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Author Topic: excess power from pv  (Read 35199 times)
JamesE
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« Reply #15 on: June 28, 2011, 10:38:02 AM »

That's only a 3A device, how does that work?
Er, you're right! It must have been some other one. Though I have strong recollection that that that is what I used, but I also had some fat ones at the time which were good for 10A+ which I used on the battery float charger. However the principle is right and it worked.
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michaelwr
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« Reply #16 on: June 28, 2011, 08:37:59 PM »

Looks like another buyer for Alan's Gizmoid, http://www.navitron.org.uk/forum/index.php/topic,9072.15.html

Makes me smile whenever I read it, looks completely dangerous but does a job.

Bodge-a-tastic!
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SnaxMuppet
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« Reply #17 on: June 28, 2011, 09:19:41 PM »

The good thing about EMMA is that it only sends power to the immersion if there is more power generated than is being used. BUT it is rediculously expensive and simply not worth the money.

We just decided to accept that we would export at 3p/kWh. It is only going to be less than 200 per year so we switched to Econ7 and use the immersion at night. It then only costs us 5p/kWh overnight and we get 3p back by exporting so our immersion only costs us 2p/kWh and I am happy with that instead of haing the cost of EMMA or complication of something home-built. 
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brackwell
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« Reply #18 on: June 29, 2011, 08:52:36 AM »

When I enquired about EMMA i now believe that for eg when you have say 1 Kw of unused elec the emma will allow the import of 2Kw grid elec to "drive" the 3Kw immersion heater for eg.

I am not sure this is what people are really wanting.  I am not good at elec but again when asking a heating element manufacturer i now believe you could put the say 1Kw excess into the "3Kw". It will of course take longer to heat the water and perhaps not to the same high temp if that is what is required ?  The problem is at the other end where if you allow more than 3Kw to the "3Kw" element it will not last so long as it will not be able to dissapate the heat fast enough.

Ken
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MikeD
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« Reply #19 on: June 29, 2011, 09:03:56 AM »

The problem is at the other end where if you allow more than 3Kw to the "3Kw" element it will not last so long as it will not be able to dissapate the heat fast enough.

Ken

As long as you keep to the normal voltage, ie 240v or so, you're never going to persuade a 3KW element to suck up more than 3KW. The resistance of the element limits the current and thus the power.

But I agree with the other bit - if I'd got a spare 1KW, I'd much rather use it to heat water slowly than either

a) export it at 3p (assuming export meter fitted) or
b) pay for the other 2KW so I can run the immersion heater at the full 3KW

So we need a suitable gizmo. I'll give it some thought....  onpatrol
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Jober
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« Reply #20 on: June 29, 2011, 10:58:10 AM »

So, all you EMMA sellers/installers - you will have to come up with a better price if you want it to sell like hot cakes!
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Sharp 235NU x 17 = 3.99kWp, SB4000TL, Littlehampton, Lat - 50.8069, South
Justme
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« Reply #21 on: June 29, 2011, 11:45:10 AM »

So, all you EMMA sellers/installers - you will have to come up with a better price if you want it to sell like hot cakes!

They also need to make it work better than was explained in a post above.


People want to STOP importing day time elec & use the "spare" PV not use the grid to top up the PV.

That is just stupid. They would be better off loosing the PV's 1kw export & using the 3kw E7 than buying in 2kw of day time power.
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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
Jonathan
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« Reply #22 on: June 29, 2011, 12:00:45 PM »


People want to STOP importing day time elec & use the "spare" PV not use the grid to top up the PV.

That is just stupid. They would be better off loosing the PV's 1kw export & using the 3kw E7 than buying in 2kw of day time power.

Not everyone has an E7 supply at home.
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Justme
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« Reply #23 on: June 29, 2011, 12:21:38 PM »

True, but then not everyone has PV either.

Either way using night time elec is still better as its going to get "lost" any way if not used.

Plus it would still be better to have the heater running at 1kw using the spare for 3 hours than having the PV topped up to 3kw via the grid for 1 hour. Assuming the tank get to cut off heat in one / three hours.
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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
Jonathan
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« Reply #24 on: June 29, 2011, 12:34:47 PM »

Justme,

I feel I must be missing something here. The subject of the thread means we are only talking about those with PV, so what does your first comment mean "True, but then not everyone has PV either."

