Although residential solar photovoltaic (PV) has been around for over forty years, it is still not well understood by many people. There is also a lot of fear, uncertainty, and doubt (FUD) about residential solar-PV from some quarters, and many misconceptions still exist. In this Gaming the Electric Grid – Basics post, I will take a stab at explaining how residential solar-PV works in the United States from a consumer point of view. I will also introduce some relatively new capabilities that can be used to improve the capabilities of a residential solar-PV system.
Update: The second post in this series is Gaming the Electric Grid – Basics.
Typical Standalone House
A typical standalone house (or multi-family building) usually has electric service from one utility company that supplies all of your electric power. This is called the “public grid”. All of your electric power comes from the public grid, and your monthly electric usage is billed by the kilowatt hour (kWh). A kWh is the equivalent of using 1000 watts of electricity for one hour. In the United States in 2022, the average residential customer purchased 889 kWh of electricity a month. Depending on where you live, the time of year, your house size and it’s overall energy efficiency, your monthly electric usage can be significantly higher than the national average.
The price per kWh is relatively low in the United States compared to many other countries, but there can be a lot of variation depending on where you live (and what utility provider you have). In August of 2023, the average price of residential electricity for the entire country was 15.93 cents/kWh. Average electric rates in some states are significantly higher than the national average.
Many utility companies now have time of use (TOU) rate plans, where the price per kWh can vary widely based on the time of day and how much total system load the utility has at any given time. This can result in much higher-than-normal electric bills in some situations, and you are completely at the utility companies’ mercy.
If the public grid goes down, you have no electricity. This can be anywhere from mildly inconvenient to quite dangerous depending on the time of year, where you live, how long the outage lasts and what electric items you have in your house.
If you don’t have electricity, you probably don’t have any whole house heating or cooling, which can be uncomfortable or even life threatening depending on the situation. If you have an extended outage, you are potentially in danger of spoiling food items in refrigerators and freezers.
Most people in the United States have this type of setup, for various reasons. Depending on your situation, priorities, and budget, you can take various steps to have some backup electricity available when the public grid is down. These are some of the most common options:
Small Portable Electric Generator that Runs on Fossil Fuel
This is usually the least expensive backup option, so it is very common. These types of generators require fuel, (usually gasoline or propane) which must be stored. Gasoline can go bad, even with fuel stabilizer. It is also likely that you will eventually run out of fuel during a widespread or extended outage. Depending on the situation, you may not be able to buy any more fuel. These generators also require some regular maintenance.
Portable gasoline generators are noisy and cannot be used indoors because of the carbon monoxide they emit. Since they must be used outdoors, they are more prone to theft. Apartment dwellers usually can’t use portable gasoline generators for various reasons.
Portable gasoline generators can usually only handle a small portion of your normal total electric load. A common scenario is to plug critical items (such as a refrigerator) directly into the generator with a long heavy-gauge extension cord.
Inverter generators are more efficient and produce cleaner electricity than basic non-inverter generators. One popular model is the Honda EU2200i.
Small Portable Solar Electric Generator with Portable Solar Panels
These systems can be more expensive to buy, but they are less expensive to operate over time. They don’t require any stored fuel and you can charge them from AC power, from your car or from solar panels.
They are silent and they can be used indoors (where they are safer from theft). Small portable solar electric generators can usually only handle a portion of your normal total electric load.
Once again, a common scenario is to plug critical items (such as a refrigerator) directly into the generator with a heavy gauge extension cord. Typical capacities for portable units run from 256 Wh up to about 3 kWh. One thing to keep in mind for planning purposes is that you won’t get the full rated capacity of one of these due to inverter losses. If your battery has a 2 kWh rated capacity, you will probably get about 1700-1800 watt hours out of it in real life.
You can connect portable or fixed solar-PV panels into the XT60 port(s) of a solar generator to charge the battery while the sun is shining. The 2 kWh Ecoflow DELTA 2 Max has two XT60 ports, which let you charge with up to 1000 watts (total) of solar power, which would give you a full charge pretty quickly (on a clear, sunny day).
Whole House Electric Generator that Runs on Fossil Fuel
This is usually the least expensive whole house solution. These types of generators can be gasoline or diesel, but usually use propane or natural gas. You can get a large enough system that can easily handle your entire normal total electric load. This will be significantly more expensive than a small portable generator.
Whole house systems are usually connected to an automatic transfer switch, so the generator engine automatically starts up and takes over the electric load in less than a minute. This is not going to be fast enough to keep something like a desktop computer from losing power, so you will want to protect sensitive electronics with an appropriately sized uninterruptable power supply (UPS).
Whole House Solar Electric Generator with Fixed Solar Panels
This type of system can be quite expensive (but costs are rapidly coming down). You can get a system large enough to handle your entire normal total electric load. They can be connected to an automatic transfer switch, so the battery takes over the electric load in less than a second, usually fast enough for sensitive electronics.
If you have enough solar panels and enough battery storage, you can run the system indefinitely during an extended grid outage. Many people grossly underestimate how much solar and battery capacity is needed to make this possible though.
For example, if your base electric load is 100 watts (which is extremely low), a 1 kWh battery will last about 8.5 to 9 hours, with nothing charging it. If your base electric load is higher, you will burn through your battery capacity more quickly.
