Grid-tied PV systems without energy storage do not reduce load in a substantial and predictable way, which will be a keystone of sustainable energy policy. We will need to institute three main objectives to reduce greenhouse gasses and localize power production to facilitate smaller, efficient local power plants.

The Nature of Grid Tied PV

Bill vonBrethorst | Planetary Systems

The Nature of Grid Tied PV
Grid-tied PV systems without energy storage do not reduce load in a substantial and predictable way, which will be a keystone of sustainable energy policy. We will need to institute three main objectives to reduce greenhouse gasses and localize power production to facilitate smaller, efficient local power plants.
Bill vonBrethorst, Planetary Systems

Summary

Grid-tied PV without energy storage will never be able to supply more than a small percentage (3-5%) of the energy requirements in the US. The current grid structure of very large scale coal power plants as base loading systems and highly extended transmission lines will never be able to adequately supply our future energy or mesh with small scale generation in a way that best utilizes grid tie systems. The grid will need to be totally redesigned to integrate small generation inputs from PV, wind, biomass and other more sustainable system inputs, the majority of which will need to utilize energy storage to provide reliable energy reduction. The current grid system essentially precludes effective reductions of greenhouse gasses by these grid tied systems as we will demonstrate, and mandatory energy reductions will be required.

Background

Advertising and press releases since around 2000 touted the “coming decrease in PV cost” due to a mainstream effect and increased sales from grid tied PV systems. The decreased cost of inverter (non-battery) systems was also touted to be a savings, but no real decreased cost per watt in PV has occurred to date. When rebates became available to the end user (mandated by local government and transferred to the end user by the utility) the taxpayer and ratepayer simply picked up the tab for a portion of the systems cost. Further, no real effective reduction of residential or commercial electrical loads has been realized, including in the state of California which has the highest concentration of residential grid-tied PV systems. The San Francisco Chronicle stated in an article in July, 2006, that California has a current generating capacity of 48,000 megawatts; in just one day in 2006, the state required over 50,000 megawatts. A report submitted by the State of California indicates that, at maximum potential, the State of California might have 1800 megawatts of Renewable inputs from PV in the year 2017, if the current level of funding and installation continues. The obvious shortfall is staggering if greenhouse gasses are to be reduced in any significant way.

A brief history of renewables is required.

Renewable energy systems utilizing battery storage began appearing in the early 80’s and by 1990 were widely available to those building homes away from the electrical grid using crude modified sine-wave inverters and contactor-type charge controllers to regulate power from solar (PV) modules. During the early 1990’s, solar (PV) modules were being produced by a variety of manufacturers, including some oil company subsidiaries, off-shore producers, etc. Due to the limited nature of the off-grid market, few if any of these companies were profitable due to the low volume of sales. In 1995, battery-based inverters became available in real sine-wave versions, paving the way for grid-interconnect.

The original cost to dealers of solar modules was then and is currently around $ 5.00 per watt with an average retail cost of around $7.48 per watt, which limited the market. According to California state data, the average installed PV system costs $40,392 for 5.4kw which is an average cost of $ 7.48 per watt (since the inverter is only 5% of the cost). The cost of a battery-based, grid-tied system using standard flooded lead acid batteries and inverters would average $25,000 because smaller arrays are possible.

With the emergence of the environmental movement and as Global Warming began to be documented in the late 90’s thru 2000, many inverter manufacturers in conjunction with the PV industry began to implement an inverter which could be connected to the grid without batteries. The theory and rationale was that batteries limited sales, were inefficient, added cost and could not easily be mainstreamed to increase PV sales in the emerging grid-tie market. These inverters were originally low voltage (48vdc) with batteries, later higher voltage units (250V+) were produced, having deleted the battery storage component. This change was purported to increase system efficiency with the intent to offset higher utility prices by selling back power in excess of load demand. At the same time, state governments, as a part of utility restructuring and de-regulation, began to implement net-metering policies which allowed funds to be credited back to the user for power generated from renewable sources. Due to the higher voltage architecture of the inverter systems, larger strings of PV panels were required due to the voltage requirements of the inverters with higher power requirements which resulted in more PV wattage being installed in systems. Now, PV manufacturers could sell more PV panels and made more profit.

