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Grid tie solar inverter power from a fixed voltage source?

Hello there!

We have a 4Kw solar system installed at our home. We also happen to have 2 seperate circuits (ie 2 electricity meters). Annoyingly the solar panels are installed on the circuit that we don't use much electricity off so most of the generated electricity flows into the grid and (I know it's selfish) we don't benifit from it at all.

There happens to be one lonely socket next to the solar inverter that is powered off the other electricity circuit and I'm fairly sure that the two circuits are on different phases. This is what I wanted to do and I was hoping someone might be able to validate this:

I install a 240v AC to 24v DC converter (PAK650-24) and then an inverter to convert this back to 240v AC to supply that lonely socket where we need the power. Our solar inverter has a clever power detecter that switches a relay when production goes above 1Kw so I would connect this circuit to that relay.

I also wanted to use a solar grid tie inverter from ebay because they seem most reasonably priced. They do however have a MPPT algorithm which is where I am not sure how it would react to a voltage source. Might anybody be able to tell me whether it would be fine to do this and most importantly about fixed voltage sources and solar grid tie inverters (which aren't really meant for fixed v sources).

Many thanks,
James 

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Does your electric company know you have this solar setup? Do they not put credit on your account fro the power you feed into the grid? Most electric companies will pay you or credit your account for any power you put back into the grid. So no matter what breaker you have the solar panels connected to you should be getting a benefit from it.
fotherby (author)  mpilchfamily5 years ago
There is no meter to measure the amount we feed into the grid. I live in the UK, there is just a meter that simply reads how much the panels generate and we get paid ~25p/Kwh for that whever it goes. But if we can then use that electricity we don't have to buy it which saves us a lot more. That's my aim, to try and use the generated electricity but on a seperate feed circuit.

I realise it's a little silly not measuring how much we feed into the grid but that is just how it works in the UK at the moment.

Did you happen to know about the solar inverter query?
Have an electrician swap the solar power to the other circuit. Or better still join the two circuits into one. This will cost a lot less than extra inverters and the other rubbish you are considering.
fotherby (author)  theoldguy5 years ago
Well we do in fact use electricity off both circuits (just less on one) I don't think it cost effective to join the two circuits. Ideally it would be better to split the power like in the idea I talk off. I realize it's a little inefficient but that doesn't actually matter too much. Electricians are expensive and I believe the idea I talk of would pay back over a couple of years. Plus, I would quite like an excuse to get my hands on a grid tie inverter and a massively powerful DC supply. Do you really think it's rubbish! Please criticise.

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E-mail:dmdsales01@hotmail.com
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Dear Sirs,
We are Guangzhou De Mu Da Photoelectric Technology Co.,Ltd. We specialized in solar power inverter , Pure sine wave power inverter , solar powered systems many years in China. We are writing you for the establishment of business relations. There are follow or more products .
Car DC-AC inverter from 130W to 2000w
Modify wave since inverter from 300w to 5000w
Pure wave since inverter from 350w to 5000w
Converter include dc 60v/48/24v to dc 12 v, the currency are inclusive of 30A/20A/15A.
If you are interested in any our items, please tell to us ,we will try our best serve to you.
Yours,
Rockey Wang
Guangzhou Demu Da Photoelectric
Technology Co.,Ltd.
Website: http://www.dmdpower.com/en
Tel:86-020-61185082
Fax:86-020-61185081
E-mail:dmdsales01@hotmail.com
Skype: wanglanbai
theoldguy5 years ago
I cannot comment much on your electricity supply as I am in Australia which may have different systems, although I doubt it as its all made in China anyway.

I also have a solar system installed, its 3.2kw, and I also have two meters. One measures grid power in and out, the other measures the offpeak power I purchase from the grid. Offpeak is power purchased from the grid when there is an excess and is controlled by a timeclock. I get mine from 7am to 3pm and use it for hot water. I don't think its in the solar equation.

Our house gets first bite at the solar power being generated and only stuff we don't use at the time goes to the grid. The cost of offpeak is virtually the same as we get paid for our excess so I don't worry about it. I just let it do its own thing.

As for the,"massively big DC supply"that you mention. I assume you mean batteries.
The solar array runs at up to 200v at least mine does. Just press the button to find out yours or look it up.

So you would need 15 x 12volt (13.4v actually when charged)batteries in series to handle it. Don't bother with fancy batteries as weight is not a problem in a house. Lead acid will do.

This number of 12v batteries will handle the 4kw output at 200 volts with an amperage in/out of 20amps(actually 19.6amp).

Look at amp hours for the batteries - if they are 60 amp hour batteries then you will have the option of using a full 4kw for 3hours before the lights go out. I'm guessing that the daily average you use is less than 20kw so batteries this size will handle all your requirements, all day and night.

The solar voltage must be greater than the battery voltage to charge them. There needs to be provision for control over the batteries charging from the grid, you don't want this to happen all the time. But maybe occasionally.

I tried to include a spreadsheet I used when deciding on which system to buy but it won't paste.

Before doing anything - run your ideas past an English electrician. Like I said I'm in the land of Oz.