Ask Jeff Yago
Solar & Energy-Related Issues
By Jeffrey Yago, P.E., CEM
Charging two different size 12v battery at the same time
I recently purchased a 15W. 12v solar charging system come with a controller. I wanted to connect the charger to my motorcycle all the time, since I don't ride it much. but at the same time I also wanted to charge a 12v deep cycle marine type battery which have much higher amps for other applications. I did asked tech support for advice. They told me to connect the battery in parallel, and the controlled will shut the power off when it senses the battery is at about 14v. I asked them would install another controller work. they don't seems to like that idea. I don't like the idea of connecting the battery that way, I think it will over charge the motorcycle battery. I need helps.
I do not like to connect different size batteries together, and it has nothing to do with your solar module. As soon as you connect both batteries in parallel to the same charging source, which ever battery has the higher voltage will immediately charge the other battery. It makes no difference if your solar charger is charging or not. I once forgot this fact and connected an RV marine battery which was fully charged to a second deep cycle battery which was discharged. I almost melted the #8 wire connecting them together since the low battery could take all the amps the charged battery could deliver as fast as possible.
The only time you should connect batteries in parallel, is if they are both the same size, type, and same state of charge. Of course you could connect two totally discharged batteries together in parallel and then connect them both to the same charge controller and there would no flow between one battery to the other since they are at the same voltage.
Your 15 watt module is way too small to do much charging, especially trying to charge a deep cycle battery. It will only charge about 1.07 amps in full sun which is about like a "trickle" charger. However, it would be about the right size to keep your motorcycle battery charged, so I would attach it to the bike and use a regular charger for the RV battery, or switch between batteries and charge separately..
Hope this helps,
We are about to build an alternative energy home here in Montana. I have heard that there are grants and financial help you can get from our government for building this kind of home. Do you know about these and if so, do you have any suggestions on how to find these?
Thanks so much.
No Federal Grants at this time that I am aware of. If you installed a solar PV system in the past 2 years there was a tax credit off of taxes you paid, but no money back, and you are too late for that one.
Some states have some fairly good tax rebates and system write-downs but each state is different. For example, North Carolina and New Jersey are pretty active in this area. Fir Montana, you need to contact :
State Energy Office Director
State of Montana
Hope this helps,
First off great web site and advice for those of us that have places off the power grid. I have several questions:
I have a cabin where I am fortunate enough to have a significant size creek that runs through my property. I have 60' of head for 1200' length of creek. My flow lets say is significant (creek is 15' + wide and several feet or more deep and is fast moving). Anyway, a local vendor sized a Pelton Wheel that would produce 700 watts an hour at approx. 16.8 kilowatts per day. The size pipe for the inlet he stated to be 5" minimum and 6" optimum estimated to take approximately 200 gallons per minute, which equates to no more than 1 or 2% of total creek water volume for the 1200' stretch run of pipe (water flow is significant even during low water months since it is primarily spring fed).
#1. Not being familiar with micro water turbines, does this appear to be one of the more efficient water turbines based on the pipe inlet size and head? I want to minimize as much as possible the size of pipe and water diverted to obtain the approx. 700 watts per hour (in other words is there different water turbines that are more efficient where my pipe size could be smaller and consequently divert less water)
#2. I plan on using appliances that are designed to use less electricity, e.g. propane washer, etc. and realize I will have to be careful what I run simultaneously. This being said, when I install a domestic well which would require a 1/2 hp pump (can't imagine going more than 100') I want to make sure I can start the pump since it will require more amps to start opposed to when it is running after startup. What would my battery capacity bank need to be designed to in order to have enough amps to start it since it appears the 700 watts per hour is sufficient for continued pump operations but short for startup (realize I also live in Idaho where the temperature is cold during winter and may reduce my batter efficiency)? Do I also account for some loss of amps based on the length of wire from my energy source (Pelton Wheel) to my well pump?
Thanks in advance,
First let me say, if you can fill a 5" pipe full with a 60 foot head, you are talking about way more power than 700 watts. Either your numbers are off or its time to talk to another vender!
