Newbie Off Grid Design Florida

Rhyolite · October 2022

I am located here in Central Florida. I would like to construct a small Off Grid system to power my pool pump (0.75 HP 230V 5.8 amps, 1.67 SF, THP 1.25) up to 14 hours a day. The secondary purpose is to run loads such as refrigerator and small lighting loads during a hurricane storm outage, potentially 3 days or more. In this mode the pool pump can be turned off or run in low speed. I am not considering grid tie because I want 9independence from the grid and battery back up.

I am a newbie as to the latest technology and have a lot of gaps. From what I read a pure sine wave inverter will be more efficient for motor loads. Knowing the cost benefit versus of a modified sine wave system would be helpful.

Challenges. I will need battery sized appropriately for running the pool pump during night time hours and alternately running a refrigerator and deep freeze during storm outage. To keep the system affordable I would consider lead acid batteries versus Lithium Ion.

My front rooftop faces south however parts of it are shaded intermittently by trees. Panel placement will be a challenge. If I must use a booster on the panels I will. Having a high voltage system might be advantageous to keep IR losses down as the batteries and panels might be some distance apart.

I would prefer to implement this system myself rather than employ one of the many "experts" that knock on my door.

Any recommendations on products and sizing would be appreciated.

Dave Angelini · October 2022

Bill can give you all math and advice. I tend to just look at the facts. That pump is a big load for that number of hours !

You can't have shade for solar to work right. High voltage is not going to help you and may be worse in shading. Saving on IR losses is way down at the bottom of the design goals if this is to work.

What is your budget? There is a point where just having a propane genset and a 500 gallon tank is far less costly and does all you want to do.

You are right to avoid the people knocking on your door. I have heard the stories. Tell them to get lost ! Good luck!

Photowhit · October 2022

Lived in North Florida on the grid and we didn't run the pool pump all night. I think it was on a grey box and ran an hour every 4 over night.

BB. · October 2022

Off Grid Solar is not cheap... Typically around $1 to $2+ per kWH (for full time off grid--For a few weeks a year backup, a large off grid solar system is not even in the ball park, cost wise) vs whatever you are paying for utility power (in California, can be $0.40 to $0.50 per kWH, in other states around $0.20 or so is common). And for backup power (a few days to a couple weeks a year) a generator is not a bad solution.

In general, a 1,000 WH (1kWH) per day is a "small system". Add a full time refrigerator, lights, small water pump, laptop computer, etc. and you are looking at 3,300 WH per day.

Your stuff (just raw numbers from post):

230 VAC * 5.8 Amps = 1,334 VA (call it Watts for now)
1,334 "Watts" * 14 hours per day = 18,676 WH = 18.7 kWH per day
18.7 kWH per day * 30 days = 561 kWH per month

Or pretty much the "average North American" home (no A/C, on natural gas/propane for heating and cooking).

We can talk about "solar friendly pumps" (More efficient, lower power, some can run directly from solar array while sun is up)... But for a first pass--I will do a calculation based on 18,676 Watt*Hours per day just to show how the math works:

18,676 Watt*Hours per day * 1/0.85 AC inverter eff * 2 days of storage * 1/0.50 max planned discharge for longer battery life) * 1/48 volt battery bank = 1,831 AH @ 48 volt FLA battery bank

The above is the "typical math" for a full time off grid home sizing for battery bank.

To charge the battery bank, two calculations for solar array. First based on 5%, 10%, 13% rate of charge for battery bank. The second based on hours of sun per day by season:

1,831 AH * 58 volts charging * 1/0.77 panel+controller deratings * 0.05 rate of charge = 6,896 Watt array minimum (for backup system)
1,831 AH * 58 volts charging * 1/0.77 panel+controller deratings * 0.10 rate of charge = 13,792 Watt nominal array (full time off grid minimum)
1,831 AH * 58 volts charging * 1/0.77 panel+controller deratings * 0.13 rate of charge = 17,930 Watt largest "useful" array for off grid system

And there is sizing the system for energy usage and hours of sun per day.

http://www.solarelectricityhandbook.com/solar-irradiance.html

Orlando
Average Solar Insolation figures

Measured in kWh/m2/day onto a solar panel set at a 62° angle:
(For best year-round performance)

