Immersion Heater - PV electricity

[old grouser]

I'm an idiot (in the Greek sense of not being one of you guys who understand electrics) but I do have a solar pv system and a conventional 3kW immersion heater, and I recognise that there is an obvious need for a system to store surplus electical energy as hot water. So there's an obvious need for some sort of switching/power reduction device of the sort you are collectively developing and discussing, and there's no reason why it should be particularly expensive, since (forgive the idiot language) it's really just an intelligent switch (I could do it myself if I sat in the airing cupboard all day with my Sunny Beam, waiting to turn on the immersion heater at those magic moments when the generation reached 3kW. Of course, it would be better if I could divert just the available surplus generation... but even I can see that this isn't an insuperable problem....). What is clear to an outsider is that there will be a sizeble market for this sort of product in, say, five years' time; that it's understandable that people would want to protect the value of their ideas; and that it's laudible that people should want to benefit us all by producing a collective, open source solution. Probably the commercial model will win; but it doesn't have to be patented. Volvo developed the 3-point seat belt, and deliberately didn't patent it. It's a commercially viable idea nevertheless. Lots of people make them. Presumably they all make a living from them. I hope that between you you'll produce a cheap, safe, viable and marketable solution soon, and that everyone will benefit. I'm impressed that you are trying...

 

[bradburts]

Not only because it wouldn't be worth it but because there would be no legal grounds to do so.

I think that the EMMA patent covers use of phase controllers.
inie meanie has downloaded the PDFs and I have posted links.
I would be interested in your and other's views as I am new to the language of patents i.e. do these patents cover a specific design or do the patents cover all designs, used in this PV context, which embody a phase controller?
Again I find it hard to understand how a patent may restrict designs which use well understood components, its would be like saying that a resistor were part of the patent claim and that therefore all solutions which use resistors are covered by the patent. Daft.
Anyway would be interested in views as the systems on offer are very expensive and competition (open or commercial) would be best.

 

[inie meanie]

I think that the EMMA patent covers use of phase controllers.
inie meanie has downloaded the PDFs and I have posted links.
I would be interested in your and other's views as I am new to the language of patents i.e. do these patents cover a specific design or do the patents cover all designs, used in this PV context, which embody a phase controller?
Again I find it hard to understand how a patent may restrict designs which use well understood components, its would be like saying that a resistor were part of the patent claim and that therefore all solutions which use resistors are covered by the patent. Daft.
Anyway would be interested in views as the systems on offer are very expensive and competition (open or commercial) would be best.

Hi Bradburts
Basically the Patent covers the principal of a household load management system that allows the spare electricity to be dumped into another house hold load. Ie. Immersion heater. I am not sure if this patent has actually been granted or is still in the applied format. If it still is in the applied state then there probably isn't too much chance of it being granted as so many other people are all working on other types of load management. It might be a bit of a scare tacktic to halt the competition.

 

[bradburts]

Hi,
U sure? M
y understanding is that the EMMA patent was registered 2 years or more ago. Others may work in this area now but as I understand it if the original first published 'design' is the patent then EMMA people have the rights.
I would be interested & very pleased to be shown to be wrong.

I have no experience of patents but as I understand it the patent falls if others have discussed similar designs before.
Please post if any such designs found.
I am sure that Star Trec have many episodes dealing with energy & load management (the crystals are always failing). Wonder if some solar powered space station attacked by klingons used load control. I'm off to check.
I'm working! I will tell the wife as I go through the last 40 years of scifi.

 

[old grouser]

I don't know much about electricity - I assume it's like plumbing but with smaller holes for the electricity to pour through - but it has just occurred to me that I do have an old friend who is an intellectul property lawyer. I'll try to get him to look at this thread and report back. (This may take some time...keep on inventing solutions...)
OG

 

[bradburts]

That would be great.
I have been researching some more & the following seems relevant:
1) (1974) Load management detailed in U.S. Patents 4,241,237 and 4,455,453 and Canadian Patent 1,155,243 (Apparatus and Method for Remote Sensor Monitoring, Metering and Control)
2) 'Smart grid' as used in 2005 "Toward A Smart Grid", authored by S. Massoud Amin and Bruce F. Wollenberg appeared in the September/October issue of IEEE P&E Magazine (Vol. 3, No.5, pgs 34–41)
Seems to me that the EMMA system is a form of 'economic demand response' that is to say it costs you nothing to use the PV and costs you to use the grid. Selecting one supply or the other is therefore an economic demand response.
I was very happy to find that load managment has been discussed since 1974. I think therefore that there is nothing to worry us in the patent, just the difference between macro and micro grids.
I also found reference to office lighting systems which dimmed as a response to grid load.
http://www.lrc.rpi.edu/resources/newsroom/pdf/2004/LoadShed.pdf
I suppose therefore/also that I/we could offer systems which dimmed lights (say a 3KW system for those with big houses) when PV output was low & before we start to tax our fragile grid.
The light is not an energy store (as discussed by EMMA) and light dimming has been done before, see link above.
Of course I would be powerless to stop someone fitting the dimming device to an immersion heater..........


