Emergency backup power with the SMA Sunny Boy inverter series
Sunny Boy inverters have a special feature that will keep your home powered in a blackout for much less cost than a battery system.
If you have a home solar system, it won’t keep your house powered in a blackout unless you have a battery system.
This is because solar inverters have a feature called anti-islanding. A solar inverter converts direct current (DC) power from solar panels into alternating current (AC) that your home and electric grid use. AC power has a frequency of 60 hz in North America. In normal operation, your solar inverter “listens” for power from the grid, and synchronizes its AC output to that of the grid.
If grid power is no longer detected, as would happen in a blackout, the inverter will shut down even if it’s sunny and your panels are capable of producing electricity. This is an electric grid requirement to protect utility workers who don’t expect offline wires to be carrying electricity. If your inverter continued to send electricity into the grid, that would be dangerous to those workers.
Normally, the only way to run your home on solar electricity during a blackout is by adding a battery system. Depending on the size of the battery and your power needs, you could have uninterrupted power for an unlimited amount of time - or least until you have a string of cloudy days.
But batteries are expensive, costing thousands of dollars even after the federal tax credit. That’s prohibitive for a lot of people. If you’re in a situation where you want to have emergency power - such as those in the PGE service area where scheduled blackouts are expected to be the norm - you might think that you’re out of luck, or will have to go with a generator.
However, there’s one alternative option that costs a lot less: the SMA Sunny Boy inverter series. These inverters from the German company SMA have a unique feature called Secure Power Supply that can supply a limited amount of power during a blackout.
The Secure Power Supply (SPS) feature of the inverter allows the connection of a power outlet that can supply up to 2,000 watts of power while the solar panels are generating electricity, even during a blackout. SPS doesn’t bypass the anti-islanding restrictions of your utility company: the Sunny Boy inverter won’t send electricity into the grid while the grid is down. Instead, the single outlet will remain powered as long as the solar panels supply electricity.
Having just one outlet of power obviously isn’t as good as having a solar battery that can power your entire house - but for households where power outages are infrequent, having a Sunny Boy inverter is a much less expensive option for supplying enough power to keep your critical items going. For example, 2,000 watts should be enough to keep your refrigerator from thawing out, and is certainly enough for you to recharge your cell phones and other electronics.
Because of the limitations, you’ll need to do a little planning to get the most out of the SPS feature when you need it. In this article, we’ll talk about how to plan to get the most out of the SPS feature. First, let’s start with an overview of the Sunny Boy inverter.
SMA Sunny Boy inverter intro
The Sunny Boy series from SMA is a line of string inverters for the residential market. There are several models in the Sunny Boy lineup, and the model number corresponds with the output capacity of the inverter in watts. For example, the Sunny Boy 3.0-US-40 has a maximum input of 4,260 DC watts and a maximum output of 3,000 AC watts, making it suitable for smaller solar home arrays.
The largest in the series is the 7.7-US-40, which has a maximum input of 10,905 DC watts and a maximum output of 7,680 AC watts. For more details and to look up other models, you can refer to the Sunny Boy datasheet.
The Sunny Boy series competes with the HD-Wave line of inverters from SolarEdge, which are some of the most popular inverters in the North American market. The Sunny Boy and HD-Wave inverters are priced similarly, but HD-Wave doesn’t have a feature like SPS, so that’s one advantage in the SMA column.
However, there may be other features that make the SolarEdge inverters a better choice for you. Be sure to speak with your solar installer about your needs.
Your solar installer or electrician will need to wire an outlet
The Sunny Boy inverter doesn’t have a power outlet on the unit itself. Instead, an electrician must wire up a power outlet and a switch to the inverter. When a blackout happens, you’ll flip the switch to activate the outlet.
The outlet doesn’t need to be next to the inverter. It can be anywhere in your home that is most useful: your garage, your kitchen, or the basement. Think of which appliances will be most critical in a blackout, and put your outlet next to them.
Of course, depending on how far the electrical run will be from the inverter, this will entail extra installation expense.
The downside to having only one outlet is if you have multiple critical appliances to power, such as a refrigerator in the kitchen and a deep freeze in the basement. There are options for this, such as a heavy gauge extension cord (such as 10 gauge) that is safe for long distance runs, or a small battery pack. Keep reading for battery backup ideas.
Power will be supplied only when it’s sunny
The SPS outlet is supplied directly by the solar panels. This means that the outlet will only work when it’s sunny enough to generate power. Depending on the Sunny Boy model, the SPS outlet has a maximum output between 1,500 and 2,000 watts. On a good day, it doesn’t take much to generate that much power - about 8 high performance panels will generate 2,000 watts in realistic conditions (represented by the panel’s NOTC or PTC rating).
It’s a different story early in the day, late in the afternoon, or on a cloudy day. As the sunlight fades, the Sunny Boy won’t be able to supply full power to the SPS outlet. Even if you have a pretty large array, you shouldn’t plan on more than a few hours of full power per day. For a short blackout, that might give your refrigerator enough runtime to get cold and to recharge your smartphones, but you’ll probably struggle to comfortably get through a long outage, or one on a cloudy day.
