How to design a Full Solar Home

Almost any new home can be a Full Solar Home

once you know how.

Choose a floorplan or general size, calculate the energy needed for that home in your area, plus vehicles, and calculate the number of solar panels you need (see below). Then combine the floorplan with the best structure to fit the solar array, starting with the options on this page.

The design approaches shown are suitable for any-

where that snow load is not an issue.

This is not about the strength of the roof. A well- insulated roof will not melt much snow. Solar panels covered in snow don’t work. These design approaches are simple, scalable and universal for areas where about 75% of new U.S. homes are built. Most homes will need much less solar than is shown. The number of solar panels it takes to produce as much energy as your home and vehicles will use annually (plus some extra) varies by location, your specific home, and how much you drive what vehicles. What you need to get started is a comprehensive calculation of the size of your solar array to enable designing the home. You can read more about this essential set of initial calculations we call the Comprehensive Solar Calculation (CSC) below. You can see the CSC for our example home here. We can do these calculations for you based on data you provide. See the Plans page. We determined that for most of Florida and many other areas 18 kW of solar panels will do the job for an average-sized home and two average EVs each driven 15,000 miles per year. Those panels with hybrid inverters, bidirectional EV charger and complete installation can be included for about $30K as part of new construction. If you need more solar than that, it will save you many times the extra cost. Go back to the calculator, increase the “Add for FULL SOLAR” amount by the appropriate percentage and see. As shown below, even more solar can fit on a smaller home than our example in this website. Combine your floorplan with a design approach that fits your solar array — with the panels facing south. It’s easy when you get past one little obstacle.

Shadows on panels cost performance. Shadows are less of an issue in summer when the sun is high in the sky (left) than in winter when it is lower (right). 3D shadow analysis is essential to maximize performance year round.

How to eliminate the rooftop problem that limits

solar.

You can’t fit many solar panels on a typical roof. Limited quantities and complicated installations increase costs. Panels that don’t face south lose 20% or more of their performance, raising costs per watt by another 25%. Of over 6 million U.S. homes with solar, and more every day, many can’t even cover the light bill because of the rooftop limits.

Reducing the tilt of the south-facing panels above from 27º to 10º at the location in the example will lose less than 2% overall output (annually). That requires only one more panel to offset the loss while you can make space for 15 more, depending on your location. The minimum tilt is about 10º for drainage and cleanliness. The farther north you go, the longer the shadows get and you hit the limit for panels sooner even as you need more. Moving the home north doesn’t reduce the solar output very much, but homes tend to use much more energy the farther north you go, both for heating and cooling (compared with Florida). That means more panels are needed. If you like this style, once you get above 30º North latitude, you may need to scale up the size of the home or take another approach.

Our example home is a “flat roof” design.

If this is a Full Solar home, where’s the solar?

So where’s all the solar?

The 2:12 sloped “shed” roof approach eliminates the shadow issue so you can rack the panels together close to the roof and fit even more solar on a home with the same footprint. “2:12” refers to the slope which rises 2 feet for every 12 feet of horizontal, an angle of 9.46°. We call that close enough to 10° for drainage. Of course, you can increase the roof pitch, but the rules change above 2:12, explained below. With these homes, the roof always faces south, but the floorplan can rotate depending on which way the front of the home faces. For any location where snow load is not a problem, these homes can fit more solar than you’ll need.

More to know about 2:12 roofs: materials and rules A 2:12 pitch is the absolute minimum for drainage of shingles and tiles, and you may need certification from the manufacturer before using them. There are numerous membrane roofing systems which are better for this application. Search “Low-Slope Roofing” and discuss with your builder or roofer. Once a roof exceeds a 2:12 pitch and more than 33% of the home’s roof area is covered with solar, additional safety rules apply. These include wider setbacks from the roof ridge and a clear, unobstructed pathway — typically 36 inches — from the eave to the top of the roof. These requirements come from the current International Residential Code and International Fire Code, and some jurisdictions add their own rules. Always consult your local building department and have engineered plans approved before starting any installation. Good news: standing-seam metal roofing works great at 2:12 pitch and there are panel mounting systems that clamp onto the standing seams without penetrations. Various configurations are approved even in High Velocity Hurricane Zones.

