Electronic switching device...??

[NikNak]

Hi all..... this is pointed (probably) at the electronic wizards out there....
or someone who may have already encountered / designed / made / bought such a device


Ok.... so i've got some solar panels on the roof generating away.... the missus has gotten used to using all the lovely 'free' lecky and either irons/washes/ dishwashes/boils/bakes etc when the suns smiling on us..... no problems so far.

However... it would be nice to know that when either she is out or busy in the garden or whatever (and i'm at work) a little electronic gizmo takes over and detects that there is (sufficient) sun, no other devices are using the electric being generated and switches the immersion heater on, saving on gas to heat the water twice a day.

Should the sun be obscured for a few minutes or a kettle is now being boiled using the electric being generated, then the gizmo switches the immersion heater off until such time the sun is back or kettle has boiled. Make sense..?

Anyone know if this is feasible / been done / product already out there...? or am i just being a complete (door) knob....



Nick

or...... is this a dragons den moment.... :idea: :?: :!: :shock: in which case you haven't read this and i'm off to see Peter Jones (hammer) :mrgreen:

 

[MMUK]

It could be done easily enough using a photocell mounted somewhere by the solar panels. You can adjust the sensitivity easily enough on the decent quality ones. Just a matter of building a changeover circuit.

 

[NikNak]

Right then.... done some... ok.... a fair bit of googling.... and come up with quite a few 'gizmos' already out there.


So next question.....

Has anyone got one of these..? and is it working as you wanted it too..?



Nick

 

[Normancb]

One of my friends who is a professional electronics man built one, but it's not trivial, because the heater draws several kW, so you only want it on if the panels are generating enough. The final system uses a counter to look at a photocell watching the LED on the generation meter and switches a tapped transformer to vary the voltage on the heater, so as only to use solar power, not bought in stuff. As I say, not trivial.

 

[monkeybiter]

Not sure how these systems are conventionally wired but, if you could turn off just the bought supply to the immo' but leave the immo' switched on, then any harvested electrons would feed the boiler, maybe not full power but all stored not wasted.

 

[RogerS]

Sensing that sufficient power is available from the solar panels is a non-trivial task. However you want to further complicate things by having another circuit to detect that the kettle has been switched on and temporarily divert solar electricity to feed the kettle ! TBH the energy saving by doing the latter is not worth the bother IMO....remember KISS.

A quick Google came up with this

Use the excess electricity generated to generate hot water (medium)

One way of using excess daytime electricity in a more controlled way is to use it to generate hot water via an immersion heater. In order to be able to do this you will need:
a standard hot water cylinder with an immersion heater fitted
a PV (or wind) system ideally rated at 2kWp or more
the PV (or wind) system and immersion heater connected to the same consumer unit
an immersion relay to reduce the electrical consumption of your immersion heater from the usual 3kW to 1kW (alternatively to replace the existing 3kW immersion heater with a 1kW heater). If the electrical consumption of your immersion heater is not reduced in this way, there is a significant risk that you have to buy in electricity to make up the shortfall – costing you more rather than saving you money. But if your immersion heater is currently used to provide all your hot water (even if only at some times of the year), down-rating its output in this way is unlikely to be useful as you may find you have insufficient hot water for your daily needs.
a current sensing relay unit to detect how much electricity is being generated by your inverter and to switch over to the immersion heater at a set point – usually 1kW. This is done on the assumption that no more than 1kW is being consumed within the home and that any excess would normally be exported to the grid.
Immersion relay
Example of an immersion relay: picture courtesy of Chris Rudge

The advice in the UK is that hot water stored in a cylinder should be kept above, or periodically rise to, above 60°C to avoid the danger of Legionella bacteria. If your down-rated immersion heater cannot do this, you will need to ensure that your boiler comes on from time to time to provide this top-up heat.
This work needs to be done by a suitably qualified heating engineer: it is not a DIY job. The cost of having this kind of system installed is likely to be £300 to £500 including VAT. The amount that can be saved in this way will depend on the type of fuel that you would normally use to heat your hot water. The highest savings will be made if you currently use oil, LPG or electricity; the lowest if you use gas (estimated average cost 4.49p/kWh).
If you normally use gas to heat your hot water you will need to consider carefully whether it is more cost-effective for you to use the surplus electricity generated in this way - even taking account of the fact that your immersion heater will be more efficient than your boiler, the payback time is likely to be twice as long as for other fuels.

 

[JustBen]

Forgive me if I'm wrong but my understanding of solar panels/grid feeding is that if you are producing and not using, it gets fed into the grid for which you get paid (and if you're lucky, it's winding back your meter).
So it shouldn't matter when you use the units.
Unless there is a significant difference between what you pay for the units and what you get paid for the units.

My father in law has panels and he pays about £5 a month for gas and elec.

 

[RogerS]

And now we know the right words to use, eBay gives you this

http://www.ebay.co.uk/itm/Solar-PV-Imme ... 3f34f0f23d

 

[Myfordman]

Forgive me if I'm wrong but my understanding of solar panels/grid feeding is that if you are producing and not using, it gets fed into the grid for which you get paid (and if you're lucky, it's winding back your meter).
So it shouldn't matter when you use the units.
Unless there is a significant difference between what you pay for the units and what you get paid for the units.

My father in law has panels and he pays about £5 a month for gas and elec.

Yes there is a huge difference between import and export units. IF you have an export meter you get paid about 3.3p per unit and charged around 13-14p when you import.

