Should I invest in grid tied solar +power wall? Need help


MASSIVE restock of EV Batteries at www.batteryhookup.com 5% coupon "POWERWALLS"

Christopher Fusco

New member
Joined
Sep 14, 2017
Messages
2
Hello, I am very new but curious to The whole power wall scene. I live in Florida down south recently hit by hurricane Irma and have been without power for 6 days now. So right now all I dream of is solar and stored electricity lol. The main purpose of this thread will be to determine cost of starting project and how long will the return on investment take place.

These are some of my details.
Live in Florida east coast.
Cost of kWh is $.12
I use about 66 kWhaverage daily(because I'm a American slob ?)
About 40kwh is used while sun is not out and 25kwh is used while sun is out.
Monthly bill for electricity is about $225-250 a month during summer and about $170-200 during winter.

Questions:
1. How many solar pannels (recommend watt panels ) would I need to have at least 80%-90% off grid for house use and battery backup for my daily use.
2.how many 18650 cells would I need granted I am getting them at $1-1.50 per celland at 2300-2400 mah.
3. What recommended wires/gauge needed to series these properly and safely.
4. What inverts, converts, wiring, BMs, etcany other components needed to have this all grid tied and costs of those items.

I guesstimated in a 30pannel 250w solar system @ about $7500 pannels only. 7kwh system and about 5,000 cells in that 2300-2400 range for about another $7500 batteries only. Not including all the other important components, let's just say for the right quality equipment another $5000 putting my total project at 20000 my return on investment is about 7-8 years ?

Is it worth it and what's the life expectancy of the cells and panels?

If anyone was to help I bless you considering I'm very vulnerable right now sitting with no power for so long.

Thanks
 

daromer

Moderator
Joined
Oct 8, 2016
Messages
5,662
Im going to answer your questions based on where I live.

First of all you need to lower your consumption for it to be worth. You have very low cost for electricity....
1. 66kWh per day is 24000kWh per year. You need close to 30kW of solar panels... That is plenty
2. Im not sure how many cells you want since it depends on sooo many factors but if you do like me. You want up to 1 week of solar storage for bad weather you would need: almost 500kWh of storage. Lets say you get atleast 10% of sun a bad week (Thats what i get.. ) then you need 350kWh atleast... Thats:
350000/8 = 43750 cells in total

3. This question is way to early to answer since you need to settle #1 and #2 first.
4. Cant tell either but depending on peak load you need a 10kW inverter. And with all gear there we talk about perhaps 4000USD?

30 panel will not cover your 80-90% total unless you have magic sun :)

7-8 years is doubtful that you will get it in. I estimate mine in 12 years...

:)

5000 cells will only give you 40kWh total storage. Lets say you use 70% of those and get 30kWh.. Wont even take you through a night :)
 

Christopher Fusco

New member
Joined
Sep 14, 2017
Messages
2
daromer said:
Im going to answer your questions based on where I live.

First of all you need to lower your consumption for it to be worth. You have very low cost for electricity....
1. 66kWh per day is 24000kWh per year. You need close to 30kW of solar panels... That is plenty
2. Im not sure how many cells you want since it depends on sooo many factors but if you do like me. You want up to 1 week of solar storage for bad weather you would need: almost 500kWh of storage. Lets say you get atleast 10% of sun a bad week (Thats what i get.. ) then you need 350kWh atleast... Thats:
350000/8 = 43750 cells in total

3. This question is way to early to answer since you need to settle #1 and #2 first.
4. Cant tell either but depending on peak load you need a 10kW inverter. And with all gear there we talk about perhaps 4000USD?

30 panel will not cover your 80-90% total unless you have magic sun :)

7-8 years is doubtful that you will get it in. I estimate mine in 12 years...

