Alternative energy advice from Ask Jeff Yago. Volume #17

Ask Jeff Yago
Solar & Energy-Related Issues

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

Sorry. Jeff no longer answers questions online

Electric vehicles

Hi There!

Seems that you folks should be building electric cars! Someone told me to purchase a Yanmar diesel engine about 29 HP and connect it to a torque converter and the average car should get 80 to 100 miles per gallon. They said it would go 80 mph to.

I don’t remember where I saw the article but they claim to have built seven of them so far.

Good luck,



It has been proven in endless testing that the same exact vehicle will get better mileage if the diesel engine option is ordered instead of the standard gasoline engine. This takes into consideration the fact that a diesel engine must be heavier construction due to the higher torque and higher compression ratios involved, and anytime you add weight to a vehicle you lower its mileage. In other words, there is enough improvement in mileage from switching to diesel to overcome the losses of the added weight.

However, the reason most people do not choose the diesel option knowing it will have better mileage and longer life before re-build is the really high cost of this option. Unless you drive much more than an average car owner, its hard to save enough in better mileage to offset the thousands of dollars more you pay for the diesel engine.

Remember, above 45 MPH it takes most of the engine’s horsepower to offset wind resistance, and this engine load does not care what generates the horsepower. This means you can improve mileage by installing a smaller engine and have a lower top speed, but you can’t do both at the same time.

As for doing this yourself, you should be able to increase your mileage, but if you can get 100 miles per gallon and also go 80 MPH you must be planning to convert your car into a motorbike!

Better re-think this one,

Jeff Yago

Solar cooker/oven

Howdy Jeff

Has someone come up with a plan to build a solar cooker/oven that would be stationary and built with brick, stainless steel etc..similar to a bar-b-q ???

Would be interested in plans if available…


Roger & Theresa Wing

Roger & Teresa:

There are many different ways to build solar ovens including stationary designs that you asked for. The problem with a stationary design is most solar ovens are used to cook foods that takes several hours to cook, and since the sun is constantly moving you need to keep re-positioning the direction the oven reflectors are facing. Unlike a solar hot water or solar pv module, a solar cook oven requires a “focusing” sun, like when you use a magnifying glass as a kid to burn leaves. They will not work on a cloudy day and do not heat if their reflectors are not facing directly towards the sun.

Here is a link to one of the better groups that provide free plans and information on building your own solar cooker. —–

Good Luck!

Jeff Yago

Paint for battery box


I am building a battery box similar to the one you describe in your article. I have been looking into the paint. Noone around here knows of any paint that is both fire and acid resistant. I can get a fire restant paint for around 85 dollars a gallon. I would prefer not to pay this much, do you have any ideas? And is the paint really that critical? Thank you in advance for your help.



If the paint is a problem, I would line the inside with the masonry backer board they sell to put behind tile in showers. It is fireproof, waterproof, acid proof, and can be found in most Lowes or Home Depots. It usually comes in 2 ft X 4 ft boards and is 1/2″ think. Be sure to use the special self-drilling screws they also sell to attach this material to wood studs. You can also use fire rated 5/8″ drywall and just don’t paint it at all.

Just a note – We are getting away from using battery boxes and doing more battery rooms, as this reduces the corrosion on the battery terminals due to the limited air circulation in the confined interior of the box. These have concrete floors with a floor drain, fire-rated 5/8″ drywall on the walls and ceiling, and a good exhaust vent at the highest point.

Good Luck!

Jeff Yago

Lamp post question


How do I convert a gas powered front yard lamp post to solar powered? What equipment would I need?



I assume the solar power for your exterior pole light is too far to run standard utility power which would be easier, so here goes.

First, dis-connect and plug the gas line, then remove all of the internal gas burner assemble inside the pole light. Next, decide if the solar panel will look OK mounted on the same pole, or if you plan to locate it separately. The easiest way to do this is to buy one of the low cost solar-powered yard lights you see at most builder supply outlets. Select a model that has an adjustable solar panel, not one that is glued down to the top of the light. These are low powered LED type lights with a polished reflector to spread out the light. This type LED light will not illuminate a large area, so if you want a light like a standard pole light you will need to install a larger system made up of separate solar components which will include a separate 12 volt gel battery, a 10 to 20 watt solar module, a solar charge controller, and a 9 watt compact fluorescent lamp having a 12 volt DC ballast. This will cost you over $300, so if you can get by with the smaller light I described at first you will save some money.

