Minimizing components (usage) for longevity and efficiency

[ang]

Hi,

I am interested in design recommendations for an off-grid system optimized for energy efficiency and components longevity.

With solar panels, it's somewhat easy - they already keep up their efficiency 20+ years and if going with a popular brand, you can get a warranty for a long period.
With battery chemistry, it's also somewhat easy - LTO which would allow me to cycle them once a day for 30 years. Not sure if longer is possible with less cycles as most LTOs I've seen have at most 30 years shelf life.

My first question is about eliminating conversions and components wherever possible.
For example, I have a 15W mini PC that takes 12VDC up to 1.5A. If I want to run it off of solar, it makes no sense to go solar -> charge controller -> battery (other than 12V) -> converter -> PC because of the compounding efficiency loss that will occur at every conversion.
As far as I know, it's not possible to go solar -> PC directly, so I assume solar -> charge controller -> PC is the shortest path to take.
This would not allow me to run it in the dark though, so is it possible to have a hybrid solution that skips the battery (to save cycles and efficiency losses) when panels provide enough power while taking from the battery when panels do not? Or one that takes the excess energy of the solar panels during a sunny day and puts it in the battery? How does such hybrid solution look like and how much does it enlarge the path and thus adds efficiency losses? Does it put more strain on any of the components, making them last fewer years?

I would like to run more small loads (chest fridge, lights, monitor, etc.) on the 12VDC system so I have to think about a house design focused around wiring (loads close to batteries close to solar) to minimize wire size/loss/cost.

If I want to run a big load, like 1kW on 12VDC, a cable length of 1 meter would lead to a 16% loss which makes it inefficient, compared to 100W/12V at 10 meters = 3%.

So my second question is: does it make sense to have multiple systems in a house taking into account my focus - longevity and efficiency?
So my 1kW or more load(s) (like an electric stove, washing machine, water heater) would be on a second battery system that is 48V and has an inverter. A second solar array too?
Assuming I use those loads when the sun is shining, can the same system as the 12V one be applied - skip the battery if possible (or mix battery + solar), charge the battery with extra energy if available? Some examples:

• 3kW solar, 5kW load, 5kWh battery = 3kW from solar + 2kW from battery
• 3kW solar, 1kW load, 5kWh battery = 1kW from solar + 2kW to battery
• evening/no sun, 2kW load, 5kWh battery = 2kWh from battery

Since inverters have a constant draw even when not used, does it make sense to have them off all the time and turn them on whenever I have to use one of the big loads (assuming at most once or twice a day for up to 2 hours)? Does that harm the inverter or does it prolong it's lifetime for not being on all the time?

Speaking of the inverter, what's the lifespan of the inverter, convertor and charge controllers? Is 20+ years common? What shortens and prolongs their lifespans?

One thing that's not clear to me is if, for example, oversizing the solar for the first system would lead to greater losses? If I have 1kW of solar + 3kWh of 12V battery and I only use 300W of loads for 6 hours mostly during the day, what are the losses occurring and how does panel wiring (or voltage) change that?

I am not an expert so correct me if some of my terms are wrong or I am missing something important.

I had these ideas for some time and decided to ask here after Will made the video about the solar -> EG4 heat pump AC

a few days ago which I really liked because it skips most components (although it probably just has some sort of charge controller inside the heat pump)

Of course, those all decisions will be supplemented by redundancy and ways to reduce the general electric load like high insulation, maybe geothermal, propane, etc. but I am not sure how relevant that is.

A bit of a long post, sorry for that, but I want to hear your opinions.

 

[MichaelK]

You are way over-thinking this. A couple of things though are setting you up for failure. Sticking with 12V only makes sense for the smallest systems. Once you start including larger appliances like a refrigerator, you are better off going to at least 24V.

It's a capacity issue. As a general rule of thumb, all items, be it an inverter, or gasoline motor, or a battery are stressed more when they are pushed at their limits of operation. That is, trying to pull 2000W out of 2000W inverter, or running your 5000W gas generator at 5000W, or trying to pull 100A out of your 100Ah battery. Your battery for example will last 20X longer if you are only pulling 10% of it's capacity instead of 80% of its capacity.

So, multiply the capacity of what you need by at least 2X-3X for whatever equipment you want to run. Focus less attention on efficiency then longevity.