Lets assume it is only 700 watts, which is 16.8 kWh per 24 hours which is still not bad since it is providing this output 24 hours per day, day after day. A typical deep cycle gold cart battery will store a little over 1 kWh of energy, and an L-16 size industrial deep cycle battery will store about 2 kWh. Therefore, if you match your battery to your daily usage and daily power consumption, you would need around 8 of the L-16 size batteries. With this much battery bank and a good inverter like a Trace or Outback sinewave model, you will have no problem starting most 1/2 HP loads.
However, before buying batteries, I would really recheck your head and flow capacity calculations as you may be selling power to the neighbors!
Two pipe steam system
I have a two pipe steam system, there is uneven heat distribution in the bldg..... the walls are hot and the floors are hot.
These valves cannot be turned off only down.
However, now that the temperature is 80 degrees due to the weather - the floors are still warm registering 84 degrees at times.
There is also vibration under floor like a grinding sound also.
There are no heating pipes under the floor only in the riser. There is water pipes under the floor.
Can you please offer me your expertise on what this issue could be, we can't figure it out
Next time please identify yourself -
There are several types of steam systems and you have not provided enough information for me to identify which type you have. Steam systems can be low pressure, medium pressure, or high pressure, they can have a condensate tank and pump at a low point or no condensate return, they can have temperature only steam traps, temperature and pressure steam traps, or even orifice type steam traps. However, I will give it my best guess based on the limited information you provided.
All piping in buildings move with a change in temperature. This can be heating hot water, steam, condensate, domestic hot water, chilled water, compressed air, you name it. Because all piping runs get longer when heated up and shorter when cooled down, we design "expansion loops" every so many feet of run which look like somebody ran the pipe around an object that is no longer there. As the pipe changes length, this combination of 4 right angle turns lets the piping flex instead of breaking. Also, a good installation will have this piping supported by a system of rollers supported by hangers tied into the floor or ceiling above. As the pipe changes length, the supporting rollers (usually located every 10 feet) roll instead of the pipe "rubbing" against a fixed support, floor truss, or wall opening. A 50 foot length of steel steam pipe will "grow" almost 1" in length when heated, so this expansion can be very loud if the piping is not allowed to expand properly or it is touching a wall or floor which will transmit the noise.
You said the noise is in the floor and you only have hot water pipes and no steam or condensate pipes under the floor. If this happens when the steam boiler is off and not heating then it would point to the domestic hot water piping as the problem. Keep in mind that every time piping passes from one floor up or down to another floor, there will be a metal support anchor that centers the pipe in the hole in the floor and helps keep the piping from dropping down. If the piping does not have the proper expansion loops and supports I have described in the horizontal runs, then the vertical supports will take the movement and not be happy about it. This could transfer expansion noise into the floor at these points.
If the system is old and not leaking, you may want to leave well enough alone or just insulate the piping to reduce cool down, since once the piping is hot it will not change length until it cools back down. Once you start working on old steam piping you usually find it starts to break or leak due to thin walls after years of internal corrosion. Make sure your boiler is not causing the noise and be sure it is operating at the right pressure. Most steam heating systems operate around 5 to 7 pounds of pressure, but check the equipment nameplate.
Solar powered generator
I want to plug in a light and radio in my garage. Rather than run an extension cord from the house, is there a product or a simple way that uses solar to do this? I want to be able to use it at night, so it would need to store energy.
The "simple" way you asked to do this with solar is not cheap.
You could buy a battery powered radio and not use any AC electrical connection. There are lots of low voltage battery-powered lights made for RV's and boats that you could power from a 12 volt RV battery that stays in the garage. They even have wall switches for this low voltage lighting and you could install more than one.
You could either charge the battery with a solar module on the garage roof, or just run your extension cord out to the garage once or twice a month and plug in a battery charger for a few hours.
If you want to power any 120 volt AC lights or appliances then you just jumped into the bid leagues for cost. Keep it low voltage DC and it will be "simple".
