Building new Off Grid Home in Panama

Panamretiree

Re: Bulding new Off Grid Home in Panama

BB. wrote: »

I usually use the "charging voltage" of ~29 volts (if 24 volt battery) for this equation:



If you normally only discharge the battery by 25% (75% state of charge), the system is going to get up to absorb set point pretty quickly. You will only see 24 volts if the batteries are well discharged (less than 50% charged).

The 0.77 derating is with "warm to hot panels" and you should not need to derate further (in freezing weather and below, you can get significantly more power--10-15% or more).

-Bill

In keeping with your thoughts on charging voltage, would you use 57.6 in the equation for a 48V system?

Ernest

Panamretiree

Re: Bulding new Off Grid Home in Panama

westbranch wrote: »

Ernest, I am not as familiar, intimately that is, as Photwhit is but from my perspective using NOCT would yield a more realistic PV production than STC does, and I think that reduction in output would include some, if not most, of the 77% degrade factor you have used in this calculation...

The array size based on the NOCT rating of 229W would be 2061 watts. Charging current from this array would be:

2061W*.77/48V= 33.06 amps

PW will chime in I am sure...

WB - when I look at the formula, I think you have a point. The difference between STC and NOCT for these panels is 25%. If you further derate them using 0.77 in the formula one could be surprised at actual output and figure that you have a good thing going when in reality, your calculations would have been closer by not using the 0.77 factor in the formula. Maybe the 0.77 derating factor is to compensate for the difference between the STC and NOCT panel ratings. I too hope PW will jump in on this one.

Cheers

Ernest

Panamretiree

Re: Bulding new Off Grid Home in Panama

BB. wrote: »

The 0.77 derating is with "warm to hot panels" and you should not need to derate further (in freezing weather and below, you can get significantly more power--10-15% or more).

-Bill

Bill - I responded to WB on this exact same issue. Using the NOCT rating for the panels already takes into account a temperature of 45 deg C. This should in essence negate the requirement for the 0.77 derating factor in the equation. From what you are saying is that it is acceptable to use the STC panel rating with the 0.77 derating for all calculations as this takes into account the NOCT panel rating.

The temperatures here are continuously in the low to mid 30s all year round, with the exception of some mornings that dip to ~24 deg C then quickly climbing up to the mid 30s. Never going to see weather below ~24 deg C unless something of the armageddon persuasion happens.

Cheers

Ernest

westbranch

Re: Bulding new Off Grid Home in Panama

here is PW's post...on page 3

Well your statements "Anticipated Array Power @ #####" are basically very wrong, it's good you are thinking about the added heat, but see if you can find the NOCT (Normal operating cell temperature) value for your panel, this will tend to run 75-85% of STC (Standard Test Conditions) which is the way panels are rated.

This why I thought you might be double dipping...

Cariboocoot

Re: Bulding new Off Grid Home in Panama

The 77% derating is average power output from the MPPT controller over hours of good sun under normal temperatures. It includes the drop in Voltage caused by panel heating and the efficiency of the controller.

The NOCT rating is equivalent to the "first loss"; the derating of panels due to heat. But it does not include the efficiency of the charge controller. Using the NOCT number is roughly equivalent to the "panel only" derating of 80% of nameplate. If you start with that Wattage rating for the panels you need to shave off 3-5% for the controller loss.

Panamretiree

Re: Bulding new Off Grid Home in Panama

NorthGuy wrote: »

I think an interesting problem to discuss here is the weather. Wet season has lots of cloudy days. This apparently very bad for solar system. I think most people know very little about Paname weather.

Do you get any sunny days during the wet season? How many? How far apart?

Does it get colder when it's cloudy? Do you need less (or may be no) air conditioning during the cloudy season?

Is your intention to survive the rainy season with the generator? Or do you want to produce some solar energy too?

NG - you are correct in your query. I have been watching the weather patterns since we started this project (should have kept a journal - coulda, woulda, shoulda). Believe I will start one now, good for historical data, and looking back to review system design intent and parameters.

AC is not only for temp, but also to dehumidify. It gets quite damp and muggy here, and mold is always an issue. A lot of water is taken out of the air when the AC is on. We are dialing back the AC units as we continue to live here and get more acclimatized. AC will continue to be an issue and concern, especially when guest come a calling.

We do get sunny days during the wet season. It has been sunny this morning but it started to cloud over, and is now back to sun. Tells me that morning sun is the sun to capture. It does have sunny periods in the afternoon. When it is raining it is hit and miss; however, one can expect that you will probably use the generator when this happens. The worst month I am told is apparently November.

Our intention is to not survive the wet season with generator alone, but with the expectation that it will be used. The main intent is to produce solar power. An issue we have is real estate is limited and a wind generator (with Chris Olson's design criteria tower-turbine etc is not feasible). This brings up the issue of installing additional panels to compensate for the wet season with the understanding that during the dry season of say 4 1/2 months, I expect us to have an abundance of power production. Hence the conundrum, do you go for the worst case scenario and fit an array(s) to compensate for the wet season knowing that during the dry season you could should expect to have the batteries hit float almost every day.