:)

5000 cells will only give you 40kWh total storage. Lets say you use 70% of those and get 30kWh.. Wont even take you through a night :)
Trying to understand how it works makes my head hurt lol. I thought If I had a 7 kWh solar setup I could generate 7kwhs per hour the sun is capturing that energy. Minus what is being used at that current time. What's left over is stored for when the sun goes down.
I know there is no way to predict having sun most days which is why I would be ok using the grid in times I don't gain sun power to use or store. My battery system backup would only be needed to be big enough to run my house at the end of the night until sun comes back out. Not to live off for weeks.

But what your telling me is I would need a 30kwh system to have enough power to use during the day plus backup my 40kwh power wall? Which if they are 250w pannels I would need like over 100 panels?
 

DarkRaven

Member
Joined
Sep 2, 2017
Messages
1,223
66kWh a day is an enormous amount by my standards. I don't know too many people in the US and don't know if this is normal but I'd say it isn't. But then I don't know what your house looks like and what your habits are and how big your family might be. 66kWh a day is the amount of energy smaller companies and small to medium offices use. On that sort of energy consumption you would get into a business contract for bigger business and enterprise customers with the local supplier around here.

With 7kW worth of solar panels you might be able to cover your daily need IF you have full sun for 12 hours and the panels facing the sun in the right angle all the time. That will probably never be the case. You need 7kW facing three different directions at least, plus a bit more for when there is no full sun on and/or you not only want to run your house but also charge your batteries. 30kW worth of solar panels sounds about right. That's 120 250W panels and about 200m of surface of your roof.

If you use 66kWh a day and want to run off grid for a whole day, as an example, you need a bit more than that depending on how efficient your inverter is going to be. Let's assume 80% so you need more like 80kWh in battery storage. Even more if you don't want to charge them all the way up and run them all the way down. You are probably looking at 100kWh of battery storage. And you won't be able to charge that battery during a usual day so once you have used the capacity it will take some days until you can do that again because your 30kW solar isn't enough to power the house and charge this enormous battery. Which would be something like 14S800P = 11.200 cells.
 

daromer

Moderator
Joined
Oct 8, 2016
Messages
5,662
Dont mix kW and kWh :) A panel produces in W or kW.. You consume over time in Wh or kWh :)

1000W solar panels can under 100% best conditions make 1kWh solar per hour.. BUT. This is without ANY losses and you need to have the sun 100% above the panel with nothing in the way and all :)

In real life you get atleast 10% in losses just in converting. Another 10% if you run battery bank and with the cables... This depends a bit on what type of gear you buy. Inverters for 1000USD or 4000USD.

Based on this calculator you would be able to do 90% with 20kW of solar on the roof. So a little bit less than I calculated. This is though grid-tie without battery backup that will take some more energy in general. I think i got 28kW of solar needed based on if I compare to my numbers. We have very little sun during winter here.

https://www.wholesalesolar.com/solar-information/start-here/offgrid-calculator

I based it on zone 4 and 3.5hours per day since i added the winter hours
Note that this assumes you have the optimal position on the panels for the sun :)
 

egam

Member
Joined
Mar 9, 2017
Messages
109
go to google project sunroof. Type in your address and see what it tells you.

I live in illinois and have about the same cost for electricity. I use around 40 to 50 kwh per day. electricity bill about 150 per month.
It told me I needed around 10 kw of solar peak watt to eliminate my power bill. it calculates my payback would be 12 years. It uses $4 per watt installed.

I am planning to put in 15 -20 kw or twice the system and do it myself. My target install rate is less than $1 for solar peak watt. So that lowers my payback to 4-6 years if I can pull it off. I have a south facing roof with a lot of area. I am also planning to get electric vehicles in the near future.

I am intrigued by the tesla power wall 2. From the video I saw from an installation from south australia, it does exactly what I want it to do. Grid tied power with a lot of self usage and backup power.

I would look at your power bill and seriously understand your loads. Which months are highest? What is driving the consumption that high?

