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Jeremy Moore
Posts: 12
Location: Hamilton, AL
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I have read through a lot of the threads and am learning a lot, but I feel like I'll get advice more specific to our circumstances by asking more direct questions. A little backstory; We're attempting to establish a cob homestead, but the reality of this coming to fruition is one that needs many years to see through. In the meantime, we are living in an old Greyhound bus we converted into a livable space which you can see here. Currently we are tied to the grid on one end of our property adjacent to a relative. Our build site and permanent location for our bus is on the opposite end of the property. That site is ready to move to except having electricity. We have the option of running a sub-panel a good distance to our site from my mothers' house. Due to the distance, the sub panel will require a significant investment (about $700-$1000). We don't use much power as it is, but unfortunately, I can't give an real accurate usage as we are currently sharing power. We run a small fridge, a small chest freezer, a desktop w/ satellite connection, and no more than 3 low-voltage lights. We run the occasional appliance (blender, juicer, toaster). In the summer, a medium size window unit is an absolute requirement as we live in the Deep South. We are already rethinking our power requirements and ways of replacing electrical usage with alternatives. The first question of many, many, many that I have is would we be better off to use the $1000 on getting a small solar system set-up? If so, where do I go to get the most "bang for my buck"? We wish to be totally off-grid with our cob homes, so why not start figuring it out now with the bus? I need details and I suspect any giving advice will also, ask away and I'll do my best.
 
John Elliott
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Small fridge -- 1 KW-hr per day
Small freezer -- 1 KW-hr per day
Other electronic and electrical items -- 1kw-hr per day
5000 BTU window A/C -- 12-15 KW-hr per day

So it sounds like your base load is ~3 KW-hr per day and you may need 4 to 5 times that much to run the A/C in the summer.

Here is a page that can help you figure the size and cost on solar panels.
 
Marcos Buenijo
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Very nice bus conversion.

I highly recommend you get access to grid power first (mainly because $1000 will not go far in purchasing an off grid solar system). After you have this available, then you may consider a solar system. This is particularly important since you will be running an a/c system. Even a small a/c unit will consume electricity at a high rate.

I suggest using the opportunity of living in the bus to take meticulous data on energy usage. This will require the use of meters to carefully measure the actual KWh consumption, along with measuring and recording the usage of individual appliances (especially a/c). With respect to using the a/c unit, I suggest emphasizing good insulation, adding a thermal mass of some form, and to operate the unit on a timer. The idea is to operate the a/c unit only during the day when a solar array is likely to be producing. When you finally get the solar system, then the practice of using a timer on the a/c will be a great deal more efficient at making use of the electricity provided, and it will be a lot less stressful on the battery system. I don't know much about cob construction, but perhaps this will provide a good thermal mass. You will require a fairly large array to support an a/c unit, but this will be good for the battery system when a/c is not required by ensuring a float charge takes place often and by minimizing discharge on the battery. Make sure to check out the thread "Efficient Air Conditioning" for a discussion of split ductless a/c systems and how they are so efficient. http://www.permies.com/t/27465//Efficient-Air-Conditioning . In your case, however, there is a good argument for sticking with a small window unit.
 
Jeremy Moore
Posts: 12
Location: Hamilton, AL
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Marcos Buenijo wrote:Very nice bus conversion.

I highly recommend you get access to grid power first (mainly because $1000 will not go far in purchasing an off grid solar system). After you have this available, then you may consider a solar system. This is particularly important since you will be running an a/c system. Even a small a/c unit will consume electricity at a high rate.

I suggest using the opportunity of living in the bus to take meticulous data on energy usage. This will require the use of meters to carefully measure the actual KWh consumption, along with measuring and recording the usage of individual appliances (especially a/c). With respect to using the a/c unit, I suggest emphasizing good insulation, adding a thermal mass of some form, and to operate the unit on a timer. The idea is to operate the a/c unit only during the day when a solar array is likely to be producing. When you finally get the solar system, then the practice of using a timer on the a/c will be a great deal more efficient at making use of the electricity provided, and it will be a lot less stressful on the battery system. I don't know much about cob construction, but perhaps this will provide a good thermal mass. You will require a fairly large array to support an a/c unit, but this will be good for the battery system when a/c is not required by ensuring a float charge takes place often and by minimizing discharge on the battery. Make sure to check out the thread "Efficient Air Conditioning" for a discussion of split ductless a/c systems and how they are so efficient. http://www.permies.com/t/27465//Efficient-Air-Conditioning . In your case, however, there is a good argument for sticking with a small window unit.


