So I'm considering doing a complete solar panel/powerwall setup for two main reason: lower my electric bill and use it as a backup in case of Hurricane outages (I live in South Florida). My normal daily usage is around 95Kwh (yes it's huge, but I tend to like it cold indoors so most of this are my 2 central AC units). Telsa's calculators are helpful but I'm not sure I'm getting the right info. With a 3 Panel / 3 Powerall setup, what would that look like in terms of savings on electric? During a hurricane power outage I would drastically cut my usage to probably 1/3 of my normal usage and just have the basics running. My home is in a perfect location for solar.. No shade, direct light, etc... I guess I'm not sure how big of a system I would need.
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Newbie to Solar/Powerwall
- Thread starter SouthFLGuy
- Start date
The kWh amount per day is incomplete. You want to know the peak amps and load for each of your ACs (written on the AC unit), your watts for hot water heater ( on the water heater), refridges, estimates for lights. That should get you into the ballpark.
At 95 kWh per day, I’d guess that’s around 10 hours of sunlight, so about 10 kW per hour? So at 300 watts per panel, that’s 34 panels to be off-grid. At 400 watts per panel, it would be 25 panels. 400 watt panels cost more than 300 watt panels.
I don’t know about battery storage, but with better answers to the above info you’d be able to decide on powerwalls.
( Happy owner of 20 panels, but not off-grid...)
At 95 kWh per day, I’d guess that’s around 10 hours of sunlight, so about 10 kW per hour? So at 300 watts per panel, that’s 34 panels to be off-grid. At 400 watts per panel, it would be 25 panels. 400 watt panels cost more than 300 watt panels.
I don’t know about battery storage, but with better answers to the above info you’d be able to decide on powerwalls.
( Happy owner of 20 panels, but not off-grid...)
Panels are generally rated at 325watts each. That means that each panel, at peak, can produce up to 325 watts of power. That means that over a course of an hour, at peak, each panel will produce .325kw hours of power (kWh).
Doing the math, if you had 30 panels, you would have a system capable of producing approximately 10kWh. Your daily production from solar with this system will vary greatly based on weather and time of the year. Expect total daily production of 5kWh on the very low end (dark, rainy November day), and maybe 80kwh on the very high end (cool, sunny day in May).
Powerwalls EACH have a capacity of 13.5kWh. Doing the match, if you had 3 Powerwalls, you would have about 40kWh or capacity.
Charging from solar, Powerwalls can each take up to about 5KW on the draw (when charging). What does this mean? It means that it will take about 3 hours of bright sunlight to completely re-charge your Powerwalls when they are depleted.
Powerwalls can expend their energy at peak rate of 5-7KW (per PW). Doing the math, if you had 3 PW's, they could send up to 15-20KW to your house at any point in time. If the grid is down and you are getting no solar production, the batteries will be fully depleted 2-3 hours.
Now, you really have to look at your homes consumption relative to the estimates I provided above. In terms of cost savings, you need to look at your per kWh cost of electricity from the utility.
Most folks with Powerwalls will run the house on solar during the day, and use the PW's at night. I personally keep my batteries at 100% and use them only for grid outages (which are frequent in my area).
If you do decide to go with Powerwalls, it is not practical to run central A/C on them in an extended grid outage. 2 outside AC units will probably be pulling 7kWh or more when running.
PS- you should really delve into the amount of electricity you are currently using. There are lots of easy ways to reduce your consumption.
Doing the math, if you had 30 panels, you would have a system capable of producing approximately 10kWh. Your daily production from solar with this system will vary greatly based on weather and time of the year. Expect total daily production of 5kWh on the very low end (dark, rainy November day), and maybe 80kwh on the very high end (cool, sunny day in May).
Powerwalls EACH have a capacity of 13.5kWh. Doing the match, if you had 3 Powerwalls, you would have about 40kWh or capacity.
