Solar PhotoVoltaic Planning

So you are thinking of installing a solar PV system on your new house. It's true that solar has come down in price, and more rooftops are sporting the shiny panels everywhere you go. But don't wait till your new house is built and then try to slap panels on the roof as an afterthought. There are several things you should keep in mind to assure that your new roof is ready to handle the additional loads, and that you won't end up spending extra to make the solar installation work.

(Image Credit: Greens MPs / CC BY-NC-ND)

Build smart so you need a smaller system

When most people first start thinking about solar power, they have a utopian image of solar panels that deliver an endless supply of free power that not only powers their house, but actually ends up making them a profit every month back from the power company! A great thought, but it's not quite that simple, and the numbers don't work out that great. Once you start crunching the data and realize how much power your family burns thru every month, you will likely find that you need a system that costs $50,000, that will barely cover your consumption. Divide out the payments, and some incentives and you may break even if you are lucky after 15 years. You are certainly helping reduce the carbon footprint, and there are other intangible benefits, but the costs tend to dishearten a lot of buyers.

Most solar companies want to sell you panels, and thus it's not in their interest to think about creative ways to tip the scales in your favor. If you are building a new home, however, planning for solar power is about far more than just planning for solar panels. Start thinking about ways you can build smarter to cut down on the energy demands of your house. For example a typical house might need a 7KV system to meet the energy needs of the household. What if you could cut down that energy load 50-70% by making smarter choices about how the house is built? Your biggest loads are from heating and cooling your home. Don't build a loose house that is simply wasting half the energy to the air outside, and then spend double keeping it comfortable. Start by building a super-insulated shell that keeps your conditioned air in, and requires the minimum amount of energy to keep it comfortable. Think about all your light fixtures, appliances, and what is consuming the most. Spend the money on building the tightest house, that consumes less energy to begin with. Drop that energy load to 3KV, or even less. Now your solar system only needs to be 1/2 or 1/3rd the size. Your total cost may be the same at first, but you will enjoy a far more conferrable home, without drafts, with better air quality. You will end up saving on a smaller heating system, smaller cooling system, maybe even get back some square footage that was lost to huge HVAC equipment. And you will have far better chances of coming out with a $0 utility bill with a far less expensive solar PV system.

Make sure your roof is built to take the extra loads

Solar PV systems put additional loads on your roof. You want to make sure your roof is ready to take the additional stress, and will give you years of trouble free performance without leaks, or costly repairs, or worse. Talk to your engineer early in the design stage, and make sure the PV system is planned into the load calculations. You can not only rest assured that your roof is ready for the extra load, you may be able to plan for mounting points that provide a solid foundation for the panels to attach to and avoid unexpected up-charges at installation time for additional reinforcements, and structural upgrades.

Think about orientation to maximize your energy returns

The amount of energy your systems outputs is dependent on, you guessed it, the amount of light that it gets everyday. You don't want to find out after your house is built, that no part of your roof provides the ideal amount of sunlight, nor do you want to install a system that is operating at 50% of its potential output. Take advantage of your home design stage to orient at least one section of your roof to provide the maximum about solar gains. For most of us in the northeast you are looking at having a south facing roof section that provides enough square footage for the amount of panels you need. But the exact angle makes a difference, as does the angle of the roof pitch. Plan these details early and get the most you can out of your investment.

Plan for wiring penetrations in advance

Ok, so you got everything right, your house is the tightest, most super insulated house in town, and the installers are on the roof. They pull out their drill and start punching holes where it's most convenient for them. So much for the airtight shell. You try to ask them to be careful, and their supervisor tells you to relax, the've done this hundreds of times, and this is the right way to do it. Plan the wiring locations, and especially any wall penetrations early with your engineer. Don't wait till the installation crew is on the clock and thinking about tearing thru your walls so they can be done before lunch time. Make sure all the penetration points are well designed and sealed off against any air leaks, and water infiltration running along down the conduits and creating water damage between your walls.

Leave room for the inverter

Solar systems output DC power, which is generally run down from the roof with heavy gauge wires to an inverter that converts it to AC line voltage that your house can use. You may be able to reduce some cost by reducing the amount of distance from the panels to the inverter. Instead of runnig 70' run of heavy lines to your basement, it may cost less to run 15' to a location in the attic, and then run lighter wires from there to you panel. Talk with your engineer, and the PV system designer to find the best location for the inverter. Regardless of where you install it, save the space for the inverter so your installation goes smoothly