More about calculating your solar array: For a Full Solar Home, you need to calculate the energy load of the home and the vehicles. We can do this for you. See the calculation for our example home here. To order, see the Plans page. You can estimate the energy usage of the home by looking at the energy bills of comparable-sized homes in your area or consulting an HVAC contractor (you’ll need one anyway). The good news is that a home with a sealed attic will use much less energy for both heating and cooling than a similar home with a typical ventilated attic, so your calculation will have some cushion. If you use gas for heating, your Full Solar Home can cover that, too. A modern reverse-cycle heat pump/air conditioner is 3.5 times more efficient than normal electric heating, and the home designs shown here will accomodate the extra panels for heating your home as well as cooling. The gas bill can be translated into kiloWatt-hours for energy calculations. Determining the energy required for vehicles/miles driven is explained in an eye- opening brief article. Details on energy requirements of hundreds of EV models — and data for virtually all fossil-fuel vehicles — from the U.S. Department of Energy are here. This makes it easy to calculate the annual kWh of power needed for your vehicles. Now that you know how much energy you need to produce each year, you can calculate how many panels you need in your location. Solar Irradiance (sunshine) varies by location, time of day and hours per day/time of year. Irradiance data by location is available online, including here. The monthly data show your location’s kW-hours equivalent of full sunshine (1 kW/square meter) which varies throughout the year. It also shows the impact of the direction the panels face and the tilt angle. From this data it is simple to calculate how much annual output you can expect per nominal kW of solar panels. Next you need to allow for the efficiencies of the inverters and various other small losses, and the natural aging of solar panels over the years. Most panels today have a 25-year linear performance warranty that specifies the amount of derating over time. A large U.S. manufacturer guarantees 98% performance at the end of the first year, and no more than 0.5% less per year thereafter, for guaranteed minimum performance of 84% at the end of 25 years. (Note: our calculations for the example home include a few extra panels to compensate for this). We can do these calculations for you. See the calculation for our example home here. To order, see the Plans page. Or you can do your own. When you know how many panels you need to meet your annual energy requirements, you’re ready to design your new home. For information about the rest of your solar system, see the Plans page. With a little effort today, you’ll create the perfect comfortable and safe home for you and your family for many years to come. And cash in, too. We’re here to help.

More design considerations: Seal the attic and insulate the inside of the roof deck with spray foam. Despite the fact that a home with a sealed attic and insulated roof deck (instead of above the ceiling) will use about 30% less energy, most new homes still have ventilated attics and most insulation above the ceiling. It may pass code, but the builder is not paying the energy bills. We recommend open-cell low-density foam like Icynene directly under the roof deck, of which 8” will provide R-32, more than adequate in all areas where these designs are suitable. (Never use closed-cell foam on a roof). You can use rock wool or sound-absorbing mats on top of your ceilings for quiet. Your choice of exterior wall insulation depends on your construction method (frame, block, etc.). Wiring for your home should include a separate small electrical panel for critical circuits. When the grid fails, your own solar power will feed your home and charge batteries. When there’s no sunshine, the small panel allows lights, refrigerator, TV and internet, etc. to run off an optional small standby battery system (which can be added/expanded at any time) until an EV is present to fully power the home normally. Don’t miss the Features page for more.

Examples of 2:12 “shed” roofs

Our example home has 45 large 400-Watt panels. You can see that none of these conventional homes of similar size can come close to that.

We solve the rooftop limits two ways: with a

flat roof or a 2:12 (or more) sloped roof known as

a shed roof style.