Solar powering a weekend cabin
I searched your archives as best I could for the information I needed, but couldn't find it. I'm sure it must be there, but it simply escaped me. So I'll ask anyway and hope for the best.
First of all, I have to be the least knowledgeable person that has ever presented you with a solar question, I'm kind of like a monkey with a math problem when it comes to all this stuff, but here goes.......
I have a 320 acre hunting place and weekend retreat on the Missouri/Arkansas stateline. Since we bought that place 3 yrs ago, we also bought an older and larger 5th wheel camper and parked it there permanently. Perhaps a key thing to mention is that we're almost never there more than a weekend, with the exception of two or three 3/4 day stays during deer or turkey season, per year. We do not have running water or electricity, and have no desire for it. The camper with its standard RV gas/electric fridge, cook stove, and 12 volt lights more than meets our needs and expectations. I haul 10 gallons of fresh water which more than meets our needs, and we keep a few 5 gallon jugs in the camper at all times for the RV toilet, for the girls on the rare times they actually go with us, the guys have to use the outhouse. For the most part we don't visit during the hot part of the summer, but our heat source during the colder months has been wood heat pumped in via gravity flow from outside, basically a standard indoor wood stove converted/jacketed into an outdoor wood furnace. Our needs have been more than met with the camper the last 3 yrs, one battery per weekend, occasionally two if the girls tag along. More space is the only thing we've been wanting, along with something reasonably attached to the earth
Within the next 30 days, we're having a metal building constructed to serve as a cabin and we'll get rid of the camper once we have the cabin operational. We will still not have running water or electricity, don't really even want it. We have agreed our needs should not be allowed to change. We'll simply hook up this cabin like a camper with 12 volt RV lights, water pump, propane stove and fridge and we'll continue to haul about 10 gallons of fresh water from home on these weekend visits. Last Friday my six 12 volt, 5 watt solar panels arrived. My thought was to simply put a little charge back on the battery during daylight hours, that we run off during the dark hours. Lights for the most part are the only thing we power up, but the 12 volt RV water pump will be a new draw on the battery that we've not had before, but that should be it. If we've made it fine in the past on one battery by itself, and as long as we don't increase our power usage from what we've grown accustomed to the last 3 yrs, wouldn't 30 watts of solar trickle charge during the daylight hrs really put us over the top now??
Can I simply wire these six, 12 volt, 5 watt solar panels together and connect them to the battery??
Can it stay hooked up all weekend??
Do I have to employ some of these different attachments I've read about like control boxes, inverters, etc... all that stuff??
Please tell me I can just keep it simple and wire these six solar panels up to the battery and forget about it from Friday night to Sunday night when we go home. All I want to do is put a little trickle charge back on the battery during the day Saturday & Sunday.
Unless I'm way off track on this all together, and assuming I can do what I've mentioned above for the most part, is there any reason I need to unhook the solar panels from the battery after the sun goes down in this weekend scenario I've laid out?? I might add, I plan to attach my solar panels to a piece of plywood, and have a quick detach mounting system attached to a post outside the cabin, no more than 6 feet from the battery location inside. I'll remove the panel board and keep it in the cabin to prevent damage and theft, and only put it out and connect it when we're there.
Jeff..........am I completely off base with all this, or am I on the right track???
Jay Don Johnson
I have a few suggestions that might help in your case. First, it would have been much better to have a single larger solar modules than six smaller ones. There are lots of electric current balance and fusing issues when you wire more than two or three modules in parallel which is what you will be doing (parallel = 12 volts, series = 72 volts). Second, 30 watts is not much power to re-charge a deep cycle RV/Marine battery which is what I hope you are using (not car batteries).
The only way this might be enough power would be if you mounted the solar modules and left them charging during the weeks you are away. TO do this you would need a good solar charge controller to protect batteries from over-charging. If you are going to bring the solar modules in each day you will not need a solar charge controller because you will not generate enough charging to raise the battery charge level. Example - A typical RV/Marine deep-cycle 12 volts battery will provide supply a 8 amp load (@ 12 volt DC)for 8 hours, or a 4 amp load for 16 hours, assuming you do not totally discharge the battery below a point that it will be damaged. A total of 30 watts of solar modules will have a total output around 2.3 amps in full sun. This means it will take 28 hours for these solar modules to re-charge this battery after it is discharged, or about 5 days with a typical summer sun-hours for your area of 5-1/2 hours per day of full sun.