Also what do you mean by "Either way using night time elec is still better as its going to get "lost" any way if not used." PV doesn't produce anything at night???

regards Jonathan
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Baz
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« Reply #25 on: June 29, 2011, 01:20:43 PM »

Not everyone has an E7 supply at home.
but everyone can get it if it makes ecenomic sense for them.
It should be possible to run on pv much of the day and E7 at night. The problem is the evening with neither and a lifestyle that maximises use in precisely that time slot.
So it comes back to needing a way of storing the excess pv for use in the evening. The grid provides such a solution but at what is seen as a huge premium. Batteries are just as expensive.
For some a change in lifestyle would help a lot.

Back to EMMA. The technical requirement is simple but the ecenomics relative to demand is still unfavourable, but should be improving with more pv installations. In effect it needs someone to come up with a design tht the far east can rip off and sell on ebay.
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Countrypaul
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« Reply #26 on: June 29, 2011, 01:29:36 PM »

When I enquired about EMMA i now believe that for eg when you have say 1 Kw of unused elec the emma will allow the import of 2Kw grid elec to "drive" the 3Kw immersion heater for eg.

I am not sure this is what people are really wanting.  I am not good at elec but again when asking a heating element manufacturer i now believe you could put the say 1Kw excess into the "3Kw". It will of course take longer to heat the water and perhaps not to the same high temp if that is what is required ?  The problem is at the other end where if you allow more than 3Kw to the "3Kw" element it will not last so long as it will not be able to dissapate the heat fast enough.

Ken

Based on this I can't see what EMMA does other than cost a lot of money. If you just use a 3kW immersion heater and are generating 1kw of PV, then you would import 2kw anyway no EMMA needed. Maybe I'm missing something?

Paul
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Other-Power
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« Reply #27 on: June 29, 2011, 01:33:39 PM »

When I enquired about EMMA i now believe that for eg when you have say 1 Kw of unused elec the emma will allow the import of 2Kw grid elec to "drive" the 3Kw immersion heater for eg.

I am not sure this is what people are really wanting.  I am not good at elec but again when asking a heating element manufacturer i now believe you could put the say 1Kw excess into the "3Kw". It will of course take longer to heat the water and perhaps not to the same high temp if that is what is required ?  The problem is at the other end where if you allow more than 3Kw to the "3Kw" element it will not last so long as it will not be able to dissapate the heat fast enough.

Ken

This is not how EMMA works!.
Please refer to the following PDF:

http://www.coolpowerproducts.com/documents/How-EMMA-Works-CoolPowerProducts-v1106a.pdf

Cheers

Jon
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My advice is based on me spending my money doing this and my job spending others money doing this.
Other-Power
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« Reply #28 on: June 29, 2011, 01:37:29 PM »

So, all you EMMA sellers/installers - you will have to come up with a better price if you want it to sell like hot cakes!

Coolpower know this and are working on this, I would say 2,500 would cover a 15 amp EMMA instillation, cheaper then solar thermal!

Coolpower also make a GVS or grid voltage stabilizing version that can be used to limit export where the export limit is less than that of the PV/Wind turbine can produce.

The EMMA only makes sense currently, due to cost, if you have 4kW of PV or a 6kW wind turbine and the demand for heat either hot water or space heating via thermal store.

I do love the idea of getting an EMMA unit that will drive a heat pump!

Cheers

Jon
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mellifera
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« Reply #29 on: June 29, 2011, 02:09:05 PM »

Trawling around the information super highway I came across 3 phase 3kW immersion heaters, they've got three 1kW elements. You could perhaps measure (with a clamp on current transformers) how much you're generating, and how much you are consuming. Subtract one from the other, add a bit of hysteresis and use the result to switch in 1, 2 or 3kW of water heating. You could even have an "open loop" design and just switch in the three 1kW elements depending on just how much you're generating - not as good but probably satisfies the old 80/20 rule. Just an idea.

Cheers, Mike.

http://www.tpfay.co.uk/OurProducts/immersion_heaters.aspx

http://www.cicn.co.uk/Merchant2/merchant.mvc?Screen=PROD&Product_Code=IIH3000-275&Category_Code=003


* large-element.jpg (56.19 KB, 300x300 - viewed 873 times.)
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