Immersion control units such as Immersun make sure you never export anything and instread dumps the power into your hot water tank.

Either way you still get paid the Feed In Tarriff which varies according to when your installation was registered as this is based of what you generate and NOT on how you use it.

 

[finneyb]

Either way you still get paid the Feed In Tarriff which varies according to when your installation was registered as this is based of what you generate and NOT on how you use it.

Well I didn't know that !!
So basically the ' Feed In Tariff ' is incorrectly named - its an installation subsidy. The bigger the PV panel the more is generated and the bigger is the FIT.

Anyone any data on how the generating power of a PV panel degrades with time?
And does this matter?

Brian

 

[dickm]

Will be interested to discover how generation degrades with time; our panels have been in since 2010, and as far as it's possible to judge, generation efficiency hasn't changed. Cost a lot to install in those days (2 or 3 times as much as now) but we do get the 45p plus FIT and a further 3p on half of the recorded generation.
After a while, as the OP says, you get used to putting dishwasher etc. on at times of max generation, which also helps. Not convinced that the complication of electronic control of dumping any excess generation into hot water would be worthwhile. We are on a 3 period "cheap" (who are they kidding?) tariff, which drives the timed immersion heater for 2 hours every afternoon, so we probably get a lot of the benefit already.
Now we just need to get SSE to pay a bit more promptly .

 

[JustBen]

My only experience with solar panels is what my father in law has shown me.

He has had his for about 3 years now and it's all been good so far.

The estimated figures he was given have be surpassed which I was surprised at.

He has a computer program that records all the data and adds it to a database/graph so he can see what was produced and when.
All very interesting if you're a bit geeky and like numbers..... Like me.

I think originally the life span was about 10 years but I think it's a fair bit longer than that now.

As for degrading, he hasn't seen a drop in production although the weather is variable so would be hard to measure in a real scenario.

He was told 7 years to break even but it's looking like it will be 6 to 6 1/2 years now, so that's good,

 

[gregmcateer]

For what my panels produce in total (whether or not I use the electricity or feed it back to grid), I receive 45p per kwh. In addition, there is an assumption that I will only use half of what I produce, so I get and additional 3p per kwh for half total produced. All of the above is increases with RPI for I think 20 years.

We tend to set the dishwasher and washing machine to run during the day at different times (and don't let the kids turn on lights unless it's sunny outside :wink: )

HTH

Greg

 

[woodshavings]

The Solar iBoost is the device that you need.http://www.biggreentechnology.com/renew ... eater.html
It switches on the immersion heater whenever there is spare power.
HTH
John

 

[Phil Pascoe]

For what my panels produce in total (whether or not I use the electricity or feed it back to grid), I receive 45p per kwh. In addition, there is an assumption that I will only use half of what I produce, so I get and additional 3p per kwh for half total produced. All of the above is increases with RPI for I think 20 years.

We tend to set the dishwasher and washing machine to run during the day at different times (and don't let the kids turn on lights unless it's sunny outside :wink: )

HTH

Greg

I'm truly delighted to know that I'm subsidising your electricity.

 

[NikNak]

Thanks for the replies so far guys.....


and yes.... to those that are unaware.... you get paid for every Kw you generate, plus its assumed you will only use half of what you generate and the other half is returned to the grid, so you also get paid for the assumed 50% returned to the grid (in reality most people will only use 1/3 of what they generate)

So in our case a 14 panel array capable of producing 3.5Kw per hr at best actually produced 3373Kwh last year. So we got paid 3373 x 14.5p per Kw generated, and a further 1686.5 x 3p per Kw returned to the grid. Plus the energy savings by using all the electric items during peak generation instead of 'buying' the electric saved us a further £120 approx.

But..... it would be great if we could just tap into that energy that's 'wasted' i.e. generated but not used, by heating our hot water tank thus saving even further by not using gas.

And a further yes.... everyone (as i understand it) is paying for all these subsidies on their bills whether you (are able) take advantage of them or not. Everyone's bills went down not so long ago by approx £50 per year(?) that's because the subsidies available for home insulation etc has all but dried up.


Nick

 

[gregmcateer]

For what my panels produce in total (whether or not I use the electricity or feed it back to grid), I receive 45p per kwh. In addition, there is an assumption that I will only use half of what I produce, so I get and additional 3p per kwh for half total produced. All of the above is increases with RPI for I think 20 years.

We tend to set the dishwasher and washing machine to run during the day at different times (and don't let the kids turn on lights unless it's sunny outside :wink: )

HTH

Greg

I'm truly delighted to know that I'm subsidising your electricity.

I thank you, sir. You're not as delighted as me, I can assure you :lol:

 

[graduate_owner]

I think the additional payment on everybody's electricity bill also helps to pay for the energy generated by those delightful wind turbines which so elegantly add to the beauty of our skylines.

Back to using solar energy, does anyone have experience of these solar pv water heater devices?

Regarding drop in efficiency, our installer reckoned they drop by typically 18% in the first few years, then stabilise. I don't know if that's true, or if it applies to dome makes and not others. What I have noticed is our generation display can show say 2.5kW on a clear, cloudless summer day, and 3.5 (instantaneously) when the sun peeps out from behind clouds in early spring. I think it's because the efficiency of the panels drops as they get warm, but I'm not sure. Perhaps I should have a solar powered water pump spraying water over the panels to cool them by evaporation.

K