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Rob Will
04-27-2008, 10:36 AM
Where are some good sources to buy photovoltaic panels? With a few pointers, I can install them myself.

What is your opinion of solar panels that track the sun? Are they worth the extra cost and will they stand up to wind?

I have 3-phase electricity w/ open Delta config (one leg measures 230V to ground). With the correct equipment, can I connect photovoltaic panels to one or both of the "normal" phases without messing with the wild phase?

There is a small hill with southern exposure and no trees directly behind my house. I also have an electrical shed out back that is the main distribution point for for the house and several buildings. Is there an easy way to connect panels out there without running wires into the house?

I realize that the cost / benefit ratio of this can be a challenge. I just think it would be a good thing to do and want to learn more.

Thanks for any advice or suggestions you care to offer.

Rob

Brian Elfert
04-27-2008, 10:49 AM
A solar system is a generally a LOT more than just the panels. There are batteries, charge controllers, and inverters among other items needed.

The panels generate DC power that must be converted to AC unless you have DC stuff you want to power. Systems can be 24, 36, or 48 volt depending on the panels and how they are connected.

I don't know if you can do a system without batteries. A system with no batteries certainly can't provide electricity at night or during low light conditions. A charge controller controls the voltage from the panels so the batteries get charged properly and don't get too much voltage.

An inverter is used to convert the DC power to AC power and they generally cost $2,000 and up for a decent sized one. I'm sure they make three phase models for even more money.

I would contact the folks at www.thesolar.biz (http://www.thesolar.biz) for a solar system. They seem to have good prices and they gave me good advice on batteries for a system that is not solar.

On edit: The reason for 24 volts and up is basically to reduce wire size required. You can do 12 volt, but that is generally for RVs that have 12 volt electrical items. 12 volt amperages can get really high and require expensive wire.

Mike Henderson
04-27-2008, 11:05 AM
As Brian pointed out, there's a lot more to a solar system than just panels. There's one big factor to check before you figure out the cost/benefit. Some power companies allow you to put your excess power into the grid through your power meter. What this does is run your meter backwards when you're supplying power to the grid.

The net effect is that you're selling power to the power company at the same price that they sell it to you. So if you can generate enough in the daytime, you can suck power off the grid at night and not pay anything until you exceed the amount you sold them.

This is not sustainable for the power company but right now, many power companies do it because it's too costly for them to install the equipment to meter the back and forth flow of power.

This allows you to use the grid as a "battery". You still need to have real batteries on site but you won't need as many. Also, it's tough to generate as much power - through solar - as most homes use, but you can reduce your power bill through solar.

Mike

Rob Will
04-27-2008, 11:24 AM
Thanks guys,
There is little danger of running the meter backwards around here (I wish there was):o. What type of bateries are we talking about, lead-acid?

Rob

Jeff Bratt
04-27-2008, 12:05 PM
I've never heard of a 3-phase solar installation, although it is technically possible. Maybe it's because residential areas generally don't have 3-phase power... Anyway, you need an inverter to convert the solar (DC) to AC and a disconnect to tie into the commercial grid. You can do a lot of the installation work yourself.

Contrary to other posts, on-site batteries are not required if you are hooked to the grid. A system that includes batteries costs much more, and is less efficient. With a grid tie installation, you can run your electric meter backwards and reduce your electric bill to zero, although generally the power companies will not pay you if you generate more than you use.

Tracking panels provide about 15% more power per day than a fixed installation, at additional cost and complexity. Most installations use fixed panels.

A recent estimate was around $9000 per installed kilowatt of solar capacity for a no-battery system. The 2'x4' panels can generate around 150-200 watts each. A rule of thumb is an average of 6-7 hours of "full capacity" power per day - if you live in the southern latitudes of the US.

Another site with more information is http://www.windsun.com/

Mitchell Andrus
04-27-2008, 1:28 PM
The net effect is that you're selling power to the power company at the same price that they sell it to you. So if you can generate enough in the daytime, you can suck power off the grid at night and not pay anything until you exceed the amount you sold them.

This allows you to use the grid as a "battery". You still need to have real batteries on site but you won't need as many. Also, it's tough to generate as much power - through solar - as most homes use, but you can reduce your power bill through solar.

