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Author Topic: excess power from pv  (Read 34602 times)
Richard Owen
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« Reply #75 on: July 27, 2011, 02:44:31 PM »

For some time, since before coming across this thread, I have been designing an immersion controller for my 4kW PV system. I now have it finished and have built as few for family and friends. Seeing as the professionals have not come up with a sensible product that is affordable send me a private message if anyone wants to buy one. It is available as a kit or ready built. I am a Chartered Engineer so the design is hopefully quite professional but ultimately the risk is yours if you want to fit one.


It functions similar to the ones mentioned on some threads here, i.e. it controls the power into the immersion to ensure that export power is reduced to near zero (as long as the hot water is not up the temperature already). But it uses simpler components to reduce the cost and size, e.g. instead of an expensive PLC (Programmable Logic Controller) it has a small PCB that I make; this does not reduce its performance. It is designed for a 3kW or less immersion but would probably work up 10kW, although I have not tested that and your utility company might object at more than 6kW. Two 3kW immersions in parallel should be OK.  It does not rely on an always on external PC either, which would burn lots of watts. No need to purchase an expensive <1kW immersion.



Would it work with my 300W Hydro Scheme?
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echase
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« Reply #76 on: July 27, 2011, 03:16:09 PM »

Donít know much about hydro but I don't see why not. But I suspect to get really fine control a lower than 3kW immersion element is desirable, as many controllers designed to work as 3kW are going to give quite coarse control when trying to reduce the 3kW to 300W, tending to turn it on fully or off altogether rather then fine controlling it over 0-300W.

In my house the minimum base load of freezers, etc. is 300W so I would have nothing to export if I only had a 300W hydro.
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Richard Owen
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« Reply #77 on: July 27, 2011, 04:40:03 PM »

My Hydro isn't grid tied. It's stand alone. I have a spare immersion slot in a tank so it would be convenient if I could use them together.

I also happen to have a 500W immersion heater I just happened on by chance.
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44 Yingli 230Wp panels feeding into 2x Solar Edge SE5000 inverters.
20x 58mm SE, 20x 58mm SW, Solar Thermal feeding 320l thermal store.
10kW heat pump.
300W of Hydro Power.
cj
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« Reply #78 on: July 27, 2011, 11:23:26 PM »

Richard, is there a description of your hydro on a thread? And is it high head or low head?  I have run of the river possibilities, but at about £900 for 100w is not cheap.  http://www.ecoresorts.net/hydro/jackrabbit-prod.htm
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Justme
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« Reply #79 on: July 27, 2011, 11:27:37 PM »

I have run of the river possibilities, but at about £900 for 100w is not cheap. 

But that £900 100watt turbine will give you nearly the same as a 1kwp £3k array over a full year.
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1200watts solar 120vdc
FX80 Solar controller
Victron 12v 3000w 120a
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cj
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« Reply #80 on: July 27, 2011, 11:49:25 PM »

I have run of the river possibilities, but at about £900 for 100w is not cheap. 

But that £900 100watt turbine will give you nearly the same as a 1kwp £3k array over a full year.

If only. That is with 6m/sec flow, that may not be all the time, there are losses of getting the 12v to the house, and approved for export, and the cost of licenses to extract water, and all the infrastructure to channel the water, and the water comes up from 30 cms deep to 3m deep in a few hours after torrential rain ie every couple of years or so. It has to withstand  1 tonne + logs floating down fast when in spate.

Then 100W x 24 hrs is 2.4kWh/24hrs I would anticipate more than that from a 3kWp pv?
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ecogeorge
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« Reply #81 on: July 27, 2011, 11:59:08 PM »

I have run of the river possibilities, but at about £900 for 100w is not cheap. 

But that £900 100watt turbine will give you nearly the same as a 1kwp £3k array over a full year.

If only. That is with 6m/sec flow, that may not be all the time, there are losses of getting the 12v to the house, and approved for export, and the cost of licenses to extract water, and all the infrastructure to channel the water, and the water comes up from 30 cms deep to 3m deep in a few hours after torrential rain ie every couple of years or so. It has to withstand  1 tonne + logs floating down fast when in spate.

Then 100W x 24 hrs is 2.4kWh/24hrs I would anticipate more than that from a 3kWp pv?
If you can get 3Kw of pv for £900 please let me know hysteria hysteria
I've obviously just made a hugh mistake tonight in sending £7200 for ..
20 BP4175 PV panels
Inverter Power-One Aurora PVI-3.6 Outdoors
DC isolator x 2
Generation meter

I may be able to stop the payment genuflect.
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cj
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« Reply #82 on: July 28, 2011, 05:46:56 AM »

Does not compute.

The Jack Rabbit is hydro and to get 1/10 of the power costs for more than 1/10 of the cost of PV. I suggest you do not cancel your pv and but a water turbine on you roof  hysteria  hysteria
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Richard Owen
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« Reply #83 on: July 28, 2011, 08:45:44 AM »

Richard, is there a description of your hydro on a thread? And is it high head or low head?  I have run of the river possibilities, but at about £900 for 100w is not cheap.  http://www.ecoresorts.net/hydro/jackrabbit-prod.htm

I've got a high head (18m) system. I live on a hill.

