Battery Storage
Battery Ready vs Battery Storage vs Off-Grid
Solar Power Patios has employed a number of off-grid and battery backed-up solutions and the intent of this section is to describe the differences and the benefits of each solution.
What does battery-ready mean?
Battery-ready means that you can add components to your existing installation without replacing your inverters or any installed wiring. This means that we utilize hybrid inverters that act as both solar (pv) inverters and battery inverters. Micro-inverters are popular because they can be attached directly to the underside of the solar panels but they are not capable of interfacing a battery to the grid. As separate battery inverter needs to be employed.
Does battery storage enable me to operate off-grid or during a power outage?
Because you have battery storage does not necessarily mean you can operate off-grid. In order to operate off-grid you need to employ either a manual or automatic transfer switch that can disconnect (island) you from the grid for the safety of utility employees. This system is generally the most expensive because it needs to operate in all modes. The following is an example of a grid-connected hybrid system with a manual disconnect switch.
What are the benefits of adding a battery?
There are two benefits - 1) to operate off-grid either temporarily or permanently or 2) to enable the homeowner to store power during the day and sell excess to the grid when the sun is up and then draw from that storage during utility peak time when power is more expensive.On-line monitoring of every inverter shows how the inverter - equipped with Lithium (LiFePO4) storage - can be used to avoid purchasing any power during peak times. Almost every utility is changing solar rates to incentivize the use of storage and they are doing so by making energy purchased and sold during peak times dramatically more expensive than that during non-peak times.
The graph below was downloaded from an actual system that is programmed to minimize power used during the peak time of 4-9 PM. It can be seen that solar energy has dropped off by 4 PM and all home consumption is being met by power from the batteries. This continues until 9 PM when the batteries are replenished by purchasing power from the grid at a much lower cost.
The system operation can be changed from Time-of-Use Discharging, Time-of-Use Charging to Maximizing Self-Consumption (buying as little energy from the grid as possible) from the web-based programming screen available to the customer.
Why not go off-grid completely and what do you need?
Once you do decide to employ batteries, it is natural to wonder why you can't go off-grid entirely. The benefits include the following:
- Prepared for an emergency
- No need for a utility grid connection agreement and be limited as to how much solar can be installed
- No need to inform the utility if the system is increased or modified since it is not grid-connected
- In California, there is no need to pay a grid-connection fee if/when NEM 3.0 is rolled out as expected
Installing an off-grid system is straight-forward and there are just a few things to verify.
- Adequate solar capacity - particularly in winter. The PV system will have to be designed to give you enough energy on a daily basis basis. Generally a solar system will have plenty of power and be oversized for summertime but it needs to be sized with safety margin in the winter time. Increasing the panel tilt is particularly beneficial for increasing winter production
- Adequate power output - It is important that the system have enough current output (amps) to serve the electrical loads that are going to be run. This includes air conditioning, electric vehicle charging and all common household needs. The typical off-grid system we employ can output 75 amps continuously at 240VAC which is capable of powering all these typical loads.
- Automatic transfer to the utility when needed - While you can operate indefinitely off-line, having a utility connection for the cost of only $15-$20/month is a low cost safety net.
Are there any drawbacks to being off-grid?
Just one - because the system is not grid connected there is no way to sell power to the electric utility. In states which do not have net metering the excess power is sold back to the grid at the incredibly low generation rate. So the benefit of selling power back to the grid is constantly reducing in value as more homeowners adopt solar without storage.