Can you power a house completely with solar panels?

Let’s say that you’ve decided not only to go solar, but you want to go all-in. Can you completely power your house with solar energy alone?

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If you’ve used our solar calculator or looked at the map of solar homes around you, you’ll know that going solar is pretty easy and increasingly common. As the price continues to drop, it becomes affordable for more people. But what if you want to go completely solar? What if you don’t want to use any fossil fuels at all in your home?

Yes, it’s possible for solar panels to supply all of the electricity your home needs. The first step is to maximize your energy efficiency with insulation, air sealing, and efficient appliances. Then, move off fossil fuel heating to electric heat pumps, and replace gas cooking and water heating with electric. Once you’ve done that, a correctly sized photovoltaic system can be used to power everything in your home. But does it make sense?

This guide will explain how you can go completely solar in your home. But before we launch into it, let’s clarify what it really means when we talk about making your house completely solar.

Do you:

  • Want to generate all of your current electricity usage with solar, but leave some appliances, like your stove and furnace, using fossil fuels?
  • Or do you want to move 100% of your home energy use to solar? This is called net zero.

That first goal is in reach for many modern homes. Going net zero - or getting close to it - is technologically possible for some existing homes, but you will need space for a larger solar array, and extensive retrofits may be required. Whichever the case, this guide will walk you through the steps.

About my house

First, let me tell you about my house. It’s a solar house, of course. Here it is:

My house with solar panels
That’s my house!

This house is in Buffalo, New York. It was built in 1910, so it wasn’t constructed anywhere near to modern efficiency standards. We bought it 10 years ago and retrofitted it for energy efficiency as best as we can.

Our net electricity usage last year was about 2,100 kWh. The average house in the United States uses 867 kWh per month, so our net annual usage was about about two and half months of the average household.

The attic is air sealed and has about R-60 cellulose insulation. The walls have blown-in insulation. The basement slab, unfortunately, isn’t insulated, but we’ve air sealed around the rim joist. The ducts for our forced air furnace are taped and wrapped in insulation. Some of the windows have been upgraded to new double-pane glass, but some are old single-pane windows with metal track storms.

All the lights inside are LED, and we use a smart thermostat to make sure we aren’t heating or cooling the house when we aren’t home. Heating is by natural gas.

The biggest electricity hog in our household is the air conditioner. Even though Buffalo has a reputation for snow, the summers can be hot and sticky.

We can’t go net zero, but maybe you can

The house is pretty small, and as you can see, the roof has the maximum number of solar panels already. Going fully net zero - replacing our natural gas usage with electricity - is not in the cards for us. We don’t have the roof or backyard space for more solar panels.

If this is something you want to attempt, here’s the approach you would take.

Get an energy audit

A professional energy audit will tell you exactly where your home energy budget is being spent. This is a great idea even if you’re aware of that fact that your home is leaky and under-insulated, because it can tell you the upgrades that will give you the biggest bang for your buck.

For example, spending a few dollars on sealing leaky ductwork in your forced air HVAC system will have a much, much higher payback than installing new windows. A good energy audit will give you a comprehensive analysis that tells you the high priority retrofits that you should tackle first.

Efficiency before everything else

If you’ve read my guide to going solar, you’ll know that the first step you should take is to make your house more energy efficient. There are some easy things you can do, after which the energy retrofits start to get more extensive, and expensive.

In my house that’s more than 100 years old, we’ve done all the easy and cost effective energy retrofits, and some more expensive ones, such as replacing some of the windows. If we wanted to completely eliminate our electricity bill in this old house, we’d either have to dial up the thermostat in the summer and suffer through the heat, or replace all of the old windows as well as rip off the vinyl siding so that we can add polyiso board around all of the exterior walls.

That would get pretty expensive for us, high enough that it would take a very long time for us to recoup the cost. But if you have a newer house, you probably have higher efficiency to start with and are in a better position.