Jan	Feb	Mar	Apr	May	Jun
4.29	4.76	5.36	5.79	5.75	4.99
Jul	Aug	Sep	Oct	Nov	Dec
4.96	4.87	4.74	4.89	4.55	4.16

Lots of sun in winter, but in summer lots of summer clouds/thunderstorms? Anyway, pick December "break even" month of sun (sometimes will need a backup genset, or turn down/off loads during bad weather, or a larger array):

18,676 WH per day * 1/0.52 off grid AC system eff * 1/4.16 hours of sun Average December day = 8,634 Watt array "December break even"

So, 8,634 Watt array minimum, and 13,792 Watt nominal... And if no/very little genset usage, 17,930 Watt array would not be "overkill".

As you can see, this is not a small system. And is based on simple plug in the numbers math.

In real life, you would probably choose to use a smaller/more efficient pump, only pump a fraction of a day, or even only run pump during the day when the sun is shining ("solar friendly" pump in the 1 HP range can easily be in the $2,000 range, or more now with inflation and supply chain issues).

I am big on doing some math "modeling" to figure out the cost/benefits of a system. Generally it is less expensive to "conserve" energy than it is to generate it.

Your thoughts/questions/etc.?

-Bill

Rhyolite · October 2022

Thanks BB . That is a pretty big system. I am paying about $0.142 per KWH or about $79 a month for the pool pump. It is a 2 speed and in winter I can get by on low speed which is a small fraction of power. I don't want a gen set at all. If the system could shut off the pump load on cloudy days that would be acceptable. I can also run the pump primarily during daytime hours. Maybe these would reduce the battery requirements.

Dave Angelini · October 2022

I get you not wanting to run a genset for this. I specialize in avoiding them for 100's of clients. You are not in a place that is perfect because of the afternoon thunderstorms. It is a challenge to do what you want unless money was not a factor.

You do have to address the shading or it will not work well. Then, for sure you will need a genset.

Rhyolite · October 2022

Dave, BB, Is there a good website or tool using Google Earth Pro and latest data that will map my roof for best placement of panels? Project Sunroof does not seem to consider the trees and, the photo database is old. several have been removed, others grown.

Photowhit · October 2022

Rhyolite said:

Dave, BB, Is there a good website or tool using Google Earth Pro and latest data that will map my roof for best placement of panels? Project Sunroof does not seem to consider the trees and, the photo database is old. several have been removed, others grown.

If you know the roofs angles and orientation, try PVWatts;

PVWatts Calculator (nrel.gov)

BB. · October 2022

If you can live with "daytime only solar pumping", there are some very nice pumps out there. Here is an example (there are many more) of one that will work from solar, batteries, and even AC power (i.e., power from solar during the day and use a transfer switch for 120/240 VAC power at night). And example (of a "higher end" solar pump--I.e., >$2,000-$3,00 or so--I am not in sales/pump engineering/well engineering):

https://www.solar-electric.com/grundfos-sqflex-40-sqf-3-solar-pump.html (example of low head/high flow rate)

General sales literature:

https://www.solar-electric.com/lib/wind-sun/SQFlex_Product_Guide.pdf

Lots of options out there... The SQF is nice--Runs on AC and DC power (genset, solar, battery). As always, the details matter.

Just as a rough rule of thumb... A Solar array driving a SQF type pump (just solar panels+pump) is a low cost (solar power side) system (pumps not cheap). On the other side, if you want day/night/solar power and add a battery bank... For various reasons, you are looking at a (very roughly) 4x more expensive solar system (panels + charge controller + battery bank + AC inverter) for the "same amount" of kWH per day of harvest.

The additional hardware cost, a 10+ year life for charge controller+Inverter, and 3-5-10 year life typical for batteries--depends a lot on what brand/type/how they are used/maintained).

If you can justify a "solar only pump" (panels + DC capable pump)--That makes things a lot easier/cheaper, at the expense of no night time/bad weather solar power harvest.

As you can see, a "cost effective" solar power + pumping system is based on trade-offs and compromises. I highly suggest doing multiple paper designs and see what works best for you.

