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Ask Jeff Yago
Solar & Energy-Related Issues

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


Effect of gusty winds on solar panels

Jeff,

We just bought a house in Western NY State - Finger Lakes area. After doing much research into several configurations, my only concern is the wind loading on photo-voltaic panels. We are looking at roof mounted panels, or mounted at ground level.

We have over an acre of land out back - with lots of sky above.

Please comment.

Regards

Orville C

Orville:

Most roof structures in areas where it snows have fairly strong roof-truss systems and the lightweight solar modules spread out over a large roof area only adds a few pounds per sq.ft. that is far below a snow loading. However, its not the weight pressing down on the roof that is the main structural concern, its "uplift". When a solar module is subject to high winds, the effect is like an airplane wing and the modules try to pull away from their roof supports.

When installing this mounting hardware, some installers drive screws only into the plywood roof sheeting and not into the large wood truss members. There have been many cases of the solar array pulling their mounting feet screws completely out of plywood sheeting resulting in a very expensive glass sail!

If you are really concerned, design a garden shed or tool shed near your house with a roof facing south, and be sure the roof trusses are spaced the same distance as the solar array mounting feet, or be sure there are "spanner" blocks of 2 x 6's or 2 x 8's between each truss where a mounting screw needs to penetrate.

Good luck,

Jeff Yago


Modular Solar RV build

Howdy Jeff,

My wife and I own a 8X24 foot Haulmark Race trailer used to haul our simple buggy and sleep in when we go to various events as well as 101 other uses. We are in the process of adding a full RV bath and kitchen to include electrical connections for both 12V and household current so that we may be slightly more comfortable on the longer outings and perhaps be able to use power tools when necessary without having to resort to a generator. Eventually, we plan on a diesel gen set but that is further out due to outright cost and how often (little) it would be used at this point.

Most of the appliances we are planning to use are of the 12v variety but there are still the odd times we have to resort to household items. Appliances include: 12v coffee pot, microwave (500-750watt), florescent lighting (TBD amount), CB/UHF radios (9v@350ma or 120v@6 watt depending on connection), auto type stereo (12v ~20 watt), portable battery charger (D, C, AA cells), GPS units (charging), Laptop computer (also functions as TV/DVD player/etc 1-2 hours a day; 19.5v @ 3.0 amp), water pump (or 2) for RV plumbing system (12v @ 10 amp max draw), clock radio (120v @ 8 watt)

Because we do a lot of automotive activities far off the beaten path we are considering starting with 2 (on hand) and eventually upgrading to 8 deep cycle 'Optima' brand batteries for our power storage (~$110 ea). Besides being shock resistant and less prone to internal damage from road vibration, the batteries are also sealed (no venting issues), able to be mounted in any position, and usable (identical) for all of our vehicles (except the motorcycles). Is this a good or bad choice? Are the batteries more expensive than other normal options?

The roof of our trailer has 8X16 available (8x8 is a grandstand/luggage rack) for solar panels which my wife and I would like to work into our overall plan and eventually use to its full potential. We are hoping that once complete we could "plug in" our trailer and use the paneled roof to help cut energy costs at our residence so that we could get a little more out of the investment when it is not being used to travel. As with the batteries, we would like to start small and work up to the complete package as we can afford to pay in cash (credit being so evil). In a few years down the road when we go to work on our off the grid home we hope to use the trailer as a temp residence and have the trailer provide the power supply for the house until the house can have its own system put in as well so it would be very nice to maximize the output of the trailer.

A problem with the solar panels is the hail storms we have every year. We have seen stones as large as baseballs and have had to replace the roof vents on the trailer due to damage every year. Luckily, the position it usually sits relative to the house and the prevailing storm directions have prevented the side of the trailer from looking like we used it for batting practice backstop.

Are there good panels out there reasonable in cost and weight that we can upgrade in sections that would stand up to hail we see here? Else, is there a way to 'armor' the panels with perhaps expanded aluminum mesh and standoffs (as we will be trying with the roof vents this year) that will not too dramatically impact the panel output?

How is a solar unit like this conventually plugged in? Do you just insert a double ended wall socket and let it run the street meter backwards?

Is there a particular converter/charger that you would suggest to use with our project that can handle the growth of the system? What of an inverter for said system? Any other advice you can give?

Thank you,

Dominick

Dominick:

Wow! thats a lot of questions! First, as stated at the header of this web site, its not possible to "design" a system in this forum due to the time required as each system is different and usually very complex. However, I will give you as few things to consider which may help.

First, it looks like you have tried to keep your elecrical loads small and that is very important. As far as batteries, I use gel cell deep-cycle 6-volt batteries on RV applications as they are sealed, can be mounted in any position, and when installed in pairs to make 12 volts, they provide much more amp-hour storage than any single 12 volt battery. The down side is they cannot be over-charged so you need to have a very good solar charge controller designed to charge gel cell batteries (different charging voltage).