These small solar modules in the 5 to 10 watt range are not intended to do what you are trying to do.. They are to leave plugged in for days at a time to keep a battery fully charged when it is not being used, or the re-charge all week a battery that is only being used on the week-end.
You should get a single 75 to 110 watt solar module which can easily be carried in and out if you are not going to leave it outside when you are gone. This will be large enough to almost match your day-to-day usage over a long week-end, and would be about 26" X 62" in size and weigh around 28 pounds. I would also add a solar charge controller and a DC rated fuse between the battery and the charge controller. If you check your RV, there is a DC fuse panel attached to the battery converter (not inverter) which should show you how all this gets wired. You may also want to check some of the back issues where I describe this type of system ---> www.backwoodshome.com/articles2/yago93.html
On another note, I would purchase a 55 gal plastic barrel. These are one-time use for transporting non-toxic liquid and food type products are many firms will give them away just to get rid of them after they are empty. I would put this up high in your new metal building (be careful, it will weigh almost 500 pounds full of water. This will gravity feed a shower or toilet without any pumps or electrical power. You can fill it with a hand-type crank pump or a 12 volt DC pressure pump from ground level rain water barrels from roof-run off, and add some bleach when you fill the tank to keep from growing algee. Note - I suggest not using this for drinking water and keep it covered to keep out un-invited 4 legged guests! You can drain the elevated tank and piping when you leave if there is a risk of freezing.
Stock tank heaters
Help, I am trying to find a way to keep my stock tanks open in Minnesota winters. I have been using regular stock heaters but last year with three going my electric bill in Jan-Feb went up by nearly $200. A sand point well is not an option, at this time. Why three? Beef, Sheep ewes and Ram different pens, plus chicken heater and a dog dish heater for the cats.
Is there a way to use solar to power the heaters? It seem they would draw to much. I'm willing to try something for next winter. The main cattle tank is in the open near the barn.
You are not the first rancher to ask me this. Of course, you can power almost anything using solar power. Unfortunately, the cost to do what you ask will most likely be far higher than you will be willing to pay. For example, using the $200 cost to run your electric stock tank heaters for 2 months and an average cost of $0.08 per kWh (you can substitute your actual cost), this equals 2,500 kWh of power usage for 2 months, or 42 kWh per day (2,500 / 60 days). The winter hours of "direct" sun at your latitude will average only about 4 hours per day, so a solar array would need to be 10.5 kW in size (42 / 4) to provide this much power every day. Using an average cost of $8 to $10 per watt for a grid-tie solar system, your system would cost over $84,000 !!
As you see, the problem is the fewer hours of sun in the winter, the high cost of solar equipment, and the wasted solar power a system like this would have in the months it is not heating the tanks. Of course you could install a much smaller and lower cost solar system for your home, and the smaller year round energy savings could equal the added $200 winter bill for just the tank heaters. A solar system that saves $20 per month for 10 months of power generation would equal the added $200 usage for the other 2 winter months, but this system would only need to be 1.7 kW in size ($20 / .08 / 30 days / 5 hrs) and would cost in the $14 to $17,000 range plus installation.
You may want to stay with the heaters you have, but consider using reduced size watering tanks just for the winter that have heavy insulation around the tank and added wind protection on 3 sides and top to reduce the heat loss. Reduce the heat loss of the tanks and you can cut this electric cost in half.
Solar converted to electric batteries
Can you hook up a solar converter to charge the batteries that power an automobile; can this technology be applied to power an entire home?
We just installed a huge generator so we have power during hurricane power loss-we live on the water in Miami Beach. This generator could be a back up...it now powers up after a 60 sec. power loss.