Charging from solar, Powerwalls can each take up to about 5KW on the draw (when charging). What does this mean? It means that it will take about 3 hours of bright sunlight to completely re-charge your Powerwalls when they are depleted.
Powerwalls can expend their energy at peak rate of 5-7KW (per PW). Doing the math, if you had 3 PW's, they could send up to 15-20KW to your house at any point in time. If the grid is down and you are getting no solar production, the batteries will be fully depleted 2-3 hours.
Now, you really have to look at your homes consumption relative to the estimates I provided above. In terms of cost savings, you need to look at your per kWh cost of electricity from the utility.
Most folks with Powerwalls will run the house on solar during the day, and use the PW's at night. I personally keep my batteries at 100% and use them only for grid outages (which are frequent in my area).
If you do decide to go with Powerwalls, it is not practical to run central A/C on them in an extended grid outage. 2 outside AC units will probably be pulling 7kWh or more when running.
PS- you should really delve into the amount of electricity you are currently using. There are lots of easy ways to reduce your consumption.
2012MS85
Member
You’re going to need a HUGE check if you really want a system that supports your 95 kWh per day consumption (think $100k BEFORE tax credits/incentives for about a 25- to 30-kW solar panel system plus a handful of PW2s). My 16.1-kW ACPV system produces an AVERAGE of 50 kWh/day (my best day was 107 kWh over the past 3 years; worst was 11 straight days of 0 kWh during a sub-zero ice&snow event...that won’t happen in FL). My system was $50k before $20k in US & IA tax credits. Your system likely needs to be at least 150-180% of mine, plus the installed cost of PW2s. Also keep in mind that many utilities are currently trying to take away from homeowners most/all of the solar savings by adding/increasing their utility company’s mandatory minimum monthly grid connection charge/demand charges. In Iowa where I live, Warren Buffett/Berkshire Hathaway Energy (MidAmerican Energy is their Iowa electric subsidiary) has received $5 Billion in wind Production Tax Credits...yet now they are pushing NEW Iowa legislation that would charge massive new monthly demand charges to every solar customer like me to “help pay for the grid” (that we all use for net metering). No one can escape the new demand charges, if passed, as we’re all legally required to be connected to the grid. When Buffet/BRK bought NV Energy in Nevada a few years back, they tried this same trick to kill home solar. Buffett only cares about his electric monopoly (that operates making billions in profit every year in more than a dozen states), and he is openly against homeowners receiving any of the financial benefits of owning solar. So beware of this risk in your state.
On a positive note, start by reducing your demand. Have you replaced every light bulb with a $1 LED bulb? (85% less energy vs traditional bulb) Are both your A/C units the MOST efficient possible? (highest possible SEER rating). If not, replace those first for far better/quicker return on investment. Do a whole home energy audit to find savings/solutions. Maybe add tint to your home windows; it works in sunny states like FL & TX. My home uses an average of 30 kWh/day (with 2 A/C units cooling 6k ft.sq. on 3 floors, used mostly during humid Iowa summers), plus another 20 kWh/day for my 4 EVs. So my demand matches supply on an annual basis (18-19 MWh/year).
On a positive note, start by reducing your demand. Have you replaced every light bulb with a $1 LED bulb? (85% less energy vs traditional bulb) Are both your A/C units the MOST efficient possible? (highest possible SEER rating). If not, replace those first for far better/quicker return on investment. Do a whole home energy audit to find savings/solutions. Maybe add tint to your home windows; it works in sunny states like FL & TX. My home uses an average of 30 kWh/day (with 2 A/C units cooling 6k ft.sq. on 3 floors, used mostly during humid Iowa summers), plus another 20 kWh/day for my 4 EVs. So my demand matches supply on an annual basis (18-19 MWh/year).
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Learning the electrical units of solar generation and your monthly electrical bill are valuable activities. Is your monthly bill about 95kwh x 30 days = 2850 kWh per month? At ~$0.20 per kWh that would be a $570 monthly bill? Note in your utility bill charge there is often a distribution charge at $ per kWh as well as a electrical charge of $ per kWh. Low states are around $0.12 total and I think Hawaii is almost $0.60 per kWh.