Thank you both for your help. Marcos, we did insulate the bus in multiple layers, floor, walls, ceiling, and we painted the roof with a reflective paint, but at the end of the day, it's still essentially a tin can with lots of windows. We have considered removing some of the windows, but it's really just another project on a list that is growing by the week. I am all for hooking off grid power myself, but my wife is another matter. The thing is, we made this move to live in a more self sufficient, sustainable matter, and thus far we both feel like we've done a lot more talking about beliefs we claim to possess but are, in fact, not practicing. I hate to put it in terms of principle, but at this point, it is a lot about principle and having to pull power off our folks' house (another red mark in the self-sustaining column). With this all in mind, we are extremely open to alternative ways of conducting ourselves, including air conditioning. I don't know for sure how we'd simply "do without" a/c. As I said, we're located in AL and it pretty much stays in the low to high 90's for nearly 4 months. It simply gets too hot in the bus to remain comfortable. I guess my next question should be, what is the realistic cost of an adequate off-grid system that would do what we need? I have done a good deal of research and the prices vary wildly. it seems like If I have a good resource, one can assemble a good system for a reasonable amount of money. IF so, where's a good source for cheap/good qualitiy components (if there is such a place)?
 
Marcos Buenijo
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Jeremy Moore wrote:Thank you both for your help. Marcos, we did insulate the bus in multiple layers, floor, walls, ceiling, and we painted the roof with a reflective paint, but at the end of the day, it's still essentially a tin can with lots of windows. We have considered removing some of the windows, but it's really just another project on a list that is growing by the week. I am all for hooking off grid power myself, but my wife is another matter. The thing is, we made this move to live in a more self sufficient, sustainable matter, and thus far we both feel like we've done a lot more talking about beliefs we claim to possess but are, in fact, not practicing. I hate to put it in terms of principle, but at this point, it is a lot about principle and having to pull power off our folks' house (another red mark in the self-sustaining column). With this all in mind, we are extremely open to alternative ways of conducting ourselves, including air conditioning. I don't know for sure how we'd simply "do without" a/c. As I said, we're located in AL and it pretty much stays in the low to high 90's for nearly 4 months. It simply gets too hot in the bus to remain comfortable. I guess my next question should be, what is the realistic cost of an adequate off-grid system that would do what we need? I have done a good deal of research and the prices vary wildly. it seems like If I have a good resource, one can assemble a good system for a reasonable amount of money. IF so, where's a good source for cheap/good qualitiy components (if there is such a place)?


I know exactly what you mean about a/c as I was born and raised in east Texas. Doing without a/c is not a practical option in the south. Unfortunately, the a/c unit requires not only a larger array, but a proportionally larger controller, battery, and inverter.

A reliable off grid power system that sees low long term costs will have a high up front cost. If you want to do it right, then it's going to take money. You want OPTIMAL here, and not merely "adequate". Expect to pay $8000-10,000 for a proper off grid PV system (and this assumes you are doing the installation). I am assuming a system that provides at least 10 KWh AC electricity for end use each day (on average) during the summer months (figure a 3 KW array). I consider this minimum for supporting a small a/c unit.

I can't recommend any source for components as a first hand buyer, but I've heard many good reviews of wholesalesolar.com. There is also excellent information at that site for education purposes. This site sells complete off grid PV systems that might interest you. At the very least it will be useful for pricing purposes.

I will make only one recommendation, and that is to consider a fork lift battery. Here is one site of interest: http://gbindustrialbattery.com/Forklift_Battery_Sizes_and_Specifications_Zone15.html . The prices include delivery in the Continental USA. There are branches all over the U.S. including many in Alabama. I have heard many independent accounts of fork lift batteries lasting 20+ years in off grid PV systems. There are accounts all over the web, but try the forums at windsun.com for a few examples. If not a fork lift battery, then Surette batteries seems to have the best reputation.



