Going off grid

[openspaceman]

1 hour ago, Peasgood said:

Interesting stuff there @Dean Lofthouse, it is something I am trying to plan for a bungalow I am working on.

My plan wasn't for such a big generator though, everybody says go for the biggest you can afford but does it really have to be that big? I was thinking 20Kva would be more than sufficient and run my workshop when required.

In my house I have a wood fired Aga type cooker that does all heating, DHW and cooking. A bit surprised you don't have similar but doesn't suit everyone I guess.

This bears some thinking about; Dean says his genset only runs for an hour or so daily, it's 30kVA so he loads it with his current use in the buildings, recharging the battery and heating water. Presumably he has it for a high peak load. Either way it is such a short run time that doesn't suit CHP which tends to need high occupancy and a long run time to justify capturing the waste heat. As such it strikes me CHP needs to be working at an optimum load to give the best conversion efficiency to electricity. Nowadays this probably means running asynchronously AC and rectifying to charge a battery bank and an inverter running current loads.

 

It's modern inverters that hold the key to this IMO as the IGBTs (insulated gate bipolar transistor) are so efficient with low resistance and capable of switching high voltages.

 

Once you get up in the 10kVA plus range I think you are bound to fall back to a diesel using rebated fuel or a spark ignition engine running on gas.

 

@Peasgood it may be worth considering one genset for when the workshop is used sized for peak startup loads and a much smaller one for when the house is occupied.

 

I'd still like to investigate  smaller chp systems using Stirling and smaller still Seebeck CHP devices once the solar isn't performing and heating is needed in the winter months.

 

My battery only buffers one day's electricity usage so some sort of generation is needed to free me from the grid and the expense is not (yet) justified. I get the impression @Dean Lofthouse and @Justme simply have no access to the grid.

 

 

[Dean Lofthouse]

You dont need a big generator, I,ve programmed the inverter to limit input from the generator to 32amp . Its a 3ph generator used for running some equipment in my yard.
Ive tapped off 240v from phase-neutrel. The only problem with tapping single phase off a 3ph is you introduce electrical imbalance, which is just as bad as mechanical imbalance. This is the reason I have limited the current draw from the inverter.

Battery wise, I,ve gone with lead acid because Lithium are silly prices still. I think better and cheaper battery technology is very close and will continue with lead acid till then.

As with all batteries, try no to over disharge them, size your battery so that you only draw down to 70% dod, your battery will last much longer.

On average we are using 7kw hours per day. You can reduce usage from your battery by boxing clever. Only do heavy usage stuff while you genny is running. Ie washing machine, have a shower, boil the electric kettle, cook tea .....

[Stere]

Some  CHP info

 

https://www.pace-energy.eu/wp-content/uploads/2020/06/PACE-T1.4-Training-Documents-Module-1-Basics-FV.pdf

[Dean Lofthouse]

This is my control cabinet, bit messy still because its work in progress.

Its taken a long time of experimenting to get here. I,m lucky because I work part time a electrical motor drives firm so have access to scrap panels sometimes.

Im happy to explain anything you see in the picture [emoji106]

 

 

[Dean Lofthouse]

This is my setup at the moment, again..still a work in progress.

[scraggs]

31 minutes ago, Dean Lofthouse said:

This is my control cabinet, bit messy still because its work in progress.

Its taken a long time of experimenting to get here. I,m lucky because I work part time a electrical motor drives firm so have access to scrap panels sometimes.

Im happy to explain anything you see in the picture

 

 

Out of interest how reliable has the inverter been ?
 I went for a Victron, based on the fact I have used Victron stuff for several years on different boat setups and they have been faultless, but these new Multiplus 2 units that have replaced the old inverter/chargers appear to be having a few issues.
Victron have already had to replace a Cerbo unit that blew whilst on test.

Edited January 8, 2022 by scraggs

[Dean Lofthouse]

Better photo

[Dean Lofthouse]

Out of interest how reliable has the inverter been ?
 I went for a Victron, based on the fact I have used Victron stuff for several years on different boat setups and they have been faultless, but these new Multiplus 2 units that have replaced the old inverter/chargers appear to be having a few issues.
Victron have already had to replace a Cerbo unit that blew whilst on test.

Ill go for Victron next Scraggs simply because they are far more common. Studer are fantastic but no uk service agents

[Peasgood]

I don't have a grid connection but was quoted £20k + vat about 18 months ago, in hindsight maybe I should have taken the offer but as I didn't have £20k at the time it wasn't viable. The price of everything has gone up (very much including electric too) since then and it would be closer to £30k at a guess given the first quote did not include 140m worth of trench for cable.

I am already running my workshop on a petrol generator, it is 6.5kw running power and is on it's limit when everything is going. I have to start things in the right sequence as the biggest motor takes a fair whack to get it going. The biggest downside is it uses 20 litres a day and running around with jerry cans to the nearest fuel station (which is not the cheapest) is a pita when I have no spare time to do so. I already have 1000l red on site so makes sense to change to diesel. 

I have a steel frame shed with a roof good for panels and a well insulated building I hope to make into a dwelling.

My line of thinking was 10-20kva generator that will run both buildings with auto start that keeps batteries topped up if needed. Probably using Growatt or Victron and as I have no batteries at the mo I was thinking to dive straight in with LiFePo4.

I can afford the mains connection now but feel being independent from the grid would be a smart move and smarter than just having a changeover switch for outages. 

I am little more than an interested amateur compared with you guys with experience and knowledge but trying to research it all. At the moment it is a bit of a tossup with grid connection or solar + batteries with generator in reserve but the cost of grid connection and price of electricity is favouring the latter right now. In fact a new 15kva generator running on red beats mains right now.

[Dean Lofthouse]

@Peasgood If you invest in a good inverter charger, they will have loads of good features. One of those is power assist or boost. If you are running on your generator and start up a big machine, the inverter will chuck in th extra power to assist your generator. Likewise the opposite, if your inverter struggles it can autostart your Generator.

 

The reason I ended up off grid is because I was quoted £120K to get connected. Which was around 600m of digging a trench down a road. I have pylons 80m away at the other side of the motorway and a motorway street lamp less than 20m away 😆

 

One other tip: make sure when you buy a generator, you get what the call a 4 pole not 2 pole.

A 4 pole runs at 1500 rpm.

A 2 pole runs at 3000rpm

For obvious reasons a 4 pole is much better fuel wise