Keep in mind that efficiency is somewhat proportional to size, but for inverters for example, efficiency is also strongly correlated with the quality of design. Higher priced low-frequency inverters may only have background consumption in the range of 700Wh per 24hr, whereas cheaper designed highfrequency units have background consumption in the range of 2400Wh per 24hr.

 

[32 volt boater]

Your totally into this. I think in a few weeks you will be answering questions instead of asking.

I say buy a few pieces and start messing around. Electric is very mathematical for sure but sun and clouds is very random. I planned and planned but it wasn't till I started messing around with the stuff did I really get it.

I suggest this book if you really want to take it to the next level https://www.ebay.com/itm/325455253326?

 

[32 volt boater]

That book made it easy for me to understand as opposed to this other book I got someplace that was a school textbook and was absolutely awful. It was almost like it was intentionally made to seem more difficult.

 

[32 volt boater]

Sticking with 12V only makes sense for the smallest systems.

Nonsense !




The only real difference on a low frequency inverter for 12-24-36-48v is the ratio of turns on transformer output.

I don't want to hear anymore about "big wires" who cares.

Anyway for an off grid system the goal should be elimination AC current all together. AC is good for electrical distribution grids but once in the house little advantage or none. The OP wants minimal parts.

Inverters should be obsolete.

Type in anything 12 volt blender, 12v toaster, 12v tv, 12 volt refrigerator, fan, the RV boat camper cabin world is all still mostly 12v and 12v stuff cheapest and most variety.

 

[MichaelK]

Nonsense !

Anyway for an off grid system the goal should be elimination AC current all together. AC is good for electrical distribution grids but once in the house little advantage or none. The OP wants minimal parts.

Inverters should be obsolete.

Type in anything 12 volt blender, 12v toaster, 12v tv, 12 volt refrigerator, fan, the RV boat camper cabin world is all still mostly 12v and 12v stuff cheapest and most variety.

You're on a boat. I'm going to assume you aren't running a 240V deep well-pump?

If you can get by with 12VDC, then good for you!

 

[12VoltInstalls]

I read your post and had some thoughts.

First, I run full time on 12V. It will run a fridge/freezer and do anything I need for a ‘house’ on 12V. You could so as well.

However, I have a propane cooking stove and a propane tankless hot water heater. I’d advise that for you as well. The monthly propane consumption for those items is quite low, and cooking with gas is a pleasure imho compared to electric burners. The water heater uses so little propane that the cost of doing it elsewise doesn’t make sense to me in my circumstance.

is it possible to have a hybrid solution that skips the battery (to save cycles and efficiency losses) when panels provide enough power while taking from the battery when panels do not

Battery-based systems work like you describe in spirit. Panels make voltage and whatever load- charging a battery, running your computer, using lights- uses the electricity produced and only ‘using’ the battery when the power required is either in excess of the PV watts being produced or after dark when no power is coming from the panels.
So we usually design to provide enough watts to both use and sufficiently charge the battery(-ies).

How does such hybrid solution look like

That’s not hybrid that’s normal.

like to run more small loads (chest fridge, lights, monitor, etc.) on the 12VDC system so I have to think about a house design focused around wiring (loads close to batteries close to solar) to minimize wire size/loss/cost.

Forget the “size/loss/cost” of it. Doing a sufficient installation to utilize your devices, etc and provide for the larger items you mentioned will likely cost “much more” in percentage than a barely functional minimalist system will. But a) a good system won’t drive you crazy, and b) the cost in dollars will not likely be outrageously more than building the minimalist route.

Figure out the watts you will need to use by going to the FAQs and doing the energy audit. The come back and share that data and then you will get input here for designing what you will need.

 

[ang]

Thanks for the great replies.

As a general rule of thumb, all items, be it an inverter, or gasoline motor, or a battery are stressed more when they are pushed at their limits of operation. That is, trying to pull 2000W out of 2000W inverter, or running your 5000W gas generator at 5000W, or trying to pull 100A out of your 100Ah battery. Your battery for example will last 20X longer if you are only pulling 10% of it's capacity instead of 80% of its capacity.

Didn't know that, I thought that's the case for batteries only but apparently not. Thanks.