Grid-tie systems

Grid-tie PV marketing promises to reduce electric bills and create a corresponding reduction in greenhouse gasses associated with fossil fuel power generation. PV is less reliable as a continuous power input than wind generation (it depends where). PV modules are greatly affected by temperature, angle of sun, altitude, air mass density, air pollution, and clouds. Therefore, with few exceptions, PV output is continuously variable and completely unpredictable. Using the present technology, grid-tied inverters without energy storage electronically try to enhance the output of the panel string using various electronic methods which increases output marginally. The intent is to maximize the few hours of daylight in which a fixed mounted solar module has the greatest output, sending this power to the house or business main electrical panel where the power generated mixes with imported utility power. If the power being produced is greater than the power being consumed, power is exported back to the grid through a bi-directional utility meter. In areas with net-metering laws, the utility would then credit the consumer for this excess power at a rate variable from wholesale to retail cost of the electricity. There is no direct tie by either mandate or code to decrease the actual load of the residential or commercial entity, thus resulting in either minimal sell-back or a very large PV array being applied.

As many areas have substantial rebates available and this rebate is based on the kilowatt value of the PV array, more large arrays are being installed. This has resulted in substantial profitability for the PV manufacturers, and high volume of sales for the grid-tie inverter sector. This is evident in the now large selection of PV manufacturers and the growing number of companies offering a non-battery inverter. The perception of lowered cost is due exclusively to the rebate available and systems only appear more affordable to consumers, but in reality, the cost of solar modules has actually gone up due to increased demand and a world-wide shortage of silicon, the primary ingredient (see Wall Street Journal-Commodity trading). Meanwhile, the USA has steadily increased its electrical overall load over the past 5 years even though literally thousands of grid-tie systems (without batteries) have been installed along with many megawatts of wind generation, both large and small.

This increase in loads has resulted in an additional 1.3 billions tons of coal being burned by US utilities this year (2007), essentially negating the touted effect of ALL the renewable sources by increasing CO2 emissions, not reducing them. All of the gains in CO2 reduction to date have only been on paper. The most egregious claim is that somehow energy can be “stored” on the grid and that every watt sold back somehow reduces greenhouse gas emissions by utilities. Simple truth in advertising warrants an examination of these claims. Further, as the effects of global warming become more severe, utilities will not be able to guarantee a level of stable electrical services as in the past and this instability will impact the inputs from renewable energy, especially grid tie systems without energy storage.

Misconceptions & “Greenwashing”

While grid tied PV systems certainly can contribute to lowering electrical costs for a majority of applications, they do not have a corresponding reduction in green house gasses and will never have this effect. One of the pitfalls of the RE market is a penchant for simply applying dollars to fix problems without any social change, which should be labeled “Greenwashing”.

Here are the most egregious claims *

  • Grid-tied PV systems are an economical way to reduce electrical billing;
    Though is this generally true, if the average PV system in California is over $40,000, then a much less expensive path to energy reduction would have been to change out any major appliances to newer, more efficient ones and use Compact Fluorescent bulbs-this would have the same general effect.

  • Grid tied PV systems are a socially responsible way to “Green up” your home;
    Installing a PV array on your roof to sell back power, taking your rebate and not substantively altering your electrical consumption does not serve the larger purpose or energy conservation because this action does not appreciably alter the lifestyle which created the excess electrical loads. Without thinking about our energy use, we will eventually end up right back where we started, with more load than the existing array can offset.