If you mean can you keep the standard car battery charged when it is parked the answer is yes. My truck has 2 heavy duty batteries and I have a 100 watt solar module on the roof that keeps them fully charged as the truck may be parked for weeks at a time. If you mean can you actually power a car, you would need a vehicle that is very efficient already like a Hybrid. However, most Hybrids cannot operate on just batteries alone without the engine. The best solar cars I am aware of are actual conversions from a standard engine to an electric motor, and a trunk full of batteries and controls. There are now companies that make these kits and one of the easiest to convert is the Chevy S-10 pickup. People with these conversions park their cars next to a solar array and charge them while they are not being used.
Of course this is a problem if you are only home at night (no sun) and you need the car during the day. Some solar PV systems supply power back into the utility grid during the day, and then just charge their electric cars at night with an equal amount of grid power for a "zero" energy usage. There are some Prius Hybrid owners adding extra batteries into the back of these vehicles which allows them to operate only on batteries with no engine when they are in city traffic. However, batteries add lots of dead weight and this really reduces vehicle speed and how far it can go on a charge.
Back in the early 80's I drove an all electric van that looked like a small UPS truck. There was some king of grant that allowed a company in Pennsylvania to build a whole fleet of these for the Post Office. However, the each required batteries that weighed over 2000 pounds each, and I could only go about 30 miles without another all night charge.
Until the all electric cars are made more efficient, about the only all solar cars you will see are those in solar competition and most look like an airplane wing with the driver laying flat on their back.
Hope this helped,
Invertor/charger ground subpanel wiring
Remote off the grid cabin questions - Generator supplied AC via extension cord to inverter/charger AC input cord on a 1000 watt continuous 12 volt invertor with built in 20 amp charger auto transfer switch hooked up to a 12 volt 200 AH battery bank and invertor output was then wired again by male end cord ( 3 wire-black to gold -white to silver -green to ground) and the other end cut off and hardwired into a small AC subpanel from HD with one 15 amp breaker installed which is then wired by romex to one outlet inside the cabin ( tv and one or two lights 100 -150 watt load range ) the subpanel is "white neutral/green ground"- bonded and then grounded by earth ground. what should I do about grounding the invertor ? another independent seperate earth gound? as the subpanel is white neutral green ground bound already is that enough of a ground? thats how you do AC in the subpanel but if i ground the invertor to the same earth ground it will complete a circut and fry it wont it? I like the ext cord setup because i can quickly completely bypass the invertor setup and run gen AC only if I have a heavier load up to the cords rating.
DC inline fuse and battery cutoff switch have been installed in the DC battery bank but I dont know what way to ground the invertor with the subpanel hookup? should I just go back to an extension cord (gangbox on the end) from the invertor ouput to the cabin or is it ok to use the small subpanel setup and romex with just the one earth ground?
I also wanted to ask about connecting a solar panel to my DC bank I understand the invertor hookup of going to opposite ends of the battery bank to even out flow should a solar panel be placed on the same pos and neg ends or the other two distant ends? or doesnt it matter?
thank you for your time
This is too much specific design detail for a "free" web site. However, I can give you some general grounding guidelines as defined by the National Electric Code:
First, you should not be wiring all this "permanent" type electrical equipment with extension cords! Also, with all this mix of wiring and grounding, if you have ANY neutral line from the generator, circuit breaker panel, or inverter tied into the ground wire or ground rod at more than one location, if you then get a loose or broken connection on any neutral wire you can fully energize the bare ground wires at 120 volts AC which can do lethal damage if you are the path to earth!
You need to check your generator manual as some generators have GFI plugs, some have a "bonded" neutral to generator frame ground, and some have a "floating" neutral and a separate ground. This can cause problems if the transfer switch does not match or if the panel dublicates this bonding to ground.
Yes, you should try to "balance" the output from the array just like the battery bank. THe frame grounds on each solar module should be connected to a contineous bare copper ground wire which "bonds" to any dis-connect box metal housings and then on to teh sme earth ground rod as the other equipment. Note, this only attaches to metal frames and not the electrical terminals.