I am overdue documenting it. I shall get round to it one day.
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44 Yingli 230Wp panels feeding into 2x Solar Edge SE5000 inverters.
20x 58mm SE, 20x 58mm SW, Solar Thermal feeding 320l thermal store.
10kW heat pump.
300W of Hydro Power.
echase
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« Reply #84 on: July 28, 2011, 09:52:02 AM »

My Hydro isn't grid tied. It's stand alone. I have a spare immersion slot in a tank so it would be convenient if I could use them together.

I also happen to have a 500W immersion heater I just happened on by chance.

With a 500W element my system will give adequately fine control with 300W input. I used a 400W electric fire as a dummy immersion when testing it and it seemed fine.
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Justme
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« Reply #85 on: July 28, 2011, 01:40:32 PM »


Then 100W x 24 hrs is 2.4kWh/24hrs I would anticipate more than that from a 3kWp pv?


I think you mis read what I put. I compared it to ONE kwp costing £3k not THREE kwp. Also going on one days PV out put is also not what I said. You average what 1kwp can do per day over a year. Its less than a 100w constant power source can provide.

Water is just more reliable that solar or wind.

So even if all your other costs increase the £900 to £3k your still going to get more energy from the water. You might get more £ from the PV FIT's that from the water FIT's I dont know.

If I had a water power source I would use it rather than any other method. Install problems can be worked, not getting any sun / wind cant.
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Navitron solar thermal system
30 x 58mm panel 259L TS
1200watts solar 120vdc
FX80 Solar controller
Victron 12v 3000w 120a
6kva genny
6 x 2v cells 1550amp/h 5C
24 x 2v cells 700amp/h 5C
Total bank 4350 amp/h 5C
brackwell
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« Reply #86 on: July 28, 2011, 02:27:08 PM »

echase,

Can you just spell out what your box achieves please,

1)What happens when the pv is less than/ and greater than the rated watts of the immersion element.

2) what happens if the PV is not sufficient and you want to use the grid as well

3) what is fail mode and does it fail safe. Could it catch fire.

4) What might be the life span if used 24/7

Sent PM

Ken
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echase
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« Reply #87 on: July 28, 2011, 04:44:54 PM »


1)What happens when the pv is less than/ and greater than the rated watts of the immersion element.

Power into immersion is reduced if PV not enough. If PV more than full on immersion plus the house load you will export excess to grid as normal, but excess will be 3kW less, which is good. 

2) what happens if the PV is not sufficient and you want to use the grid as well

Just drawn grid power as normal, it does not go through this box.

3) what is fail mode and does it fail safe. Could it catch fire.

It is a smallish metal box with full fuse protection and earthing. Worst case scenario is failed output so immersion does not get a feed but rest of house will be normal. Box can't catch fire even if the internals were to self destruct due to component failure (unlikely as fuses protect from this), but I can't be responsible for the way in which it's connected to the house and so for any damage due to failure to comply with relevant regulations or user error, e.g. if you use too thin connecting wire to immersion the house could catch fire but not my box. Caveat emptor.

4) What might be the life span if used 24/7

I'd say >10 years at 24/7 and > 20 years at a typical PV output, which is only large for <20% of a year. But that is not a tested claim. Immersion element life will be lowered by the extra use it will get compared with say using gas for heating the water. But reduction is small because it will be running at low power most of the time. Life increased relative to a full on element on Economy 7. Also element is not difficult to change, unlike repairing a gas boiler. I offer a 1 year warranty; once it's run OK for 1 year to prove there are no niggling defects it is difficult to see why it would fail in the 2 - 10 year period as there are no moving parts apart from one irregularly used switch.
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brackwell
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« Reply #88 on: July 28, 2011, 05:17:43 PM »

Thanks,
Thats all good and its good to see you have considered the safety issue and covered your backside.  However i dont think there are any H&S types on here -its not in the spirit.

Ken
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cj
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« Reply #89 on: July 28, 2011, 05:46:35 PM »


Then 100W x 24 hrs is 2.4kWh/24hrs I would anticipate more than that from a 3kWp pv?


I think you mis read what I put. I compared it to ONE kwp costing £3k not THREE kwp. Also going on one days PV out put is also not what I said. You average what 1kwp can do per day over a year. Its less than a 100w constant power source can provide.

Water is just more reliable that solar or wind.

So even if all your other costs increase the £900 to £3k your still going to get more energy from the water. You might get more £ from the PV FIT's that from the water FIT's I dont know.

If I had a water power source I would use it rather than any other method. Install problems can be worked, not getting any sun / wind cant.

OK. The problem with Hydro is the infrastructure costs are so high, and for a low output system, the water 'extraction' licence route is not really viable. Dip the Jack Rabbit in the river (perhaps on a tethered floating pontoon might be, but no FiTs, make all the environmental improvements and the cost would soon be £6k - £20k, but not for 100w even 24/7.
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