diy solar

diy solar

New home build, off grid day 1 planning

Quattrohead

Solar Wizard
Joined
Oct 13, 2021
Messages
3,732
Location
Florida
Hello all,
I am planning to build a new house and have the desire and opportunity to go off grid due to no city water/sewer, so I will have my own well and septic.
House is in the Florida central east coast area and will be 6" ICF concrete walls, closed cell spray foam roof insulation and high quality double pane windows and doors, variable speed HVAC heat pump and hybrid water heater. In other words very energy efficient. The heat load calculated to around 2.5 tons for 2500 sq/ft.

I have a spreadsheet of the electrical circuits and I am wondering how to split them up between 24/7 essential circuits and non critical circuits.
Initially it seems obvious...AC and keep the lights on at night !!!!
But I would also like some fail over built in, as in if one solar system develops a fault I can switch essentials over to the "other" system.
I am using Emporia to monitor our power usage at our current old house built in 1980 so it basically acts like a greenhouse LOL, terrible insulation. I don't think our usage pattern is going to change too much, thinking less AC load replaced by pool and well pumps.
 

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How much are you looking to spend on the power system?

Just FYI, unless you want to spend a lot, nobody does an electric stove or any other heating off of batteries. It's all gas or propane.
 
My energy requirements ?
Having learned our energy use from Emporia, our highest month of use (August) is around -
55% 730 kWh/m HVAC
12% 150 kWh/m Hot water
5% 75 kWh/m Dryer
3% 35 kWh/m Stove
25% 320 kWh/m outlets/lamps/small appliances etc
Like I said in my first post, I think the overall energy use pattern will be similar but HVAC load moves towards the pumps.

What size should my panel generation be, Inverter(s) and batteries for nights and say 3 days of no sun. I do plan on having the system be able to use a generator to recharge the batteries as a last resort.

I will have unlimited space for panels on the ground and some great south and east facing roof space too. I kind of like the roof option to "shade" some of the heat off the roof but also like the ground option for cleaning and maintenance.
Oh, I should have also said I am an elecrto-mechanical engineer and am well capable of putting this all together myself along with the excellent support of this user forum.
Thanks Will and co for making such a useful resource.
Cheers, Kevin.
 
How much are you looking to spend on the power system?

Just FYI, unless you want to spend a lot, nobody does an electric stove or any other heating off of batteries. It's all gas or propane.
I will spend what it takes, expecting over $200k for the house alone. No gas here and Mrs QH want's a flat top stove. Heat will be from the heat pump, maybe 15 mins 10 days a year !!!
 
I will spend what it takes, expecting over $200k for the house alone. No gas here and Mrs QH want's a flat top stove. Heat will be from the heat pump, maybe 15 mins 10 days a year !!!
I’m no expert but it seems to me you shouldn’t have any problem using a flat electric cooktop (induction?) provided you have enough battery storage. Same with heating.
 
I will spend what it takes, expecting over $200k for the house alone. No gas here and Mrs QH want's a flat top stove. Heat will be from the heat pump, maybe 15 mins 10 days a year !!!
Check out https://www.altestore.com/store/calculators/off_grid_calculator/ for a good calculator. Just FYI, your usage is extreme compaired to what most people off-grid people are using. With quick math, you need about $330,000 worth of batteries to last you 3 days. Correction? is that green screen looking thing per month or year? I was thinking it was a monthly total, but now I see the blue year thing highlighted.
 
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Oh well… cooking with gas or propane beats electric anyday.
You won’t see any chefs with electric stove tops by choice…
 
Check out https://www.altestore.com/store/calculators/off_grid_calculator/ for a good calculator. Just FYI, your usage is extreme compaired to what most people off-grid people are using. With quick math, you need about $330,000 worth of batteries to last you 3 days. Correction? is that green screen looking thing per month or year? I was thinking it was a monthly total, but now I see the blue year thing highlighted.
Yep you are right, it's yearly. Actually about 6 months so far since I started using Emporia. That screen shot was to show my usage % of loads. Sorry I was not very clear on that.
 
You could install propane to run the cooktop and clothes dryer. A backup generator could also be run off propane. Sizing a system for the worst case could get expensive and you might still need standby power. If your wife wants to cook on induction then just allow batteries to support that. We love our induction cooktop. We had a large gas one at the last place and it was great for some stuff but overall I'll stay with induction.
 
Below is general numbers and not recommendations on items or even correct sizing.

So 6395kwh / 182 days (6 months) = 51 kwh used per day.
3 days * 51 kwh = 154 kwh of battery.

