Basic PV Components - What and How Big?

[charlie b]

My company is doing the MEP design for a high-end private residence. The owner is considering putting a PV array on one of the buildings, either for water heating or for power. I have not done (and would not do, at least for this project) any PV design. That will be handed over to a PV supplier. We are in the early stages of design, and I need to get the architect to reserve some real estate for the PV-related equipment. Presuming it is only for generating power, and they want enough to cover the house and pool energy, here are my questions:

• How many “boxes” should I show on the floor plans, to represent PV-related components?
• What should I call each box (e.g., battery, inverter, etc.)?
• About how much space should I get the architect to set aside for this equipment?

 

[GoldDigger]

If you are really talking about heating the pool rather than running a pump, then you need to keep in mind that electrical resistance heating is one of the least efficient things you can with PC.
Solar thermal panels, on the other hand, can often be economical.

As for the size of the equipment, that really depends on how big a PV system is involved and whether it will be grid tied without batteries, off grid with batteries, or a hybrid of the two.
There are so many possible combinations of AC and DC wiring that I do not see much point in prewiring or even designating device space without some idea of the eventual system design.

 

[SolarPro]

Based on the fact that this is big spread with electric water heating, pool pumps and so forth, it's unlikely that the customer will be able to to offset all of their on-site energy consumption with a roof-mounted PV system. That being the case, the dedicated roof area will determine the PV system capacity and expected energy generation. For back of the napkin purposes, you can assume about 1kW of PV capacity per 100SF of roof area. Inverters get more powerful and compact every year, so the space requirements for any ground-mounted components are unlikely to be a problem, given that this is a large residence. If it is an issue, you can just specify module-level inverters, in which case you likely only need an additional ac electrical panel at ground-level.

The best way to ensure that the system that meet thee customer's expectations—for example, do they want/need battery or generator backup?—is to find a quality solar contractor and loop them into the project early, during the planning phase.

 

[TommyO]

My company is doing the MEP design for a high-end private residence. The owner is considering putting a PV array on one of the buildings, either for water heating or for power. I have not done (and would not do, at least for this project) any PV design. That will be handed over to a PV supplier. We are in the early stages of design, and I need to get the architect to reserve some real estate for the PV-related equipment. Presuming it is only for generating power, and they want enough to cover the house and pool energy, here are my questions:

• How many “boxes” should I show on the floor plans, to represent PV-related components?
• What should I call each box (e.g., battery, inverter, etc.)?
• About how much space should I get the architect to set aside for this equipment?

So - assumably this house will be on the grid?

Is this solar PV or solar pool heating thermal?

If PV, you need a space for the inverter(s). Not too different in size from a surface mount electrical breaker panel. Preferably located in garage or on north side of building (out of the sun)
And you need conduit to/from the inverter to the array and to/from the main electric panel.
How many inverters depends on how many kw of panels there will be. (which is related to how much power the owners will use)
Going to >10kW of panels may require extra work - depends on the AHJ.
Quite likely 10KW of panels or less and 1 inverter - but you could put in space in the plans for 3 inverters to allow for more. (relatively little space needed and lots easier to have the space and not use it than need the space and not have it.)

The bigger problem for the architect IMO is where to put the panels. (on the roof? how much roof faces south? or at least east and west? Required setbacks from the edges? ) Or if it's a ground-mount array, then it's where on the site does it go - what is the shading, etc.


If this is high-end and the owner really wants it, you may need to find a spot in garage or something for a Tesla powerwall. (waste of money IMO - but could very well be on the wish-list for a high-end residence)
Speaking of Tesla - you should also make sure you have a spot for the electric car charger - or at least spots with 220V power in the garage - probably multiple spots since I'm sure it's >2 stalls.
If the owners will be using electric car, that can be significantly more electric usage.

 

[ggunn]

My company is doing the MEP design for a high-end private residence. The owner is considering putting a PV array on one of the buildings, either for water heating or for power. I have not done (and would not do, at least for this project) any PV design. That will be handed over to a PV supplier. We are in the early stages of design, and I need to get the architect to reserve some real estate for the PV-related equipment. Presuming it is only for generating power, and they want enough to cover the house and pool energy, here are my questions:

• How many “boxes” should I show on the floor plans, to represent PV-related components?
• What should I call each box (e.g., battery, inverter, etc.)?
• About how much space should I get the architect to set aside for this equipment?

My advice is to subcontract the design work to an experienced PV provider very early in the project planning and let them work with the architect to lay out the modules on the roof and the positioning of the rest of the gear. Most rooftop solar is grid tied PV, but the number of modules and inverters, AC combiner panel (if needed), discos, meters, etc. and the space needed to accommodate that stuff is highly variable and very much dependent on the design and size of the system as well as the regulations imposed by the NEC and local ordinances. Most systems don't have batteries, but some do. Solar water heating is also out there and it is a very different animal from PV.

Free advice and worth every penny.

 

[jaggedben]

• How many “boxes” should I show on the floor plans, to represent PV-related components?
• About how much space should I get the architect to set aside for this equipment?

Reserve a 3ft wide space from floor to ceiling in a room that can provide the NEC required working space, such as the garage or a large utility room.
For every 10kw above the first 10kw, make the space 2ft wider.
If outside, put it where it won't get sun, e.g. north side.

• What should I call each box (e.g., battery, inverter, etc.)?

You can just call the whole space 'PV equipment' or 'PV BOS' ('Balance of System)'.

If there's going to be a battery (e.g. Tesla Powerwall), give it's own separate 3ft space nearby.

For back of the napkin purposes, you can assume about 1kW of PV capacity per 100SF of roof area. ...

Seems like that could be a large overestimate, depending on if you include fire setbacks if whether it's tilt up. It could be as much as 1.6kW per 100sf if you just count the area directly covered by modules.

The best way to ensure that the system that meet thee customer's expectations—for example, do they want/need battery or generator backup?—is to find a quality solar contractor and loop them into the project early, during the planning phase.

My advice is to subcontract the design work to an experienced PV provider very early in the project planning and let them work with the architect to lay out the modules on the roof and the positioning of the rest of the gear. ...

I can't agree more with the parts in red. It's so important. The architect needs to consider the PV when designing the roof and its support, and should get feedback from a solar professional on how to do so. I can't tell you how frustrating it is to be brought into a new construction project after the contractor has already built the roof in the absolutely worst possible way for mounting PV or orienting the modules. (A couple recent projects have had me alternating between shaking my head at the stupidity and tearing my hair out over the difficulties.) Obstructions such as vents and chimneys, and how they get routed to the roof, need to be considered, too.