One could install a 24V system (or 48V system for that mater) with two strings of 4-L16 420 amp hour batteries and during the dry season alternate the use of each string say 3 days on - 3 days off - one day both strings on-line. With this type of cycling, I would think the afternoon/early evening would be a good transition point - would have to monitor and see. This type of cycling is used for engines, etc, and works quite well. I would think the batteries would age the same with this type of operation. A good point of discussion probably.

I think I mentioned this from another post in that should we get cooler temps, say below 70 deg F or colder would require an armageddon event.

With help from this forum I am trying to "what if" the project so that by end month it is as good as it can be and the rest will be history as we say.

I have learned quite a bit in the past months, and thank you and everyone else for their time and support.

Cheers

Ernest

Panamretiree

Re: Bulding new Off Grid Home in Panama

westbranch wrote: »

here is PW's post...on page 3

Well your statements "Anticipated Array Power @ #####" are basically very wrong, it's good you are thinking about the added heat, but see if you can find the NOCT (Normal operating cell temperature) value for your panel, this will tend to run 75-85% of STC (Standard Test Conditions) which is the way panels are rated.

This why I thought you might be double dipping...

WB - PW's statement is exactly why I went to using NOCT for panel calcs and CC sizing. Still had to verify CC size with the STC rating so that I would not overdrive the CC should the array put out some good power numbers.

Cheers

Ernest

BB.

Re: Bulding new Off Grid Home in Panama

We are only talking about a couple of percent when looking at 57.6 or 58 or 59 volts charging. Realistically, if you are withing 10% of the "real numbers", you are usually doing well.

The difference between 57 volts / 48 volts = 1.1875 or ~ 20% larger array--That is significant.

When doing these calculations from an "engineering" point of view, I usually want to make sure your system will not under-perform vs your expectations. But, frequently you end up with a bunch of derating factors that may tend to push you towards oversizing your system... For example, as string of "typical" deratings:

0.81 panel derating * 0.95 controller derating * 0.80 battery derating * 0.85 inverter efficiency = 0.52 end to end derating.

0.81 panel derating and 0.95 controller eff are pretty real. 0.80 is used for flooded cell and 0.90 can be used for AGM. In real life, a flooded cell can be >0.90 efficient and an AGM can be upwards of ~0.98 efficient. But, a lot of this depends on your particular usage... For example while flooded cell batteries are >>0.80 efficient when cycled from 0.50 to 0.80 state of charge, they probably drop below 0.40 efficient at >90% state of charge (equalization is close to 0.0 useful efficiency).

For the Battery Bank, the neat thing is when you have more loads, the average battery SOC drops, and therefore becomes more efficient--sort of supporting your heavier loads (poor weather, guests, miss-planning, etc.).

Solar panels on a MPPT charge controller are less efficient in hot sunny weather--but fortunately, that is when we get the most sun. They are somewhat more efficient in cold water (near freezing and below by 10-20%)--which helps out in winter. Etc.

Anyway, we could add 3% wiring drop, another few percent for the "hot" copper wiring losses on the roof (copper resistance rises with temperature), another couple percent for dirty panels, etc...

But, that would drop our 52% typical derating even lower (or force even a more expensive system on you). That is why I almost always bring up the discussion of alternative power (utility power, generator, etc.) into the discussions... Making the array 50% larger to account for a few days of worst case loads and/or a few more days of pure solar during bad weather--The additional arrays (even if you double them) are not going to generate appriciable power during a week of dark/stormy weather. On my 3.5 kW array which will generate around 15-19+ kWH on nice days, will drop as low as 0.5 to 1 kWH per day during stormy weather.

And, you should not plan on "needing to use" 100% of your predicted power every day... Some days you will have more sun/energy available--other days less. You will just have to plan your usage and be flexible (when to wash, when to irrigate, etc.).

For me, I have grid power (pure GT system--So my "solar numbers" are always maximum power the array can output--no full battery bank in the afternoon reducing solar array production). But for an "off grid" person, there are going to be times when the weather is bad. And your choice is to either cut back power usage dramatically (so you don't damage the battery bank). Or spend a few dollars (or ten's of dollars) per day on fuel to get you through the dark times. (and/or install alternative power sources like wind or hydro to help).

What you do during the dark times is your choice... My suggestion is to accept that you will get close to 100% of your electricity from solar for ~9 months of the year and size the solar array (and battery bank) to support that. And accept that you will be using the generator/alternative power/conservation at times during the 3 months of "winter".

