Ask Jeff Yago
Solar & Energy-Related Issues
By Jeffrey Yago, P.E., CEM
Inverter Source Question
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
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, thats 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,
Well pump advice
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!
Old Solar panels
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!
Pump volume for in-floor heat
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 as 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.
You 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.
Just a suggestion,
Golf cart generator/starter
I have been researching DC motors to produce 12v @ 20+ amps at about 800 rpm. I see these golf cart generator/starter motors might work.
What do you know about these motors? Can they produce 20-25 amps 12v DC power and at what rpm's. My application is to produce power from a turning engine 1-1/4" shaft on a sailboat when sailing. I can produce about 800-900 rpm's using a 6:1 pulley ratio shaft to motor at 6-7 knots.
Sounds like you are trying to re-invent the wheel. Several companies make an off-the-shelf water turbine that is self-contained and you just drop in a fast moving stream or pull behind a boat to generate electricity.
Since the internal generator and propeller drive are designed to rotate at the correct RPM for the typical speed through the water you are talking about, you do not need pulleys, belts, or drives, and all battery charging controls are built-in. These units are light weight, small, and specifically designed this application.
Check with any of the solar suppliers that advertise in the magazine.
Alternative Energy Education
I've been reading Backwoods Home for a while now, and I really dig the information and ideas you guys have for alternative energy. I've seen solar energy put to use in war machines over the last few years, and when I'm out of the Army, I'd like to help put alternative energy to some GOOD use.
Where and how does one go about getting himself into the alternative energy industry? What college degree should one pursue? What schools (preferably in Colorado / online) have useful programs?
I've got alot of college cash waiting to be put to good use. I'd sure like to spend it on something besides operating MIL-SPEC spacecraft and fighting wars for non-Libertarian candidates. I've done both for my entire adult life, and it's not all it's cracked up to be.
Thanks for your time,
You are really in luck. Colorado is almost the center of solar research in the US, and has a very strong educational program in solar power. The Solar Energy Research Institiute is world known and is located right in Golden Calorado. The state also has a very strong non-profit solar educational group with extensive information and resources you can access here:
Good luck and thanks for your service,
Cabin in the woods
We have a cabin in the woods that we would like to retire to. However we have been informed that we cannot get easements to run electricity to it. I would like to set somrthing up using a propane generator and batteries but don't know where to start. Right now we have a gas generator, propane lights, and some DC lights using a deep cycle marine battery.
You are not the first person to ask me this, and I have many articles in the back issues of Backwoods Home Magazine that describe how to do it. Check the back issues section and the past questions section of the Home Energy page where I have addresed this.
I have been emailing the Government of Ontario, Ontario Hydro, and manufacturer's / suppliers of grid tie equipment to get a list of hybrid inverters that would meet the hook-up criteria and be able to act as a backup power supply in the event of the grid going down since net metering has become available here in Ontario. To date the government has sent me a list of grid dependent inverters [as] they don't have a list of hybrids. Ontario hydro has referred me to the governments list and I haven't had a reply from a manufacturer/supplier that gives the info, they seem to want me to commit to buy from them before they will tell me makes models and prices. This has made the proces of costing very frustrating.
I understand there may be more than the inverter involved, eg a grid sensing automatic cutoff switch to isolate the house so that a poor lineman doesn't get zapped.
Can you help or direct me to where the specific equipment is listed and priced.
I am not sure what you mean by a "hybrid" inverter, and I doubt you will ever get an up-to-date list of anything from your government or mine.
Basically, we refer to two inverter types - grid-tie and battery based. A grid-tie inverter has no battery bank and cannot provide any back-up power when the grid fails as it is using the utility grid as its "battery".
A battery based inverter uses a 12, 24, or 48 volt DC battery bank to produce 120 volt AC electrical power, although some models now produce 120/240 VAC output without "stacking" (using two inverters together).
Almost all residential-size battery-based inverters include a battery charger feature that can charge the battery bank any time there is an active utility grid connection. The battery bank can also be charged by a separate solar array, wind turbine, water turbine, or separate battery charger powered from a generator.