Picking a large battery at random.
Big Battery 17kwh pack for $7,000.
154 kwh / 17 kwh = 9.05 batteries.
9 batteries 8 $7,000 = $63,411 in batteries.

Solar panels (without mounts or wires) run about .60 a watt.
51,000 wh needed / 5 hours of sun, * 2 for partly sunny, = 20,000 watts of solar needed.
20,000 * 0.60 = $12,000 in solar.

Looks like you need at least an 100 amp service to run all the AC loads.
100 amps AC * 240 = 24,000 watts.
Contex XW Pro 6.8kw ($3,200 * 4) = $12,400

So about $87,811 for the basic items. You still need charge controllers, wires, solar panel mounts, taxes etc.
Around $100,000 sounds right with taxes and all the extras.
 
And if you are wondering how people (like me) live off-grid, we conserve power and pick the right technology for the purpose. I use, at most 10kwh a day. Hot water/cooking is propane ($50 to fill a 25 gallon tank once a year is cheaper then about anything else). And I find used deals on equipment. I just picked up 8 used 230watt panels for 0.20 a watt.
 
Everyone around me is off grid. 50kwh/day is quite normal for summertime use with AC in operation.

Inductive electric cooktops are great, i use one in my cabin.

If you want a cost effective system you will need to run a generator occasionally rather than making your battery 3 times the size.
 
Everyone around me is off grid. 50kwh/day is quite normal for summertime use with AC in operation.

Inductive electric cooktops are great, i use one in my cabin.

If you want a cost effective system you will need to run a generator occasionally rather than making your battery 3 times the size.
You must live in the upper class area of the off-grid community:). Around me, it's 10-20kwh/day at most.
 
Arrrgh electrical units ?
How do I convert kWh/d into kW of inverter output ??? Split phase 120/240V
 
Arrrgh electrical units ?
How do I convert kWh/d into kW of inverter output ??? Split phase 120/240V
Energy units, not always electrical. Once you convert it into watts, the volts does not matter for the purpose of energy calculations.

As 10kw Inverter running at full load for 24 hours (one day), is (10 * 24) = 240kw a day.
A 10kw inverter at 120v (10,000 / 120) = 83 amps (at 120v).
A 10kw inverter at 240v (10,000 / 240) = 42 amps (at 240v).
 
Below is general numbers and not recommendations on items or even correct sizing.

So 6395kwh / 182 days (6 months) = 51 kwh used per day.

Maybe you should replace the battery in your calculator :)

6395 / 182 = 35,1 kWh / day
3 day = 105 kWh

3 days * 51 kwh = 154 kwh of battery.

Picking a large battery at random.
Big Battery 17kwh pack for $7,000.
That is maybe one of the most expensive battery.

For $2700-$3000 you get 14,4 kWh EVE cells.
8 pack gives you 115 kWh and it costs 8x3000 = $24,000 (+BMS +cable +box +...)
 
Maybe you should replace the battery in your calculator :)

6395 / 182 = 35,1 kWh / day
3 day = 105 kWh


That is maybe one of the most expensive battery.

For $2700-$3000 you get 14,4 kWh EVE cells.
8 pack gives you 115 kWh and it costs 8x3000 = $24,000 (+BMS +cable +box +...)

Thanks for the correction on the math.

I picked an easy off the shelf battery. There is cheaper. And as you stated, DIY is always an option, if OP wants to do the footwork and assume the risk.
 
Thanks for the correction on the math.

I picked an easy off the shelf battery. There is cheaper. And as you stated, DIY is always an option, if OP wants to do the footwork and assume the risk.

There is the 10kWh complete pack that @Will Prowse tested for $3800:

Or 13,4kWh (280Ah so it is really 14,4 kWh) version for $5100. :


With 10 year warranty.
So there are good options :)
 
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You must live in the upper class area of the off-grid community:). Around me, it's 10-20kwh/day at most.

I live in Australia, where you can get a 4kw dual string MPPT charger, associated PV, racking and cabling for well under $1k second hand.

Two of these linked into a decent hybrid inverter / 500ah of LiFePO4 / an 8kw diesel generator - you have all the power you need for well under $30k AUD.

A decade ago when i set up off-grid all electric with reverse cycle aircon it was virtually unheard of. Pretty much everyone that has seen my system since then now has one similar.

Biggest problem with people recommending off grid systems is they have never actually lived off grid with a decent system. You’d be amazed how many “professional” installers still oversize batteries - and worse still orient panels for overall maximum production rather than maximising morning and evening production.
 
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