Going off grid

[openspaceman]

8 minutes ago, Justme said:

From memory diesel engines loose 1/3rd to wet heat, 1/3rd to dry heat & noise & 1/3rd to rotational force. Then add in the electrical efficiency & you can see why its not very efficient to use a genny.

Yes I think this is a reasonable ball park for where the heat goes, bigger diesels will be about 40% conversion to rotary motion.

 

You will have a good idea of the actual cost of electricity produced by your set up and my point was that during winter it is a shame to waste that exhaust and coolant heat if you are heating a building. The further point is  it can be better to run a generator at its efficiency sweet spot  for a reasonable time, say at least an hour, and satisfy your load plus charge a battery even though there are inherent losses in charging a battery because optimising running the genset  can make up for these losses. Obviously for 3/4 of the year I'm optimistic my solar PV will supply all my needs now it is backed up with the battery but would like a renewable source of non grid electricity at this time of year.

 

A bit of a warning of what might become a long term issue when the weather doesn't keep the windmills turning is that the wholesale price for electricity is now 3 times what I am paying on my fixed deal and also more than the cap for those on variable tariffs. Of course this is unsustainable for the electricity retailers .

[donnk]

do the math.

 

a genny over mains is madness. work out how much electricity you can buy with the cost of the genny, repairs and fuel. it will be years before it pays for itself if ever.

 

Best bang for your buck is grid connected battery so you can time shift your grid electricity demand to when its very very cheap. Battery supplies the house when its expensive.

 

I do this with a tesla Powerwall, it takes input from my solar (shit in winter) and then fully charges from 1am - 3am for 5p kw/h. We then use this electric in the evening/day when it would cost 25p kw/h.

 

Electric cars will be able to do the same, vehicle to grid.

 

You can put it through the books as well for vat and corp tax if you have home office.

 

 

[openspaceman]

@donnk you haven't been paying attention go to the naughty step.

[Watercourse management]

Thanks openspaceman this is all gold information. We’re spending around 2 grand a year on electricity now due to go up to over 3 thousand a year, I need three phase purely to run my machining workshop, the inverter I’m using at the moment is good but I cannot use more than one machine at a time so three phase generation is always the end goal.

There looks to be some large secondhand wind turbines coming up for sale locally as there green deal is coming to an end so it would be nice to incorporate one of these with Pv and the generator with a battery bank then export any excess power to the biomass buffer tank if that sounds feasible.

Reading between the lines it seams to me that you need to go big on your renewable system to get a decent power return.

Had a quick look at TEG thinking perhaps it could be incorporated with the biomass boiler but the efficiency compared to cost looks a bit scary.

[openspaceman]

39 minutes ago, Watercourse management said:

Thanks openspaceman this is all gold information. We’re spending around 2 grand a year on electricity now due to go up to over 3 thousand a year, I need three phase purely to run my machining workshop, the inverter I’m using at the moment is good but I cannot use more than one machine at a time so three phase generation is always the end goal.

There looks to be some large secondhand wind turbines coming up for sale locally as there green deal is coming to an end so it would be nice to incorporate one of these with Pv and the generator with a battery bank then export any excess power to the biomass buffer tank if that sounds feasible.

Reading between the lines it seams to me that you need to go big on your renewable system to get a decent power return.

Had a quick look at TEG thinking perhaps it could be incorporated with the biomass boiler but the efficiency compared to cost looks a bit scary.

I guess you would need to work out the run time and power requirements of the machines, is the current inverter a single phase input and a 3ph output? We used these a lot on the biomass boilers I worked with for the feed augers when there was no 3ph available but they tended to be only 3/4 hp motors and only one per boiler, the rest being constant speed induction motors. I think they are only readily available up to 2kW but they get around the demand for a large start up inrush current to some extent by having a soft start at lower frequency initially.

 

How do big wind turbines produce 50Hz? do they use inverters?

 

If you must have a large 3ph diesel generator to run the workshop then consider putting a plate heat exchanger in the coolant and running it into your buffer tank, many diesels used for stationary use will likely have been used in boats and a water cooled exhaust manifold may be available.

 

It comes back to my earlier point that if you must satisfy the peak power then you will not run optimised for much of the time.

 

When I first looked into off grid power in the 70s one could get hold of little (probably weighed two tonne)  triple expansion steam engines that ran ships electrics from coasters and trawlers which were being scrapped and I always fancied one of them gently swooshing away , later on a visit to Kew Steam Museum I saw the 5kW (IIRC) mini turbine that used to steal steam from the main boiler and keep the lights running, made about 1905 I think. I wonder about using a flash boiler in the combustion chamber of a biomass boiler and converting a turbocharger to an impulse turbine and doing something similar using a 400Hz alternator from and aircraft to avoid having to step down the gearing too much.

 

Yes TEG seems to be too far off mainstream to be cost effective. Caterpillar had a 5kW TEG running off the exhaust of a big rig in America, it eliminated the alternator but I cannot find any reference to it now.

[Dean Lofthouse]

I'm living off grid and have done for some time.

14x 325w panels

600ah 48v battery

48v 2kw Turbine on a 60ft tower

8kw Studer inverter charger

200 litre water tank with 2 heating elements, top is 3kw bottom is 1.5kw

30kw generator

 

Solar/wind  charges the battery then dumps into the bottom element of the water heater. I don't need to start the generator at all in for 7 months of the year. We have more than enough power to run fridge/freezer, kettle, toaster, hot air fryer, hot water for shower every day, television lights, everything.

 

When days start to shorten, we start using stove to boil a kettle

 

When days really start to shorten we come home from work and cook tea with Genny running, if Genny is running it automatically give priority to battery and bottom element in water tank, then brings in top element in tank when battery gets near full.

 

Don't need to run Generator for any more that 1.5 hours per day in dark winter. 

 

 

 

[openspaceman]

Thanks for chipping in Dean, is the battery lead acid? That's 15kWh to 50% DoD.

 

You don't make use of the heat from the genset either then?

[Dean Lofthouse]

Thanks for chipping in Dean, is the battery lead acid? That's 15kWh to 50% DoD.

 

You don't make use of the heat from the genset either then?

No heat use from genset, it is a waste I know. Battery is lead acid. I,ll post a picture of the control cabinet in daylight tomorrow.

I find the wind turbine is a waste of time unless its gale force winds. All lighting in the cabin are led and draw very little power. Heating is via a log burner.

 

[Watercourse management]

Great information, are the deep cycle lead acid batteries best for the job? Also how do you size the battery bank, I was thinking of monitoring the electricity meter when I’m not in the workshop for a week to see what the domestic draw is.

[Peasgood]

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.