AU2021201004A1

AU2021201004A1 - Solar hot water system

Info

Publication number: AU2021201004A1
Application number: AU2021201004A
Authority: AU
Inventors: Evan Kaufline
Original assignee: Battery Pv Pty Ltd
Current assignee: Battery Pv Pty Ltd
Priority date: 2020-02-26
Filing date: 2021-02-16
Publication date: 2021-09-09

Abstract

A solar hot water heater system comprising: one or more solar photovoltaic panels which are wired to provide power using direct current, an electric resistance dual element heating assembly which can be used with both direct current and alternating current, said dual element heating assembly immersed in a tank containing water and a control unit to turn power on and off to the dual element heating assembly when the water in the tank reaches a set temperature and said control unit capable of changing power supply to any one of the heating elements in the dual element heating assembly either in DC mode or AC mode depending on availability of incident solar energy and the water temperature inside the tank. 1 LL

Description

LL AUSTRALIA

Patents Act 1990

COMPLETE SPECIFICATION

Standard Patent

SOLAR HOT WATER SYSTEM

The invention is described in the following statement

Technical Field

The present invention relates to a photovoltaic (PV) powered solar hot water

system and a method for controlling a photovoltaic powered water heating

system to prevent build-up of legionnaire bacteria. In particular, the present

invention relates to a solar hot water system that uses electrical power generated

by a photovoltaic energy source in Direct Current (DC) form without being

converted to Alternating Current (AC) form. The heating arrangement of the

present invention can also be used in other heating applications such as heating

floors and spas using direct current from a photovoltaic energy source.

Background

The most common electric hot water heaters use high voltage electric heating

elements immersed in a tank that are connected to an electric grid power source.

These tank heaters are usually powered by 240 V, AC power to keep the hot

water tank warm and ready to use. The power to run these heaters is drawn from

the local power grid in most cases. A typical hot water tank uses heating

elements with an energy rating of about 3600 W which can rapidly heat the

water in the storage tank for use, and rapidly reheat the tank when a lot of hot

water is used.

Photovoltaic arrays are typically used in domestic scenarios to generate

electrical power for storage in batteries or for supplying electrical power to the

utility grid. Photovoltaic arrays produce DC electrical power whereas household

appliances including electrical hot water systems use AC power. Thus, typical

photovoltaic arrays convert DC supply to AC power supply prior to using in any

domestic application. Prior patents on this subject show the photovoltaic panel

connected to an inverter, which takes the low photovoltaic panel voltage and

converts it to 240 V AC. This power is then used to power conventional hot

water tank heating elements. This process is inefficient and significant amount

of energy is lost in the conversion process.

The prior art discloses some hot water heating arrangements that use DC

electricity directly without any conversion to AC in heating the water. But most

of the existing products that use DC power have two separate heater assemblies,

at least one having a dedicated AC heating element and at least one having a

dedicated DC heating element and associated controllers. Having two separate

heating element bundles make hot water apparatuses more expensive and

complex to operate and maintain.

Some patents that disclose photovoltaic direct current water heating systems

recite adding and removing resistive elements using relays to change the

resistance of the heater elements to match the peak power being produced by

the solar panels. High resistance in the morning is incrementally switched to

low resistance at noon and then incrementally back to high resistance in the late

afternoon. That system is complicated and needs a number of different

resistance heaters connected to relays to achieve this variable resistance.

In addition, the prior art hot water systems that use dedicated separate AC and

DC heating elements at different levels in the tank have the problem of creating

layers of water at different temperatures inside the water tank. Some of these

layers can stay stagnant for extended periods of time. This can cause or increase

the susceptibility of the water heating system to bacterial growth. Most species

of Legionella bacteria live in water that is stagnant and they survive under a

wide range of temperatures. The formation and multiplication of such bacteria

can be prompted in hot water tanks where stagnant water layers at different

temperatures are present and where the water temperature is suitable for

bacterial growth.

The hot water system of the present invention overcomes above drawbacks by

using a heating element that can be used with either an AC electricity supply or a DC electricity supply to heat water. In addition, the present invention is suitable for preventing build-up of legionnaire bacteria.

Summary of the invention.