When I use PV Watts, I look for the poorest 3 months of production, toss those, and then find the fourth poorest month and use that as the "break even" number. For example, use Managua Nicoragua as being close and I can use PV Watts to give us 12 months of seasonal sun averages. Fixed array facing south with 12 degree from horizontal tilt:

Month      Solar Radiation (kWh/m2/day)
1      5.61     
2      6.10     
3      6.29     
4      6.22     
5      5.12     
6      4.40     
7      4.70     
8      4.84     
9      4.81     
10      4.71     
11      4.96     
12      5.06     
Year      5.23

Their lowest fourth month is October at 4.71 hours of sun per day (still pretty good, usually we use ~4 hours of sun for planning in North America). Lets say you want 8kWH per day during most of they year (if you have heavy summer A/C or other seasonal power needs, need to check into those numbers too):

8,000 WH * 1/0.52 typical system efficiency * 1/4.71 hours of sun = 3,266 Watt array minimum suggested

But, you also need to look at the battery bank charging requirements too (large battery bank needs large charging current). Assuming an 800 AH @ 48 volt battery bank:

800 AH * 58 volts charging * 1/0.77 panel+charger derating * 0.05 rate of charge = 3,012 Watt array minimum
800 AH * 58 volts charging * 1/0.77 panel+charger derating * 0.10 rate of charge = 6,026 Watt array nominal
800 AH * 58 volts charging * 1/0.77 panel+charger derating * 0.13 rate of charge = 7,834 Watt array "cost effective maximum"

Because you have pretty high amount of "average sun", your array does not need to be too large. However, if you have a lot of power use and need a larger battery bank, the battery bank charging requirements push you towards a larger array.

Again, a lot of this depends on your power usage... If mostly during the day, and you can cut back on usage during bad weather, then a smaller battery bank may be a better deal. If you charge during the day and use power at night, and cannot cut back on usage too much (fridge, lighting, business), then a larger battery bank is going to be the curse.

In reality, you may only have a week or two of generator run time during winter (may cost you a few hundred dollars in fuel)--Because for many locations, even during the winter you will still have more sunny/clear days than heavy cloud days. You will need a backup genset anyway--So just have enough fuel to support those days when it is needed.

After a year or so--You can always revisit the Solar Array/Wind turbine vs genset question and decide if you want to invest in more panels/RE power or continue with the present fuel usage.

Sizing the battery bank to the loads, for me, is the most critical step. Batteries are there for 5-8 years and you don't really want to add a mix of old and new batteries over time--You end up with batteries failing randomly over time and the mess to diagnose/prevent a bad battery from killing others/and replace every few months (kind of like a mix of old and new tires on a car--you are having to always futz with them).

Don't get too deep in the few percent side of the calculations. You can easily affect your power usage by a factor of 2x (larger or smaller) based on your energy habits and electrical appliance selection. I carry out the calculations to 3 or 4 places, not because my calculations are that accurate... I do it so you can repeat my calculations (and catch my errors) and follow where each set up numbers comes from and is used next.

For the most part, your power measurements (from array, load usage, etc.) will be, at best, 5-10% accuracy. You will never be able to measure the improvement by using heavier copper wire with 1% loss vs 3% voltage drop loss. But--Everything adds up as seen above into the "terrible" 52% end to end AC system efficiency. So every point in the project from panels to wiring to inverters to loads--You are looking to get the most efficient devices/configurations you can--Because the losses all add up very quickly.

-Bill

Cariboocoot

Re: Bulding new Off Grid Home in Panama

A slightly over-sized system is far preferable to an even slightly under-sized one.

NorthGuy

Re: Bulding new Off Grid Home in Panama

Panamretiree wrote: »

Hence the conundrum, do you go for the worst case scenario and fit an array(s) to compensate for the wet season knowing that during the dry season you could should expect to have the batteries hit float almost every day.

That's the most important question that affects sizing of the whole system.

In a cloudy day, I usually get 10-15% of what I get in sunny day, but if there's a thunderstorm, I get less than 1%. I would think clouds in Panama are somewhat thicker. Assuming 5% and 8 hours of production, you will only get 4kWh even from 10kWh. That doesn't look like something worth chasing.

If you get sunny breaks, then capturing them may be a good idea. But it's hard to judge because you don't know how much you get. According to PVWatts data posted by Bill, it's not too bad at all. If you get 4 sunny hours a day during your rainy season, that's great. Doesn't sound like a rainy season at all. Might be a PVWatts mistake as well. But if you do get some sun in the rainy season, I would simply size everything for the rainly season. If you don't like how it works during sunny season, you simply flip off few breakers and use less of an array. Or you run air conditioning harder, boil water and find other loads. Too much power is an easy problem to solve.

Just curious, you said that the space is limited. How many panels can you install?

Panamretiree

Re: Bulding new Off Grid Home in Panama

NorthGuy wrote: »

That's the most important question that affects sizing of the whole system.

In a cloudy day, I usually get 10-15% of what I get in sunny day, but if there's a thunderstorm, I get less than 1%. I would think clouds in Panama are somewhat thicker. Assuming 5% and 8 hours of production, you will only get 4kWh even from 10kWh. That doesn't look like something worth chasing.

