Alternative energy advice from Ask Jeff Yago. Volume #36

Ask Jeff Yago
Solar & Energy-Related Issues

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

Sorry. Jeff no longer answers questions online

String lights to light dark steps

Hi Jeff,

I am looking for solar string lights (like Christmas lights) to run down my deck steps to light the steps for safety. Right now the wired lighting leaves dangerous shadow areas. The challenge is that the steps are on the north so I will need 75 – 100 linear feet of lights to run from the south side along the deck rail then down the steps (my preference). OR I need 50 linear feet of plain wire between the solar collection to where the lights start then have them run 30′. Ideally the lights would need to be bright for 8 hours. What is your suggestion?

Eileen Obermiller


Not to talk you out of solar, but being on the North side of the house and all the other issues of running wires a long distance, why not just buy a string of white LED Christmas lights. If you check out a recent article I did on LED Christmas lights, you would see that I measued these as using only 2 watts of electricity for the entire string. That is less power that your cell phone charger uses.

Good luck,

Jeff Yago

Condo unit energy solution


We live in a condominium apartment and a good part of the year we receive a lot of wind. We also have several south facing windows and a deck with good exposure to the sun. With condominium rules and regulations, we’re not able to put solar panels on the roof. Is there a solution to energy independence when you live in a condominuim like this one?


Tanna Settle


Yes, been there, done that. My big concern would be reducing my electric loads and emergency power. When we lived a year in an apartment complex in the middle of a large city during the construction of our solar home, there were several power outages. Although this never affected us due to the emergency preparations listed below, we got a big laugh watching everyone bail out of the complex 5 minutes after the power went out and head for Mom’s house or a hotel. I still can’t believe how un-prepared most apartment and condo dwellers are.

First, reduce your energy usage. What difference does it make if you save 500 watts by reducing your electric loads by 500 watts, or keep the loads the same and install a 500 watt solar system – your bill still goes down the same amount, and you didn’t spend $5000 for a small solar system you aren’t allowed to install anyway.

Replace every light, and I mean every light, with compact fluorescent lamps or halogen. Buy the “warm” color fluorescent lights, which may require going to a lighting store. For most applications, a 15 to 25 watt compact fluorescent lamp will work where you had a 75 to 100 watt incandescent bulb. Anywhere you need really good color quality like a bathroom mirror or kitchen, replace with halogen. A 45 watt halogen bulb is blinding and has great color. It can replace an incandescent bulb 2 to 3 times its wattage.

Most likely your next biggest load is your refrigerator, and if it is over 10 years old it was built before major changes were made in the Federal energy guidelines. Also, if it came with the condo, it probably was “spec” quality, which is at the low end of efficiency even if its newer. You can replace this energy hog without the permission of the condo association. Finally, if you do not have one already, replace the standard wall thermostat with a good quality programmable unit, also something you can do without permission and this can really save if you are gone most of the day.

Next, be prepared. Since you have limited storage space take one small closet or under one bed and make that your emergency storage room. Build up a pantry in the upper half with foods that will store a long time and require minimum preparation. Buy a canned heat camping stove. These fold up and take very little room, yet easily heats a pan of water to prepare rice, instant heat-and-serve meals, etc. Add a few gallons of bottled water and 2 or 3 LED type flashlights. Extra batteries is a must have. Add a small battery radio and extra trash bags, paper plates, plastic utensils, and you are ready for anything!

There have been many past articles in Backwoods Home on how to make an emergency pantry and what you should have on hand at all times. I suggest reading these back issues for more ideas.

Good Luck,

Jeff Yago

WiFi transmitters with solar panels

Hello Jeff,

I’m impressed with the responses you provide to energy related questions and I hope you will educate me more on this subject.

I have a project involving 1 long range wifi transmitter and 4 repeaters.

I need to power each repeater with solar energy. The manufacturers of the wifi equipment told me each transmitter or repeater requires 12V DC and 2amp power.

I intend to mount these on roof tops. I also intend to use 12V batteries. The project is in West Africa (around the equator). So, there will be enough sunlight…for 12 hours and then darkness. I want the repeaters to run for 24 hours.

How many batteries do I need for each repeater.

How many hours will a 12V 600W 28Ah power cell battery sustain the 12V DC 2amp repeater.

Urgent response will be highly appreciated.


Isidore Chidi.