The present invention provides a more cost-effective water heating system that

is easier to operate and maintain using DC voltage derived from a photovoltaic

power source. The hot water system of the present invention comprises a hot

water tank control unit combined with a customised heating element which uses

DC power sourced from PV electric solar panels to heat water combined with

AC power from the electricity grid to maintain the lowest permissible water

temperature in times of insufficient sun light. The device is completely

automated and uses a digital thermostat to govern which source of power to

draw from to heat the water inside the storage tank. Another advantage of the

present invention is that the novel AC, DC heating element assembly can be

retrofitted to any existing storage hot water tank and is adaptable to suit

different size usage needs. The device can also be used to heat pools, spas and

under floor heating.

In another aspect of the present invention, it provides a solution to health risks

associated with accumulated bacteria that breed in water storage systems that

run at temperatures below 50C for prolonged periods of time by ensuring that

the water temperature is raised to 60C at least every 72 hours.

Detailed description of the invention

A preferred embodiment of this invention provides a dual element 3600w

heating assembly that fits into the standard single element flange of any existing

storage hot water tank. The 3600w rating allows the maximum permissible solar

DC power to reach the water in the tank in turn reducing the amount of AC grid

power required to an absolute minimum bringing power purchasing costs to as

low as possible. Unlike prior art devices, the heating element of the present

invention can be used either with DC voltage or AC voltage. This eliminates the

need for having two separate heating elements, one for DC voltage and the other

for AC voltage. During the availability of solar radiation, the heating element

will heat up the water using DC current derived from photovoltaic cells without

being converted to AC electricity. In the absence of solar radiation, the same

heater unit can use AC grid supply to heat up the water using AC electricity.

The control of temperature and changing over from DC to AC and vice versa is

done automatically using a controller.

The control box of the present invention is rated at IP 65 weather rating, which

makes it suitable for mounting outside right next to the hot water tank exactly where it needs to be to minimise associated cable lengths. This enables easier maintenance and installation while keeping costs to a minimum.

The hot water heating system of the present invention further comprises a

removable circuit control card. In the event of a fault the physical unit itself can

remain in the original location with the isolators intact while the control card is

removed for replacement or for maintenance. This in turn allows for easy of

installation with no additional external isolators required thereby minimising

time and cost.

The control device is suitable for On Grid as well as Off grid applications. By

which in an Off grid situation where mains grid power is not available the

control unit simply substitutes Battery or Generator power as a means of backup

AC power to boost the AC element in times of little or no sunshine while

continuing to source its DC element power from its dedicated solar panels.

Another aspect of the present invention is to provide an effective method for

controlling and preventing growth of bacteria inside the water tank. The

effective prevention technique of the present invention is to ensure that the

water temperature inside the tank reaches 60C at least every 72 hours by means of an internal counter which resets to zero every time the water temperature inside the tank reaches 60C. If the temperature inside the tank does not reach

C within the 72 hours time frame the AC grid power is activated to boost the

water temperature to the desired 60C and the whole cycle starts again. This

programmed feature makes the whole unit hygienically safe to use. Any existing

units without this feature would need to raise the minimum temperature settings

to manage the bacteria and it turn raise power running costs making it much less

efficient.

To determine the temperature of the water within the holding tank, the water

heaters include temperature sensors. Typically, a temperature sensor is placed

above and proximate to each heating element. Thus, the individual temperature

sensors can determine the localized temperature of the water proximate the

individual heating elements. This allows for localized heating of the water in the

water heater to, again, improve efficiency.

The heating element assembly and the circuitry used in the hot water tank of the

present invention is described in more detail below with reference to figures 1

and 2.

FIG. 1 illustrates an embodiment of the dual element heating assembly of the

present invention which can be used using either AC or DC power supply. As

shown in figure 1 the heater assembly has two separate heating elements. Each

of these heating elements are typically around 20 ohms and has an energy rating

of around 3,600 watts. As shown if Figure 1, the two elements are connected to

flange which is of the same dimensions as the heater flange of an existing AC

hot water tank. This makes it suitable for easily retrofitting the heating element

assembly of the present invention to any existing hot water tank powered by

grid supply. Functionally, both heating elements shown on figure 1 are same

and can be used either with AC or DC electricity supply. At times when the DC

power supply from the PV cells is not available, one of the heating elements

shown in figure 1 can be used for heating water using AC grid supply.