Mike

Mike I know you're using extreme shorthand while summing up the concept - as long as we all remember that this arangement will go away as soon as the power companies sell closer to zero power during the day and normal capacity at night and on rainy days. Once the model goes 'upside-down', rates will go up to feed the beast (utility shareholders) and will effectively wash out any consumer benefits. The more people with installed panels, the sooner the model collapses. If we all had panels, who would we sell power to? The utilities don't store it for evening use.

Also, the 'battery' analogy is a quickie hook for a concept... we all know that the power company has to generate 'fresh' power at night. The power you pumped into the 'battery' on a sunny day is used up the instant it's created.

Mike Henderson
04-27-2008, 3:14 PM
Mike I know you're using extreme shorthand while summing up the concept - as long as we all remember that this arangement will go away as soon as the power companies sell closer to zero power during the day and normal capacity at night and on rainy days. Once the model goes 'upside-down', rates will go up to feed the beast (utility shareholders) and will effectively wash out any consumer benefits. The more people with installed panels, the sooner the model collapses. If we all had panels, who would we sell power to? The utilities don't store it for evening use.

Also, the 'battery' analogy is a quickie hook for a concept... we all know that the power company has to generate 'fresh' power at night. The power you pumped into the 'battery' on a sunny day is used up the instant it's created.
You're absolutely right, Mitchell. There's no way the power company can buy power at retail prices and stay in business. And my "battery" concept is just an economic concept - as you pointed out, there is no storage in the grid.

You also pointed out one of the problems of some renewable energy sources - the power company has to have the generation and distribution capacity to supply reliable power, even when the sun isn't shining and the wind isn't blowing. When you add the reliable generation and distribution costs to the renewable generation capacity, it makes the renewable energy very expensive.

But because of the cost of solar installations, there's not many of them yet and many power companies are doing as I mentioned - buying power at retail. But that won't last forever.

I was not trying to mislead people and appreciate you expanding on the shorthand I used.

Mike

Mitchell Andrus
04-27-2008, 4:37 PM
I was not trying to mislead people and appreciate you expanding on the shorthand I used.Mike

There are still some who cling to the pie-in-the-sky concepts and just don't 'get it' yet. You should see some discussions on forums devoted to this stuff.... Yikes!!! You'd think converting junkyard Vegas to electrics and putting 100 55 gallon drums of warm water in everyone's basement are real-world solutions.

Short-term, we need to get our own, state-owned oil production to produce oil for the USA so we don't have to buy at world prices. Not too much to ask of the greatest nation of earth. Long-term, a "Manhattan Project" style approach to nuclear power generation and cut the BS. Sooner or later, homes on oil and/or heat will need to convert to electric... we can't handle it as-is.

Chris Padilla
04-27-2008, 4:55 PM
I'm heating my pool using the sun...still need 'lectricity to run the pumps, however. :)

Change is always in the air....

Jeff Bratt
04-27-2008, 4:56 PM
Around here, the power company has already broken out some costs in the electric bill. We have separate charges for "distribution" and "generation".

While you are correct that the power companies cannot in general "buy at retail", the actual price of generating power is not the same all the time. "Peak power" - during the day - is expensive, while "night power" is cheap. Especially in the sunbelt, peak time is in the afternoon, when solar power is most available. So the power companies are actually OK with getting power from your solar panels during the day and then providing you with power at night. Most retail customers don't (yet) have time sensitive pricing, but large facilities often do.

Some of the most expensive electricity is generated by natural gas "peaker" plants that are built to be turned on quickly during heat waves, and then only get used three or four times per year. And there are already power "equalizing" plants that pump water uphill at night and then will use that water to drive generating turbines if needed during the day. And newer commercial air condition systems will "make ice" - or chill some appropriate refrigeration liquid at night, then use that for cooling/air conditioning during the day.

While the cost of solar power is generation is not now economically competitive with established baseline generation facilities, if costs associated with emissions of sulfur compounds, carbon dioxide, etc. get factored in the economic equation gets much closer. And if the efficiency of solar cells continues to increase, it will become viable solution for large-scale power generation.

For a proposal about very large-scale solar power generation see - http://www.sciam.com/article.cfm?id=a-solar-grand-plan

Joe Pelonio
04-27-2008, 5:05 PM
I don't think it would work here, we go as many as 35 days without seeing the sun. I have decorative a solar light in the patio that light up nicely in July and August. :mad:

Rob Will
04-27-2008, 5:07 PM
OK, let's keep this small and simple. What if I want to install a solar powered security light system on the roof of my shop?