  • A larger the PV array equates to a more affordable the system with rebates;
    A larger array can become a liability. PV modules will age; decrease in output eventually and the larger the array, the higher repair or replacement cost. Further, as utility cost per KWh increases, your array will become smaller in relation to the amount of utility costs it will offset. In net metering situations, as the rate goes up, the demand factor goes up also and the increase in utility cost does not transpose to the PV generation as this and your load remain static. The array cannot displace more surge loads unless the size of the array is increased. . Every penny increase in utility cost will have a negative effect on the relative output of the connected PV array. Larger PV arrays mean larger replacement and maintenance costs.

  • Grid-tied PV systems will combat Global Warming and reduce CO2 emissions;
    By far, the largest misconception regarding grid-tied PV systems is the claim that each kilowatt produced is directly correlated to a corresponding reduction in CO2 output from a utility source. Nothing could be further from the truth and this data, which is easily available from the government and private sector, proves this dramatically. According to the US Department of Energy, Renewable sourced inputs still remain at less than 1% of the total aggregate, and overall use of coal by utilities without substantial emissions controls is up. Nearly every state has a permitted new coal fired plant being or one about to be constructed. Coal fired plants simply cannot respond to grid-tie inputs (hundreds of miles away) by reducing fuel consumption. The average coal fired power plant is rated at about 500 megawatts. The fuel and water used are always available and the steam supply is constantly level because they are all base loading plants, with computerized fuel and steam input. Even at best, grid tied PV is marginally available as a power source using grid-tied non-battery technology given the intermittent capability of PV output. Given the great distances of transmission, the losses due to transmission and the current financial and regulatory issues relating to utility power, PV will likely never contribute more than a single digit peak load reduction in very sunny areas and will not have the impact that mandatory energy conservation could have. Grid-tied PV systems without energy storage will never have a measurable impact on real power production. The all-electric home, electric stove, electric heat and the all-electric future envisioned in the 1950’s is neither feasible nor realistic when confronted by the damaging and destructive means required to supply that electric power on the massive scale required by 300 million people. Simply look at China for a chilling preview.

Energy Storage-the magic bullet

Energy storage has been the key to the increased efficiency of hybrid cars combining batteries and a smaller engine with electric motor systems. Even utilities recognize the need for energy storage when using renewable resources. Australia will be the first to employ utility-scale energy storage from VRB (note-1) systems. VRB Power Systems Inc. is an energy storage technology developer which is marketing, selling and manufacturing products utilizing the patented VRB Energy Storage System (“VRB-ESS™”). The VRB-ESS can economically store and supply large amounts of electricity on demand and is focused on stationary applications.

Simply converting PV energy to AC and putting this energy out on the grid may make sense from an accounting standpoint, but PV without storage does not make efficient use of the energy produced. Generally, grid tie systems without batteries consist of a very small (in terms of KVA and electromagnetic mass) inverter which is electrically unable to push great amounts of power back into an “infinite” grid. Think of the grid as a great pipe with very high pressure water flow, into which a miniscule and less energetic stream is injected. The source of this flow is a very high pressure pump. Even multiple small streams injected cannot sustain the high pressure flow exerted by the main pump, and if that main pump were removed, the pressure and volume would drop drastically. In the case of grid-tied inverters (without energy storage), these inverters have very little mass, and cannot remain connected to the grid without the main base loading generators being on-line also. Any instability and the grid-tied PV systems all, by design, are off-line.

Main base loading generators are, at this point, mostly coal fired. A constant, computer controlled amount of steam and fuel are required to maintain the turbine output. No variation based on load is ever permitted in the fuel and steam levels. Therefore, no short-term grid input (PV or other) will affect the CO2 emissions of these plants outside of real (24 hour a day) load reduction.

