Today’s solar technologies are relatively simple, compact and efficient. The basic technologies are generally divided into electricity-producing; and water/space heating.

Photovoltaic technology (PV) converts direct sunlight into direct current (DC) power via the photoelectric effect. The DC power is then either stored in batteries for later use or inverted to utility-compatible alternating current (AC). Solar electricity production can significantly reduce or conceivably eliminate your monthly electric (energy) costs while providing a hedge against future rate increases. PV systems on the roof or ground are quiet and have no moving parts (except for trackers). PV on your home or business minimizes our overall dependence on carbon-based fuels and conserves valuable natural resources.

Residential home values increase at 20x the annual energy savings according to the National Appraisers Institute.

(Example: $1,000/yr x 20 = $20,000 increase in home value when solar is added).

Net Metering measures the difference between the electricity you use from the utility versus the electricity you produce from your solar array. Net metering allows the customer-generator to use the utility grid like a battery bank account. The customer can deposit kilowatt hours into it and withdraw them later when they need to use them at no “net” cost to them. When one produces more kilowatt hours (kWh) then one uses, the “excess” power gets metered back into the grid at the same rate the utility would be billing you at that time-of-use (TOU). If you could manage to sell all your excess kWhs back to the utility at their peak value then the better your investment’s rate of return!

Solar water heating (SHW) and space conditioning by the sun has been happening since the beginning of time. Two major types of system designs prevail-

Passive systems just act as storage tanks that get “preheated” by direct exposure to sunlight. This preheated water is distributed through the system with normal domestic water pressure. These systems have a drain, pressure relief and tempering valves built into the design. Freezing may be a concern for some climate zones if the system is not drained back and/or remains dormant for days between use.

Active systems usually have some primary and secondary storage tanks with a separate circulating pump that are controlled with thermostats that detect when the water temperature difference is great enough to be activated. Primary storage tanks usually have a closed-loop heat transfer liquid such as food grade propylene glycol which can absorb much more heat than water. This heated liquid circulates between the collectors and storage tank(s) and preheats the ‘domestic’ water side when sun is available as described above. Active system sun collectors may be composed of vacuum tube heat exchangers, or tube/shell types. If the primary heating loop leaks or fails, domestic water would become contaminated with food grade propylene glycol and need replacement.

Solar Fraction

Collector number and capacity is based on a winter solar (fraction) heat gain target of 30%. This means a winter heating cost of $3000 would have offset solar 'savings' of $3000 x 0.3=$900

Space conditioning accompanied with solar hot water systems is often done using a ‘radiant’ floor method. This method has a series of closed tubing loops in the sub-floor area that can be flow-adjusted and sent to where the heat is needed. The radiant heat in the floor rises and is preferentially absorbed into a body’s thermal mass and not wasted on heating the room air. The trick is to properly size the hot water supply tank and have a back-up fuel supply to augment the difference in energy required to maintain the desired temperature during the coldest months of the year.

GeoExchange

Another type of heating/cooling system is called 'Geothermal' or GeoExchange. This technology takes advantage of the constant mantle temperature of the earth's crust (between 50-60°F depending on geography). Piping sections containing circulating liquid (water, glycol) are placed in the ground (under ponds, in trenches, or deep vertical holes). Fluid is pumped through the system either absorbing or releasing heat depending on desired room temperature. Heat exchanges utilizing compressible liquids with high heat capacities. Solar water heating as well as photovoltaic applications may be integrated into various configurations.

Rebates

Currently (2009) there are rebates available through the California Solar Initiative (CSI) and must be interconnected with the utility grid to qualify. These rebates will be decreasing as more solar electric capacity is brought online over the next ten years. These rebates are calculated online based on the size (output) of the system in kW, the inverter efficiency, and system design efficiency compared with an optimal site location in Orange County, California.

Tax Credits

Federal investment tax credits have been extended for eight years (2016). These apply to both residences and businesses; one for PV and one separate tax credit for hot water. The ITC is capped at 30% of the after-rebate system cost (no cap for businesses or residences). If you do not owe any income tax, you would not be able to take the ITC (or carry the option forward for more than one year).