If you get sunny breaks, then capturing them may be a good idea. But it's hard to judge because you don't know how much you get. According to PVWatts data posted by Bill, it's not too bad at all. If you get 4 sunny hours a day during your rainy season, that's great. Doesn't sound like a rainy season at all. Might be a PVWatts mistake as well. But if you do get some sun in the rainy season, I would simply size everything for the rainly season. If you don't like how it works during sunny season, you simply flip off few breakers and use less of an array. Or you run air conditioning harder, boil water and find other loads. Too much power is an easy problem to solve.

Just curious, you said that the space is limited. How many panels can you install?

The annual daily average down here is supposed to be 3.5 hrs, still not a bad amount. There have been days of late where this has not happened, but it did rain.

The space I have available to me is the roof area. I can easily fit 12 front and 12 back. On the ends an easy 9 at each end. So say 42 total and a little area to spare. Benefits of a PV roof: cooler attic, and roof tile and fasteners should last longer. This is all predicated on SWMBO, and the development (should not have a problem with them as they are promoting this development as eco-friendly and what better way to do this than to have a solar powered home in the development up and running). Have no problems with 12 front and back. The back ones will get shade the closer to sunset; however, this should not affect the overall harvest. SWMBO is on side with this project as well (I have mentioned this on a few occasions) and has told me that cost is not an issue.

Our lives have been slowed down considerably by coming here and retiring. The cost of living is less, we do not spend money on things such as movies, spontaneous purchases such as things from Toys or Us for Dad (Home Depot, Lee valley and the likes), or other things like these (they don't exist). Car Insurance (PL&PD) $250.00 a year, good health insurance $1300.00 for two, medications down here are a quarter of the price that we used to pay, doctor's visit (consult) $20.00. The list goes on. We get up between 6 and 6:30 in the morning and are ready for the sandman somewhere around 9:00 PM. I haven't turned on the TV since February - another reason for this is we bought one of those new Samsung Smart TVs and it won't turn on - it has outsmarted me so far. We do drink a few more beer here than we did up home, it's only $11.50 a 24 though.

Getting back to the topic at hand, I'm fairly certain that the battery bank, be it configured as a 24V or 48V system, is adequate for the loads we should see for the life of them.

As for the array size and number of panels, everything is imported, so I'd like to do it once. As you mention, can always turn off panels to adjust the array to the system requirements.

This is the same with the system size, 24V or 48V. Do I go with an inverter that will take me into the future, or do I go with one that fits todays requirements.

Cheers

Ernest

Surfpath

Re: Bulding new Off Grid Home in Panama

NorthGuy wrote: »

That's the most important question that affects sizing of the whole system.

Ernest,
Realise that you are in the thick of details, deratings and absorb times, but there are some pearls of wisdom here.

First off, as Coot said, it is always better to have a slightly overbuilt than underbuilt system for your batteries. And, yes, I believe you should plan your PV array for the rainy season, but not to go nuts, because your generator will always help you in times of real need. It sounds like you are planning to do this, great.

I believe most of the weather in Panama is convectional and ITCZ driven. I am not a weatherman, but the practical outcome is that from mid-May to mid-December when heated moist air sweeps through the country it is frequently hot, rainy & cloudy. Most of the time you will experience 3-4 hours of intermittent sunshine a day with the rest being mostly cloudy and very periodically rainy. That 3-4 hours of sunshine will provide your 'bulk' charge, and the rest of the day when your (say) 2,500 watts of PV produces (say) 300w - you'll still be fine because you will be in absorb. When the sun does peek out and it's during midday, that's when you'll run the laundry.

I would be surprised if there was a sunshine/rain pattern during the day in Panama. In this aspect, I believe load timing will be of significant importance to you. Perhaps more so than if you were in winter, where the sunlight is generally less, but arguably more predictible than in the rainy season tropics. You may have to always keep that one eye to the heavens to see when you can run your day loads.

When a weather system sweeps through and you have 3 days of really heavy cloud cover and only (say) 150w coming from your array, that's when you run your genny to perform your bulk (and do the laundry at the same time ideally).

From what I have read your L16's will need a healthy dose of amps to 'stir' them. Make sure you have a -minimum- 10% (or 0.1 from B's post below) PV to Bank rate of charge. Because you will have "cloudy sunshine" during the rainy season you wont see those high amps that you typically get in the dry. So occasionally running your genny to approximate this 10% will be a good thing as well.

And to confirm BB's advice, beware of large battery banks: "If you charge during the day and use power at night, and cannot cut back on usage too much (fridge, lighting, business), then a larger battery bank is going to be the curse". Well said.

NorthGuy

Re: Bulding new Off Grid Home in Panama

It would be hard for me to live in the clmate where it's always 30+C without AC. Do you get used to it with time?