The rub comes when you want to use a battery based inverter to "sell" power back to the utility grid. Some inverters have passed very strict testing to obtain the right to do this and some inverters either cannot provide this "sell" function, or have not been approved for legally doing this. There are several major tests any inverter must pass in order be UL1741 and IEEE 929 listed, and these codes will be indicated on the equipment nameplate.
The first test is to verify the inverter will shut off its "sell" output back to the utility grid if the grid fails. As you stated, this is to protect any linemen working on a downed power line nearby. The second big test is called "anti-islanding" and this is to make sure your inverter cannot be "fooled" by your neighbor's inverter also connected to the same power line into thinking the grid is still active and continuing to operate when the utility grid is actually down. There are other tests including waveform, harmonics, voltage regulation, and power factor, but having both codes listed on the nameplate should guarantee to any local inspector that this inverter is "approved" to sell power back to the grid.
There are actually several inverters that are battery based, that can provide emergency power, and are also listed to sell power back to the grid. These include:
- Outback #GTFX2524 - 2500 watt @ 24 VDC (sealed) 120 VAC output
- Outback #GTFX3048 - 3000 watt @ 48 VDC (sealed) 120 VAC output
- Outback #GVFX3524 - 3500 watt @ 24 VDC (vented) 120 VAC output
- Outback #GVFX3648 - 3600 watt @ 48 VDC (vented) 120 VAC output
- Xantrex #SW4024 - 4000 watt @ 24 VDC (must have GTI option added) 120 VAC output
- Xantrex #SW4048 - 4000 watt @ 48 VDC (must have GTI option added) 120 VAC output
- Xantrex #SW5548 - 5500 watt @ 48 VDC (must have GTI option added) 120 VAC output
- Xantrex #XW4024 - 4000 watt @ 24 VDC provides dual 120/240 VAC output
- Xantrex #XW4548 - 4500 watt @ 48 VDC provides dual 120/240 VAC output
- Xantrex #XW6048 - 6000 watt @ 48 VDC provides dual 120/240 VAC output
- SMA "Sunny Island" #SI4248U - 4200 watts @ 48 VDC (must be used with separate "Sunny Boy" grid-tie inverter)
- Beacon Power M4 Plus - 4000 watts @ 48 VDC
- Beacon Power M5 Plus - 5000 watts @ 48 VDC
Note - Many of the above US inverters are also available with 230 VAC @ 50 cycle output for export.
I may have left out one or two other brands, but these are the most common residential size inverters out there.
I have 2-80 watt & 2-120 watt modules 200 feet from C-40 controller. I am connecting them in series to get 86VDC to controller (max 125VDC). At the controller I want to add another module (175watt @ 43VOC). The system voltage is 24VDC.
What voltage can I expect at the controller?
Is this OK?
What can you expect from the controller - how about smoke?
The C-40 controller is not intended to be connected to a solar array that has a different voltage from the battery bank. The reason for the high 125 VDC nameplate limit on the input voltage for this controller is to protect the controller during no load and low temperature operation when any solar module will have an open circuit voltage that is much higher than its normal operating output voltage.
Think of it this way - this is a pulse-width design controller which means it is just acting as an on-off switch to turn on and off the flow of electricity from the solar array to the battery. Depending on how charged or dis-charged the battery is, the controller will cycle this switch to the "on" or "off" position for different lengths of time (pulse-width), but its just acting as a switch and does not "convert" the higher voltage from a solar array into a lower battery voltage. Putting this high voltage into the low voltage battery is not good and could either over-heat or dry out the battery bank.
You have two options:
1. Purchase a maximum Power Point Tracking (MPPT) solar charge controller which does adjust battery charging voltage and will allow connecting a higher voltage solar array to a lower voltage battery. It will check the voltage input of the mis-matched modules and adjust the output current and voltage to the correct levels.
2. Buy a second C-40 controller and put each solar module group on its on controller, connected to the same battery bank. They will work together.
Good luck, and buy a fire extinguisher.
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