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Hi Alan,   I'm in the same position.  

My next step was:-

I was given an old 24V 1.4 kW UPS.   I've removed the old internal batteries, and upgraded to some 12V heavy duty car batteries in series.   

I can charge the batteries with two 12V heavy duty chargers which I have, but the biggest problem as mentioned elsewhere on this site is is inrush current to the transformers, and voltage spikes on the way out.  I've heavily snubbed and current limited the SS switch, and although this obviously works better in MK2 A/F mode it is very inefficient, but it was to prove a point.  In most of the day it's fine, but the 'chattering' of the switch either end of the day, or in cloud is slightly disconcerting.

I have two clearly identified UPS sockets in the house, one for the computer/childrens' game room, one for the TV, and they automatically switch over in the evening, currently they run for a couple of hours, on spare, inefficiently collected energy collected through the day.

I'm currently repairing two 10 Amp Farnell switched mode power supplies (again which I was given) which I'm hoping are more happy being pulsed --- yet to be proved.

My switch mode supplies can be programmed with a variable output voltage, so back to the books to see the best strategy to charge 12V car batteries, as quickly, and as efficiently as possible during daylight 'over production' hours.

I accept this in very inefficient but with in my case free batteries, free UPS, free chargers and plenty of development time, two hours of evening computer use for free, it's another way of reducing the bills.  :-)

If your interested when I've replaced all the X and Y class caps in the switched mode supplies, I'll let you know progress.

The key to this for me, is all the bits were free.

Simon

My suggestion for your battery chargers is to switch the d.c. side. OK, you've transferred the transformer / smps losses onto your fixed load, but you are no longer switching the transformer inductance or starting up the smps every few seconds.

I use Eltek chargers and they work really well though they are more common in 48v. The only thing I had to change in them was a small relay to one exactly the same except for the material the contacts are made from.

If that hadn't worked I was going to do what Robert has just suggested. Quality DC SSR's do seem quite a bit more expensive than AC ones though. I did get some on eBay in readiness but never used them so can't comment on quality.

Yes, good idea Robert.  As you say then I've transferred the transformer/SMPS losses into fixed load but that is not so bad in a no load i.e DC side open. 

The priority of this load is no 2, after the immersion heater, and before other resistive loads, which works well, it minimises the chattering of the current charge system.

Just reading up on best battery charge curves/characteristics, will have a go at switching the DC side and see how it goes.

Certainly first version works well, but probably stressing the switch, even with snubbing....

What seems clear is when everything else has been fully charged/heated, and we still have spare energy there becomes a need to save every last drop, it's an addiction.

Next I was going to build a water tower - no not really!!

What you really meant: "Next I was going to build a water tower heated swimming pool and a heat pump for the winter months - no not really!!"

I tried to do the sums once and, bearing in mind massive assumptions, it seemed it would only go part way to providing the heating for the winter. If anyone else wants to have a go...

It has crossed my mind but it would have to be a big pool! I have a 15ft above ground round one and it's been like having a bath at times if I've forgotten to turn the heat pump off!!

I've just done the sums again - assuming no losses at all, and that you can get the "pool" to 100°C throughout at the end of the summer, and you draw out 3 kW of heat for 15 hours a day for 100 days over the winter to take the water down to 0°C, you need about 40 m³ of water. I can't even begin to guess what the losses might be.

Here is a question,

Why are you diverting, is it because you don't get any credit for the power you feed back into the grid ?

In the UK it is not the norm to have an export meter (yet) the meters in use are usually only capable of measuring import. The exported amount is guestimated to be 50% what you produce.

Therefore solar PV attracts a "feed-in" tarriff subsidy for each Kw produced plus a small purchase price for half of that Kw as it is assumed to be exported.

So the bottom line is you get paid an amount set by generation regardless of whether you export 90% or 10% therefore the intention is to use as much as you can as it is effectively free electric, hopefully offseting/reducing the energy purchased when the suns not out in the process.

Paul 

Another storage device in the home is a fridge/freezer.  But we need to make it use power when the sun is up. I have been considering turning mine off for say, a couple of hours before dawn. Has anybody tried this?

I haven't tried it but I have considered it since the freezers we have in the garage have something like a 18hr safe period for power outages etc. So in theory these could be switched of in the evening and start back up in the AM on PV without any problems..

However I didn't really see enough gain to justify the risk, as overnight we have a Economy7 tariff so it's around a 1/3 of the price and so if the sun doesn't reliably come up before the freezers have to be powered up they are costing 3 times as much to run, therefore if on average 1 in 3 mornings is gloomy I'm not gaining.

Add to that the possibility of a powercut on a gloomy morning ruining hundreds of pounds worth of food led me to the conclusion I was over thinking power management stuff and it was better to leave it alone :-)

Paul

Slightly off-topic question sorry, but in the UK how does your supplier obtain the 'generation' total from your PV panels, in order to calculate the FiT? Is this automated or do they have to send a meter reader to check the inverter total each month?

