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Archive for July, 2008
Thursday, July 31st, 2008
I want to use a 12 volt circulating pump or pumps to move the hot water through the slab at our off grid cabin.
We will use a LP fired 40 gallon hot water heater set at 90 degrees. From what I know, I have plenty of power from my solar generator, since many of the 12 volt pumps use very little energy.
My question is how many pumps do I need and how much volume do I need to move through the floor? Is it better to move the water through the floor faster or slower to insure all of the heat has been removed from the water?
We have 850 feet of 1/2 inch tubing, divided into 3 loops. The slab has 2 inches of high density foam stood on edge around the perimeter and 4 inches of foam beneath the 4 inch slab. Thank you
You have two problems. First, pump sizing and pump flow rates must be calculated for the specific application, and it varies depending on the flow rate, water temperature, floor thickness, spacing between each heat pipe in the floor, pressure drop of the pipe being used, and if you will have any additives like antifreeze. In other words, check with the supplier of the tubing as most provide easy sizing tables that will help you determine the pressure drop and pumping head. I will suggest that many of the systems we have been involved with had pumps between 1/20 and 1/12 HP for most applications. Keep in mind an AC water pump will not have brushes inside and a DC water pump will have carbon brushes that will need to be replaced about every 2 years. Most people now use AC pumps and an inverter.
Your larger problem is the water temperature and water heater. Many are designed to heat cold ground water entering around 50 to 60 degrees and always have cold water entering at the bottom and the hot water out the top of the tank. Some tank water heaters and almost all instant type hot water heaters will fail if piped into a re-circulating hot water loop as the return water temperature stays above 90 degrees. Again, you need to check with a supplier in your area who supplies radiant heating equipment before making a mistake you cannot fix without a jack hammer.
Radiant floor heating systems are my favorite type of heating as it is simple in operation. However, like most things that look simple in operation, they require far more design effort than may appear.
Wednesday, July 30th, 2008
Our house has been running on the grid for about five years since our batteries finally expired after 10 yrs and we couldn’t afford replacements.We are buying new batteries soon and getting the system up again.
I had an electrician come in to look at things and he mentioned that I should check to see if the panels were still working. With the inverter on (batteries not yet installed) they were putting out the expected voltage in full sun. The electrician mentioned said that without being able to place a load, he couldn’t say if the panels would produce the amps needed and that expected voltage readings didn’t mean the amps were “good”.
I have 8 Solarex panels, a Trace SW4024, APT powercenter 5 and 12 Trojan T-105′s, a 24V system. The house runs fully AC through the inverter. These panels are 15 yrs old.
Do you understand his statement and if so, how can I check to see if the panels are putting out.
Your electrician is half right. Yes, the voltage of a solar array is fairly constant regardless of load and is mostly affected by ambient temperature. If you put a volt meter on the output leads they could read almost normal even if the modules are in bad shape. However, solar modules this old are just getting started and should last 30 or more years unless the glass or backing breaks down and allows moisture to reach the tiny foil connections between the glass and the backing.
Please note, I do NOT recommend the following for any high voltage solar array unless you really know what you are doing and are wearing all kinds of safety equipment. However, a low voltage array (12 to 48 volts DC) will not be damaged if you shorted the positive and negative leads together while in full sun, although you can get some amazing arcs when you later pull the connected wires apart. Have the electrician read the current passing through this wire loop and this current should be above 80% of the nameplate short circuit current, depending on how much sun and how clear the sky that day. The short circuit rating is printed on the label on the back of the modules. Tell your electrician that he must use an amp probe and amp meter that will read DC current, as a standard AC amp meter will not work.
When the 1993 National Electric Code first came out and proposed having a DC ground fault breaker on the solar array output, most were designed to short the positive and negative leads of the array together during a ground fault condition. Needless to say, this made for very lively solar charge controllers during a fault condition and many looked like toasters with glowing parts inside. This requirement was later changed and now allows just tripping a circuit breaker.
Bottom line, if the solar array was working right up until the batteries failed, most likely they are fine, and will not be damaged regardless of having the output wires not connected to anything, or shorted together all this time.
Don’t worry, be happy!
Tuesday, July 29th, 2008
We have been farming organically for 32 years. We would appreciate advice on digging and hooking up a hand pumped water well for use when electricity fails.
You have 4 ways to go with this:
1. If your area has a high water table (do not need to drill deep to hit water) and the ground is not hard solid rock, you can buy a well point kit. This kit includes a hard steel pointed end with screened side openings that you attach to galvanized steel pipe you buy locally in threaded 10 foot long sections. It also includes a metal cap that screws on the top end that you strike with a sledge hammer and drive into the ground by hand. As you drive each 10 foot long section into the ground, you stop, unscrew the striking cap, and add another section of pipe. Then back on the step-ladder and start again until you reach the right depth. These kits also include a hand powered pitcher pump (like your grand-father used!) which is attached last. source – www.solar.realgoods.com or www.backwoodssolar.com
2. If that is too much work, they also make a hand powered pump kit that you locate at your existing well and attach to the existing piping coming from the well pump below. This hand pump can be used during a power outage to “suck” water from the existing well piping and send it to your house using the same piping. However, it is not intended for high flow rates or wells deeper than about 200 feet. (about $650) source – www.solar.realgoods.com or www.backwoodssolar.com
3.You can also install an inverter with battery back-up and wire to a separate circuit breaker panel. Re-route your power wiring going to the well pump, your refrigerator, and several lighting circuits to this new panel and let the batteries power these loads during a power outage.
4. Purchase a generator and a can of gas!
Monday, July 28th, 2008
If you were going to buy a stove to put in your basement for heat (and cooking) in the event of a blizzard or national emergency what would you buy for your home?
