Solar powered photovoltaic (PV) panels convert the sun’s rays into electricity by exciting electrons in silicon cells using the photons of light from the sun. This electricity can then be used to supply renewable energy to your home or business.
Building a solar or solar-ready home without installing a Koolbridge Solar Smart Load Center would be like constructing a new home without a thermostat to control the heating and cooling unit.
Dr. Paul Dent, Founder and Chief Technologist, Koolbridge Solar
Grid-Tie / Grid-Interactive Systems
The most economic solar energy system has no battery, and uses a grid-tie inverter only. The grid-tie inverter generates a current at the momentary voltage of the grid, and pumps it out through the electric meter to wind it backwards, or at least reduce the rate at which units are being clocked up. If the grid fails, it is mandatory that such an inverter automatically shut down to protect personnel who may be attempting to repair the fault. Therefore with such a system, despite his substantial investment in solar power, the user is without power during utility outages. Such outages occur much more frequently in the USA compared to Europe due to the greater reliance on overhead distribution lines in the USA. In rural areas of NC for example, outages occur due to lightning strikes, pick-ups running into poles, ice storms and hurricanes, and an electric alarm clock cannot be relied upon to keep time for more than a day or so in such areas.
Stand-Alone and Battery Back-Up Systems
To prevent the outages described above, the battery-backup type solar system may be used. This uses a stand-alone inverter to convert DC battery power to AC house current. These inverters are not grid tied, and therefore have to meet fewer regulations, making them simpler. In a total off-grid system, the stand-alone type system is sized to supply all the house power, and a very large battery is needed. The user has then, however, a zero electricity bill. In a smaller battery back-up system, solar array and battery only supply power as a back up to the grid for the length of a utility outage. There is little or no reduction of the electricity bill in this case, and this type of UPS system would be used only where no-break power was the most important requirement.
To derive more economic benefit from a battery back-up system, once the battery is fully charged, it makes sense to use the excess power now available from the array to reduce the utility bill. There are two ways in which this could be done:
(a) Transfer some of the loads from utility to solar, even when grid power is available, or
(b) feed the excess power through a grid-tie inverter to the grid (e.g. to wind the meter backwards)
Single Metering Vs. Dual Metering Systems
In some jurisdictions, the utility is allowed to insist that power fed back to the grid go through a separate meter, called an export meter, and the tariff they pay to receive electricity is at their discretion and can be significantly less than the tariff at which they sell electricity via the import meter. Some US and European States have this dual-metering system, but until recently, the export tariff was subsidized so that users received more per KwHr exported than they paid for KwHrs imported, as an incentive to invest in solar. In Germany, these subsidies have been reduced now. In the long term, governments are expected to eliminate subsidies altogether. Therefore, there is currently a move in Germany to install more systems of type (a) above. Panasonic is developing a version of electric car vehicle batteries for this move, which are technically the best type of battery, although likely to be more expensive than current lead-acid accumulators.
In NC, the Utility Commission has ruled that utilities must allow the single metering system, in which solar owners receive benefit for the power they generate at the full tariff of 10c/KwHr.
There is also a non-profit organization called NCGreenpower, that subsidizes the tariff received from utilities for solar power fed to the grid. Since this requires that power fed to the grid be measured separately from power drawn from the grid, the dual metering system is required. The utilities are one major source of funds to NC Greenpower to fund the subsidies, because the result is to encourage owners to invest in the dual metering system, which ultimately will present no competition to the grid when the subsides vanish at some point in the future. This is because the utilities can determine to pay as little as they choose for power fed to them through the export meter. Thus, far from being altruistic, NC Greenpower has the effect of sabotaging long term solar competition to oil and coal by directing the investment into systems of the dual-metering type whose economics are totally controlled by the utilities.