If it is Air conditioning, you are money ahead if you can reduce your need for A/C

1. Air sealing your house. Cheapest. (get a blower door test)
2. Extra attic insulation.
3. higher efficiency heat pump.
4. Desuperheater on your heat pump to preheat your hot water. This uses waste heat to heat your water. (electric water heating can be 40% of the bill)
5. Load control...to dump excess solar to your hot water heater. (peter and michael have good videos on this)
6. Heat pump water heater instead of straight electric. this uses half the power of straight electric.
7. Solar...you will now need much less solar. Have at least 3 quotes for someone else installing. If you are installing yourself, you need to learn.
8. power wall purchased at the same time. This will allow you to take a 30% federal tax credit on the batteries because they are part of the solar install.

9. A good backup generator. If you are buying a power wall system, the minimum needed to get through week will be too expensive. Going a Whole week is not needed for florida. You get sun almost every day. In the event the batteries get drained, you can still recharge the batteries with a generator during an outage. So you need shore power plugin for the generator.
 

wim

Member
Joined
Apr 6, 2017
Messages
556
40 - 50Kwh a day? that's a lot of power... 150$ a month? that's cheap....

I use 24 Kwh a day and pay 240 Euro a month, and if feeding back into the grid we have to pay extra... (100 Euro / Kw inverter / Year) for a 10Kw inverter it is 1000 Euro/Year extra...
So a solar setup with battery's is the way to go for me. Payback for solarless than 7 year :)
 

daromer

Moderator
Joined
Oct 8, 2016
Messages
5,662
In Sweden the payback time is lower if you just grid-tie than batteyr. Grid-tie and do it your self perhaps 8 years meanwhile battery 12. And if you let someone do grid-tie then 12-15 only... :)


Egam: 10kW of solar and it covers 50kw/day? That sounds like you have summer all the year around :) Im would love to live on such a place. We have winter months where we get 10% of the sun compare to summer....
 

dougal

Member
Joined
Sep 13, 2017
Messages
41
There seems to be a bit of confusion between an investment generating (!) a payback and theemergency back-up system that our friends in Florida wished they already had.
When I specified the (optional) spare tyre for.my car, the number of years before my investment was recouped simply did not enter the consideration!

The expensive inverter to convert battery Direct Currentto mains-like Alternating Current needs to be sized for the peak (not average) demand that it would have to cover. Peak is also a part of the consideration for a battery pack, but not so much for the solar where a battery is part of the system.

I too think that your first step should be to understand where all that energy you are usingis actually going to - and then seeing what can be done to reduce it (both peak and total).
A massive system to support massive consumption mighthave a payback of under ten years, but it is also going to involve a pretty massive capital outlay, and might be dominant in your environment, your space.
More energy-efficiency would allow a much smaller and cheaper system, which would be easier to justify as emergency insurance rather than a pure investment.

One aspect of an aircon environment is that you are paying for aircon power as well as the basic electric power that every product uses.
Take a lightbulb for example. A traditional 100 watt lightbulb generates 100 watts of heat, and you are going to use perhaps another 40 watts on the aircon to shift that heat outside. So replacing that 100 watt bulb with an equally bright approx 10 watt LED bulb is going to save you MORE than the 90 watts per bulb thatyou might initially expect. And you'd also need a much smaller solar/powerwall system to keep the lights on when the mains goes off.
 

egam

Member
Joined
Mar 9, 2017
Messages
109
daromer said:
In Sweden the payback time is lower if you just grid-tie than batteyr. Grid-tie and do it your self perhaps 8 years meanwhile battery 12. And if you let someone do grid-tie then 12-15 only... :)


Egam: 10kW of solar and it covers 50kw/day? That sounds like you have summer all the year around :) Im would love to live on such a place. We have winter months where we get 10% of the sun compare to summer....



Its kind of weird, but thats what project sunroof tells me. i put in $150 per month and it says 8.5 KW system. taking up 599 square feet of my available 1286 square feet of space for solar on my roof.

$150/.12 $/kwh = 1250 kwh/month this is 41.7 kwh per day on average. In reality, my energy use is 30 per day in the spring and fall and 50 per day in the summer and winter. I have some radiant electric floor heat, an electric hot tub spa, and air conditioning in the summer. I also have a heat pump water heater. My main home heat is forced air natural gas.

