Cheapo ebay inverters and general advice for a first timer

[x4dow]

Are these cheapo "all in one" charge controllers any good? (more leaning into the 48v setup , also as its also mppt controller, not pwm)

5KVA Solar Inverter 48V 230V Pure Sine Wave Off-Grid Built-in 80A MPPT Charger | eBay

Pure sine wave inverter Built-in MPPT solar charge controller Configurable input voltage range for home applicances and personal computers via LCD setting Configurable AC/Solar Charger priority via LCD setting Configurable AC/Solar input priority via LCD setting Compatible to mains voltage or...

www.ebay.co.uk

3KVA/2400W Hybrid 24VDC 230VAC 50A PWM Pure Sine Wave Inverter UK | eBay

Find many great new & used options and get the best deals for 3KVA/2400W Hybrid 24VDC 230VAC 50A PWM Pure Sine Wave Inverter UK at the best online prices at eBay! Free delivery for many products.

www.ebay.co.uk

Looking to play around with the idea of making a small diy setup.

main questions:
My main requirement is to be able to charge the batteries from grid too ( not just solar) and this kind of controllers seem quite good value for what they offer
do I need any certifications/qualifications to hook the AC into these? (AC out just going to an extension where i'd plug a frige/chest freezer + some other bits ocasionally)
Regarding grounding. do I have to put a earth rod for this on its own? or can/should hook it to the grid's "ground"? Same goes to the AC out, shouldnt that have a ground too ? surely i shouldnt just use the AC's L and N wires without some sort of grounding?
Do I need the landlord's permission to hook something like this? (solar panels apart, i can always put them on the ground/my own shed)

any general tips would be welcomed

 

[snoobler]

Welcome to the forum.

If you're okay with no support and no warranty if there's a problem, go for it.

If you are in the U.S., http://watts247.com

Consult the manual for grounding requirements.

 

[x4dow]

Welcome to the forum.

If you're okay with no support and no warranty if there's a problem, go for it.

If you are in the U.S., http://watts247.com

Consult the manual for grounding requirements.

Thank you snoobler
I'm in the UK

 

[snoobler]

I would look for a UK distributor for MPP Solar and/or Growatt if you're looking for low-end stuff. They will be my go-to if I ever want to play around with something. If I want to rely on it, I go with the high end stuff, Victron, etc.

 

[snoobler]

One last thing about those... They say they have a "surge" or overload rating, typically twice the max continuous rating. Please do not design anything that might rely on a those surge ratings. Their surge is basically for milliseconds, which is insufficient to deal with the surges associated with motors. Assume a motor has a surge of at least 4X it's run power. If it exceeds the rated continuous power, it's not likely to work.

 

[x4dow]

One last thing about those... They say they have a "surge" or overload rating, typically twice the max continuous rating. Please do not design anything that might rely on a those surge ratings. Their surge is basically for milliseconds, which is insufficient to deal with the surges associated with motors. Assume a motor has a surge of at least 4X it's run power. If it exceeds the rated continuous power, it's not likely to work.

Im aiming to run a chest freezer that draws 350w ocasionally and a small fridge and potentially use spare energy to warm up a hot tub (2050w) with battery storage if charge from night cheapo night rate electricity (only if i really scale it to have ~10kwh storage). so technically i only need 2500~W max (continuous) , I assume the 48V one above should handle that without issues?

 

[snoobler]

IIRC, there's an "LV2424" MPP Solar unit that should get you there.

2050W of heating from batteries is brutal. It will take hours to raise it 2-3 °C. 10kWh of batteries is expensive.

Most solar grid-replacement costs take 8-10 years to break even.

Handy water heating calculator:

Water Heating Calculator for Time, Energy, and Power

The calculators on this page compute how long it takes to heat water, how much energy is consumed, and how much heating power is required.

bloglocation.com

 

[x4dow]

IIRC, there's an "LV2424" MPP Solar unit that should get you there.

2050W of heating from batteries is brutal. It will take hours to raise it 2-3 °C. 10kWh of batteries is expensive.

Most solar grid-replacement costs take 8-10 years to break even.

Handy water heating calculator:

Water Heating Calculator for Time, Energy, and Power

The calculators on this page compute how long it takes to heat water, how much energy is consumed, and how much heating power is required.

bloglocation.com

thing is though, on my variable tariff ( i pay different rates every 30min) i can get electricity costing like 2-5cents per kwh at night ( sometimes price even goes negative and we get paid to use it) and can go as high as £0.35 during 4-7pm ( 40-45 us cents).
Charging them via AC just to discharge during that 4-7PM peak could potentially pay back £0.30 per kwh/day on savings. so a 10kwh battery ( that would cost me £4000~) would be paid back in savings in more like 4-5 years

 

[snoobler]

So, £0.33 savings maximum per kWh?

If you invest about £1600 in this system (inverter/charger and batteries alone) to get 3 hours of run time per day, you will save 6.15kWh * £0.33 = £2.03/day

788 days - not as bad as I thought.

What about a timer that just limits the heater to operate during the cheap power period?

 

[x4dow]

So, £0.33 savings maximum per kWh?

If you invest about £1600 in this system (inverter/charger and batteries alone) to get 3 hours of run time per day, you will save 6.15kWh * £0.33 = £2.03/day

788 days - not as bad as I thought.

What about a timer that just limits the heater to operate during the cheap power period?

i can turn off the tub at 4-7pm, so i already try and avoid that usage as much as possible. but theres loads i cant avoid. like cooking (electric oven) that goes on at 4-7pm. I could wire that to it instead of the tub for example. theres a good 3-5kwh of usage in my home around that time (pc/oven/etc) that i could use that system to power it (even without installing any solar panels) and would pay off the batteries in 3-5 years. heres a graph of my grid price average for the last year per time of the day (price in £ cents)

 

[x4dow]

worth noting thats "average" , i had lows as low as -9 (9 negative), and high between 4-7pm is capped at 35p, but its almost always above 30 lately

 

[snoobler]

Averages probably are the numbers you need to use since that's likely what the net cost will reflect.

As long as you run the numbers, and it makes sense to you, that's all that matters. An electric oven is likely higher than 2050W. Ours is 3500W, but I don't know what's typical.

Getting it to work in the time frame you want may be a manual process. I don't know of a means of designating peak and off peak times.

 

[x4dow]

Averages probably are the numbers you need to use since that's likely what the net cost will reflect.

As long as you run the numbers, and it makes sense to you, that's all that matters. An electric oven is likely higher than 2050W. Ours is 3500W, but I don't know what's typical.

Getting it to work in the time frame you want may be a manual process. I don't know of a means of designating peak and off peak times.

i feel like i would get a faster (and easier) return on having it grid tied and automated, but this is not my home (rental) so likely wont be able to do that until i get my own place