 
Marcos Buenijo
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I'm discussing one possible way to provide cooling in a humid region. I think this can be practical for a small space. Heated air can be used to regenerate silica gel desiccant. The procedure is to blow heated air through a bed of silica gel contained in an insulated vessel. The moisture will be released and expelled with the air. I read the results of a study that showed air heated to at least 160F will regenerate silica gel efficiently. In that test the air was heated by solar. An alternative heat source could be had with a small furnace where hot combustion gases are mixed with air to take the temperature down. Once regenerated the bed can be flushed with fresh air to get rid of any undesirable gases, and also cooled by the fresh air. Once regenerated, flushed, and cooled the air in the home can be passed through the silica gel at a low rate for drying. Once the air is dry, then it's possible to achieve cooling with micro evaporative coolers that are available on the market. It may be possible to configure the system such that a small portable evaporative cooling unit (generally available for around $100, see Amazon) can pull outside air into the home through the desiccant, then through the wet pad for cooling... or the air in the home can be circulated through the system in a closed loop, or both.

In principle, it's also possible to make use of the heated air passing through the bed. For example, it might be used for water heating (waste not, want not). So, it may be possible to devise a system that regenerates the desiccant while also heating water. That is an interesting prospect.

NOTE: For clarification, the desiccant bed would have to be regenerated daily with heat to make this work. Some kind of a small batch biomass furnace might be devised (like a TLUD) to do this in a few hours. I see no reason why this cannot be devised to be unattended during operation. You would need roughly 50-100 pounds of silica gel which would be around 20-40 gallons. The desiccant would last indefinitely. Expect to pay about $1.50 per pound. Crystal cat litter is often pure silica gel, and should work... or at least you could do some testing with it if this interests you.

ADDENDUM: I wasn't going to go here, but I figured I would throw this out for your consideration even though I do not necessarily consider it to be the best alternative. It can be viable to provide all your energy needs with a small genset and battery/inverter system IF the home is small and the electrical requirements are very modest, and if the heat from the system is put to good use. Personally, if you can get your average electricity consumption under 5 KWh a day, then I think this can be a viable option. Note that if you desire to avoid the use of fossil fuels/commercial fuels, then a small wood gasifier can be used. If you are not averse to using a commercial/fossil fuel, then natural gas is a good idea if you have it available. The philosophy behind this approach is that, if you were to make use of heat on a daily basis for such applications as desiccant drying, water heating, and/or space heating, then this heat might be provided by the genset while it's in operation. In fact, many small engines are contained in a shroud and an internal cooling fan cools the cylinder, and this heated air mixes with the engine exhaust as it's expelled from the unit... this might be used directly in heating applications like desiccant regeneration and/or water heating. Heated water can be used for space heating purposes easily by fashioning a micro hydronic heating system (store heated water in an insulated vessel, then use an inexpensive and reliable magnetic drive pump - dc available - to circulate hot water through a small fan coil unit for air heating). If the proportion of heat/electricity is ideal, then this can be a highly efficient configuration since very little energy will be wasted. Note that this has advantages and disadvantages, but you really can't beat a modern photovoltaic set up with respect to performance and convenience... unfortunately, the upfront costs for a proper system can be daunting. Note that the PV system will require a backup generator and you'll need a small furnace for heat anyway. This approach seems particularly appealing for space heating and water heating applications, but if the desiccant evaporative cooling system were to prove effective, then it could be adopted during the summer months as well (while also providing water heating). Again, it can be efficient (in principle). This discussion is mainly to encourage outside the box thinking.
 
Brian Knight
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Location: Asheville NC
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Thats certainly some out of the box thinking Marcos. Look forward to more on this.

I have to question the desire to strive for off-grid solar installations. The reasons for being off-grid are obvious but I feel the need to remind or inform others of the two main reasons for staying grid-tied:

1. Grid tied is usually much more affordable. This goes for upfront costs and long term maintenance.

2. Its better for the environment and society. Battery production has some nasty consequences but its the contribution to the grid during peak demand hours that really helps the environment and society. A grid-tied PV system contributes clean energy to the surrounding neighbors which exponentially reduces the waste of electricity that is lost during grid transport and conversion. Peak demand production is the main driver for building new fossil fuel plants.

Off-grid makes the most sense in remote locations with no infrastructure. If the infrastructure is nearby then off-grid is turning its back on society and ignoring the convenience of the grid as a battery which should have less environmental (and monetary) consequences than using deep cycle batteries and fossil fuel generators for backup.
 
