Solar panels require a frequency and voltage reference to provide a steady power source, this reference is usually provided by the battery or the grid. While it is not common, it is possible to use a solar panel directly without a battery or the grid as a reference, but you need to use an electronic called DC to DC converter, which stabilizes the voltage at a certain level.
Figure 1. Solar panel directly powering a load – Source: Electrical TechnologyIf you are curious about how you can use a solar panel directly without batteries and how this works, then you should keep on reading this article. Here we explain how to power a load directly with a solar panel, why batteries are necessary, and the pros & cons of using a solar panel directly without a battery.
The best power output for a single solar panel is defined by several aspects, like the solar panel efficiency, the technology used for the different types of solar panels, but most importantly, the Maximum Power Point (MPP) regarding the IV curve (Figure below).
Figure 2. IV Curve of a solar cell/operation at the Maximum Power Point. Source: PVEducationAs you can see, there is a specific voltage and current that allows a solar panel to get to the MPP, but photovoltaic (PV) modules can operate at a wide range of voltages and currents. A PV module can deliver power on demand as long as the voltage and current are enough to deliver it, but during the whole process, the values for the current and voltage are not fixed. This voltage and current instability make powering a DC load like electronics or home appliances virtually impossible.
So you cannot connect the load directly to the solar panel without a voltage reference like a deep cycle battery or the grid, what can you do? There is one simple solution that works to power a small or medium load with a solar panel without solar batteries or the grid. To achieve this, you need an electronic called DC to DC converter.
Powering a load with a solar panel without batteries using a DC to DC converter can be a little tricky. This converter is designed to operate at a certain stable voltage, which means you need to configure the DC to DC converter to operate at the maximum voltage the panel can produce and hope that the solar panel will operate at that voltage for as long as possible. While the panel operates at said voltage, the DC to DC converter will do its work and deliver the stable voltage output.
A Charge Controller is a type of DC to DC Converter, which is why it could create some confusion, but this device cannot convert power from a solar panel without a battery. The Solar Charge Controller operates by regulating the flow of power from the solar modules to the batteries, charging them and finally sending the remaining power directly to the inverter. The charge controller is designed to use the batteries as reference voltage output, which is why it needs to have a battery connected.
The DC to DC converter, works different. This device does not require batteries and does not use them for a voltage reference. Instead, the DC to DC converter has input voltage reference in DC and provides an output voltage in DC. This means that if the solar panel has a voltage within the input range voltage of the DC to DC converter, then the device will be able to provide a fixed output in DC.
You might be wondering if you can use a hybrid or grid-tied inverter to connect the panels directly to the load? The answer to this is a big no. Grid-tie inverters, use the grid as reference, which is not the case for hybrid inverter. These inverters will have problems with the varying voltage, causing problems for the frequency regulation and voltage output. Inverters are delicate electronics that cannot have such variable inputs without a voltage reference.
Yes, this one you can do, but only for small loads. You can power an AC load, using the DC to DC converter which provides the steady DC voltage for the input of the inverter, however you need to keep in mind that the inverter must be an inverter charger or battery inverter. In this case, the solar panels should get full sunlight to deliver a steady voltage, the DC to DC converter will operate at the rated conversion voltage, and the inverter will produce the AC pure sine wave inverter to power the small or medium load.
Off-grid PV systems require batteries for two main reasons: voltage and frequency stability and energy storage. In this section, we explain why they are so important and why you cannot just use solar panels to power a load in off-grid PV systems.
The main reason why solar panel installers deem as necessary the usage of solar energy storage in off-grid PV systems is the stability for voltage and frequency. When an AC load demands power, this happens in a matter of milliseconds, and the power demanded has the potential to destabilize the voltage or the frequency of the network, in this case, the home.
To avoid losing voltage and frequency stability, the solar inverter has a series of control devices in place that provide it with the ability to increase or decrease the power output while keeping the voltage and frequency stable. There is only one requirement for the solar inverter to achieve this: have a stable voltage source at the input, which is why batteries are extremely necessary for an off grid solar system.
The second reason why batteries are so necessary for an off-grid solar panel installation is because of energy storage. Off-grid homes only produce power during sunlight hours, which means that during evening hours when the sun is starting to hide and during the night, the solar panels will not produce energy, causing the off-grid home to be left entirely without power.
