Solar power for garage addition

[Mesozoic]

I'm in the process of having plans drawn up for my garage addition, which will double the area of my existing 900 sqft unit (attached) for a total of 1800 sqft. Based on the way the trusses run, my general contractor (personal friend) has stated that the entire roof (built up roof) will need to be replaced in the process. I am considering implementing solar power collection to run HVAC for the entire garage, but I'm unsure if that's a realistic proposition and/or what type of infrastructure would be needed. Does anyone have any experience with this?

I live in southern Arizona where sunlight is plentiful. I'm imagining that I need some kind of energy storage unit, like a giant capacitor or battery array, as well as a controller/inverter to make the power useful to power an HVAC system. I'm also unaware of what structural amendments might be wise to make to minimize roof related repairs as a result of physically supporting the solar panel units and conduit.

 

[mm08822]

Since you are having plans drawn up, I would have the roof loading sized to handle worst case of 1 side completely covered in panels.
Make sure the drawings include notes stating trusses are sized to handle the future solar panels (size XxY and W pounds/sqft) so you don't get hung up with more design cost later if you do go ahead with solar. This way today's plans cover the future need.

Consider the pitch of the trusses equal to ( or as close as practical) to your latitude degree. At least the solar side.

Any chance to orient the garage roof plane due south?

Forget batteries - too much cost upfront and ongoing maintenance. Stay with string inverters or micro inverters. Both much cheaper and more reliable.

Look into AZ regulations for PV solar now so you at least understand today's requirements.

 

[Git]

I think you need to have a couple of solar contractors come out to your house and 'educate you' about what is going on in your area with solar. Listen to their sale pitch, but make it clear your not going to be signing a contract with them that day

Like mm08822 posted, unless you have money to burn, using batteries is not going to be cost-effective. You probably need what is called a 'grid-tied' system. Any excess electricity your panels generate flows back on to the electrical grid and you get credit for it. Conversely, when you need electricity at night, you use (pay) for electricity from the grid.

Solar can be a win-win - both for the homeowner and the environment, but the numbers have to work for you. You're in a good area for exposure, but they're also needs to be a reasonable net metering agreement (how much the utility will pay for your excess solar energy) in place to make it work

 

[theoldwizard1]

I am considering implementing solar power collection to run HVAC for the entire garage, but I'm unsure if that's a realistic proposition and/or what type of infrastructure would be needed.
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I live in southern Arizona where sunlight is plentiful. I'm imagining that I need some kind of energy storage unit, like a giant capacitor or battery array, as well as a controller/inverter to make the power useful to power an HVAC system.

You just jumped into VERY DEEP WATER ! Too much to cover here.

First, it will be EXPENSIVE ! Second, why just the garage ?

The REALISTIC approach is to install a "grid tie" system. You "harvest" the solar energy and sell what you don't need back to the power company.

This actually cost effective (assuming you size the system correctly). Typical pay back is less than 10 years (and this keeps ging down as solar panels get less expensive).

 

[kd3pc]

You might be better served speaking with an HVAC firm that does "solar" as you phrase it. You will be hard pressed to run a large HVAC system with "solar". You will require quite a bit more than panels, and even in AZ, payback for all that may be decade or longer, if then. Night time = no PV panel power, so you will need batteries.

Check with your local power company about grid tie and what is required and what it costs to do so.

 

[99LeCouch]

Like others have said, solar and batteries to run HVAC by itself is very expensive. It can be done, but be prepared for sticker shock. Li-ion batteries are expensive in cash, lead-acid batteries need a lot of time managing charging and lots of space to house enough to cover the load. The cheaper option is a grid tie system that is sized to generate enough electricity to cover annual use.

And, find out your local electric utility's policy on billing for customers with solar power systems. It could be net metering with a rolling credit for excess generation, it could be they pay wholesale for excess generation. The billing determines how beneficial it is to install solar, and how fast it pays back. Unless the system is supposed to be islanded, and not tied to the grid.

 

[PNWguy]

The only thing that really going to matter, is how the power company treats any "extra" power you generate.

