Change of plan.

[mr.s.p]

I have a 250w panel attached to a chinese gridtie, it has been working well for some time now.
On overcast days it produces about 50w which is enough to run my computer which draws around 50w 24/7. On the occasional sunny day, the output rises to over 200w and the excess leaks out onto the grid. The meter turns backwards, but only rewinds the 10ths of units, not the whole units. I guess there is something in the mechanics of the meter that makes this happen.

Recently the electricity board came and swapped my meter. When I asked why, they said it is normal to swap meters every few years.
The old meter had a spinning disc and went backwards if I was making more than I was using. The new meter is a small plastic box that doesn't seem to care which direction the power is flowing, it just registers the fact.
The upshot of which is if I don't use what I'm making, I now get charged for letting it leak out onto the grid.

Any ideas for detecting this condition and switching on extra loads to prevent this? I would rather waste the electricity than get charged for giving it away.

 

[Nigel Goodwin]

As far as I'm aware, if you expect to 'sell' your surplus back to the electricity company you have to notify them, and assuming they agree you will have a suitable meter installed. I would suggest you forget the gridtie idea, and simply charge leadacid batteries, and use the power from those yourself via an inverter.

 

[Mr RB]

At such a low output (200W) maybe you could hook the inverter output to your hot water system element, which is probably a 4kW or 6kW heating element. All the solar power you make will go into your hot water and come off your hot water bill.

 

[mr.s.p]

Nigel: I have no desire to 'sell' electricity, I just wish to save £100 pa by running my computer on home produced electricity during the hours of daylight. I see your point about batteries and and an inverter, but the cost of the batteries, charge controller and inverter is 3 years in the wrong direction.

Mr RB: Good plan; But my hot water system is powered by solid fuel for 8 months of the year and an electric shower for the summer months. I don't have an immersion heater but I could fit one to use only as a dump load.

The problem is overproduction of electricity when the sun actually shines. I know the sun doesn't shine very often but when it does, I get charged for giving my surplus energy away. I was thinking about a circuit that measures the current flow and diverts the surplus into a dump rather than into the grid.

Anyone got any ideas about how such a circuit could be built?

 

[tcmtech]

The problem is overproduction of electricity when the sun actually shines. I know the sun doesn't shine very often but when it does, I get charged for giving my surplus energy away. I was thinking about a circuit that measures the current flow and diverts the surplus into a dump rather than into the grid.

Anyone got any ideas about how such a circuit could be built?

If you are worried about 200 watts you either have an incredibly low power consumption as a whole or way to much time on your hands.

Two simple solutions I have is to either increase your base load to absorb the 200 watts when its available or put a switch on the thing and just turn it off when you are not needing it.

Just out of curiosity how much power do you actually think you may be sending back in KWh per month and how much do you think you are actually saving by running your system?

 

[mr.s.p]

I have a low consumption of electricity, I use around 1800 kw/h a year and I create around 180 kw/h per year, so I guess I'm saving about 10% or £30 a year.
I have a computer that runs 24/7 and the rest of my usage is intermittent, (toaster, kettle, washing machine and shower).
Boosting my base loading is counter productive.
And yes, I have a lot of time on my hands.

 

[tcmtech]

So what you are saying is you could go work for minimum wage in your country for six hours of just one day of the year and more than make up the 30?

I am just going to leave it at that.

 

[strantor]

Recently the electricity board came and swapped my meter. When I asked why, they said it is normal to swap meters every few years.
The old meter had a spinning disc and went backwards if I was making more than I was using. The new meter is a small plastic box that doesn't seem to care which direction the power is flowing, it just registers the fact.
The upshot of which is if I don't use what I'm making, I now get charged for letting it leak out onto the grid.

Any ideas for detecting this condition and switching on extra loads to prevent this? I would rather waste the electricity than get charged for giving it away.