Remove the adjustable solar panel and fabricate a small aluminum “U” bracket and attach the solar panel on top of the pole light and facing south. Remove and re-use as much of the LED light and reflector and associated control wiring and battery and install in the pole lamp housing. You will need tools that can cut the plastic and metal to “bend-bump-and grind” the parts to fit. You can buy a solar charge controller that will use the solar panel for a photo-cell type control to turn the light on and off at night, so don’t worry about trying to find a DC photo-cell.

You can make this look neater if you can locate the solar panel and a weather-proof battery box several feet away the pole and run the wire underground. If you decide to build your on system from parts, check out my article titled Build A Simple Solar-Powered Outdoor Light in Issue #92 dated March 2005, which shows photos and wiring diagrams.

Good Luck,

Jeff Yago

I want to use solar energy to power my business

Dear Jeff,

I am very interested in making my new candy business an eco-friendly one from the ground up. More specifically, I want to power it with solar energy, but don’t know how to start. I live in Santa Clara, CA, where they have their own power plant, and they encourage solar energy systems in the city.

Please help!


Kristen Scott
Artisan Candies company


Reality Check!!

Example – Lets take just one electric candy kettle that has a 2,500 watt heating element, that you use a total of 8 hours per day (multiply by as many kettles or hours you actually have!)

The average price for a grid-tie solar power system (no batteries or generator) runs around $10 to $12 per watt these days, and you can expect 4 hours of winter sun and 6 hours of summer sun, depending on your geoggraphic location and market area.

2,500 watts X 8 hrs = 20,000 watt-hrs. per day needed for EACH kettle.

20,000 watt-hrs / 6 hrs / 80% efficency = 4,166 watt array.

4,166 watts X $10.00/watt = $41,666 for EACH kettle.

If you wanted to power a string of compact flourescent lights and maybe several small refrigerators instead, you may be able to do this for a more reasonable cost, but you will not be able to justify powering ANYTHING that includes electric heating elements unless you plan to sell lots of candy!

Good Luck,

Jeff Yago

Electric fence


Can you run electric fence wire through PVC with a hole drilled in it without it shorting out the fence?

Thanks, Claude


I assume you are talking about using PVC pipe as a fence “post”. PVC is an insulator type material and will not normally conduct electricity. Of course, if the posts get wet from rain the water running down the outside will provide a electrical shorting path, but this would be true for any type fence post material.

Most PVC piping for domestic water, waste vents, and sewer are white in color. Most PVC for electrical conduit is dark gray in color. Gray electrical conduit has better fire retardant and sunlight resistance than the white, but both are very close in their electrical resistance. The downside is neither are very strong in bending, so unless you are using a very large diameter pipe, a determined animal that can stand a mild shock may push it over after a few attempts.

Good Luck and keep the cows in!

Jeff Yago

Solar inverter

Dear jeff,

I came across your website and was fascinated by it. Most especially when I came accross the column talking about the solar inverter.

I would want to know how it works, how long can it work and the cost implication. I am not in the USA right now but I might be very much interested in it.

Also I would want to know if it is possible to get a 220v or 240v wet or dry cell battery suitable for an inveter.

Thanks in anicipation for your response

Biodun Oshodi


Over the years I have written many articles in this magazine that describe inverters, how they work, and how they are wired. I suggest you read through the back issues, many online.

Most battery-based inverters are designed for a 12, 24, or 48 volt battery voltage. For larger storage capacities, most people use multiple “strings” of individual 2-volt or 6-volt deep cycle batteries that add up to 48-volts. Since you can get a 2-volt cell (dry or wet) from several amp-hours to over 1,000 amp-hrs per each cell, you can make up any capacity battery bank, but most of the larger residential inverters are designed for a 48-volt battery.

They do make commercial special order inverters for very large industrial application that you can order almost any input and output voltage you want, but we are talking about $30,000 units.

Hope this helps,

Jeff Yago

Large amp-hour batteries


I have heard of 3,000 and up amp-hour batteries that come in bolt together sections. Can you please tell me who manufactures these batteries?