Total charges for a solar system should be around $3.50 per watt ( might be lower!). So for a 10 kWh system, you could expect to pay around $35k before tax incentives just for the solar system. Powerwalls would add more $$$.
In good weather, 10 kWh should generate about 2,000 kWh per month, assuming 8 hours of sun and 25 days of good weather. Not off-grid, but close.
Unless you really are using 95 kW per hour...
2012MS85
Member
@Thp3 has many good points and data to contemplate, but I’d caution that his expected solar output seems far too optimistic. I’m in Iowa, which has good solar output...but clearly not as great as OP would enjoy in FL. I’d expect a possible 30% improvement over my Midwest location in terms of overall annual output based on many online sources available to anyone who wants to do the research. My 16.1 kW (gross) ACPV solar system (14 kW net, which is true max output...but not the rating most discuss, certainly not quoted by most solar salesmen) produced a bit over 18 MWh annually (over each of the past two years). So that’s an average of 1,500 kWh per month (spring/summer high is 2.5 MWh vs snowy winter worst month was 0.5 MWh). So to extrapolate my 1.5 MWh monthly average with a 16.1 kW system, a 10 kW system (62% of my kW setup) in Iowa should produce about 0.93 MWh on average per month (1.5 / 16.1 x 10). Add an estimated 30% improvement for sunny FL (0.93 x 1.3) and that’s 1.2 MWh that I’d predict for a typical 10 kW FL solar system. It’ll clearly have higher output in the summer with longer daylight hours and less in the winter when we enjoy fewer hours of sunlight. I’d welcome others with real-world FL home solar to share your ACTUAL data so the OP has real data to consider. FYI, every single solar proposal I received greatly exaggerated the solar output my system should/would produce (essentially quoting a best case scenario). My results match fellow Iowans’ solar production.
Solar only produces “peak” output when the sun is directly overhead, and the rest of the day creates a bell shape around that peak. That’s why you can’t simply calculate 8 hours times one’s peak rating (8 x 10) and expect 80 kWh on a perfectly sunny day without a single cloud. Four hours before and after the peak moment at mid-day will be some far lesser amount (~50% of peak). I’ll share a snapshot of this bell curve output in a future post.
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Unfortunately yes I'm using an average of 95kwh per day (the bill is about $400). So I think I also need to go back to the drawing board and see what I can do to first lower this on a daily basis. I work from home so that's probably a big reason why. It's a medium/large house at 3,000 sq ft and 2 AC units. And this 95kw is before buying my Model 3 which will be in a few months. Realistically I know that my usage is very very high. So I think I also need to look at insulation, windows, applicances, etc... My spouse and I fight over the temp (I'm always hot). If I had to guess, most definitely the AC is what is affecting my usage numbers. For the backup piece, sure a generator is cheaper but it's not the future either.
I have a 2800 square foot house. I need about 10kWH per day to run ESSENTIALS (fridge, well pump, oil furnace fan, LED lights, internet). With a 6.6KW PV and two Powerwalls i can pretty much self-sustain with that level of energy consumption in an extended grid outage..... the exception possibly being November/December and/or in situations of major ice/snowfall.
2012MS85
Member
Here are three snapshots of a recent “perfect solar day” that occurred on April 19, 2019. My total solar production was 105 kWh, which was extremely close to my all-time daily record of 107 kWh that occurred exactly one year prior. Some may be surprised that my record wasn’t set during a longer summer day, but the reason for that is HEAT...the enemy of solar
Solar systems love sun (go figure), but they perform to their peak potential when they’re not limited by extreme heat and humidity that obviously occurs in summer. My 1st snapshot above depicts my 15-minutes of energy output at the peak window of 2:15-2:30pm (3.5 kWh in 15 minutes, which equates to my ideal NET capacity rating of 14 kW...so 14 kWh of solar energy produced in one hour). So even my PERFECT output is only 87% of my system’s gross kW rating (14.0 / 16.1). The 2nd snapshot shows my output 4 hours before peak (10:15am)...1.7 kWh in 15 min, which equates to 6.8 kWh...or 42% of gross rating. My 3rd snapshot shows 6:15pm output of 1.6 kWh, which equates to 6.4 kWh...or 40% of gross rating.
