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Solar Sizing for a Water System  RSS feed

 
Sherry Bagley
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We will be moving off-grid very soon and I feel like I keep reinventing the wheel. I know lots of people are off-grid so it seems like much of this stuff should be SOP (Standard Operating Procedure). Here's my latest confusion, and let me warn you that I am a real newbie at all things electrical. I am working out our water system. It is rainwater to a 1st Flush diverter to the holding tank, then through a SHURFlo strainer, a Flojet 12-volt water pump, and a SHURflo pre-pressurized accumulator tank. From there cold water lines feed directly to the faucets with potable water running through a Big Berkey. I would like to use an electric tankless water heater on the hot water lines to avoid propane and I'm looking at a Ks-94 that is rated at 12 KW @ 240v. We are very frugal with our hot water usage, so I would estimate 10-15 minutes a day for the shower and maybe another 10-15 minutes for general hand and body washing. I have heated water for dishes before and that is definitely do-able during the winter with the wood stove, but having hot water from the tap for dishes is a true pleasure in the summer.

Can someone help me with the math to figure out A) if this system would work, and B) how much solar I would need. Oh and the area we are moving to averages 5.5 hours a day sun and I realize I will probably have to supplement the power with a generator in the winter.

Thanks
 
Topher Belknap
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Location: Midcoast Maine (zone 5b)
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Instant hot water with a 12,000 Watt draw is going to make your batteries VERY unhappy. That is just an enormous current. Better would be a tanked system with a lower power draw over a long er period of time. Best would probably be a solar hot water system with a heat pump backup. IMHO, of course. Some combination would also work.

Thank You Kindly,
Topher
 
allen lumley
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Sherry Bagley : Think on it this way, a hundred watt light bulb uses 100 watts in one hour of constant use, (Ten) 100 watt light bulbs burning constantly for 1 hour
is one Thousand watts in one hour, a kilowatt/hr, and you had hoped to use an instant on tankless hot water system with 12 Xs the draw, Properly planed for, you
can have a very small microwave that you always unplug after use and plug in just before using ! Always with one Eye on the meter prominently mounted in your
kitchen to monitor the health of your Batteries !

Go to a camping store to buy a toaster rack that fits on top of a cooking range or a single gas burner, Elect toasters and Electric coffee/hot Tea are not worth the
power draw ! This is actually the start of your personal re-education program, In many ways, you will come to view Propane and its ease of use to be a friend to
be budgeted for and not your enemy ! For the Craft ! Big AL
 
Sherry Bagley
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Thank you Topher and Allen. Every bit of advice is greatly appreciated. You are both telling me what I knew to be true but kept thinking I must be doing the math wrong. That 12Kw water heater is a killer. Got it. I went back to the drawing board again and found the Reliance 6 6 SOMS K 6 Gallon Compact Electric water heater which uses 1650 watts on 110v for 14 amps. That sounds a lot better! I was bothered by a tank system that would constantly draw energy to maintain the temp for maybe 30 minutes total use time per day, but then I saw a review by some genius who installed it on a switch and would just let it preheat for 15 mins or so before using it and then shut it off after. Perfect!

So now I need to figure the panels and batteries to power the 12 v, 5 amp pump for about 45 mins/day and the 1650 watt heater for about 30 mins/day. I do intend to run a red neck solar water heater using coiled black hose in the loop, but I want to calculate my needs based on worst case scenario where the weather (zone 6) doesn't support the direct solar water. For extended cloudy periods I will also be able to use the generator to charge the batteries if necessary.

I know propane very well. I have lived in a conventional on-grid house for 30 years with propane for heat, water and stove. After the price per gallon tripled last winter, I can tell you that propane may end up being a necessary evil if I can't find another way, but it is no friend of mine.

