This energy if in excess of what's being used by the home gets exported, or effectively wasted.

So that neatly brings me to ION ....

As we're connected to the grid, solidly there's no need for a soft start.  A CT fitted to the grid tie inverter that could determine whether 1 KW or not was being developed and then activate a relay, for arguments sake, would suffice.

My system although rated at 2000 Watts output rarely develops more than 1.8 but as I posted earlier has now passed through 2.75 MWH !!

I hope the above makes sense?

Cheers Graham.


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Well if your sure a full load  of 1kW connected wouldn't cause a problem with the rest of your domestic usage, you could try something as simple as
a current transformer  driving an AC power relay that kicks the load in over I kW.  For adjustment you could shunt away some of the current from the CT with a rheostat in parallel with the relay to act as trip point adjustment. You could also try putting the rheostat in series with the relay.

Alternately you could full wave rectify and filter the output of the CT and drive  a burden resistor then a more sensitive DC relay in pilot duty mode to a much larger load handling relay. Also  there are solid state power relay modules that operate on low voltage and low current.

You have too many choices.

Regards



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Dear ION.

Your last post certainly brings to mind the " KISS " acronym!!   O0

So....

Let's make it slightly more complicated, shall we?

My solar panels are mounted upon the roof of my workshop with the grid tied inverter inside. A hefty cable connects the workshop to the house and main distribution box.

Would there be a way of determining energy direction? Obviously on many occasions the workshop will be taking up to 3 to 4 KW to drive my heavy machinery and would naturally " kick in " the immersion heater. Would I need 2 CT's and a comparator?

Cheers Graham.



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Dear ION.

Your last post certainly brings to mind the " KISS " acronym!!   O0

So....

Let's make it slightly more complicated, shall we?

My solar panels are mounted upon the roof of my workshop with the grid tied inverter inside. A hefty cable connects the workshop to the house and main distribution box.

Would there be a way of determining energy direction? Obviously on many occasions the workshop will be taking up to 3 to 4 KW to drive my heavy machinery and would naturally " kick in " the immersion heater. Would I need 2 CT's and a comparator?

Cheers Graham.

Dear Graham

If you only intend to use solar power to feed the heater, then you only need to monitor your solar output to the domestic or to the grid and set the trip point, no need to worry about direction as you will only monitor the solar output.

Yes it gets more complex if you want direction control, and yes, 2 CT's and burden resistors connected in series out of phase might work.

Only first cup of coffee so subject to sluggish engine errors.

Regards


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Bump....

Well, nearly 12 months has elapsed and two weeks ago I installed what I have nicknamed the " summer string " an extra 1040 watts that will readily available between late February to late November.

Having studied the newer generation of systems I now understand what Brad was writing about where the entire domestic electricity installation is placed between the grid and the solar panels. However my system is grid tied but in a different place.

Being " oldschool " I was looking for a simple way to divert some of the energy that would normally be given away to do something useful!

Our water heating is provided by an oil fired boiler/furnace augmented by a multi fuel stove. Having two different heaters, UK regulations stipulate that a " circuit neutraliser " be used to combine these systems. This simple device is merely a space where the " waters " can circulate freely. I'm going to put a hole into the side of it and fit a 600 watt winter pool frost heater.

More to come....


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To continue....

Trawling eBay I noticed a neat little gadget from China. Where else?  :)

It's a motor overload protector that can be calibrated up to 10 amps. For an amazing price of £3.48, free shipping, I couldn't have bought the CT for much less! This will be my " brain " of the operation.

I did look at various " wireless " schemes but they're either way too expensive or beyond my understanding of this new " programmable era we live in.

Ion did suggest a CT on the export leg of the inverter so all I have to do is run a pair from the normally open relay contact from the workshop to the house to operate another relay to switch the 240 volt 600 watt heater.

I'll keep you posted as I progress.


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Good grief....

I really must get my arse " in gear " I went into the workshop to find something and checked the inverter....

The system has just passed 250 KWh in a month!! Despite there being poorer sunshine than in previous years.

Storage, we really do need to find a cheaper alternative!

Cheers Graham.


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Hi Graham,

The long wait for overunity makes me look for alternatives. Solar panels could be the solution.

But I have the impression that the nominal power indicated by the manufacturers has very little to do with the average power that can be expected from it.
In particular, since I do not live in California or Saudi Arabia, I would like to know what proportion of the rated power we have when the weather is overcast, for example completely cloudy. Is it 1% or 50%? It's the order of magnitude that interests me, I can't find the data. Can you give me some information? Thank you.


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F6,

i am sure Graham has similar data, but Chet asked this some time ago to me and my answer was given here:
https://www.overunityresearch.com/index.php?topic=2933.msg49569#msg49569

Bottom line, my 6KW system (24 x 250W panels) gives at a summer sunny day max 41KWh (44 absolute max. recorded)
And at a clouded day (few days difference) 7KWh, so a 6:1 ratio.

I live in The Netherlands.