Marcos Buenijo
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Brian Knight wrote:I have to question the desire to strive for off-grid solar installations. The reasons for being off-grid are obvious but I feel the need to remind or inform others of the two main reasons for staying grid-tied:

1. Grid tied is usually much more affordable. This goes for upfront costs and long term maintenance.

2. Its better for the environment and society. Battery production has some nasty consequences but its the contribution to the grid during peak demand hours that really helps the environment and society. A grid-tied PV system contributes clean energy to the surrounding neighbors which exponentially reduces the waste of electricity that is lost during grid transport and conversion. Peak demand production is the main driver for building new fossil fuel plants.

Off-grid makes the most sense in remote locations with no infrastructure. If the infrastructure is nearby then off-grid is turning its back on society and ignoring the convenience of the grid as a battery which should have less environmental (and monetary) consequences than using deep cycle batteries and fossil fuel generators for backup.


I must say I totally agree with you here. Objectively, the off grid power system makes sense only where grid power is not available and where providing it is cost prohibitive. Unfortunately, the benefits provided by a grid-tie PV system is partly dependent on legislation (net metering, etc.). That said, I think those who desire to go off grid with respect to energy have never been in more favorable position than today. The battery is probably the main impediment, but my recent research into forklift batteries in RE systems has me confident that a surprisingly cost effective system is possible. I am aware of many forklift batteries in off grid RE systems that have lasted 20+ years, and one that lasted more than 30 years. The price/KWh of these batteries is also lower than any alternative I've yet found. Also, I understand that most of the material in lead acid batteries is recycled, and the scrap from a spent forklift battery is worth several hundred dollars.

 
William Trachte
Posts: 38
Location: Deerbrook, Wi
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Because of philosophy, seemingly high outage rates in the North Woods, easement questions and the cost of burying a line 1700' from the road, we went in to the building process with a serious commitment to off-grid. We became members of the Midwest Renewable Energy Association, attended at least a dozen seminars, and subscribed to Home Power Magazine to educate ourselves in hopes of building a modest, properly-sized 1200kw off-grid system ourselves. We bought 9) 15 watt panels and many batteries, practicing for two years on reduced demand; finally living in our shed for 6 months while the house was being built. This project can be done, if you are willing to literally "learn to be an installer", as by definition, you will be installing sophisticated components you can't afford to ruin by "wiggling in". There is no short-cut, and for us, the choice was between getting a homestead up and running in a year or learning a new profession. Sad as it is, until it becomes "plug-and-play", it seems unlikely that a homeowner has the money, time and skill to pull it off, but you are welcome to try. The components amounted to about $13K; having someone do it for you made it $26K, and that put it well beyond our resources, if not general sanity. The final deal-breaker is the batteries. Spending $8-10K on a battery bank that, even if you do everything right, will end up a biohazard somewhere in ten years, is not a value proposition we chose to entertain. And then you get to buy some more. I'm not sure I'd count on reports of 20 or 30 years of use: speaking to a rep from Trojan, we were assured that how they are kept and used greatly effects life. Being a Yankee, I can well believe that AC is not really optional thereabouts, and that kind of demand just might spell doom for a battery. Before you scorn the grid-tie: it is popular for a reason. Maybe you can put the panels on her house and pay your mom back that way. We plan to eventually go grid-tie when the dust settles, as we did resolve the easement issue and pony up for the buried line @ $12 a foot around 500' as our solution. Sorry if that seems bourgeois, but we're old. Two years on, the decision seems wise, in spite of the half-dozen outages per year. That's why you have a generator.
Best of luck, and apologies for the presumption
 
allen lumley
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William Trachte : You did not say whether your bus was Nose to the sun or side facing the sun, Also My next plan will not work if you are even slightly worried about your roof
leaking, ether bus ! You can install a trellis on the sunny side of your busses, with special attention to blocking the late afternoon sun in the west !

You can easily Trellis up to 5' taller that the bus, I would go with just Sweet peas at ground level, and then hang pottery jugs filled with more peat moss or perlite or vermiculite
than dirt and multiple planting spots on the sides, and even some shallow planters on the roof, In these locations I would go withWild cucumber, also called Balsam Apple, or
spiny cucumber, this can stand very poor soil likes water, and creates a lot of shade with out blocking the wind much, and it is so easy to prune flap a stem and pull, if started
early enough you should be in a green cave by the middle of the summer. Oh Yes , I said that the wild cucumber (non Edible but safe for kids) loved water, if you can get a pump
up weed sprayer you can easily spray your hanging pots ,and the water that is sprayed on the roof that misses your shallow planters will evaporate and help cool the busses outer
shell ! All the water that you need should come dripping out of your air conditioner ! Just a thought, while not helping to Build your Future cob House, it will make returning to the
bus a little more pleasant !