Everything should take place in the circuit breaker panel - It should have a neutral buss bar to connect all the neutrals (insulated white wires) and a separate grounding buss bar to connect all the bare copper ground wires, and the #6 bare copper wire to the ground rod driven in the ground. All whites and bare grounds should remain separated and not share the same connection points. However, you will have a single "bond" between them using the green bonding screw that comes with the breaker panel - refer to the instructions.
The inverter should have 3 wires over to the circuit breaker panel, black (hot) connected to main panel input circuit breaker, white (neutral) , and a bare copper ground wire to the indicated grounding screw on the inverter. Remember, standard circuit breaker panels are designed for 120/240 which requires an L1 and L2 input, so if you supply from only a single 120 volt inverter, you will only be able to use circuit breakers down one side of the panel. Note how they will alternate left and right on the buss bars.
Since you are wiring the generator directly through the inverter first, your loads on the circuit breaker panel are limited by the 20 amp transfer switch inside the inverter. This means if your generator is larger than 2400 watts (20 amps x 120 volts) your inverter will not handle anything above this amount. If you have a larger generator, I would have two circuit breaker panels, wire the generator directly to the "main" panel as 120/240 volt, so you can power larger loads. Put a separate circuit breaker in this panel that then feeds the inverter input. Come out of the inverter and supply the buss bars in a smaller separate sub-panel. Any loads on this panel will operate anytime generator is running, not running, no difference. Any loads on the main panel will only operate when the generator is running, but this will keep them from running down the battery since they do not go through the inverter. In all cases, all the neutrals are connected to neutral buss bars (which are tied together from panel to panel), all the bare copper grounds are connected to the grounding buss bars (which are tired together from panel to panel) , and you only bond the neutral to the ground at ONLY one bonding screw point.
I would use wet rated UF wire from the generator to the house, and NO extension cords. These are not sunlight resistant, they are not insulated for this type application, and they are not heavy enough.
Hope this gets you started, but please be careful and get some expert help,
Solar heating and hot water radiators
I live in a 100 + year old house, which is heated by an old oil furnace. Heat is distributed by hot water radiators. I am going to have to replace the furnace in the near future and since I already have a radiant heating system in place, I'm wondering if the technology exists that would allow me to heat and store enough hot water to heat my house using solar energy. I know that I could heat my domestic hot water, but if I could heat the house itself too, that would be ideal.
In terms of my geographic context, I live in Nova Scotia.
Any feedback you could provide would be greatly appreciated.
Due to the high cost of solar hardware, it is usually not cost effective to install on old and un-insulated homes. We only put solar heating systems on very well-insulated homes with specific window placement, very high insulation values in the floors, walls, and ceilings, and calk every crack and construction joint to stop air infiltration. This is usually too costly to do on homes this old. However, your hydronic heating system can be re-used and is a very good way to heat.
I would spend my money on a new high-efficiency combustion type hot water boiler and re-use your existing hot water heating loops unless this piping is starting to have problems. The money you save on fuel will far exceed the cost/pay-back for a solar space heating system on this type home.
Getting into the energy conservation field
I live in Richmond and am considering a change in careers. I'm currently an IT professional, but would like to learn about careers in the Solar/alternative energy fields. I have a degree in Industrial design and my fiance' is an Architect AIA, LEEDap.
One of our goals is to build a solar house, so I've been doing research and have visited solar houses and find that the field is very interesting to me and want to look at possibilities of a career change. However, I have no idea about the various roles in the discipline or even the certifications required to work in the field.
Thus, I'm writing you to get some direction/perspective on the possibilities. If possible, I'd like to discuss the options. If you are still in the Gum Springs area as I've read, I'd be glad to buy you lunch and have a talk. If not, a phone call or email would suffice.
Any amount of direction you can give me would be greatly appreciated!