Assuming that you run AC 24/7 (20kWh) plus other loads gives you 27kWh/day. At 3 hours a day, you'll need 9kW production, which, with Bill's 77% derating gives you 38 x 305W panels. Your roof is fairly flat, so 42 panels is enough to run all your loads and AC 24/7. You do have enough space to accomoade even the biggest system. Although, AC is such a big load that it's worth estimating more accurately. 20% error is 4kWh per day! Perhaps, a more efficent one can be used?

Average numbers don't tell the story. 3.5 hrs/day annual average may mean 7 hrs/day during dry season and nothing during wet season. Imagine, you size everything for 3.5 hrs/day. In the dry season, it'll be too much. In the wet season, the extra panels will produce so little that the size of the array will not really matter. If that's the case, you may fare the same with an array sized for 7 hrs/day - half the size! I would try to get production data for different seasons, e.g. monthly as PVWatts. If the data that Bill has posted do not look realistic, perhaps someone with grid-tied array may provide some information.

westbranch

Re: Bulding new Off Grid Home in Panama

On the brighter side , on those partly sunny, partly cloudy days, you will be able to observe many 'edge of cloud events', where your power input SPIKES momentarily...http://forum.solar-electric.com/showthread.php?18569-Solar-Panels-Exceeded-Ratings&highlight=edge+of+cloud%27
http://forum.solar-electric.com/showthread.php?1592-edge-of-cloud-events&highlight=edge+of+cloud+event%27
too bad they had SNOW! to get it...

vtmaps

Re: Bulding new Off Grid Home in Panama

Panamretiree wrote: »

Do I go with an inverter that will take me into the future, or do I go with one that fits todays requirements.

If you can, size your inverter so that it runs cool. (is that even possible in Panama?) That means you rarely, if ever, run it at its max output. The largest load I have ever run on my 3500 watt inverter is 2000 watts and I have never heard the fan turn on while inverting. The fan does come on sometimes while charging, even though I limit charging input from generator to 9 AC amps. Charging seems to make more heat than inverting.

When you have a larger inverter, you don't have to worry about the fridge turning on at the same moment the laundry starts spinning.

If you do go with an inverter for the future, go 48 volts... if your loads grow, that is the future.

The downside of a larger inverter may be its larger self consumption.

--vtMaps

jeffkruse

Re: Bulding new Off Grid Home in Panama

We have been in some tropical depressions here that have lasted 7 days. Not much sun gets through then.

I have also seen temperatures as low as 63 degrees here. 66 is a common low at night. We are at 500’. I realize our locations are not the same but they are similar.

BB.

Re: Bulding new Off Grid Home in Panama

Future proofing... Always a nice idea--But don't get carried away.

I like to assume that the charge controllers and inverters will last ~10+ years (batteries may last 5-15+ years depending on lots of things).

So, the "horizon" is only ~5-10 years out for most people before they need to service their system anyway. Over-sizing a system can have its own issues (large battery banks can be a pain and expensive, need a larger solar array--Large inverters can use more power when idle/be less efficient at lower AC loads, etc.).

In ten+ years, you may be looking at a completely different brand/model of AC inverter/charge controllers/etc (after 10 years, most electronics are no longer manufactured--replace by something better/faster/cheaper). So make sure you leave room for changes to the layout and servicing of your major system components.

-Bill

Photowhit

Re: Bulding new Off Grid Home in Panama

westbranch wrote: »

here is PW's post...on page 3

Well your statements "Anticipated Array Power @ #####" are basically very wrong, it's good you are thinking about the added heat, but see if you can find the NOCT (Normal operating cell temperature) value for your panel, this will tend to run 75-85% of STC (Standard Test Conditions) which is the way panels are rated.

This why I thought you might be double dipping...

I'm late getting back to the thread, As Westb found I was talking about the temperatures before we got into system derating. I do thing if NOCT values are 75% of panel STC ratings, some further derating of the system should be looked into. mid 30s Centigrade as an average, 35 degrees C = 95 degrees Fahrenheit, the NOCT values are not based on the environment temperatures but the panel temperatures, which are likely to be well above the NOCT values with such a high ambient temperature. I believe the NOCT values are based on ambient temperatures of 75 degrees Fahrenheit.

Bill's post #279 does a good job of breaking down the derating item by item, you may need to plug in 70% on panel ratings though.

Also read post #280, don't know if panels are locally available, but a large part of panel costs is shipping here, easier/cheaper to have a larger array planned, than adding later.

Hard to tell from your information on weather and the isolation I looked at earlier. I was thinking you were similar to our desert SW. Storage/batteries might also be a concern if you will have periods of cloudy weather when you are trying to use 12-15Kwh a day. My 800Ah battery at 24V only represents one nights storage running the Air conditioning! I will be prudent and only AC the bedroom most nights.

