Off-Grid Battery & Solar PV
In a remote location or any location that doesn’t have an electrical grid, Solar PV plus batteries can supply reliable ongoing electricity to power usual house-hold functions. How big a system depends upon the power output needed. In most Western Culture situations, a generator is also needed to provide power when the battery power drops too low. Generators are run by burning a fossil fuel (diesel or propane).
The style of battery greatly affects how the batteries are used and how long they last. Battery life has many contributing factors to its variability including temperature, proper discharge and recharge, and optimal application usage.
Battery-Backup for Grid-Tied Solar PV
Solar PV can be installed today in a system in which the solar energy keeps the batteries fully charged and the remaining power reduces how much electricity the building pulls from the grid during daylight hours. The batteries are present for the instance when the power goes out (ie the grid goes down). In an outage, grid electricity may be off for a few hours or for several days. The size of the battery system is based upon how much power is needed to run the “critical load” breaker panel and for how long. The cost and complexity of having batteries for backup purposes is generally fairly high. In most residential cases, a more appropriate and cost-effective means of backup power is found in a generator.
Grid-Hybrid Battery Storage
Batteries can be used to store solar energy and then allow the owner to utilize battery power at night or anytime to reduce the purchase of highest cost peak power when a utility charges the highest per kWh rate for electricity used during the peak time of day or season. Battery power can also be used to keep the building’s total grid energy usage low over time so that keeping the customer in the lowest price in a tiered rate structure.
In this situation, the battery needs to be capable of fulling discharging and then quickly recharging, like the batteries in cell phones and electric vehicles.
These systems are more complex in terms of wiring and inverters. In most circumstances, battery power cannot be fed back into the grid for net metering. Battery power can only reduce what the building takes from the grid, but any excess fed back into the grid for credits must come from solar alone. In states with low cost electricity like ours, the high cost of adding batteries, their inverter, extra wiring makes solar + batteries very expensive, but in areas with high-cost electricity or in islanded grid systems, residential size solar + batteries may make economic sense.
Adding batteries to an existing solar system is possible. The process is called “AC coupling” and it is vital to have an experienced professional design the new system and an experienced electrician install it.
Major advancements are occurring rapidly in the area of battery storage and matching inverters including work that is being done right here in Washington State.
Large Scale Storage
Utilities in WA and elsewhere are exploring the benefits of Solar + Storage on a much larger scale. Since clean renewable solar and wind energy are variable due to clouds and weather, storage offers a way to save the electricity from a peak producing times to use in peak usage times. Batteries and other storage methods are being added to the grid to even out supply and demand regardless of the presence of renewable energy.
Links to current articles
Washington State Moves Forward With 5 MW Solar-Plus-Storage Facility
(October 26, 2018, from Solar Industry magazine); link to article