All examples shown are only 50 feet wide and fit almost any building lot. All can be scaled up or down. The “flat roof” approach shown in our example home allows the solar panels to face south, at any desired tilt, regardless of which way the home faces, with the panels invisible from the street. The “flat roof” is actually two very low slope parts also tilted back for drainage, and the solar panel angles are adjusted by mounting hardware. The panels shown are shown facing south at a 27º tilt, optimal for its design location in Port Saint Lucie, Florida. The rows of panels are spaced to avoid shadows year-round. Reducing the tilt angle makes the shadows shorter so you can fit more rows of panels. While a panel facing east or west rather than south loses about 20% of performance, the tilt angle of a south-facing panel is much less critical.

Home faces south, panels face south at optimal tilt. If the home faces north, flip the panels. Full Solar Home. Home faces west, panels face south at optimal tilt. If the home faces east, flip the panels. Full Solar Home.

IQ-8.1

Shown: 45 panels @ 400W = 18 kW

Max capacity 60 panels = 24 kW

48’ x 52 Footprint’

25’ 10”

Click to stop.

The 2:12 sloped roof approach eliminates the shadow issue so you can rack the panels together close to the roof and fit even more solar on the same size home. “2:12” refers to the slope which rises 2 feet for every 12 feet of horizontal, an angle of 9.46°. We call that close enough to 10° for drainage. Of course, you can increase the roof pitch, but the rules change above 2:12, explained below. With these homes, the roof always faces south, but the floorplan can rotate depending on which way the front of the home faces. For any location where snow load is not a problem, these homes can fit more solar than you’ll need.

More about calculating your solar array: For a Full Solar Home, you need to calculate the energy load the home and the vehicles. We can do this for you. See the calculation for our example home here. To order, see the Plans page. You can estimate the energy usage of the home by looking at the energy bills of comparable-sized homes in your area or consulting an HVAC contractor (you’ll need one anyway). The good news is that a home with a sealed attic will use much less energy for both heating and cooling than a similar home with a typical ventilated attic, so your calculation will have some cushion. If you use gas for heating, your Full Solar Home can cover that, too. A modern reverse-cycle heat pump/air conditioner is 3.5 times more efficient than normal electric heating, and the home designs shown here will accomodate the extra panels for heating your home as well as cooling. The gas bill can be translated into kiloWatt-hours for energy calculations. Determining the energy required for vehicles/miles driven is explained in an eye- opening brief article. Details on energy requirements of hundreds of EV models — and data for virtually all fossil-fuel vehicles — from the U.S. Department of Energy are here. This makes it easy to calculate the annual kWh of power needed for your vehicles. Now that you know how much energy you need to produce each year, you can calculate how many panels you need in your location. Solar Irradiance (sunshine) varies by location, time of day and hours per day/time of year. Irradiance data by location is available online, including here. The monthly data show your location’s kW-hours equivalent of full sunshine (1 kW/square meter) which varies throughout the year. It also shows the impact of the direction the panels face and the tilt angle. From this data it is simple to calculate how much annual output you can expect per nominal kW of solar panels. Next you need to allow for the efficiencies of the inverters and various other small losses, and the natural aging of solar panels over the years. Most panels today have a 25-year linear performance warranty that specifies the amount of derating over time. A large U.S. manufacturer guarantees 98% performance at the end of the first year, and no more than 0.5% less per year thereafter, for guaranteed minimum performance of 84% at the end of 25 years. (Note: our calculations for the example home include a few extra panels to compensate for this). We can do these calculations for you. See the calculation for our example home here. To order, see the Plans page. Or you can do your own. When you know how many panels you need to meet your annual energy requirements, you’re ready to design your new home. For information about the rest of your solar system, see the Plans page. With a little effort today, you’ll create the perfect comfortable and safe home for you and your family for many years to come. And cash in, too. We’re here to help.