Solar pumping (solar panels + VFD + 3 phase) water pumps are becoming more popular for off grid/agricultural water pumping.

Here is a quick search for solar vfd for water pump. I know nothing about website or vendor:

https://solarinverterguru.com/Solar PV VFD for Water Pumps Description.html

The VFD (variable frequency drive) takes the variable DC voltage/current from the solar array and converts it to the appropriate frequency and VAC to run the 3 phase water pump. The VFDs designed to work with solar array give you "soft start" (no surge current) and will vary the frequency (RPM) to the 3 phase motor--Morning and evenings, spin pump slower to match low solar harvest. Mid-day, higher frequency to spin the pump faster (more flow, higher pressure, etc.) as there is more solar power available.

The SQF basically integrates the solar aware VFD into the pump electronics. And (I believe--Not a pump engineer), the SQF usually use permanent magnet AC motors. The PM add another 10-20% more efficiency over standard 3 phase induction motors (again, rough numbers).

There is a bunch of options out there. Finding somebody who has knowledge of the brands/models out there and who can match them to your needs.

Matching VFDs to solar array and the correct three phase pump motor (VFDs tend to output square wave AC--And this is "hard" on standard AC induction motors--There are "inverter" induction motors designed to work with VFDs).

Again--I am not a pump/well/vfd/etc. engineer. The above links are to give you an idea of what is available in general. And a place to start your research.

-Bill

Rhyolite · October 2022

I am rethinking this. Mostly because I want to keep the pool pump I have, it is new and the cost to replace and install could be better spent on panels.

1) Grid tied solar array and inverter sized to offset $80 per month in 563 KWH/Month at 14.2 Cents/KWH. This would approximate the pool pump during summer time. During winter the 2 speed pump will run on a fraction of the power.

2) Battery bank and charge controller sharing the GT solar array and maintaining a reserve charge. Battery bank size and inverter sized in accordance to providing small lighting loads and refrigerator for 3 days. AC side of inverter through manual disconnect panel.

Has anyone done similar?

BB. · October 2022

#1 is the way to go usually... No solar backup power during utility failures (there are a few different options for backup--But don't really seem like a good match for backing up a pool pump).,.

#2--Generally a solar array must be dedicated to one MPPT controller. Two (or more) MPPT controllers cannot manage a single array because each assumes to be in 100% of Voltage/Current curve for the array. Two MPPT controllers would "confuse each other" as they each try to manage current to operate the array at Vmp-array-operating-temperature/light point.

There are ways of having (for example) an array->GT inverter->main panel/transfer switch hybrid/offgrid AC inverter->battery bank. Basically GT Inverter=>Utility in "normal operation" and GT Inverter=>Off Grid inverter's AC output. There are several methods to "manage" the power output from the GT inverter--First is a simple on/off switch to the GT inverter--Battery bank Full, GT inverter output off; battery needs charging GT inverter output on (just using a simple relay or other method).

2nd is to get a GT Inverter and Hybrid inverter that are designed to work together... GT Inverter outputs 100% of available energy at 60 Hz, and outputs 0% at 61/59 Hz and proportional in between frequency. This is sometimes called a "micro grid" setup. It is a bit more of a challenge because you have to get the equipment that will talk together correctly.

It can work... But now you are (potentially) locked in to a smaller set of suppliers down the road.

Otherwise, just a 3.3 kWH/3,300 WH per day system (100 kWH per month) to run fridge/lights/other small loads, a 647 AH @ 24 volt battery bank (such as 8x 6 volt @ 200 AH lead acid batteries), a 1,200 to 3,600 Watt AC inverter, and, depending on your location/amount over paneling around 2,500 to 3,000 Watt dedicated array to run a fully off grid system.

I can go through the detailed math for your requirements--But this is a pretty close estimate of what such a system would look like.

-Bill

Dave Angelini · October 2022

I do your 2nd choice often with the Schneider mppt-100-600vdc and their inverter chargers. Out west this is a way around all the man made power outages for existing grid tie systems.

I never saw that you put in a budget or addressed the shading? If you are not using the best pump available to reduce load, you probably have a low budget. This is not inexpensive to do if you want it to be reliable.

As the boss said here, conservation is first. It gives you more options down the line.