We cannot provide design or sizing for a specific project since this web site is intended to provide information that would be useful to all readers. However, I can give you some general battery sizing information that should allow you to figure this out on your own. I can also tell you that a 28 amp-hr battery is very small for this much load.

First, make sure this equipment is not positive ground. Some repeater and transmitting equipment is positive ground, while all US electrical and off-grid solar inverters are negative ground. I don’t know why this is reversed, but this can really cause you installation problems.

Normally, we size the battery bank for a maximum 50% daily discharge. This means a 100 amp-hour 12 volt battery can provide 50 amp-hour load per charge-discharge cycle. There is also some efficiency losses when charging and when discharging, so add some extra for this. Lets estimate a 10% loss so we end up with 45 amp-hours per cycle. Since you will have about 6 to 7 hours per day of charging in Africa (early and evening hours will not provide much charging even if you have 12 hours of sun), this means the battery is discharging 18 hours per day and charging for 6. With our example of 45 amp-hours of available energy, this works out to about 2.5 amp load per hour (45 / 18). This also means the 6 hours of charging must provide 55 amp-hours of charge (including 10% loss during charging) in 6 hours of sun, plus power the load while also charging the battery. This would require a solar array that puts out about 9.1 amps (55 amp-hr / 6 hr) plus the electrical load. Since you will not have a perfect solar day every day, in reality you will need a solar system that can provide more charging and more battery storage than one day, so for 3 days of carry-over, our example would need about 300 amp-hours of battery capacity and about three(3) solar modules in the 100 to 130 watt range.

Hope this helps, but you need to really up-size your planned system.

Good Luck!

Jeff Yago

Inverter to sub-panel

Click photos to enlarge
Click photos to enlarge


I have some solar questions and I cannot seem to find the answer to them.

I am trying to connect my inverter to a sub panel but I am not having much success. First let me explain my set up to you:

I have a small solar panel charging 2 6-volt and 2 12-volt batteries (the 6 volts are in a series then to parallel with the 12’s).

I also have a charge controller hooked up to these. I then have my wires which go to my inverter. I then have a two prong pigtail which goes to a subpanel.

This subpanel supplies power to 2 outlets and 2 small fluorescent lights. This part of the system was not set up by me but worked with our previous cheap 250 watt inverter but this was stolen so we purchased a Cobra 1000 watt modified sine wave inverter and it won’t work. (By the the way this system is entirely off-grid. There is not even electricity in the neighborhood.)

I am confused as to why the cheap inverter worked fine yet this somewhat nicer one doesn’t. I have included some pics of the subpanel wiring. Any help that you can give will be appreciated.




Although I have seen many small off-grid systems wired like this, before I make any suggestions, for the record I will tell you this would never pass an electrical inspection. There are many code violations and although most are not major, this really should be re-wired to code. Since this web site is for general questions and cannot get into specific design or code issues, I cannot be more specific than these general comments below.

First, since all of your circuit breakers are rated higher than the output of your inverter, they will never trip. Any over-load condition will shut down the inverter by its internal overload or temperature safety limits. Although this inverter is most likely too small for what you are trying to do, it still has a 2000 watt surge rating for a brief period. This equals about 18 amps which is greater than the temperature rating for your “plug” assembly, and this is un-safe. Your inverter problem is most likely due to the mis-matched battery bank being too small for this larger inverter. The battery bank is the first place I would check. Now that you have an inverter that is 5 times larger in capacity than your old inverter, it is drawing 5 times more amps from the battery bank. For example, at the full rated load of 1000 watts @ 115 VAC, this equals almost 100 amps draw at 12 volts DC assuming a 90% efficiency. If you added in the surge load, this inverter could draw up to 200 amps for a very brief period. If you are using car batteries or lightweight RV batteries, or if they are deep cycle batteries but are over 3 years old, you will most likely need to replace them all, and do not mix and match. Use the same size and voltage batteries if you have more than one.

Good Luck,

Jeff Yago

Motion detector & compact fluorescent lamps


The box of a motion detector light fixture says “Do not use CFL”.

Why not?


R. Reyna

R. Reyna:

This statement does not apply to all motion detector devices, but it may apply to “cheap” models. Lower cost electrical switching devices are designed for “resistance” type loads like an incandescent bulb, which is easy to turn off and on.

