Questions - Inverter with limiter..

[Spikeuk]

Hi Guys,

I'm looking to fitting a solar array myself, to bring down electricity costs.

Im a complete noob so please comment / correct me / advise - would be greatly appreciated!

 

I run a computer server storage array which is using 1200w power 24/7  I would like to bring electric costs down a bit using PV.

 

It doesnt have to produce 1200w constantly but just to bring down costs.   I don't want to export back to the grid otherwise I have to mess about with telling power company etc- and then only getting paid 5p while still paying 30p per kwh.

 

Off grid - With a off grid system I need to buy some expensive large batteries Lifepo4- which may or may not fail within a couple of years if im cycling them low regularly... from what I can tell this seems really expensive and may not save much money due to battery costs. 

 

Grid tie -   I don't want to export,  I want to use what I produce - I realised you can get grid tied inverters which have 'limiters' - from what I have read do not feed any power back to the grid,  theres a C clamp to go onto the mains cable on your house meter which monitors power usage,  the inverter then provides as power as possible to meet the demand reading from the meter cable - this way you are using PV power and grid power at the same time without exporting  - is this correct?   this sounds ideal as I can use power from PV during day when panels are active as its produced and do not need any batteries?, any shortfalls in PV are substituted by grid power? i.e.  700w pv 400w grid for my 1200w load?

 

Do I need to inform power company if its grid tie with limiter as i am not feeding back?  or just get qualified elec to install.

 

Also  Im looking to install system garage roof,  approx 50m from my main meter where the 'C' clamp needs to go for the limiter. (long cable length for c clamp to inverter -not accurate readings)   

Could I not just use the C clamp on the plug socket cable directly where the 1200w load is pulled from and the PV will try to output upto 1200w?

 

I have smart meter fitted,  SMETS2 i think is the type,  I read somewhere possible problems with smart meters?

 

Any advice would be greatly appreciated!

 

Thanks guys!!!

 

 

[ProDave]

No easy answer. 

 

The least hard is a grid tied inverter that complies with G98 and will generate no more than 3.68kW (you can have a larger capacity of panels connected to it)  you have to notify that to the DNO under G98 but they cannot say no and there is no charge.  The DNO is still stuck in the mindset that you might export all that is being generated.

 

A DIY system won't allow you to get paid for any that is exported so the easiest way to avoid export is fit a solar PV diverter to send any excess to your immersion heater to heat your hot water a bit.  That and your server should ensure you never export anything.

[billt]

1 hour ago, Spikeuk said:

Do I need to inform power company if its grid tie with limiter as i am not feeding back?  or just get qualified elec to install.

 

The answer to that is yes, you or your electrician are supposed to inform the DNO, even if you don't export anything. It's being connected to the grid with a gt inverter which matters.

[SteamyTea]

Take a simple scenario of adding your server as the only load to the grid. It just draws in the 1.2 kW.

Now if you fit a grid tied 1 kW PV system, all the power that produces will go to the closest load, your server. Grid imports will be reduced in direct proportion. So while the DNO needs to be told, this is a safety matter, you will never be exporting.

Now with a small system, most of the time it will not produce the nameplate power, that is just the way daylight works with PV.

So it is usual to oversize the module arrays so that the mean generation is closer to the load, so maybe a 2.5 kW system would be better. You can run the numbers though PVGIS and see what comes out. There will be optimal sizes, both performance and financial for your needs, even allowing for exporting unused generation. But the setting up will be cheap and simple. No need for load sensing switched and spikey changeovers.

But first, is there anyway you can reduce the server load, the heat given off would heat my house nicely. Maybe I should build one and rent it out, except I can only get 5 mb connect speeds.

Edited November 29, 2021 by SteamyTea

[DamonHD]

Agreed with Steamy here...

 

I used to have a continuous load about half of yours, partly from still running an ISP:

 

https://www.earth.org.uk/saving-electricity.html#2007-07

 

In the end I squeezed everything I needed into a Raspberry Pi (well, I'm being extravagant and using two at the moment!) and it has run completely off-grid for over a decade, by drawing ~2W.

 

Rgds

 

Damon

 

[Nickfromwales]

11 hours ago, Spikeuk said:

Could I not just use the C clamp on the plug socket cable directly where the 1200w load is pulled from and the PV will try to output upto 1200w?

Nope. PV output will be linear to the amount of sunlight hitting it at any one time. That cannot be controlled. Where the electricity goes is also not under your control, as anything consuming power when the PV is producing will take an equal share. Producing electricity via PV offsets the amount of paid-for grid electricity you import, and the only part of PV you can 'direct' at a load is when you have surplus energy AFTER the house CU has taken its fill, and then there is energy trying to export back to the grid. That can be harvested by utilising a diversion controller to manage the excess to an assigned 'dump load', such as heating a hot water cylinder. 

The electricity produced by the PV will inject, via a dedicated MCB, into the consumer unit for general use. The output, aka generation, from the PV will push or pull on the grid connection and that offers a position where import and export can be identified. That is where your CT clamp MUST be installed. If you fit the CT clamp on the supply plug of the load then electricity is only ever 'seen' flowing towards the load, which is then recognised as imported energy. The clamp would never know when you are producing more than your base load there as it would not be able to register electricity flowing in the 'opposite direction'. That can only be done at the meter itself or at a strategic position on the meter tails, eg immediately upstream ( this can be at the main switch in the CU if that is easier than getting to the meter, providing you only have one CU ).

I would agree that anything less than a couple of kWp would not be an economical investment, when considering time / labour / economy of scale. 

[SteamyTea]

48 minutes ago, DamonHD said:

Agreed with Steamy here...

About time.

 

If only people did not want to send multi meg pictures of their privates to each other, we could have a much faster internet.

when I send a picture from my phone, by default, it send the full size image, that then gets viewed on a tiny screen.  30k would be ample, just like it was back in 1998.

[Nickfromwales]

4 minutes ago, SteamyTea said:

If only people did not want to send multi meg pictures of their privates to each other, we could have a much faster internet.

I've apologised once, lets leave it there OK?

[DamonHD]

9 minutes ago, SteamyTea said:

About time.

 

If only people did not want to send multi meg pictures of their privates to each other, we could have a much faster internet.

when I send a picture from my phone, by default, it send the full size image, that then gets viewed on a tiny screen.  30k would be ample, just like it was back in 1998.

At the time I don't think JPEGs existed, and it was USENET ASCII art sex pictures (often involving animals) that caused me a certain amount of bandwidth grief...

 

Rgds

 

Damon

[SteamyTea]

4 minutes ago, DamonHD said:

At the time I don't think JPEGs existed

1992 the format was released.

Some of those old, grainy, artefact edged, colour corrupted images will be considered charming one day, just like sepia pictures are.

Edited November 29, 2021 by SteamyTea