Figure 2 is an electrical circuit diagram showing the use of the novel heating

assembly of the present invention.

As shown in figure 2, the circuit card is supplied by two separate sources of

power which are the AC Grid and DC Solar PV panels which are electrically

isolated from one another. The DC voltage used can be in the range of 150-600

volts and the AC voltage used is 240 volts. The AC Grid power is used to

supply the control circuit power which operates the temperature sensors, relays and contact coils. The AC power is also used as a backup boosting power source in times of minimal sunlight. The DC Solar PV power is the predominant water heating power source. The DC power enters the circuit card and travels through a normally closed contact which operates and opens the circuit once the water temperature reaches approximately 90C, disconnecting the power to the

DC side of the element. Once the temperature drops below that selectable 90C

figure the contractor closes and the power travels through to the heating element

once more. The AC power enters the circuit card and travels through the two

temperature sensors which are set to approximately 90C for the DC and 30C for

the AC. The power then travels through a normally open contact which operates

and closes once the water temperature drops below that selectable 30C figure

and onto the AC side of the heating element. When the temperature rises above

C the contact opens and disconnects the AC power once more.

At any given time, both separate heating elements can be powered separately by

each AC power and DC power. The associated controllers and temperature

sensors will determine which power source to be used.

Claims

Claims defining the invention are as follows:

1. A solar hot water heater system comprising: one or more solar photovoltaic

panels which are wired to provide power using direct current, an electric

resistance dual element heating assembly which can be used with both direct

current and alternating current, said dual element heating assembly immersed in

a tank containing water and a control unit to turn power on and off to the dual

element heating assembly when the water in the tank reaches a set temperature

and said control unit capable of changing power supply to any one of the

heating elements in the dual element heating assembly either in DC mode or AC

mode depending on availability of incident solar energy and the water

temperature inside the tank.

2. A solar hot water system according to claim 1 where the DC voltage used is

150-600 volts and the AC voltage used is 240 volts.

3. A solar hot water system according to claim 2 where the control unit further

comprises inbuilt AC and DC isolators.

4. A solar hot water system according to claim 3 where in the control unit is

suitable for On Grid as well as Off grid applications, in which in an Off grid

situation where mains grid power is not available the control unit simply substitutes Battery or Generator power as a means of backup AC power to boost the AC element in times of little or no sunshine while continuing to source its

DC element power from its dedicated photovoltaic panels.

5. A solar hot water system according to claim 4 where the power output of the

dual heating elements are 3600 Watts each.

6. A Solar hot water system according to claim 5 where in the control unit is

rated at IP65 whether rating.

7. A solar hot water system according to claim 6 wherein a digital thermostat is

used to govern the source of power either DC power from photovoltaic panels

or AC power from the grid.

8. A solar hot water system according to claim 7 where in in the control unit

includes a removable circuit control card.

9. A hot water system according to claim 8 which includes a means to ensure

that the water temperature reaches 60 degrees Centigrade at least every 72

hours.

10. A hot water system according to claim 9 where the means to ensure that the

water temperature reaches 60 degrees Centigrade at least every 72 hours

includes a counter which resets to zero every time the water temperature inside the tank reaches 60 degrees Centigrade.

11. A hot water system according to claim 10 which includes a means to

activate AC grid power to boost the water temperature to the desired 60 C if the

water temperature does not reach 60 C within the 72-hour timeframe.

12. A solar hot water system according to any one of the claims 1 to 11, wherein

the tank containing the water is an existing domestic hot water tank and the dual

AC, DC heating element assembly is retrofitted to an existing domestic hot

water tank.

13. A method of preventing build-up of legionnaire bacteria using a hot water

system as defined in any one of the claims 1 to 12, said method comprising:

• Ensuring the water temperature inside the tank reaches 60C every 72

hours by means of an internal counter which rests to zero every time the

water temperature inside the tank reaches 60C.

• Activation of AC grid power if the temperature does not reach the

required 60 C within a period of 72 hours to boost the required

temperature to the required 60C and commencing the whole cycle again.