Mounting solar modules on an RV roof is always a problem due to orientation. They will need to tilt up for most partsmof the U.S. for maximum power, yet they cannot travel in an up position unless you want a sail. R & B Enterprises (360-598-6781) make a solar module lift kit that will raise and lower two solar modules up to 80 watts each, but this means you still need to orientate your RV so they are facing south or south-west when tilted up, and this may not be possible where you plan to park. Also, I hav found that its hard to find space on an RV roof for more than one of these lift systems since there are usually roof-top AC units, antennas, vents, and skylights that reduce roof area. I think you will find that only 2 modules in the 80 to 100 watt size range will limit the amount of power you generate except during the summer months, and most likely will not be enough to power anything in a separate home you want to connect.

As for hail, solar modules are very strong tempered glass, but what you describe could be a problem. You should not mount anything over the modules as this can cause a very big reduction in their solar output, but you could place some type of plywood covers over them during the the months hail is a problem and you are not on the road.

As for connecting to your home's electrical system, I would not. What you describe can be a very high risk of "back-feeding" your RV and causing major electrical damage. There are systems that can be connected to multiple buildings that include transfer switches or other safety devices, but for a small system like you are planning I think you will find the added cost is not worth the effort.

Bottom line, stick with a system designed just for your RV and its small electrical loads and be safe.

Jeff Yago


Water towers

Jeff,

I live in an area where the water system is under private ownership. The owner refuses to do anything about the amount of air in the water. We have lots of air, sometimes it takes 15 to 20 minutes to get a good stream of water. My question is, how tall and what capacity water tower would I need to be able to have a constant good flow of water?

Fred Carson
New Braunfels, TX

Fred:

You really have not provided enough information to be able to address this proble. For example, why is there any air in the system in the first place? Is this a pumped system, gravity flow, are you near the end of the pipe or near the beginning, does it have pressure tanks or booster pumps? I will make a few suggestions, but caution that all the above issues can affect the results you could achieve.

First, as to your question of tower height, you will increase water pressure 1 psi for every 2.31 feet of height you raise your tank (not counting piping losses). However, there are plumbing devices made to remove air from tanks and plumbing systems. There are also special expansion tanks and "air scoops" that remove air and you may want to talk to a plumbing contractor.

Finally, before going to the trouble of building a raised outdoor water tank, you could have the "city" water flow into a non-pressurized 100 to 200 gallon tank located in your garage or basement. Then have a pressure pump take water from the bottom of this tank and re-pressurize it for your home's plumbing system. You would need an expansion tank and pressure switch to turn this pump on and off (like a well system). All air coming into the tank would exit from the top of the tank through a screened vent. A back issues of this magazine has an article I wrote that describes this type of water system.

Many farm suppliers sell these plastic water tanks that have threaded fittings built into the top, sides, and bottom for easy pipe connection, but make sure they are labled safe for drinking, as some are only for chemical sprayers.

Gook luck,

Jeff Yago


Standby generator

Hello Jeff:

Now that is the new year - with hurricane season around the corner - YIKES - I am now in the process of purchasing a standby generator. My question is: Will a hard start kit for my a/c reduce the surge that would be normal when the a/c kicks in? Will that allow me to purchase a smaller Kw generator? For example - Kohler has a 12 Kw generator that claims it will start a 4-ton unit. (I have a 5 ton unit).

I know that this question is not artfully written but I hope you get the drift.

Thank you.

Sherry Cooper

Sherry:

First, it's a "soft" start kit and yes that is good to have on any large motor loads you plan to power from a generator. I recommend them for well pumps also. Although you have a 5 ton AC unit which is fairly large, if it is a newer model it may have a 2 speed compressor or even a dual compressor which would start up at about half of the full loading. You might check the owners manual.

A 12 kW generator is a nice size for most homes unless you have an all electric home in which case you don't want to have the electric range and oven operating and pumping water at the same time you are also trying to start the air conditioner. A little common sense will go a long way in reducing generator loading.

Remember, when they say a generator will start a certain size air conditioner, thay are basing that on having no other loads powered at the same time. However, after a large motor load is started, you can usually add other loads without over-loading the generator since large motor (or compressor) start-up can be 300% of normal run loads.

Good luck!

Jeff Yago


How big of a system do I need?

Dear Jeff,

I am building a small cabin in the mountains this summer, no more than 800 sq ft. It will be a weekend retreat for now, possibly a full time residence down the road. It will need to do the basics for now...a few lights, small TV, toaster, small microwave, etc. It will be in southern Utah with plenty of sunlight.