Cost/Benefit Analysis

The return on investment (ROI) varies depending on your circumstances (i.e. the cost you pay per kilo-watt hour [kWh], peak demand rate schedule, energy efficiency, energy conservation effort, etc.). In California, the average ROI for residences after rebates and tax credit deducted is anywhere between 6-10 years assuming an average monthly energy bill is about $100-$150. The average payback for commercial (business) investments is usually 3-6 years depending on financing costs, etc. Rebates may still be taken ‘lump sum’ for the systems’ expected performance less than 30kW. Or the customer-generator may elect for quarterly payments based on actual system performance during the billing period. If this option is selected, the rebate will be paid periodically over five years. The exported power must be accurately metered (+/-2%) and recorded by a (certified) third party who then securely reports the information to the CSI processing center for customer payment.

Wind Turbines

Wind turbines now come in all sizes and kW ratings (as low as 1 KW to 1 MW).  You must have the minimum amount of wind in order to reap the maximum power from a utility-tied wind system.  Often, wind combined with PV provides the optimum power production balance.  Seasonal variations may add cost benefits over many years.  New technology includes advances in material composition, turbine design that essentially means less moving parts, less maintenance, better reliability, etc.  These systems have had very good operating history and are guaranteed over warranty by the manufacturer when properly installed.

Installation may be restricted by building codes or above ground (overhead) obstructions such as power lines, airspace, etc. Typical support towers range from a few meters to 80 feet in height.  Optimum conditions include at least an acre of unobstructed air space and clearance from which to draw maximum wind power benefits. Inverters on the market can accommodate multiple inputs that may tie together PV arrays coupled with one or more wind turbines (hybrids).  All systems may be designed with battery storage and AC or DC feed to the house or business.  The batteries are continuously charged and used as the primary power source.  External grid utilities may also be inter-tied to recharge batteries if environmental factors limit renewable production.

Fuel Cells

This rapidly emerging technology may potentially power microscopic size devices up to full scale commercial power plants!  Fuel Cells (FC) hold great promise for an economical, non-polluting, silent energy supply for years to come. FC are being developed for computers which will allow people playing a DVD movie on their laptop to watch it around the world several times over without needing a recharge! When recharge was necessary, it would be as simple as a short blast from a small (non-ozone depleting) aerosol can to restore its full life (watch out Energizer Bunny!).

The types of fuel cells currently on the market and being prototyped in (zero emission) vehicles include natural gas, propane, hydrogen, and methanol to name some. They all pretty much make use of the removal of an electron(s) from a source of fuel (hydrogen atoms) by preferential migration of the positively charged hydrogen atoms (H+) through a porous medium. The electron(s) must take the long way around thereby completing a circuit as they meet up and recombine with H+’s. Eventually fuel cells will be able to commercially hydrolyze and separate water into hydrogen and oxygen gases which will then supply the process indefinitely. The waste product is water vapor…

Hybrid Systems are composed of more than one technology integrated together. Examples include: PV and SHW; Wind, PV; Wind, PV, SHW.

Back-Up Systems generally require a ‘smarter’ inverter which can sense power (frequency and voltage) losses, subsequently disengage itself from the grid and can island (supply energy) on its own assisted by other sources like battery storage, generators, etc.

Off-Grid Systems must be designed (12V, 110V, etc.) and sized for the amount of amp-hours/day that will be required to run appliances, lights, etc. plus a contingency storage capacity (usually around 30%). Off-grid applications pose both a challenge to minimize dependence on external fuel sources and an opportunity to blend technologies like small hydro, with solar PV and hot water, small wind turbine (and back-up generator with alternative fuels production on-site) so you can guarantee yourself a reliable and sustainable power supply year round making “hay” when the sun shines and storing it in the “barn” for later.

Performance Monitoring/Reporting System (PMRS) is now required as part of the solar rebate process when you install systems exceeding 50kW capacity (drops to 30kW in 2010) and receive payments under the performance-based incentive program. It is a primary goal of the CSI to insure that each solar electric system is designed, installed and performs at their optimum in order to yield the greatest benefits for the rate payers of California who essentially fund the rebate program. Most PMRS platforms are now web-based with secured wireless telecommunications to a central processing function that provides real time display and data recording, retrieval, trends and forecasting.

There is also a 1% minimum expenditure cap of the total system cost before a performance monitoring system would be required. So if the PV system retails for $50,000 before rebates, etc., the 1% cap would be $50,000 x 0.01 = $500. This means if the cost of a PMRS exceeds $500, there would be an exemption from it being a requirement.

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