First steps - help needed

[brianlowe]

I've been reading web sites, watching videos and scouring suppliers' catalogues for a while now, and I feel like I have a handle on the vocabulary and the component parts, but actually deciding on even the basics of a system has me confused.

Here's a system that's settling in my head, but before I start spending actual money I need someone to point out where I'm being stupid...

I'm in the UK so it's going to need to serve 240v AC at 50Hz.

I'll have a constant load (fridge/freezer, network hub, CCTV base unit, security lighting, etc.) amounting to about 400W so ~ 10kWh per day.

I'll have short-term loads (coffee maker, washing machine, tumble dryer, hair dryer, power tools, etc.) amounting to no more than about 3kW at any moment, and in use for short periods (coffee maker takes a couple of minutes (several times every day), washing machine cycle takes 90 minutes, 2 or 3 times per week, etc.) averaging ~ 5kWh per day.

I expect a large inverter to have an 'idle' draw of a couple of Amps, so I'd like to keep it powered down until/unless there's a high load demand. I'll have a small-ish inverter to power the constant loads (maybe this https://www.bimblesolar.com/offgrid...s/1000w-high-freqency-inverter-48v-SHI1000-42), wired to a distribution box and a set of power outlets, which I'll mark "24h". A second, large inverter (maybe this https://www.bimblesolar.com/offgrid...rs/3000w-high-freqency-inverter-48v-SHI3000-4) will be wired to a separate distribution box and a separate set of power outlets, which I'll mark "Not 24h" (or something).

If my battery is 48v the inverters will need to draw 10A and 65A respectively, so to wire the battery to the inverters I'll get away with 14 gauge (1.5mm) for the constant load and 4 gauge (25mm) for the high load.

Drawing 16kWh per day from a 48v battery will take 333AH, so to make up a 3 day 'reserve' I'd need 1000Ah.

To collect solar energy I'll roof mount a P.V. array of 12 x 255W (30.5v, 8.3A) panels (like these https://www.bimblesolar.com/solar/individual/255w-amerisolar-used) (arranged 2S 6P) giving (up to) 61v and 50A (3kW) and feed the result into an MPPT controller (something like this https://www.bimblesolar.com/offgrid/mppt/Tracer6415AN).

My location gets 3.5 sun hours per day (on average), so solar is going to give me 10kWh at most, but wind is plentiful here so I'll supplement it with a wind turbine. Noise may be an issue and VAWT seems the quieter design, but there are way to many warnings about false claims by suppliers on power output so I may need to go with a standard horizontal design, unless someone can recommend a good VAWT supplier.

Power from the wind turbine will go into a 2nd controller, (something like this https://www.bimblesolar.com/offgrid/mppt/midnite-mppt/midnite-classic-150-mppt) with both outputs simply connected in parallel across the battery (I watched Will's video assuring me that they will not fight if I connect them this way).

For a 48v battery I found this... https://www.ruixulithiumbattery.com/12v-2560wh-lifepo4-set-with-200ah-cells-without-bms
labelled 12v, 2560WH, 200Ah (for additional confusion the same thing without a BMS is offered for $120 more)

Stringing 4 in series (for $3750 / £2300) gives me my 48v, but still only 200Ah.

Do I really need 20 of these (4S 5P) to supply my system? Can I start out with 200Ah and see how it goes, and add another 200Ah set later if necessary?

That's the plan so far. If my logic is flawed, please correct me. If I'm being naive or stupid, please point out where I'm wrong. If I've missed anything important, please let me know.

 

[Newenough]

Its the 3 day reserve time thats hurting you. Do you really need it? If you go that many days without the potential for Sun consider more wind turbines instead of more battery. Also, you may want to have an additional charge source such as a small inverter generator. Have your day or two of battery and use the gen to charge if needed. At 200ah X 48v (about 10kwh) a small 2300 watt should get you to 80% charge in 4-5 hours. 1 gallon or less of fuel? A lot cheaper than all the extra batteries. Then if you like add more batteries over time. It would also give you time to learn your system and how to maintain it with less risk. JMHO.

 

[svetz]

...deciding on even the basics of a system has me confused. ... before I start spending actual money I need someone to point out where [I don't get it]...

Hey Brian!

Measure twice and cut once! Love it! Let's dig in and see... I've tried to summarize your post to the facts and questions, and answered what I could; although I might not have gotten the questions right; so just straighten me out anywhere I went wrong.

I'm in the UK so it's going to need to serve 240v AC at 50Hz.

For real? Wikipedia lists the UK is listed as 230V @ 50 Hz (although, there's a +/- 8%, so you could easily see 240V in your house) and that bathrooms may have lower voltage "shaver supply units ". Probably doesn't make a difference for this, but I worry there's a sweet spot for the efficiencies that might otherwise be off.

Facts

1. Normal devices amount to 400W, 400 W x 24 hrs / 90% inverter efficiency ~= 10.7 kWh/day total power
2. Special devices draw 3kW for 90 minutes, roughly twice a week, motor inrush amps unknown.

Questions

1. Q: If I have two inverters, one would draw 10A@48V and the other 65A@48V. What gauge do I need?
   A: see What wire gauge should I use? Or, jump to the Calculators.
2. Q: Drawing 16kWh per day from a 48v battery will take 333AH, so to make up a 3 day 'reserve' I'd need 1000Ah.
   A: Correct! But, doesn't include DoD, temperature, or draw rate losses, see Battery FAQ
3. Q: PV array of 2s6p 255W (30.5v, 8.3A) gives 61V and 50 Amps?
   A: Correct! But, you also need to factor in temperature correction for voltage and amperage on your coldest day, see Figuring out how many panels in series and parallel based on your MPPT. Get those numbers and validate against your MPPT.
4. The insolation map has 3.5. So, the 3 kW PV array will generate 10.5 kWh/day on average?
   A: No, you'll have other losses (wire, MPPT, battery), I generally use an 80% efficiency, so more like 8.4 kWh/d
5. Q: a 4s5p configuration of 12v @200 Ah cells provides 1000 Ah@48V?
   A: Correct!
6. Q: Can I start out with 200Ah and see how it goes, and add another 200Ah set later if necessary?
   A: Yes, but.... see Incrementally adding DC batteries
7. Q: Do big inverters have higher idle draw? If so, does it make more sense to get two inverters and leave the little one on 24x7 and only power up the "big one" when I want to do laundry?
8. Q: Can someone recommend a quiet wind turbine?

Hopefully others can help you out with the ones I couldn't answer. If any of it doesn't make sense please let me know.

 

[brianlowe]

Its the 3 day reserve time thats hurting you. Do you really need it?

I guess not. 3 days just seems to be the common advice.

Also, you may want to have an additional charge source such as a small inverter generator.

Brilliant!
I have a 3kW generator which has been powering tools (and the beer fridge) while the build progresses. I'll be sure to look for a charge controller with a utility input so the generator can be brought on when needed.

 

[brianlowe]

For real? Wikipedia lists the UK is listed as 230V @ 50 Hz

That's correct. We're nominally 230v @ 50Hz, but appliances are still sold labelled as 240v and that's what people expect. I don't suppose the difference is noticeable in most cases though. Most of Europe thinks they're on 220v but they're nominally 230v too.

Q: Drawing 16kWh per day from a 48v battery will take 333AH, so to make up a 3 day 'reserve' I'd need 1000Ah.
A: Correct! But, doesn't include DoD, temperature, or draw rate losses, see Battery FAQ

I wasn't taking into account depth of discharge. Back to the calculators...

Q: PV array of 2s6p 255W (30.5v, 8.3A) gives 61V and 50 Amps?
A: Correct! But, you also need to factor in temperature correction for voltage and amperage on your coldest day, see Figuring out how many panels in series and parallel based on your MPPT. Get those numbers and validate against your MPPT.

I also wasn't taking into account panel performance changes due to weather. Back to the calculators...

Q: The insolation map has 3.5. So, the 3 kW PV array will generate 10.5 kWh/day on average?
A: No, you'll have other losses (wire, MPPT, battery), I generally use an 80% efficiency, so more like 8.4 kWh/d

and I was making assumptions about rated output and ignoring losses.

Lots to think about while I adjust my calculations.

Thanks!

 

[Newenough]

I guess not. 3 days just seems to be the common advice.

Brilliant!
I have a 3kW generator which has been powering tools (and the beer fridge) while the build progresses. I'll be sure to look for a charge controller with a utility input so the generator can be brought on when needed.

I feel you would be better off looking for an inverter/charger that meets the need For generator backup charging (Victron MultiPlus line are awesome). An mppt controller/inverter/charger (all on one type) I feel puts to many "eggs in one basket" and you're limited by the systems performance in any one of the 3 jobs asked of it.. Seperate componates also reduce the impact of a total system loss if it fails. You are also able to upgrade components as needed. Inverter/charger (backup charge source), MPPT CC's as main source for charging. If your inverter should go, you can have a cheapo backup unit on hand until the replacement arrives. If an MPPT should go (or no sun), you can charge via genny until repaired or sunny again.

As for your generator. 3kw is a good size but is it an inverter type? Thats pretty important if you like your more sensitive electronics (computer, frige, AC) to stay healthy. Non inverter types are notorious for killing or severely shortning the life of said devices.

 

[brianlowe]

As for your generator. 3kw is a good size but is it an inverter type? Thats pretty important if you like your more sensitive electronics (computer, frige, AC) to stay healthy. Non inverter types are notorious for killing or severely shortning the life of said devices.

"inverter type" didn't figure in any way when I was looking for a generator. I got a balance between power and price, with just the proviso that it had an electric start (I can't expect my wife to do the recoil start thing when I'm not there). I'll look at the manual and see whether it's output is smoothed or regulated in any way, or needs to be conditioned.