The power grid is an extensive regional system connecting large power generation stations such as coal-fired steam, hydropower, and nuclear power generators with wind and solar renewable power generation. The power grid can act as a huge battery into which power producers supply electrical power.
Most domestic solar power installations are tied to the power grid via a solar inverter. The solar inverter must convert the solar-generated direct current into alternating current of the specified voltage and operating frequency to be accepted by the power grid via a net metering device.
The grid-tied solar inverter system consists of the following elements:
- Solar panel array
- Solar inverter
- Net Metering Device
- Grid connection
Let’s look at how grid-tied inverters sell domestically generated solar power to the grid during peak solar production hours and buy back grid power when needed.
Why Is Grid-Tied Solar Power So Popular?
The lowest possible way to invest in solar power generation to save money on your power utility bill is to install a grid-tied solar system. Solar panels are relatively cheap and can be bought for $0.50 per watt. Solar inverters are also cheap and needed to convert the solar DC to grid AC.
Off-grid power systems require battery storage capacity, which is very expensive. The power grid can be used as a “free” battery in a grid-tied system. The inverter can convert the solar power generated between 9 am and 3 pm daily from DC to AC and fed back into the power grid.
Most households only require significant amounts of power after 5 pm until about 9 pm. A net metering connection is required with the local power utility company, and you will be required to sign an agreement to “sell” your solar power at an off-peak rate and buyback power during peak demand at peak rates.
The problem with solar power has always been that it is produced when it is not needed. To use the solar power generated during the day at night, costly power storage devices (battery banks) are required. This considerable investment was a deterrent for many wanting to use solar energy.
Initially, the agreements with the power utility companies were to buy and charge for each unit of electricity (kWh) at the same rate. This was not favorable to the power utility companies as they bought power when there was no or low demand.
They had to sell power at that same rate during peak demand hours. They thus changed the compensation model to one where they bought solar-generated power from domestic producers at off-peak rates and sold those households’ power at peak rates during the peak demand times.
The power utility companies still feel they are being used as the “backup battery” and are now proposing a fixed monthly connection fee for domestic solar producers whether they are generating power.
Off Grid Systems
This will drive domestic solar power producers to go for completely off-grid systems and become completely independent of the power utility companies. It will require homeowners to invest in significant power storage capacity such as a Tesla Powerwall 2 or equivalent.
Such power storage battery systems are expensive but have a lifespan of twenty-five to thirty years and a complete system payback on investment of five to ten years depending on the amount of sunlight in your area and power use.
Can Grid-Tied Inverter Be Converted To Off-Grid System?
When comparing a grid-tied system with an off-grid system, several changes and additional components are needed to convert from a grid-tied system to an off-grid system. Let’s compare the two systems and see which components can be carried over or introduced.
|Grid-Tied System||Off-Grid System|
|Solar Panel Array||Solar Panel Array – carry over|
|Inverter to Grid AC||Replacement needed|
|Net Metering||No longer needed|
|Grid Connection||No longer needed|
|Solar charge controller|
The existing solar panel array can be tied into the new off-grid system via a solar charge controller that will regulate the solar DC to the optimal charge voltage and current required by the battery bank.
Additional solar panels can be added should you have sufficient available roof space or space for a ground-mounted array.
The old inverter will most likely no longer be useful in the off-grid system as it was sized to convert the solar power to grid AC and not to power a specified number of appliances.
A power inverter of sufficient size will be connected to the battery bank to convert the battery-supplied DC to AC of a voltage and operational frequency as required.
The most significant cost component to such a conversion will be to buy the right size battery storage capacity. The cost of battery storage capacity is $1.00 per Watt-Hour, meaning that a 30kWh battery capacity needed by the average US household will cost $30,000.
A full conversion from grid-tied to off-grid could thus cost in the region of $40,000 in one adds the solar charge controller, power inverter, and perhaps some additional solar panels. Still, the payback is five to ten years, and the convenience of never suffering another power outage is priceless.
Are Hybrid Inverters A Good Alternative?
Hybrid inverters convert the direct current generated by the solar panels into either grid-power or to power some household loads or both. Hybrid inverters are more complex and thus more expensive and still require the approval of local power utility companies to connect.
Whether the local utility companies will be charging fixed monthly connection fees regardless of the power sold to or bought from them will determine the future of hybrid inverters.
I think staying connected to the power grid is just postponing the inevitable. You should invest if you can afford the upfront investment to install a complete off-grid power supply system. Even financing over ten years will make for a prudent investment that will give you free power for twenty years.
As old technology power generation facilities age and need to be replaced, it is likely that grid power will only become more expensive with each passing year. For those that can afford to make the switch to off-grid power independence now, you should not delay.