Higher priced low-frequency inverters may only have background consumption in the range of 700Wh per 24hr, whereas cheaper designed highfrequency units have background consumption in the range of 2400Wh per 24hr.

This is way too much consumption, I should definitely consider leaving it off most of the time if I even end up getting one.

I suggest this book if you really want to take it to the next level https://www.ebay.com/itm/325455253326?

Thanks for the suggestion, I will look into it. The situation right now does not allow me to get stuff to practice with.

Type in anything 12 volt blender, 12v toaster, 12v tv, 12 volt refrigerator, fan, the RV boat camper cabin world is all still mostly 12v and 12v stuff cheapest and most variety.

That's one of the main reasons I want to stick mostly to 12V, the availability of appliances.

However, I have a propane cooking stove and a propane tankless hot water heater. I’d advise that for you as well. The monthly propane consumption for those items is quite low, and cooking with gas is a pleasure imho compared to electric burners. The water heater uses so little propane that the cost of doing it elsewise doesn’t make sense to me in my circumstance.

I do like propane as well but I do not consider it off grid, I consider it as a back up so I would like to avoid using it in a normal day.

Panels make voltage and whatever load- charging a battery, running your computer, using lights- uses the electricity produced and only ‘using’ the battery when the power required is either in excess of the PV watts being produced or after dark when no power is coming from the panels.

Doesn't the electricity still "pass" through the battery adding wear to it?

Figure out the watts you will need to use by going to the FAQs and doing the energy audit. The come back and share that data and then you will get input here for designing what you will need.

I am still early in my phase of planning and I haven't yet decided what I am willing to give up and what not but I will do that in the future.

 

[12VoltInstalls]

Doesn't the electricity still "pass" through the battery adding wear to it?

No. The entire circuit has an electrical potential.

Think of water pipes as an analogy; not entirely scientifically accurate but it’s useful. The battery is like a pressure tank installed on a tee in the pipe. The charge controller is like the water pump. (Ignore high/low pressure regulation for this analogy)
When you turn on the water (electrical load), the pressure (voltage) drops and the pump kicks on and water flows (amps) and the pressure bladder tank(battery) ‘balances’ the sudden opening of the valve and maintains pressure(volts) in the line at the level of demand(watts). If the demand doesn’t exceed the capacity (available flow) of the pump the pressure tank remains/maintains static. You don’t use the available pressure storage in the tank (battery). The water(electrical potential) is supplied by the pump((charge controller) merely passing by the tank.
I hope that created a good visualization.

like propane as well but I do not consider it off grid,

Whether a liquid or compressed gas fuel is used- or expensively supplied solar, or wood - it’s all off-grid if not connected to the power grid. And buying a 250 gal propane tank would give you enough fuel to last for years as well as supply a backup generator. The advantages are several, not the least of which is - if one is of a prepper mindset- you would have a huge time-buffer to not be weather vulnerable or at equipment failure risk (especially in cold latitudes) should shtf or some teotwaki event occur. That’s secure independence.

If one is not connected to the grid that is by any logical definition: off grid.

You are way over-thinking this. A couple of things though are setting you up for failure. Sticking with 12V only makes sense for the smallest systems. Once you start including larger appliances like a refrigerator, you are better off going to at least 24V

Welllll…. I do and have run a 120V refrigerator of various sizes for several years now on a 12V system. It hasn’t exhibited any signs of compromise or poor performance. 60-90W or even a bit more doesn’t stress a 1200W psw inverter (it does kick on the inverter fan for a second when the refrigerator cycles on)

The way I see it is <2500W 12V is totally fine so it gives freedom to select 12V items if one wishes to be 12V. Although I personally would probably keep 2000W as the ceiling.

Once your system is “so large” that you require more than 2000W regularly (really 1500W load, steady, stops being a small solar power system) that’s the time - in my mind- to go all in and just run at 48V and invert split phase and be done with it. Maybe keep a 400W-panels 12VDC separate for lighting and basic device charging as an emergency backup or something. IMHO

 

[JCSchwarb]

I read your post and had some thoughts.

First, I run full time on 12V. It will run a fridge/freezer and do anything I need for a ‘house’ on 12V. You could so as well.