Fort Pierre, SD
Great question. I have designed several totally off grid homes in the extreme north including northern Idaho and believe me, that’s rural! We designed propane fired hot water boiler systems for all of these. These boilers are very efficient, are smaller than a 2-drawer file cabinet, and are self-contained with all controls. They also only require a very small fractional HP circulating pump to move the heating hot water through all the baseboard radiators in each room. We also have used the same type boilers with radiant floor heat which is really efficient. You will however, need a small backup power inverter or small generator to power the pump and temperature controls.
If this is not what you want, there are some great non-electric wood stoves, and provide both space heat and a cook top. Some can connected to your existing ducted air system and some are hydronic and can be piped into your baseboard hot water heating system, but this would require electric power to operate any pumps or fans. Our solar home has a central hydronic wood stove that can heat the entire home if I don’t want to run the propane hot water boiler, and we have a separate wood cook stove in the kitchen/dining area that we use on cold winter days that really puts out the heat with very little firewood. It looks like it was made in 1860, but actually there are now several manufacturers making new stoves that look like the old wood stove of the turn of the century.
I advise clients to install an in ground propane tank that is 500 to 1000 gallons in size, as this gives you months of space heating, domestic hot water, and cooking if the power goes out and the weather is too bad to re-fill a smaller tank. The short answer is, you need 2 stoves – a propane boiler or cook stove and a wood stove for heating and/or cooking.
Good Luck and let us know how this works out for you,
Sunday, July 27th, 2008
I have a client in Canada looking for a 1100 to 1500 watt solar inverter (24 V?) with 220 VAC output and it must be made in the USA or Canada?
Thanks for your time,
Both OutBack and Trace Engineering (Now Xantrex) inverters are very good quality and made in Washington State, USA.
StatPower also manufacturers inverters and they are located in Burnaby, BC, Canada. They were recently bought out by Xantrex, but are still located in Canada. Their pure sinewave “PROSINE” inverters are good quality for small applications, but I found their “Prowatt” modifined sine wave inverter to be fairly lightweight and un-forgiving when overloaded. I would also note that although this is a Canadian manufacturer, the inverters I have serviced made by them had internal circuit boards manufactured in China.
Outback, Trace, and Statpower all offer export versions of their inverters having a 50 cycle output if that is an issue for you. Most American inverters have a 120 volt AC output at 60 cycle, but all manufacturers offer an optional transformer that will convert 120 volts to 240 volt
Here is the link to Statpower in Canada – http://www.powerupco.com/inverters/statpower.php
Saturday, July 26th, 2008
I was hoping you can point me in a right direction :
Question#1 – I live in eastern Canada and am looking for material/reference /books or guidance from you on starting out with solar (ie) Solar panels – generator-battery and banks – hooking up ..consumption would be for approx 6 months a year including a small fridge, tv, radio and possibly 4 cf lights. (wood stove would most likely be my heat/cooking source since my place will only be approx 12×24 on beam posts )
Question #2 with question #1 in mind, I would like to adopt a system to add to the panels /batteries in the future for a permanent residence .
Thanks for you time Jeff .keep in mind when you read this, I have 0 experience in this field, so all the help I can get would greatly be appreciated.
The best advice I can give you is to go back and read the many articles I have published in Backwoods Home Magazine over the years on this exact same subject.
- Water – A safe supply when you are off the grid – Sept 2001 Issue #71
- A solar Primer – Nov 2001 Issue #72
- Battery Powered Weekend Retreat – Sept 2003 Issue #83
- Solar Power 101 – Batteries – May 2004 Issue #87
- Solar Power 101 – Batteries cont. – July 2004 Issue #88
- Solar Power 101 – Inverters – Sept 2004 Issue #89
- Solar Power 202 – Solar Arrays – Nov 2004 Issue #90
- Build your own solar powered water pump – Jan 2005 Issue #91
- Build a solar powered Outdoor light – Mar 2005 Issue #92
- The care and feeding of Solar Batteries – Sept 2005 Issue #95
- Walden Pond – The solar version – May 2006 Issue #99
- Walden Pond – the solar version, part 2 – July 2006 Issue #100
- Solar powered Refrigerators – Nov 2006 Issue #102
You can read many of these on the web site, but I suggest ordering the back issues on CD. They are low cost and include all of the graphics.
Friday, July 25th, 2008
I heard about a 30 amp solar collector that was built on a trailer. I thought by Independent Energy Systems. But I can’t find them and was wondering if you had any info. on portable solar collectors.
Not sure what you mean by a “30 amp solar collector”. This is not usually how we reference their capacity. If you are talking about a “30 watt” solar collector (we call them solar “modules” if the generate electricity, and solar “panels” if the make hot water), but a 30 watt solar module would be about 10″ X 36″ in size so it would not need a trailer. If you are talking about a 30 kW solar array, this would definitely require a semi-tractor trailer to move around as it would be over 90 feet long.
If your interest is trailer mounted solar power systems in general, check the next issue of Backwoods Home Magazine (#108) as I will have a 2-part article on how to build your own using a 6 ft X 12 ft enclosed utility trailer.
Thursday, July 24th, 2008
I was wondering why someone hasn’t come up with having an exercise bicycle set up in their house hooked up to generate electricity for the house.
Has that ever been tried before? Bike in the home for 2 hrs a day and live off the grid?
Like all good ideas, others have thought of it before us. Over the years there has been several different manufacturers of this product. Some are like a bike stand so you can use your own bike, and others are like exercise bikes with just one wheel.
The most recent entry is the “Human Power Trainer” at www.windstreampower.com