I have some questions about solar panels that are installed on a resident and interconnected with the utility. If you do not have batteries to store the energy, would any power that is not being used as it is generated go back onto the utility system. One of the reasons I ask this is since the power is being generated during the day and not being stored this would drastically increase your pay back period because the utility is buying it back at about 1/4 of what they are selling it to you for. Any thoughts.
Solar panels on residential
- Thread starter HEYDOG
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- Location
- Massachusetts
An interconnected system without battery back up will basically either slow your meter or if producing more than you are using will spin the meter backwards.
Some utilities will only by it back at wholesale prices and sell it back to you at retail prices.
At first that sounds unfair but they still have to maintain the equipment that you are using to 'store' your excess energy.
Some utilities will only by it back at wholesale prices and sell it back to you at retail prices.
At first that sounds unfair but they still have to maintain the equipment that you are using to 'store' your excess energy.
- Location
- Placerville, CA, USA
- Occupation
- Retired PV System Designer
That is correct in some jurisdictions.
If your state has a Net Metering law, then POCO will credit you for any excess that you produce at the same rate they charge you for it. They typically give you a monthly status and clear out any credit you may have at the end of the billing year.
If you also have Time Of Day (TOD) or Time Of Use (TOU) metering, then they will pay you for your daytime excess at peak rates and charge you at off-peak rates for what you buy at night. This can work out well if nobody is home during the day!
If you do not have Net Metering, your POCO's meter may record separately the flow into your house and the flow out (on an intantaneous basis) and pay you one rate for your excess (usually the lowest rate that they pay for power from other sources) and charge you full retail rate on what you use.
If you have the latter situation, you will want to arrange your power loads as much as you can to not have excess power during the day. That is, if you would be using the power some time in the 24 hour cycle regardless, use it during the day to the extent that you can.
Unless there is a separate production meter (usually to keep track of Solar Renewable Energy Credits), they have no idea how much you are producing and using immediately yourself.
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ggunn
PE (Electrical), NABCEP certified
- Location
- Austin, TX, USA
- Occupation
- Consulting Electrical Engineer - Photovoltaic Systems
As others have said, it depends on your utility's rules regarding PV interconnections. One of the pieces of homework that anyone considering PV for their residence is getting those rules and running a few theoretical scenarios to figure out the "what if's". FWIW, it is almost never financially advantageous to install a PV system with batteries on a residence that has reliable grid power.
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- Location
- Placerville, CA, USA
- Occupation
- Retired PV System Designer
The most common exception to that is when the grid power is unreliable and the extra cost of batteries returns continuity of power, which has a value of its own. But in most cases a generator would do that at lower cost.
Unless you use a hybrid inverter designed to work off grid and also sell excess power back to the utility, you would have to switch your panel array connection between the standby off grid system and the grid tie system as needed.
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