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Ask Jeff Yago
Solar & Energy-Related Issues

By Jeffrey Yago, P.E., CEM
Jeff Yago

Filters and water heater for eco-lodge

Hello Jeff,

First I'd like to say "Thanks" for the wealth of information you impart on these pages. They constitute the best "Outback How To Guide" I've been able to locate.

Now for my case: I'm attempting to start a small eco-lodge in a remote part of South America. There are actually two properties adjacent to each other and I have one question concerning each.

Property A: A solid rock cabin with a 2,500 gallon storage tank at the top of the property. Here we ran 3/4" tubing going to the house where it is further reduced to 1/2. We would like to add hot water for showers and maybe dishes but since there is only one set of tubes to this cabin, I wonder how to go about this. The cabin's location gets plenty of early morning/afternoon sun but little to none after 3 pm and although electricity is free it's not very consistent. Because of this I'd prefer to go solar if the expense is not outrageous. All tubing inside the house is some sort of plastic but I don't know if it's PVC or ABS(maybe even something else). Given these constraints, do you have any advice on how best to go about getting hot water for showers and dishes in our little rock cabin that is not setup for it?

Property B: This is the actual lodge portion and here we need a filter of some type. Our filling tube is located at street level 100 yards from us running down a steep hillside and to the lodge where the 4,000 gallon storage tank is. Buried in rocky soil and running 100 yards or so through public property we have little control over who does what to it and have been having semi-annual failures in the tubing. These are usually punctures on the top of the tube so we still get water but it does bring a fair amount of sand with it. Do you know of any sort of field maintainable filtration system that would be able to remove this much sand if/when it happens again?

Thank you for any advice,

Chuck Huber

Chuck,

I cannot go into this level of design on a "free" web site due to time limitations and prefer to give answers that can benefit others also. However, I will try to provide some general ideas. First, years ago there as some "tubing" sold in the US to replace the more expensive copper piping and most of these early installations failed. Later attempts with plastic did great for cold water piping but not so good with hot water piping. Todays plastic domestic water piping you find at the local builders supply are pretty good, but most likely the "tubing" you refer could either be some of this early attempts at domestic water piping or actually real "tubing". If it is real tubing, it may not be designed for the pressures, hot water temperatures, and sun exposure you may experience where you are. You may want to check this out before doing any major plumbing changes as it may be a type that is near the end of its life already.

Your cabin application sounds like a perfect place for a simple solar hot water system. The sun heats water in panels on the roof all day which is circulated through a large insulated storage tank. At night the circulation stops and the tank of hot water is piped only to the shower and sinks that require hot water. This means you will need a second section of piping that is only for hot water. The existing cold water piping will have a connection that supplies water to the "bottom" of this tank and the hot water connection will be at the "top" of the tank which improves temperature stratification (hottest water stays at top).

Your second application is probably having piping failures due to the high head pressure from the water being supplied down a steep hill. Water produces 1 psi of pressure for each 2.31 feet of fall or elevation change. Simple pressure reducing regulators are easy to find for this type application, but be sure there is a filter of some type and valving that will allow changing or cleaning the filter without working under high pressure. There are endless types of sand filters and water filters on the market, and you should not have a problem finding one for your needs. However, I would address the pressure issue first.

Good luck,

Jeff Yago


Question about solar street lighting

Dear Jeff,

What's the advisable power a high efficiency DC lamp should have when used in a park or public illumination? What about the SOX lamps consumption? I understood the components are the same (except the array size). Is that right? Can I use regular headlamps or do you advise something special?

What's the differences between the solution you describe, that seems to be quite cheap (although I have no clue yet about total price for a pole) and those expensive being sold by many companies?

Thanks for your help,

Carlos

Carlos,

Under no circumstances would I use a regular car headlight. These have a focused light that is designed to produce a very bright light in a very limited area, and they are not designed for energy efficiency.