The goal here (if you have the budget) is to have a system that has enough battery capacity to run your entire house electrical load for an extended period, with the help of the solar-PV production you have available.
A starting point would be the ability to run your electric load entirely from your batteries during the night, and then have enough solar-PV output to run your electric load and charge your batteries during daylight hours.
This works well on clear, sunny days (especially during the summer), but you will want to have additional battery capacity and solar-PV output to make it through cloudly days and bad weather.
This post has some more information about home generators and what they typically cost. Consumer Reports has a good article about the pros and cons of inverter generators.
Net-Metered Grid-Tied Solar PV System
This is the most common type of residential solar PV system in the United States. If you see a house with solar panels on the roof, it is usually a standalone net-metered grid-tied solar PV system. A standalone grid-tied solar PV system can reduce or even eliminate your monthly electric bill. It can also help insulate you from future rate increases from your electric utility provider.
Another benefit is a reduction in your carbon footprint, since much of your electric usage is powered directly by the sun. Finally, a standalone grid-tied solar PV system can feed excess electricity back into the public grid during the day which helps improve grid stability and reduces the need for the electric utility to use peaking power plants during very high total grid load periods.
One big weakness of a standalone grid-tied solar PV system is what happens when the public grid goes down. This is an unwelcome surprise to many people, but with most systems, your solar PV system will automatically shut down when the public grid goes down. This is done to avoid backfilling the public grid with electricity, which could injure or kill utility workers. Because of this, you won’t be able to get any electricity from your solar panels during a grid outage.
It is possible to buy special inverters with separate secure power supply (SPS) circuits that will let you pull up to 2000 watts from a dedicated outlet connected directly to the inverter in your solar PV system (during daylight) when the public grid is down. SMA is the only inverter vendor that I am aware of that offers this capability. Another problem with a standalone grid-tied solar PV system is that it only generates electricity when the sun is shining, and your solar panels are not obstructed. This may seem obvious, but some people don’t realize this. If your panels are covered by enough snow or leaves, you won’t get any production.
If it is cloudy outside, your solar production will be reduced, sometimes quite significantly. You will also see decreased solar production during the winter (in your hemisphere) since there are fewer hours of daylight and the sun is lower in the sky. How far you live from the equator affects how low the sun gets in the sky during the different seasons. When the sun is lower in the sky (closer to the horizon), the solar rays have to pass through denser air that is also not as clear, which reduces your solar energy output.
Whole House Battery Storage System with Fixed Solar Panels
This is the most expensive option (but costs are coming down rapidly). There are lots of Federal, State and local tax incentives and rebates available depending on where you live and what utility provider you have.
This type of system lets you automatically charge your batteries from the solar PV system or the public grid. You can run off of the batteries at night or when the public grid is down.
There is no fuel to store, and you can run indefinitely during an extended outage with a properly sized system. Once again, it is very common for people to underestimate how much battery capacity and solar-PV output is necessary to make this work.
Batteries Are Great!
Having some battery capacity (with or without a solar-PV system) gives you a whole range of additional capabilities and options. Some of these are relevant during normal conditions and some are mainly useful during a grid outage.
For example, a smaller capacity solar generator is very useful for camping or when you just want some electric power anywhere off-grid. Even a smaller capacity solar generator can give you some capability to run a small electric load during a grid outage or when you are off-grid. Having any sort of solar panel output will extend the run time of whatever batteries you have available.
Another example is using your battery capacity to minimize your grid usage when grid electric rates are higher than normal. Perhaps your electric provider has TOU rates where electricity is more expensive from 5PM until 9PM.
With most solar generator systems, you can configure them (perhaps with the help of a smart plug) to purposely run some of your electric load off of the battery rather than pulling from the grid when electric rates are high. You also can configure them to charge the battery when grid rates are low. If you have any solar capacity, you would also want to use that to recharge your batteries as much as possible rather than charging from the grid.
How Do I Get Started?
No matter what type of system you have now or what your budget is, you should start by looking at your recent electric bills. You want to know how much you are paying per kWh, how many kWh your home uses per month and whether you are on a TOU rate plan or not.
Once you know this basic information, you can start trying to figure what things in your home use the most electricity and whether there is anything you can do to easily reduce their usage without feeling like you are making major changes to your lifestyle or daily routine.
You can use something as simple as a Kill-A-Watt meter to measure the actual watts usage of anything that you can plug into it. You can also investigate getting a home energy audit from your utility company or an outside firm so you can understand what improvements or changes would give you the best return on investment.
Doing some simple and inexpensive things to reduce your base and peak electrical usage is something you should always do as a first step before getting a solar system or any battery storage. This lets you get by with a smaller solar or battery system and saves you money on your electric bill regardless of what else you do.
This is just an introduction to a large subject that has many nuances. I have further posts planned that will cover what I have done along these lines in my current house. Recently, I had a SPAN smart electric panel and a Tesla Powerwall 2 battery added to an existing grid-tied solar-PV system, and I have learned a lot about the system through first hand experience…
In the meantime, here are some great resources for further reading.
The second post in this series is Gaming the Electric Grid – Basics.
If you have any questions about this post, please ask me here in the comments or on Twitter. I am pretty active on Twitter as GlennAlanBerry. Thanks for reading!