DE4204437C2 - Plant for heat energy generation using photovoltaics - Google Patents

Description

The invention relates to arrangements for thermal energy Obtained when the photovoltaic effect is used.

The use of the photovoltaic effect is always with that Problem associated with the resulting electrical power fluctuates depending on the solar radiation and thus only those consumers are sensible who have this at all times Can take up services. Usually are between photovoltaic generators and consumers energy buffers arranged. In smaller plants, batteries are used as energy buffer is used, for larger systems is via inverters a coupling with the electrical supply network is established and used this for buffering.

Another difficulty in using photovoltaics results from the characteristic curve of the Si solar cells. The Ur The voltage of a Si solar cell corresponds approximately to that of the locks voltage of a Si diode and is in a sensible work area hardly dependent on the radiation intensity; the generator current increases proportionally with the radiation intensity. The Internal generator resistance is therefore not constant.

Consumers with constant internal resistance can only use one Operating point, d. H. for a certain radiation intensity grant fit. With the already low efficiencies Such consumers are prohibited by photovoltaic generators by itself.

In order to make the necessary adjustment for optimal energy utilization in To guarantee every working point are corresponding rules circuits known (MPT - maximum power tracker).

These control circuits are usually in the inverters or charging circuits with mains or battery backup inte grated.  

For the Mpt and the coupling to an energy buffer are at the known solutions always costly active electronic Circuits required. Buffering with the electricity supplier The supply network is also problematic because the solar energy is often available at times of low load stands and thus the control problem only relocated to the network can be.

To justify this expense are inevitable Photovoltaic systems from a minimum size of 1 kWp required Lich. The electrical energy obtained with such systems is very expensive and therefore only economical for a few applications meaningful.

The solution proposed in DE 33 35 520 C2 Power adjustment between a solar generator and one Consumers - with constant performance - through shunt Circuits is for optimal energy utilization in the sense not suitable for the task set here. The consumer must with a fixed power, the shunt circuit then convert the excess energy into heat.

In the performance range below the specified consumer Power then inevitably results in energy losses.

The well-known solar panels are more energy efficient were in which mostly a liquid as a heat transfer fun yaws. These systems require at least one circulation device and a control device, its cost and energy requirements are in turn justified only for larger performance areas. In addition, wear occurs due to moving parts (pumps, etc.) and the systems are not maintenance-free.

The invention has for its object by loading the photovoltaic generator with an inexpensive passive Consumer, coupled with a suitable energy storage so far the technical effort for heat energy generation lower that a sensible operation even with smaller plants becomes possible.

According to the invention, the electrical consumer provides a series circuit of semiconductor diodes. The number of diodes is so chosen that the sum lock voltage or sum Z- Voltage is the terminal voltage value of the photovoltaic Generator with medium radiation intensity. voltage losses over longer connection cables or possibly series diodes in photovoltaic modules can also be considered  become.

The temperature dependence of the terminal voltage photovoltaic Modules are taken into account by the fact that the sum locks Dim voltage (or Z-voltage) according to the most unfavorable value sioned or adapted by appropriate measures.

The semiconductor diodes are attached to heat-conducting supports arranges, which in turn has good thermal contact with the surface of the components in the form of conventional heating cartridges. For larger capacities, the use of heat carrier liquids or pastes sufficient convection be secured.

The heating cartridges are used to heat a solid, liquid or gaseous storage medium. The is particularly suitable Arrangement for heating hot water tanks. At same The electrical heating cartridges can have geometric dimensions in the existing hot water tank simply against the solar Cartridges are exchanged. The advantage here is that initially only a definition of a specific terminal chip value of the photovoltaic generators (solar modules) must follow. By connecting additional modules in parallel, sluggishly an increase in performance of the system - with observations possibly limit parameters - take place.

This arrangement does not require any other system components except possibly control devices and no additional auxiliary energy and is maintenance free.

The performance of a system is based on costs probably tend to under-dimension. In combination with a conventional network heating, however, this is not a problem table.