There are really good low pressure sodium (brown street light color you see along interstates) which are one of the lowest energy using wide area lighting you can buy which are available with 12 volt DC ballasts. There are also some really good LED type "blocks" that are water-proof and designed for street lighting purposes. These are the lowest energy using lights ever made and they also are designed for solar charged battery power. Both types are available from the solar advertisers you find in this magazine. They are expensive, but you will not need $2000 worth of solar modules to power them like you will need with your car headlight versions!

Good luck,

Jeff Yago


Outdoor light

Hello Jeff,

I would like to ask a question about your article "Build a simple solar powered outdoor light". What would it cost to build and install that system?

Thank you,

Joshua Reinbrecht

Joshua:

Its always hard to talk costs related to solar systems as the really good pricing requires larger quantity orders. Also, because all the established solar installers are still having problems finding solar modules due to the strong overseas markets, its hard for someone only wanting to buy one or two modules to find anyone willing to take the time to process their order.

A rough "rule of thumb" these days is to expect to pay around $10.00 to $12.00 per watt for a basic solar system depending on sizing and battery capacity. Systems are not priced or sold this way, but it seems to average out in this price range. The smaller the system size, the higher the cost will be on a per watt basis.

Be careful when ordering solar hardware over the Internet as many web sites have solar modules listed, but they may not actually have any in stock and you may be waiting over a month before they are even shipped.

Good luck!

Jeff Yago


Water problem

Jeff,

We are off the grid and are using a Rinnai continuum (? did I spell that right) 2520 water heater. We're getting white little gritty buildup in our faucets, and think we should use a water softener. Being on solar, we would prefer a magnetic water softener, using no energy! Any recommendations.

Dawn Reynolds

Dawn:

Not sure what this is since there are many different types of hard and soft water issues. I strongly suggest having a sample tested before you invest in any "gadget" type solution. For example, most suspended solids like sand will plug up small openings in faucets and shower nozzles but usually will not harm piping. Dissolved solids like calcium and sulfate can leach out of the water and build up over time and plug piping and reduce the heat transfer of water heaters and coils. Chemicals in the water that can cause bad taste can usually be corrected by carbon filters.

I have cut open old copper and galvanized steel piping in old homes and found them completely filled up with a hard chemical buildup except for a tiny opening remaining down the middle. This type chemical buildup will destroy a water heater or heating coil.

Not all particles are affected by magnetic fields and many times it requires a salt brine water softener to correct a hard water problem. A salt brine water softener uses very little electricity which is only used to power an electronic timer to switch a solenild valve every few days, so I would not be concerned about electrical power usage. The older style units had a dial timer using a clock motor which had the lowest energy usage if you can still find them.

Regardless, test the water first and request information on what to do to correct based on a real lab analysis. There are some very good certified well water testing labs advertising on the Internet that you send $20 to $30 and they will send you a sample bottle which you return in a mailer they provide. Your test results are mailed back in a few days and will include helpful written information that describes what each test result means.

Many states offer free well water testing kits and you may want to check with them first if cost is an issue.

Good luck!

Jeff Yago


Dual batteries question

Jeff,

How about if i wanted to add to batteries to my camping trailer/ Tent trailer that only has one right now. Wanted both to be charged by solar while I was dry camping, providing me with more hours of power.

Concerned about connecting too batteries together.

Then once I'm done camping i can just unplug the solar and be on my way.

Can both batteries be charged by the truck while I'm going down the highway?

Mike

Mike:

There are several things to consider and I suggest you read my article about adding a solar panel to keep a spare battery charged in a truck camper shell, Issue #93 in the May/June 2005 issue.

The short answer is, unless you use heavy batteries like a deep cycle RV/Marine battery, you will not get much life out of the proposed system. You can connect both 12 volt batteries together in "parallel" which means you connect the positive to the positive and the negative to the negative. When you attach a volt meter to the combined batteries you still should read 12 to 14 volts, depending on charge level. If you read 24 to 28 volts, you have wired them in series which will damage any 12 volt light or appliance you attach, and if you attach each terminal to the opposite terminal on the other battery, you will get a really big fire and melted cables!

