Why should I get solar panels for my home?
The decision to go solar can seem complicated. We explain some of the reasons why solar for your home can be great.
Now that you’ve had an energy audit, got your hands sticky with some duct-sealing mastic, got yourself and your friend quite dusty with a cellulose insulation blower, scored a free smart thermostat from your utility company, and upgraded all your light bulbs to LED, your home is looking pretty darn energy efficient. If you want to take it to the next level, it may be time to consider solar photovoltaics.
There are a lot of different reasons why you would want to go solar. Some of them are economic, some are environmental, while other people like the intangible feeling of being energy self-sufficient. These are all great things, and ultimately the decision is a personal one.
In this article, we’ll do our best to go over some of the most common reaons go to the trouble of adding solar panels to their home.
Can solar panels help you get off the grid?
Let’s start off with a common misconception, which is that having solar panels means your house will have power even if the electric grid suffers a blackout.
For the vast majority of homeowners who install solar, this is not the case. When the power grid shuts down, your solar PV system stops working too. But why is that? Most systems are interconnected to the electric grid, which means that power can flow in both directions between your home and the grid. When you generate more electricity than you need, the excess power flows from your panels into the grid where it can be used by your neighbors. But if you need more electricity than the system is making, your house can draw that extra power from the grid.
This interconnection means that your inverters, which are the components in your system that convert the direct current (DC) power that your panels generate into the alternating current (AC) of the electric grid, must stay in sync with the electric grid’s frequency, which is 60 hertz in North America. If your inverters stop detecting a signal from the grid that they can synchronize with, they automatically shut down.
It’s also a safety issue. If grid power goes down, having your inverters continue to send power into transmission lines that utility repair workers expect to be unpowered can be extremely dangerous.
If you really want to be independent from the grid, you need a battery system. DIY solar enthusiasts have been doing this for decades with lead-acid batteries - often repurposing second-hand car (bad) or marine deep-cycle batteries (better) - in cabins and other low power installations. This type of battery chemistry can store less power and is less durable than the latest technology, but it does have the advantage of being cheaper. The preferred chemistry these days is lithium-ion, which is the same technology in your cellphone, laptop, and most electrified cars. While the cost is still relatively high, the same market forces that have driven down the cost of photovoltaics is making lithium-ion cheaper every year.
Even so, the current price of batteries for home solar is still quite high, possibly as much or more than the rest of the photovoltaic system. For example, the Tesla Powerwall is a well-known brand. Their cost estimate for a 30 kWh system that includes two lithium-ion Powerwalls, hardware, and installation is $14,500. You could instead choose lead-acid which is cheaper upfront, but lead-acid has a lower lifespan and is less able to retain its original capacity after repeated discharge cycles compared to lithium-ion.
Fortunately, solar battery systems are eligible for the federal solar rebate as long as the batteries are to wired up to be charged only from your solar panels, and not from utility grid power. Other local rebates may or not include batteries, so do your research.
Reasons you might want to go with a battery system
At current prices, it doesn’t make financial sense for most people to include batteries in their photovoltaic system. Despite that, there are a few reasons why you still might choose to go with a battery system.
You don’t have net metering. If your utility company doesn’t provide net metering, you have to pay attention to the time of day that you use electricity, because it affects the financial payback of your photovoltaic system. With a battery system, you can keep more of your solar electricity rather than send it into the grid then get compensated at a lower net billing rate. If you’re not familiar with net metering, we wrote a whole article about it. TODO
Your utility doesn’t allow interconnections. In some states, utilities are not required to allow you to connect your photovoltaic system to the grid at all. If this is the case for you, then just like in a situation where your utility doesn’t provide net metering, no interconnection means that you don’t have any opportunity to sell your electricity back to the grid, at any price. So if this the case for you, but you still want to go solar, you’ll need batteries to make sure that you can actually use all of the power you generate.
Your utility power is unreliable. It’s pretty annoying when the power goes out while you’re trying to binge watch some Netflix. With batteries, your home automatically switches over to battery power when a blackout happens. If you live in an area with frequent power dropouts, that might be annoying enough to convince you that the extra cost is worth it.
You’re way out in the woods. If you’ve got a home or cabin away from civilization, grid power might not even be an option, or it may be an option for you to pay the utility company to run service to your property, which could cost tens of thousands of dollars. If that’s the case then solar plus batteries, along with a generator backup, could be your best option, especially if you spend a significant amount of time at the property.