How big of a system do I need and where can I get one affordably?

Do golf cart batteries work?

Thanks for your time.

Brent Toft

Brent:

Check the next 2 issues as I just completed a 2-part article that describes exactly what you want to do. Note in the article that its not the size of your cabin that matters, its the amp draw of your electrical loads and the number of hours each operates that determines system sizing. Yes, golf cart batteries are a very good battery to start with when you are on a tight budget, as they are low cost and available locally. However, under a daily deep discharge/charge cycling, do not expect over 3 years life. I like the heavier L-16 size battery which has the same footpring as a golf cart battery, but is much taller and weighs slightly over 100 pounds. These have heavier plates and more space for liquid and sediments so they last much longer. Check the next two issues..

Jeff Yago


Locating batteries

Dear Jeff,

My husband and I will be installing solar panels on our Montana cabin this summer and I am wondering where the best place to put our battery bank will be (4-6 golf-cart batteries). My home office, where most of our electricity will be used, is upstairs in our loft area. The solar panels will be mounted on the A-frame roof right above the office. Unfortunately, especially during the winter when we are using our wood stove, the upstairs gets and stays really hot – typically 80 degrees, sometimes as high as 90. Although we have a covered front porch, outside temperatures at 5200 feet in the mountains were as low as -30 this winter. The downstairs stays a more moderate temperature, but the bedroom and bathroom are small and don’t offer a convenient space to store the bank and the living room and kitchen contain our open flame sources (wood stove and propane fridge and range). Can you give some advice on how best to situate this setup with respect to temperature? Thanks!

Lisa Eidson
Greenough, Montana

Lisa,

Locating the batteries is always a big issue in system design due to the problems you have already identified. I try to avoid putting batteries in a sealed battery box with a vent pipe because the confined space increases the concentration of gasses and really increases the corrosion build up on all of the terminals. Most of my systems are larger and we usually have a battery room with powered vent and fire rated walls. However, you could build an insulated battery box with a gasketed lid having a 2" PVC vent pipe to the outside if you locate it under the house, in a basement, or in a crawl space with some protection from the cold weather.

People have also used old refrigerators for battery boxes as they are insulated and fairly cheap, as long as you remove the locking latch and add an external vent pipe. Some of these are buried in the ground on their back up to the door opening in freezing areas. You want a tight gasketed door, but you want the latch to give if there is a gas explosion so the lid can harmlessly swing open instead of holding in the pressure which could blow out the walls!

I would not put a battery bank upstairs due to weight and safety issues. We had to do this for a demonstration solar home several years ago due to complete lack of floor space anywhere else in the small display home, but at least we used sealed gel batteries and did not have any issues with venting gasses.

If you locate the battery box inside the home on the first floor, you could make it into some kind of table top support with storage space above to reduce loss of floor area, but you still will need access for battery servicing. Althought more expensive, using 6-volt gel cell type batteries will reduce the risk of hydrogen gas if the batteries are located inside.

Good luck with your project,

Jeff Yago


Sunroom heat

Jeff

Do you have any suggestions on how to heat a sunroom on the north side of an existing log cabin (heated by a woodstove with backup electric heat). The sunroom would be constructed on a block foundation with crawl space underneath (30"), a sloped roof (no attic or insulation). 120 sq.ft. area of space consisting of mostly windows with an R value of 3. 12'ceilings. No boiler in the house so radiant heat is out unless I consider electric radiant heat. Any suggestions?

Thanks,

Mary Cicale

Mary,

Hope you have a big check book as this construction will have a high heat loss due to your plans to not insulate the walls or ceilings, and being located on the North side with lots of windows.

Since you will not have any direct sunlight entering windows with this orientation, I would call it a dark room instead of a sunroom! You did not indicate where you are located, so I will assume you need winter heating as that is what you asked.

Our house attached green house is 12 by 24 with double glass windows on south wall, and lots of insulation at each end wall and ceiling. This sun space in Virginia requires no heating as the insulated thick masonry floor and back walls are heated up by sun all day, and slowly give off this heat at night.

Most house plants do not do well around propane gas, so I would not recommend using any kind of gas heater if you plan to have any live plants in this room. This would limit you to electric heaters or hot water heaters heated by a remote wood fired or gas fired water heater. Do not be surprised if this costs as much to heat as your cabin!

Jeff Yago


Battery hook up charger

Dear Jeff,

What is the correct way to hook up a charger to a battery operated golf cart. Hook to cart first, and then to the 110 volt outlet , or hook to 110 outlet and then plug in the cart batteries. I have always done it the first way,plug in the cart & then plug in the 110. I had new batteries installed, and the installer said to plug into the 110 volt first, and then plug in the cart.