If you really want to dry camp for an extended period, I would replace the existing battery and install two 6-volt golf cart batteries. These will take up about the same space as two RV/Marine batteries, but they will be heavier. However, they will provide power for a much longer period and are designed for a heavy charge/discharge application.

Yes, you can charge the batteries in an RV while driving down the road if your camper has a "round" 7 or 9 pin connector. These include a heavy positive and negative wire on two of the pins for this purpose. However, you most likely have one of the small flat type cables that only provides brake light and turn signal control which is about all they put on smaller RV's and trailers.

No matter what type system you end up with, if you try to connect two separate batteries together where one could be heavily discharged and one is fully charged you can get some major current flow from the higher charged battery to the lower charged battery and could even melt the wire. Inter-connected batteries should remain at the same charge levels in relation to each other. I strongly suggest that you review the discussion in the reference article where I talk about using a battery "isolator" which is made for this type application. There are two types. You can get a model that will charge two separate batteries from a single alternator (or solar array) , but will not drain down the reserve or RV battery when trying to start the truck. You can also get a model that will let you completely drain down the RV battery without draining the truck battery and leave you stranded.

Why don't you renew your subscription?

Good luck,

Jeff Yago


Hybrid autos

Jeff:

Spotted your article about using hybrid autos. I'd say your rather ignorant about cars. You said nothing about electrics. Now if you mention poor range then you really ignorant! Mine gets 200 miles per charge!!

It's all about political money!!!!

Sincerely,

Tom Grosch

Tom:

That is an amazing gift you have of instantly knowing another person is ignorant without knowing anything about them or their background. Just for the record, I owned two all-electric battery vans from 1987 until 1996 and drove one in the city whenever I was going someplace less than 10 miles away - it got lousy mileage and believe me I am very familiar with that feeling in your stomach when the battery gauge is reading empty and you are 20 miles from nowhere. (the second electric van was for parts to keep the first one operating)

I also spent a year as an intern during my engineering education back in 1968 working for a company that was designing and track testing both early development of battery powered cars - no doubt this was years before you were even born. You may be correct that I am ignorant, but that just goes to show you I really fooled the schools that awarded me engineering degrees, the patent office that has awarded me six US patents for my electrical engineering designs, and the National Association of Professional Engineers that awarded me their "Order of the Engineer", their highest recognition given for a lifetime achievement of engineering profession excellence.

Maybe when every parking meter in every town has a plug-in jack to re-charge everyone's all electric vehicles then the outlook for all-battery powered vehicles will change. But until then, I stand by my article's assessment of this current market. Now please excuse me as I need to go pick up my political payoff check ......

Jeff Yago


Solar powered golf cart

Jeff:

Can you guide me through retro-fitting a golf cart with solar panels on the roof instead of plugging it in at night?

Thanks. CC

CC:

First you need to know what the total battery system voltage is. Older golf carts had six golf cart batteries at 6 volts each, for a total system voltage of 36 volts. (system will actually measure higher when fully charged).

Newer golf carts have switched to using six batteries at 8-volts each (4 fill caps on top instead of 3) for a total system voltage of 48 volts (will measure higher when fully charged).

Next, you will need to buy a solar charge controller rated for this system voltage and array current. The array current is the maximum amps the solar module or modules are rated for at short circuit, plus 25%. I like to use a power-point tracker design charge controller. They are more expensive, but will put more charge into a battery, especially during lower sun angles (your module not facing directly towards sun) and other low solar conditions.

You will need a DC rated fuse between the positive battery system connection and this charge controller to protect this new wiring from a system short. All solar charge controllers have clearly labeled terminals indicating which ones are for the battery and which ones are for the array. Each set will have a positive and a negative wire.

Finally, you will need to mount the solar module(s). Most golf carts have a light duty sun roof. If you are mounting the modules on the cart roof, mount it flat. This is not the best mounting angle if you live in a northern state and is really not good for winter months, but assuming you will only use the cart in the spring-summer-fall months, the flat mounting keeps it exposed to the sun no matter where you park.

