Power meters and Solar Power

It's not fair to force them to buy power at their retail rate.

jsw

Who said it had to be fair?

Regards, Tony

In the fullness of time, smart meters will be able to register exported power as well as imported power. However, the amount paid for export is so low (currently 3p per unit) that it is better to try and arrange to consume as much solar power generated as possible. eg Do the washing when the sun is shining!

Bob

Here in Oz, if we install solar systems, any energy in excess to our use is purchased back by the supply authorities at a highr rate than that at which we buy it, so it is in our interest to have them meter all of this "negative" stuff separately, with a special meter.

JW²

It is said that in UK we will get 'smart meters' that will cope with this but for now separate meters are used for import and solar generation with an assumption that 50% of power generated is fed back to the grid. Solar microgenerators are paid about 4x the import purchase price for what they generate.

Bob

Oh they do register it, they also trigger an LED on the meter and set a flag in the data that is read by the handheld meter reader such that the meter owner knows immediately that an attempt has been made to corrupt the meter readings - usually by the use of an external 'black box' connected by nails through the cable either side of the meter.

A number of the old style disc meters also couldn't run in reverse either, pure mechanics in that case rather than a bit of software in the new ones. That didn't prevent meters from being slowed or being near permanently stalled but it stopped them being wound back by 'black boxes'

If you want a digital meter to accommodate import and export all the energy companies in the UK will fit them on request *if* you have appropriate protection in place to prevent islanding.

The metering is absolute. There is never *any* assumption.

There are two meters, one on the local generation that meters all its output (effectively this is fed into the household side of the system) There is another meter on the external connection to the grid that measures all import (consumption)and export (generation) by the premises

Under the feed in tariffs you get paid for what you generate regardless of local consumption at one rate. You pay for all you import from the grid at another (much lower) rate which is usually the same as all other consumers.

Circa 40p per kWh generated, circa 12p per kWh imported

So generate say 10kWh and you receive a payment of GBP 4

Consume 10kWh and you pay nothing

Consume 12kWh and you pay 24p - this is taken off the GBP 4 payment so you receive GBP 3.76

Something doesn't add up with the above so I presume there is something missing. Maybe it's Generate say 10kWh and you receive a payment of GBP 4 Whilst doing so consume 10kWh and you pay nothing and still get payment of GBP 4

Henry

Your comment about the assumption of 50% feed into grid is contrary to what I have been told and have re-checked today. Quote

" Interim approach to exports

To prevent the need for installing an additional export meter before Smart Meters are introduced, it will be possible to 'deem' the level of exports as 50% of the total generation of the system."

My agreement with Scottish Power does not mention this however but I have opted in to receive the additional export payment and my system has now way of indicating the amount exported overtly. Although my supplier meter is equipped with an IEC 1107 interface, no meter reader that has called since its installation has used an IEC1107 reader to read it.

I will have to wait until my first FIT payment advice turns up some time in May to see how they work it out.

I have a design for a IEC1107 reader interface somewhere. Maybe I'll build one and see what my meter(s) can tell me.

Bob

That is part of the story Henry but also

Consume 12kWh whilst generating 10kWh - you still get a payment of GPB4 credited to your bank as well as a bill for 24p

The import and export accounts are completely separate and indeed can be from different providers. Once you have signed up for FIT with your current supplier, you can then move to another supplier for import and you do not have to change the contract you have for FIT.

Bob

I do the drying when the sun is out. The washing machine needs >25A to start unless I push the motor back to loosen the belt. It doesn't adapt well to non-grid sources, not even a 3750W generator.

jsw

I'm getting a picture forming in my mind...

Overshot water wheel, sides filled in with perforated plates. slightly leaky buckets, so that a proportion of the water falls into the enclosed centre of the wheel. Washing inside wheel.

Now all you need is the river and a way to cope with the bubbles floating downstream :-)

Mark Rand RTFM

SNIP

I think there are two entirely separate arguments here. The first is coincident or noncoincident PV generation.

"Generate 10KWh, consume 10KWH, pay nothing"

This is ONLY true if generation and consumption is simultaneous AND the instantaneous consumption rate never exceeeds the instantaneous generation rate.

This means that the full 12p rate is paid at any time that the daytime consumption rate exceeeds the PV generating level and also for all of the evening and night consumption.

The 50% deemed rate is only concerned with the presence or absence of an export meter.

If an export meter is fitted approximately 3p extra is paid for every KWh feed back into the grid. However most small systems have no export meter and the accepted compromise is to assume tha half the generated power qualifies for this extra payment.

Jim

Socks can already escape from a closed washing machine. You want to let them loose to cross-breed? There'll never be another matching pair again!

jsw

Pfft! Washing machines? Have you learned NOTHING from the two hundred years of collective engineering experience available here? Lateral thinking, sir..wear garters and keep your socks ON when in the bath!

Chris Edwards (in deepest Dorset) "There *must* be an easier way!"

ay!" =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0

But it HURTS when I pound them clean with a rock.

jsw

Their lawyers, when we forced them to accept power from small producers.

jsw

The time that consumption and generation take place is as near as dammit irrelevant.

You might export all day and consume all evening and night.

Assume you have no load during the day and the PV's generate 10kWh. In the evening and overnight you consume 44.5Kwh

The 10kWh is paid at 41.5p per kWh you get paid GBP 4.15

You also get an addtional 3p per kWh for any export giving a total payment of GBP 4.45

If the 44.5kWh consumed is charged at 10p per kWh you get charged GBP

The net charge is zero.

Apart from the capital investment of course!

Bob