As far as sizing the entire solar needs, I am focusing on supplying the mechanicals first and will add the small amount needed for personal luxuries after that. We don't use a microwave, hair dryer, or drip coffee maker. We very rarely even have lights on in the house. We do have the tv on for 2-3 hours in the evenings. Our tv right now uses 170 watts/hr and uses an old school antenna (so no energy for a satellite). We also run 2 pc's, 2 monitors, and an internet modem 24/7 right now. BUT that's on-grid convenience. That usage and probably some of the components will be much improved on when we're actually off-grid. Until we get moved and see what is actually available, I don't even know if we'll be able to get digital signals for a tv antenna or what kind of internet we'll end up with (maybe none for awhile). We'll be cooking on a rocket stove and charcoal grill outdoors while the weather holds and a wood stove indoors during the winter (which is also our heat source). I also have a two burner propane (ugh!) camp stove that I can use if necessary (mostly when I'm canning). We already use battery clocks and alarm clocks, a manual clothes agitator and clothes line, and an old fashioned percolator for coffee and hot water for tea. My granny flip cell phone only needs charged about once a week and I have adapters to charge it and my Kindle in the car while I'm driving.

I'll be the first to admit I REALLY don't know it all (or even a little bit!), but I'm also not totally unprepared for the transition. I just really get hung up on the calculations relating solar energy generated and stored to projected usage.

Thanks again,
Sherry
 
allen lumley
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Location: Northern New York Zone4-5 the OUTER 'RONDACs percip 36''
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Sherry Bagley : I certainly understand doing the math several times and getting an answer I didn't like ! Sometimes just having a second person to bounce things
off of is a big help ! That too is a good reason to come to Permies.com, and as a member you can come here 24 /7 and expect to talk to someone who wants
to talk about what you want to talk about !

Two Things, and I will wait until you have another question you think we can help you on !

You should always have a list of projects to do when your batteries are full and you still have any solar gain ! Could you to goto our sister site Richsoil.com and
scroll down to and clickon Electric heaters, and take just a few minutes to review the difference between on the grid living and off grid frugal living !

Finally, back to that nasty old propane, if you are going to be living off of the grid and be dependent on a generator for back-up you should L@@K into A Gasoline to
propane conversion for your Generator, The propane burns much cleaner, and while the propane has fewer units of energy stored in it for an equal amount of Gasoline,
it also runs much cooler with less energy wasted as heat than gasoline, much less wear on your system, and no problems of water in gasoline like you get with E-85
Gasoline. If you go months without using the generator and that is the goal you are working towards-> Then a conversion may only pay as a safety factor ! Big AL

 
Topher Belknap
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Location: Midcoast Maine (zone 5b)
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If you are going to do the math for yourself, and I commend you for that remember:

Watts, Kilowatts, horsepower, BTUs/hour, are measures of power. That is energy per unit time. A rate of energy consumption (or production).

Watt-hours, kiloWatt-hours (not kiloWatts/hour; the dash mean multiply), BTUs, Gallons of Oil, etc. are measures of energy.

This is very hard to get straight in one's head, I know well! But it is the only way to avoid massive confusion.

Thank You Kindly,
Topher
 
Topher Belknap
Posts: 205
Location: Midcoast Maine (zone 5b)
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Sherry Bagley wrote: I was bothered by a tank system that would constantly draw energy to maintain the temp for maybe 30 minutes total use time per day, but then I saw a review by some genius who installed it on a switch and would just let it preheat for 15 mins or so before using it and then shut it off after. Perfect!


Do the math there as well. As an example: A thirty-gallon tank at 50°F brought up to 120°F, will require 17,493 BTUs. (30 gallons * 8.33 pounds / gallon * (120 - 50) * 1 BTU / Pound * Degree). 17,493 BTUs / (3413 BTUs / kWh) = 5.12 kWh (plus some losses, of course). Note that decent tank hot water heaters will maintain temperature with only small losses, it is a worth lowering if you can, but look at the wattage rating on that timer....

We don't use a microwave


Microwaves are really efficient ways of heating water with electricity. You might want to consider one.

We already use battery clocks and alarm clocks


I grew to hate batteries, single use ones are frankly evil, rechargables are an improvement, but charging them on PV power is massively inefficient or a pain in the neck. All my clocks now wind up. Turn a key for a minute once a week, and I'm done. If that doesn't work for you, get a 12v clock and use PV battery directly.

Thank You Kindly,
Topher
 
wayne fajkus
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I got rid of my alarm clock and calculator years ago. My phone replaced them
 
Rebecca Norman
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Sherry,
It doesn't make any sense at all to heat water with solar electricity. It will take much smaller collector area to heat water with the sun's light and heat directly, than to turn the sun's radiation into electricity and then turn that electricity into heat. Actually not a "much" smaller collector area, but a MUUUUCCCCHHH smaller collector area.