If I make no attempt to grid tie the panels, what would be required to operate about 300 watts of fluorescent security lighting?

Rob

Mike Henderson
04-27-2008, 5:20 PM
OK, let's keep this small and simple. What if I want to install a solar powered security light system on the roof of my shop?

If I make no attempt to grid tie the panels, what would be required to operate about 300 watts of fluorescent security lighting?

Rob
Cost is a serious problem. Let's say you run those lights 8 hours per day, 365 days per year, and you pay $0.15/kwh. The total cost of those lights will be about $131 per year (if I did the math right).

There's almost no way you could recover your cost for a solar installation, especially since you'll have maintenance costs for the system.

Mike

Rob Will
04-27-2008, 5:33 PM
There are still some who cling to the pie-in-the-sky concepts and just don't 'get it' yet. You should see some discussions on forums devoted to this stuff.... Yikes!!! You'd think converting junkyard Vegas to electrics and putting 100 55 gallon drums of warm water in everyone's basement are real-world solutions.

Short-term, we need to get our own, state-owned oil production to produce oil for the USA so we don't have to buy at world prices. Not too much to ask of the greatest nation of earth. Long-term, a "Manhattan Project" style approach to nuclear power generation and cut the BS. Sooner or later, homes on oil and/or heat will need to convert to electric... we can't handle it as-is.

Actually Mitchell I asked the question because we need to explore energy sources other than burning fossil fuels. I have a 10,000 gallon diesel fuel tank in my front yard that needs to be filled before next month. Believe me, when that bill comes in the mail it brings a $35,000 reminder as to just how much we are dependent on fossil fuels. With the amount of fuel that my business consumes, I have no illusion about finding any one easy solution. Fortunately, I can afford to buy a couple of solar panels. There is nothing wrong with having an open mind and trying to learn about new technologies that may eventually help us all.

Rob

Jeff Bratt
04-27-2008, 6:54 PM
A grid-tie system is simpler - however - quick and very rough estimate:
One panel puts out 150-200 watts. So two panels would power the 300 watt security lights while the sun is shining. Now, those panels cost several hundred dollars each...

If you want 8 hours of light (at night) that's 2.4KW-hrs
Should be 2-3 panels, charge controller plus battery storage for 12Vx200 amp-hrs, times a reserve for cloudy days. That will add several hundred dollars. If part of the service time is during the day, the battery storage capacity could be lower.

If you want 24 hour light: 300 watts x 24 hours = 7.2KW-hrs
Looks like 7-9 panels, battery storage for 12Vx500 amp-hrs (for nighttime), reserve, etc. Total will be thousands of dollars.

As Mike pointed out, costs for a completely off-grid system are high. You'll have to contact a solar system dealer for actual estimates. Also for an estimate of solar radiance in your area.

However, for a grid-tie scenario, if you just bought - let's say - 2 panels at $800 each. They will work, almost maintenance free (cleaning if doesn't rain?) for 20-25 years. At Mike's $130/year ($0.15 per KW-hr for 300 watts x 8 hours per day), there is a payback, but the time is still quite long - 12 years. If the price of electricity goes up, that time could be shorter. Note: this does not include an inverter - and 2 panels is probably too small an installation to justify a grid tie. Still, the payoff times are usually in the 15-20 year range.

Is that 10,000 gallons of diesel for generating your own power? Then you would have to figure your own power costs for comparison.

Brian Elfert
04-27-2008, 9:16 PM
One issue with renewable energy that is not always on is that many power generating plants cannot just start up in an instant. A number of power plants have generators that cannot ever be shut down except for overhaul. The armature in the generator is so heavy that it will flat spot if it ever stops spinning.

We do have lots of peaking power plants for high demand days, but they are much more expensive to run.

Mike Henderson
04-27-2008, 9:35 PM
One issue with renewable energy that is not always on is that many power generating plants cannot just start up in an instant. A number of power plants have generators that cannot ever be shut down except for overhaul. The armature in the generator is so heavy that it will flat spot if it ever stops spinning.
Brian - Just a question for interest - How are those generator armatures installed originally or after an overhaul so as not to create a flat spot? In other words, what's the difference between the original install and a shutdown?

Mike

Rob Will
04-27-2008, 11:34 PM
Good point Mike,
If I do this, it will be more or less a demonstration project. I think it would be fun to do but you're right.....not much chance of making a profit.

For now, I'm just fishing to see if costs have come down and if there is a practical way to do this.

