Off grid linking to generator

Talk Electrician Forum

Help Support Talk Electrician Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

binky

retired and loving it!
Supporting Member
Joined
May 7, 2008
Messages
14,579
Reaction score
1,739
Location
Sunny Plymouth
Had a look at a old farm house in deepest rural Devon. The customer has a 6kW diesel generator with battery back up, and is looking to add PV to save on fuel costs. So question is, can anyone offer any guidance to linking systems, potential problems, such as conflicting voltages interfereing with each other etc etc. I'm going to read up on tis anyway, but would appreciate any real-world experience.

One other question for those who are used to working with battery systems, how long do batteries last? The customer is complaining that they die every 2 years, which sound rather short lived?

 
What is the charge discharge cycle on the batteries? What type and size of batteries? Is he completely killing them before charging? What sort of charger is he using? Where are they stored, and temp range?

More Qs to follow.

 
Right, owner tends to not use leccy during daylight hours, bar about 1/2 hour at lunch time, genny then runs for evening until bed time. If you look at piccy below, it looks like current system was thrown in by a man who suppossedly knows what he is doing and his sparky mate - look to back of battery pack at switch fuse wiring. At the mo I think they are avoiding the batteries, as they have mentioned they set the genny to run when they need it. The Inverter is a Frontius. Genny and batterries are in concrete outbuilding.

Photo0158.jpg


 
Im on the phone Binky, but will reply later. Couple of points, if the batteries get really cold it will kill them, sitting on concrete will kill them, I'll have more time later, and we'll try to figure something out.

Btw, battery volt and rating, Ah, if you know it.

 
Not sure how these systems work so this is guess work - but here are a few thoughts.

To my mind the simplest way would be for the PV system to charge the batteries via a hefty transformer and diodes (charger) and use the inverter as the default supply.

All that needs to be decided then is when to run the generator or use the inverter.

This could be done automatically - but would be complicated. I don't believe a standard swap over is possible as the generator will also charge the batteries and increase the inverter voltage - in other words the systems are not independent as they would be with a mains backup.

The only system I can envisage working is a sensor which detects a low voltage at the battery. When this is sensed relays/contactors with appropriate time delays would remove the load on the inverter, power up the generator, connect the generator and run for at least 30 mins before powering down the generator and reconnecting the inverter - allowing time for the batteries to charge. This time delay would be necessary as I presume the sense voltage would rise as soon as it is taken off load - causing rapid changeovers between the systems.

I reckon most of this would have to be bespoke stuff - very time consuming!

Alternatively a manual switch over might be the order of the day - or a semi automatic system that removes the inverter load when the voltage is low.

Hope this makes sense!

 
Last edited by a moderator:
Off the wall suggestion - how does he make hot water? How about using the solar panels to heat water and save energy that way?

 
Surely you've got to charge the batteries off the DC side from the panels via a regulator (if needed) and then output through an inverter,,, then maybe a changeover switch with the genny as a second supply (but also use the genny to top up the batteries?)

But in all honesty that would be one hell of a set up to match the 6kW genny with PV,,, how big is the battery bank?? Must be freaking huge!

 
Customer mentioned that matey the genny installer installed lorry batteries, which might explain short life, as these are not deep discharge type. Hadn't thought about cold affecting batteries either Steps, though I wouldn't have thought these get a chance to cool down:^O

There is currently just 4 batteries (as seen in picture) didn't think to take details which was a bit silly of me.

As far as control gear goes, this stuff must already existing somewhere, I'm not re-inventing the wheel, and PV panels are already fitted to many items such as canal boats, yachts etc etc. So not too worried about this, but it is kind of looking that to integreate genny and PV, we need to re-configure the whole system.

 
Gen sets also run better at optimum load.

With Steps on the batts.

Though if they are runing hot that ain't good either.

You may need to temp monitor the batts?

 
you dont get FiT = feed in tariff,

and AFAIAA they have changed the conditions for the generation tariff as well, so you would need to check up on this,

BTW, its the gen tariff that is worth the money, NOT the FIT.

HTH.

 
You can get a traiff for off -grid, not connected to house, but someone was telling me the other day that you could get FIt for a house at the normal rate - but it doesn't appear on offiical tariff chart. Will do some checking uo tonight and report back

 
Top