Any electrical load having a transformer type load (older fluorescent lights have ballasts) produce much higher loads on the switch contacts in the motion switch when they open. Also, newer compact fluorescent lamps have replaced the ballast type transformer with an electronic ballast, which sometimes either affects, or is affected by, the electronics in the motion sensor.

More expensive devices have added switching capacity and filters.

I once had a motion sensor light overheat and melt down when connected to a modified sine wave inverter due the cheap quality of the motion switch not being able to handle the power quality. Like they say, you get what you pay for.

Good luck and buy a fire extinguisher,

Jeff Yago

Alternative heat


In our 2 story – plus basement home the heat, hot water (showers), stove and dryer are all run off of propane. There is also a gas fireplace on the main level. We are considering replacing our gas fireplace with an alternative heat source that would be serve as a primary source of heat.

In our area the wood stoves, pellet stoves, and woodburning fireplace inserts are readily available at a reasonable cost.

Do you have an opinion on which would more efficiant in the long run?

Thanks Shannon


For a house this large it will be hard to heat the entire house from a fireplace. Pellet stoves are the easiest to use, but I never like having to buy and store all those bags of pellets and you will go through a lot of bags if you try to have this as the main heat source. For me, a wood stove is a wood stove and I like to toss in several large split logs then leave it alone for a few hours at a time. If you can find a large insert that will fit and still include one or more fans to circulate the heat that may improve the heat distribution.

If you are really serious about having this the main heat source, then I would go for one of those outside wood boilers that look like a small metal out-building. You fire these up with wood and the heated water is piped to the existing heating system in your home for distribution. Many options and models available, and no wood chips tracked across the carpet!

Good luck,

Jeff Yago

Selling power to utilities

I have enjoyed Jeff Yago's articles. His most recent, "Solar Wind and Energy Credits" got me to wondering about the state of deregulation in the power industry.

In the 90's I had a friend that worked for one of the local power producers in Indiana. Deregulation was supposed to open up the market for buyers and sellers.

Now I live in Tennessee, serviced by a power cooperative that buys from TVA. They have a green power program that charges the customer a higher rate so they can sleep at night, knowing their power came from a renewable source, such as wind, hydro, solar, etc. I have had no trouble sleeping without this comfort.

For the homeowner producing power, the cooperative credits the customer's account for any surplus produced by the customer at the higher "green power" rate. When the customer draws power, they are billed at the higher green power rate. There are no cash payments for an account that produces more power than it consumes. This is the electric company's equivalent of cell phone plans, where you carry a bazillion anywhere minutes that never get used.

My question for Mr. Yago, is it possible to sell power to another company or cooperative, allowing me (if needed) to buy power from my local cooperative at the normal rate?


Pat Barden


Many of the problems you have identified are well known to the solar industry and as they say, the times, they are a changing. What many want more than tax credits is a national feed-in tariff. All electric utilities have multiple sources of power, and they constantly change the mix of which generators are providing the “base” grid power based on time of day and demand. For example, most utilities will run their coal fired plants full out 24/7 as this reults in their lowest cost to produce power. Unfortunately, it can take several days to re-start a coal fired plant after it has been shut down, so they cannot just turn several on and off as their demand changes. To handle these temporary system peak demands, which usually happen in the late afternoon, they will usually fire up natural gas turbines which are much higher cost to operate, but can be started and stopped fairly quickly and are used for peaks lasting only a few hours. Lastly, some utilities have pumped storage or other temporary types which may only be able to provide power for a few minutes or maybe a half-hour, but these can be started instantly.

The catch to all this is the power companies want to pay back the solar homeowners for any afternoon electricity they sell back at their “base” cost to generate power which typically is in the 4 to 8 cents per kWh, at a time when their actual cost for the temporary afternoon peak load may be over 30 cents per kWh. Since the solar sell back occurs at the exact same time as the utilities are needing to generate the extra peak power at their highest cost, what we are really fighting for is for solar to be paid at this peak rate, not the average or base rate. There are some utilities in states that cannot meet demand now and these utilities are very friendly to solar as a way to avoid building costly new power plants. There are other states where the electric utilities have plenty of capacity from coal or nuclear and they could care less about solar and do not need the sell-back power.