I look forward to hearing from you,
Sorry I cannot meet as I am covered up and traveling almost every week. I will however, provide a few suggestions:
There are plenty of people selling solar hardware and parts, just check the Internet. However, most do not really understand how to design, size, and install the technology. I just took on a client who ordered all his components over the internet. He saved thousands of dollars, but ended up with thousands of dollars of mis-matched parts, hardware that was not right for their application, the wrong size and type cables and fuses, missing parts, and they could not find anyone in the state who knew how to make it work. This is actually very common.
The real shortage is in qualified solar installers. Since an installer must know more about electrical codes and wiring than anything else, a good installer would be somebody who was a licensed electrician first, and attended additional training classes to learn the solar part. I have seen many others try it the other way and fail. They knew alot about solar systems, but did not know which end of a wire cutter to hold, what type grounding methods will pass an electrical inspection, how many wires are allowed in a certain size conduit, and a thousand other code requirements to keep the solar system from burning down a house by starting an electrical fire.
Check out the NAPCEP licensing program for solar installers. Many of the classes can be taken on line. There semi-annual testing has had an increase of over 50% since last year, and it may double this year. You would need an electricians license, understand all sections of the National Electric Code then go for the NABCEP certification.
The states of California, Florida, New Jersey, and Arizona install 96% of all solar systems in the U.S. at this time. If you really want to get into the field, these are the states where you can really gain experience.
Wishing you success in your goals,
Solar Powered Attic Fans in Hawaii
I live in Oahu HI, and even though we live up pretty high, 800 ft, the heat gets pretty darn hot in the summer. Yes Hawaii kind of does have a summer.
Anyways, insulating the attic/roof to keep our one level house cool isn't very cheap. We just went up in the roof and it has no insulation at all, and it is smoking hot, and you can feel the heat on your hands by touching the ceiling. The walls are cool though. The carport connects to the house and has a vent up front. And there is no vent in the rear of the house.
Will a Solar powered Attic fan cool our house any? The average temperature is 80 degrees out side. With doors open and all the windows open it is very warm, around 80-90 degrees. In the attic its only insulation is the sheetrock for the ceiling throughout the house. We have soffit vents on the side of house throughout.
We have split AC's in the bedrooms, but no AC anywhere else throughout the house.
Thanks, Steve Sumner
An attic vent fan would really help your case as long as you have several other things taken care of. Generally, we either fully insulate the under-side of a roof (commercial buildings with un-insulated drop ceilings), or we do not insulate the roofs at all and instead put heavy insulation on the ceiling (with attic above).
You cannot do much about your hot roof and the roof shingles are designed for what you "feel" as hot. However, this heat will transfer down into the underside space. This is really true when you have an attic with un-insulated underside of the roof and only insulated the ceiling beoiw. However, this is also the best arrangement to benefit from an attic powered vent fan. Almost all homes are designed with a "soffit" vent, which is a long louvered metal strip just under the roof eve around the sides of your home. Older homes had round holes covered with screen before the made the aluminum vent strips. In addition, homes usually have a "ridge" vent, which is a space at the very top peak of the roof that runs end to end to let out the heated air as cooler air enters into the eve vent below. Sometimes this ridge vent is there, but you cannot see it from the outside as some newer types "lift" up a small space under to top row of roof shingles. If you do not have this ridge vent then you will have metal or wooden louvers covered with screening at each end of the side walls at the peak of the roof. These are not there to make you cool. This venting is to take away moisture which can damage the insulation.
If you already have an insulated ceiling below the attic space, then by all means, adding a powered attic fan at one end of the sidewall of this attic space will drop the attic temperature 10 or more degrees, and this will lower the hot ceilings of the rooms below which reduces your air conditioning loads. They also make solar powered vents that fit into a cut-out in the actual roof, but this is more difficult to install and seal out the water than an end wall vent fan. Some people is areas that do not require much air conditioning will install a large "box" fan in the ceiling of the home, which blows air out of the house up into the attic. Of course this will require leaving open a few windows so air can get in to make up for what is being exhausted up into the attic, and lots of vents in the attic so this air can get hot. If your humidity is low, this air flow will not only cool the home, but reduce the temperature in the attic which also makes the home cooler.
Hope this helps,
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