My system is designed for our summers, our heat usually comes with sun, I feel I have minimal storage for my system and hope to be able to use much of the solar energy in the summer time directly for Air conditioning.

Panamretiree

Re: Bulding new Off Grid Home in Panama

NorthGuy wrote: »

It would be hard for me to live in the clmate where it's always 30+C without AC. Do you get used to it with time?

You do get used to it. In my case, dropping a few pounds would not hurt. I'm 6'2" and would like to be around 215 lbs, only have to drop 20. We have started to increase the temperature on the bedroom AC and over time, should get to where AC would only be required for an hour or two first thing before going to bed. Fans are the big issue down here. Sufficient air flow over you when resting/sleeping can make all the difference. Have sourced some good low wattage fans by Emerson, just have to get them here. You can also sit in the bar under their fans and put back a few coolies as well. I've fallen asleep in a chair before.

Cheers

Ernest

Panamretiree

Re: Bulding new Off Grid Home in Panama

BB. wrote: »

Future proofing... Always a nice idea--But don't get carried away.

I like to assume that the charge controllers and inverters will last ~10+ years (batteries may last 5-15+ years depending on lots of things).

So, the "horizon" is only ~5-10 years out for most people before they need to service their system anyway. Over-sizing a system can have its own issues (large battery banks can be a pain and expensive, need a larger solar array--Large inverters can use more power when idle/be less efficient at lower AC loads, etc.).

In ten+ years, you may be looking at a completely different brand/model of AC inverter/charge controllers/etc (after 10 years, most electronics are no longer manufactured--replace by something better/faster/cheaper). So make sure you leave room for changes to the layout and servicing of your major system components.

-Bill

Good point(s) all round. I would like to think that there should be some major advances in solar technology, much like the PC/laptop - had a PC Jr in the mid '80s - "156K the most powerful computer you will ever need". I am dedicating the back wall of my workshop to the solar system components, and the battery bank, lots of room.

The entry level XW4548 would seem to be the least/best devil in the bunch. The battery bank would be a single string 8-L16 420AH batteries. This also comes close to the 100AH per 1kW of inverter power, and from a cost perspective, it is only $210.00 more than the XW4024.

Looking at the electrical specs, these two inverter/chargers are close in the specs. See attached picture.

Attachment not found.

These inverters are very close in specifications. From the inverters I've seen on the various web sites leads me to believe that there is a 4 kW threshold for 24V systems. Don't know if this is true, but it seems to be presented this way.

The array size will also fit the 48V system setup in that I can put 12 panels into one array on the roof facing East configured with 3 panels in series and 4 parallel strings. This gives an array size at STC of 3660W, at NOCT an array size of 2748W. This size of array should be sufficient for our needs, but as has been commented, it is easier to install a few more panels later than to add batteries and other components. I will have space on the backside for additional panels if required.

On the other hand, go with a 24V system, and should one upgrade to a 48V system in say 10 years, the wire size would be acceptable, and change out inverter and batteries at the same time. The array panels can be configured for a 48V system. Not a lot of downside. The 24V array would have to be 2 arrays of 6 panels each, 2 panels in series with 3 parallel strings for an array size of 1830W each. Again these would be facing east. More panels can ale be added on the backside later. Have a large enough combiner for expansion as well.

I would have two CCs here, even if one were to be spare at the start (48V system).

Both systems would have Generator Support, which also helps keep the system down to a dull roar.

Another layer pealed away.

Cheers

Ernest

BB.

Re: Bulding new Off Grid Home in Panama

Power has not changed very much... We were buying (small mini-mainframe computer mfg.) switching power supplies for $0.50 per watt in volume (1,000's to 1kW). (back 35 years ago)

You are not paying much difference today for AC inverters/etc...

The difference from a designer point of view is that there is higher integration for analog circuitry, and now we could throw a small microprocessor in there to take care of some of the older hardwired functions.

Overall, the 15+ year old Xantrex SW power systems have very similar performance (efficiency, ability to support loads, remote start gensets, etc.) as the XW does today (50,000 foot point of view).

There are certainly a lot more modes on the XW system today, and integration between inverters/solar chargers/communication to Internet, etc. is there--But that stuff (communications, storage, higher performance processors, etc.) are almost free because of the lower cost for computing.

But all the rest, switching transistors, large capacitors, copper and hand wound torridal transformers, etc. all still cost a lot of money and still have to be fairly "large" to handle the currents involved. Nobody has change the basic laws a physics.

The PC Revolution has all been around "soft" requirements for "1's and 0's" and that scaling down switches/wiring/etc. has allowed more and more capacity on a chip. (cheap 16 kByte Eproms were the big thing 30 years ago). Today we are looking at 16 GByte memories for the same price. And most of that has been from "economies" of scaling (smaller circuits, packing more electronics/functions/1's&0's in the same space).

But interestingly enough, the power usage in this PC's has actually skyrocketed over these years. These modern high speed (high power) processors can have an amazing heat sink.