Start with The Solar Nerd cost calculator

To find out how many solar panels you need to meet your current electricity needs, just plug your current monthly kWh usage into the calculator. The calculator takes into account your local climate, and uses your estimate of your roof’s angle and orientation to make an accurate projection of your solar power generation and the number of solar panels that you’ll need.

Level 1: moving your current usage to 100% solar

After running the calculator, you’ll have a good estimate of how many solar panels you’ll need to generate 100% of your current electrical usage.

If you know your roof’s dimensions, you can roughly estimate if you can fit that number of panels on your roof. Or, if you’re ready, work with a professional solar installer who will be able to give you detailed site proposal.

What happens if I can’t get a solar array large enough to supply 100% of my electricity?

If your goal is to provide 100% of your electricity with solar, it’s possible you won’t have enough roof space to generate that much power. If so, here’s a few things to look into:

  • Do more to reduce your energy usage. Have you already done all the easy energy efficiency upgrades that you can? If not, you definitely want to start there. If you’ve already taken that step, you may need to consider more extensive energy retrofits. Are you already using electricity for heating or cooling? If so, see how efficient your equipment is. If it’s older and inefficient, consider upgrading to better, more efficient equipment.
  • Use the highest efficiency solar panels you can. With solar panels, there’s a pretty wide range of efficiency, from around 16% up to 23%. That’s almost a 50% difference, so switching from cheap panels to the highest efficiency ones on the market can dramatically reduce the number of panels you need. SunPower and LG are two companies currently making excellent high efficiency panels.
  • Use power optimizers or microinverters. In many conditions, power optimizers and microinverters will extract more power from your solar array than less expensive string inverters. (Our guide to solar inverters explains this in detail.) This can improve the output of your system without increasing its footprint.
  • Consider creative ways to expand your array. If you can’t fit any more solar panels on your roof, you could consider different options for expanding your array, such as using the roof of your detached garage, a ground mount in your yard, or even a solar awning or canopy. Check out these cool-looking residential projects.

Think about whether net zero is possible - or even desirable.

If you’ve managed to achieve our level 1 - generating 100% of your current electricity needs with solar - congratulations! That’s a great achievement, and if every homeowner did this, it would have an immensely positive impact on the economy and our environment.

Taking it to the next level - going net zero, or even getting close to it - is a goal that some people have. It’s much more feasible to design a new house to be net zero, but if you’re retrofitting an existing home, it can get seriously expensive to add enough insulation and upgrade your heating system to make your home efficient enough to power it completely with solar.

Still, it is possible. One builder was able to retrofit a 20-year-old house to be net zero, and here’s another one in North Carolina.

An important thing to note is that, in addition to a tightly sealed building envelope with lots of insulation in the attic, these homes also use advanced framing techniques so that more insulation can be packed into the walls.

This can involve double thick walls, or a type of engineered wall called a structural insulated panel (SIP). This is a feature that’s not easy to retrofit into an existing home.

These homes also take care to insulate the basement walls and slab. If that wasn’t done at the time of construction, this can be an expensive retrofit.

Deep energy retrofits may never pay for themselves

There’s something of an 80/20 rule when it comes to net zero homes. That is, you can spend relatively less money to get most of the way toward a net zero house, but the final steps to get to 100% energy self-sufficiency can get very expensive.

As described by the good people at Green Building Advisor, deep energy retrofits are often misguided, and a lot of savings can be achieved with more modest approaches to energy efficiency.

Ways to switch from fossil fuels to electricity in your home

Listed below are upgrades you can make to switch to electricity for the various applications that natural gas or heating oil are commonly used for in the home.

Solar heating

It’s possible to heat your home directly with solar energy by installing solar thermal collectors on your home. These are panels that mount on your roof like photovoltaic panels, but instead of using sunlight to generate electricity, they directly collect the warmth of the sun and transfer that heat inside your home. My article about heating your house with solar power describes this further.

Switch your oil or natural gas furnace to a heat pump

Most homes use some type of fossil fuel for heating: natural gas is most common, but some areas of the country, especially in the northeast, use heating oil.