But data is strongly depending on the amount of cooling the panels receive.
Ideal is strong cold winds around the longest day (21 June) without any clouds.


The panels produce heat while working (can get up to 70°C) and dropping their efficiency with 1/3 (say from 15% to 10%)
Therefor my 6KWh system rarely delivers more then 4.3KW.

Only at partly clouded days i see them peak to 6.3KW when the sun comes out from behind a thick cloud, but
quickly dropping to 4.3KW again.

 
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Hi Graham,

The long wait for overunity makes me look for alternatives. Solar panels could be the solution.

But I have the impression that the nominal power indicated by the manufacturers has very little to do with the average power that can be expected from it.
In particular, since I do not live in California or Saudi Arabia, I would like to know what proportion of the rated power we have when the weather is overcast, for example completely cloudy. Is it 1% or 50%? It's the order of magnitude that interests me, I can't find the data. Can you give me some information? Thank you.

Good morning F6FLT.

My " Penny " dropped a little over 3 years ago.

Our rented accommodation is a little over 300 years old and South facing. Our landlord was very reluctant to allow the attachment of Solar panels to the aged slated roof. My only alternative was to fit the original 2KW ( 8 by 250W ) panels to the roof of the workshop that I built at the back of the house. Not ideal as the panels become partially shaded in late winter.

Despite the minor inconvenience the system went on to produce 3.7 MWh up until last month, when I decided to add an extra " string " of four 260 W panels.

As stated in my previous post we've already passed a quarter megawatt hour in a month!

This morning is drab, medium Grey full cloud and drizzle but still " belting out " 550W !

Personally I'd recommend Solar PV, having reduced our monthly electricity bill by 2/3 the original system had virtually paid for itself. This years intention is to reduce our Oil consumption by using the surplus to heat our domestic water.

Cheers Graham.


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Itsu, Graham,

Thank you for the advice and the very concrete information provided which will help me a lot in the decision. Production seems to be better in cloudy weather than I expected. Here (West France) I must have a little more sunshine than in the Netherlands, so all this looks good.

I still have to estimate the cost, because half the roof is facing due east, and the other half due west, so I have to double or almost double the panels for a good distribution of production over the day.
Then I have to evaluate if I really want to be autonomous (I have a large roof surface), in which case I have to plan for large batteries, or if I stay connected to the grid.

One last anecdotal question, just out of curiosity: is there a small production on full moon nights?


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Grum
 Thermal storage might be worth looking at I believe one square meter of water holds an enormous  amount of BTUs
Also a few members here have done experiment cooling the panels I believe tinman shared remarkable results in efficiency
 If the cooling water could be stored in a few cubic meters there could be 1 million BTUs available at the proper temperatures
   

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Itsu, Graham,
One last anecdotal question, just out of curiosity: is there a small production on full moon nights?

I too wondered about that question....

The reality is no, I've been out to the workshop where my inverter lives on several bright moon occasions, nary a glimmer, she sleeps.

Cheers Graham.


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Itsu, Graham,

Thank you for the advice and the very concrete information provided which will help me a lot in the decision. Production seems to be better in cloudy weather than I expected. Here (West France) I must have a little more sunshine than in the Netherlands, so all this looks good.

I still have to estimate the cost, because half the roof is facing due east, and the other half due west, so I have to double or almost double the panels for a good distribution of production over the day.
Then I have to evaluate if I really want to be autonomous (I have a large roof surface), in which case I have to plan for large batteries, or if I stay connected to the grid.

One last anecdotal question, just out of curiosity: is there a small production on full moon nights?


Well, many have asked that question, just do a google search.

Personally i never seen any effect, but the resolution of my detecting system is to rough i think.

I have seen the effect of a lunar eclipse last year, i think, on a solar system which had a watts resolution or so and the eclipse was clearly visible. (dip).

It was on the spaceweather.com website (has no search capability i see).


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I have just discovered this article, or how to use light radiation (infrared, heat-related) "backwards".
It's so obvious, and I haven't even thought about it! Terrible >:(


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I have just discovered this article, or how to use light radiation (infrared, heat-related) "backwards".
It's so obvious, and I haven't even thought about it! Terrible >:(

I just checked your link.

Here the BIG problem would be the " clear sky " bit!!   ;D


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Cadman started an interesting topic here [trying to harvest from mixing known effects
and build.........

Quote]  A 24/7 Solar-Seebeck-Peltier generator.[end quote

http://www.energeticforum.com/renewable-energy/21143-thermo-electric.html

he's a cool builder guy !!

Grum
sorry if off topic ,please remove if "too" far out...





   
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I just checked your link.

Here the BIG problem would be the " clear sky " bit!!   ;D

A big problem, in misty or rainy countries, but not a bigger problem than the functioning of solar panels at night...  ;)

The principle is clever, because temperature is not a local data, but what is "seen" in a certain solid angle. So if we "see" a cold temperature somewhere in the distance, then we can exploit the difference with the temperature we "see" elsewhere, for example on the ground. This difference can be very large if you look at the space vacuum on a clear day.


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