You just want to be independent. Some people go solar simply because they like the feeling of being self-sufficient. These days, it’s possible to have a completely comfortable and modern home that gets water from rainwater collection, energy from battery-backed wind and solar, and disposes of waste with composting and a septic system. In this case, being off-the-grid is more of a philosophical standpoint then a financial one. It’s easy to see the appeal.
The environmental impact of solar
The environmental benefits of solar are well-known but still debated. We think that solar is absolutely a more environmentally-friendly alternative to fossil fuels, but to understand why you first need understand its cradle-to-grave lifecycle.
Solar panels are semiconductor devices that turn sunlight into electricity. They are normally made of silicon, and have no moving parts. When photons of sunlight strike the surface of solar cell, electrons are excited and flow along the wires of the panel, creating electricity.
There is no pollution when this happens, and because there are no moving parts involved, a solar panel doesn’t emit any sound even when it’s sending out hundreds of Watts of electricity.
This process is pollution-free but solar electricity isn’t completely clean because the full lifecycle impact, from mining the raw materials to manufacturing to disposal, must be considered.
As far as raw materials go, the components in a solar panel include the semiconductor layer, which is made up of multiple solar cells that are joined together with wiring. This layer is sandwiched by layers of acetate. The backside of the panel is a layer of polymer, and a durable sheet of glass forms the top. Finally, a strong aluminum frame holds all these layers together.
These materials are non-toxic except for a small amount of lead that may be used in the solder at wiring joints. Overall, a typical silicon-based panel is 76% glass, 10% polymers, 8% aluminium, 5% silicon, 1% copper, and less than 0.1% other metals such as silver, tin, and lead. The exception to this is thin film solar cells, which are rarely used in residential applications. Thin film uses different materials for the semiconductor, which can inlcude toxic elements such as cadmium and telluride.
Regardless of their toxicity, these are materials that are mined, shipped to a factory, manufactured and assembled into solar panels using energy that may or may not be from a renewable source, and then transported to a distribution center, your installer, and then finally your home. All of these steps have an energy and pollution footprint.
What happens when solar panels stop working? So far, this hasn’t been a massive problem because the widespread deployment of solar is a recent phenomenon, and solar panels can last a really long time. Today, it’s common for a commercial solar panel to come with a 25 year warranty, but you can expect them to last longer than even that. Because solar cells do not have moving parts, they don’t physically wear out as they age, but they do lose efficiency over time due to exposure to UV light exposure. The newest panels today may lose only about 0.5% efficiency every year. That means even after 25 years, your panel could still be generating 88% of it’s original specification. That’s a lot of years of pollution-free electricity, and a lot of early generation solar deployments are still operating.
Eventually, solar panels do reach the end of their life. Just like with other waste streams, reuse should be a higher priority over recycling, and sometimes this is possible because panels are sometimes replaced even while they are still working because the customer wants to upgrade to newer, more efficient technology. There is a used market that already exists for these panels, and they can find a second life from buyers in the US or in developing countries.
Repairing panels and then reusing them as products for the used market is another possibility. Glass breakage, frame, and wiring failures are some of the top reasons for panel failures, which are all potentially repairable issues.
Even so, with millions of panels being installed worldwide, the waste stream for this technology will be a growing problem. The International Renewable Energy Agency estimates that the cumulative waste stream could reach 78 million tons by 2050. This means that there will need to be a recycling solution.
Much of the material - glass and aluminum - can be handled using current recycling streams. Semiconductor recycling is more of a challenge, but it is possible. One company, PV CYCLE, has demonstrated that they can recycle as much as 96% of the semiconductor material in a panel. As this waste stream develops in the decades ahead, we can expect more companies to enter this industry. It’s likely that Germany, having had a significant PV market earlier than the US, will be the first country to develop a robust PV recycling industry. But tackling this problem will require both industrial innovations as well as a regulatory framework, in the same way that some US states have developed regulations around the disposal of e-waste.
So what does this all mean?