Think inie meanie was right. Would be great to have a proffessional's view though!

 

[suntrap]

The difference between patent theory and practice is that even if a patent is ultimately invalid, if the company holding it decides to prosecute you because you are selling a product that infringes it, you could spend a large amount of money defending yourself in court.

 

[bradburts]

The difference between patent theory and practice is that even if a patent is ultimately invalid, if the company holding it decides to prosecute you because you are selling a product that infringes it, you could spend a large amount of money defending yourself in court.

Agreed.
I hope however that as the prosecuting company would need to spend money they would not, especially if there is a lot of 'holes' on clear display!
I will post as many 'holes' as I can find and hope that the wiser explain their validity.
I hope that somewhere along the line someone will think that the route is open for their own system to go to market but at a much lower cost.

BTW, old growser,
You're right, the control systems being discussed are quite simple. A microcontroller monitors both PV generation and home use using a pair of current transformers. The microcontroller then controls the amount of power going to the immersion heater using a phase controller. A phase controller is a posh name for the circuit in your light switch dimmer, it works by switching the AC on some way into each AC wave cycle and therefore limits the amount of power being transmitted in each cycle.
Some are using simply relays which have the advantage of being even simplier to design. The problem with a relay solution is that a relay cannot be switched on/off within the AC wave and therefore a relay will clock any meter at the relay's load's rating, typically 3KW for an immersion. The relay's PV generation trigger point must therefore be much higher than the phase control system. Using a lower watt immersion heater lowers this threshold but at cost and hastle. Adding a diode in series would reduce the 3KW to 1.5KW. Your trigger point PV generation would then be, say, 2KW, 1.5KW for the immersion and 0.5KW for the home.
You're right you could be the control system by sitting in your airing cupboard, with unemployment and energy prices going the way they are you may be able to employ someone to do this, start a company and see if you can get an intern! Technically you would be open to prosecution (if you think that the patent is valid) though as 'a switch' is described in the patent, the patent also covers Thyristors which suggests use of a phase controller (which is just a more advanced switch synchronised to the AC waveform).
Most in this forum (it would seem independently arrived at design that) think that a phase controller would be the best way to go. By far the most effective system is a phase controller as it allows you to control power dumping with a high level of resolution thus sucking up all the excess power rather than having to reach a generation threshold related to the immersion heater's power rating.

 

[suntrap]

Phase controllers (despite my intention to use one) have two disadvantages:

- they generate heat
- they generate electromagnetic interference, which to suppress properly (i.e. to comply with regulations for a commerical product) is bulky and expensive for this sort of current

Actually, aren't there regulations stipulating that power factor correction is needed on any appliance drawing over a certain amount? This would add even more to the cost. And the use of a simple diode to reduce power consumption by half would also need power factor correction in this case.

There's no reason why an immersion heater controller should need to sense both house and PV current; if it gets a sniff of the voltage waveform you can tell which way the current is flowing in a meter tail so one current transformer is all you need.

 

[bradburts]

Hi suntrap,
Having just one CT would be a nice simplification.
Forgive my ignorance but how would you sense the direction by looking at the voltage waveform?
Your right power factor will drop. I recently scanned the low voltage regulations looking at CE marking but did not see anything about power factors. Do you have a link?
I agree heat could be an issue. I gather that Rds values can be really very low these days though.
RF is always fun. Best bet with RF is to sacrifice a cat under the full moon, that’s what the RF engineers I know do, I'm sure.
What do you think the EMC problems would be?
I am not sure that there would be a major EMC problem though.
I have read a few application notes and have not seen any mention of EMC, the application notes are very detailed as well (enough for a softee like me to understand!).
Also I don't remember the EMI rules forming a distinction between continuous emissions and discrete and a relay switched on or off would chatter albeit for a short duration.
A phase controller would pulse giving you a step at 50Hz for sure.
13Amps is a lot to switch but how many multiples before we get to a regulated band?
Have you done any calculations? Is the simple on/off at 50Hz circuit in the face of the standards or marginal?