My bus was a '63 had an old Servile gas refrigerator and was parked in a dump, a 1/4 mile from my 1st Job Site. It Travelled around a lot 'till called into the service and then was
parked as a hunting camp. There the wild cucumbers took over and buried the bus so that pulling vines was the ist job of the young kids taken to hunting camp for a treat ! Some
fine memories, now we camp in a Yurt ! Hope that you can use this ! Big AL !
 
Marcos Buenijo
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William Trachte wrote:The final deal-breaker is the batteries. Spending $8-10K on a battery bank that, even if you do everything right, will end up a biohazard somewhere in ten years, is not a value proposition we chose to entertain. And then you get to buy some more. I'm not sure I'd count on reports of 20 or 30 years of use: speaking to a rep from Trojan, we were assured that how they are kept and used greatly effects life. Being a Yankee, I can well believe that AC is not really optional thereabouts, and that kind of demand just might spell doom for a battery.


Good advice in the main post. I am just addressing these particular comments. First, lead acid batteries are mostly recycled. In fact, I verified that a certain major manufacturer of forklift batteries will pick up a discarded battery system without charge due to the value of the scrap. Second, I agree that one should not count on a battery system lasting 20 or 30 years in the off grid setting. However, all else equal, it is reasonable to expect a forklift battery to last about twice as long as batteries more commonly used in off grid solar applications (such as golf cart batteries or other "deep cycle" batteries often sold for "marine" applications). Ten years is virtually assured with proper care, and 15-20 years is the norm. How a battery is used definitely affects its life. Temperature extremes (especially high temperatures), excessive discharge, leaving in a partially discharged state for extended periods, excessive charge rates, water loss... all these will lessen battery life. An AC unit can challenge a battery system. However, with proper management, all of the factors that contribute to early battery death can be avoided.

Jeremy, if you're still following this thread and if you are still interested in an off grid solar system, then know that you can make it happen even when running a small AC unit. However, you will have to adopt certain strategies including opportunity loading and load management. Good news is that it's possible to automate these processes. An AC unit can be placed on a timer to minimize battery discharge at night. It's also possible to power the unit with a relay that permits operation only when solar flux is high enough to prevent a net battery discharge. The latter approach will allow the solar array to approach or reach a full battery charge each day while also running the AC much of the time (or even all of the time) to allow for several hours AC use at night, and without ever seeing significant battery discharge. I know that it all seems so complicated and technical, but it really is fundamentally simple. Again, I expect a 3 KW array would be ideal where an AC is relied upon during the extended summers in the south. Today a 3 KW array can be had for $3000, a MPPT charge controller for $650 (Midnite classic), inverter for $600 (1100 watt, 24v, Exceltech) or go with a 2000w version for $1100, battery for $2500 (forklift battery at 20 KWh rated storage capacity at 20 hour rate - price includes delivery), cables and racking equipment for about $1500. You could build your own panel mounting system and save $1000 or so. Total cost for hardware could be under $8000. You still need a backup generator ($1000 for a Honda EU2000i), and a battery charger (good one will be $300 or so). $10,000 should get the whole enchilada (not including your labor). The cost of solar hardware is a great deal less today than even the recent past. Also, limiting the size of the battery system will greatly reduce the cost of the system. In this case it makes more sense to operate a generator on those unusual days of very low solar flux as opposed to purchasing a massive battery system required to take the system through several days of inclement weather. Also, in your case, since you need a large system primarily to support an AC system during the summer, then you will have fewer such days - and you may just get by without having to use the generator by simply cutting off the AC during these times. The large array will be useful during the summer months to heat water as an opportunity load during the day, and maintaining fewer loads during the winter months will protect the battery from significant discharge while also buying a few days of inclement weather. Finally, I wanted to add that using a fairly large array with limited loads normally during the day is a great system for opportunity loading. You could run many fairly high power loads as long as the array is putting out well and avoiding any battery discharge. Examples include: an additional AC unit, clothes washer, electric cooking (small induction cooker, electric crock pot, etc.), water heater.
 
