Technical Disclosure Bulletin

Cypress Technologies Corporation

1.  TITLE OF INVENTION:

Solar Energy Sharing Module

2.  DESCRIPTION OF INVENTION:  In describing the technology, the following points are presented:

1. the general purpose;
2. a technical description;
3. the advantages and improvements over the existing methods, devices or materials; and,
4. the economic potential or commercial applications for the technology.

(a)  General Purpose

The Energy Sharing Module (ESM) is designed to provide a means for a single grid-tied UL-1741-compliant inverter to be safely connected to multiple dwellings within a single building, for the purpose of sharing the generated energy.  This product is specifically targeted towards apartment buildings, where a single building might have two, four, or more apartments.  An ESM is connected to the output of an inverter, which is fed by an array of photo-voltaic (PV) cells.  The ESM routes power from the inverter to one of its outputs.  There is one output for each apartment, and each day power is routed to a different apartment.  The ESM measures and records how much power has been routed to each dwelling, and uses this information to determine which output should next be selected.

The following diagram shows how an ESM would be integrated into a solar power system.

The ESM consists essentially of an array of “contactors” (relays), which are connected to the output of the inverter.  An internal circuit board senses the power being produced by the inverter, and controls the closing of the appropriate contactor.

Note that although this module is targeted to PV systems, it will work with any generating system that implements a UL-1741-compliant inverter.

An important safety feature of the module is that it is impossible for the control system to connect two dwellings to the inverter at the same time, even if the control system fails.  This is accomplished with an array of relays, which allow the contactor-coil-current to flow only through one control path.

The control electronics are powered by a separate small solar panel, and the control circuit is electrically isolated from the grid-connected power.

The entry model ESM (ESM32-5) is designed to operate with single-phase 240V inverters, up to 32 amps output (approximately 7.5Kw).

(b) Technical Description

The ESM is connected to the output of the inverter.  Inside is an array of contactors, one contactor per dwelling, with a control circuit board and an LCD for displaying pertinent information, such as the amount of energy distributed per dwelling, etc.  A low-wattage 12-volt PV panel, mounted separately, provides the power required to operate the contactors and control board.

The ESM powers up when sufficient PV energy is available to energize the control system.  Typically this would be fairly early in the morning—much earlier than the time when the inverter would normally become active.  When first powered up after installation, the ESM will select Contactor 1, connected to the first dwelling.  The UL-1741-compliant inverter will detect the presence of the grid, and will prepare for power-up.  The inverter will not power up until there is sufficient PV energy available from the PV array, and until a minimum start-up “OFF” time has elapsed.  (The off-time is a requirement of UL-1741-compliant inverters, and prevents an inverter from powering up before the grid has become stable, especially after the grid has become de-energized or disconnected for some reason.)

At some point the inverter will begin to generate energy, which is sourced either to the dwelling, or through the point-of-common-coupling (PCC) and into the grid.  The amount of energy generated is calculated, and recorded within the ESM, and used to determine which dwelling to select for subsequent connections.  Only one dwelling is connected through the ESM to the inverter at any point in time.  After one day of operation (one PV-generating period), the inverter will become inactive, due to decreasing sun-light.  This period of time will vary from day to day, depending upon weather conditions, time of year, etc.

On following days, the ESM powers up as described previously.  The ESM determines which contactor will be connected (which dwelling), based upon the following factors:

1. The order of the dwelling.  The ESM always begins with the first dwelling when first initialized, and proceeds sequentially from that point on.
2. The status of the dwelling.  The ESM can sense if electric service has been disconnected from a particular dwelling, and will not maintain a connection to that location.  The ESM will re-test each day for re-connection of this unit.
3. The total energy sourced to the dwelling.  The ESM measures and records how much energy has been sourced to each dwelling, and will prioritize connection to the dwelling with the least energy as determined by the sharing algorithm (see below).

The total quantity of energy sourced to each dwelling must be calculated and recorded in order for each dwelling to receive a “fair share” of the available energy being produced.  There are primarily two factors which must be considered:

1. The amount of energy generated from day to day.  This varies based upon the weather and other factors.
2. The number of dwellings connected to the ESM.  This will vary, due to residents moving in or out.  For example, in a complex of 8 apartments, all 8 may be connected to the ESM, however, several may be disconnected at any given time.  As residents move in and out, this number varies.

The ESM uses the above factors and determines the “energy-rate” for each dwelling based upon the following equation:

Energy Rate = Kwh / days

Where “Kwh” is the total number of killo-watt hours sourced to a particular dwelling within the sampling period, and “days” refers to the number of days that a dwelling has been connected.

The equation is constructed so that each dwelling receives an equal share of energy, per day of connection.  This prevents an unbalanced share of energy from being sourced to a dwelling which has been off-line (such as when an apartment is unoccupied), and then comes back on line.  For example, assume that the ESM has been sourcing energy to 4 of its 5 dwellings for 25 days and then the 5th unit comes on-line.  If the ESM used an equation based only on the total KWh (and not factoring in the number of days connected), it would have to source a high amount of energy to this new occupant.  In effect, this would be giving a new occupant the benefit of energy generated during the time when this person was not a resident.

(c)  Advantages Over Existing Systems

Without an ESM, if the owner of an apartment system intended to install a PV generating system, the owner would have to install one PV system per apartment, with each PV system having its own inverter.  For example, a single apartment building having 4 apartments would require 4 separate arrays, with each array having an inverter.  The most obvious benefit of installing an ESM is that it would be more cost effective, since one inverter and one ESM would replace four inverters.  The savings increase with the number of dwellings being served.

Another benefit of the ESM is that it can share energy much more accurately among the connected dwellings, as compared to 4 systems with 4 separate PV arrays.  This is because separate arrays would not necessarily generate the same amount of energy over a given period, due to the arrangement of the panels on the roof and other factors.  In contrast, the ESM is able to measure the generated energy produced and sourced to a given dwelling, and thereby guarantee that the energy is shared more evenly.

Remote Monitoring

The current design of the ESM does not include a remote monitoring feature.  However, this is a logical next step.  This would enable a central location--typically the office in an apartment complex—to monitor all ESM’s within an apartment complex, so that fault conditions could be quickly detected and resolved.

(d)  Economic Potential and Commercial Applications

This product would significantly reduce the cost of installing a solar system onto any multi-dwelling facility, specifically apartment buildings.  The amount of savings would be proportional to the number of dwellings connected to the ESM.   Any application requiring multiple loads to be connected to a single inverter in a sequential fashion could benefit from this invention.