In general, your panels will be making electricity during the day, and the house/garage will be using some of that power. Some days, you'll be using less power than you make and other days you'll be using more power than you make. If you have a surplus of power at the end of the month, some power companies will pay you and others will just keep it. This varies around the country.

Depending on how your power company deals with the excess power will determine how long it takes to pay off the system.

Call a few solar installers, and be ready to give them the last 12 months of electric bills. In AZ, I could see you paying off the system in as few as 7 years (for example, you pay $25,000 now and over 7 years save $25,000 off your power bill - after that , your power is free). It's possible to get loans on the system if you don't have the cash. There are other financial options as well.

But you really need to call a few installers *now* before the plans for the new roof are complete.

 

[dcg9381]

I am considering implementing solar power collection to run HVAC for the entire garage, but I'm unsure if that's a realistic proposition and/or what type of infrastructure would be needed. Does anyone have any experience with this?

I have some experience with it. I've installed a few residential solar arrays for home builders and installed one for myself on a garage with HVAC.

Short answer for what you want to do:
Install a solar array (assuming your roof is oriented correctly) large enough to offset your HVAC (really, total) electrical costs monthly.

Get with your electrical utility provider. Ask them about solar and "net metering". Basically you want to treat the grid like a battery. When you have lots of sun and you're not using the AC, the meter runs backwards. When you're using AC and not producing enough power, it runs forward. You try to get enough solar that your energy use is "near zero" (net). It's like a maintenance-free battery that stores energy credit (dollars) in most cases as long as you balance things out.

In my area, my utility provider tallies my energy use and energy credit every month. Last month (it's been hot) - I used a little more power than I produced and had a $12 bill. This is for a shop that probably fully spins up the HVAC only twice a week.

Producing MORE solar power than you need doesn't help you - typical utilities "buy" credit (if they will buy credit at all) at wholesale prices, so the payback on produced power is very low. You want net use near zero. I can sell my provider power, but they only give me a fraction of what they charge me when I buy power from them.. But they have to offset energy use in a 1:1 manner as long as I use more power than I produce.


You can do all this "off grid" - but the costs of batteries, required maintenance, and finite life of batteries makes this sort of storage non-ideal and much more expensive than using the grid. Do it only where there is no utility or grid....

The only real use case for battery power (or Tesla-style battery cells) is areas of the US where the cost of electricity can vary substantially at certain times. And even in those cases, it may still not make sense.

 

[FrancisJ]

Net metering ended in AZ and the current rates don't pay..............I'd stick with evaporative cooling augmented with refrigerated for those nasty Monsoon Season weeks, spend the money saved on 1/4" rattle snake fencing....

FJ
Univ of AZ Class of 87 (EE)

 

[Bretny]

AAA the grand dreams of "free" power.

 

[dcg9381]

Yuck. AZ did killl net metering recently.

OP, ask your utility what the deal is on their interconnection agreement. If you don't want to go through it, you can post it here. What I'm reading says that the removal of net metering only impacted the credited rate by about 10%, which still makes things feasible. Assuming I've got that right.

If not feasible, it'd simply mean that you downsize your array just to cover your "typical" usage of power during the day... Basically so you're consuming most of what you produce rather than sell it back to the grid.

I'm still in the "no" category on storing solar power - the required batteries are expensive and/or maintenance hassles. And even the Tesla stuff - requires more than one to be able to handle the sort of high-amp use that can be typical of some of our garages.

 

[FrancisJ]

Tesla makes hyped garbage, products that are simply stupid --- like their "solar shingles" which only work on certain roof orientations and limit the pitch (photon capture optimization) forcing architects to go with unattractive (lower pitch) roof lines.

 

[Kaizen]

Systems like this that I have seen are very well designed by pro’s if they have no grid tie in. Look at the payback and incentives if you buy the panels. It is huge differences state to state. As said do a grid tie so you have cooling at night in summer. Also consider you will need great insulation and super efficient minisplit s or the like. All costs will drive up your roi


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