More design considerations: Seal the attic and insulate the inside of the roof deck with spray foam. Despite the fact that a home with a sealed attic and insulated roof deck (instead of above the ceiling) will use about 30% less energy, most new homes still have ventilated attics and most insulation above the ceiling. It may pass code, but the builder is not paying the energy bills. We recommend open-cell low-density foam like Icynene directly under the roof deck, of which 8” will provide R-32, more than adequate in all areas where these designs are suitable. (Never use closed-cell foam on a roof.) You can use rock wool or sound-absorbing mats on top of your ceilings for quiet. Your choice of exterior wall insulation depends on your construction method (frame, block, etc.). Wiring for your home should include a separate small electrical panel for critical circuits. When the grid fails, your own solar power will feed your home and charge batteries. When there’s no sunshine, the small panel allows lights, refrigerator, TV and internet, etc. to run off an optional small standby battery system (which can be added/expanded at any time) until an EV is present to fully power the home normally. Don’t miss the Features page for more.

If this is a Full Solar home, where’s the solar?

So where’s all the solar?

Reducing the tilt of the south-facing panels above from 27º to 10º at the location in the example will lose less than 2% overall output (annually). That requires only one more panel to offset the loss while you make space for 15 more, depending on your location. The minimum tilt is about 10º for drainage and cleanliness. The farther north you go, the longer the shadows get and you hit the limit for panels sooner even as you need more. Moving the home north doesn’t reduce the solar output very much, but homes tend to use much more energy the farther north you go, mainly for heating (compared with Florida). That means more panels are needed. If you like this style, once you get above 30º North latitude, you may need to scale up the size of the home or take another approach.

How to design a Full Solar Home

Almost any new home can be a Full Solar Home

once you know how.

Choose a floorplan or general size, calculate the energy needed for that home in your area plus vehicles, and calculate the number of solar panels you need (see more below). Then combine the floorplan with the best structure to fit the solar array, starting with the options on this page.

The design approaches shown are suitable for

anywhere that snow load is not an issue.

This is not about the strength of the roof. A well- insulated roof will not melt much snow. Solar panels covered in snow don’t work. These design approaches are simple, scalable and universal for areas where about 75% of new U.S. homes are built. Most homes will need much less solar than is shown. The number of solar panels it takes to produce as much energy as your home and vehicles will use annually (plus some extra) varies by location, your specific home, and how much you drive what vehicles. What you need to get started is a comprehensive calculation of the size of your solar array to enable designing the home. You can read more about this essential set of initial calculations we call the Comprehensive Solar Calculation (CSC) below. You can see the CSC for our example home here. We can do these calculations for you based on data you provide. See the Plans page. We determined that for most of Florida and many other areas 18 kW of solar panels will do the job for an average-sized home and two average EVs each driven 15,000 miles per year. Those panels with hybrid inverters, bidirectional EV charger and complete installation can be included for about $30K as part of new construction. If you need more solar than that, it will save you many times the extra cost. Go back to the calculator, increase “Add for FULL SOLAR” by the appropriate percentage and see. As shown below, even more solar can fit on a smaller home than our example in this website. Combine your floorplan with a design approach that fits your solar array — with the panels facing south. It’s easy when you get past one little obstacle.

We solve the rooftop limits two ways: with a

“flat roof” or a 2:12 (or more) sloped roof known

as a shed roof style.

Examples of 2:12 “shed” roofs

More to know about 2:12 roofs: materials and rules A 2:12 pitch is the absolute minimum for drainage of shingles and tiles, and you may need certification from the manufacturer before using them. There are numerous membrane roofing systems which are better for this application. Search for “Low-Slope Roofing” and discuss with your builder or roofer. Good news: standing-seam metal roofing works great at 2:12 pitch and there are panel mounting systems that clamp onto the standing seams without penetrations. Various configurations are approved even in High Velocity Hurricane Zones. Once a roof exceeds a 2:12 pitch and more than 33% of the home’s roof area is covered with solar, additional safety rules apply. These include wider setbacks from the roof ridge and a clear, unobstructed pathway — typically 36 inches — from the eave to the top of the roof. These requirements come from the current International Residential Code and International Fire Code, and some jurisdictions add their own rules. Always consult your local building department and have engineered plans approved before starting any installation.

How to eliminate the rooftop problem that

limits solar.

Our example home is a “flat roof” design.

25’ 10”