Solar power station in the mountains

A house in the mountains is a dream of many people. It is pleasant to live away from civilization, enjoying the sounds of nature and clean air. At the same time, not everyone is ready to give up amenities like a refrigerator, internet or lighting.

Usually a gasoline or diesel generator is used for autonomous power supply, but then the very idea of ​​outdoor recreation is violated. Electricity should be generated without noise and odor, and the best solution to this problem is your own solar power plant.

In the summer of 2019 we were approached by the owner of a small mountain house located near the village of Bachevo (Razlog municipality, Blagoevgrad district). Task — make two mini-systems: a solar hot water collector and three photovoltaic modules for electricity.

Given our extensive experience in installing and monitoring solar collectors, we have offered the customer, instead of two small systems, to make a complete power plant. You can read more about the benefits of this solution in our article on Photoelectric Water Heating.

The power of photovoltaic modules is proportional to illumination, but when heated, their efficiency decreases. In many cases, mountainous areas have increased potential for photovoltaics, due to a more transparent atmosphere and cooler climate.

Given the budget constraint and the need to heat water in the boiler, we have determined the optimal configuration for the whole system. Twelve solar modules Trina Solar of 280 watts, which together produce 3.36 kW under ideal conditions. In practice, this means 2-3 kW in a typical sunny day.

Most 80 liter water heaters come with a 3kW heating element, which is too much for our system. So we offered the customer a horizontal boiler ELDOM Green Line with 2 kW heater, to use the batteries as less as possible when the water is heated.

The Green Line water heaters have a built-in heat exchanger: this allows for use of hot water from the wood stove to be used for fresh water heating in the winter. In this case, the power plant must only power up the pump that pumps the heat carrier through the water heater and the radiators.

On sunny days, photovoltaic modules will provide enough energy to heat the water in the water heater. On cloudy days, when the power of the modules is about 1.5 kW, an additional 500 Watts will be taken from the batteries.

In the most cloudy weather, such as in the rain, solar power plants typically provide 5 to 15% of rated power. In our case, it is 170-500 Watts: enough for a refrigerator, TV, and router. It is better not to switch on the water heater at that time so that the batteries are not discharged.

We have put all the electronics and fuses in the NENCOM branded box. To convert the DC voltage from photovoltaic modules and batteries to 230 volts Victron Energy invertor MultiPlus-II with power 2.4 kW is used.

The inverter has a built-in charger that allows you to charge the batteries from an external network or generator. As a reserve, we connected to the inverter a gasoline generator with a capacity of 5.5 kW, which was available from the customer.

During the day, excess solar energy is stored in batteries so that it can be used in the night. We connected four 12V Victron Energy AGM Super Cycle lead-acid batteries with a capacity of 230 A·h each. The batteries are connected in series so that the rated voltage of the block is 48 volts.

Useful energy reserve allowed for «Super Cycle» with a discharge depth of 80% represents 230×48×0.8≈8.8 kW·h. n practice, taking into account the losses, this means that fully charged batteries in the dark will be able to deliver 1 kW of power for 8 hours — or for 16 hours 500 W.

In order to heat 80 liters of water in a water heater from 10 to 60 °C it takes about 5 kW·h of energy, considering heat losses (with a heating element of 2 kW it will take 2.5 hours).So it is quite possible to heat the boiler even at night using only half of the battery capacity, but it is better not to misuse it as the number and depth of cycles «charge-discharge» affect battery life.

For the same reason, owners of autonomous power plants should always, whenever possible, plan their main daylight consumption so that they can use solar directly, not through batteries.

On sunny days it is advisable to switch on the washing machine, use power tools and heat the water in the water heater to the maximum possible temperature. Not only does this approach extend battery life and reduce energy loss, but it also allows the photovoltaic system to reach its full potential.

The exact location of all components of the power plant was pre-modeled, so it did not take long to install the site.

The metal box reliably protects the electronics from accidental damage and improves the appearance of the system. All cables are hidden in corrugated and cable channels.

We have equipped the plant with a remote monitoring module that shows the current status and detailed statistics, and also allows you to change the system settings. Due to the constant monitoring of a large number of power plants, we know how they operate under different meteorological conditions.

For example, on December 7, 2019 in the village of Bachevo it was cloudy and the solar modules were covered with a 3 cm layer of snow. However, the power plant generates 140 watts (4% of the rated power of the modules), which guarantees the operation of eight cameras for surveillance, lights and charge the battery.

Of course, at high snow thickness, production stops. Therefore, in snowy areas, it is recommended to install solar panels at a great angle: the snow will slide on the surface of the modules faster under its own weight. It is best to anticipate this at the construction stage of the site. At the same time, a large tilt angle will slightly reduce generation during the summer months when the sun moves high above the horizon.

It is important to take into account the client’s specific tasks, wind load, aesthetic appearance and many others. Considering all of these factors, including easy access to the roof to clear the panels from the snow, we, along with the homeowner, decided to install them at a small angle parallel to the south slope of the roof.

In addition to the monitoring system, we installed a water temperature sensor in the water heater and a contactor to remotely activate the heating element. At any time it is possible to see the current water temperature or statistics on its changes with details every minute. You can switch the water heater on or off directly from the phone and set certain conditions for the water heater to do it himself.

The real cost of this project in July 2019 is 17 270 BGN (8 830 €) with delivery, installation and VAT. Prices for solar power plant equipment are gradually decreasing, so in future such a system may cost less or generate more energy for the same money.