Here in the US they're swapping over all the meters to "smart meter" - digital units that transmit your usage data wirelessly back to the electric company so they don't have to read your meter. I've read that these devices just measure power, they don't care about direction. So they actually CHARGE you for donating electricity back to the grid. I think it was Debe who brought it up; ask him, but I think he said you can tell the power company you want a directional meter and they have to install one and pay you for what you put into the grid.

 

[mr.s.p]

strantor: You live in the land of the free, but I live in rip-off Britain.
tcmtech: I'm sorry my electricity usage isn't to your liking, how much would I have to use before I'm allowed to ask for circuit ideas?

 

[strantor]

well debe lives in australia, so that's where 50% of my info is coming from

 

[tcmtech]

I mentioned it already. This is a cheap of solution as I can come up with.

Two simple solutions I have is to either increase your base load to absorb the 200 watts when its available or put a switch on the thing and just turn it off when you are not needing it.

The last possible option would be to find out exactly how much power you are putting back and what its actual value is then base your efforts on that. If your present return on the overall system investment numbers out to being 15+ years before you break even on money saved you might as well just call it a hobby and spend what ever you want!

Hobbies have little to no ROI numbers or spending limits but being cheap has yet to ever save more than it costs!

 

[mr.s.p]

Well as I explained in my first post, I would like to increase my base loading to absorb the extra power.

Standing and watching a meter and switching on a load every time the sun shines through a gap in the clouds is one option, but I'd prefer to automate it by using a circuit to detect the over-abundance of power and switch in a load automatically and then disconnect it again when the sun vanishes back behind the clouds.

I have a clamp type meter that measures the current being drawn from the grid, but it is not directional. How do you measure the direction of the current flow?
Once I can detect the direction of the flow, I can use a pic or similar to drive a triac or relay to switch in a dump load if the current is flowing the wrong way.

And yes, it's a hobby, it keeps my brain active and I enjoy it.

 

[tcmtech]

If it was me I would just buy my own old style mechanical watthour meter and run everything through that and use a simple directional sensor to detect which way the rotor was going.

 

[strantor]

or you could just disconnect from the grid. Seems a little silly to connect a 50W solar panel to the grid IMO

 

[Mr RB]

If your computer runs 24/7 it's likely enough "baseload" to use up all your generated power. I would run the solar into a decent sized car battery and then inverter to computer. You could take the whole lot off-grid, problem solved.

 

[mr.s.p]

Thank you for all the comments about it being a bad idea and not worthwhile etc.

Now that I am fully aware that I am being foolish by attempting to do something so impossibly pointless and unworthwhile, has anyone got any ideas on how to actually build a circuit that detects the direction of AC current?

Other than inserting a mechanical meter into the supply line and detecting which way the little disc spins, which sounds a bit too Heath Robinson / Rube Goldberg for guys that supposedly know about electronics and electricity.

 

[strantor]

Deleted Abusive.
Moderation.

 

[mr.s.p]

The power companies in the UK require type approved equipment and licensed installers. This makes it very expensive.
So in answer to your question; Yes I did investigate before I discounted it.

How about a circuit to measure the direction of AC current flow instead of more criticism?

 

[debe]

I have a 1.5Kw solar system & grid tie inverter, been installed & running for about 30 days now. Had to get an Import/Export meter fitted, it tallys up consumed power & exported power. I dont use a lot of power about 5 to 6 KW a day was my average before instaling solar. Some smart meters will actualy bill you for any exess power (needs to be impot/export meter). Currently my meter is showing 135Kw Imported & 110Kw Exported. Current pricing for power is 28c/Kw imported, 20c/Kw for exported. Hot water is Solar/LPG boosted, house heated by wood slow combustion fire (wood free) only cost running chain saw. As we move into winter i expect the solar output will be a lot less. Import/export meter cost $306 to be fitted.

 

[mr.s.p]

Sounds like a worthwhile investment debe. If I had 1.5kw, I'd go for an export meter too.

Still looking for an electronic circuit to measure the direction of AC current if anyone has one?