If you are going to mount the solar modules on a garage roof or pole structure, you can direct the modules south to south-west with a tilt in the 30 to 45 degree range (lower for southern states, higher for northern states.) You will want to provide some type of quick dis-connect battery plug and short cable so you can "plug" the cart into the solar array when parked nearby. You will not need to dis-connect the regular battery charger wires since the charge controller will not allow any charger electric flow to "backup" into the solar system wiring.

You should have a minimum of 75 watts of solar module capacity for this size battery bank or you will never get the batteries fully charged unless the cart is parked for several days between light usage.

Most solar modules under 125 watts in size will be rated for a nominal 12 volt battery charging. Most larger solar modules will be rated for nominal 24 volt battery charging. This means you will need three (3) solar modules rated at 12 volts each to charge a 36 volt golf cart, or four (4) to charge a 48 volt golf cart. If each module is rated for 40 watts, you would have a 120 watt array (3 x 40 watt)at 36 volts, or a 160 watt array (4 X 40 watts) for a 48 volt array. In both cases, all modules are wired in series (positive to negative to positive to negative .... from first battery to last battery.

If you meter the solar array when completed, the 36 volt array will actually measure from 51 to 62 volts if not connected to a load. The 48 volt array will actually measure 68 to 84 volts when not connected to a load. Do not panic! All solar modules produce a higher voltage than their nominal battery voltage rating since there would be no charging voltage flow unless the charging source is at a higher voltage than the battery. The solar charge controller is designed for these higher array voltages.

Hope this helps and good luck,

Jeff Yago


Car alternator

Hi Jeff,

I have a 1987 vw fox I converted to electric, using a Jack & Heintz G29 aircraft starter/generator.

I am using a series controller(alltrax 7245) traction pack is 72 volts dc

I am wanting to make a homade alternator to quick charge or to help charge the batteries by using an auto alternator with an output of 180 amps but I need to have 72 volts dc coming out of it also and not just 14.8 volts

I will run the alternator off of a 3 hp propane engine that will sit in a cargo hauler (hitch mounted) then wired to the batteries.

How can I increase the voltage of the 180 amp alternator to supply 72 volts or even 75 volts dc?

I have seen some adj. regulators but have only gone up to 24 volts I was told there was a way but forgot how and where found that info last year.

Best Regards,

Craig Smith

Craig:

You can't beat those aircraft starter motors as they were really built for heavy duty use, and as you found out, they work just as good as a generator as they do a motor. It sounds like you have a good system for the VW, but sorry to say there is no easy way to convert an alternator from low voltage DC to a much higher voltage DC. Yes, they make electronic DC to DC converters, but these are usually only for small loads like a 12 volt DC electronic device you are trying to power from a 48 volt DC battery, and they are not cheap.

The only suggestion I have is to look for a small DC motor/generator that is in the 80 to 96 volt range and drive this with your gas engine. This would be a common voltage, but most likely it will be too heavy for a lugging around in the back of the VW.

Good luck,

Jeff Yago


Deep well pump

Hello Jeff,

I have a deep well--about 600 ft plus and it's hooked up to an electric pump--whenever the power goes out--no water. I've been searching for a way to install a manual pump ( I know that it's too deep to draw from that depth by hand and that I would probly need a pump of some sort). I don't know who to go to for this information or who might install these kinds of things. I wouldn't mind solar or even a small generator to run the pump but I don't know how to get started--I'm just one woman and the well is capped.

Thanks,

Liesa O Penrod

Liesa:

As you stated, thats a really deep well, and its very hard to do this much lift in a single pipe rise. I'm not even sure what kind of pump you have that could do this unless its either a very large motor or a very slow fill rate. As for pumping without power, sounds like you need a very very long rope and a well bucket!

Actually I suggest you check with Dankoff pumps at http://www.dankoff.com/

They make some very special pumps that operate on battery, solar, or back-up power and have many different models. I am sure they will have a pump that meets your needs and they are very good to work with.