As electric demand continues to increase nationally each year, at some point all electric utilities will finally come to the table and be glad to buy all the solar power they can get, as this “locally produced” power goes to the local community loads and is not lost traveling along thousands of miles of power lines. There are a few a few states that do allow the type of cross-state purchasing and selling of power that you are hoping for, and there are also a few states that now allow trading solar credits. This is when an electric utility is required by their state to purchase a certain amount of their electricity from renewable energy when they do not have any. There are companies called aggregators that go out to hundreds of small solar grid-tie homeowners and “sign them up”. Nothing changes between you and your local utility, but the aggregator gets to claim that he is representing your excess power. They then “bundle” these separate accounts into one large portfolio which they sell to the utility that needs to show they are being credited for so much solar power, even though this power never actually gets wired from your home to their account several states away. These guys are paying very good rates just to “claim” your excess solar power and it will depend on your state and your local utility if you can take part in this program.

If all this still sounds confusing, it is, but give the industry a few more years and we will have all this worked out. One thing you can be sure of, if some utilities are already fighting to purchase all the solar power they can get and at much higher rates then your local utility is willing to pay, you can bet the future looks very bright for all solar homeowners even if it will take longer then they were hoping.

Good luck and be patient,

Jeff Yago

Hydronic woodstove

Hi Jeff,

I have a fireplace in my basement and wood like to augment my propane/hydronic heating system with a wood stove fireplace insert similar to your setup. My question is about the water jacket that you use. Is it off the shelf product? Custom? Can you provide insight into the set-up that you did not detail. Your expertise would be appreciated!

Thom Pecoraro
Stephentown, NY


This is another great example of class action lawsuits forcing great products off the market.

Throughout the 1970’s energy crisis there were several nationally sold fireplace inserts and fireplace grates that heated water. This made it easy to pipe all the wood heat to hydronic baseboard heaters in other parts of the house, or to a hot water coil in the ductwork and heat the return air being ducted to the other rooms without operating the electric strip heaters or gas burners. I purchased several of these “Hydro-Heaters” for other projects, including the one I now have in our solar home. I had it the new unit boxed up and put in storage for almost 15 years, then installed it in 1992, and it has worked perfectly for the past 16 years.

There also was a firm in northern California I visited in the late 1990’s that was making a great wood-fired hot water heater for remote home-sites. It looked like a standard gas hot water heater, but the bottom half was a fire-box and the flue went up the center. You built a small wood fire and waited about 30 minutes, then you had enough hot water for several showers and dish-washing. They made a “tank-less” version that was just a fire-box surrounded by a water jacket, and you pumped the heated water to a larger storage tank or hot tub. I also purchased one of each and am still keeping them for future since this firm is now out of business and to my knowledge was the last company still making these in the US.

What happened was most state and federal agencies viewed these products the same as a steam boiler since they can explode if not properly installed. For example, all of the models that were sold in the 1970’s always came with a temperature relief valve and a pressure relief valve. If you have a large fire going and the water pump stopped pumping when the power went out, without any water flow the water jacket would quickly turn all water still left in the heater to steam. I have witnessed several times when this happened and all the only thing you saw was some some steam safely venting to a floor drain or outside. However, if the relief valves were not properly installed, the pressure could reach a level that would rupture the steel jacket or under extreme cases even explode. There were not only cases of tank ruptures due to missing relief valves, but even a few cases where a relief valve was piped to the outside and a small drip through the valve due to a weak spring would run down the pipe and freeze during winter weather. After several days the relief valve’s discharge pipe would totally plug up with ice, then if the pressure increased due to a power outage stopping the pump there was no place for the pressure to vent.

I know that there are millions of these wood fired hot water heaters and hydronic fireplace grates being sold in third world countries every year, and I think the California manufacturer moved his operation to Mexico years ago, but I am not aware of anyone making a hydronic fireplace insert that is legal today. If any reader out there can provide this information we all would be grateful, but I think the cost to get these UL listed and the cost for liability insurance for any manufacturer makes this impossible today.

If you really want to heat your home with wood using a hydronic system, I suggest installing one of the many outdoor packaged units you see advertised in Backwoods Home, and in an article I provided on this subject. Since these outdoor units use a non-pressurized water jacket system to pipe hot water to heat the home, they are safe and easy to install.

Good Luck!

Jeff Yago

A solar soccer complex

Hi Jeff

I am building a 6 soccer field complex on a 26.77 acre lot. There is a well on the property; not sure what it pumps.

I am keen on keeping this a natural facility and happened to come across the Solar panel discussion.