So, what does it mean for solar electricity pollution when you look at all of the factors from mining to end-of-life? There have been hundreds of life cycle assessments of solar photovoltaics, with varying results between them. The National Renewable Energy Laboratory took a smart approach and evaluated 400 of these studies, selecting 46 that met their criteria. Summarizing all these results, they concluded that photovoltaics, from cradle-to-grave, results in 40 grams of greenhouse gas pollution per kilowatt hour of electricity generated. In comparison, a coal power plant generates about 1,000 grams per kWh, and the most efficient combined cycle gas turbine plant generates about 490 g/kWh. This means that solar is about 25 times cleaner than coal, and more than 10 times cleaner than natural gas.
How distributed solar can help the electric grid
Even though solar panels on your roof are awesome in a science fiction sort of way (silent and clean electricity from the sky!), it’s not without opposition. For example, state regulators in Arizona ruled in 2016 to roll back the state’s net metering policy, partly on the argument that solar incentives unfairly benefit homeowners who can afford the upfront cost and gain monetary benefits from having solar, while simultaneously avoiding the cost of contributing to grid maintenance through the purchase of utility electricity.
While it’s true that the electric grid, with its interconnected system of transmission lines, transformers, generators, fossil fuel supply chains, control centers, and metering system can be thought of as the largest machine in the world, and this machine is definitely not inexpensive to maintain, distributed generation can actually lower the cost for other users on the system through some important mechanisms.
While the term “grid” suggests a regular and evenly distributed set of wires, in fact the North American electric grid resembles the freeway system, with long stretches of transmission line that meet at busy interchanges. You know what driving is like: you’re crusing down the freeway at a nice clip, only to have to lift off the gas and slow to a crawl when you hit a busy merge at rush hour. The grid is a little like that too. Electric grid rush hour occurs in the evening when everybody comes home from work and switches on their appliances, or in the middle of summer when air conditioners are blasting, or in those dead cold days of winter when heating and hot water systems are cranking away.
When this happens, a traffic jam can happen at the intersections where operators in one region need to borrow power or send power from a neighboring part of the grid. If the demand is too high, those grid intersections may not have enough capacity to carry the needed power, even though transmission lines in other parts of the grid have plenty of spare capacity. When this happens, an area can experience a drop in voltage or, in a worst case, a brownout.
Distributed solar can help this by generating electricity in the same place it’s used. Basically, if your power is originating from a few feet above your head, you’re not placing any load on the grid. In fact, because even most smart meters aren’t smart enough yet, your utility company doesn’t know in real time that your solar panels are generating thousands of Watts of power. They can only see your solar generation as a drop in demand in your area.
With distributed solar, you’re helping to reduce the electric rush hour traffic jam and defer or completely avoid expensive grid upgrades that can cost billions of dollars.
There are limits to everything, of course. An imaginary electric grid that is made up only of distributed solar would need a substantial amount of energy storage and demand management in order to operate. But this isn’t a very good argument against solar. Even before the advent of intermittent renewables such as wind and solar, the grid has always been comprised of a variety of different generators, such as coal, gas turbine, oil, and nuclear, each of which has capabilities that are useful in different situations. With intermittent renewables, the need for a mix of electric generators isn’t new.
Meanwhile, the cost of utility-scale batteries is benefiting from economies of scale, as well as the possibility of recycling used electric car batteries for grid storage applications. For example, in 2017 Tesla installed a 129 mWh battery in South Australia that is replacing work that is normally performed by gas turbine power plants. The battery is already significantly profitable, and is helping demonstrate the economic argument for using massive batteries as grid storage.
One more important benefit of distributed solar that it makes more efficient use of electricity that is generated. About 5% of the electricity from power plants is wasted as heat as it travels down transmission lines and through substations on its way to your home. Wires aren’t perfect conductors, so the farther that electrons have to travel, the more electricity is lost to electrical resistance. But if the electricity is being generated up on your roof, there is essentially no distance to travel and no losses. For reference, that 5% of electricity that is lost is about equal to the entire power output of the state of Pennsylvania in 2017. This is a huge amount of electricity to essentially throw away, and big benefit that distributed solar can contribute.
- Why Distributed? from IEEE power & energy magazine
- Life Cycle Greenhouse Gas Emissions from Solar Photovoltaics from NREL
- Technology-specific Cost and Performance Parameters from IPCC
- Life Cycle Assessment Harmonization from NREL
- State-level generation and fuel consumption data from EIA