Hopefully these real-world Iowa solar production numbers and bell charts are helpful to OP and anyone else considering home solar. Good luck
@SouthFLGuy there have been a lot of useful information in this post. I would also suggest you look into a solar co-op. Solar United Neighbors is a multi-state organization that has co-ops in many Florida counties. It's a non-profit organization that helps people considering solar to install in groups. The basic idea is a large group of people send out a request for bids from local installers, the group vets and selects an installer and use bulk buying power to lower the per watt cost of the installation. Unfortunately they were not active in my county when I installed solar panels but I used one of the installers they selected in another county when I expanded my system. I wish they were available when I wanted solar.
Solar United Neighbors
I would also suggest you checkout Google's Project Sunroof. It will give you a very general overview about the amount of sunlight you can expect per year and size of system you may need to offset a certain percentage of your bill. There was another site that told you average sun hours per day your home can expect.
Project Sunroof
I agree with everyone who suggests you get an energy audit and see what non-solar things you can do to your home to reduce your demand. Simple changes can have a great impact. You can also check your utility. They may have tools to help you reduce your demand based on your usage. They may offer rebates on energy efficient upgrades. You also need to check your utility to see the maximum size (kW) solar system they will allow. My utility considers anything about 10kW as commercial and imposes extra restrictions, the co-op will let you know these things.
I live in central Florida, and in the summer It seems to rain everyday in the afternoon. I have a 10kW system with two powerwalls and I can run my entire house off the powerwalls including AC on a sunny day for 24 hours (depending on the season). I also think about the best time of the day to run certain loads. Disclaimer my energy needs are significantly less than yours, about 30kWh average per day.
Solar United Neighbors
I would also suggest you checkout Google's Project Sunroof. It will give you a very general overview about the amount of sunlight you can expect per year and size of system you may need to offset a certain percentage of your bill. There was another site that told you average sun hours per day your home can expect.
Project Sunroof
I agree with everyone who suggests you get an energy audit and see what non-solar things you can do to your home to reduce your demand. Simple changes can have a great impact. You can also check your utility. They may have tools to help you reduce your demand based on your usage. They may offer rebates on energy efficient upgrades. You also need to check your utility to see the maximum size (kW) solar system they will allow. My utility considers anything about 10kW as commercial and imposes extra restrictions, the co-op will let you know these things.
I live in central Florida, and in the summer It seems to rain everyday in the afternoon. I have a 10kW system with two powerwalls and I can run my entire house off the powerwalls including AC on a sunny day for 24 hours (depending on the season). I also think about the best time of the day to run certain loads. Disclaimer my energy needs are significantly less than yours, about 30kWh average per day.
I forgot to mention this before, checkout the mayor of South Miami's blog. He ran a test to see if he could survive off grid for 1 week using his Powerwalls. On day 6 he does some rough calculations about whole house generators vs Powerwalls. Our area was affected by hurricane Irma in 2017. We were lucky, and lost grid power for only 34 hours. Some were without power for 2 weeks. The powerwalls worked. We did not notice the grid was gone until the hurricane passed and I checked the app.
The one negative of the powerwall performance during Irma was that the AC did not work. I called Tesla after things settled down determined that I needed a SureStart soft-starter. Tesla had the part installed and now the AC works without the grid. Luckily post hurricane the area was cool and ceiling fans were all we needed, but I did appreciate Tesla resolving the problem relatively quickly.