Thanks,
Rob

Chris Padilla
04-28-2008, 1:51 AM
Rob,

Do a web search on Homepower magazine. It might help guide you.

Mitchell Andrus
04-28-2008, 7:52 AM
There is nothing wrong with having an open mind and trying to learn about new technologies that may eventually help us all.

Rob

Absolutely right. I replaced my home gas furnace with a high efficiency unit. Savings in gass will not cover the cost of the unit for 15 years assuming the cost of nat gas stays on-pace with CPI.... Short term pain, long term benefits.

Open minds are a good thing. Our collective bent towards flash-in-the-pan come-ons and painless, quick solutions encourages the snake oil salesmen. They are going to be out there, and so are the gullible with money to burn. Today's solar technology is yesterday's whale oil.

See my sig.

Rob Will
04-28-2008, 10:57 AM
[quote=Mitchell Today's solar technology is yesterday's whale oil.
See my sig.[/quote]

So do you see any application for solar power?

Like you, I have high efficiency gas furnaces.
Good equipment is not cheap - regardless of the energy source.

Rob

Mike Cutler
04-28-2008, 11:18 AM
Brian - Just a question for interest - How are those generator armatures installed originally or after an overhaul so as not to create a flat spot? In other words, what's the difference between the original install and a shutdown?

Mike

Mike

The generators very rarely stop moving, and when they do it is for very short periods of time. It is done though. Ours is offline right now.
A "convential" turbine driven generator will operate at 1800 RPM. When the turbines are taken off line for repairs, PM's and mod's the entire turbine, or just the genrator can be kept rolling at a very slow RPM.
While flats spots are certainley a consideration, the combined length for a multi stage turbine generator is pretty long, and there are 100's of tons of weight involved. Of more consideration is sagging along the shaft which would induce vibration when the turbine is up to speed. 100's of tons of rotational mass at 1800 RPM,any induced vibration can be a very bad thing. 5-7 mills can easily be felt throughout the whole station .
Removing a generator, Armature/Stator, is a very big operation. I've only seen it done twice in my 25 years of working at a nuclear power station.

As to the other point brought up in this thread, not by you, about it taking too long to bring a power plant online. That's a misconception. A gas fired turbine can be brought online very quickly to provide power. There are companies that maintain their gas turbines idle and only bring them online for short periods of time when the cost of electricity is high. Of course they can also delay bringing them online and drive the price higher. Some of these turbines may only be placed online for just a few hours.


Mitchell

I'm going to disagree with some of your position, but I respect the things you have brought up as discussion points.
Electrical generation rates are not going down.They are only going to go up, and now that distribution is seperate from generation in some states. You actually have two seperate bills combined into one, each independent of the other. Either of which can be increased. Creating a situation where solar power can be a viable alternative for powering a residential application.
To go totally off the grid might cost upwards of $35K for me.
With my average electrical bill, here in CT, that system would pay for itself in about 19 years. With the orientation, area, and pitch of my existing roofs,a low profile system could be close to 96% efficient according to the calculators.
Retrofitting an existing home to solar can be very cost prohibitive, but a new construction home, designed from the ground up is a viable option. If I were building a new home. It would be solar/geothermal. Not totally off the grid, but supplemented.
Don't worry about the electric company losing any money on paying residential generation rates for a solar powered system. We're not going to lose money, I promise. The reserve capacity can be sold on the market, and there is always a need for power.
I believe that in a few years we will begin to see more individual solar systems in residential applications. Of course then it will get intersting to see how the feds and states get their share of the pie.

Greg Funk
04-28-2008, 1:55 PM
Mike I know you're using extreme shorthand while summing up the concept - as long as we all remember that this arangement will go away as soon as the power companies sell closer to zero power during the day and normal capacity at night and on rainy days. Once the model goes 'upside-down', rates will go up to feed the beast (utility shareholders) and will effectively wash out any consumer benefits. The more people with installed panels, the sooner the model collapses. If we all had panels, who would we sell power to? The utilities don't store it for evening use.

Also, the 'battery' analogy is a quickie hook for a concept... we all know that the power company has to generate 'fresh' power at night. The power you pumped into the 'battery' on a sunny day is used up the instant it's created.
The model of treating the power company works quite well with respect to solar power because you really can't put up enough panels to come anywhere close to replacing current conventional power sources. But it can be useful to reduce utilities requirements to build new capacity for growth. If solar power supplied 5-10% of overall electrical requirements that would mean fewer new gas or nuclear plants would need to be built. Electrical prices will continue to rise with the price of natural gas, solar panels will come down in price and the payback and economic viability will continue to improve.