Attachment not found.

The amount of power "per bit flip" is extremely small this days. I still remember Core Memory.

Forrester's coincident-current system required one of the wires to be run at 45 degrees to the cores, which proved impossible to wire by machine, so that core arrays had to be assembled under microscopes by workers with fine motor control. Initially, garment workers were used. By the late 1950s industrial plants had been set up in the Far East to build core. Inside, hundreds of workers strung cores for low pay. This lowered the cost of core to the point where it became largely universal as main memory by the early 1960s, replacing both inexpensive low-performance drum memory and costly high-performance systems using vacuum tubes, and later transistors, as memory. The cost of core memory declined sharply over the lifetime of the technology: costs began at roughly US$1.00 per bit and dropped to roughly US$0.01 per bit. Core was replaced by integrated semiconductor RAM chips in the 1970s.

The advancement of electronics has been amazing over the decades.

In the end, I would not expect any "revolutionary" changes to off grid power (solar, inverters, charge controllers). You will see incremental improvements (look at the PWM/MPPT charge controller changes)... But you are still looking at the same ~60 to 90 amp @ 48 volt limits for the typical charge controllers.

-Bill

westbranch

Re: Bulding new Off Grid Home in Panama

As to advancements I see things like those being built into/around the Classic CC 'family', like the soon to be released WHIZ Bang 'communicating shunt', so that the CC knows just how much amperage actually went into a battery, and the upcoming KID CC , a smaller version of the Classic, to fill in the product void around 30A, and a MN Inverter, supposed to be 'module-arized' or ? with better features than others... we just have to wait and see...

Panamretiree

Re: Bulding new Off Grid Home in Panama

BB. wrote: »

Power has not changed very much... We were buying (small mini-mainframe computer mfg.) switching power supplies for $0.50 per watt in volume (1,000's to 1kW).

You are not paying much difference today for AC inverters/etc...

The difference from a designer point of view is that there is higher integration for analog circuitry, and now we could throw a small microprocessor in there to take care of some of the older hardwired functions.

Overall, the 15+ year old Xantrex SW power systems have very similar performance (efficiency, ability to support loads, remote start gensets, etc.) as the XW does today (50,000 foot point of view).

There are certainly a lot more modes on the XW system today, and integration between inverters/solar chargers/communication to Internet, etc. is there--But that stuff (communications, storage, higher performance processors, etc.) are almost free because of the lower cost for computing.

But all the rest, switching transistors, large capacitors, copper and hand wound torridal transformers, etc. all still cost a lot of money and still have to be fairly "large" to handle the currents involved. Nobody has change the basic laws a physics.

In the end, I would not expect any "revolutionary" changes to off grid power (solar, inverters, charge controllers). You will see incremental improvements (look at the PWM/MPPT charge controller changes)... But you are still looking at the same ~60 to 90 amp @ 48 volt limits for the typical charge controllers.

-Bill

Come to think of what you are saying is definitely true. The last ship I was on was gas turbine powered for both propulsion and electrical generation and had a lot of electronics in the engineering department, but mostly for control issues, not so dissimilar to the older boiler driven ships. Instead of going to a valve, pump, etc, people now sit at a console and push buttons. Same equipment as in years gone by but operated differently. Cogeneration plants are an example as well. Containing HP steam (500 PSI or greater) still requires the technology and equipment of yesteryear, but we use automated controls to operate it.

Good Points.

Cheers

Ernest

Panamretiree

Re: Bulding new Off Grid Home in Panama

So the new question that I postulated in an earlier post, is there a kW threshold between 24V and 48V systems; ergo what appears to be 4kW. Just a question.

Cheers

Ernest

inetdog

Re: Bulding new Off Grid Home in Panama

Panamretiree wrote: »

So the new question that I postulated in an earlier post, is there a kW threshold between 24V and 48V systems; ergo what appears to be 4kW. Just a question.

Not a hard and fast rule, but around 4kW is where the battery current to the inverter hits about 200A in a 24 volt system and drops back to only 100A in a 48 volt system. Some people would recommend making the switch at even lower power. It is also affected by the largest AH 2V battery you can get. At some point you have to either go to 48 volts or go to battery strings in parallel. If you are using L16 size batteries, for example, you would be forced to 48 volts sooner than if you could get and use larger 2V batteries.

NorthGuy

Re: Bulding new Off Grid Home in Panama

Panamretiree wrote: »

So the new question that I postulated in an earlier post, is there a kW threshold between 24V and 48V systems; ergo what appears to be 4kW. Just a question.

You can build a larger 24V system. Say 3 XW4024 together. However, I don't see any advantages of 24V system over 48V system (unless you have 24V loads, but even then the 24V loads must cope with higher equalization voltages, and not all of them can). I do see advantages of higher voltages.

Moreover, higher voltage system, e.g. 72V or 96V would be better, but these voltages may kill you.