You are confusing some extremely different levels of power usage. You can run your phone, laptops, and led lights 24 hours a day without turning them off, and it will still use only a fraction of a 15 minute electric-heated shower.

led light bulb (equivalent light to about 60W incandescent in my experience): 2W. So 4W over your desk or 10W for a whole room.
Charging a laptop: 25 to 60W
Charging a phone: 5 to 10W
Any appliance that creates heat, such as a toaster, hair dryer, or water heater: minimum 1000W, more likely over 2000W, or you originally mentioned an instant model at 12,000W(!)

That one water heater draws as much power as 6000 LED bulbs or 200 big fat laptops.

When you design for off-grid living, the first thing you do is find all the ways you need to generate heat, and make sure that you are not doing them by electricity, but by any other means. Then you can size your PV system small, and still use your phones, computers and lights to your heart's content. For hot water, install a solar water heating system that uses the sun's light and heat directly. Much cheaper, and much smaller solar collector area.

Same with heating water with a generator in the winter. You'd burn less fuel if you simply used a fuel-burning water heater of any type. Why convert chemical energy > heat > electricity > heat instead of converting chemical energy > heat directly?

Every time you convert energy from one form to another, some energy is lost; or conversely we speak of the efficiency of the process. If you want heat from the sun, use it directly instead of turning it into electricity and then back into heat.

I say this not only from facts and numbers, but this is the system I live on. We've got 50 teenagers living in a sprawling campus: we leave the corridor and outside lights on all night, the kids often leave their lights on all day by mistake or habit, a dozen mobile phones, a computer classroom with small laptops, a decent sized flat TV. When the sun is shining and the batteries are charged, we use a blender, laser printer, clothes washer or power tools. We do all this with under 4kW of solar panels because our house heating, water heating and cooking are all done with other sources of heat. Our PV panels could supply one third of your 12kW instant water heater, at noon on the best sunny day.

Another way of putting it: 150 of us using LED lights, laptops and phones with abandon = your 12 kW water heater.

Meanwhile, a solar water heater with a solar collector area equal to about 1kW of PV will give you enough hot water for a small family to wash dishes freely and take judicious showers as you plan to do. Of course it will have an insulated storage tank so you canhave hot showers in the early morning.

 
allen lumley
pollinator
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Location: Northern New York Zone4-5 the OUTER 'RONDACs percip 36''
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Rebecca Norman : Your point on using the available solar energy to heat water directly is very well taken, even if we needed to use an additional energy source to
Boost water temps, nearly direct conversion of light energy photons will beat the use of Electrical panels to make electricity and then use the electricity with losses
of useful energy to inefficiencies more than doubled by converting, storing, and re-converting the energies available to do other work

I belong to a group that bids on odd-lots of used solar panels now being replaced as part of preventative maintenance programs, the panels are retested/calibrated
by a 3rd party,providing a new number for the panels current efficiencies, and the panels are sold based on current/expected performance, caveate emptor, often
a large panel is simply used as a trickle charger for an Electric Fence, or other back up battery unit, excess power is often dumped into resistance wiring/a light bulb!

I want to take this time and space to re-state, -often in the middle of the day your batteries are at say 80% of charge and need to have the rate of charge slowed
way down to the increase the longevity of the batteries and curtail the need for frequent re-watering of your Batteries !

This is the exact point that it pays to have a list of jobs that are best done by using Electrical energy! That point may be close to 14 vts with a new set of well charged
and/or maintained batteries and may even dip into the 10 vt range for old, tired batteries, perhaps the few ergs of energy available at that time could light ether an
incandescent, -Light and useful Heat, or just an LED or the LEDS rechargeable batteries, to allow you to do a visual inspection of the batteries water levels and battery
cable condition ! Turning on (and off ) a low watt appliance is Not the same thing as accepting yesterdays constant vampire energy losses.

Stated another way, many newer appliances need not use any standby power, especially if not plugged in, and use much less energy to do their job now! Energy Xs
time determines watts, ether cut down on energy use, cut down on time or use the surplus as available ! For the good of the Crafts ! Big AL
 
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