However, I have a propane cooking stove and a propane tankless hot water heater. I’d advise that for you as well. The monthly propane consumption for those items is quite low, and cooking with gas is a pleasure imho compared to electric burners. The water heater uses so little propane that the cost of doing it elsewise doesn’t make sense to me in my circumstance.

Battery-based systems work like you describe in spirit. Panels make voltage and whatever load- charging a battery, running your computer, using lights- uses the electricity produced and only ‘using’ the battery when the power required is either in excess of the PV watts being produced or after dark when no power is coming from the panels.
So we usually design to provide enough watts to both use and sufficiently charge the battery(-ies).

That’s not hybrid that’s normal.

Forget the “size/loss/cost” of it. Doing a sufficient installation to utilize your devices, etc and provide for the larger items you mentioned will likely cost “much more” in percentage than a barely functional minimalist system will. But a) a good system won’t drive you crazy, and b) the cost in dollars will not likely be outrageously more than building the minimalist route.

Figure out the watts you will need to use by going to the FAQs and doing the energy audit. The come back and share that data and then you will get input here for designing what you will need.

Well said. The direct DC route is where I started my thinking until I started calculating the lower cost of HFI and LFP batteries it didn’t make sense to try to run direct “inverterless” DC, just add a few more panels and battery to add the inefficiencies back in. Solved for a lot less complexity and cost.

I read your post and had some thoughts.

First, I run full time on 12V. It will run a fridge/freezer and do anything I need for a ‘house’ on 12V. You could so as well.

However, I have a propane cooking stove and a propane tankless hot water heater. I’d advise that for you as well. The monthly propane consumption for those items is quite low, and cooking with gas is a pleasure imho compared to electric burners. The water heater uses so little propane that the cost of doing it elsewise doesn’t make sense to me in my circumstance.

Battery-based systems work like you describe in spirit. Panels make voltage and whatever load- charging a battery, running your computer, using lights- uses the electricity produced and only ‘using’ the battery when the power required is either in excess of the PV watts being produced or after dark when no power is coming from the panels.
So we usually design to provide enough watts to both use and sufficiently charge the battery(-ies).

That’s not hybrid that’s normal.

Forget the “size/loss/cost” of it. Doing a sufficient installation to utilize your devices, etc and provide for the larger items you mentioned will likely cost “much more” in percentage than a barely functional minimalist system will. But a) a good system won’t drive you crazy, and b) the cost in dollars will not likely be outrageously more than building the minimalist route.

Figure out the watts you will need to use by going to the FAQs and doing the energy audit. The come back and share that data and then you will get input here for designing what you will need.

 

[12VoltInstalls]

The direct DC route is where I started my thinking until I started calculating the lower cost of HFI and LFP batteries it didn’t make sense to try to run direct DC.

That’s fine if you are satisfied with that.
I do like that my lights work and can charge my phone even without an inverter in place. But that’s me, my outlook. You are free to have your own perspective.

Just “my thoughts” though. It’s possible within $200 to have a 10A Epever, a 100W panel, a fuse box, and a bunch of LEDs with a cheap 12V fla battery and have a secondary backup if you have to swap in a backup inverter or something should a failure occur. I’ve had backup 12V long before I ever bought a solar panel and it’s been handy a few times.

 

[Hedges]

Didn't know that, I thought that's the case for batteries only but apparently not. Thanks.

Battery wear may be proportional to current draw, but for electronics assume it is square of current.
Heating is proportional to power dissipated, which is I^2R.

Lifespan of transistors and capacitors cuts in half with every 10 degrees rise. Cool enough, some other failure will happen first, but running hot can make these parts fail sooner.

For example, I have a 15W mini PC that takes 12VDC up to 1.5A. If I want to run it off of solar, it makes no sense to go solar -> charge controller -> battery (other than 12V) -> converter -> PC because of the compounding efficiency loss that will occur at every conversion.
As far as I know, it's not possible to go solar -> PC directly, so I assume solar -> charge controller -> PC is the shortest path to take.
This would not allow me to run it in the dark though, so is it possible to have a hybrid solution that skips the battery (to save cycles and efficiency losses) when panels provide enough power while taking from the battery when panels do not? Or one that takes the excess energy of the solar panels during a sunny day and puts it in the battery? How does such hybrid solution look like and how much does it enlarge the path and thus adds efficiency losses? Does it put more strain on any of the components, making them last fewer years?

For simplicity, and AGM battery might fit this application.

Consider 12V 100Ah battery, 10 hours without sun at 1.5A = 15 Ah or 15% DoD.
A quality (expensive) battery might last 10 years (see last page)

http://sunxtender.com/pdfs/Sun_Xtender_Battery_Technical_Manual.pdf

Use a 20A charge controller, two PV panels (or strings) oriented for 9:00 AM and 3:00 PM winter sun.
Load consumes 360 Wh/day, assume battery is 70% efficient, need 500 Wh. If 2 effective hours sun in the winter, 250W of panels. Maybe two, 250W panels would be good.

The battery could cost $360, the two panels (used) about $100. Just need a charge controller. About $0.15/day to operate, power costs you $0.45/kWh (about my utility rates).

 

[Checkthisout]

Let us know when you're in a situation that allows you to afford buying stuff. We can be of better help then.

 

[CJM]

Nonsense !

View attachment 123629View attachment 123630


The only real difference on a low frequency inverter for 12-24-36-48v is the ratio of turns on transformer output.

I don't want to hear anymore about "big wires" who cares.

Anyway for an off grid system the goal should be elimination AC current all together. AC is good for electrical distribution grids but once in the house little advantage or none. The OP wants minimal parts.

Inverters should be obsolete.

Type in anything 12 volt blender, 12v toaster, 12v tv, 12 volt refrigerator, fan, the RV boat camper cabin world is all still mostly 12v and 12v stuff cheapest and most variety.

Motsenbocker’s book diy grid is all about 120vdc https://yugeshima.com/diygrid/

 

[12VoltInstalls]

Motsenbocker’s book diy grid is all about 120vdc https://yugeshima.com/diygrid/

Looked at the site with its one-step away from the affiliate link so I guess it doesn’t ‘technically’ violate the terms and conditions of the site here?

Interesting opinions in the book apparently.
It has an agenda - reading a number of reviews that’s obvious. So unfortunately it misses opportunities to explain to readers so they might understand that our entire culture is grid dependent and there’s more to it than money-hungry corporations keeping society under their thumb. Not quite convinced from the reviews that many would benefit for the $25 to get the publish-on-demand book.

 

[CJM]

Looked at the site with its one-step away from the affiliate link so I guess it doesn’t ‘technically’ violate the terms and conditions of the site here?

Interesting opinions in the book apparently.
It has an agenda - reading a number of reviews that’s obvious. So unfortunately it misses opportunities to explain to readers so they might understand that our entire culture is grid dependent and there’s more to it than money-hungry corporations keeping society under their thumb. Not quite convinced from the reviews that many would benefit for the $25 to get the publish-on-demand book.

I contacted Mots because of my interest in 12Vdc (or 24vdc). I‘m building a 600 square feet offgrid home situated in the Netherlands.

Mots replied: ’I’m doing 120Vdc and buy cheap 48vdc ebike batteries in China’. He’s advocating to build a system with few parts and low cost.

But building diy a house according building regulations and designing a solar system is hard to do.
Help of grid electricians is not an option, they don’t have a clue (solar and grid are a close connection) . A battery???? Grid tied don’t need one, so they don’t have the skills to do. With dc you’re pretty much on your own.

interesting your doing 12Volts offgrid. Where can I find concrete information?

 

[CJM]

Looked at the site with its one-step away from the affiliate link so I guess it doesn’t ‘technically’ violate the terms and conditions of the site here?

What do you mean? Do I miss something? The moderator did not react, so maybe I’m not acting against the forumrules......

as far as I know, the more techsavvy can make the ‘products’ themselves.

Use of Interrupted Direct Current Power By Appliances - Motsenbocker Marvin

Direct current (“DC”) power such as from solar panels is used by home appliances directly without conversion to AC. The large direct current spark problem is alleviated by interrupting the DC current

www.freepatentsonline.com

 

[CJM]

a few days ago which I really liked because it skips most components (although it probably just has some sort of charge controller inside the heat pump)

'Made in China' customizing to vdc is possible I read -like washing machines an Airco.

 

[CJM]

That book made it easy for me

hard to find. No alternatives on pdf?

 

[CJM]

Anyway for an off grid system the goal should be elimination AC current all together.

but giving hands and feet to something is the next fase.