For a family to be comfortable and have uninterrupted power 24/7, it is necessary to have an energy storage system which is the same as saying: batteries. The batteries allow the home to achieve solar self-consumption, ensuring that the family has power at home during daytime and nights, and they allow the use of solar energy during power outages or during cloudy days when the PV systems might not be able to generate enough energy to power the load.
The capacity of the backup energy storage system depends on the power consumption of the home and the desired autonomy. A homeowner wanting a higher autonomy can install twice or three times the required storage capacity to ensure power for several days when the panels are not generating enough energy.
While powering a load without a battery can be performed, there are several cons attached to it, but also a few pros:
Powering a load with solar panels without a battery can be achieved by using a DC to DC inverter, and an additional DC to AC solar inverter if we are dealing with an AC load. Doing this can be quite complex since the solar panels need to have the voltage for which the DC to DC converter input is designed for (usually the maximum voltage) for the converter to operate and deliver a power output, otherwise, the converter will shut down entirely.
This is not worth doing in most cases, since it is better and safer to have a battery or at least use the grid as a voltage and frequency reference like grid-tie PV systems do. Even small solar devices like a solar powerbank, and similar ones, include the battery for voltage stability reasons.
Using solar panels to enjoy one of the best alternative energy sources can be great, but it is important to consider every necessary component like batteries. Using solar panels without batteries does not provide stability, it is unreliable, and might require technical skills, which is why we do not recommend it.
Grid-tied systems are the most common type of PV system that do not require a solar energy storage system to operate. The reason for this is that the grid-tie solar inverter uses the grid as a voltage and frequency reference, delivering that same voltage and frequency to the home. During a blackout, the grid-tie PV system will not operate for safety reasons and because the inverter lacks the adequate reference to provide a stable power output regarding voltage and frequency.
A grid-tied inverter is only designed to operate when there is a voltage and frequency reference, the grid is usually this reference. These types of solar inverters are not designed to operate using batteries and cannot charge them with solar power, which is why they are not compatible with off-grid homes. For off-grid installations, you will need an inverter charger or hybrid inverter.
Off-grid homes without a battery cannot be powered entirely using a DC to DC converter, since this only works for small and medium loads. In this case, a large PV system will not take full advantage of the generated energy, causing all that excess energy go to waste. Grid-tied homes, on the other hand, have the net metering system which accounts for the excess generated energy and grants you credits that can be used in future months to offset electricity bills.
Hi,
I'd like to install solar panels on my house. My goal is to reduce my bills, carbon footprint, and dependency to the grid.
That last point is important to me, but not enough to make me buy an expensive battery.
Not knowing much about solar, I naively assumed that any solar installation would be able to power my house in the event of an outage.
I mean, I have solar panels, I have an inverter, what else would I need.
But from what I understand, the problem is that grid tied inverters are designed to draw as much power from the panels as possible ans send it to the their output. Then you use what you use, and the rest goes to the grid.
The solution would be to use an hybrid inverter, but many seem to only do what I want if you add a battery to the system, and I don't want that. Reading through the descriptions in online stores, it's never really clear whether the offline capabilities are available without battery.
For now the only system that seems to do what I want is Enphase IQ8 which is not available for now, or some overpriced inverters like the sol-ark.
But even with the IQ8, this is not perfect because it's a micro inverter and I really don't need that. My system will be composed of 16 405Wc panels, all on the same roof with nothing to make shadows on them except clouds. And from what I understand, micro inverters are less efficient, right ?
I think one common solution is to use AC coupling, but from what I've read it only works down to a certain power, if the load is too low then the frequency goes up too much and the inverter shuts off.
This is what I understand. Am I wrong ?
What I want is quite simple : a system that can produce electricity at full power and send the surplus to the grid when it is online, and that can also work off grid by giving me from 0W to full power depending on my load, without any battery.
Do you have any advice about that ? Should I look for an hybrid inverter or for micro inverters ?
Micro inverters are more expensive but my supplier gives me a 25 years warranty on them vs 10 years for classic or hybrid inverter
Thanks