Use of excess PV generation

[rogeriko]

A much simpler solution would be to take a small cheap solar panel and a DC relay with a couple of resistors and adjust it so that the relay operated only in full sun but not when it was cloudy. This relay could turn things on and off depending on the power of the sun and of course would operate in tandem with your existing panels.  Anyone care to make one and market it go ahead, probably sell well.

[cj]

A much simpler solution would be to take a small cheap solar panel and a DC relay with a couple of resistors and adjust it so that the relay operated only in full sun but not when it was cloudy. This relay could turn things on and off depending on the power of the sun and of course would operate in tandem with your existing panels.  Anyone care to make one and market it go ahead, probably sell well.

There is surely a much more efficient and accurate way of comparing generation to consumption?

Apart from the morals of using PV to heat water, as opposed to say oil or gas, it is all energy, better to use renewable than fossil, and we are all being encouraged to change energy use by taxation, so lets arrange our generation most efficiently. It seems odd if not iniquitous that we import at 12p - 18p unit, but only export at 3.1p. Yes they need mark up, but that sounds very inefficient. At least we are using our OWN investment capital to save the world's fossil fuel, it is saving power compared to having the system switched off or the money left in the bank at zero interest ie minus interest after inflation, by never having had the installation done.

Anyway back to the point, how COULD a system be designed to use excess power more effectively?

Wrap a coil of wire, or have clamp on monitors on the PV single wire and the house grid supply conductor, and compare the two. Use this to switch on a 1kW upper, or a 2kW lower, or both, depending on whether total EXCESS power is 1, 2 or 3kW.  Thus has the advantage it works with any type of inverter, need to electrical connection on the sensor side, and does not switch on for a predetermined time in sun/cloudy intervals, nor need a separate pv array sensor that may react differently to the main PV array.

Technically one coil round the grid, in series with one coil round the PV in ANTI PHASE, compare that to one coil just round the grid. If we import more, or they are the same, we do not switch on the immersion, if we are exporting more than 1, 2 or 3kw the  appropriate relays are operated to switch the appropriate contactor for the immersion heaters.  (obviously some historysis is required to be built in)                                                         

[michiel]

How about Coolpower's "EMMA" system?
Not cheap, but can be efficient in the right installation.

[Justme]

How about Coolpower's "EMMA" system?
Not cheap, but can be efficient in the right installation.

It might be electrically efficient but its def not cash efficient.

[michiel]

As I said, in the right installation, with a large enough 'overproduction', and a large enough store (pool) for diverted (immersion) heat, it can be efficient.
You can not generalise!
I agree, it would not be efficient on a 2.5kW PV / small bungalow setup!

[guydewdney]

been there. Done this. Got the magic box that does exactly this - in 500w steps, with two lots of comparison clamp meters, for each phase.

[Justme]

As I said, in the right installation, with a large enough 'overproduction', and a large enough store (pool) for diverted (immersion) heat, it can be efficient.

You would be better off spending the money on a solar thermal system to heat the pool.

All this "I must use all that I make" shows what a sausage state this country is really in. Everyone is only in it for themselves. The FIT's that encourage self greed should be changed pronto. People will be using more total energy just because it there. We should be using less & only using it for jobs that other power sources cant do.

Real off setting of energy is ok but to use more just because it is there is madness.

[billi]

will we see people washing their cars with hot water in summer on a daily basis ? 

[cj]

As I said, in the right installation, with a large enough 'overproduction', and a large enough store (pool) for diverted (immersion) heat, it can be efficient.

You would be better off spending the money on a solar thermal system to heat the pool.

All this "I must use all that I make" shows what a sausage state this country is really in. Everyone is only in it for themselves. The FIT's that encourage self greed should be changed pronto. People will be using more total energy just because it there. We should be using less & only using it for jobs that other power sources cant do.

Real off setting of energy is ok but to use more just because it is there is madness.

What energy is being used just because it is there? That is dumb, but DHW is required, using 100% efficient self generated PV is better than all of the losses of the distribution over the network. Mains gas is compressed and decompressed wasting power etc.  I for one have looked at thermal set up, but it would be exceedingly expensive and would never pay for itself as a retro fit. (New tank, carpets up, etc etc) I am not going to provide a £7k subsidy just to have a 'feel holier than thou' factor or to stop others ranting I should have thermal solar. Thanks, but no thanks.

Prices and taxes are set to encourage sensible use of resources. If not, they need to be changed. As I say importing at 12p or 18p and exporting at 3.1p is not the way to encourage NOT using your own production.

Guy, is there any published info on an incremental use system, or does the wheel have to be reinvented? 

[guydewdney]

sorry - no - the system was made bespoke for me by Alan, who no longer posts on here, and I have no idea how it works - its a big eeprom chip in it though.....

[Ben55]

I'm probably going to start a fight and get shouted at by everyone, but I'll take a punt anyway.

Maybe I'm being a bit socialist here, but what's wrong with letting the excess go to the grid, isn't that a very 'we're all in it together' approach?

If the excess can be 'bottled' efficiently then fine, but if system losses are high isn't it more socially acceptable to send it round to your neighbours?

Please, please, please don't take this as an insult, I just wonder what is more efficient. If export was accurately measured can you get 3.1p worth of returns, or is it just the perception that all unmeasured export is technically free at the moment.

I have no agenda here, I'm genuinely interested.

Cheers    Martyn   

I guess we all have a different situation.

I'm planning to get my hot water heated during sunny days, using my fair share of the solar juice, maybe 50% of it.
I've added loads of extra tank insulation,  so the water holds the heat till evening.

Mowing, and some washingmachining yes; but not every day...LOL

I won't be designing complex circuits to utilise  100% of the spare PV; I'll let the neighbours have some

A timeswitch will ensure that the immersion heater is on during brightest hours, say 11am till  3pm BST

And I've bought  a transformer to give half the volts, ie 1/4 the power, ie 750watts, which summer days should cope with easily.