For that reason you might want to think about getting a portable battery pack.
Portable battery packs to help you get through outages
One way to make full use of the SPS feature is to use the outlet to charge a battery pack, and then use the battery to keep your appliances running. This has the advantages of freeing you from deciding on the ideal placement for the outlet, and it lets you still have power after the sun goes down.
There are a wide range of batteries available, and the one you choose will be a balance between cost and how much power you need. Some battery packs are even large enough to run some refrigerators. If your needs are more modest - like keeping your electronics charged - you can spend a lot less money.
Small battery packs
A useful tool to have, regardless of whether you’re planning for a blackout or not, is a portable lithium-ion based car jump starter. These are small lithium-ion battery packs that have alligator clips you can attach to the battery terminals of your car to give it a jump start when you accidentially let the battery drain (such as by leaving your lights on).
They’re small enough to keep in your glove compartment, and the lithium-ion battery will stay charged for a long time, in contrast to lead-acid battery jump starters that need to be topped up more frequently.
A good jump starter battery pack will also have USB ports so that it can double as an emergency power source. If all you want in a blackout is to keep your phone charged, this is a good, cheap option. As an example, the Trekpow G39 has enough peak output to jump start a large engine, and has USB 2 and USB Type-C ports to charge your devices.
It sells for about $80, but use the Amazon link below for latest pricing.
Medium battery packs
If you need a little more power - say, to power a laptop, internet router, or tv - you’ll need a battery with higher wattage.
The NEXPOW power station below should fit the bill. In addition to USB 2 and USB Type-C ports, it has a standard 110 volt outlet that you can plug your household devices into.
Its maximum continuous power output is only 120 watts, so you can’t use it to power large appliances, but 120 watts should be enough power to recharge your laptop or power a smaller TV.
With 178 Wh of capacity, this little battery pack can sustain its full 120 watt output for about 90 minutes. However, unlike the TrekPow, it’s not a car jump starter.
Large battery packs
If you have more serious power requirements - like running a refrigerator - but don’t want to commit either to a home battery or use a generator, you’ll want to look at the high end of portable battery banks.
When your goal includes powering appliances with a motor, you’ll need to consider not just the continuous current draw of the appliance as its running, but the start up power as well. For a fraction of a second after startup, an electric motor will draw much more power than it normally uses. After the motor is spinning, it will settle into its rated power usage.
That startup current may be listed in the manual, but if not you can try look on the motor itself. Look for an LRA rating in amps, and multiple that by 120 volts to get the wattage.
For example, if the compressor motor on your fridge says “LRA 5A”, that means it briefly uses 600 watts upon startup. To power that motor, you’ll need a battery that can handle at least 600 watts.
Your fridge might need more or less than that, so check the specifications. In any case, a standard household outlet on a 15 amp breaker will supply a maximum of 1,800 watts, so if you have a battery with at least that rating, you should be able to run your refrigerator or deep freeze.
The Nature’s Generator battery pack below should fit the bill. It has a maximum output of 1,800 watts and a 720Wh capacity, which means that it should let you run a refrigerator compressor continuously for about an hour.
It has multiple 120v outlets, a 12v outlet, 2 USB outlets, and even a connector to let you plug a solar panel directly into it. (A flexible solar panel would be a useful combination if you want to take this camping.)
This battery pack is a beast, and more expensive that the other options we’ve listed too. If you want more battery power than this, you should start to consider a household battery such as the Tesla Powerwall.
Disadvantages of the Sunny Boy Secure Power Supply
The SPS feature of the Sunny Boy series is definitely a neat feature, and it might be all that you need if you aren’t prone to frequent blackouts. But in addition to the things mentioned above, there are two important considerations:
- It requires manual intervention. The SPS feature requires the homeowner to flip the switch to active the SPS outlet and then to go around the house to figure out which appliances to selectively power from the one available outlet. Obviously, you have to be home to do this. If a blackout happens while you’re at work, your fridge is going to start defrosting until you get home and are able to plug it into the SPS outlet - and hopefully the sun is still shining. With a home solar battery like the Tesla Powerwall, the switchover to battery backup is automatic.
- The power is intermittent. Because the SPS relies directly on your solar panels, the power supply will be spikey. If a cloud passes briefly overhead, your power may drop suddenly, and spike again as the cloud moves on. That type of inconsistent power could be bad for sensitive devices plugged into it. One of the battery packs above will give your devices and appliances a steady supply of power, so you can avoid this problem by using the SPS outlet to charge the battery and then only run your devices from the battery - but this two-step process adds inconvenience.
Those are significant disadvantages, but perhaps not much of a problem if your emergency power requirements are modest. One of the battery packs listed here could be enough for you to get through the next blackout, and they’re certainly cheaper solutions than a full-blown solar battery that can power your entire house.
Given that Sunny Boy inverters sell for roughly the same cost as a SolarEdge inverter, the bonus feature of Secure Power Supply might be enough reason for you to choose SMA.
If you’re not sure which way to go, be sure to bring it up with your solar installer. Use the links below to get quotes from qualified solar professionals near you.