Of course, if you do not have enough batteries for 48V, you must go with 24V.

Panamretiree

Re: Bulding new Off Grid Home in Panama

inetdog wrote: »

Not a hard and fast rule, but around 4kW is where the battery current to the inverter hits about 200A in a 24 volt system and drops back to only 100A in a 48 volt system. Some people would recommend making the switch at even lower power. It is also affected by the largest AH 2V battery you can get. At some point you have to either go to 48 volts or go to battery strings in parallel. If you are using L16 size batteries, for example, you would be forced to 48 volts sooner than if you could get and use larger 2V batteries.

The batteries I have been able to source locally are US batteries - L16 6V at 420AH. I can also get the RE L16 2V at 1100AH. From what I can gather is that the L16 RE 2V batteries are the L16 6V batteries with the internal cells joined in parallel to make the 2V batteries (my understanding comes from the various posters on this forum) Trojan and Rolls Surrette do this as well; however, Rolls Surrette has a 2V single cell battery as well.

Getting 12-L16 RE 2V 1100AH batteries would cost me about $1200.00 more than 8-L16 6V 420AH batteries here in Panama. I have not gone through the exercise of sizing an array for the L16 2V batteries. Having said this, 2 strings of L16 6V 420AH batteries requires an array size of approximately 3600W (I did the calculations in another post) that I would install as two small arrays of 1830W (6 panels each - 2 panels in series with 3 parallel strings per array). Using the L16 2V 1100AH batteries gives me usable 550AH. These two small arrays would probably accommodate the L16 2V 1100AH batteries; however, can always add another small array if needed.

Using the L16 2V batteries would give an additional 2kW of power to use in my system, not a bad thing.

Maintenance would be the same as the L16 2V 1100AH batteries each have 3 cells to look at, but because the cells are joined internally should only need to use one cell cap for the entire battery (I think). Haven't actually seen one except in a brochure.

Would be able to use the extra battery power, ~2kW, for 2 hours of AC each night. Not a bad trade off.

Having said all this, the L16 2V batteries are still driving up the ante. I have learned that there is a balance when it comes to battery banks, DoD, SoC, array size, ability to adequately charge the battery bank, economics, etc.

We do have an AC requirement that the extra power from the L16 2V batteries might compensate for especially in a 48V system. AC here in Panama is not just about cooling down the living space, but also to dehumidify in the wet season. Operating the AC units that we had installed in another house at 220V and operating at 4 amps requires 880W per hour. Operating for say 4 hours (on timer) to transition into the quiet hours would require another 3520W from the battery bank. With my calculated night time loads, I would now need ~8000W of power for night time loads. Still only ~25% DOD for night time loads. Bring into the equation guests, etc, and the additional power during the dry season would be well received.

Another sentiment on these forums is that batteries cycled between 50 and 80 percent for 7 to 10 days is quite acceptable, after which one must bring the battery bank up to a full SOC. This could very well be the case during the wet season.

You have made me think of the system in a very different way. Have to digest this new thought train.

It is interesting that companies have gone to the effort to change the L16 6V battery line into an L16 2V battery line, must be some logic to it and economic cost benefit as well. I wonder how effective and well received this change has been. These hybrids have been out for a few years, and because of this, I wonder if anyone who has them can comment on how well these 2V batteries do the job.

Getting back to your post, thanks for the information, and thanks for making me think of the system in a different light.

Cheers

Ernest

Panamretiree

Re: Bulding new Off Grid Home in Panama

NorthGuy wrote: »

You can build a larger 24V system. Say 3 XW4024 together. However, I don't see any advantages of 24V system over 48V system (unless you have 24V loads, but even then the 24V loads must cope with higher equalization voltages, and not all of them can). I do see advantages of higher voltages.

Moreover, higher voltage system, e.g. 72V or 96V would be better, but these voltages may kill you.

Of course, if you do not have enough batteries for 48V, you must go with 24V.

Just commented on inetdog's post below. Looked at the battery requirement from a different perspective. Have to think a bit more on the post I did.

Cheers

Ernest

Panamretiree

Re: Bulding new Off Grid Home in Panama

Was browsing the other threads, especially the one by Chris Olson and his new genet, Subaru Robin SGX3500 diesel generator. Went on line and looked at it and it is a nice unit.

The other reason I went and looked at the Subaru Robin web site was to determine if there was a distributor here in Panama and there is. Have been looking at Honda web sites, but without the same success. Subaru Robin has a commercial grade SGX3500/5000 gas generators with AVR. Specifications are close to the Honda generator that Chris uses, but there is no mention of a surge capacity - I suspect there is, but it is not stated.

Will be contacting the distributor in Panama City to get more information.

Cheers

Ernest

Photowhit

Re: Bulding new Off Grid Home in Panama

Look around for electric forklift batteries, Panama City is 1.5 million people? and a harbor city... Often the best value in batteries.