To get the FiT you need an approved generation meter fitted, Then every 3months you submit a meter reading online, pretty much the same way the import meters get read in a majority of cases. Except if you don't submit an import reading you still get billed an (over)estimated amount where as if you don't submit a generated reading you get nothing, so you sort of claim it in a way, I guess.

Right - so it is an extra meter. Thanks for clarifying that! Certainly a great way of billing if you are smart enough to employ PV diversion! A little bit jealous we don't have that down here in NZ...

Understood,

In South Africa we have load shedding all the time due to the miss management of the state utility and it being severely overloaded , we have been trying to get them to understand that sustainable energy is good for the country and if everyone can help if would be good. But alas they don't seem to understand, finally government has agreed to allow this but it's up to each municipality/council to manage and decide for them selves if it's allowed is said council.  I most council their revenue is made up by 85% from income from the electricity they sell. So with that in mind they have been dragging their heals to implement facilitation of this for 5 years. 

The only fortunate thing is I have an old mechanical meter which rolls backwards when I feed-in and due to the councils efficiencies they don't know how to stop this. All that said it's extremely frustrating that we have a government that is not intereted in evolving and developing.

So with the old mechanical meter you sort of have net-metering like they have in parts of the US where you just pay for what you import over and above what you export. that's probably not a bad thing as I'm guessing you would pay more for each imported Kw than you would get selling it to the grid.

It could be worse, in parts of the world, like Spain I believe you actually get charged for exporting to the grid so diverting has a different purpose there. It just has to dump the energy anyway possible, rather than export to avoid charges how wasteful is that ?  

Paul

Yip, Cape Town is 1 of 4 councils that support Net-Meetering and will pay to the same rate as the pay the utility for power "45c" and the sell it on for R1.45. After going through a few hurdles it can be done, however 90% of Cape Town have prepaid meters and should you export the unit's climb rather than decrease, so like Spain unless to install and get registered with the council one would have to divert or they would be charge at the same rate as when they import to export.

I am lucky, only thing is I have to fly under the radar until my council wakes up, I currently have  a 2kw array and busy installing another 3kw, this should reduce my total usage from about 2000 units to 500 I have had to install these over the last 2-3 years for fear that the council finds out. At this point I can't add anymore else the council would assume I am either using too little or I a have tampered with my meter or I am stealing electricity (which happens allot here). I have capacity to install 10kw but can't until it become legal.

But it's cool I am watching this thread in the event I get caught and need to implement diversion.

But it's cool I am watching this thread in the event I get caught and need to implement diversion.

No problem, several "Mk2" systems of mine are already operating in South Africa :-)

Robin

www.mk2pvrouter.co.uk

Does anyone know the history behind the location of the "generation meter" in the UK?  It seems had they installed that exact same meter beside the import meter (electrically) then it would measure exports rather than generation.  I wonder what the logic was for wanting to measure generation, rather than export?

Most of the FIT payment in the UK is for generation, hence the location of the extra meter.  The term "Feed In Tarriff" is not helpful since it conveys the wrong message.   Logically, one would expect a "Feed In Tarriff" to be paid in accordance with the readings from an export meter.

To encourage people to put panels on their roofs, some financial encouragement was required.  By linking these payments to the amount of energy that was generated, the payback rate could be more or less guaranteed.   If payments had instead been predominately based on the amount exported energy, fewer householders would have been encouraged to put panels on their roofs.  At least, I assume that was the thinking.

Getting PV panels onto roofs is part is the UK's plan for meeting its carbon reduction targets as imposed by the EU. 

Ok fellows I am new to this site but I am quite clearly confused.  Have you all not noted that you cannot achieve EMC compliance by modulating power over 200w by using Phase Angle technology! Therefore you cannot add a CE mark to your device and that will mean it would be illegal to sell!...

I think that some more research should be made!! 

Most systems here do not use Phase Angle control, they use Burst Mode control hence no EMC complications.

If a CE-approved SSR is used for implementing Burst Mode control, then the system is effectively CE-approved

If a diverter system is built for home use, then it is not being sold.

OK?

I use one of Robins units to divert to a kitchen floor but as it only draws 1kw the other 3kw often goes to waste so I sometimes use it to charge my BEV (Nissan Leaf). Most PHEV/BEV cars use either a J1772 or Type2 inlet and monitor a 1000Hz Square wave sent by the charging station or EVSE. The duty cycle of this 'pilot' signal can be modified by the charging station to lower the charge rate from the chargers maximum to a minimum of 6A (per the spec).

Many charge stations contain a din mounted EPC unit to deliver the pilot signal, this unit is often made by Mainpine and has the ability to accept a fixed resistance across two pins allowing charge rate to be set manually i.e for a given resistance cap the max rate:

196  ohms 6A
237  ohms 9A 
267  ohms 11A 
348  ohms 16A 
732 ohms 32A

Using modified EmonRX code and a digital pot is how I charge the BEV.

I did a video a while ago showing the veroboard version, It was a bit of a jumble as the sun wasnt very good that day!

https://www.youtube.com/watch?v=T3kcoCcrKSg

https://www.youtube.com/watch?v=2mj1wM2mxwk