You are talking about a commercial grade battery and there several good manufacturers to consider. However, due to the much longer 15 to 20 year life expectancy and heavy weights, these batteries are really expensive.

You need to be very careful when deciding which model to buy, as many of these really heavy duty batteries are designed for stand-by UPS type applications. This means they are designed to stay on a very small trickle charger for a year or more, then deliver their full power for a few hours, then go back to trickle charge until the next power outage. Even though they have very large amp-hour ratings, UPS type batteries are not designed for the daily heavy charge-discharge cycle that is typical for an off-grid solar project. Check the depth-of-discharge (DOD) chart verses the number of discharge cycles for the battery you want, as this will give you a better idea of how long it will last depending on how deep the discharge.

Here are a few links to the batteries you are asking for:

Good luck!

Jeff Yago

Battery backup power

Dear Jeff,

I would like to make use of a battery backup power system, which will be used during the day and will be loaded at night (with lower priced electricity) or during a sunny day by solar cells. The system should have an output of 220v, with a running watts of around 12.000W and a starting volt amps of around 28.000 VA. Does such system exists and who manufactures these ??

Thanks in advance,

Kind regards,

Rob Erkelens


You are making a classic error that most people make when starting to look at solar. You probably checked your electric bill to see what your maximum loads were and then want to know what it will cost to supply all this load without any changes to your electric system or electric loads. Since the average cost these days for a solar power system runs between $10 and $12 per watt (depending on system type and options), this means the system you just described will cost between $100,000.00 and $144,000.00.

Now that you have had this reality check, you see why this is not how you buy a solar power system. First, you need to identify only those electric loads that are critical and really need to operate from solar or battery power. Next, you need to decide how long these loads will operate for a given period, which will determine battery and array size. Finally, you decide if adding a generator would be better than adding more battery capacity to achieve a longer off-grid run-time.

There are many system design options and yes, you can power 12, 24, or 48 volt DC loads, and 120, 220, 240, or 480 volt AC loads, Yes, you can have any size battery capacity, although there is a trade-off on physical space and cost when selecting a battery type and amp-hour capacity.

Finally, let me give you Yago’s design rule #4 – you will never generate electrical power cheaper than the electric utility. If you decide to “time-shift” your electric usage by charging up batteries all night using lower cost power, then use this stored energy to power your loads during the day, you will still not come out ahead due to the efficiency losses of about 20% during the battery charging process, plus another 10% loss during the inverter process (30% total), plus the very high cost for the batteries that must be amortized as part of these operating costs.

If you really want to time-shift your loads and your local utility offers lower cost power at night, the answer is very simple. Wash clothes, wash dishes, heat up your hot water tank, charge your cell phones, run the pool filter pump, and pre-heat-or pre-cool your home during the lower cost time period. You can use timers to do this automatically if you want and you don’t need batteries or $144,000.00 solar power systems!

Welcome back to earth!

Jeff Yago

Generator Shed

Hey, Jeff.

I want to put a generator outside of my house, need a shed to put it in, may want to build it myself, didn’t want to give almost $900 for it, as I saw one on the Internet, any suggestions.



Many people build their own generator sheds, but there are a few things to beware of. You should start with a concrete pad with at least 16″ of clearance around all sides of the generator. I usually build the shed using typical 2 x 4 construction like building a small play house. You can use any type siding, but make sure the roof has lots of over-hang and sloped away from where you place the access door. Actually you may need two access openings – one at the front starter end of the generator, and one on the side at the control panel.

I like to line the inside with a good 3/4″ to 1″ foil-faced insulation board to reduce noise. You will also need a large opening where the exhaust exits the enclosure. This exhaust is very hot so I usually make the opening large, then add a metal rain hood above this opening.

You do not want this to be air tight as the generator needs combustion air, lots of cooling air, and releases exhaust gases. I usually take some left over canvas or heavy rubber and attach across the top of the main opening. This hangs down and keeps out the weather without being an air tight door.

If your generator has a gas tank, you will need to hinge the top roof to allow raising it up to access the fill cap. Finally, when I poured the concrete pad, I inserted a very large steel “eye” bolt before it hardened. I then chained the generator with a large chain and padlock to keep it from walking away as they sometimes do.

Good luck!

Jeff Yago

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