DIY Powerwall / Battery

[Dabop]

DC-DC buck and boost converters are pretty cheap and efficient.
Laptop and many electronic power supplies have a wide input voltage range.
They have a bridge rectifier on the input but would still work if fed from DC in their band.
A DC supply at 48, even 60 to 70 volts for example might be useful distributed throughout a home.
High enough to be useful and to keep the amperage modest, enough to tingle without being too hazardous.
I have a telco 48V / 30 amp power supply that is about 98% efficient. It could notionally supply a 30A DC ring without wasting any more heat than a 100W lightbulb. I can't imagine running more than 1.5kW of electronics in a house or workshop. You wouldn't use it to power heating loads.

You'd be surprised- most newer Australian offgrid homes use 96v nominal battery banks, with 15kw or more of inverter hanging off them!!!!

Even my own for the house is a 48v 12kw inverter- designed to run the entire house and a hobby workshop- which will be including two separate split cycle A/C units eventually, and when I want to 'play in the workshop' will have to be able to handle the lathe, mill and other heavy current users like the welders, plasma cutter etc...

(I got the 48v inverter 'cheap' as 'old new stock' as 48v really isn't used much these days except for small 'dongas' ie weekend camping cabins)

It's a LF (far superior to HF inverters for inductive loads) a 12kw LF like mine can supply 36kw for up to 20 seconds, where an identically rated 12kw HF inverter will only supply 24kw for less than half a second!!!

There is a downside however- a LF is big- and HEAVY... my 12v 8kw HF inverter can (just) be picked up in one hand- about 11kg, where the only slightly larger in capacity 12kw LF weighs in at a massive 72kg!!!

It took three people to load it into the cab of the tilt tray, and I used the winch to unload it!!!

 

[johnb80]

Anyone that's following this thread, Fogstar have some excellent battery pricing at the moment, 15 kWh including BMS and Cased for £1799. Just add an inverter (circa £800) and youre up and running with 15 kWh storage plus a 5 kW inverter.

 

[Sideways]

Excellent.
A buddy bought a tesla powerwall solution just a few months ago that gave him about 14kWh including the inverter functionality. Cheaper than my Fronius BYD gear but still cost over £7k fitted.

 

[johnb80]

Excellent.
A buddy bought a tesla powerwall solution just a few months ago that gave him about 14kWh including the inverter functionality. Cheaper than my Fronius BYD gear but still cost over £7k fitted.

Tesla Power wall is a very expensive option for battery storage, I'm sure it's superb quality but beyond my price range.

 

[Jameshow]

Anyone that's following this thread, Fogstar have some excellent battery pricing at the moment, 15 kWh including BMS and Cased for £1799. Just add an inverter (circa £800) and youre up and running with 15 kWh storage plus a 5 kW inverter.

How much would sufficient solar be for such a set up.
Thinking of a off-grid mens shed using 12hwh 2x week.

 

[johnb80]

How much would sufficient solar be for such a set up.
Thinking of a off-grid mens shed using 12hwh 2x week.

Use one of the online calculators to decide. You need to input your roof details and power requirements, it will then model what you can expect from any proposed solar setup.

 

[Sideways]

How much would sufficient solar be for such a set up.
Thinking of a off-grid mens shed using 12hwh 2x week

However much you can reasonably install, it's unlikely to be enough for 2-4 months through the winter.
With 9kW (24 good panels) on our roof, we've only been averaging about 2.5kWh a day through the endless gloom of the last fortnight :-(

In mid summer, 4kW of panels in a good position would probably fill a 15kWh battery in a day.

 

[Terry - Somerset]

A sad reality for solar power in the UK - when you most need the energy domestically (Oct-Mar) you are least likely to generate it.

Solar only make real economic (and environmental)sense if used to charge an EV - a roughly average mileage of ~200 miles per week is likely to require ~50kwh. A nominal 4kw array may do this for 6-8 months a year making motoring fairly cheap!