Tony Masterson
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John Elliott wrote:Small fridge -- 1 KW-hr per day
Small freezer -- 1 KW-hr per day
Here is a page that can help you figure the size and cost on solar panels.


Does it matter what type of voltage the freezer uses due convertor efficiency? 110v AC or say 12v DC.
What about gas powered freezers like this one: http://www.alibaba.com/product-gs/1393713880/Gas_power_chest_freezer.html
Not promoting it in any way but it runs on 12v, 110v, 220v and gas.
Is a natural gas freezer worth investigating or is it utterly inefficient?
 
Marcos Buenijo
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Tony Masterson wrote:Does it matter what type of voltage the freezer uses due convertor efficiency? 110v AC or say 12v DC.
What about gas powered freezers like this one: http://www.alibaba.com/product-gs/1393713880/Gas_power_chest_freezer.html
Not promoting it in any way but it runs on 12v, 110v, 220v and gas.
Is a natural gas freezer worth investigating or is it utterly inefficient?


The main factor affecting efficiency in a freezer is the insulation. Also, all else equal, a larger freezer is more efficient with respect to the quantity of food refrigerated per unit of energy consumed because the surface area/volume ratio of the larger freezer is lower. All else equal a compressor powered by DC will be more efficient due to no inverter losses, but in practice DC motors (especially 12 volt) are often less efficient due to much higher current. Generally, the efficiency of the motor or compressor is not enough to make a difference in overall efficiency. Insulation and freezer size are the important factors to consider. There is also thermostat setting and ambient temperature with a lower thermostat setting and higher ambient temperature adversely affecting efficiency.

An absorption freezer is generally very expensive. Sure, they use a lot less electricity than a conventional freezer, but the amount of fuel consumed does not justify it in the long run. They made more sense for off grid use in the past when solar hardware was a lot more expensive. Today, with quality panels selling for $1 per watt or less, it makes little sense to go with an absorption freezer (my opinion).
 
Agustin Magnus
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Hello,

I guess my advice is a hybrid of what many others are suggesting. Don't beat yourself up about being "sustainable" or adhering to a green purity test...just connect to the grid with the $$ you have right now. Work first toward lowering your need for electrons to the lowest absolute level. Buy yourself a Kilawatt meter(http://www.amazon.com/P3-International-P4400-Electricity-Monitor/dp/B00009MDBU) to get data on all the devices you use. What can you live without? What behaviors can you change without too much fuss? What natural forces can you take advantage of to perform the same tasks as your electronic gear?
You mention building an earthen structure. These are perfect for your climate. Use earth for the house, use earth and water to cool it. ANY evaporation will cool a surface, even in humid AL. Don't go out and buy a swamp cooler. Soil is usually wet in Alabama, no? When you build your home, bury a cooling tube that will pull air through it over a long distance. This air travels into the home on those blazing Alabama summer days/nights, losing heat as it goes. The hot air in the home "wants" to rise and expand, so let it do that by opening a skylight or vent at the top of the structure. Be sure to put a drain and caps/valves in your cooling tubes. I bet you can find examples to both heat and cool your new home this way. Look into how aboriginal peoples cooled their structures in similar climates. Size your new HVAC system to the home by putting in more tubes...
Lastly, when you've built your cool new home, turn the bus into a lumber drying kiln or...
I hope that helps some and best wishes...

 
Agustin Magnus
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Sorry, I forgot about your PV question. Not worth buying with the $$ you have right now. I've built several PV systems for autonomous platforms in one of the worst parts of the continental US(for insolation) and even when we oversize the system capacity by 4-5 times we still work in a deficit for much of the winter. Usually that means turning off some things for a time. Again, start with your usage.
 