SomiSolar
If you do decide to get quotes for solar + storage, it may be useful to see what a whole house generator would cost as well. It should not cost you anything to find out other than time. Because of your large energy requirements, the expense of covering that load may prevent you from going completely off grid, but you can see what it would cost to keep your family comfortable post hurricane/grid outage.
The one negative of the powerwall performance during Irma was that the AC did not work. I called Tesla after things settled down determined that I needed a SureStart soft-starter. Tesla had the part installed and now the AC works without the grid. Luckily post hurricane the area was cool and ceiling fans were all we needed, but I did appreciate Tesla resolving the problem relatively quickly.
SomiSolar
If you do decide to get quotes for solar + storage, it may be useful to see what a whole house generator would cost as well. It should not cost you anything to find out other than time. Because of your large energy requirements, the expense of covering that load may prevent you from going completely off grid, but you can see what it would cost to keep your family comfortable post hurricane/grid outage.
View attachment 401591 View attachment 401592 View attachment 401593
Here are three snapshots of a recent “perfect solar day” that occurred on April 19, 2019. My total solar production was 105 kWh, which was extremely close to my all-time daily record of 107 kWh that occurred exactly one year prior. Some may be surprised that my record wasn’t set during a longer summer day, but the reason for that is HEAT...the enemy of solar
My 1st snapshot above depicts my 15-minutes of energy output at the peak window of 2:15-2:30pm (3.5 kWh in 15 minutes, which equates to my ideal NET capacity rating of 14 kW...so 14 kWh of solar energy produced in one hour). So even my PERFECT output is only 87% of my system’s gross kW rating (14.0 / 16.1). The 2nd snapshot shows my output 4 hours before peak (10:15am)...1.7 kWh in 15 min, which equates to 6.8 kWh...or 42% of gross rating. My 3rd snapshot shows 6:15pm output of 1.6 kWh, which equates to 6.4 kWh...or 40% of gross rating.
Hopefully these real-world Iowa solar production numbers and bell charts are helpful to OP and anyone else considering home solar. Good luck
Thanks so much! This really helps me see a perfect kind of day and those expecations!
This is exactly what I wanted to read - someone's real-life experience in South Florida. It's a really cool read.
Yeah, AC has a large initial peak pull of amps to start the electric motor compressor. The refrigerator may also have such an issue. I had a slow start system, greater than 50% less amperage I think, installed on my geothermal system. That reduced my current needs. Running electric motors use much less amperage than at initial start. That’s why you should check the appliance.
I also have a whole house natural gas generator, in addition to solar panels, for loss of electric power from the grid.
hodad66
Member
Great info on the "SureStart soft-starter" as I am interested in hurricane backup also. I could make due with the ceiling fans
& fridge if I have to but for a 2-3 hour blackout I sure would like to still have AC. Small house (765 under air) system to be
determined with the Tesla inspection crew coming out on Tuesday. I'm hoping that 2 PW's will work fine. In general I keep
the thermostat at 81 degrees with ceiling fans & 79 to sleep. My highest month was last July at 1156kwh.
& fridge if I have to but for a 2-3 hour blackout I sure would like to still have AC. Small house (765 under air) system to be
determined with the Tesla inspection crew coming out on Tuesday. I'm hoping that 2 PW's will work fine. In general I keep
the thermostat at 81 degrees with ceiling fans & 79 to sleep. My highest month was last July at 1156kwh.
I am plannig to install a metal roof with flexible panels between some of the ridges. I figured I coud install about 40 panels of 300w rating? (I am just, today, beginning my analysis.) And space for a few more sorter less capacoty ones - 29 at 140 W. In Michigan,, facing SSE no trees, I hope to be essentially off the grid. SO, assuming 50% of the day - week etc gets the sun, and generates 10 KW per hour, does the power go directly into the Powerwall (PW) then, is released when needed? Wll 2 powerwalls do the job? I will get the amps list. Since I understand that Michigan has now changed the netmetering to be useless, I am unsure how to proceed. I also have a whole house generator for essentials.