Without going too deep, as I am not a technical person, would Soalr panel energy work for 1) Bathrooms, 2) Watering the sports fields?

Thank you in advance



It depends on where you live and if utility power is close by and easy to connect. If you are in a state that offers solar incentives, this can really reduce the cost for any alternative energy system. If you are not near a utility line, they may charge a very high fee to run power to a remote location. Having addressed these first, here are the solar suggestions:

1. A solar hot water system can easily provide hot water for your bathrooms and any snack bar type sink. Since your afternoon or early evening usage matches the solar afternoon peak and stored up solar heated water, you most likely would need little or no backup hot water heater.

2. It is not feasible to power any heating equipment from a small solar system, so if this location is subject to freezing weather you would either need to drain down any piping that could freeze or have heating equipment powered by the electric grid, natural gas if available, or oil/propane equipment.

3. If your only load was a well pump for ground watering you could easily install a pole mounted solar array and solar DC well pump which would provide water when the sun was shining and no pumping when the sun goes down. If you have local utility power, you will find it may be less costly to stay with a standard well pump and no solar.

4. There are a few grants for non-profits to help pay for demonstration solar projects and you may be able to find one to offset most of this cost, but I am not aware of anything for private or commercial applications.

Hope this helps, now play ball !

Jeff Yago

Mix-n-match PV panels

Greetings Jeff,

For the past couple of years I’ve been scouring the local Craigslist for used PV panels in preparation for my ultimate plan to move off-grid. I have been very fortunate in that I have amassed approx. 1.3 (rated)Kw of 12v nominal panels for an average of just about $3/watt. I realize that when dealing with this much rated capability it is normally recommended to up-size to a 24 or 48v system, but to keep things as simple as possible (KISS) I’m planning on sticking with 12v.

The drawback to this is that they are a mish-mash of manufacturers, sizes, and specifications (which also makes it difficult to wire in series for higher voltages). My primary concern lies in the fact that the open circuit voltages range from around 17v up to over 21v. It is my understanding that (in layman’s terms) voltage is roughly equated to ‘line pressure’.

With this in mind I’m wondering if the panels with a higher voltage specification would generate a ‘back pressure’, as it were, preventing the panels with a lower voltage specification from adding to the overall current (kind of like a garden hose trying to augment the flow of a fire hose). I asked an engineer friend of mine who’s been living off grid for almost 20 years now, and even he was stumped.

Chuck Farley


You did not say how many modules you have, but with a total of 1300 watts and all are nominal 12 volt, I assume we are talking about 22 to 26 modules. With your desire to keep everything at a nominal 12 volts, this means you will have all 22 to 26 modules wired in parallel, and that is not good. There are many reasons why this is not practical, but the big one is the UL label on the back that says the size of a series fuse required. For example, a typical module in this size range will probably be listed as requiring a 15 amp “series” fuse. If the modules have an average output of 5 amps, this means if you have more than 3 modules in parallel, it is possible for one module to have an internal “short” and all the current from the other 3 modules will be routed through this failed module and could cause a fire.

To reduce the number of parallel modules, I would set this up for 24 or 48 volts nominal. This means the modules will be wired in “groups” of 2 or 4 in series. Even with identical modules with the same model number you can have as much as a 10% difference from one module to the next, so you want to “match” the strings. Lay them all out where they receive the same amount of sun at the same time, then go down the line on a clear day and mark on the back what voltage each is producing. Next, using a meter that can read DC amps, short the positive and negative leads through the amp meter and also note this reading. You need to be fast as any change in sky conditions will throw off your readings.

Now try and “match” high and low modules in the same string so each separate string has the same voltage and amperage. The problem is not in having slightly different voltage modules in series, the problem is avoiding having multiple strings in parallel that have far different voltages. This is the same problem as hooking up different batteries in series. You will always have one or two individual cells wired in series that are lower or higher than the others, and the battery will settle on a voltage that levels these highs and lows. But if you have batteries with different voltages wired in parallel, the higher voltage battery will try to “charge” the lower voltage battery.

You should use a good quality MPPT type charge controller which will try to sort out any remaining mis-match. If your modules are really mis-matched and it is hard to do the above, you may want to use multiple charge controllers so you will have fewer modules wired in parallel. These can still charge the same battery bank.

Good luck,

Jeff Yago

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