If you want to power from a generator, check the sive of the circuit breaker supplying the well pump and this may give you some idea of the generator size you will need. I am sure its a 2-pole breaker (240 volt) and I am guessing its at least a 30 amp service, based on the well depth. If you want to keep the same well pump, you will need to add a transfer switch for this circuit and supply from a generator.

Good luck,

Jeff Yago


More modules or change inverter?

Hi Jeff,

I have 12 Kyocera 170 watt solar modules hooked to an Outback MX 60 (I think) charge controller and Xantrex SW 2024. I will eventually (I only have 4 batteries now - a temporary setup) have 24 6 volt golf cart batteries (225 amp hours) hooked to this.I figure I get about 257 kWh a month out of this (if my math is right.)

I want a little more, like maybe 310 kWh per month. Someone suggested that instead of buying more modules and another charge controller I should sell my Xantrex and get an 3,000 watt Outback 48 volt inverter. The inverter plus the "mate" would cost maybe $1,300 out of pocket after the sale of the Xantrex. Maybe. I was told the Outback 48 v is about 20% more efficient, so I could use the 12 modules and charger I have now and get a nice power boost, probably close enough to what I want to satisfy me. Plus, the Outback inverter would be pure sine wave not modified so the quality of power would be better - no appliance burps.

This seems reasonable to me, but I'm a pure novice at this. Financially, would it make sense? My present setup is wired in a series of 3 so I'd need to buy 3 modules which alone would run about 2,100 dollars, and then another $500 or so for another charge controller.

If I did the Outback inverter, would I have to rewire the modules to the charge controller, as well as the inverter and battery bank wires?

Thank you for your opinion.

Kate

Kate:

Sounds like you have a good start, but are receiving some advice I don't agree with (so what's new?). Anyway, all of todays name-brand inverters are fairly efficient. Yes, a few percentage points make a big difference if you are talking about a very large solar array, but it will not be enough alone to be the reason for a change. However, I am not sure you have provided the correct information. Trace Engineering (Xantrex) never made a 2kw version of their SW series that I am aware of. Their inverter line started as the modified sinewave inverter models 2512 and 2524. Their first sinewave inverters were 4kW and later added a smaller 2.5 and 3.0 kW kW grid-tie model, but no 2 kW model that I know of.

If you compare the efficiency of the Outback sinewave inverters and the same capacity Xantrex sinewave inverters, they are both about 94%. The Xantrex SW2512 and SW2612 were still rated at 90% efficient. Even the original non-sinewave Trace 2500 series inverters had an efficiency ratings above 85%. There has been some major efficiency issues between these brands related to grid-tie when selling back to the grid, but not in battery-inverter modes.

One of the best efficiency improvements you could make in an existing solar power system was changing from the older fixed charge controllers to the new power-point tracking style which was a real improvement in annual energy conversion, although these do not add much if you only compare summer operation. But you indicated you already have an Outback MX-60 charge controller which is about as good as it gets right now.

Here is Jeff Yago's solar design rule #1 - You never have enough solar modules.

Yes, you do not want to waste the solar energy you collect on a system with poor efficiency, but you would need to gain at least 10% to equal the gains of adding just one solar module.

Here is Jeff Yago's design rule #2 - Even new battery banks are not efficient and usually are never re-charged correctly causing premature failure.

So if you can use the solar at the time its actually being collected, this is more efficient. Your solar array will very rarely, if at all, ever actually produce its nameplate output rating, and 75% of this nameplate rating will be closer to your actual system performance. Added to this solar output reduction, charging a battery with a solar array looses about 15 to 20% in heat and chemical conversion losses. Then when you actually use this stored energy, you loose another 10% or more in converting this stored chemical energy back into AC electricity. The inverter losses you are worried about are only a small part of these total system losses. Adding to this is the poor efficiency of most appliances and lighting that will be consuming this energy and you really see the problem.

So even with the best inverter, the best battery, the best charge controller, the most efficient appliances, and the best battery charging procedures, there are just going to be system losses you must live with. So if you really need more solar power out of your system, you need to put more into it - go back and read my Rule #1.

Good luck,

Jeff Yago



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