Net metering in Illinois allows you to store up credit in the summer days and spend it in the winter and at night.

I was being conservative when I wrote 10 KW system.


Below is the detailed analysis provided. Roughly $4/watt installed with net metering figured.

Up-front cost of installation

Based on a 8.5kW installation.

$34,701

Total payments over 20 years​

$0:Modern solar arrays use micro-inverters and should require no maintenance during their first 20 years.

$4,953: Remaining utility bills assuming2.2% annual price increases.
[size=undefined]
$4,953[/size]

State and Federal Incentives​

$10,410:Federal Investment Tax Credit (ITC)

$0:State tax credit
[size=undefined]

-$10,410[/size]




Solar Renewable Energy Credits (SRECs)​

Varies based on market price. Available for 10 years.
[size=undefined]
-$2,985[/size]



Total 20-year cost with solar​

Includes above costs and incentives.
[size=undefined]
$26,259[/size]



Total 20-year cost without solar​

Assumes2.2% annual increase in electricity prices.
[size=undefined]
$44,499
[/size]
 

daromer

Moderator
Joined
Oct 8, 2016
Messages
5,662
Interesting!
I couldnt run it where I live though so cant compare to what I calculates in sweden compare to what I used. (I have been running my system for 1.5 year now)
 

WallBender

Member
Joined
Sep 16, 2017
Messages
41
Those numbers are a bit high for US from my experience, but not unrealistic, my area's power is around $0.14/kwh and my bill runs $35-80 depending on what I'm doing. Most of my family seems to run $100-120/month

To convert that to KWh/day I use about 14kwh/day and most other people I know are around 26kwh/day.

Typical American home has electric hot water, electric stove, microwave, and a boat load of wall chargers, computers, huge tv's (vs standard sizes 10 years ago), AC and sometimes electric heaters.

Anyway, to show more options, how about a system that's more like a UPS rather than grid-tie? For example you use 66kwh/day when the power is on, if you can drop that number a lot to keep the bare minimum going (say hot water, lights, light computer use) you could size your system much smaller if you don't do other high draw activities that would eat the battery's power up faster like instead of watching the large tv, use a laptop or a cell phone. This would keep your life powered when the power's out, but doesn't do much more. It's similar to buying a generator, but instead of buying fuel for it, you pre-buy solar panels so you'd never have to refill if you don't drain more than panels can offer overall as stored in the battery bank.

This setup can go two ways in my mind, huge battery bank with less panels (store power up before power outage, and rely on the batteries alone to keep you going) vs smaller battery bank with more panels (sized more for dialy use when the power's out and if the power doesn't come on for a month, you'd be less effected).

I currently use UPS's in this kind of manor, when my power's out my desktop, router, and modem have backup power (should be lights too but didn't wire for it yet). Once the power goes out, I shut down my desktop and use my laptop, and only use it when I really need to instead of just general youtube watching, gaming etc. My UPS only has 2x 7ah 12v batteries, so it doesn't last all that long but gets my bare min done (I work online).
 

higher_wire

Member
Joined
Aug 30, 2017
Messages
61
You're really concerned with back-up power, so you should focus first and foremost on the powerwall. Build a sufficient amount of storage to last you up to a week on limited usage; that is, take down the heavy hitters such as AC and water heater during outages. You can add solar in the future.

Also keep in mind that a hurricane might be detrimental to solar panel health, so you might not even be able to generate your own power following a storm. A properly-built powerwall in a safe location will at least give you the back-up power you need.
 

ChrisD5710

Member
Joined
Sep 13, 2017
Messages
161
here is a link You may find usefull:

https://solarpowerrocks.com/florida/

and check conditions at Your local Utility Company, they will tell You how much they will pay You for each KWh You upload to the Grid and if there are increased Yearly rates for extra meters etc.

greetings

ChrisD5710 :)
 
Top