Managing and using your generated power - a whacky idea?

[ProDave]

P = I x V is indeed correct.

But more important. P = v2/r (Voltage squared over resistance, can't do superscript on the forum)

The resistance of your immersion heater remains the same. So by running the heater on a lower voltage, it will consume less power.

Apart from losses, power in = power out on a transformer, so the power in to the transformer will be just a little more than the now reduced power of your immersion heater.

So a 1KVA site transformer will be plenty.

In my case, I had a 500VA autotransformer. I little under rated but I tried it and it works, and it hasn't melted. yet.

 

[Borwick]

Dave,

Many thanks for clearing that up - off to eBay now!

My "control" system will be much less swish than yours. I have a 3.8kW array but in Cumbria, there are a lot of days when it just won't be enough to power even a downrated immersion heater together with the basic household usage. So, I am just going to have a 2 way switch on the inverter so I can flip the system back to mains. I can even use that without the inverter on one of our few sunny days.

I have resigned myself to just getting a hot water subsidy from pv rather than a "freebie" but the inverter will greatly help with that.

I saw a less refined system where there was a relay to the immersion linked to a photo sensor in a watertight jam jar on the roof so when the sun shone strongly, the immersion would come on.

Many thanks,

Jon

 

[steptoe]

Hey Borwick, where abouts? Im in Skelwith Fold (near Ambleside) today doing a solar,.

 

[ProDave]

I saw a less refined system where there was a relay to the immersion linked to a photo sensor in a watertight jam jar on the roof so when the sun shone strongly, the immersion would come on.

That's not good in my opinion. What if your washing machine is on or some other high load appliance?

My system and many of the better ones on sale take into account load in use.

Example. It's sunny here today. The dump load was on. I've just boiled the kettle for a cuppa. As the kettle went on, the dump load switched off. When the kettle had finished, the dump load came back on. Same if the washing machine or dishwasher was on etc. So the dump load ONLY comes on when there's spare exported power to be used up for free.

 

[NozSpark]

You know what Dave, you ought to package it and sell them (maybe as a kit)

 

[ProDave]

You know what Dave, you ought to package it and sell them (maybe as a kit)

I've thought about it but haven't had time. Perhaps a project for the dark winter days.

 

[Borwick]

Hey Borwick, where abouts? Im in Skelwith Fold (near Ambleside) today doing a solar,.

Millom. Not the best weather to be up on a roof!

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That's not good in my opinion. What if your washing machine is on or some other high load appliance?My system and many of the better ones on sale take into account load in use.

Example. It's sunny here today. The dump load was on. I've just boiled the kettle for a cuppa. As the kettle went on, the dump load switched off. When the kettle had finished, the dump load came back on. Same if the washing machine or dishwasher was on etc. So the dump load ONLY comes on when there's spare exported power to be used up for free.

Dave,

Your system is far more swish than what I am putting in for the moment. However, it won't be without refinements. The transformet has 2 outlets and the tank cupboard is next to the kitchen, so I will keep a kettle in there too!

I am doing work on the house and lots will change so when it has settled down, I will refine the set-up. Perhaps even buy myself one of your kits for Christmas ... ! Many thanks.

 

[WorcesterRenew]

The Arduino and RPi projects are excellent solutions - see also http://openenergymonitor.org/emon/ and the stuff on there about controlling an immersion.

Wondered if anyone here had looked at the ImmerSUN - a commercial product that is affordable and fully proportional, i.e only uses the 'spare' generated power.

 

[Borwick]

Just to chip in that I have now connected up a 3.3 kva site transformer to my 3kw immersion heater.

I have tried to show the crude wiring in my avatar. I did not want to change much in case I did not like the result.

Anyway, it works! The draw is metered at around 870w and this falls seemingly as the water heats up. Current is around 4A.

When I connect a kettle, I find it has a similar draw and boils a pint of water in around 3 minutes, so useful but not when you are parched!

When I want to use the immersion without the transformer I can attach an adapter to the lead with a female 110v connector and a 3 pin plug on the other.

The only minor problem is that the contact breaker by the main switch board tends to trip out eery 4 or 5 goes. Perhaps I need another contact breaker.

The kettle does not switch itself off when it boils, perhaps this is because it is an old kettle. Fortunately, the thermostat on the immersion heater does cut out when the water is hot.

Mine is a top-mounted immersion heater and I have not yet explored whether the whole tank is getting heated or just the upper part. I expect that there will be sufficient convection for the whole of the tank to heat up even with the less powerful heating effect.

Middling day in Cumbria yesterday and managed to fill a tank with hot water over the afternoon with no contribution from nPower, thanks!.

 

[binky]

ImmerSun ain't exactly cheap, seems to be the new bandwagon game to jump on!

Dave, how about selling your design rather than building a product?

 

[Jon Walker]

ProDave - You're not not bonkers or a Twatt (nice photo by the way), but you have got too much time on your hands!

Why not just buy an ImmerSUN which is the solar geeks wet dream, as it powers up the immersion from the surplus PV in 1% (3W) increments up to 3kW, more details here: