New build off grid solar

[Givitago]

Hello all ,read lots on the web but not any real world answers,so my question is ..new build 100 m2 bungalow 8kw solar on roof SW facing 30' pitch Estimate NEED 5KWH day ,is it viable,how much battery backup needed,how much generator input .

Thought about combined controller inverter charger ..but 8kw very high,how about 8kw inverter(grid tie type) separate 3 kw (48v) inverter and 48v forklift type battery charger,all in with panels and roof mounts £3500-£4000 plus battery bank say 16 X 6v 225ah lead acid £2600.

  Got to put 3kw on to offset oil heating,also grid connection £3k so not a vast initial cost difference ...BUT your thoughts/experiences PLEASE !

 

[TonyT]

Pop over to the navitron forum, loads of offgridders there

[ProDave]

Are you hoping the solar PV will power the whole house? What about heating? do you not have a mains connection?

 

I am not sure that FLT batteries are still the "go to" storage medium now.

[SteamyTea]

Start by going here:

https://re.jrc.ec.europa.eu/pvg_tools/en/#PVP

Fill in all the details and then get the daily file.

 

Averages on there own are of little use, you need to know your usage standard deviation.

And having large batteries is only useful for a very short period of time, they need excess generation to charge up on the few sunny days to cover the one dull afternoon.

 

Start looking at all the things that you can get rid of that use power.

Edited January 27, 2021 by SteamyTea

[Givitago]

The 5 kw day figure is the minimum we would need ,(fridge ,freezer,lighting( led) central heatinvcontrol /pump .etc.,is there a chart anywhere showing daily anticipated production per kw of panels for the winter period ?

Edited January 27, 2021 by Givitago

[PeterW]

6 minutes ago, Givitago said:

The 5 kw day figure is the minimum we would need ,(fridge ,freezer,lighting( led) central heatinvcontrol /pump .etc.,is there a chart anywhere showing daily anticipated production per me of panels for the winter period ?

Try this

https://www.in2gr8tedsolutions.co.uk/info/solar-generation-calculator.php

 

Edited January 27, 2021 by PeterW
Wrong url

[Givitago]

Just done above interesting but of little practice use tells me I should vat APX 7000kw yr..if only it was evenly spread !

[Conor]

(possible unreliable anneicdote content)

 

I visited a guy's house that does PV and off-grid installations. He had 20pkw array, and was planning a wind turbine. His rule for installations up here in the dizzy latitudes was to install 4x your typical daily demand. basically because PV production in the winter is 1/4 of the summer. Battery storage flattens the demand during the day, allowing to run a kettle and oven at the same time, even if you're only producing a couple kw. 

 

[Givitago]

Yet another figure 1/4 production in winter, I've read 1/5th and more than once 10%..

  Any body got any thoughts on the idea of using a forklift charger..would it be highly inefficient? they certainly have a proven reliability record and are available at low cost 

[SteamyTea]

1 minute ago, Givitago said:

would it be highly inefficient

Compared to newer lithium technology, yes.

It is also very large.

 

If you hope to get the full capacity out of chemical storage i.e. 1kWh storage and 1 kWh usage, then the efficiency is pretty appalling, all the components get hot, which s just throwing the energy away.

This is why batteries are huge.  They are , in effect, oversized.

 

Which ever way you go being an off gridder, you will end up with a generator.  Look into combined heat and power units.  Then find a way to make them quieter.

 

[Givitago]

Agree acid battery storage is not ideal,but lithium is just to expensive at the moment,but as more ex car cells become available I suspect wet storage will be gone,so may be viable to buy cheaper wet now with say 5 yr life then Upgrade ?As for generator would love to have some idea how much it would have to contribute,

 I still think that the right initial setup (cheap/reliable/ not overly inefficient,with VAT back and no grid connection fee MAY be viable,also I have to spend circa £2 on solar for SAPs,wasted money as it's returns would be negligible for us

[DamonHD]

We are having a discussion over here...

 

https://www.fieldlines.com/index.php/topic,150161.msg1054611/topicseen.html#msg1054611

 

about how lead-acid can be just as efficient as lithium if you don't spend too much time at the final charging stages.  Also the technlogy is safer (especially if you are a coward and go for gel like me, or AGM) and much better tuned from a large number of excellent manufacturers.

 

Scruff's suggestion is that it doesn't have to move, stick with lead-acid in some form.

 

(I was using Lithium (LFP - Lithium Iron Phosphate) in my off-grid system, but have stopped for now.)

 

Rgds

 

Damon

 

PS. You can download my actual generation figures in London for a ~5kWp E- and W- facing split array, down to 1-minute resolution, here:

 

https://www.earth.org.uk/data/SunnyBeam/

 

Edited January 28, 2021 by DamonHD