Here in BC solar power is still a long way from economic viability as we have cheap (6c/kWHr) hydro power (and not enough sun) but we can't build new powerplants for that price anymore so our rates will slowly rise and eventually it might be viable here.

Greg

Mitchell Andrus
04-28-2008, 4:10 PM
So do you see any application for solar power?

Rob

ANY??? Yea. Passive heating for non-essentials such as pools and storage-freindly low use systems like showers and dishwashers.

In areas where the sun works best - we need it least. On St Maarten solar works GREAT - but not for heating homes. You don't need to heat homes where the sun shines the hottest. In Upper Saskatchawan heating is needed the most but the sun doesn't shine with enough intensity... Solar is not the solution we hope it is.

When lower class people living in the rust belt states start paying $2K, $3K, $4K for heating costs in an average sized home - look out. The solution for these homeowners isn't going to be a $30,000 solar system that only supplies 50% of their heat.

Are you willing to take down a few 60 foot trees on your property so your neighbor's panels catch the sun? Me neither. Tell your neighbor his trees are casting too much shade on your proposed solar feild and see what happens. Medium scale solar isn't the solution and the faster we realise this, the faster we'll move towards a real-world solution.

Lee Schierer
04-28-2008, 4:23 PM
I'm heating my pool using the sun...still need 'lectricity to run the pumps, however. :)

Change is always in the air....Speaking of change, you can pump the water with a windmill and be completely green! :D

Mitchell Andrus
04-28-2008, 4:23 PM
Mike


I believe that in a few years we will begin to see more individual solar systems in residential applications. Of course then it will get intersting to see how the feds and states get their share of the pie.

Tell your next door neighbor to take down his trees because they cast too much shade on your proposed panel location.... Let me know how this goes.

People who can affort to install systems, can affort to buy power at market rates and then the proposal is moot. There isn't enough insentive for the average homeowner - who, by the way, ask thier kids to set up their ipods.

I think we'll be on widespread nuclear/electric decades before we see even moderate use of individual solar systems.

Jeff Bratt
04-28-2008, 5:07 PM
I previously provided a link to an article that proposes a plan large-scale solar power generation for the US. The obstacles for solar power are economic, not technical (like fusion reactors). Experimentation in solar power generation is on-going. There are generating plants in the southwest that have been running for years. As the cost of fossil fuels and emission controls rises, and solar cell conversion efficiencies get better and manufacturing costs fall, solar power is already becoming economically viable.

Solar is not the only choice for new large-scale power generation, nuclear and geothermal are additional possibilities. Just as today, the power grid in the future will include a mix of technologies. And there is "inertia" in the system - for example, the cost per KW-hr of hydropower from existing dams is really cheap, partly because the infrastructure is already built. But that doesn't mean building lots of new hydro is a good idea - construction costs are high, and suitable locations are scarce. But this example of a power source that doesn't burn a fuel is a good example for development of future electrical generation facilities.

John Hemenway
04-28-2008, 5:51 PM
We just (last November) installed a 4.2 Kw array. In California you can 'sell' back power to PG&E. During the summer peak hours (noon-6pm) we get 3x normal rate for excess but pay 3x for what we use. Shifting use (dishwasher, dryer, aquarium lights) to off peak and paying 1x for off peak means we are net producers. We pay electric bill once per year. So far we owe about $220. This will come down as we are just getting into the real production time. It's mostly cloudy Nov. to March here and few clouds and no rain April thru Oct.

Our BPV (before photovoltaic, :) ) use was about $250/month. System cost about $25K. At current rates for power we will break even in 10 years - less if (!) rates go up.

One place I see the utility making money is not actually paying for power we generate but giving us credits. If there is an overproduction on our part they get it for free. We have jokingly considered running extension cords to the neighbors so they can tap off our 'extra'.

Is it the solution? No. If it was possible to actually sell back to the grid then it would be possible for investors to buy into PV for profit. I believe this is what happens in Germany.

Mike Cutler
04-28-2008, 7:23 PM
There isn't enough insentive for the average homeowner - who, by the way, ask thier kids to set up their ipods.