Owen

Owen:

There are good reasons for either way. I like to hook up first to the battery as this reduces the risk of a spark when making the final connection, and if there is any hydrogen around the battery this reduces the risk of ignition. However, almost all of the hydrogen is generated near the end of the charging process, and this makes avoiding a spark more critical when dis-connecting under power.

Most large charging barns at golf courses have rows of chargers "plugged in" to the 120 volt power all the time, and they connect and dis-connect the battery plug from the golf cart whenever they need it. Most of the newer chargers "sense" the battery state of charge, and usually start up the charging process and end the charging gradually, which can also reduce the risk of the older all or nothing chargers. Hope this helps.

Jeff Yago


Question on grid-tied inverters

Hi, Jeff,

I am reading your Solar Power 101: Solar Arrays article, it is very educational, but I did not understand how grid-tied inverters do not use batteries. Can you explain it. Thanks,

Regards,

Tom Huang

Tom:

This can be confusing due to the terms used. First, there are two types of inverters, which determines how and if a solar array can be connected directly to the utility grid. Remember, any inverter converts DC electricity into AC electricity, regardless of how it is connected to a solar array.

What we call a "Grid Tied" inverter, is an inverter specifically designed to take the D.C. voltage output from a solar array, convert it directly into 120 or 240 volts AC, then transfer this energy into the utility grid turning the electric meter backwards in the process. Since no battery is used, the inverter is not limited to a low voltage, so most grid tied systems usually wire many more solar modules in "series" to allow using small wire with lower wire losses due to the higher voltage and lower current. Grid tied system arrays over several hundred volts DC are not un-common, and can really shock the be-jebees out of you if you need to work on them!

A battery connected inverter is designed to be connected to a battery bank and usually will not operate properly if not connected to a battery, which is typically 12, 24, or 48 volts. This means the solar array will be wired with more "parallel" strings of modules due to the lower voltage limitation of the battery bank, although some solar charge controllers will allow the solar array to be at a slightly higher voltage than the battery to reduce wire losses. Most battery-inverters are also connected to the utility grid, but in most cases, this is to allow the inverter to operate as a battery charger when the solar array has had a long period of no sun.

Now to make this a littile more confusing, some battery connected inverters that use the utility grid to re-charge the batteries as described above, include a program mode that allows them to also sell solar power back to the utility grid after the battery has been fully charged to avoid wasting the excess solar power. However, these inverters are usually not as efficient as the "grid tied" inverter in this mode, but this is not usually a problem since there will be very few times the battery is fully charged and there is still sun available.

Most of the first solar power systems had a battery bank since many of these were to provide power in areas not served by the utility grid. Later, as solar module costs came down and utility costs went up, many more systems were "grid tied" and did not include any battery bank. Of course the down side is this reduces the electric bill but provides no emergency power if the grid goes down.

I think many potential solar buyers are re-thinking things and want the main function to reduce their electric bills, but at least have some limited battery back-up capacity with a reduced size battery. This can also be a problem since most battery banks need the charge-discharge cycle typical for an off-grid system to keep their electrolyte mixed, which will not happen if 99% of the time all the solar power goes directly into the utility grid and the battery just sits there.

Hope this helps,

Jeff Yago


Cooling question

Jeff:

Where I'm looking at building my house on the farm there are several ground springs that run year round and have done so for the last 30 plus years that i can remember. Is it feasible to tap into this cool water source, run it thru several coils (like evaporating coils that a/c units use or several radiators) then pull air across/thru these coils to provide cool air in my home via a duct work system?

Thanks,

Bob
in North Mississippi

Bob:

Under certain conditions it is possible to do what you suggest, and this has been done for years from wells and ponds. Although I am sure this water is really cold in the winter, odds are it may not be as cold in the summer when you need cooling. This is important, as you need water going through a cooling coil below 50 degrees or you will cool the air without removing the moisture so you r home will be cool and humid which is not good! Every major manufacturer of air conditioners offer an optional water cooling coil sized to fit into the main supply duct from any air conditioning system. You will need one coil for each air handling unit in your home. I would buy one of these commercial coils as they are designed for minimum air resistance on your fan, they have a balanced water flow pattern from top to bottom of the coil, and they do not use lead solder or other harmful materials that you may encounter trying to use an old car radiator.

If your water stays above 55 degrees in the summer but is still below 65 degrees, you can still have real energy savings using a water -source heat pump. These are designed to pump cool water from a well, pond, creek, or pool through their heat exchanger, and will then produce really cold air from their compressor cycle. Since you will be using surface water for either application, you will need some way to keep sand, dirt, and small fish out of your water intake, and any screen will require regular cleaning unless your water source is really clear. Hope this helps,

Jeff Yago



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