Grid-tied systems with batteries, with virtually the same or smaller PV array, and with reasonable energy efficiency, can power major loads including refrigeration, fans, washers, dishwashers, lighting and other loads from stored energy rather than instantaneous power from the grid or PV. Independently powered using battery based inverters can effectively soak up the load surges, thus these loads are removed from the grid (isolated by the local lower generation and not transferred to the grid).. In addition these systems, using a reduced solar array and advanced lead-acid, sealed AGM (note-2) battery systems can supply as much as 50% of the homes load on a 24 hour a day basis. This “flywheel” (a flywheel continues rotating even though the motivation force is removed) effect would have a very significant effect on the grid compared to the few hours daily that a grid tied system without batteries can deliver full power. With the same numbers of grid tied systems with batteries this 24 hour a day load reduction will benefit the utility and the environment since nearly all AGM batteries are completely recyclable. If 100,000 homes were fitted with PV-energy storage systems, instead of non-battery systems, the electrical profile of these homes would be reduced by over 70% as an aggregate. The resulting extra cost of the battery systems, would be more than offset by the reduction in solar modules while giving the same effect, and the overall cost to the consumer would be reduced even further by the same rebates.

Conclusions

Powerful interests want to continue using coal and nearly every state in the USA has plans underway to build a new coal fired plant with inadequate emission controls. No carbon sequestration scheme has been adequately tested or proven to work at this time. All parties seem to favor a free-market approach, which will create more blind alleys and waste more time than we have to spare. Our present electrical load demands require coal fired plants be used as base loading systems and no one seems inclined to reduce load, just as people continue to drive gas-guzzling autos in the face of rising gas prices. We can no longer afford to pretend that electrical power can actually be transmitted effectively for hundreds of miles in the face of factual evidence related to large transmission losses. Over 79% of our electrical power comes from coal and coal is a primary contributor to greenhouse gasses. By employing the same technology of hybridization used in automobiles to electrical power, utilizing primary battery energy storage at the end-user level, we can quickly achieve superior results in actually reducing electrical demand on a 24 hour a day basis. Grid-tied PV systems without energy storage do not reduce load in a substantial and predictable way, which will be a keystone of sustainable energy policy. We will need to institute three main objectives to reduce greenhouse gasses and localize power production to facilitate smaller, efficient local power plants.

  1. A mandatory energy standard will need to be established for homes, businesses and energy producers based on the European model where the use of the structure is modeled on the lowest energy use possible in that area and climate. Although this may be perceived as rationing, it will be just as necessary as it is controversial. Our survival depends on viewing energy as a valuable commodity and equally valuing the side effects of how we get that energy. No carbon credits, just carbon reduction-you cannot pay for the privilege of polluting.

  2. Use of renewable energy inputs should be required with rebates tied to energy conservation and reduction including wind, PV, thermal and all must include an energy storage component. All incentives need to be tied to a production credit rather than a rebate from the utility for long term incentives such as in Washington State’s production credit law-they pay consumers up to $ 0.26 per kwh produced from the RE source. In order for the energy standard to be viable, cities and rural areas will need to maximize the storage of energy to bring load reductions to a fully realized 24-hour a day minimum and maximum which is predictable and reliable.

  3. Emphasis needs to be placed on a mix of energy resources with local control. In some cases this will still be coal, with superior emission controls and with limited carbon sequestration technologies, other areas may require small-scale nuclear plants as are used in France, where the average plant is not over 100 megawatts. There can be no distinction between carbon sequestration and nuclear waste, as both will impact all our futures and either will do us great harm if not carefully controlled. Energy will and should cost more; we cannot delude ourselves into constantly looking for cheap energy-it never existed in the first place.

Note-1: The VRB Energy Storage System (VRB-ESS) is an electrical energy storage system based on the patented vanadium-based redox regenerative fuel cell that converts chemical energy into electrical energy. Energy is stored chemically in different ionic forms of vanadium in a dilute sulphuric acid electrolyte. The electrolyte is pumped from separate plastic storage tanks into flow cells across a proton exchange membrane (PEM) where one form of electrolyte is electrochemically oxidized and the other is electrochemically reduced. This creates a current that is collected by electrodes and made available to an external circuit. The reaction is reversible allowing the battery to be charged, discharged and recharged.

Note-2: AGM, absorbed glass mat batteries have been used for over 40 years in telecommunications and commercial applications and are more efficient, not affected by environmental conditions and are usually sealed and maintenance free with very long life cycles.

 

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