If you want to switch away from gas or oil, your best bet is an electric heat pump. A heat pump is an air conditioner in reverse: it extracts heat from the outside environment, and pumps it into your home. There are two types: air-source and ground-source (aka geothermal) heat pumps.

My article on home heating discusses heat pumps in more detail.

Use a ductless mini-split/multi-zoned heat pump

A ductless heat pump doesn’t used forced air ducts, but instead uses narrow pipes that carry heated or cooled refrigerant to one or more indoor wall-mounted ducts that distribute the conditioned air.

A system with multiple zones, also known as a mini-split system, is helpful for energy efficiency because it allows you to target your heating or cooling to only the areas of the house where it’s needed. For example, if your bedrooms are on a second floor, you don’t really need to heat the first floor while you’re sleeping.

In combination with a smart thermostat, a ductless mini-split can help you have a lot on your heating and cooling bills.

Switch your gas clothes dryer for electric or a clothesline

Most people choose natural gas clothes dryers, because standard electric clothes dryers that use electric resistance to provide the drying heat are inefficient and expensive to operate.

In addition, most clothes dryers are vented, meaning that they take conditioned air from your home, heat it up, blow it into the drying chamber, and then vent it outside. Because it is taking your conditioned indoor air and blowing it outside, your clothes dryer is making your HVAC system work harder.

A more efficient option is a ventless condensing dryer. Condenser dryers use your indoor air, heat it in a heat exchanger, circulate it in the drum to absorb moisture from the wet clothes, then send it to a second loop in the heat exchanger where the air is cooled. Cooling the air causes water to condense out, which is collected and sent to a drain. The same air is then recirculated in the drum, and the process is repeated until the clothes are dry.

Another type of efficient electric dryer uses a heat pump to generate heat instead of an electric coil. Heat pump dryers are also ventless, and even more efficient than condensor dryers.

Both heat pump and condensor clothes dryers are energy efficient electric alternatives to natural gas. Downsides: fewer products on the market, and a 50% to 100% higher price tag.

The best option of all? Use a clothesline. It’s free, uses zero energy, is more gentle on your clothes, and your clothes will smell better.

Swap your gas cooktop for induction

Induction cooktops use electricity to generate magnetic fields that heat up your cookware directly. They’re energy efficient, and are as responsive and powerful as cooking with gas.

The main disadvantage is that they’re still a little pricey, but the cost is coming down all the time.

Use a heat pump water heater - maybe

This is a type of storage hot water heater that uses an electric heat pump to heat up the water. These are much more efficient than conventional electric water heaters. However, they are also very pricey: 2 to 4 times more expensive than a natural gas or electric resistance water heater.

There’s a downside with using a heat pump water heater in a cold climate, however. Because the heat pump extracts heat from the indoor air, using a heat pump water heater in a cold climate will cause your furnace to work harder. This is a bit of a zero sum game, so if you live in a cold climate, it would probably make sense to stick with a natural gas heater. Heat pump water heaters can be a great choice in warm climates, though.

Going 100% solar electric is possible, but it’s not worth extreme measures

As you can see, there are a lot of appliance upgrades and home renovations that make it possible, if you want, to completely eliminate your fossil fuel usage at home and power it with solar electricity.

Is it worth it? Getting to net zero in a building that wasn’t designed for extreme efficiency could be expensive and involve extensive renovations. Some of the appliances required, like heat pump water heaters, don’t make sense in every climate.

But getting most of the way toward energy self-sufficiency, even with an older home, is certainly possible with high efficiency solar panels, added insulation, air sealing, efficient appliances, and zoned heating and cooling systems.

By avoiding extreme renovations and making selective upgrades, you can get most of the way toward energy self-sufficiency and recoup your investment in energy savings within a reasonable timeframe. For most homes, that’s a smarter and more economical approach than doing everything possible to reach the arbitrary benchmark of net zero.

TAGS:
#Energy Efficiency #Heating and Cooling

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