Marcos Buenijo
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Jeremy, I don't know anything about cob construction. If the insulation and thermal mass of this structure is very good, then you should have no problem whatever in cooling it with an air conditioner powered by photovoltaics. I alluded to this in a previous post, but I never described it directly. It's possible to operate even a fairly large a/c unit with a PV array during the day and cool the mass. This is certainly the most practical solution. Here is one configuration: Consider a 2.5 KW array, 24 volt battery, and Midnite controller. The controller can deliver up to 2300 watts (90+ amps at 25 volts). So, it would deliver the vast majority of the energy generated by the array at all times(*). Now consider a one ton a/c unit operated on a timer and/or operated with a relay energized off the controller itself (I understand that the Midnite can be configured such that a relay is energized once the battery goes into absorption). While the a/c unit is operating and drawing about 1150 watts from the inverter (about 1350 watts from the battery/array system when factoring inverter losses), the balance of the energy from the controller would go into the battery and whatever other loads are powered. So, as long as the array is putting out more electricity than required by the loads, then the battery will see a net charge. Transients in solar flux could reduce the array output and lead to a net battery discharge while the a/c unit is running, but the a/c unit would keep running as long as the battery is in absorption, so it would still support a/c for a while until this happens. A timer might still be provided as a redundant feature to prevent the possibility of drawing down the battery with the a/c unit (timer might allow the a/c unit to come on only from 9 am to 5 pm, or something like this). I'm confident that a modest home of cob construction would be cooled very well with this approach. I don't think you'll have a problem, but the system still requires the initial investment.

(*)Also note that I understand the Midnite and other controllers will limit the charge rate to its max, so a 3000 watt array might be used with a Midnite that is limited to 2300 watts at a nominal 24 volt battery. An idea I like is to position two arrays differently, one for morning sun and one for afternoon sun, to flatten the energy production profile during the day. Since panels are relatively inexpensive compared to the whole package, then this seems reasonable... and it will buy a couple more hours of a/c operation each day without dipping into the battery. Also, the Midnite can deliver twice this wattage with a nominal 48 volt battery.

NOTE: Another approach is using two smaller window a/c units where one is on a timer, and the other is on a relay. This would lessen the starting surge seen by a single larger a/c unit, and it would permit operating one of the smaller units on the battery for a longer period if desired.

Sorry so wordy, but there are just so many possibilities!

 
Leslie Bronk
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If your fridge runs AC - start off with a kill-a-watt meter. It is an inexpensive meter. Just plug it into the wall socket, and then plug in your appliance and let it run for a few days and then calculate out how many watts (and/or amps) on average you use per day. You'll need to know this information. And it will help you identify where the most electricity load actually is. (Hint - it isn't the lightbulbs... it's the fridge, a/c and computer.) You'll have to determine what you can live without and what your real priority is. Also learn on a small budget that you might only be able to run a couple of things at a time.

I've lived in an RV and home (in FL and NM - both hot places), and measured each appliance using a Kill-A-Watt meter to determine the average daily energy loads for solar. I also was sharing an electric bill and didn't know what my real KWH usage was in the RV. The kill-a-watt meter was so accurate that when I left, I found out the impact of my departure was exactly the estimated drop on KWH on the bill.


I'm going to presume you'll figure out the fridge is the most important. The refrigerator will be running off a battery during the late evening and night and early morning. You won't know what size battery you'll need until you know the average amphours it needs to suck out of the batteries during the hottest part of the summer.

The output from the solar panels gets throttled down to what the battery actually requires for proper charging. What that means at the practical level is that during the day, there are a whole bunch of extra watts available for consumption besides just charging the battery (if you have enough solar panels) to run the TV, internet, etc. You'll want to do those things during the day when turning those things on doesn't drain the battery, and leave the battery for the most critical thing after late evening until morning - the fridge. Get some solar lanterns for interior lights if you must.

Even doing things as minimal as possible, you'll still need a charge controller to charge the batteries properly AND for the occassional Equalizing Charge. Since you are off-grid, the only way you can equalize is with a charge controller using your solar panels (as long as your system is fully charged by 1pm and you have a cloudless day) .... or by running a generator (defeats the purpose of sustainability, doesn't it....)

You'll also need some kind of invertor to change the DC current from the batteries into AC for the fridge to use. You don't absolutely have to buy an invertor made for solar systems. I've seen a set up where the guy had a small invertor like you might find in installed in a "guy's truck"; and he just plugged in whatever he needed at the moment into it. The washing machine, a light bulb, a power tool. But he had an LP fridge. I don't know if he could have plugged that in - it depends on watts and Amphours. More than likely it was enough. But you have to measure. His used golf cart batteries probably had enough amps for the fridge, he just never tried it - not knowing how to use his solar system.... (FYI - I helped him get a different charge controller and system/monitor, and now he knows what he can and can't do, and rarely ever fires up the generator.)