706jim · October 2022

Reading through the various comments here it's interesting to note the "average" power consumption for a building using propane for cooking and water heating. My island cottage generally consumes 3-4 kw-hr per day powering lights, fridge, satellite, TV and water pump.
My system easily creates this much power but the extra capacity helps a lot when sun conditions are marginal. And one more commendation for my old Trace inverter still running flawlessly after 28 years!

JRHill · October 2022

I thought it was not allowed to be off grid in FL? I suppose you can get around that by having a meter and pay the basic charge but not use the grid power?

Anyway, I understand power rates vary greatly around the country. And I can understand having a back-up system to claim independence and self reliance. And I can appreciate grid tie systems to some degree, esp with tax stuff. But generally speaking, I can't imagine going off grid to save money. To me the payback is when the cost to bring grid power in is greater than the cost, personal or hired time included, of the whole reliable off grid picture. For me/us, off grid was not a choice. There was and is no way to pencil out the cost of power lines even over multiple generations. If I totaled all our costs over the years and ignored all my labor with non hired, we have paid crazy prices per KwH.

But it has been one of the most pleasurable hobbies I've had since I quit 1/4 mile drag racing motorcycles. But I can always run some mild racing fuel in the generator to enjoy the exhaust smell. And racing fuel lasts a long time for generator use (wink).

Photowhit · October 2022

JRHill said:

I thought it was not allowed to be off grid in FL?

And I can appreciate grid tie systems to some degree, esp with tax stuff. But generally speaking, I can't imagine going off grid to save money.

Pretty much any off grid system to save money requires running a lot of time off the array and less time off stored energy. BUT I can see possibilities with inexpensive LiFePo4 batteries and handbuilt battery bank. I'm more nervous about the freezing and the reliability of the battery cells than Lead acid.

I will claim to be cheaper than the grid in Central Missouri, heating with wood and having some sponge bathes off the wood stove or heated kettle 100-120 days a year max. But I load shift and deal with long periods of cloudy days by reducing loads. I don't use a generator. Also a minimal user of electric where I live spends 30+ cents a kWh for grid electric.

Heating with solar is really a nonstarter anywhere in the US other than the desert is silly.

I haven't spoken to sellers in Florida lately, but the situation is likely similar to when I lived there. There aren't restrictions to being off grid, in fact some places there is no grid to connect to. But some requirements to receive a certificate of occupancy, which might be difficult off grid.

Rhyolite · October 2022

There was a gal in SW Florida a few years back who lived in one of the suburbs and she decided to collect her own rainwater and also go solar. When she contacted the utilities to cut off her water and power they went ballistic and threatened to cancel her Certificate of Occupancy. I don't know how that turned out, but there are plenty of vacant properties that are without services. The only way I can see that the city would have standing is if you are connected to sewer and therefore getting free sewer service by not paying for water.

Rhyolite · October 2022

I am still studying this problem from a couple different angles. Reducing consumption is of course a huge goal. The other is to set up solar generation so that we can have stored energy for a few critical loads during a sustained outage. I could simply get a generator but frankly I have enough problems with lawn mowers and other gas operated stuff requiring fuel storage and handling. I have a simple lead acid marine battery and small inverter that has come in very handy for short outages. This Ian outage ended with spoiled food and loss of connectivity to internet.

Photowhit · October 2022

Rhyolite said:

There was a gal in SW Florida a few years back who lived in one of the suburbs and she decided to collect her own rainwater and also go solar. When she contacted the utilities to cut off her water and power they went ballistic and threatened to cancel her Certificate of Occupancy. I don't know how that turned out, but there are plenty of vacant properties that are without services. The only way I can see that the city would have standing is if you are connected to sewer and therefore getting free sewer service by not paying for water.

Yes, she was just a complete idiot. Has nothing to do with the ability to go off grid in Florida. It was a loaned house on a lot in Cape Corral (I believe), no ability to do proper sanitation. No contact to try to work with the rules...

Newbie Off Grid Design Florida

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Orlando
Average Solar Insolation figures

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Newbie Off Grid Design Florida

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OrlandoAverage Solar Insolation figures

Categories

Orlando
Average Solar Insolation figures