That has a positive effect in most applications the heat storage in the winter half-year usually in coupling  with building heating (oil, gas or other fuels) be driven and only in the summer half year the use of the elek trical heating.

The performance of the photovoltaic system comes to this Needs conveniently close.

An increase in the overall efficiency for a larger fluctuation range in the inherent temperature of the photovoltaic solar modules can acc. Fig. 1 can be achieved in that a thermal switch 3 in thermal coupling with the module 1 bridges some diodes of the solar heating cartridge 2 from about the middle of the temperature range. Several staggered thermal switches are also conceivable, but the efficiency is quickly reduced by the expense.

A simple overtemperature protection is possible in that a further thermal switch 4 in thermal coupling with the solar heating cartridge bridges all diodes of the solar heating cartridge from the selected critical temperature (e.g. 85 ° C).

example 1

Depending on the selected terminal voltage of the solar modules, n Si diodes pressed into round aluminum sheets. The diameter this sheet is smaller than the inner diameter of the used pressure-resistant cartridge case. By means of appropriate Bores in these sheets and insulating spacers they are attached to each other on insulated metal carrier bolts attached in a row. Via wire bridges between the carrier plate and the free connection of the subsequent diodes electrical series connection realized.

One of the carrier bolts becomes conductive with the - from the connection side - last diode connected. The second support bolt is connected to the diode of the series circuit, which  for the possible temperature compensation the corresponding Ab handle represents.

Using insulating spacers, this is lined up Sheet metal existing column is centered in the cartridge. The remaining cavity is filled with thermal oil and the Cartridge towards the outer end with an elastic seal Separated silicone rubber. Before this rubber seal is a fixed carrier plate arranged, the one hand the chew Chuk seal protects and on the other hand the connection clamp and the possibly installed thermal switch attached are.

Example 2

In a household with a 200 l hot water tank, photovoltaic solar modules with 600 Wp are installed. (Modules with 22 V; 2.5 A - 2 modules in a row and 6 in parallel, so that the connection values are 44 V, 30 A.) In addition to the existing heating cartridge, a solar heating cartridge according to Example 1 is installed. In the summer half year, an average yield of 5 KWh / day can be expected. A temperature increase of about 20 ° C for the 200 l content of the storage is achieved.

At the usual hot water temperature of around 40 ° C it can a quantity of over 100 l can be withdrawn daily.

The electric heating cartridge can of course par be operated allel. For parallel operation given many control options. It is particularly cheap Operation of the normal heating cartridge via night current, apart from cheaper tariff is a call heating over the entire Achieved during the day.

Claims (4)

1. Plant for heat energy generation by means of photovoltaics with solar cell modules installed according to general rules without active control and adjustment circuits between photovoltaic modules and the consumer, characterized in that the electrical consumer consists of a series connection of semiconductor power diodes or power Z diodes, whose total lock voltage or total Z voltage corresponds to the terminal voltage of the photovoltaic modules present at low radiation intensity, the semiconductor power diodes or power Z diodes being arranged on support structures in such a way that sufficient heat transfer from the diodes to the surface of the in the form the known heating cartridges running consumers is guaranteed and this consumer is coupled to a heat storage device. 2. Plant for heat energy generation by means of photovoltaics Claim 1, characterized in that the heat storage direction is a hot water tank. 3. Plant for heat energy generation by means of photovoltaics according to claim 1 and 2, characterized in that one or more thermal switches 3 are installed in fixed heat coupling with the generator 1 and when their temperature limit is exceeded, which corresponds to the mean or partial value of the possible temperature range, bridges one or more diodes of the solar heating cartridge 2 , the voltage component of which is closest to the total voltage of the temperature-dependent voltage change of the clamping voltage of the solar module 1 . 4. Plant for heat energy generation by means of photovoltaics according to claim 1 and 2, characterized in that a thermal switch 4 is arranged in fixed thermal coupling with this parallel to the diode series connection of the solar heating cartridge 2 , whose switching temperature corresponds to the maximum permissible temperature of the Heizespei chers.