That said..... that kind of invertor was not a true sine wave - and you need true sine wave for your computer equipment...



For the air conditioner

I've lived without AC in FL and NM - both hot hot places, but one humid and one not....

In your neck of the woods, you are in a humid area, swamp coolers (evaporative) doesn't work well. Been there, done that. What does help cool the RV a bit is a large roof over the RV/bus to stop direct sunshine on the roof & sides to drop the temperature 10+ degrees, and open the windows. Sit outside in a screened in tent if you have to. It isn't the most ideal temperature, but you can survive. I did for many years that way. But drink a kit more water, electrolytes, and dressing really skimpy helps too! Simply sponging cool water over skin also helps. People lived for thousands of years without AC and somehow managed as a species. People also survived without heating a 2000 square foot home also. It is easy to put on a 2nd blanket or even a 3rd, and sleep in 40 degree weather... you'll probably sweat under 3 blankets...

Anyway, solar cells typically are used to charge batteryies. You can charge them direct without a charge controller, but batteries really don't like that and it decreases the life of the battery. A charge controller regulates the volts/amps/watts to ideal conditions for the battery.

If you ask the invertor manufacturers, they might even tell you that you can't run the house during the day direct off the solar panel without the battery --- something about inconsistent peaks and valleys in voltage output from the solar panels due to changing light conditions from clouds, people walking by, chemtrails, etc. You start to understand this when you watch a system that is connected and watch the voltage changes, and the amp changes and even postive amps (amps flowing into the battery), and negative (amps flowing out of the battery because the load in the house is greater than the extra previously unused amps available from the solar panels).

Assuming you'll figure out that the most critical thing at night time is just the fridge and maybe a light now and then... you'll need to determine how many amphours your fridge needs from late in the afternoon, thru the night, and thru the early morning hours. There are about 6 hours a day (winter) in your area where the fridge would be pretty much running off the sun (thru the solar system equip) as opposing to using any of the amps from the battery. The fridge doesn't run all the time, which is where the kill-a-watt meter will really help you. Leave it plugged in for a week in the hottest part of the summer to get your average worst case load (with and without cloudy days). Once you make note of your avg watthours avg amphours, you can call any solar dealer and ask what is the smallest size battery you can get away with. There are also websites that help you do the calculation once you have those numbers.

The biggest problem I found calling dealers direct is they want to sell you a system they know will work, and not necessarily hold costs down to a minimum. In the end, they are probably right. Improper charging and care of the battery will lead to dead batteries ($$$$$) before you know it. A lot of people kill their batteries in the first couple of years due to improper charging and maintenance (adding distilled water, checking water levels regular, using a hydrometer regular, checking voltage regular, and equalizing charge when stratification is noted...)

I've found the deep chest freezer is more energy efficient than the fridge. During extended months of no power after one of many hurricanes, I used the freezer instead of the fridge. I made ice blocks in it, and then used an ice chest for daily "refrigerated" type stuff instead. I did that before going solar, and wouldn't hesitate to do that again even on solar.

DC refrigerators & freezers are pretty pricey.... plus you still have to buy the solar panels & charge controller & battery....

During the early evening, thru the night, and until the sun is high enough to start charging the batteries, most of the time it is my fridge that is sucking the energy out of the batteries since I pretty much crash when the sun goes down. It depletes the batteries about 10-15% every night.... but I have pretty big batteries.



Also, there are people out there selling used equipment in these hard times. Don't overlook it. Wiring it together correctly and safely is another story
Try to make sure whatever charge controller you get has an LED readout area so you can actually learn what is going on with the volts, amps, battery status, charge status, output from the solar panels, etc. You might not learn it right away, but you'll learn one thing at a time and sooner or later it will stick.

Good luck with going off-grid. Hope you can achieve it, because one of these days electricity is going to be completely unaffordable for a period of time.

If solar is out of your reach - think about getting big LP tanks and getting an LP fridge instead. You can always use old cooking oil for lamp oil and other old world methods.

I know that dealing with the heat after a lifetime of being spoiled was the hardest for me... but I'm still here, still kicking Even when it is 120 degrees outside (real temp, not adjusted for humidity) - misearable at that temp, but can survive it.





I've also lived in hot & steamy FL, and oven hot NM. A couple of things to note.



The fridge and refrigerated A/C use up the most energy.
 
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