Mitchell

I love your insight. That sentence is absolutely perfect.:D
I still think that you will see a growing shift to solar power in some form. Will everybody be able to do it? Unfortunately no. To be truly efficient requires some pretty ideal conditions, and the neighbors trees are certainly part of it.;)
It's starting in the southwest and the southern states, where the condition are more ideal, but even here in the Northeast it can be done.
I'm not sure that it's simply a question of affording solar, versus buying at market rates. I would expect that a viable, professionally designed system would also return some of the investment at the sale of the house. It's a numbers game though, no doubts there.

Lest it sound as if I'm some nostalgic hippie, with stacks of High Times magazine and the Whole Earth Mother News laying around. Believe me, I'm not. I'm just a guy trying to figure out why it is that here we are, in the most technologically advanced country in history, and the most economical solution to heat a house is to burn wood like a cave man.:eek:
The price of electricity is going to go up significantly in the next decade or so. The demand is only going to increase,and the supply is not increasing at the same rate. The cost benefit of alternative sources of energy will change.

By the way. I like your position on Nuclear Power. I'd like to see more plants built also. We, as a country, do need to address the long term waste issues associated with nuclear power to move forward though.


Oh yeah. Tennessee would be perfect for solar.:D,

Jason Roehl
04-29-2008, 7:28 AM
Honestly, I think nuclear is where it's at. Solar, wind and hydro power are all "piddle power". Even together they can't come close to providing a significant amount of the energy this country uses. All of them are limited in where they can be successfully deployed. That said, I think they have their place. While I don't have a PV panel, I do have a solar hot-air box on my roof that does help in the winter--on a sunny day in the winter it can keep the furnace from running for about 6 hours. I'm looking into building another of my own design at some point, perhaps even adding a PV panel to power a DC fan for the system (but that's the expensive part).

Mitchell Andrus
04-29-2008, 8:00 AM
I do have a solar hot-air box on my roof that does help in the winter--on a sunny day in the winter it can keep the furnace from running for about 6 hours. I'm looking into building another of my own design at some point, perhaps even adding a PV panel to power a DC fan for the system (but that's the expensive part).

Jason... pictures please.

Jason Roehl
04-29-2008, 7:29 PM
Sorry it took so long to get one up, Mitchell, but I thought I had one somewhere (didn't find one), and that whole work thing got in the way, too. Anyway, here it is:

The panel is approximately 4'x8'. I measured it months ago, but don't recall those quantities exactly, so 4'x8' is as good as it gets for now. The solar "box" contains a thermostat of sorts, the ducting is all 6" insulated, the blower is ~0.2 HP/380 CFM, with a fuse and switch located in my pantry (the hot air duct runs from the attic down through the pantry to the basement). The intake for the system is in the main floor hallway, outside the bedrooms. The house is a rectangular bi-level, with the bedrooms at one end over the garage, and a family room, 1/2 bath and stairs next to the garage. The hot air blows into the family room downstairs. I'm thinking of building another box and maybe putting a stronger blower on the whole thing--it needs a new blower anyway. The existing one didn't work when we moved in last June, but I got it going for a while. The leads out of the motor are shot, though, and the squirrel cage squeals to a halt. The assembly was left exposed in the attic, and I think there were condensation issues on the exposed metal of the blower housing, so it's partly a rusty mess. Whatever I do, I will enclose the blower in an insulated box.

Mitchell Andrus
04-29-2008, 9:44 PM
What provisions have you made for dumping heat during a power failure? - Assuming you don't want to over heat (and can) to the point of causing damage or a fire. Have you measured power-off upper limits a bright summer day?

Jason Roehl
04-29-2008, 10:15 PM
There are no provisions for over-heating. When it's warm enough outside that we don't need it anymore, I flip the switch. It was not operational last summer (like I said, we moved into the house in June), and I didn't get it running until maybe late September. Otherwise, I'm sure it's no different from any other enclosed space in the summer--it will get hot, kind of like an attic. Remember, this is just a box--nothing real special about it--no PV, no electronics, no heating elements, just a box that get hot in the sun with a thermostat that triggers a small fan. What comes out of the one HVAC diffuser is comparable (probably a bit warmer) than what comes out of an HVAC diffuser connected to a forced-air gas furnace. If/when I build another, it will be an insulated box, painted black on the inside with double-strength glass. The inside will have an s-shaped airpath with spoilers in it. (Actually, I want to build and install 4 or more on our church, which also houses a daycare, to cut down on the propane bill in the winter).