 

[johnb80]

A sad reality for solar power in the UK - when you most need the energy domestically (Oct-Mar) you are least likely to generate it.

Solar only make real economic (and environmental)sense if used to charge an EV - a roughly average mileage of ~200 miles per week is likely to require ~50kwh. A nominal 4kw array may do this for 6-8 months a year making motoring fairly cheap!

If you consider a tariff like Tomato Energy at 5p kWh off peak, it would be hard to justify solar for car charging.

 

[johnb80]

A sad reality for solar power in the UK - when you most need the energy domestically (Oct-Mar) you are least likely to generate it.

Whilst it is true you generate less during these times, Mar to Oct works well for me, I use a lot of what I generate for air conditioning, running EV's and all of the usual cooking/refrigeration/washing etc.

 

[Agent_zed]

If you consider a tariff like Tomato Energy at 5p kWh off peak, it would be hard to justify solar for car charging.

but how long will that last before the energy companies up the price. Off-peak elec is only cheap so the energy companies can keep generators running at periods of low demand.

Once everyone is charging their cars will there be off peak electric or at least anywhere near the same amount?

 

[johnb80]

but how long will that last before the energy companies up the price. Off-peak elec is only cheap so the energy companies can keep generators running at periods of low demand.

Energy is cheap to attract people to use it during periods there's a surplus. People are encouraged to use energy during these periods with attractive pricing.

Once everyone is charging their cars will there be off peak electric or at least anywhere near the same amount?

The demand will increase with the uptake of EV's, heatpumps and ZEB's but supply will also increase with windfarm and solar farm developments. I dont think the off peak rates will disappear any time soon.

 

[Terry - Somerset]

Energy is cheap to attract people to use it during periods there's a surplus. People are encouraged to use energy during these periods with attractive pricing.

The demand will increase with the uptake of EV's, heatpumps and ZEB's but supply will also increase with windfarm and solar farm developments. I dont think the off peak rates will disappear any time soon.

IMHO the price gap between off-peak and peak will diminish rapidly over the next few years. Best guess - 3-4 years.

Energy demand
Current peak demand is ~45GW falling off-peak to ~30GW midnight to 6am. Assume (slightly flawed assumption) that 15GW is surplus off peak capacity - a total of (say) 90Gwh. There is a similar peak/off-peak split during the warmer months, albeit at a lower level.

Off peak is currently prime time for charging EVs when (a) they are likely stationary at home, and (b) when they currently they enjoy cheap rates.

Energy supply
Over the last year green + nuclear has delivered ~50% of demand, the balance from gas and interconnects. Currently peak demand is met through expensive and polluting gas.

Green/nuclear energy are effectively free at the point of generation, gas expensive. Transition to green energy will tend to moderate the speed with which off-peak rates are withdrawn. I believe this will be at a slower rate than the increasing demand from EVs.

EV demand
A simplistic estimate - surplus off-peak capacity (90GW per day) would be consumed by 2.25m EVs charging twice a week during off peak times with averagely 20kwh. 40Kwh per week allows a typical EV to be driven 150-200 miles. 20kwh is ~33% of typical EV battery capacity.

Not all EVs will be charged off-peak - some away from home or on longer journeys. A guess - when the population of EVs increases to around 3m, most off peak capacity will be consumed and any price differential largely eliminated.

Currently there are over 1m EVs registered - I would expect that to reach 3m in ~3 years given current government targets.

Other technological impacts may include the development of V2G which would tend to increase cheap off-peak demand, and the use of domestic solar for daytime charging reducing domestic peak demand.

 

[johnb80]

IMHO the price gap between off-peak and peak will diminish rapidly over the next few years. Best guess - 3-4 years.

Too many assumptions in there for me, time will tell I guess.

One thing for sure, it the off peak rate disappears or is significantly affected, my plan B will come into operation with more solar panels, more battery and Ill be departing the National Grid for my energy supply.