Solar Off-Grid Living Question

[Hristo Botev]

Because the Internet is a gigantic mess for me for this kind of question, and because I'm a total noob on this topic, I'll ask you smart folks here:

Theoretically, can solar panels power all of a home's energy needs, including air conditioning, in north Florida?

Assume for the sake of this question that the home is built from scratch with energy efficiency and off-grid living in mind. House size would likely be somewhere around 1,500 sq. ft with 3 to 4 bedrooms, designed to have all the bedrooms except the master upstairs so that the upstairs could be shut off when not in use and/or during the hottest months.

In addition or as an alternative to answering, I'll also welcome reading recommendations on this topic to get up to speed.

Thanks.

[ducknald_don]

I suppose you could work out the energy consumed by your air conditioner then size out your panels. The problem is the temperature falls quite slowly through the evening whilst the output of your panels is going to be zero once the sun has gone down.

[7Wannabe5]

Yes, here's a simple calculator. You may also need significant battery storage. However, having such a system off-grid may be in violation of building code.

https://sunwatts.com/solar-calculator/

[ducknald_don]

Personally I'd start with passive schemes like insulation, shading, evaporative cooling and the orientation of your house.

[7Wannabe5]

Evaporative cooling is less effective in humid locations like Northern Florida. Wet bulb is what’s gonna get you.

[bostonimproper]

Given $ and assuming new build, simplest approach would be to find a “net zero” or “zero energy” builder. You want a combination of heat avoidance, passive cooling, energy efficiency, and solar power + batteries to get to the point you’re looking to be. Better to build for efficiency than try to overcompensate for an inefficient system.

Some nice resources on the Florida Solar Energy Center website. Example links (some on the older side, but give you a sense of core principles/techniques):
-Heat avoidance: http://www.fsec.ucf.edu/en/publications ... n-2-80.pdf
-Energy efficient home designs (with floor plans): https://energyresearch.ucf.edu/consumer ... e-designs/
-Principles of energy efficient home design: https://energyresearch.ucf.edu/wp-conte ... Manual.pdf

[AxelHeyst]

Theoretically, can solar panels power all of a home's energy needs, including air conditioning, in north Florida?

Yes,assuming you have enough area available for panels. But the size and cost of such a system if designed for "no downtime" will be quite large. It's just a matter of # of panels and capacity of battery storage.

Generally the approach is to define how many hours of the year you are okay with the system *not* keeping up with demand, depending on x days of clouds etc, and design the system accordingly. For the X hours it doesn't keep up you have either backup generator or Character Development / Grid Collapse Test Scenario Time.

The cost to reduce X gets very high the smaller X gets.

[white belt]

Book recommendation: https://www.harvestingrainwater.com/pro ... -new-2019/

Although the title would indicate the book is only about harvesting rainwater, it also digs into a ton of aspects of passive heating and cooling, positioning solar, and so on. It will give you the tools to evaluate and plan your property based on latitude and other factors. What’s going to bring your solar system costs down is first maximizing the potential for passive cooling.

As 7WB5 points out, your region will pose unique cooling challenges due to high humidity. Evaporative cooling won’t work very well, but passive cooling techniques like shading will still make a huge difference. Florida houses are notoriously poorly insulated so that’s also something to consider if you know you’ll have to be running A/C due to wet bulb temperatures. Basement bedrooms and ground floor spaces will be much easier to cool than second floor spaces, however I know basements might be rare in that region.

Read this article: https://www.lowtechmagazine.com/2014/09 ... oning.html

If you master the use of fans to achieve thermal comfort for your family (both the circulating room type and the mini personal type), you should be able to set the thermostat to ~85 degrees in summer months. That would allow you to still keep humidity in check while reducing energy consumption significantly. That means you can size your solar system smaller.

In terms of A/C, central air systems may be the norm in the USA, but mini split systems common in the rest of the world could be more efficient for how you plan on using your system (e.g. only cooling rooms when people are in them).

[Hristo Botev]

Really appreciate all the info! Having grown up in Florida, I never knew that the old homes I loved so much were called "Cracker" homes.

This seems totally do-able!

[macg]

I have a few friends in CT that are using solar as their only energy source all year long, including throughout the summers when AC is used regularly / constantly. As others have said, it's just a matter of enough panels & battery storage.

[rube]

Consider also what exactly the aim is. Do you want off-grid? Why? Or do you want to be energy neutral or positive?
Or do you want to have low or fixed energy costs?
Or, a comfortable home?

Off grid with 99.9% certainly, requires overcapacity 99% of the time and is definitely not cheaper nor more environmentally friendly than being connected to the grid.

But as pointed out by others, start at the basis: reduce the energy required and know what is left, how much you need.
Go from there and at several point you have to make compromises and decide what is the best solution for yourself.

Note also that the techpart can always be added, well kind off. But the passive part, i.e. insulation, thermal mass, solar heating and/shading is all much more fixed at the design so that is most important.
Later on you can, within limits, aalways decide to add (more) storage batteries, another AC system, more solar or more efficient panels etc.

[theanimal]

J&G had similar questions recently. You may find a good starting point/some more things to think on here viewtopic.php?p=252877#p252877

+1 to the Rainwatwer Harvesting books. Both Volume 1 & 2 are excellent .

[Green Pimble]

I've recently heard about nickel-iron batteries, which you may want to look into if you are planning to store energy. I don't know if the hype is to be believed, but they seem to have extremely long lifespans and tolerate all sorts of abuse. The main downsides are their weight and bulk, but this is not a problem for an off-grid home.

Good luck!

[Married2aSwabian]

Personally I'd start with passive schemes like insulation, shading, evaporative cooling and the orientation of your house.

This is the best advice. How long do you plan to live in this home after building it?

If the answer is 10 years or more, you would be well-served to design for passive solar, max insulation and shade in FL. Ventilation is also v important in tightly insulated homes. This a plan we’d thought about building on our property some years ago:

https://www.sunplans.com/house-plans/French_Cowgirl_2

Since you’re main concern is cooling, you could consider geothermal for HVAC. This is especially efficient/ lower cost if you have open land and / or a pond onsite. Underground temps (just 4’ down) like to stay around 55 deg F. Just ask any burrowing animals … they’re smarter than us and v comfortable without electricity. You just want to avoid having to run big compressors as in most central air systems - that’s where the big power consumption happens. With geothermal, you only have pumps and fans. Not cheap, though. We had a local contractor give estimate for a system here in MI about 6 years ago and it came in around $25k. Excavating is a big part of cost, so if you have a connection there, you could save a lot.

Understanding your current power consumption and how you might reduce it upfront, is also key. Devices like this are helpful:

https://www.amazon.com/P3-International ... 122&sr=8-5

You’ll get accurate power consumption numbers for any device plugged into it.

A ground-mounted solar array would definitely be the way to go, so you can have shaded house.

I had a subscription to this mag for many years:

https://www.homepower.com/

But they stopped publishing in 2018 - v good source of info. Some articles still relevant - especially for planning.

[MidsizeLebowski]

Certainly possible, as others have said just a matter of sizing the system appropriately. In addition to passive solar design having a reservoir of cool air in the form of an arbor affronting a window on the ground level paired with some high windows which have a direct line of airflow from the cool intake would be helpful.

I second the Lancaster books, The Barefoot Architect has some useful tropics design as well as of course anything permaculture related from Bill Mollison. A search of permaculture tropics design should yield quite a bit! Is this a future project you’ve got in the works?